Fluid Therapy for Hemorrhagic Shock (Box 44.5)
K. Gary Magdesian
With the exception of prompt hemorrhage control, the key component to early trauma care is adequate fluid resuscitation. Traditionally, replacement with isotonic crystalloids of three times the volume of shed blood has been the approach in human trauma patients.
Up to eight times the blood loss volume has been administered in severe shock states, because isotonic crystalloids distribute throughout the extracellular fluid compartment by volume, such that only 25% of the administered volume will remain within the circulating plasma volume.Despite its importance, high-volume resuscitation is not innocuous; acute respiratory distress syndrome (ARDS) has been described in patients that received massive crystalloid resuscitation after trauma.1 Severe trauma patients enter a phase of SIRS, with some patients developing multiple organ failure
■ BOX 44.5
Fluid Considerations for Horses With
Acute Hemorrhage and others entering a compensatory antiinflammatory response syndrome (CARS). This latter syndrome causes immune suppression and increased susceptibility to infections. Commercial LRS brands used to contain a racemic mixture of L- and D-lactate. Those solutions, along with artificial colloids, namely dextrans and some hydroxyethyl starches, had proinflammatory effects.2 Nonracemic LRS contains only the L-lactate form and does not share in the proinflammatory effect. It appears that the D-lactate (nonmammalian form) is largely responsible for the inflammatory reaction to racemic LRS because removing it from the solution eliminates this effect. These fluids, both artificial crystalloids and colloids, can also cause neutrophil activation and upregulation of adhesion molecules. Most currently available forms of LRS contain only the L-isomer form of lactate. Hypertonic saline, on the other hand, has been shown to be immunomodulatory and causes suppression of neutrophil oxidative burst activity and neutrophil-endothelial adhesions.5-8 Hypertonic saline counteracts the inflammatory effects of dextrans when used in combination.9 Therefore hypertonic saline has potential advantages for early fluid resuscitation of patients with significant blood loss, after the source of hemorrhage has been controlled.
This should be followed with isotonic crystalloids, perhaps acetate-containing fluids, such as Normosol-R, or physiologic saline rather than racemic LRS. Hypertonic saline should not be used in cases of uncontrolled hemorrhage because it may raise blood volume and pressure too quickly. Plasma similarly does not result in inflammatory cell activation. If hetastarch is used in patients with acute blood loss, hemorrhage must be controlled before its administration because of rapid volume expansion as well as dose-dependent induction of coagulopathies.10-15Aggressive fluid resuscitation in the face of uncontrolled hemorrhage cannot be justified. Such fluid protocols can exacerbate bleeding as a result of increases in blood pressure, disruption of clots, and hemodilution of clotting factors. Instead, a protocol of hypotensive resuscitation should be followed when bleeding cannot be stopped directly.16 With hypotensive resuscitation, low volumes of crystalloids or whole blood should be administered to maintain organ vitality without normalizing pressures. A goal of maintaining a MAP of 60 mm Hg will still allow end-organ perfusion while allowing for hemostasis.