Shock

Shock is a state of inadequate tissue perfusion resulting in cellular hypoxia, lactic acidosis, and organ dysfunction.

Four stages: Initial → Compensatory → Progressive → Refractory.

1. Initial

• ↓ Tissue perfusion → cellular hypoxia.
• ↑ Lactic acid → metabolic acidosis.
• The liver cannot clear lactate because of ↓ O₂.

2. Compensatory

Physiologic mechanisms attempt to preserve MAP and pH.

Key responses

• Hyperventilation → ↓ CO₂ → ↑ pH.
• Sympathetic activation: norepinephrine causes vasoconstriction; epinephrine increases HR and cardiac output.
• Baroreceptor activation.
• RAAS: Na⁺ and H₂O retention.
• ADH (vasopressin): water retention.

Blood is shunted away from the kidneys, GI tract, and skin, and preserved for the brain, heart, and lungs.

Clinical signs

• Tachycardia.
• Normal or near-normal BP.
• ↓ Urine output.

3. Progressive (decompensated)

• Compensatory mechanisms fail.
• Worsening metabolic acidosis.
• ↓ Cardiac output.
• Hypotension.
• Oliguria.
• Altered mental status.

4. Refractory (irreversible)

• Severe cellular and organ damage.
• Multi-organ failure.
• Brain damage.
• No response to fluids or vasopressors.
• Death imminent.

Mnemonic: CHODE.

1. Hypovolemic shock — most common

Cause: ↓ Intravascular volume, usually hemorrhage (internal or external).

Key findings:

• Tachycardia.
• Narrow pulse pressure (early).
• Hypotension (late).
• Cool, clammy skin.
• ↓ Urine output.
• Altered mental status.

2. Cardiogenic shock

Cause: failure of the heart to pump effectively.

Most common cause: a large myocardial infarction.

Other causes: arrhythmias, cardiomyopathy, acute CHF, valvular rupture, cardiac contusion, and air embolism.

Key findings: hypotension, pulmonary edema, ↑ JVP, and cool extremities.

3. Distributive shock

Pathophysiology: ↓ Systemic vascular resistance and relative hypovolemia due to vasodilation.

Types: septic, anaphylactic, and neurogenic.

Key findings: warm, flushed skin (early); wide pulse pressure; hypotension despite normal volume.

4. Obstructive shock

Cause: mechanical obstruction to blood flow.

Examples: cardiac tamponade, tension pneumothorax, and massive pulmonary embolism.

Classic clues: hypotension, elevated JVP, and clear lungs (tamponade).

5. Endocrine shock

Causes:

• Acute adrenal insufficiency: sudden steroid withdrawal or stress without a steroid dose increase.
• Hypothyroidism: ↓ Cardiac output → hypotension.
• Thyrotoxicosis: reversible cardiomyopathy.

CO: cardiac output. SVR: systemic vascular resistance. N: normal.

• Tachycardia is an early sign.
• Oliguria = shock until proven otherwise.
• Elevated lactate = tissue hypoxia.
• Warm versus cold extremities helps identify the shock type.