Balance Week 10

B10A1. What systemic, bedside, and end-organ findings identify shock even before hypotension develops?

Answer: Shock is inadequate tissue perfusion and oxygen delivery relative to cellular needs. Look for tachycardia, tachypnea, weak or thready pulses, cool clammy or mottled extremities, delayed capillary refill, anxiety or confusion, thirst, oliguria, and rising lactate. Hypotension may be absent early because sympathetic vasoconstriction preserves arterial pressure despite low flow.

Extra Information:

• Warm extremities and bounding pulses can occur early in distributive shock rather than excluding shock.
• A normal blood pressure never rules out impaired microcirculation or oxygen delivery.

Source: Pearl Shock Prework slides 3, 19–21, 52 | First Aid 2025 p. 317

B10A1. Why are altered mental status, oliguria, and skin mottling useful signs of organ hypoperfusion?

Answer: Reduced brain blood flow causes agitation, confusion, or lethargy. Reduced effective renal perfusion and sympathetic and RAAS activation decrease urine production. Cutaneous alpha-1 arteriolar vasoconstriction redirects blood toward vital organs, producing cold, pale, mottled skin and slow capillary refill. These changes demonstrate failed tissue delivery rather than merely an abnormal number on the monitor.

Extra Information:

• Persistent oliguria and a worsening mental examination indicate progression despite a potentially preserved systolic pressure.

Source: Pearl Shock Prework slides 20–23, 26, 51–52 | First Aid 2025 pp. 316–317

B10A1. What findings favor early distributive shock over hemorrhagic or cardiogenic shock?

Answer: Early sepsis or anaphylaxis causes inflammatory mediator–driven arteriolar dilation and increased venous capacitance, so SVR falls. The patient may have warm flushed skin, relatively bounding pulses, and low diastolic pressure despite hypotension. Hypovolemic and typical cardiogenic shock generally trigger high SVR and cool, clammy extremities. Neurogenic shock is a distributive exception characterized by relative or absolute bradycardia.

Extra Information:

• Sepsis can later become cool with falling cardiac output or septic cardiomyopathy.

Source: Pearl Shock Prework slides 19, 32, 39–43 | Shock Answer Key pp. 2–3 | First Aid 2025 p. 317

B10A1. Why can a child with severe shock have a normal systolic blood pressure until very late?

Answer: Children mount pronounced sympathetic tachycardia and arteriolar vasoconstriction to maintain MAP despite decreasing preload and stroke volume. Hypotension appears when compensatory reserve finally fails, making it a late danger sign. Earlier clues include persistent tachycardia, abnormal skin perfusion, agitation or listlessness, low urine output, and lactate elevation.

Extra Information:

• Do not wait for a low BP before recognizing and treating pediatric shock.

Source: Pearl Shock Prework slides 21–23

B10A2. Classify a patient into the four major shock categories by the primary hemodynamic defect.

Answer: Hypovolemic = absolute intravascular volume loss → low preload → low stroke volume and CO. Cardiogenic = intrinsic cardiac pump failure → low forward CO with often high filling pressures. Distributive = pathologic vasodilation and venous pooling → low SVR and relative hypovolemia, with CO varying by phase. Obstructive = impaired cardiac filling or blood outflow → low CO despite a potentially intact myocardium.

Extra Information:

• Identify the dominant defect as tank volume, pump, vascular tone, or flow obstruction.

Source: Pearl Shock Prework slides 7, 18–19, 50 | Shock Answer Key p. 1 | First Aid 2025 p. 317

B10A2. What bedside clues distinguish hemorrhagic and nonhemorrhagic hypovolemia from cardiogenic shock?

Answer: Both can cause hypotension, tachycardia, cool skin, low CO, and compensatory high SVR. Flat neck veins, low CVP, dry mucosa, bleeding history, vomiting, diarrhea, or diuretic losses favor hypovolemia. Elevated JVP or CVP, pulmonary crackles, an S3, MI symptoms, new murmur, arrhythmia, or pulmonary congestion favor cardiogenic shock because ventricular filling pressure rises behind the failing pump.

Extra Information:

• Acute RV infarction can cause cardiogenic shock with raised JVP but relatively clear lungs.

Source: Pearl Shock Prework slides 18–19, 24, 33–37, 51 | Shock Answer Key pp. 1–2 | First Aid 2025 pp. 316–317

B10A2. How do septic, anaphylactic, and neurogenic distributive shock differ clinically and mechanistically?

Answer: Sepsis: infection and host inflammatory mediators cause widespread vasodilation, capillary leak, and abnormal tissue extraction, typically fever or infection clues with tachycardia. Anaphylaxis: allergen-triggered mediator release, especially histamine, causes vasodilation, permeability, bronchospasm, often urticaria, wheeze, or angioedema. Neurogenic: high spinal cord injury interrupts sympathetic pathways → low vascular tone and loss of cardiac sympathetic stimulation → hypotension with bradycardia.

Extra Information:

• All three can cause low SVR but require different cause-directed treatment.

Source: Pearl Shock Prework slides 7, 40–43 | Shock Answer Key pp. 1–3 | First Aid 2025 p. 317

B10A2. Which specific findings distinguish tamponade, tension pneumothorax, and massive pulmonary embolism as causes of obstructive shock?

Answer: Tamponade causes pericardial compression, hypotension, elevated JVP, muffled heart sounds, and potentially pulsus paradoxus. Tension pneumothorax causes abrupt respiratory compromise, unilateral absent breath sounds, severe hypotension, and impaired venous return from high intrathoracic pressure. Massive PE causes acute RV pressure overload with hypoxemia, tachycardia, elevated JVP, and reduced LV filling, often after immobilization or DVT.

Extra Information:

• The obstruction must be removed rather than treating it as a primary pump or volume problem.

Source: Pearl Shock Prework slides 44–48, 51 | Shock Answer Key pp. 1–3 | First Aid 2025 p. 317

B10A3. How are MAP, CO, and pulse pressure related to shock, and why can MAP remain normal as CO falls?

Answer: MAP ≈ CO × SVR when CVP is small, while CO = HR × SV. MAP from cuff pressure ≈ DBP + one-third(SBP − DBP) at ordinary heart rates. If preload loss lowers SV and CO, baroreceptor-mediated vasoconstriction raises SVR and tachycardia helps maintain CO, temporarily preserving MAP. Pulse pressure = SBP − DBP and often narrows as stroke volume falls and vascular tone rises.

Extra Information:

• MAP is a pressure surrogate, not a direct measurement of organ flow.

Source: Pearl Shock Prework slides 15–17, 21, 26 | First Aid 2025 pp. 316–317

B10A3. Calculate systemic vascular resistance from MAP, CVP, and CO and interpret a cardiogenic-shock example.

Answer: SVR = [(MAP − CVP) / CO] × 80 dyn·s/cm⁵. If MAP = 65 mmHg, CVP = 15 mmHg, and CO = 2.5 L/min, SVR = [(65 − 15)/2.5] × 80 = 1600 dyn·s/cm⁵. That elevated resistance reflects compensatory vasoconstriction in a low-output state. The factor 80 converts mmHg·min/L into dyn·s/cm⁵.

Extra Information:

• Subtract CVP because flow depends on the pressure difference across systemic circulation.

Source: Shock Week Equation Worksheets Answer Key p. 2 | Pearl Shock Prework slides 15–16

B10A3. How do CVP, PCWP, and LVEDP help locate a shock patient's hemodynamic problem?

Answer: CVP estimates right atrial filling pressure and correlates imperfectly with RV filling. PCWP estimates left atrial pressure and often reflects LV end-diastolic pressure when conditions permit. Low CVP and wedge suggest depleted venous return. High CVP and high wedge suggest biventricular congestion or tamponade. High CVP with low wedge suggests predominantly right-sided obstruction such as massive PE. Interpret pressures with intrathoracic and pericardial pressure because a high measured pressure need not mean high chamber filling volume.

Extra Information:

• Neck veins help assess venous congestion, while lung crackles support elevated pulmonary venous pressure.

Source: Shock Answer Key pp. 2–3 | Shock Week Equation Worksheets Answer Key pp. 2, 4 | Pearl Shock Prework slides 48, 51

B10A3. Calculate cardiac index and stroke volume in the cardiogenic shock worksheet.

Answer: Cardiac index = CO / body surface area. With CO 2.5 L/min and BSA 2.0 m², CI = 1.25 L/min/m², indicating markedly low flow indexed to body size. Stroke volume = (CO × 1000) / HR. With HR 110 beats/min, SV = 2500/110 = 22.7 mL/beat, showing that tachycardia is compensating for low volume ejected per beat.

Extra Information:

• A patient's HR can be high even when CO remains inadequate because stroke volume is severely depressed.

Source: Shock Week Equation Worksheets Answer Key p. 2 | Pearl Shock Prework slide 17

B10A3. What is the relationship between mixed venous oxygen saturation, oxygen extraction, and the arterial-venous oxygen difference?

Answer: When arterial oxygen content and tissue demand are relatively stable, low CO reduces DO₂ → tissue extraction increases → SvO₂ decreases → arterial-venous oxygen content and saturation differences widen. Conversely, impaired tissue extraction or high flow can raise SvO₂ and narrow the difference despite disease. Approximate saturation gap = SaO₂ − SvO₂, while true oxygen content difference = CaO₂ − CvO₂ in mL/dL.

Extra Information:

• Faculty flags SvO₂ below 65% as abnormal and below 50% as dangerous.
• Do not confuse the venous saturation itself with the arterial-venous difference, which usually moves in the opposite direction.

Source: Pearl Shock Prework slides 10–13, 32 | Shock Answer Key pp. 2–3

B10A3. How do HR, skin temperature, JVP, and lung auscultation together improve hemodynamic assessment over a single BP reading?

Answer: Tachycardia usually represents sympathetic compensation for falling SV, except in neurogenic shock or severe conduction disease. Cool mottled skin suggests high compensatory SVR, while warm skin can indicate distributive vasodilation. Flat JVP suggests low right filling pressure, elevated JVP suggests right congestion or obstruction. Crackles and an S3 suggest elevated left-sided filling pressure, whereas clear lungs with a high JVP raise concern for PE, RV failure, or tamponade.

Extra Information:

• Reassess these findings after each intervention because both shock physiology and fluid status change.

Source: Pearl Shock Prework slides 19–21, 33–40, 51 | Shock Answer Key pp. 2–3

B10A4. Explain the progression from compensated to decompensated and irreversible shock.

Answer: Initial low perfusion activates sympathetic vasoconstriction, tachycardia, ADH, and RAAS → BP may be preserved despite rising extraction and declining urine output. With continued volume loss or pump failure, these mechanisms cannot maintain effective CO and MAP → hypotension, confusion, absent peripheral pulses, and severe organ hypoperfusion. Prolonged hypoxia depletes ATP and injures membranes and mitochondria → cell death, organ failure, and eventually shock that cannot be reversed simply by restoring flow.

Extra Information:

• Hypotension and acidosis may be late findings.

Source: Pearl Shock Prework slides 20–23, 26, 30–31, 52 | First Aid 2025 pp. 203–204, 317

B10A4. What hemorrhage severity pattern and vital signs suggest compensation versus decompensation?

Answer: In the faculty framework, compensated hemorrhagic shock is approximately less than 25% blood loss, with maintained systolic pressure, increasing HR or vascular tone, and possible narrowed pulse pressure. Progressive or uncompensated shock is roughly 25–40% loss, with falling BP, tachycardia, oliguria, and anxious or confused mental status. Profound loss greater than 40% can produce severe hypotension, lethargy, minimal urine output, and circulatory collapse.

Extra Information:

• The lecture explicitly uses up to 24.9% or roughly 1250–1499 mL as the compensated teaching cutoff, despite differing tables for volume ranges.

Source: Pearl Shock Prework slides 27–31

B10A4. Recall the four commonly taught hemorrhagic shock classes and the progression of heart rate, BP, urine output, and consciousness.

Answer: Class I:

Extra Information:

• These are approximate teaching classes, not exact cutoffs for deciding whether a real patient needs resuscitation.

Source: Pearl Shock Prework slide 28

B10A4. Why do late shock patients lose urine output and mental clarity, and what predicts worse outcome?

Answer: Persistently inadequate perfusion reduces renal filtration and cortical oxygen delivery. Neurohormonal responses retain salt and water while renal tubular ischemia progresses. Cerebral hypoperfusion causes worsening confusion, somnolence, or coma. Falling urine output, new mental status change, sustained hypotension, and inability to clear lactate suggest unsuccessful compensation and increasing risk of multiorgan failure.

Extra Information:

• In children, hypotension is especially late.

Source: Pearl Shock Prework slides 20–23, 29–31, 52 | First Aid 2025 p. 317

B10A5. What is the initial stabilization sequence when shock is suspected, regardless of cause?

Answer: Rapidly assess airway and breathing, support oxygenation or ventilation if needed, check pulse and perfusion, obtain IV or IO access, connect cardiac and pulse-oximetry monitoring, and repeatedly reassess mental status, BP, pulse, and urine output. Draw targeted labs including lactate while evaluating immediately reversible causes. Restore oxygen delivery by treating the specific defect in volume, pump, vascular tone, or obstruction rather than relying on a normal monitor reading.

Extra Information:

• Oxygen delivery depends on both cardiac output and arterial oxygen content, so airway support alone does not correct severe low-flow shock.

Source: Pearl Shock Prework slides 8, 14, 20, 50–52 | Shock Answer Key p. 1

B10A5. How is early hypovolemic shock resuscitated, and what physiological changes should occur after fluid replacement?

Answer: Stop hemorrhage or ongoing fluid loss. For nonhemorrhagic volume depletion, appropriate isotonic crystalloid replenishes intravascular volume → venous return and preload rise → stroke volume and CO improve along the Frank–Starling relationship → DO₂ rises and extraction stress decreases. Severe hemorrhage requires bleeding control and blood-product resuscitation as clinically appropriate. Recheck perfusion because large fluid doses do not treat every shock type.

Extra Information:

• Hemoconcentrated Hb can fall after effective fluid resuscitation without worsening oxygen delivery.

Source: Shock Week Equation Worksheets Answer Key p. 1 | Pearl Shock Prework slides 24–26, 38, 50

B10A5. Why can a large IV fluid bolus worsen cardiogenic shock?

Answer: The failing LV already has elevated LVEDP and PCWP. Additional fluid may minimally increase forward stroke volume but raises pulmonary capillary hydrostatic pressure → interstitial and alveolar edema → worsening hypoxemia. Stabilization therefore prioritizes treatment of the cause, cautious preload assessment, inotropy when low-output physiology requires it, and a vasopressor if hypotension is severe. Diuretics may help congestion when hemodynamics allow.

Extra Information:

• In the faculty example, CI = 1.25 L/min/m² and PCWP = 26 mmHg indicate low output with congestion.

Source: Shock Week Equation Worksheets Answer Key p. 2 | Pearl Shock Prework slide 38 | First Aid 2025 pp. 316–317

B10A5. What resuscitation priorities distinguish septic, anaphylactic, and neurogenic shock?

Answer: Septic shock combines relative or actual hypovolemia with low SVR, so early fluids plus source-directed management are followed by vasopressor support if perfusion pressure remains inadequate. Anaphylaxis requires immediate intramuscular epinephrine for alpha-1 vasoconstriction, beta-2 bronchodilation, and beta-1 cardiac support, alongside airway support and fluids. Neurogenic shock requires assessment for spinal injury, cautious fluids, and vascular-tone support because loss of sympathetic signaling persists despite volume replacement.

Extra Information:

• Neurogenic bradycardia is a key contrast with most other shock types.

Source: Pearl Shock Prework slides 38, 40–43 | Shock Answer Key p. 3 | First Aid 2025 pp. 241, 317

B10A5. How does the definitive intervention differ for tamponade, tension pneumothorax, and massive PE?

Answer: Tamponade: urgently relieve pericardial fluid pressure to restore transmural chamber distention and filling. Tension pneumothorax: urgently decompress pleural pressure to restore venous return and ventilation. Massive high-risk PE: provide cardiopulmonary support and urgent reperfusion or clot-directed therapy when indicated to relieve acute RV afterload. Fluids or pressors may temporarily support circulation but do not remove the mechanical blockage.

Extra Information:

• Tamponade can have high wedge and CVP despite a small effective LV filling volume.

Source: Pearl Shock Prework slides 44–48 | Shock Week Equation Worksheets Answer Key p. 4 | First Aid 2025 p. 317

B10A5. What two strategies increase oxygen delivery and what practical measures reduce oxygen demand during shock?

Answer: Since DO₂ = CO × CaO₂, improve flow with appropriate preload, contractility, vascular tone, and HR, and improve arterial content with oxygenation and sufficient hemoglobin. Decrease VO₂ by treating fever, pain and agitation and by reducing excessive work of breathing. This improves the supply-demand balance and may move tissue above the critical oxygen delivery threshold where oxygen consumption becomes supply dependent.

Extra Information:

• Raising PaO₂ alone often gives a relatively small CaO₂ increase when hemoglobin is already nearly fully saturated.

Source: Pearl Shock Prework slides 4, 8, 14 | First Aid 2025 p. 687

B10A6. Which targeted history questions most efficiently narrow the differential diagnosis of an undifferentiated shock patient?

Answer: Ask about visible or occult bleeding, trauma, GI losses, burns or diuretics for hypovolemia. Ask about chest pain, known heart failure, arrhythmia, or new murmur for cardiogenic shock. Ask about infection, fever, allergen or drug exposure, and spinal injury for distributive causes. Ask about recent immobilization or DVT, chest trauma, and pericardial disease for obstructive causes. Interpret each answer together with perfusion, JVP, lung findings, and ECG.

Extra Information:

• History and setting are explicit first-line classification tools in the faculty lecture.

Source: Pearl Shock Prework slides 18, 40–44, 51 | Shock Answer Key p. 1

B10A6. How do physical exam findings discriminate right-sided obstruction from left ventricular failure?

Answer: Elevated JVP with clear lungs, sudden dyspnea, and evidence of RV overload favors massive PE or isolated RV failure. Elevated JVP with muffled heart sounds and pulsus paradoxus suggests tamponade. Elevated JVP with unilateral absent breath sounds suggests tension pneumothorax. Elevated JVP with bilateral crackles, S3, or marked pulmonary congestion favors left-heart failure or biventricular cardiogenic shock.

Extra Information:

• Absence of one classic sign does not safely exclude an immediately life-threatening obstruction.

Source: Pearl Shock Prework slides 44–48, 51 | Shock Answer Key p. 1 | First Aid 2025 pp. 316–317

B10A6. Which first-pass laboratory and bedside investigations help classify shock, and what does each answer?

Answer: ECG identifies ischemia or arrhythmia. Bedside echo assesses pump function, pericardial fluid, and RV strain. Lung imaging helps identify pulmonary edema, pneumonia, or pneumothorax. CBC helps assess anemia, leukocyte response, and platelets. CMP evaluates kidney function and electrolytes. Blood gas evaluates oxygenation, ventilation, and acid-base status. Lactate supports impaired tissue metabolism but does not by itself establish shock type. Troponin and BNP help investigate a suspected cardiac cause.

Extra Information:

• The faculty prework explicitly emphasizes history, exam, ECG, chest X-ray, and selective labs before labeling etiology.

Source: Pearl Shock Prework slide 51 | First Aid 2025 pp. 316–317, 609–610

B10A6. A patient is hypotensive after trauma with CVP 20 mmHg, PCWP 21 mmHg, and low CO. Why is primary hypovolemia an incomplete explanation?

Answer: In isolated hemorrhagic hypovolemia, low circulating volume lowers both CVP and PCWP. Concomitantly high right- and left-sided measured filling pressures with low output suggest restricted filling from tamponade or severe biventricular congestion. In tamponade, pericardial pressure approaches intracardiac diastolic pressure, so measured pressures rise despite a very small ventricular distending pressure and low end-diastolic volume.

Extra Information:

• In the worksheet, PCWP 21 minus pericardial pressure 19 leaves only about 2 mmHg effective transmural filling pressure.

Source: Shock Week Equation Worksheets Answer Key p. 4 | Shock Answer Key pp. 2–3

B10A6. How should a clinician interpret changes in CO, SVR, SvO₂, and lactate after fluids in suspected sepsis?

Answer: Before fluids, venous pooling and capillary leak may lower preload and CO. Effective resuscitation can raise preload and CO while SVR remains low from vasodilation. SvO₂ may increase as global DO₂ improves, although impaired extraction can also elevate it. Lactate and clinical perfusion should be trended with mental status, urine output, and capillary refill rather than assuming that a high venous saturation guarantees adequate tissue oxygen use.

Extra Information:

• Persistent low CO after resuscitation raises concern for septic myocardial dysfunction.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 19, 38, 49

B10LG1.1. Define shock at the systemic and mitochondrial levels, including why normotension does not exclude shock.

Answer: Systemically, shock means inadequate perfusion to meet organ metabolic requirements. At the cell, oxygen supply to mitochondria becomes inadequate for effective oxidative phosphorylation and ATP generation. Oxygen delivery depends on forward blood flow and the oxygen content of that blood, not just arterial pressure. Increased SVR can temporarily preserve MAP despite low CO, so a normotensive patient can have significant shock.

Extra Information:

• Monitor actual perfusion signs such as mentation, urine output, and extraction, not BP alone.

Source: Pearl Shock Prework slides 3–4, 8, 15–21, 52 | First Aid 2025 p. 317

B10LG1.1. Explain oxygen delivery and arterial oxygen content with the correct units and conversion factor.

Answer: CaO₂ = (1.34 mL O₂/g Hb × Hb in g/dL × SaO₂ as a fraction) + (0.003 mL O₂/dL/mmHg × PaO₂ in mmHg). CaO₂ is mL O₂/dL blood. DO₂ = CO in L/min × CaO₂ in mL/dL × 10 dL/L, giving mL O₂/min. The Hb-bound term dominates, so low hemoglobin or low CO can cause tissue hypoxia with a seemingly adequate PaO₂.

Extra Information:

• The slide prints DO₂ = CO × CaO₂ conceptually and the equation worksheet supplies the ×10 for mixed units.

Source: Pearl Shock Prework slides 8–9 | Shock Week Equation Worksheets Answer Key p. 1 | First Aid 2025 p. 687

B10LG1.1. Calculate CaO₂ and DO₂ for Hb 16 g/dL, SaO₂ 98%, PaO₂ 95 mmHg, and CO 2.5 L/min.

Answer: CaO₂ = 1.34 × 16 × 0.98 + 0.003 × 95 = 21.30 mL O₂/dL. DO₂ = 2.5 L/min × 21.30 mL/dL × 10 = approximately 532 mL O₂/min. Despite normal oxygen saturation and elevated Hb from hemoconcentration, delivery is impaired because volume depletion lowers venous return and CO.

Extra Information:

• This exactly matches the faculty GI-fluid-loss simulation and illustrates why Hb and SaO₂ cannot substitute for flow.

Source: Shock Week Equation Worksheets Answer Key p. 1 | First Aid 2025 p. 687

B10LG1.1. Define VO₂, oxygen extraction ratio, and the critical oxygen-delivery threshold in shock.

Answer: VO₂ is tissue oxygen consumption. Oxygen extraction ratio O₂ER = (CaO₂ − CvO₂)/CaO₂, normally roughly 20–30%. As DO₂ falls, tissues initially extract more O₂, preserving VO₂. Below a critical DO₂ threshold, maximal extraction is reached, VO₂ becomes delivery dependent, aerobic ATP production falls, and lactate rises. Using saturations approximately, (0.98 − 0.48)/0.98 = 51% extraction in the faculty hypovolemic case.

Extra Information:

• The ratio using saturations approximates the true content ratio when hemoglobin and dissolved fractions are comparable.

Source: Pearl Shock Prework slides 4, 10–13 | Shock Week Equation Worksheets Answer Key p. 1

B10LG1.2. List the major causes of hypovolemic and cardiogenic shock and identify their defining mechanical defects.

Answer: Hypovolemic shock is an underfilled vascular compartment: hemorrhage, dehydration from vomiting or diarrhea, burns, excessive diuresis, or third-spacing from pancreatitis or peritonitis → decreased preload. Cardiogenic shock is failure of cardiac forward pumping: acute MI, severe heart failure, cardiomyopathy, myocarditis, severe tachyarrhythmia or bradyarrhythmia, or acute major valve dysfunction → decreased effective stroke volume despite potentially high filling pressure.

Extra Information:

• Hemorrhage is a subset of hypovolemic shock, not a fifth category.

Source: Pearl Shock Prework slides 7, 18, 24, 33–37 | Shock Answer Key p. 1 | First Aid 2025 p. 317

B10LG1.2. List the causes and shared physiology of distributive shock.

Answer: Major causes include sepsis, anaphylaxis, and neurogenic shock from high spinal injury. Adrenal crisis, severe drug-induced vasodilation, and toxic-shock syndromes can also cause distributive physiology. Shared defect: systemic arteriolar vasodilation lowers SVR, while venodilation increases capacitance and pooling → relative hypovolemia and low effective filling pressure. Capillary leak can create an additional true intravascular volume deficit.

Extra Information:

• Neurogenic shock commonly has bradycardia, unlike septic and anaphylactic shock.

Source: Pearl Shock Prework slides 7, 18, 40–43 | Shock Answer Key p. 1 | First Aid 2025 p. 317

B10LG1.2. List the obstructive causes of shock and explain the shared decrease in forward flow.

Answer: Massive pulmonary embolism acutely raises RV outflow resistance and restricts blood reaching the left heart. Tamponade raises pericardial pressure and restricts ventricular diastolic expansion. Tension pneumothorax raises pleural pressure, reduces systemic venous return, and can compress cardiac structures. All lower LV stroke volume and CO through a mechanical obstacle, often causing compensatory tachycardia and higher SVR.

Extra Information:

• Unlike cardiogenic shock, the dominant initial cause is blockage rather than intrinsic LV muscle failure.

Source: Pearl Shock Prework slides 7, 18, 44–48 | Shock Answer Key p. 1 | First Aid 2025 p. 317

B10LG1.2. What role do adrenal crisis, myxedema, and extensive burns play in shock classification?

Answer: Adrenal crisis can create distributive hypotension by insufficient cortisol-dependent vascular responsiveness and may add volume depletion when aldosterone is deficient. Severe hypothyroidism or myxedema can lower HR and contractility, causing a low-output state. Extensive burns produce plasma leakage and major intravascular depletion, predominantly hypovolemic physiology, often with inflammatory features. Classify by the predominant hemodynamic defect instead of assuming every cause fits exclusively in one box.

Extra Information:

• The faculty lecture lists Addisonian crisis, myxedema, and burns under other causes and the worksheet groups adrenal crisis with distributive shock.

Source: Pearl Shock Prework slide 18 | Shock Answer Key p. 1 | First Aid 2025 p. 317

B10LG1.3. Trace the baroreceptor and sympathetic response to falling MAP from receptor to cardiac and vascular effects.

Answer: Reduced carotid sinus and aortic arch stretch lowers baroreceptor firing → medullary autonomic outflow increases sympathetic activity and reduces vagal influence. Beta-1 stimulation raises SA-node rate and myocardial contractility, helping CO. Alpha-1 stimulation constricts arterioles, raising SVR, and constricts veins, improving venous return. Thus MAP may be preserved while skin and renal flow fall.

Extra Information:

• This compensatory rise in afterload can increase the workload of an already failing LV.

Source: Pearl Shock Prework slides 15–16, 20–21, 26, 36–38 | First Aid 2025 pp. 241, 316

B10LG1.3. Trace renin–angiotensin–aldosterone activation in shock with every major trigger and effector.

Answer: Reduced renal perfusion pressure, increased renal beta-1 sympathetic stimulation, and reduced macula-densa NaCl delivery promote juxtaglomerular renin secretion. Renin converts liver angiotensinogen to angiotensin I, then ACE forms angiotensin II. Angiotensin II acting at AT1 receptors raises SVR and stimulates adrenal zona glomerulosa aldosterone. Aldosterone increases distal nephron sodium reabsorption and accompanying water retention, supporting blood volume and preload.

Extra Information:

• Sustained RAAS activation can worsen congestion in cardiogenic shock.

Source: Pearl Shock Prework slides 26, 36 | First Aid 2025 pp. 316, 606–607

B10LG1.3. What does vasopressin or ADH do during shock, and how do V1 and V2 receptors differ?

Answer: Low effective circulating volume and arterial pressure stimulate nonosmotic ADH release. V1a receptors on vascular smooth muscle signal through Gq and intracellular Ca²⁺ to promote vasoconstriction. V2 receptors on collecting duct principal cells signal through Gs, cAMP, and PKA to insert apical AQP2 channels, increasing free-water reabsorption. These responses defend pressure and volume but can worsen water retention or hyponatremia.

Extra Information:

• The faculty slide highlights vasopressin alongside epinephrine and angiotensin in compensated hypovolemia.

Source: Pearl Shock Prework slide 26 | First Aid 2025 pp. 316, 606–607

B10LG1.3. Explain why compensatory catecholamines can be both beneficial and harmful in cardiogenic shock.

Answer: Reduced CO lowers MAP and baroreceptor stretch → catecholamine release raises HR, contractility, and arteriolar SVR to sustain perfusion. However, increased afterload makes a weak LV pump against higher resistance, and tachycardia increases myocardial oxygen demand while shortening diastolic filling and coronary perfusion time. Therefore the same compensation can aggravate ischemia and reduce forward flow when pump failure is severe.

Extra Information:

• RAAS and ADH also retain fluid, potentially worsening pulmonary edema.

Source: Pearl Shock Prework slides 33–38 | Shock Week Equation Worksheets Answer Key p. 2 | First Aid 2025 p. 316

B10LG1.3. What three broad neurohormonal consequences explain tachycardia, narrow pulse pressure, and oliguria in compensated hypovolemia?

Answer: Increased sympathetic beta-1 drive causes tachycardia to partly replace lost SV. Alpha-1 arteriolar vasoconstriction maintains diastolic pressure as SV falls, narrowing pulse pressure and preserving MAP. RAAS and ADH promote sodium and water retention and, with reduced renal blood flow, decrease urine output. All follow the initiating loss of venous return and effective circulating volume.

Extra Information:

• Profound blood loss eventually defeats these compensations and systolic pressure falls.

Source: Pearl Shock Prework slides 21, 24–27, 30–31 | First Aid 2025 pp. 316–317

B10LG1.4. Which organs are preferentially protected by sympathetic blood-flow redistribution during early shock, and which are sacrificed?

Answer: Autoregulatory and neurohormonal mechanisms attempt to preserve coronary and cerebral perfusion because the heart and brain have high metabolic requirements and limited tolerance of ischemia. Alpha-1 vasoconstriction preferentially reduces perfusion of skin, splanchnic organs, and kidneys, producing cool extremities, impaired gut perfusion, and reduced urine output. Redistribution is protective only temporarily because sustained hypoperfusion damages sacrificed organs.

Extra Information:

• Preferential perfusion does not imply that cerebral or myocardial flow remains adequate in advanced shock.

Source: Pearl Shock Prework slides 20–21, 26–27, 37, 52 | First Aid 2025 pp. 316–317

B10LG1.4. Why do the brain and heart have priority when circulating volume and cardiac output fall?

Answer: The brain relies heavily on continuous aerobic glucose metabolism and has little oxygen reserve, so perfusion deficits rapidly impair consciousness. Myocardium has high basal oxygen extraction and must receive adequate coronary blood flow to sustain contractile pumping. Loss of cerebral or coronary delivery amplifies shock by causing neurologic dysfunction, myocardial ischemia, arrhythmia, and further CO depression.

Extra Information:

• The clinical signs of failed cerebral sparing include new confusion and lethargy.

Source: Pearl Shock Prework slides 20–21, 29, 35–37, 52 | First Aid 2025 pp. 316–317

B10LG1.4. Why do renal and intestinal dysfunction emerge when compensation is prolonged?

Answer: Persistently elevated sympathetic tone and RAAS divert flow from renal and splanchnic vascular beds → reduced oxygen and substrate delivery → renal filtration falls, tubular cells become ischemic, and intestinal mucosal barrier function deteriorates. Sustained microvascular hypoperfusion can contribute to systemic inflammation, ischemic organ injury, and multiple-organ failure even if large-artery pressure is temporarily maintained.

Extra Information:

• Track urine output as an accessible sign of end-organ perfusion rather than assuming maintained BP means the kidneys are safe.

Source: Pearl Shock Prework slides 20–21, 37, 52 | First Aid 2025 pp. 203, 317

B10LG1.4. Which organ regions are particularly vulnerable to sustained global hypoperfusion and why?

Answer: Watershed territories and metabolically demanding tissues are vulnerable when cardiac output stays low. Brain: border zones between ACA, MCA, and PCA territories, and particularly sensitive hippocampal, cortical, and cerebellar neurons. Heart: LV subendocardium. Kidney: medullary straight proximal tubule and thick ascending limb. Liver: centrilobular zone III. Colon: splenic flexure and rectosigmoid watershed. These regions have limited perfusion reserve or high oxygen requirements.

Extra Information:

• Preserving bulk cerebral and coronary flow does not prevent all regional ischemic injuries in prolonged shock.

Source: First Aid 2025 p. 206 | Pearl Shock Prework slides 20–21, 52

B10LG2.1. Predict the seven hemodynamic parameters in hemorrhagic shock and explain the causal sequence.

Answer: CVP ↓, LA pressure or LVEDP ↓, CO ↓, SVR ↑, HR ↑, SvO₂ ↓, and arterial-venous O₂ difference ↑. Blood loss → reduced stressed circulating volume → decreased venous return and preload → decreased SV and CO. Baroreceptor activation raises vascular resistance and HR, while tissues extract more oxygen from reduced flow, lowering mixed venous saturation.

Extra Information:

• Hemoglobin may initially remain normal or rise because fluid loss causes hemoconcentration.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 24–31 | First Aid 2025 p. 317

B10LG2.1. Predict the seven hemodynamic parameters in classic LV cardiogenic shock and explain why high afterload can be harmful.

Answer: CVP ↑, LA pressure or LVEDP ↑, CO ↓, SVR ↑, HR ↑, SvO₂ ↓, and arterial-venous O₂ difference ↑. Myocardial pump failure → reduced forward SV and CO → blood accumulates behind the LV, raising wedge and often systemic venous pressures. Reflex sympathetic constriction raises SVR, which preserves pressure but increases LV afterload and can further reduce forward flow. Tissues extract more O₂, so SvO₂ falls.

Extra Information:

• Early or isolated LV failure may elevate wedge before CVP, so the table represents a typical congested presentation.

Source: Shock Answer Key pp. 2–3 | Shock Week Equation Worksheets Answer Key p. 2 | Pearl Shock Prework slides 33–38 | First Aid 2025 pp. 316–317

B10LG2.1. Contrast the hemodynamic pattern of septic shock before and after effective fluid resuscitation.

Answer: Before fluids, CVP and left filling pressure often ↓, CO is variable or ↓ from low preload, SVR ↓, HR ↑, SvO₂ is variable, and A–V O₂ difference is variable. After effective fluids, CVP and left pressures normalize or ↑, CO often ↑ into a hyperdynamic state, SVR stays ↓, HR is often ↑, SvO₂ typically ↑, and A–V O₂ difference often ↓. Capillary leak and vasoplegia persist even after the tank is refilled.

Extra Information:

• Septic myocardial dysfunction can keep CO low despite adequate filling.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 19, 38–43, 49

B10LG2.1. Why can a septic patient have a high SvO₂ and still have severe tissue hypoxia?

Answer: Sepsis may cause a hyperdynamic CO and impaired microvascular distribution or cellular oxygen extraction. Consequently, oxygen-rich blood returns to the venous circulation even while some capillary beds and mitochondria remain inadequately supplied or unable to use O₂. High SvO₂ therefore can represent poor extraction rather than adequate metabolism, often with a narrowed A–V oxygen difference. Interpret it with lactate, perfusion, and clinical trajectory.

Extra Information:

• In pre-fluid low-output sepsis, SvO₂ can instead be low because extraction increases.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 10–13, 19, 32, 49

B10LG2.1. Predict the seven hemodynamic values in neurogenic shock before fluids and identify its defining exception.

Answer: CVP ↓, LA or LVEDP ↓, CO often ↓, SVR ↓, HR ↓, SvO₂ ↓ or normal, and A–V oxygen difference ↑ or unchanged. Spinal cord injury interrupts descending sympathetic tone → venous pooling and arteriolar dilation plus loss of cardiac accelerator activity. Vagal influence remains, producing bradycardia rather than the compensatory tachycardia seen in most shock types.

Extra Information:

• A calculated SVR of 1120 dyn·s/cm⁵ can be in a reference range but is inappropriately non-elevated when MAP is only 52 mmHg.

Source: Shock Answer Key pp. 2–3 | Shock Week Equation Worksheets Answer Key p. 3 | Pearl Shock Prework slides 40–43

B10LG2.1. How does neurogenic shock change after fluid resuscitation, and what fundamental defect remains?

Answer: Fluids often raise CVP and venous return toward normal, so CO may normalize or improve. SVR remains low because sympathetic arteriolar tone has not been restored, and HR can remain low from absent sympathetic cardiac stimulation. SvO₂ and A–V difference may normalize or vary with improved delivery. A vasopressor may be required despite normal filling because the primary problem is loss of vascular tone.

Extra Information:

• The worksheet lists post-fluid HR ↓, SVR ↓, CO normal or ↑, and mixed venous saturation normal or ↑.

Source: Shock Answer Key pp. 2–3 | Shock Week Equation Worksheets Answer Key p. 3

B10LG2.1. Predict tamponade hemodynamics, distinguishing measured ventricular pressure from effective preload.

Answer: CVP ↑, measured LA pressure or LVEDP ↑, CO ↓, SVR ↑, HR ↑, SvO₂ ↓, A–V O₂ difference ↑. Rising pericardial pressure externally compresses the heart and elevates recorded intracavitary diastolic pressures, often toward equalization. Yet transmural filling pressure = intracavitary pressure − pericardial pressure becomes small, so actual end-diastolic volume and SV fall. Sympathetic responses elevate HR and SVR.

Extra Information:

• Example: PCWP 21 minus pericardial pressure 19 ≈ 2 mmHg net distending pressure.

Source: Shock Answer Key pp. 2–3 | Shock Week Equation Worksheets Answer Key p. 4 | Pearl Shock Prework slide 46 | First Aid 2025 p. 317

B10LG2.1. Predict tension pneumothorax hemodynamics and explain why CVP can rise despite diminished venous return.

Answer: Measured CVP ↑, LA pressure or LVEDP ↓, CO ↓, SVR ↑, HR ↑, SvO₂ ↓, and A–V difference ↑. Trapped pleural air elevates intrathoracic pressure, compressing venae cavae and right-sided chambers → systemic venous return and LV filling decrease. The high surrounding thoracic pressure elevates measured central venous pressure even while effective transmural filling and forward output decrease.

Extra Information:

• Unilateral absent breath sounds and immediate clinical deterioration point to the obstructive mechanism.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 44–46 | First Aid 2025 p. 317

B10LG2.1. Predict saddle PE hemodynamics and explain opposite right- versus left-sided filling pressures.

Answer: CVP ↑ and RV pressure ↑, but LA pressure or LVEDP ↓, CO ↓, SVR ↑, HR ↑, SvO₂ ↓, and A–V O₂ difference ↑. Obstruction of pulmonary arteries abruptly raises RV afterload, causing RV dilation and dysfunction with high right-sided pressure. Less blood reaches pulmonary veins and LV → low left preload and systemic flow. Reflex tachycardia and vasoconstriction follow.

Extra Information:

• Faculty example: CVP 20, RV pressure approximately 48/20, LVEDP 4, CO 2.0 L/min, mixed venous saturation 40%.

Source: Pearl Shock Prework slides 47–48 | Shock Answer Key pp. 2–3 | First Aid 2025 p. 317

B10LG2.1. Contrast the most discriminating preload, CO, SVR, heart-rate, and saturation patterns across the four shock classes.

Answer: Hypovolemic: low preload, low CO, high SVR, high HR, low SvO₂. Cardiogenic: often high filling pressure, low CO, high SVR, high HR, low SvO₂. Distributive sepsis after fluids: low SVR, often high CO, high HR, sometimes high SvO₂. Neurogenic: low SVR with bradycardia and variable CO. Obstructive: low CO and high SVR with filling pressures dependent on the site of blockage, such as high CVP but low left preload in PE.

Extra Information:

• The key distinguishing decision is whether the primary defect is filling volume, pump function, vascular resistance, or physical obstruction.

Source: Shock Answer Key pp. 2–3 | Pearl Shock Prework slides 18–19, 32, 48–50 | First Aid 2025 p. 317

B10LG2.2. Why does oxygen delivery below a critical threshold cause lactate production despite ongoing glycolysis?

Answer: Reduced oxygen reaching mitochondria limits O₂ as the final electron acceptor at complex IV of the electron transport chain → oxidative phosphorylation and mitochondrial ATP synthesis decline. NADH cannot be reoxidized efficiently through the ETC, so cytosolic lactate dehydrogenase converts pyruvate to lactate while regenerating NAD⁺, allowing glycolysis to continue producing limited ATP. The rise in lactate signals a stressed supply-demand balance in type A hypoperfusion.

Extra Information:

• Glycolysis provides only about 2 ATP per glucose compared with much greater aerobic yield.

Source: Pearl Shock Prework slides 3–6 | First Aid 2025 pp. 203, 610

B10LG2.2. How do reduced CO and arterial oxygen content both contribute to the lactate rise in shock?

Answer: DO₂ = CO × CaO₂. Severe hemorrhage reduces CO through low venous return even when PaO₂ and SaO₂ are normal. Respiratory failure reduces SaO₂ and thus CaO₂, while severe anemia reduces Hb-bound oxygen content. Any combination lowering mitochondrial delivery beyond compensatory extraction can reduce aerobic ATP production and shift pyruvate toward lactate. Increased metabolic demand can worsen the imbalance at a given delivery.

Extra Information:

• A normal PaO₂ cannot exclude delivery-dependent lactic acidosis.

Source: Pearl Shock Prework slides 4, 8–14 | Shock Week Equation Worksheets Answer Key p. 1 | First Aid 2025 pp. 610, 687

B10LG2.2. What laboratory pattern identifies lactic metabolic acidosis and how can a concurrent respiratory problem be detected?

Answer: Tissue hypoperfusion may raise L-lactate and produce a high-anion-gap metabolic acidosis with low bicarbonate and pH. Compute AG = Na⁺ − (Cl⁻ + HCO₃⁻). For metabolic acidosis, expected respiratory compensation is PaCO₂ = 1.5 × HCO₃⁻ + 8 ± 2. A measured PaCO₂ higher than predicted reveals superimposed respiratory acidosis, for example respiratory muscle fatigue or ARDS with ventilatory failure.

Extra Information:

• Lactate is useful for trend assessment but is neither exclusive to shock nor sufficient to classify its cause.

Source: Pearl Shock Prework slides 20, 51–52 | ABG Answer Key p. 1 | First Aid 2025 pp. 609–610

B10LG2.2. Why can lactate remain high after arterial pressure improves?

Answer: Raising MAP does not automatically restore uniform capillary perfusion or mitochondrial oxygen utilization. Persistent low microvascular flow, impaired clearance due to hepatic hypoperfusion, catecholamine-related glycolysis, or another metabolic cause can keep lactate elevated. Reassess cardiac output, perfusion signs, oxygenation, and the disease process rather than equating pressure normalization with complete restoration of cellular metabolism.

Extra Information:

• Faculty stresses that the true target is oxygen delivery to mitochondria rather than BP alone.

Source: Pearl Shock Prework slides 3–4, 15, 19–21, 52 | First Aid 2025 pp. 203, 317

B10LG2.3. Mechanistically contrast compensated versus uncompensated hypovolemic shock before focusing on BP.

Answer: Compensated: modest blood-volume loss → low venous return and SV → baroreceptors drive tachycardia and arteriolar vasoconstriction, while RAAS and ADH retain water. Systolic BP can remain near normal, but pulse pressure narrows, urine output decreases, skin cools, and anxiety appears. Uncompensated: continued loss overwhelms these responses → CO and MAP fall, tissue extraction reaches its limit, mental status worsens, urine output falls severely, and anaerobic metabolism increases.

Extra Information:

• The faculty's compensated cutoff is less than 25% blood loss, but clinical deterioration takes priority over a numeric category.

Source: Pearl Shock Prework slides 21, 26–31 | First Aid 2025 p. 317

B10LG2.3. Why can pulse pressure narrow before systolic hypotension becomes obvious during blood loss?

Answer: Blood-volume loss lowers end-diastolic filling and stroke volume, reducing the systolic pressure rise produced by each beat. Sympathetic vasoconstriction maintains or increases diastolic pressure through higher resistance. As SBP moves downward and DBP is maintained, SBP − DBP narrows, providing an early sign of reduced SV despite preserved MAP.

Extra Information:

• Tachycardia is a compensation for reduced SV, not evidence that CO has normalized.

Source: Pearl Shock Prework slides 15–16, 21, 26–31

B10LG2.3. Explain why approximately 30–40% blood loss produces marked tachycardia, oliguria, and altered mental status.

Answer: By class III or progressive hemorrhage, venous return becomes too low to maintain SV and CO despite catecholamine stimulation. Systolic pressure drops, kidneys receive less blood and activate salt-retaining pathways, and cerebral perfusion begins to fail. HR can reach approximately 120–140/min, urine can decline to 5–15 mL/h, and the patient may become anxious or confused. This reflects decompensation of the pressure-preserving reflexes.

Extra Information:

• With loss above 40%, the chart shows HR >140, severely reduced BP, negligible urine, and profound mental-status changes.

Source: Pearl Shock Prework slides 28–31

B10LG2.3. What is the central warning about normotensive hypovolemia in adults versus children?

Answer: Adults may remain normotensive with compensated hemorrhage approaching about one-quarter of circulating volume because tachycardia and increased SVR defend MAP. Children often maintain pressure even longer because of strong vasoconstriction, with sudden late cardiovascular collapse when reserve is exhausted. In both, tachycardia, skin changes, worsening mentation, and low urine output can precede hypotension.

Extra Information:

• Recognize shock from perfusion rather than waiting for a threshold BP.

Source: Pearl Shock Prework slides 21–23, 27–31

B10LG2.4. Trace the earliest reversible cellular changes caused by prolonged shock-induced ischemia.

Answer: Inadequate oxygen delivery → impaired mitochondrial oxidative phosphorylation → ATP depletion → Na⁺/K⁺-ATPase and Ca²⁺ pump activity fall. Intracellular Na⁺ and water accumulate, causing cell and organelle swelling. Ribosomes detach from rough ER, lowering protein synthesis, and plasma membranes develop blebs with chromatin clumping. Early restoration of perfusion may reverse these changes before membrane and mitochondrial destruction becomes irreversible.

Extra Information:

• Cell swelling is the earliest characteristic morphologic sign of reversible cell injury.

Source: Pearl Shock Prework slides 3–6, 52 | First Aid 2025 p. 203

B10LG2.4. How does prolonged low oxygen delivery progress from reversible injury to irreversible mitochondrial and membrane damage?

Answer: Sustained ATP depletion and Ca²⁺ homeostasis failure → intracellular calcium accumulation activates phospholipases, proteases, and endonucleases. Mitochondria lose membrane integrity and electron transport function, preventing ATP recovery. Plasma membrane rupture allows enzymes to leak, lysosomal rupture promotes autodigestion, and nuclear changes progress through pyknosis, karyorrhexis, and karyolysis. This produces irreversible cell injury and necrosis.

Extra Information:

• Mitochondrial dysfunction both results from and amplifies shock-induced energy failure.

Source: Pearl Shock Prework slides 3–6, 52 | First Aid 2025 p. 203

B10LG2.4. How does intrinsic mitochondrial apoptosis differ from necrosis following shock-related cell injury?

Answer: Mitochondrial apoptosis is regulated by BCL-2 family proteins. Proapoptotic BAX and BAK permeabilize mitochondria → cytochrome c release → caspase activation → cell shrinkage and apoptotic bodies with comparatively little inflammation. Severe ischemic necrosis produces ATP failure, membrane disruption, enzyme leakage, and inflammatory cell injury. Both can occur with prolonged tissue stress, but extensive energy failure favors necrotic injury.

Extra Information:

• BCL-2 and BCL-xL inhibit mitochondrial cytochrome c release, opposing apoptosis.

Source: Pearl Shock Prework slide 52 | First Aid 2025 pp. 203–204

B10LG2.4. What is reperfusion injury, and why can restoring oxygen paradoxically worsen cellular damage?

Answer: Reoxygenation of previously ischemic tissue can generate reactive oxygen species, recruit inflammatory leukocytes, and aggravate calcium-related mitochondrial injury. These processes can damage membranes, proteins, and DNA even as circulation is restored. Reperfusion is still essential to salvage threatened tissue, but time-dependent irreversible injury explains why untreated shock can progress to multiorgan failure despite later correction of systemic pressure.

Extra Information:

• Rapid treatment matters because restoring flow cannot resurrect cells that have already undergone necrosis.

Source: Pearl Shock Prework slide 52 | First Aid 2025 pp. 203–204, 206

B10LG2.4. Why do mitochondrial failure and cell death cause multiorgan dysfunction in prolonged shock?

Answer: Insufficient mitochondrial ATP impairs renal tubular transport, neuronal ion gradients, cardiomyocyte contraction, and intestinal epithelial barrier integrity. Ongoing hypoperfusion and inflammation cause cell swelling, death, capillary injury, and microvascular malfunction. Kidney injury worsens fluid and acid-base control, cardiac dysfunction further lowers CO, and barrier failure can amplify inflammation, producing a self-reinforcing cycle of multiorgan dysfunction and potentially death.

Extra Information:

• Early shock may be reversible, while late cell and organ injury may persist after apparent hemodynamic improvement.

Source: Pearl Shock Prework slides 3–6, 37, 52 | First Aid 2025 pp. 203–204, 317

B10LG2.5. Distinguish an inotrope, a vasopressor, a vasodilator, and a diuretic by the variable each primarily changes.

Answer: An inotrope raises myocardial contractile force and often CO, helping pump failure. A vasopressor raises vascular tone and SVR to defend perfusion pressure in vasodilatory or severe hypotensive shock. A vasodilator reduces resistance and afterload, potentially improving forward output when BP tolerates it. A diuretic promotes sodium and water excretion, lowering congestion and filling pressure but potentially worsening low preload or hypotension.

Extra Information:

• Select therapy by the patient's volume status, vascular tone, pump function, and cause rather than by BP alone.

Source: Pearl Shock Prework slides 14, 38, 50 | First Aid 2025 pp. 241, 245, 316

B10LG2.5. Why does dobutamine improve low-output cardiogenic shock, and what is the signaling pathway?

Answer: Dobutamine predominantly stimulates cardiac beta-1 receptors → Gs activates adenylyl cyclase → cAMP and PKA signaling increase calcium availability in cardiomyocytes → stronger contraction and greater stroke volume. Some beta-2 vasodilation may reduce SVR. It can increase HR and myocardial O₂ demand, worsen tachyarrhythmias, or lower BP, so it is selected for pump failure with careful pressure assessment.

Extra Information:

• It does not remove coronary artery obstruction or reverse the cause of myocardial injury.

Source: Pearl Shock Prework slide 38 | First Aid 2025 pp. 237, 241

B10LG2.5. Explain milrinone's dual inotropic and vasodilating actions and important adverse effects.

Answer: Milrinone inhibits phosphodiesterase-3. In cardiomyocytes, inhibited cAMP degradation increases cAMP → calcium handling and contractility improve. In vascular smooth muscle, increased cAMP inhibits myosin light-chain kinase → vasodilation, decreasing preload and afterload. This inodilator profile may help selected low-output heart failure but can cause hypotension, tachycardia, and ventricular arrhythmias.

Extra Information:

• Unlike dobutamine, milrinone increases cAMP downstream of the beta receptor.

Source: Pearl Shock Prework slide 38 | First Aid 2025 p. 245

B10LG2.5. Why is norepinephrine a logical vasopressor for persistent septic vasodilation?

Answer: Norepinephrine strongly stimulates alpha-1 receptors on vascular smooth muscle → Gq, IP₃, and intracellular calcium increase → arteriolar constriction raises SVR and MAP. It also has beta-1 activity that can support contractility. In adequately evaluated septic shock, it counters persistent loss of vascular tone after initial volume resuscitation without requiring a primary increase in oxygen saturation.

Extra Information:

• Monitor perfusion and cardiac output because excessive vasoconstriction may worsen ischemia or afterload.

Source: Pearl Shock Prework slide 38 | First Aid 2025 pp. 236–237, 241

B10LG2.5. Compare phenylephrine, epinephrine, and norepinephrine by their receptor actions and shock effects.

Answer: Phenylephrine is primarily alpha-1 agonism, producing vasoconstriction with little direct inotropy and possible reflex bradycardia. Norepinephrine has strong alpha-1 and some beta-1 effects, raising vascular resistance with some myocardial support. Epinephrine stimulates alpha and beta receptors, providing alpha-1 vasoconstriction, beta-1 inotropy and chronotropy, and beta-2 bronchodilation, making it essential in anaphylaxis. High adrenergic activity can provoke tachyarrhythmias or increased oxygen demand.

Extra Information:

• Alpha-1 signals Gq while beta-1 and beta-2 signal Gs.

Source: Pearl Shock Prework slide 38 | First Aid 2025 pp. 236–237, 241

B10LG2.5. Explain dopamine's dose-related hemodynamic effects and why it cannot replace volume in hypovolemic shock.

Answer: Dopamine's receptor profile varies with dose: lower doses have dopaminergic effects, intermediate doses recruit cardiac beta-1 stimulation and raise HR and contractility, and higher doses recruit alpha-1 vasoconstriction to raise SVR. Tachyarrhythmias and increased myocardial oxygen demand are important concerns. In hypovolemia, drug-induced vascular tone cannot restore the missing blood or fluid volume, so source control and volume replacement remain primary.

Extra Information:

• Do not use low-dose dopamine as a substitute for treating renal hypoperfusion.

Source: Pearl Shock Prework slide 38 | First Aid 2025 pp. 241, 607

B10LG2.5. When do loop diuretics or vasodilators help cardiogenic pulmonary congestion, and when can they make shock worse?

Answer: In congested heart failure with adequate perfusion, diuretics reduce salt and water, lowering filling pressure and pulmonary edema. A vasodilator can reduce LV afterload and improve forward flow when BP permits. In frank hypovolemia or severe hypotensive pump failure, either intervention can further reduce effective filling or perfusion pressure. Neither diuresis nor afterload reduction automatically fixes the initial low-output cause.

Extra Information:

• A high PCWP and crackles favor congestion, while a flat JVP and low wedge argue against reflexive diuresis.

Source: Pearl Shock Prework slides 38, 50–51 | Shock Week Equation Worksheets Answer Key p. 2 | First Aid 2025 p. 316

B10LG2.5. Match initial cause-specific treatment priorities to hypovolemic, cardiogenic, distributive, and obstructive shock.

Answer: Hypovolemic: control losses and replace fluid or blood. Cardiogenic: assess congestion and ischemia, support contractility with an inotrope when needed and use a vasopressor if critically hypotensive. Septic distributive: fluids and infection control, then vasopressor for sustained vasoplegia. Anaphylactic: epinephrine and airway management. Neurogenic: restore appropriate filling plus vascular tone. Obstructive: relieve tamponade, tension pneumothorax, or high-risk PE rather than relying on fluids or pressors as definitive therapy.

Extra Information:

• Faculty mnemonic is assess and treat preload, afterload, and pump.

Source: Pearl Shock Prework slides 38, 40–50 | Shock Answer Key p. 1 | First Aid 2025 pp. 241, 317

B10B1. Which structural and physiological factors determine gas diffusion across the alveolar–capillary interface?

Answer: Fick diffusion is proportional to surface area, the gas diffusion coefficient, and the partial-pressure gradient, and inversely proportional to membrane thickness. Oxygen must cross alveolar lining fluid and type I epithelium, the shared basement membrane or interstitium, and pulmonary capillary endothelium to enter blood. Edema or fibrosis increases diffusion distance, while emphysema reduces effective area. Poor ventilation or perfusion can impair oxygenation even with a structurally intact membrane.

Extra Information:

• CO₂ diffuses more readily than O₂, so hypoxemia can precede hypercapnia in many lung disorders.

Source: First Aid 2025 pp. 679, 684–686 | ARDS supplied study guide LO 3

B10B1. Compare perfusion-limited and diffusion-limited gas transfer, including how ARDS changes exchange.

Answer: In healthy lungs, O₂ generally equilibrates with alveolar gas early along the capillary, so transfer is mainly perfusion limited. Fibrosis, edema, or loss of alveolar surface area can prevent full equilibration, especially with exercise, producing a diffusion component. In ARDS, barrier injury causes protein-rich alveolar flooding, collapse, low-V/Q regions and shunt, while inflammation may increase effective diffusion distance. Combined mechanisms lower arterial oxygenation.

Extra Information:

• CO is used as a diffusion-limited test gas for DLCO, whereas N₂O is a classic perfusion-limited gas.

Source: First Aid 2025 pp. 684–686, 697 | ARDS supplied study guide LOs 1, 3

B10B1. How do ventilation-perfusion mismatch, shunt, and dead space differ physiologically in acute respiratory failure?

Answer: Low V/Q means blood flow is relatively high compared with ventilation, reducing oxygenation. A true shunt has perfusion but essentially no ventilation, V/Q = 0, so blood bypasses effective oxygenation and responds poorly to supplemental O₂. Dead space has ventilation without perfusion, V/Q approaching infinity, wasting ventilation. ARDS creates important shunt and low-V/Q units from flooded or collapsed alveoli and may increase dead space through microvascular injury.

Extra Information:

• Pulmonary embolism acutely increases regional dead space because ventilation persists despite lost perfusion.

Source: First Aid 2025 pp. 682, 685–686, 697 | ARDS supplied study guide LOs 1, 3

B10B1. Why are ARDS lungs stiff, hypoxemic, and often difficult to oxygenate with supplemental oxygen alone?

Answer: Inflammation injures capillary endothelium and alveolar epithelium → protein-rich fluid leaks into airspaces and surfactant becomes ineffective → alveoli collapse and the lungs become poorly compliant. Blood continues passing some unventilated alveoli, forming intrapulmonary shunt, so adding FiO₂ cannot fully oxygenate that bypassed blood. Inflammation and hypoxic vasoconstriction also raise pulmonary vascular resistance and can strain the RV.

Extra Information:

• Positive end-expiratory pressure can recruit unstable alveoli and reduce repeated collapse, improving oxygenation.

Source: First Aid 2025 pp. 683, 685–686, 697 | ARDS supplied study guide LOs 1, 3

B10B2. How do type I pneumocytes support alveolar gas exchange, and what happens when ARDS damages them?

Answer: Type I pneumocytes are flattened simple squamous epithelial cells lining roughly 97% of alveolar surface. Their thin cytoplasm supports rapid O₂ and CO₂ diffusion and helps maintain the epithelial barrier. In ARDS, type I injury disrupts tight epithelial separation → edema fluid and proteins enter alveoli, diffusion and ventilation deteriorate, and denuded surfaces contribute to hyaline-membrane formation and collapse.

Extra Information:

• Type I cells are optimized for exchange, whereas type II cells are the major regenerative source after injury.

Source: First Aid 2025 pp. 679, 697 | ARDS supplied study guide LOs 1, 4

B10B2. State all key type II pneumocyte functions and how each affects ARDS recovery.

Answer: Type II pneumocytes are cuboidal cells with lamellar bodies that synthesize and secrete DPPC-rich surfactant. They proliferate and differentiate into new type I and type II cells during repair. Alveolar epithelial Na⁺ entry through ENaC and basolateral Na⁺/K⁺-ATPase promote osmotic fluid removal. Injury to type II cells therefore reduces surfactant production, worsens alveolar collapse, impairs edema clearance, and slows epithelial repair.

Extra Information:

• Surfactant proteins SP-A and SP-D also contribute to innate alveolar host defense, as described in the supplied ARDS guide.

Source: First Aid 2025 pp. 679, 697 | ARDS supplied study guide LO 4

B10B2. Compare type I pneumocytes, type II pneumocytes, and alveolar macrophages by location, structure, and function.

Answer: Type I cells are flat and cover most alveolar surface for gas diffusion. Type II cells are cuboidal, often at alveolar corners, and provide surfactant and epithelial regeneration. Alveolar macrophages reside on the airspace surface and phagocytose particles or pathogens while releasing inflammatory mediators. In ARDS, macrophage-triggered inflammation and neutrophil recruitment injure the exchange barrier while type II injury weakens repair and surface-tension control.

Extra Information:

• Hemoglobin breakdown in alveolar macrophages can produce hemosiderin-laden heart-failure cells in chronic pulmonary congestion.

Source: First Aid 2025 pp. 679, 316, 697 | ARDS supplied study guide LOs 1, 4

B10B3. What is pulmonary surfactant made of, where is it produced, and what physical force does it reduce?

Answer: Surfactant is produced by alveolar type II pneumocytes and stored in lamellar bodies. Its principal phospholipid is dipalmitoylphosphatidylcholine, or DPPC. The surfactant film reduces air-liquid surface tension at the alveolar interface, increasing lung compliance, lowering work of breathing, and preventing end-expiratory collapse of small alveoli. The supplied guide additionally identifies SP-B and SP-C as film-stabilizing proteins and SP-A and SP-D as host-defense proteins.

Extra Information:

• Surfactant deficiency in a premature infant causes neonatal respiratory distress, whereas ARDS typically causes acquired inactivation and loss.

Source: First Aid 2025 p. 679 | ARDS supplied study guide LO 4

B10B3. Use Laplace's law to explain how surfactant prevents small alveoli from emptying into large alveoli.

Answer: For an ideal spherical alveolus, collapsing pressure P = 2T/r, with surface tension T and radius r. Without surfactant, as radius decreases the required distending pressure rises, so small alveoli tend to collapse into larger ones. Surfactant molecules become more concentrated as an alveolus shrinks, lowering T enough to stabilize small alveoli. This improves end-expiratory patency and reduces the pressure required to reinflate the lung.

Extra Information:

• Loss of surfactant lowers compliance and predisposes to atelectasis and intrapulmonary shunt.

Source: First Aid 2025 pp. 679, 683, 697

B10B3. Explain how protein-rich ARDS edema causes a positive feedback loop of surfactant failure and lung injury.

Answer: Inflammatory injury causes protein-rich fluid to enter alveoli, interfering with the surfactant layer. Type II cell damage also decreases surfactant replacement. Surface tension rises → dependent and small alveoli collapse → shunt and hypoxemia worsen, compliance falls, and larger pressures are needed to reopen alveoli. Repeated collapse and recruitment can add mechanical epithelial injury, sustaining edema and pulmonary dysfunction.

Extra Information:

• PEEP helps preserve alveolar recruitment, while low tidal volume reduces overdistension injury.

Source: First Aid 2025 pp. 683, 697 | ARDS supplied study guide LOs 1, 4

B10B4. What sequence should be used to interpret any ABG, including possible mixed disorders?

Answer: First check pH for acidemia below 7.35 or alkalemia above 7.45. Next assess PaCO₂ and HCO₃⁻ to identify respiratory versus metabolic primary change. If metabolic acidosis is present, calculate AG = Na − (Cl + HCO₃) and expected PaCO₂ using Winter's equation. If respiratory disorder is primary, check whether renal bicarbonate compensation matches the acute or chronic time course. Finally evaluate PaO₂, FiO₂, and the A–a gradient or P/F ratio for oxygenation defects.

Extra Information:

• Compensation does not explain a pH overshoot in a simple primary disorder, so actively search for a mixed disorder.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610, 685–686

B10B4. Distinguish the four primary acid-base disorders and their expected compensations.

Answer: Metabolic acidosis: primary HCO₃⁻ ↓ and pH ↓, with compensatory hyperventilation lowering PaCO₂. Metabolic alkalosis: HCO₃⁻ ↑ and pH ↑, with compensatory hypoventilation raising PaCO₂. Respiratory acidosis: primary PaCO₂ ↑ and pH ↓, with delayed renal HCO₃⁻ retention. Respiratory alkalosis: PaCO₂ ↓ and pH ↑, with delayed renal HCO₃⁻ excretion. Acute respiratory disturbances have less renal bicarbonate adjustment than chronic disturbances.

Extra Information:

• Time since onset explains why two patients with similar PaCO₂ may have different pH values.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610

B10B4. An ABG shows pH 7.28, PaCO₂ 24, HCO₃⁻ 12, Na 139, and Cl 102. Identify the primary disturbance, anion gap, and respiratory compensation.

Answer: The low pH and HCO₃⁻ identify metabolic acidosis. AG = 139 − (102 + 12) = 25 mEq/L, a high-anion-gap acidosis consistent with lactic accumulation in hypovolemic shock. Winter's predicted PaCO₂ = 1.5 × 12 + 8 ± 2 = 26 ± 2, so the actual PaCO₂ of 24 is at the lower end of appropriate respiratory compensation rather than a clear second disorder.

Extra Information:

• This reproduces the faculty ABG C pattern for the patient in hypovolemic shock.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610

B10B4. Compare ABGs in acute hypoventilation, chronic CO₂ retention, panic-related hyperventilation, and acute pneumonia.

Answer: Acute hypoventilation or opioid effect: PaCO₂ rises, pH falls, and HCO₃⁻ increases only slightly. Chronic neuromuscular hypoventilation or COPD: PaCO₂ remains high but kidneys retain enough HCO₃⁻ to partially normalize pH over days. Panic hyperventilation: low PaCO₂ produces acute respiratory alkalosis. Early hypoxemic pneumonia can stimulate tachypnea and low PaCO₂, sometimes alongside metabolic acidosis from sepsis.

Extra Information:

• The faculty ABG key uses B for pneumonia after morphine, D for panic, F for chronic hypoventilation, and A for pneumonia with tachypnea.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610, 686

B10B4. How do you distinguish acute versus chronic respiratory acidosis from changes in HCO₃⁻?

Answer: An acute PaCO₂ increase has little time for renal compensation, so HCO₃⁻ rises by roughly 1 mEq/L for every 10 mmHg PaCO₂ increase over 40. Over several days, renal ammonium excretion and bicarbonate retention increase HCO₃⁻ by roughly 3.5–4 mEq/L per 10 mmHg PaCO₂ rise. For example, PaCO₂ 54 with HCO₃⁻ 31 and near-normal pH suggests a chronic component, while PaCO₂ 55 with HCO₃⁻ 22 and pH 7.26 suggests an acute process or an added metabolic acidosis.

Extra Information:

• Evaluate the entire ABG because bicarbonate may be abnormal for an independent metabolic reason.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610

B10B4. A dyspneic patient has pH 7.30, PaCO₂ 35, PaO₂ 64, HCO₃⁻ 18, Na 137, and Cl 101. What disorders and gas-exchange abnormalities are present?

Answer: Primary high-anion-gap metabolic acidosis is present because AG = 137 − (101 + 18) = 18 mEq/L. Winter's expected PaCO₂ is 1.5 × 18 + 8 ± 2 = 35 ± 2, so measured 35 is appropriate compensation. PaO₂ of 64 demonstrates hypoxemia. On room air at sea level, PAO₂ ≈ 150 − 35/0.8 ≈ 106, yielding A–a gradient ≈ 42 mmHg, indicating additional gas-exchange abnormality beyond pure metabolic acidosis.

Extra Information:

• The faculty ABG answer sheet labels this as pattern A in pneumonia with tachypnea.

Source: ABG Answer Key p. 1 | First Aid 2025 pp. 609–610, 685–686

B10B5. Explain the sigmoid oxygen–hemoglobin dissociation curve and recall PaO₂ versus SaO₂ anchor points.

Answer: Hemoglobin binding is cooperative: binding one O₂ favors the relaxed high-affinity state for subsequent O₂, creating a sigmoidal curve. At PaO₂ near 100 mmHg, SaO₂ is about 97–98%. At PaO₂ around 60, SaO₂ is about 90%. At tissue or mixed venous PO₂ around 40, saturation is about 75%. The flat upper portion protects pulmonary loading, while the steep lower portion facilitates substantial oxygen unloading from modest PO₂ changes.

Extra Information:

• P50, the PO₂ giving 50% Hb saturation, is approximately 26–27 mmHg in normal adult blood.

Source: First Aid 2025 p. 687 | ARDS supplied study guide LO 6

B10B5. Which factors shift the oxygen–hemoglobin curve right, and how does the shift affect P50 and tissue unloading?

Answer: Higher CO₂, acidity or H⁺, 2,3-BPG, exercise, and temperature shift the curve RIGHT. In the Bohr effect, increased CO₂ and H⁺ stabilize the low-affinity deoxyhemoglobin state. Hemoglobin affinity for oxygen decreases, so P50 increases and tissues can unload more O₂ at a given PO₂. Mnemonic: CADET face Right = CO₂, Acid, 2,3-DPG, Exercise, Temperature.

Extra Information:

• Fever, acidemia, and hypercapnia in critical illness often favor right shifting.

Source: First Aid 2025 pp. 687–688 | ARDS supplied study guide LO 6

B10B5. Which factors shift the oxygen–hemoglobin curve left, and why may high saturation still coexist with tissue hypoxia?

Answer: Low CO₂, alkalosis, hypothermia, low 2,3-BPG, fetal hemoglobin, carboxyhemoglobin, and methemoglobin shift remaining functional Hb toward higher O₂ affinity and lower P50. This favors lung loading but impairs peripheral release. CO poisoning also occupies Hb binding sites, lowering total O₂ content despite a possibly normal measured PaO₂, while cyanide blocks mitochondrial oxygen use without necessarily altering the Hb curve.

Extra Information:

• HbF binds 2,3-BPG less strongly, which helps transfer maternal oxygen to the fetus.

Source: First Aid 2025 pp. 687–689 | ARDS supplied study guide LO 6

B10B5. Why are PaO₂, SaO₂, CaO₂, and oxygen delivery not interchangeable measures?

Answer: PaO₂ measures dissolved oxygen tension, SaO₂ is the fraction of functional hemoglobin sites carrying O₂, CaO₂ is the total volume of oxygen in arterial blood, and DO₂ is CaO₂ multiplied by cardiac output. Severe anemia can lower CaO₂ despite normal PaO₂ and SaO₂. Low CO can lower DO₂ despite normal arterial content. CO or methemoglobin can impair Hb-bound transport while PaO₂ remains near normal.

Extra Information:

• CaO₂ includes a large hemoglobin-bound term and a much smaller dissolved oxygen term.

Source: Pearl Shock Prework slides 8–10 | First Aid 2025 pp. 686–689

B10B6. Derive and apply the alveolar gas equation and A–a gradient on room air at sea level.

Answer: PAO₂ = FiO₂ × (atmospheric pressure − water vapor pressure) − PaCO₂/R, with R about 0.8. On room air at sea level, PAO₂ ≈ 0.21 × (760 − 47) − PaCO₂/0.8 ≈ 150 − 1.25 × PaCO₂. A–a gradient = PAO₂ − measured PaO₂. For PaCO₂ 40 and PaO₂ 60, PAO₂ = 100 and A–a = 40 mmHg, abnormally widened in most young adults.

Extra Information:

• In room-air calculations, use the measured PaCO₂ to estimate alveolar oxygen tension.

Source: First Aid 2025 p. 685 | ARDS supplied study guide LO 5

B10B6. What is the approximate normal A–a gradient and how does it separate hypoventilation from ARDS?

Answer: Expected normal A–a gradient is approximately age/4 + 4 mmHg, so it rises somewhat with age. In pure hypoventilation or reduced inspired oxygen, PAO₂ and PaO₂ both fall with a relatively normal gradient. In ARDS, alveolar collapse and flooding cause shunt and V/Q mismatch, so arterial PaO₂ falls disproportionately and the A–a gradient widens. The calculation distinguishes impaired lung gas transfer from simple reduced alveolar oxygen supply.

Extra Information:

• A normal A–a gradient does not mean PaO₂ is normal.

Source: First Aid 2025 pp. 685–686, 697

B10B6. Compare the response to 100% oxygen in pulmonary shunt, V/Q mismatch, and hypoventilation.

Answer: In true shunt, blood perfuses nonventilated alveoli, so even 100% inspired oxygen has limited ability to raise oxygen content in that shunted blood. In typical V/Q mismatch, some alveolar ventilation remains, so increasing FiO₂ more effectively raises PaO₂. In pure hypoventilation without major parenchymal disease, oxygen administration can raise PaO₂ despite elevated PaCO₂. ARDS often has a major shunt component and therefore disproportionately difficult-to-correct hypoxemia.

Extra Information:

• Raising oxygen does not directly solve CO₂ retention if alveolar ventilation remains inadequate.

Source: First Aid 2025 pp. 685–686, 697