Update on trauma care in Canada. 4. Resuscitation through the three phases of hemorrhagic shock after trauma.

There are three phases of acute hemorrhagic shock after trauma. In phase I (from injury to operation for control of bleeding) the patient suffers from low cardiac output, tachycardia, reduced organ perfusion, oliguria and decreased capillary hydrostatic pressure, which in turn reduces extravascular fluid loss. Contraction of the interstitial space matrix replenishes plasma volume. Optimal therapy includes blood and crystalloid replacement to restore plasma volume, red cell mass and interstitial fluid. Three litres of crystalloid are usually required for each litre of blood lost. After operation, a period of obligatory extravascular fluid sequestration occurs as the intracellular and interstitial spaces expand (phase II). Optimal replacement therapy during this phase maintains plasma volume. Replacement is provided according to the patient's vital signs, because extravascular fluid expansion cannot be influenced by therapeutic manipulation. Phase III is a mobilization and diuretic phase. During this phase systolic hypertension may occur, and the patient must be treated with restriction of fluid, diuresis and careful monitoring of the heart and lungs. Attempts to alter these physiologic responses with supplemental albumin have proved detrimental. The albumin causes salt and water retention in the nephron, leading to weight gain, higher central filing pressures and worsening pulmonary function, and a greater need for diuretic and inotropic therapy. Albumin therapy also induces relocation of non-albumin proteins into the interstitial space, leading to impaired immunocompetence and coagulation. Successful resuscitation is facilitated by adaptation to these physiologic responses of hemorrhagic shock rather than manipulation of them.