Upon completion of the chapter, the reader will be able to:
List the most common etiologies of decreased intravascular volume in hypovolemic shock patients.
Describe the major hemodynamic and metabolic abnormalities that occur in patients with hypovolemic shock.
Describe the clinical presentation including signs, symptoms, and laboratory test measurements for the typical hypovolemic shock patient.
Prepare a treatment plan with clearly defined outcome criteria for a hypovolemic shock patient that includes both fluid management and pharmacologic therapy.
Compare and contrast relative advantages and disadvantages of crystalloids, colloids, and blood products in the treatment of hypovolemic shock.
Outline the elements of damage control resuscitation in traumatic hemorrhagic shock patients.
Formulate a stepwise monitoring strategy for a hypovolemic shock patient.
The primary function of the circulatory system is to supply oxygen and vital metabolic compounds to cells throughout the body, as well as removal of metabolic waste products. Circulatory shock is a life-threatening condition whereby this principal function is compromised resulting in inadequate cellular oxygen utilization.1,2 When circulatory shock is caused by a severe loss of blood volume or body water, it is called hypovolemic shock. By definition, hypovolemic shock occurs as a consequence of inadequate intravascular volume to meet the oxygen and metabolic needs of the body. Rapid and effective restoration of circulatory homeostasis using fluids, pharmacologic agents, and/or blood products is imperative to prevent complications of untreated shock and ultimately death.
ETIOLOGY AND EPIDEMIOLOGY
Practitioners must have a good understanding of cardiovascular physiology to diagnose, treat, and monitor circulatory problems in critically ill patients. The interrelationships among the major hemodynamic variables are depicted in Figure 13–1.3 These variables include mean arterial pressure (MAP), cardiac output (CO), systemic vascular resistance (SVR), heart rate (HR), stroke volume (SV), left ventricular size, afterload, myocardial contractility, and preload. Although an oversimplification, Figure 13–1 is beneficial in conceptualizing where the major abnormalities occur in patients with circulatory shock as well as predicting the body’s compensatory responses.
Hemodynamic relationships among key cardiovascular parameters (A). Solid lines represent a direct relationship; the broken line represents an inverse relationship. In (B), the alterations typically observed in hypovolemic shock are highlighted with arrows depicting the likely direction of the alteration. (Panel A from Braunwald E. Regulation of the circulation. I. N Engl J Med. 1974;290:1124–1129, with permission.)
Hypovolemic shock is caused by a loss of intravascular volume either by hemorrhage or fluid loss (eg, dehydration). There is a profound deficit in preload, defined as the volume in the left ventricle at the end of diastole. Decreased preload results in subsequent decreases in SV, CO, and eventually, MAP. As such, restoration of preload becomes an overarching goal in the management of hypovolemic shock.