Treating traumatic hypovolemia: Which fluid to choose?

Nursing, Jan 1998 by Sandrock, Jean

When a trauma victim arrives at your emergency department (ED) in hypovolemic shock, your first priorities are to administer oxygen and locate and stop any hemorrhaging. But when you start fluid resuscitation, what you give and how fast you give it aren't necessarily straightforward. Research hasn't settled which fluid is best or whether one administration method is superior to another. To start sorting out the controversies, let's look at how fluid types compare.

CRYSTALLOIDS: OLD FAITHFULS

The primary crystalloid solutions, lactated Ringer's solution and 0.9% sodium chloride solution, are inexpensive and readily available. Because of their high osmotic pressure, these isotonic solutions draw water from the cells or interstitial spaces into the intravascular space, raising the patient's blood pressure. Because acidosis may accompany hypovolemic shock, lactated Ringer's solution, with its higher pH, is generally the fluid of choice.

For over 40 years, crystalloids were given using a 3:1 ratio-3 ml of crystalloid solution for every milliliter of actual or potential blood loss. But such aggressive, high-volume therapy often resulted in massive edema, pulmonary congestion, brain swelling, and disseminated intravascular coagulation. To avert these complications, current guidelines suggest an initial 20-ml/kg bolus, with subsequent boluses as needed.

A newer and somewhat controversial fluid for resuscitation in trauma patients is 7.5% hypertonic saline, with or without dextran. As with other colloids, hypertonic saline draws fluids from the intracellular and interstitial spaces to the intravascular spaces. But because it exerts a higher osmotic pressure, as little as 250 ml can be effective. In most cases, small amounts of another crystalloid solution must also be administered.

Hypertonic saline also exerts a potent vasoconstrictive effect, increasing blood pressure and venous return to the heart, which raises cardiac output. Don't use it if the patient's hemorrhage is uncontrolled, however-hypertonic saline increases the risk of death by pulling fluids from the cells, further depriving them of oxygen. Instead, wait until the patient's hemorrhage is controlled by a pneumatic antishock garment, a tourniquet, or surgery. Initial research has shown that hypertonic saline is more effective in treating penetrating trauma requiring surgery than blunt traumatic injuries. More trials and research are needed to refine this treatment.

BLOOD: PROVIDING VOLUME AD MORE

A trauma victim who's lost 30% to 45% of his blood volume needs more than crystalloids. If you've given a patient 2 liters of a crystalloid and he's still hypotensive, the physician should order blood while continuing to look for the cause of hypovolemic shock.

If the patient has a hemothorax, autotransfusion is an option that eliminates the risk of transfusion reaction. If autotransfusion isn't possible, however, a transfusion of banked whole blood can restore volume and provide clotting factors and red blood cells (RBCs). However, because whole blood has both RBC antigens and plasma antibodies, the patient and donor must be ABO identical or the patient will have a transfusion reaction.

An alternative to whole blood is packed RBCs. Because they have little plasma, the patient and donor needn't be ABO identical, only ABO compatible. In an emergency, however, when you don't have time for typing and crossmatching, you can give any patient type O-negative RBCs, which have no A or B antigens. Type O-negative blood is considered the universal donor type and should be readily available for emergencies. The disadvantage of RBCs is that they don't provide much volume and so should be given in conjunction with other fluids.

Giving type-specific blood (which has been typed but not crossmatched), is an option when time is crucial, but it's more likely to cause a transfusion reaction than crossmatched blood. Use typespecific blood without crossmatching only in an emergency.

Researchers are now testing a blood substitute-diasparin crosslinked hemoglobin (HemeAssist that could become a safe, readily available fluid that would provide the oxygen-carrying capability of blood without the risk of a transfusion reaction.

COLLOIDS: PUMP UP THE VOLUME

Colloids have a similar osmotic action to crystalloids, but whether they're a better option is controversial. Albumin, the most commonly used colloid, is a natural blood component that can be given without typing and crossmatching. Hetastarch is similar to albumin and can exert an osmotic effect for up to 36 hours. Dextran is a hyperosmotic glucose polymer that's also similar to albumin. However, it can reduce platelet adhesion, dilute clotting factors, and increase the risk of bleeding; it also poses the risk of allergic reaction.

Theoretically, these colloids increase volume with less risk of causing pulmonary congestion. But in the early phase of injury, when the inflammatory response increases capillary permeability, proteins in colloids can leak into interstitial tissue, causing edema, skin breakdown, and pulmonary congestion. Colloids also may cause renal insufficiency in some patients.