NMS. Surgery

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Chapter 1 ♦ Principles of Surgical Physiology

II. Types of shock: Table 1-5 summarizes types of shock. A. Hypovolemic shock: Most common type of shock; hemorrhage is the most common reason for hypovolemia. Loss of plasma volume (e.g., with major burns, third spacing, or GI losses) can also result in hypovolemia. Decreased preload decreases CO and oxygen delivery to cells. 1. Clinical presentation: Increased lactate production occurs as normal aerobic cellular metabolism progresses to less energy efficient anaerobic metabolism, resulting in cellular damage and death. 2. Treatment (preload restoration): Blood and plasma volume. a. Aggressive volume administration is needed, through two large- bore IVs. b. Stop ongoing blood loss and transfuse blood as needed. c. Consider central venous access for monitoring and high-flow fluid administration. B. Cardiogenic shock: Caused by myocardial ischemia, congestive heart failure, and valvular diseases. 1. Clinical presentation: Blood volume remains normal, but loss of contractility results in decreased perfusion. 2. Treatment: Restore pump function either by increasing contractility or decreasing afterload . Nitroglycerine can help reverse cardiac ischemia. C. Neurogenic shock: Caused by vasovagal response, cervicothoracic spinal cord injury, or spinal anesthesia. 1. Clinical presentation: Loss of sympathetic tone leading to peripheral vasodilatation. 2. Treatment: First increase preload , then increase afterload with phenylephrine. D. Septic shock: Toxins released by microbes result in profound hyperinflammatory physiologic derangements, including third spacing of fluids (decreased preload ), cardiac dysfunction (poor contractility ), and reduction in SVR (decreased afterload ). 1. Clinical presentation: Hypoperfusion. The hyperinflammatory response is characterized by increased metabolism and oxygen demand. Cellular hypoperfusion and anaerobic metabolism lead to organ dysfunction and death. 2. Treatment: Increase preload, and control infection. E. Obstructive shock: 1. Clinical presentation: CO with elevated CVP resulting in hypoperfusion from a physical obstruction (e.g., tension pneumothorax, cardiac tamponade, massive pulmonary embolism, venous air embolism, and severe cardiac valvular stenosis). 2. Treatment: Fluid resuscitation ( preload ) followed by prompt relief of obstruction. a. Tension pneumothorax: An injured lung develops a one-way valve that allows air into but not out of the pleural space. (1) Increase in pleural pressure, displacing the heart and mediastinal

structures (e.g., vena cava, aorta) and compressing them to the contralateral side with decreased venous return to the heart.