Emergency War Surgery NATO Handbook: Part II: Response of the Body to Wounding: Chapter X: Compensatory and Pathophysiological Responses to Trauma

Response to Therapy

United States Department of Defense

The hemodynamic response to the initial fluid infusion falls into one of three categories. A small number of patients will respond to the initial fluid bolus with a prompt normalization of blood pressure and will maintain hemodynamic stability. Further therapy is directed at replacing ongoing losses. This response is usually seen in patients with volume deficits of less than 20%. The majority of patients will show a transient response to the fluid bolus. Over time, the initial improvement dissipates, requiring further administration of volume to restore and maintain hemodynamic stability. Most of these patients have experienced a 20-40% volume loss, and may have ongoing bleeding necessitating surgical intervention for control. The third category consists of that small number of patients who show minimal or no response to fluid boluses and usually have an exsanguinating hemorrhage, requiring immediate surgical control. The clinical picture of this subset of patients may be compounded by myocardial dysfunction, necessitating invasive assessment of volume status and myocardial function.

The use of blood transfusions should be limited to cases of severe and ongoing hemorrhage where blood loss exceeds 30% of the total blood volume (i.e. 1500-2000). Red blood cell concentration (hematocrit) determines the blood's viscosity and oxygen-carrying capacity. The goal in blood transfusion is to optimize oxygen delivery to the cells. While an increasing hematocrit allows for a greater oxygen-carrying capacity, the concomitant elevation in viscosity can cause a decreased cardiac output secondary to increased vascular resistance, which impedes the delivery of oxygen to the cell. Viscosity varies little between hematocrits of 20-35%, however, it rapidly increases above this level. In patients who are hypermetabolic and able to elevate their cardiac output, a hematocrit of 30-35% is adequate to ensure sufficient oxygen transport in the systemic circulation. However, in the maximally stressed patient, there may be no further reserve to increase cardiac output to meet the fixed elevated peripheral oxygen needs. Under these circumstances, an infusion of red cells will increase the hematocrit and may increase delivery of oxygen to the tissues.

Transfusions may be associated with complications, including transfusion reactions, transmission of disease (donor pool dependent), and coagulopathy (in patients receiving massive transfusions) secondary to either dilution or a disseminated intravascular coagulation (DIC)-like state. Transfusion related transmission of an immunosuppressing virus is but one of many transfusion-related infectious complications. Transfusion of massive quantities of blood may result in hypothermia, which may be partially avoided through the use of a blood-warming apparatus.

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Operational Medicine 2001

Health Care in Military Settings

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