Shock

What is shock?

The state of inadequate tissue perfusion that leads to insufficient delivery of oxygen and nutrients to cells

What do cells do as a result of shock?

They switch from aerobic to anaerobic metabolism, causing a buildup of metabolic waste which without timely reperfusion, this process results in cellular dysfunction and eventual cell death

What are the classifications of shock on the basis of cause?

• Hypovolemic shock

• Cardiogenic shock

• Septic shock

• Anaphylactic shock

• Traumatic shock

• Neurogenic shock

• Obstructive shock

What is hypovolemic shock?

When ther is inadequate circulatory blood volume

What is cardiogenic shock?

When there is a sudden fall in cardiac output from acute disease of the heart usually caused by MI, severe HF, Dysrythmias, or cardiomyopathy

What is septic shock?

When there is a severe systemic infection leading to widespread vasodilation and capillary leak

What is anaphylactic shock?

When there is a severe allergic reaction to an allergen causing airway swelling, bronchoconstriciton, vasodilation, and hypotension

What is neurogenic shock?

When there is a spinal cord injury or anesthetic accident causing loss of sympathetic tone

What is the main physiologic issue in neurogenic shock?

Peripheral vasodilation leading to blood pooling, hypotension, and bradycardia

What is obstructive shock?

A physical obstruction that is preventing adequate cardiac output often caused by tension pneumothorax, pulmonary embolism, or cardiac tamponade

What causes traumatic shock?

Severe injury leading to blood loss, tissue damage, or both

What are the steps to the pathophysiology of shock?

• Decreased effective circulating blood volume —>

• Decreased venous return to the heart —>

• Decreased cardiac output —>

• Decreased blood flow to tissues —>

• Decreased oxygen delivery —>

• Cellular hypoxia —>

• Anoxia and metabolic dysfunction —>

• Inflammatory mediators get released —>

• Vascular permeability increases —>

• Shock worsens

Why does vascular permeability increasing worsen shock?

Proteins leak out causing decreased oncotic pressure and more fluid loss

What lab helps evaluate severity of shock?

Lactic acid (indicates metabolic acidosis)

What is the formula for cardiac output?

CO = HR x SV

What is normal cardiac output?

4-8 L/min

What is preload?

Volume of blood in the ventricles at end diastole

What increases preload?

Increased venous return or fluid volume

How does increased preload affect contraction?

More stretch means more stronger contraction (Frank Starlings law)

What is afterload?

Resistance the left ventricle must overcome to eject blood

What increases afterload?

• Vasoconstriction

• Hypertension

• Aortic stenosis

How does increased afterload affect the heart?

Requires more force to pump blood

What is stroke volume?

The amount of blood pumped by the LV each breath (50-100 ml)

What determines stroke volume?

• Preload

• Contractility

• Afterload

What controls heart rate?

Autonomic nervous system

How do you increase preload?

IV fluids

How do you increase afterload and vascular resistance?

Vasopressors

How do you increase contractility?

Inotropic agents like digoxin or dobutamine

What are clinical features of shock?

• Very low BP

• Shallow sighing and respirations

• Subnormal temperature

• Feeble and irregular pulse

What are the stages of shock?

• Initial stage

• Compensatory stage

• Non progressive stage

• Progressive stage

• Irreversible stage

What happens in the initial stage of shock?

There is a drop in blood flow which leads to hypoxia, anxiety, and tachycardia. Then, anaerobic metabolism cellular response to the hypoxia kicks in

What happens in the compensatory stage of shock?

The body employs neural and hormonal responses to improve BP and O2 delivery and the body compensates for reduced perfusion by increasing heart rate and BP

What happens in the non progressive stage of shock?

The reflex compensatory mechanisms are activated and perfusion of vital organs is maintained

What happens in the progressive stage of shock?

There is tissue hypo perfusion, onset of worsening circulatory blood volume, increased capillary permeability, fluid shifts, and metabolic imbalances like acidosis

What happens in the irreversible stage of shock?

Severe cell and tissue injury even if hemodynamic effects are corrected (survival is not possible)

What are the two major categories of causes for hypovolemic shock?

• Blood loss

• Dehydration

What are common causes of blood loss leading to hypovolemic shock?

• External bleeding

• Internal bleeding

• Trauma

What are common causes of dehydration leading to hypovolemic shock?

• Vomiting

• Diarrhea

• Burns

• Excessive sweating

• Excessive diuretic use

What are the signs of hypovolemic shock?

• Heart rate increases

• Blood pressure decreases

• Urinary output decreases

• Mental status changes occur (confusion, restlessness, ALOC)

What hormone increases water reabsorption to raise BP?

ADH

How does ADH help in hypovolemic shock?

Increases water retention which increases BP and decrease urine output

What does aldosterone do during hypovolemic shock?

It increases Na reabsorption, increases water retention, and excretes K

What system causes vasoconstriction and stimulates aldosterone release?

Renin angiotensin system

What triggers sympathetic activation in hypovolemic shock and what is the sympathetic response to it?

Hypotension which triggers the sympathetic response is vasoconstriction and increased heart rate to try and raise BP

Which organs are prioritized during hypovolemic shock?

Heart (coronary vessels) and brain (cerebral vessels)

What is the main problem in cardiogenic shock?

Decreased cardiac output leading to decreased tissue perfusion

What types of dysfunction can cause cardiogenic shock?

• Systolic dysfunction

• Diastolic dysfunction

What is the primary treatment goal in cardiogenic shock?

Provide inotropic support to improve cardiac output

What are common symptoms of cardiogenic shock?

• Chest pain

• Shortness of breath

• Severe fatigue

• Decreased urine output

• Cool, clammy skin

• Dizziness

• Anxiety

How does the Frank Starling mechanism compensate for cardiogenic shock?

It increase preload which increases stretch and therefore increase contractility

What structural changes in them mycardium occur during chronic compensation?

Hypertrophy

What neurotransmitter is released during neurohumoral activation?

Norepinephrine

What does norepinephrine do in cardiogenic shock?

Increases heart rate and contractility

What hormonal system is activated in increase blood pressure and volume?

Renin angiotensin aldosterone system

How do cardiac events lead to pulmonary edema?

• MI, arrhythmia, or CHF —>

• Failure of myocardial pump —>

• Decreased cardiac output —>

• Decreased tissue perfusion —>

• Decreased fluid movement out of pulmonary vasculature —>

• Pulmonary interstitial edema —>

• Alveolar pulmonary edema

What is the mortality rate of septic shock?

Approximately 50%

What is the mediator cascade that leads to septic shock?

LPS —> TNF —> IL-1 —> IL-6/IL-8 —> NO and PAF

What happens when inflammatory mediators are released in low quantities?

Local inflammation

Which cells are activated during local infalmmation?

• Monocytes/Macrophages

• Neutrophils

• Endothelial cells

What complement components are activated in local inflammation?

• C3a

• C5a

What systemic effect occurs in the brain during moderate mediator release?

Fever

What systemic effect occurs in the liver during moderate mediator release?

Production of acute phase reactants

What systemic effect occurs in the bone marrow during moderate mediator release?

Increased leukocyte production

What happens to cardiac output in septic shock?

It decreases

What happens to peripheral resistance in septic shock?

It decreases (massive vasodilation)

What vascular complications occur in septic shock?

• Blood vessel injury

• Thrombosis

• DIC

What major respiratory complication can develop?

ARDS (acute respiratory distress syndrome)

What is anaphylactic shock?

An allergic reaction condition in which the CO and BP often decrease drastically resulting primarily from an Ag-Ab reaction that takes place immediately after an antigen to which the person is sensitive enters the circulation

What cells release histamine during an allergic reaction?

• Mast cells

• Basophils

What triggers mast cell degranulation?

Allergen binding to IgE antibodies on the mast cell surface

What does histamine do to veins and arterioles?

Causes venous dilation and arterioles dilation

What does histamine do to veins and arterioles?

Causes venous dilation and arterioles dilation

How does histamine affect vascular resistance and blood pressure?

Lowers vascular resistance which lowers blood pressure

What does histamine do to capillary permeability?

Increases permeability

What is the consequence of increased capillary permeability?

Fluid and protein leak into tissues

What symptoms can histamine release cause?

• Rash

• Wheezing

• Vomiting

What medications counteract histamine effects?

• Antihistamines

• Steroids

• Epinephrine

• Inhaled beta 2 agonists

What is the primary cause of neurogenic shock?

Spinal cord injury leading to loss of sympathetic vascular tone

What autonomic imbalance occurs in neurogenic shock?

Unopposed parasympathetic domination

What happens to systemic vascular resistance?

SVR decreases due to massive vasodilation

What happens to blood volume in neurogenic shock?

Volume is unchanged, but vasodilation creates relative hypovolemia

What happens to heart rate in neurogenic shock?

Bradycardia

What is the sequence of pathophysiology in neurogenic shock?

Loss of sympathetic tone —> vasodilation—> decreased SVR —> decreased cardiac output —> decreased tissue perfusion —> impaired cellular metabolism

What is the primary treatment for neurogenic shock?

Vasopressors

What is obstructive shock?

Shock caused by a physical obstruction that prevents normal blood flow through the circulation

What are the three most common causes of obstructive shock?

• Cardiac tamponade

• Tension pneumothorax

• Pulmonary embolism

How does cardiac tampanade cause obstructive shock?

Fluid in the pericardial sac compresses the heart which leads to impaired filling and then decreased cardiac output

How does tension pneumothorax cause obstructive shock?

Air trapped din the pleural space shifts mediastinum which leads to compressed vena cava and then decreased venous return

How does pulmonary embolism cause obstructive shock?

A clot blocks pulmonary circulation which leads to increased RV pressure and then decreased LV output

What are common symptoms of obstructive shock?

• Severe SOB

• Chest pain

• Rapid heart rate

• Decreased urine output

What is the primary treatment goal of obstructive shock?

Remove the obstruction and stabilize hemodynamics

What interventions may be required?

• Needle decompression

• Pericardiocentesis

• Thrombolytics

• Supportive medications

What does chronotropic refer to?

The heart’s rate of contraction (SA node)

What is a positive vs negative chronotropic effect?

Positive means increased heart rate, negative means decreased heart rate

What meds cause positive chronotropic effects?

• Atropine

• Dobutamine

• Epinephrine

• Isoproerenol

• Caffeine

What meds cause negative chronotropic effects?

• Beta blockers (metroprolol, atenolol)

• Calcium channel blockers (verapamil, diltiazem)

• Digoxin

• Amiodarone

What does dromotropic refer to?

The rate of electrical conduction through the AV node

What drugs cause positive dromotropic effects?

• Digoxin

• Epinephrine

• Norepinephrine

• Dobutamine

What drug cause negative dromotropic effects?

• Beta blockers

• Calcium channel blockers

• Digoxin

• Antiarrhythmic agents

What does inotropic refer to?

The strength of myocardial contraction