Emergency War Surgery NATO Handbook: Part II: Response of the Body to Wounding: Chapter IX: Shock and Resuscitation

Pathophysiology

United States Department of Defense
Peer Review Status: Internally Peer Reviewed

Early post-hemorrhage circulatory changes are compensatory, all serving to preserve perfusion of the vital organs, Vasoconstriction, shunting, and fluid shifts all contribute to the attempt to maintain perfusion of vital vascular beds. A more detailed account of these homeostatic mechanisms operative in the shock state is provided in Chapter X, dealing with the physiologic response to trauma For our purposes here, suffice it to say that the response to hemorrhage is graded and complex. The circulating blood volume represents approximately 7% of body weight, or about 5 liters in the 70 kg man. In the young healthy individual, a significant blood loss can be tolerated without major changes of the blood pressure early on. The foregoing may not apply to the older casualty, to the depleted casualty, or even the younger casualty as the interval between wounding and initiation of therapy lengthens. The following is offered as a guide in assessing the volume of acute blood loss:

1. Up to 15% blood volume loss (Class I hemorrhage). Mild tachycardia is the only clinical sign in all uncomplicated situation. This represents a blood loss of 500 cc or less in the 70 kg person. The blood pressure, respiratory rate, urine output, and mental status are within normal limits. The capillary blanch test is normal, refilling occurring within two seconds. These Casualties should be resuscitated with crystalloid solutions.
2. 15-30% blood volume loss (Class II hemorrhage). This degree of loss in the 70 kg soldier amounts to 750-1500 cc of blood. Clinical findings include a pulse greater than 100/minute, a slight decrease in the blood pressure, an altered capillary blanch test response, and subtle central nervous system changes including inordinate anxiety or fright. The urine output is only minimally depressed. This class of patients call also be resuscitated with crystalloid alone.
3. 30-40% blood volume loss (Class III hemorrhage). This represents a 1,500-2,000 cc blood loss in the standard male. Tachycardia (usually at greater than 120), tachypnea, diastolic and systolic hypotension, and scanty urine output are apparent. These casualties will require blood in addition to crystalloid for resuscitation.
4. Over 40% blood volume loss (class IV hemorrhage). This degree of hemorrhage is clearly life threatening. It amounts to a hemorrhage in excess of 2,000 cc. All of the classic signs of shock are present. The skin is cold, clammy, and pale, and the mental faculties are clearly depressed. These casualties not only require large-volume blood replacement in addition to crystalloid, but in addition to volume replacement often times require immediate surgical intervention if resuscitation is to be successful. That is to say, they require operation for resuscitation rather than resuscitation for operation.

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