TRANSFUSION : CLINICAL PRACTICE Fluid and Blood Therapy in Trauma

Initial fluid resuscitation in conjunction with temporary hemostasis should aim at maintenance of vital organ perfusion above critical levels. Judicious use of fluids is indicated in this early stage. Complete volume replacement is done once permanent hemostasis has been achieved. Mild (20%-40%) hemodilution produces hypercoagulability, while further hemodilution results in hypocoagulability. Resuscitation using balanced crystalloid solutions and balanced colloid solutions preserves coagulation better than resuscitation with 0.9% saline or saline-based colloids; it reduces blood loss and improves acid-base profile. Hypertonic saline is popular in the prehospital setting and is also beneficial for ongoing in-hospital resuscitation. Both hetastarch and hypertonic fluids have favorable effects on endothelial swelling, microcirculation, and immunologic function; both are equally or more efficient than standard mannitol-based therapy in head trauma patients with intracranial hypertension. Large volumes of high-molecularweight hetastarch are associated with coagulopathy. Patients are surprisingly resistant to acute normovolemic anemia, even in the presence of cardiovascular risk factors. Hemodilution down to hemoglobin of 7 g/dL is safe for most patients, provided they are not actively bleeding, are adequately volume-resuscitated, and high inspired oxygen concentrations are used. On the other hand, with transfusion of stored red blood cells, the immediate increase in oxygen delivery often does not translate to increased oxygen consumption and might even worsen tissue acidosis. Red blood cell transfusion might be an independent risk factor for mortality and other complications. Late immunologic effects of allogeneic blood transfusion are poorly understood. Warm blood transfusion from a “walking blood bank” is popular in the military trauma setting and might be more efficient than standard transfusion therapy. In the setting of ongoing severe hemorrhage, massive transfusion protocols with concomitant administration of red blood cells, plasma, and platelets should be implemented. Recombinant factor VIIa is a new exciting modality of treating transfusion-associated coagulopathy and hard-tocontrol bleeding in trauma patients; its exact place in trauma care remains to be determined. Initial evaluation of an acutely volume-depleted trauma patient will include a primary and secondary survey according to Advanced Trauma Life Support protocol, an estimate of blood volume deficit (Table 1), rate of the ongoing blood loss, and an evaluation of cardiopulmonary reserve and coexisting hepatic or renal dysfunction. The major goal in resuscitation is to stop the bleeding, replete intravascular volume, and restore tissue oxygenation. Perfusion pressure and oxygenated blood flow to vital organs are important determinants of outcome. Management priorities in an acutely bleeding trauma patient include ventilation and oxygenation, assessment of perfusion, estimation of volume-replacement requirements, establishment or verification of adequate intravenous access, measurement of blood pressure, placement of electrocardiogram (ECG), pulse oximeter and capnograph, and laboratory studies. Placement of arterial line and close monitoring of systolic pressure variability, temperature, urine output, arterial blood gases, hemoglobin, hematocrit, electrolytes, and parameters of coagulation is routine in severely injured mechanically ventilated patients. Consideration is given to use of additional monitors (e.g., central venous catheter, pulmonary artery catheter, transesophageal echocardiography) and provision of anesthesia as needed. For induction of anesthesia in hemodynamically unstable patients, etomidate or ketamine is useful. Titrated opioids, scopolamine, midazolam, and amnestic concentrations of volatile agents can then be used for maintenance of general anesthesia until the intravascular volume deficit has been corrected and bleeding is under control. Neuromuscular relaxants and other agents are given as clinically indicated. Vol. 18, No. 1, 2008 International TraumaCare (ITACCS) 43 Table 1. Estimation of Blood Volume Deficit in Trauma Patients Site Volume (mL) Unilateral hemothorax 3,000 Hemoperitoneum with abdominal distention 2,000–5,000 Full-thickness soft tissue defect, 5 cm 500 Pelvic fracture 1,500–2,000 Femur fracture 800–1,200 Tibia fracture 350–650 Smaller fracture sites 100–500 Timing and Aggressiveness of Fluid Resuscitation Early aggressive fluid resuscitation aimed at restoration of “normal” hemodynamics has been the mainstay of trauma management for years. However, in animal models of uncontrolled hemorrhage, this strategy leads to increased duration and volume of bleeding and decreased survival. The proposed mechanisms include dilution of clotting factors, decreased blood viscosity, and blow-out of hemostatic plugs with increasing blood pressure (Table 2). Hypotensive resuscitation, where the rate of fluid infusion is carefully titrated to a predetermined level of lower-than-normal blood pressure, has been advocated in patients who are not pregnant and do not have traumatic head injury. The question of immediate versus delayed fluid resuscitation for hypotensive trauma patients was addressed in a landmark randomized clinical trial that demonstrated improved survival, shorter hospital stay, and fewer postoperative complications in patients who did not receive fluid resuscitation until arrival to the operating room. The study was limited to isolated penetrating torso injuries, and the receiving trauma center had a rapid response time such that most patients were in the operating room within 1 hour of injury. Benefits of delayed fluid resuscitation in the prehospital setting include minimal delay in transfer and surgical intervention and avoidance of increased blood pressure or hemodilution, which could disrupt the clot or alter resistance to flow around a partially formed thrombus. To date, no human study has shown detrimental effects of delayed or hypotensive resuscitation on survival, but so far the conclusive evidence on its superiority in trauma or ruptured abdominal aortic aneurysm is lacking. Consequently, in uncontrolled hemorrhagic shock, resuscitation is aimed at restoration of radial artery pulse, restoration of mental function, and systolic blood pressure of 80 mm Hg, until the bleeding is surgically controlled. Higher blood pressures (systolic blood pressure >100 mm Hg, mean arterial pressure >70 mm Hg) are generally sought in head-injured and in pregnant patients. This approach provides satisfactory resuscitation of the trauma patient until surgical control of bleeding is achieved. Table 2. Disadvantages of Immediate Fluid Resuscitation Decreased blood viscosity Blow-out of hemostatic plug Dilution of coagulation factors Increased blood loss Delayed transport to definitive care Fluid Options