TABLE 12-1 -Classification of shock by mechanism and common causes

Hypovolemic shock	Loss of blood (hemorrhagic shock) External hemorrhage Trauma Gastrointestinal tract bleeding Internal hemorrhage Hematoma Hemothorax or hemoperitoneum Loss of plasma Burns Exfoliative dermatitis Loss of fluid and electrolytes External Vomiting Diarrhea Excessive sweating Hyperosmolar states (diabetic ketoacidosis, hyperosmolar nonketotic coma) Internal ("third spacing") Pancreatitis Ascites Bowel obstruction
Cardiogenic shock	Dysrhythmia Tachyarrhythmia Bradyarrhythmia "Pump failure" (secondary to myocardial infarction or other cardiomyopathy) Acute valvular dysfunction (especially regurgitant lesions) Rupture of ventricular septum or free ventricular wall
Obstructive shock	Tension pneumothorax Pericardial disease (tamponade, constriction) Disease of pulmonary vasculature (massive pulmonary emboli, pulmonary hypertension) Cardiac tumor (atrial myxoma) Left atrial mural thrombus Obstructive valvular disease (aortic or mitral stenosis)
Distributive shock	Septic shock Anaphylactic shock Neurogenic shock Vasodilator drugs Acute adrenal insufficiency

Reproduced, with permission, from Saunders CE, Ho MT (editors): Current Emergency Diagnosis & Treatment, 4th ed. McGraw-Hill, 1992.