2. Materials and Methods


HOW-TO SESSION: FIELD ANESTHESIA AND PAIN MANAGEMENT 4. Discussion


A review of literature from the past 10 years describ- ing fluid resuscitation for acute blood loss in human medicine was undertaken. Current trends in fluid choice and volume of fluid administered were reviewed.


3. Results


In human medicine, a strategy has been developed called Damage Control Resuscitation (DCR) to re- suscitate patients with acute hemorrhage.2,3 The goal of DCR is early prevention and/or treatment of the lethal triad. The lethal triad consists of coagu- lopathies, hypothermia, and acidosis.3 Metabolic acidosis occurs from hypoperfusion leading to organ/ tissue damage from decreased oxygenation and a switch to anaerobic metabolism. Hypothermia re- sults from hypoperfusion and, if used in treatment, the use of cold resuscitation fluids. Coagulopathies primarily occur from hypoperfusion and tissue trauma. Other factors including loss of procoagu- lant proteases, dilution of blood from fluid resusci- tation, and organ dysfunction from acidosis and hypothermia also potentiate coagulopathies.4–6 One of the key points in the DCR resuscitation


plan is permissive hypotension. A minimum vol- ume of intravascular fluid replacement is adminis- tered at a rate to maintain mean arterial blood pressure at 50mmHg and systolic blood pressure at 80 mm Hg. These pressures are considered suffi- cient to maintain organ perfusion without potenti- ating hemorrhage. Proponents of DCR cited a 40% survival rate in DCR-resuscitated patients versus a 16% survival rate in patients not undergoing DCR resuscitation strategies.7–10 DCR is now the stan- dard of care for resuscitating patients with blood loss in human medicine.7 The DCR strategy has emerged over the past decade and is in opposition to the strategy used during the past century, when rapid volume expansion with crystalloid fluids was used in cases of hemorrhagic shock. Permissive hypotension should not be confused


with prolonged hypoperfusion. Prolonged hypoper- fusion and failure to maintain blood pressure at DCR-recommended levels results in decreased per- fusion to vital organs and tissues leading to meta- bolic acidosis, hypothermia, and coagulopathies. Coagulopathies are associated with increased mor- tality in patients with hemorrhagic shock.11–13 The second key point in DCR resuscitation is the


type of fluid chosen for initial resuscitation. The DCR strategy recommends the use of plasma as the initial resuscitation fluid. This early use of plasma aids in prevention of a coagulopathy, one component of the lethal triad.14 Human studies claim a 46% reduction in mortality rate when plasma was used in equal parts with whole blood as opposed to the use of more blood than plasma.14 Also, fresh, warm, whole blood has been advocated over packed red blood cells.7,15,16


Different strategies are used to treat acute blood loss in veterinary patients. Some clinicians limit intravenous fluid therapy in an attempt to maintain low blood pressure and limit further hemorrhage. The risk of limiting fluid therapy is hypovolemic shock and subsequent cardiovascular collapse. Without appropriate fluid volume, organs do not receive adequate perfusion and oxygenation. In op- position, some clinicians advocate more liberal use of crystalloid and colloid fluids to maintain blood pressure in a range closer to normal to preserve organ perfusion and prevent hypovolemic shock. The risk with this method is that further hemor- rhage may occur. Veterinarians also vary in what fluid should be


used in resuscitation. Crystalloid fluids are typi- cally inexpensive, easy to administer, and readily available to most practitioners. However, the majority of the fluid rapidly leaves the vascular compartment and moves to the interstitial space. Colloid fluids are more expensive and require spe- cialized equipment to administer. Fresh, whole blood requires the presence of a donor and ideally, a laboratory to perform a cross-match. Plasma re- quires refrigeration for storage. Both require spe- cialized IV lines with a filter designed for administration of blood products. Anaphylactic re- actions may occur with either. Hydroxyethyl starch, a synthetic colloid, does not require refriger- ation or specialized equipment to administer, but it has been associated with coagulopathies. Also, col- loids may increase the blood pressure more than desired and may potentiate further bleeding. Extrapolating data and strategies from human medicine and applying it to veterinary medicine may assist the veterinarian in establishing a treatment plan for resuscitative fluids in acute hemorrhage cases. Application of DCR strategy to veterinary medicine will guide the practitioner in choice of re- suscitative fluid in hemorrhagic shock. Plasma and potentially warm whole blood should be the initial resuscitation fluid. Plasma provides addi- tional clotting factors. Warm blood is used to pre- vent hypothermia because the coagulation cascade is less effective at lower body temperatures. Fresh, whole blood is preferred over packed red blood cells. Interestingly, this practice is already routinely per- formed in equine medicine because a blood bank with packed red cells from equids is not available. DCR protocol recommends minimal administra-


tion of crystalloid fluids because they dilute coagu- lation factors and may increase coagulopathies. However, in the equine patient, financial con- straints and availability of colloids may prevent ad- ministering the volume of plasma and whole blood needed to maintain mean arterial blood pressure at 50 mm Mg. Crystalloid fluids, therefore, are re- quired in these cases.


AAEP PROCEEDINGS  Vol. 59  2013 459


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