Although isotonic saline solution is most commonly used in the initial management of hemorrhagic shock, debate continues over the value of adding colloid to the resuscitation regimen. Albumin has fallen into disfavor, but purified protein fraction (PPF) and fresh frozen plasma (FFP) continue to be recommended and used. Central to the issue are the effects of fluid resuscitation on the pulmonary interstitium. 15 Proponents of protein replacement argue that saline resuscitation of hemorrhage results in a fall in intravascular oncotic pressure and a reversal of the normal gradient favoring intravascular fluid retention. Theoretically, this may lead to pulmonary edema and impaired tissue oxygenation. Colloid administration is advocated because it raises oncotic pressure in the pulmonary capillary bed. This argument ignores the fact that the pulmonary capillary endothelium permits considerable flow of fluids, including plasma proteins, between the capillaries and the interstitium. A fall in intravascular oncotic pressure is compensated for by a fall in pulmonary interstitial oncotic pressure, thereby minimizing changes in the pressure gradient. It appears likely that pulmonary capillary hydrostatic pressure [measured as pulmonary artery (occlusion) wedge pressure] is far more important than pulmonary capillary oncotic pressure in determining the amount of fluid flowing to the interstitium. Maintenance of the pulmonary artery occlusion pressure below 15 mmHg is probably the most important factor in preventing pulmonary edema. Systematic reviews of clinical studies have found no clear benefit to colloid resuscitation compared with crystalloid resuscitation.16 Clinicians inclined to use albumin, PPF, or FFP in the resuscitation of hemorrhagic shock should question whether the undocumented benefits of this therapy are worth the substantial increase in cost or, in the case of FFP, the risk of disease transmission.
Alternatives to the use of naturally occurring colloid preparations include synthetic colloid solutions such as hydroxyethyl starch (HES) and dextran 70. The volume-expanding properties of HES are equivalent to those of 5% albumin. These agents differ significantly from albumin, however, in that they remain predominantly in the intravascular space because of their high molecular weight and branched structure. Their plasma-expanding effects are more prolonged than those of albumin, and interstitial edema is not a significant concern. Their inability to restore oxygen-carrying capacity, however, is a significant disadvantage shared by all crystalloid and colloid solutions with the exception of blood.
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