Comprehensive Study Guide on Clinical Shock and Emergency Shock

Introduction to Shock

• Definition: Shock is a clinical syndrome characterized by a failure to adequately perfuse and oxygenate vital organs. It is recognized by features of tissue hypoperfusion.

• Tissue Hypoperfusion Indicators:

  • Hypotension: Generally considered to be a Systolic Blood Pressure (SBP) less than $90\,mmHg$ in adults. Values may be higher in young, fit, or previously hypertensive patients.

  • Tachycardia: Heart rate $>100/min$ is common, though it may be absent in patients with cardiac/neurologic causes, those taking $\beta$-blockers, or some hemorrhagic shock patients experiencing paradoxical bradycardia.

  • Altered Consciousness: Includes fainting (especially on standing or sitting up), resulting from decreased cerebral perfusion.

  • Poor Peripheral Perfusion: Cool peripheries, clammy/sweaty skin, pallor, and decreased capillary return. Note: Early-phase endotoxin septic shock may present with vasodilation and warm peripheries.

  • Tachypnea: Increased respiratory rate.

  • Purpuric Rash.

  • Oliguria: Decreased renal perfusion resulting in low urine output.

Clinical Features and Identification

• Box 30.1: Clinical Features Criteria: Shock is indicated if more than two ($>2$) of the following are present:

  • Hemodynamic: SBP $<100\,mmHg$ or a drop of $>40\,mmHg$ from baseline; Pulse $>100/min$.

  • Skin: Capillary refill time $>2\,sec$ or cold/pale/mottled extremities.

  • Renal: Oliguria ($<0.5\,mL/kg/hr$) or an acute rise in serum creatinine.

  • CNS: Glasgow Coma Scale (GCS) $<15$, confusion, or agitation.

  • Global: Increased lactate (in the absence of hypoxemia).

• Emergency Context:

  • Shock is a time-dependent and reversible condition if caught early, but leads to multiple organ dysfunction and death if untreated.

  • Septic shock is the leading cause of death in the Intensive Care Unit (ICU).

  • Mortality rate exceeds $20\%$ across all shock categories.

  • Shock constitutes approximately $1\%$ of all Emergency Department (ED) visits.

Pathophysiology of Shock

• The Cascade of Failure:

  1. Vasoconstriction leads to failure of pre-capillary sphincters.

  2. Peripheral pooling of blood causes inadequate perfusion.

  3. Cell hypoxia leads to an energy deficit.

  4. Lactic acid accumulation and anaerobic metabolism occur, causing a fall in pH and metabolic acidosis.

  5. Cell membrane dysfunction leads to failure of the "sodium pump."

  6. Intracellular lysosomes release digestive enzymes.

  7. Toxic substances enter the circulation.

  8. Capillary endothelium damaged.

  9. Efflux of potassium ($K^{+}$) and influx of sodium ($Na^{+}$) and water.

  10. Further destruction, dysfunction, and cell death.

Classification and Distribution

• Four Major Types:

  1. Hypovolemic: Low blood volume.

  2. Cardiogenic: Impaired cardiac output.

  3. Distributive: Vasodilation (includes Septic, Anaphylactic, and Neurogenic).

  4. Obstructive: Mechanical obstruction.

• Prevalence Distribution:

  • Cardiogenic Shock: $51\%$

  • Septic Shock: $38\%$

  • Hypovolemic Shock: $7\%$

  • Anaphylactic Shock: $4\%$

  • Dengue Shock Syndrome: $0.4\%$

Initial Approach and Management

• Diagnostic Clues:

  • Fever/Warm extremities: Suggests Septic shock.

  • Trauma/GI bleeding/Vomiting/Diarrhea: Suggests Hypovolemic shock.

  • Volume overload/Cool, clammy extremities: Suggests Cardiogenic shock.

  • Spinal cord injury/Neurologic deficits: Suggests Neurogenic shock.

  • New medication or allergen exposure: Suggests Anaphylactic shock.

• Initial Stabilization Steps:

  • Simultaneous stabilization and determination of cause.

  • Workup: Complete Blood Count (CBC), Basic Metabolic Panel (BMP), infectious workup (blood/urine cultures, chest imaging), ECG, and bedside echocardiography.

  • Access: Establish two large-bore IVs; consider central and arterial lines if vasopressors are required.

  • Fluid Bolus: Multiple liters of Normal Saline or Lactated Ringer (except in cardiogenic shock).

  • Monitoring: Continuous pulse oximetry.

  • Vasopressors: Norepinephrine if hypotension persists after fluids.

• Swan-Ganz Catheter (Pulmonary Artery Catheter):

  • Used for monitoring critically ill patients (mostly ICU).

  • Measures pressures in the right atrium, right ventricle, pulmonary artery, and the filling pressure (wedge pressure/PCWP) of the left atrium.

  • Components include balloon inflation port, thermistor connection, and Cardiac Output computer connection.

Cardiogenic Shock

• Definition: Heart cannot generate output sufficient for tissue perfusion; SBP $<90\,mmHg$ with urine output $<20\,mL/hr$ and adequate or elevated left ventricular (LV) filling pressure.

• Causes:

  • Acute MI: Most common cause.

    • LV dysfunction ($71.3\%$

    • RV infarction ($13.5\%$

    • Acute mitral regurgitation ($8.0\%$

    • Ventricular septal rupture ($5.3\%$

    • Ventricular free wall rupture ($1.8\%$

  • Non-ischemic: Valvular heart disease ($49.3\%$), cardiomyopathies ($42.3\%$).

• Clinical Features: Ill-appearing, cool extremities (high SVR), JVP elevated (engorged neck veins), pulmonary congestion.

• Diagnosis: ECG for ischemia/arrhythmia; Echocardiogram for Ejection Fraction (EF) and mechanical complications.

• Swan-Ganz Targets: Cardiac output $>4\,L/min$, Cardiac Index (CI) $>2.2$.

• Treatment:

  • Emergent revascularization (PCI or CABG) for MI.

  • Preload reduction: Loop diuretics, dialysis, or Nitroglycerin.

  • Vasopressors: Norepinephrine (first-line). Note: SOAP II trial showed higher mortality with Dopamine compared to Norepinephrine.

  • Inotropes: Dobutamine or Milrinone to increase inotropy and decrease afterload.

  • Afterload reduction: Sodium nitroprusside (IV), Hydralazine, or Captopril (Oral).

  • Intra-aortic Balloon Pump (IABP): Decreases afterload and myocardial oxygen demand; increases cardiac output.

  • Advanced support: ECMO or Left Ventricular Assist Devices (LVADs).

Hypovolemic Shock

• Pathophysiology: Decreased circulatory volume leads to decreased preload and cardiac output, with a compensatory increase in SVR.

• Classification by Volume Loss:

  • Class I: $10-15\%$ loss. Vitals, CNS, and urine output are normal.

  • Class II: $15-30\%$ loss. Pulse $>100$, normal BP, decreased pulse pressure, delayed capillary refill, mild tachypnea, anxious, urine $20-30\,mL/hr$.

  • Class III: $30-40\%$ loss. Pulse $>120$ (weak), decreased BP, marked tachypnea, confused, urine $20\,mL/hr$.

  • Class IV: $>40\%$ loss. Pulse $>140$ (nonpalpable), marked BP decrease, absent capillary refill, lethargic/coma, negligible urine output.

• Causes:

  • Hemorrhage: Trauma, GI bleed, ruptured AAA, ectopic pregnancy.

  • Nonhemorrhagic: Vomiting, diarrhea, dehydration, burns, third-space losses (bowel obstruction).

• Treatment: Intubation for severe cases. Crystalloids and electrolyte replacement for nonhemorrhagic; Blood products and massive transfusion protocols for hemorrhage.

Septic Shock

• Definition: Hypotension induced by sepsis persisting despite adequate fluid resuscitation.

• Pathophysiology: Severe decrease in SVR due to peripheral vasodilation (warm skin). Cardiac output is normal or increased, but Ejection Fraction (EF) is decreased due to reduced contractility.

• SIRS Criteria (Systemic Inflammatory Response Syndrome): Two or more of the following:

  • Fever ($>38^{\circ}C$) or hypothermia ($<36^{\circ}C$).

  • Hyperventilation (RR $>20\,bpm$) or $PaCO_2 <32\,mmHg$.

  • Tachycardia ($>90\,bpm$).

  • WBC count $>12,000/hpf$, $<4,000/hpf$, or $>10\%$ band forms.

• Progression: SIRS $\rightarrow$ Sepsis $\rightarrow$ Septic Shock $\rightarrow$ Multiple Organ Dysfunction Syndrome (MODS).

• Treatment:

  • Fluid bolus: Usually $30\,cc/kg$ of body weight.

  • Empiric broad-spectrum IV antibiotics (maximum dosage) after obtaining cultures.

  • Vasopressors: Norepinephrine, Vasopressin, or Phenylephrine if hypotension persists.

Neurogenic Shock

• Causes: Failure of the sympathetic nervous system due to spinal cord injury, head injury, or spinal anesthesia.

• Clinical Features: Peripheral vasodilation, warm/well-perfused skin, bradycardia (paradoxical), decreased SVR, and low/normal PCWP.

• Treatment: Judicious IV fluids, cautious use of vasoconstrictors, Supine or Trendelenburg position, and maintenance of body temperature.

Obstructive Shock

• Causes: Massive Pulmonary Embolism (PE), Cardiac Tamponade, or Tension Pneumothorax.

• Clinical Features: High JVP, limited cardiac output, and compensatory increase in SVR.

• Specific Interventions:

  • Cardiac Tamponade: Pericardiocentesis or pericardial window.

  • Tension Pneumothorax: Needle thoracostomy followed by chest tube.

  • Massive PE: Thrombolysis (systemic or catheter-directed tPA) or thrombectomy.

Clinical Assessment Tools and Stages

• Shock Index (SI):

  • Formula: $SI = \frac{Heart\,Rate}{Systolic\,Blood\,Pressure}$.

  • Used as an early assessment tool for circulatory status in trauma and sepsis.

• Stages of Shock:

  • Compensated: $15-25\%$ fluid loss. Normal BP, tachycardia, redistribution of blood to brain, heart, and adrenal glands.

  • Decompensated: $25-35\%$ fluid loss. Hypotension, anaerobic energy production, worsening metabolic acidosis, and renal failure.

  • Irreversible: $>35\%$ fluid loss. Profound hypoxia, cell death, non-responsive to inotropes, intractable acidosis, MODS, and death.

Complications

• Acute Kidney Injury (AKI).

• Acute Respiratory Distress Syndrome (ARDS/Shock Lung).

• Disseminated Intravascular Coagulation (DIC).

• Multi-organ failure.

• Death.

Questions & Discussion

• Contributors: Group A members: Bile Ali Mohamoud, Ikaram C/qadir Ahmed, Laki Seid Mohamed, Nadiira Mohamed Said, Filsan Seid Farah. Course: Emergency Medicine.

• References: Oxford Handbook of EM (5th ed), Tintinalli's EM (9th ed), EM Secrets (6th ed), Step-up to Medicine (6th ed), Harrison’s Principles of Internal Medicine (21st ed), MacLeod's Clinical Diagnosis.