Chapter 36

Shock

1 Define shock

Shock is a state in which blood flow to and perfusion of peripheral tissues is inadequate to sustain life. Although they are not included in a rigid definition of shock, for USMLE purposes, hypotension and oliguria or anuria are associated findings. Tachycardia is also usually present.

2 List the five primary clinical types of shock

Hypovolemic, cardiogenic, septic, anaphylactic, and neurogenic.

3 What should you do if a patient is in shock?

Keep the patient alive with the ABCs (airways, breathing, and circulation) while you look for the cause of the shock. Give oxygen and fluids unless the patient is in congestive heart failure. If congestive heart failure is present, avoid fluids.

4 How should fluids be given if a patient is in shock?

Many patients in shock need fluid. The standard intravenous bolus is 10 to 20 mL/kg of normal saline or lactated Ringer solution; infuse 1 to 2 L as fast as it will go. Then reassess the patient to determine whether the bolus helped; positive signs include increases in blood pressure and urine output. Do not be afraid to give a second bolus if the first bolus leads to no improvement. Watch for fluid overload, which may cause congestive heart failure. Make sure that no bilateral crackles can be heard on lung examination. Place a Foley catheter to ensure accurate monitoring of urine output.

5 What should you do if fluid challenges fail to raise the blood pressure?

Use invasive hemodynamic monitoring (i.e., Swan-Ganz catheter) to help determine the cause of the shock and to guide therapeutic decisions.

6 What are the classic parameters of each type of shock?

TYPE OF SHOCK	CO	PCWP	SVR	SVO2
Septic (early)	High	Low	Low	High
Hypovolemic	Low	Low	High	Low
Cardiogenic	Low	High	High	Low
Neurogenic Anaphylactic	Low High (but can be variable)	Low Low	Low Low	Low Low

CO, Cardiac output; PCWP, pulmonary capillary wedge pressure; SVR, systemic vascular resistance; SVO₂, systemic venous oxygen saturation.

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