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12-20: Shock

Warren J. Gasper; James C. Iannuzzi; Meshell D. Johnson

ESSENTIALS OF DIAGNOSIS

ESSENTIALS OF DIAGNOSIS

  • Hypotension, tachycardia, oliguria, altered mental status.

  • Peripheral hypoperfusion and impaired oxygen delivery.

  • Four classifications: hypovolemic, cardiogenic, obstructive, or distributive.

GENERAL CONSIDERATIONS

Shock occurs when the rate of arterial blood flow is inadequate to meet tissue metabolic needs. This results in regional hypoxia and subsequent lactic acidosis from anaerobic metabolism in peripheral tissues as well as eventual end-organ damage and failure.

CLASSIFICATION

Table 12–1 outlines common causes and mechanisms associated with each type of shock.

Table 12–1.Classification of shock by mechanism and common causes.
View Table||Download (.pdf)
Table 12–1. Classification of shock by mechanism and common causes.

Hypovolemic shock

 Blood loss

  Traumatic hemorrhage

   Exsanguination

   Hemothorax

   Hemoperitoneum

   Fracture (femur and pelvis)

  Nontraumatic hemorrhage

   GI bleed

   AAA rupture

   Ectopic pregnancy rupture

 Volume loss

  Burns

  Skin integrity loss (toxic epidermal necrolysis)

  Vomiting

  Diarrhea

  Hyperosmolar states (eg, hyperosmolar hyperglycemic state)

  Third spacing (eg, ascites, pancreatitis)

  Decreased intake

Cardiogenic shock

 Dysrhythmia

  Bradycardias and blocks

  Tachycardias

 Myocardial disease

  Left or right ventricular infarction

  Dilated cardiomyopathy

 Mechanical

  Valvular

   Aortic regurgitation from dissection

   Papillary muscle rupture from ischemia

   Acute valvular rupture from abscess

  Ventricular aneurysm rupture

  Ventricular septum rupture

  Ventricular free wall rupture

Obstructive shock

 Tension pneumothorax

 Pericardial disease

  Pericardial tamponade

  Constrictive pericarditis

 High-risk (massive) PE

 Severe pulmonary hypertension

 Auto PEEP from mechanical ventilation

Distributive (vasodilatory) shock

 Anaphylactic shock

 Septic shock

 Neurogenic shock

 Drug-induced vasodilation

 Adrenal insufficiency

Reproduced with permission from Stone CK, Humphries RL (editors). Current Emergency Diagnosis & Treatment, 7th ed. NY: McGraw-Hill, 2011.

PEEP, positive end expiratory pressure.

A. Hypovolemic Shock

Hypovolemic shock results from decreased intravascular volume secondary to loss of blood or fluids and electrolytes. The etiology may be suggested by the clinical setting (eg, trauma) or by signs and symptoms of blood loss (eg, GI bleeding) or dehydration (eg, vomiting or diarrhea). Compensatory vasoconstriction may transiently maintain the blood pressure but unreplaced losses of over 15% of the intravascular volume can result in hypotension and progressive tissue hypoxia.

B. Cardiogenic Shock

Cardiogenic shock results from cardiac failure with the resultant inability of the heart to maintain adequate tissue perfusion. The clinical definition of cardiogenic shock is evidence of tissue hypoxia due to decreased cardiac output (cardiac index less than 2.2 L/minute/m2) in the presence of adequate intravascular volume. This is most often caused by MI but can also be due to cardiomyopathy, myocardial contusion, valvular incompetence or stenosis, or arrhythmias. See Chapter 10.

C. Obstructive Shock

Pericardial tamponade, tension pneumothorax, and massive PE can cause an acute decrease in cardiac output resulting in shock. These are medical emergencies requiring prompt diagnosis and treatment.

D. Distributive Shock

Distributive or vasodilatory ...

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