Fluid Resuscitation and Blood Replacement in Patients with Polytrauma

Abstract

Hemorrhage is the most common cause of shock in patients with polytrauma, leading to cellular hypoxia and death. A large body of experimental and clinical research has greatly expanded our knowledge of cellular mechanisms and clinical outcomes in resuscitation of patients with hypovolemic shock. However, the fundamental principles of fluid resuscitation have not changed during the past few decades. Aggressive resuscitation to correct tissue hypoperfusion within 24 hours of injury is associated with improved clinical outcomes. Initial volume expanders of choice are crystalloid solutions, with blood and blood products used for patients who are hemodynamically unstable, patients with Class III and Class IV hemorrhage, and patients with ongoing uncontrolled sources of bleeding. The incidence of immunologic and infectious complications associated with blood transfusions in resuscitation of patients with polytrauma has not been shown to be any higher than in other clinical settings. Massive resuscitations, however, are associated with specific complications such as hypothermia, coagulopathy, and abdominal compartment syndrome. Novel blood substitutes, hypertonic saline, and minimally invasive hemodynamic monitoring techniques have the potential of optimizing fluid resuscitation in patients with polytrauma. Additional research using standardized animal models and randomized clinical trials is needed.

It is intuitively obvious that blood loss is bad, and blood loss to a degree that causes physiologic derangement particularly is worrisome. It is equally intuitive that restoring the circulating blood volume to normal, as rapidly as possible, is appropriate. Unfortunately, the technical aspects of this process, from choice of intravenous catheter, to which fluid should be infused at what rate, is not so clear cut, and in fact, can lead to disastrous consequences if done so without careful and thoughtful consideration. The classic clinical scenarios in which the orthopaedic surgeon would be dealing with exsanguination are well described (severe pelvic fracture, multiple long bone fractures). If such a patient is encountered in a well-established trauma system, skilled trauma surgeons and emergency room physicians may be available to take the lead with volume resuscitation. However, a situation may arise where the orthopaedic surgeon is the primary physician in attendance for a patient with hypovolemia who is bleeding. In such situations, a thorough understanding of principles of resuscitation from hypovolemia by the orthopaedic surgeon is critical to the optimal outcome of patients with polytrauma.

Hypovolemia is the most common cause of shock that occurs in patients sustaining trauma. One of the primary advances in the care of these patients in the twentieth century has been the recognition of the need for early and aggressive volume resuscitation using blood and intravenous fluids, which has resulted in a significant decrease in mortality and morbidity after trauma.⁸ Principles of resuscitation are based on the premise that prompt restoration of adequate oxygen delivery to the tissues minimizes cellular ischemia and cell death. These principles have not changed significantly during the past few decades.

However, important progress has been made in the areas of timing, volume, and choice of fluids used for resuscitation. Several specific clinical and laboratory parameters also have been identified as end points of resuscitation to guide therapy.¹⁴ More recently, a better understanding of cellular pathophysiologic mechanisms have led to controversies regarding the use of colloids, and targeting resuscitation to subphysiologic blood pressures until the source of hemorrhage is controlled.^11,29

The following treatise reviews the most recent literature in fluid resuscitation in patients with polytrauma. It provides a framework that the clinician can use to rapidly assess the volume needs of the injured patient, and outlines the most appropriate means to achieve an optimal outcome during the resuscitation of the patient who is injured critically.

Clinical Indications for Resuscitation

Hemorrhage is the most common cause of shock in patients with polytrauma. The American College of Surgeons defines four classes of hemorrhage in its Advanced Trauma Life Support course (ATLS) course based on hemodynamic parameters¹ (Table 1). In general, patients with Class I hemorrhage do not require fluid resuscitation. However, ongoing monitoring is essential because continuing blood loss may worsen a patient’s clinical status to a higher class.

Table 1: Classification of Shock

Delivery Systems

Two large bore peripheral intravenous cannulas (16 gauge or larger) generally are adequate for resuscitation of the patient with trauma. If peripheral veins are not accessible, an 8.5-French catheter may be placed in the femoral or subclavian vein using the standard Seldinger technique.¹² Rapid infusing systems, which can infuse fluids at rates reaching 1000 mL every 5 minutes or less, can be used for rapid resuscitation, if needed. All intravenous fluids should be warmed to at least body temperature before infusion. This can be accomplished by using solutions stored in a monitored, heated storage unit, or by using an in-line fluid-warming device.

Use of Crystalloids

Indications

Class II hemorrhage or higher is an indication to start fluid resuscitation in patients with trauma. Cystalloids are the initial volume expanders of choice in this clinical setting.

Fluid Options

Lactated Ringer’s solution and normal saline are the two most commonly used isotonic solutions. The advantage of lactated Ringer’s solution is that the L-lactate isomer in the solution is metabolized by the liver and kidney to generate bicarbonate, which provides a buffer against lactic acid generated by tissue hypoperfusion, thereby assisting in returning the pH to normal.¹³

Volume

A general guideline for replacement is a ratio of 3:1, for example, to infuse 3 mL of crystalloids for each mL of estimated blood loss. Some experimental data indicate that ratios as high as 10:1 may be more appropriate because of ongoing hemorrhage, capillary leak, and decreased serum oncotic pressure.^7,20 An initial bolus of 1–2 L generally is used. The actual volume infused in a specific patient may be higher or lower than those suggested by these guidelines and are determined by the desired end points of resuscitation.

Complications

Massive resuscitation has been associated with increased hemorrhage in clinical and experimental settings.^2,16 This has been attributed to hypothermia, dilutional thrombocytopenia, dilution of procoagulant factors, decreased blood viscosity, and blow-out of hemostatic plugs when blood pressure is raised to normal or super-normal levels. Large amounts of normal saline infusions have been associated with hyperchloremic acidosis, which may worsen the acidosis caused by lactic acid because of hypoperfusion. Intraabdominal hypertension and abdominal compartment syndrome also have been associated with massive resuscitation, and can occur in the presence or absence of an intraabdominal injury.^21,25

Use of Blood and Blood Components

Indications

Class III hemorrhage or higher is associated with hypotension, and generally requires blood transfusions for resuscitation. The appropriately chosen blood components will restore the volume of circulation and enhance oxygen carrying capacity and coagulation. Although the National Institutes of Health Consensus Conference recommends using a hemoglobin ≤ 7 g/dL or a hematocrit ≤ 21% as a transfusion trigger, this is not appropriate for use in resuscitation of patients with trauma because acute blood loss is not reflected in initial laboratory measurements of the hemoglobin or hematocrit.²⁷ The clinical parameters of tachycardia, hypotension, and mental status changes are more relevant than laboratory values when acute hemorrhage is occurring, especially early in the patient’s course.

Component Options

Uncross-matched Type-O packed red blood cells are used for initial resuscitation in emergent situations, until cross-matched blood is available. In the presence of coagulopathy, hypothermia, or when packed red blood cell transfusion exceeds six units, platelets and fresh-frozen plasma (FFP) should be administered. Autologus blood transfusion using cell salvage, either in the operating room or postoperatively, is an option that is becoming widely available, and will afford protection against exposure to blood-borne transmissible disease.

Volume

Blood resuscitation should proceed aggressively until hemorrhage is controlled surgically because simultaneous treatment of hypovolemia and anemia is the immediate goal. Adequacy of resuscitative efforts, and the need for additional blood products are dictated by the patient’s physiologic status. Transfusion of one complete blood volume within a 24-hour period, which amounts to 10 units of packed red blood cells in a 70-kg adult, is considered massive transfusion. Anticipation of the need for massive transfusion early in resuscitation is critical to optimize resource use and clinical outcome because many hospital blood banks may be depleted quickly and need time to mobilize additional blood component resources.

Complications

The incidence of immunologic and infectious complications associated with blood transfusions in resuscitations of patients with trauma has not been shown to be any higher than in other clinical settings.²² Immunologic complications include febrile reactions (one in 200 units transfused), simple allergic reactions (one in 333), transfusion-related acute lung injury (one in 5000) and acute hemolytic reactions (fatal, one in 250,000–600,000; nonfatal, one in 6000–33,000).³¹ The risks of transfusion-related viral infections include HIV (one in 1.8 million), Hepatitis C (one in 1.6 million), and hepatitis B (one in 220,000).⁵ Specific complications associated with massive transfusion include hypothermia, coagulopathy, citrate toxicity, acidosis, hyperkalemia, and decreased 2,3-DPG.³⁵ Most of these can be prevented or treated by appropriately using warmed products, FFP, platelets, and specific electrolyte replacement therapy.

Monitoring End Points of Resuscitation

End points of resuscitation refer to parameters that are measured serially in an individual patient to assess adequacy of resuscitation therapy in correcting shock. These parameters can be divided into three categories: clinical signs, invasive and noninvasive hemodynamic measurements, and laboratory markers. Most commonly used clinical signs consist of normalization of heart rate, blood pressure, and urine output. Commonly used hemodynamic parameters include measurements of volume status or preload, cardiac output, mixed venous oxygen saturation, and oxygen delivery. These may be obtained by different invasive and minimally invasive techniques. Laboratory markers include arterial lactate level, pH, and base deficit. There is a large body of clinical and experimental literature comparing the value of these parameters, including several reviews.^14,17,19,28 Most authors concur that clinical signs alone are inadequate measures of adequacy of resuscitation. Hemodynamic parameters are useful guides, but normalization of systemic acidosis as manifested by correction of base deficit and lactic acidosis probably are the best markers of adequacy of resuscitation. Correction of these parameters within 24 hours has been associated with improved outcomes.²⁸

Special Situations

Geriatric Patients

In the 2000 census, there were almost 35 million people 65 years and older, representing 12.6% of the total US population.⁶ Many of these patients will sustain serious injuries requiring aggressive care. Principles of fluid resuscitation in injured elderly patients are the same as in younger patients. However, physiologic changes associated with aging, the presence of comorbid conditions, and use of prescription and over-the-counter medications makes their assessment and monitoring more challenging.³³ Over-resuscitation has consequences as devastating as under-resuscitation; the decrease in physiologic reserve observed in our aging population leaves little margin for error. Early invasive monitoring frequently is a useful adjunct to fluid resuscitation.

Pregnancy

Some of the hemodynamic changes associated with pregnancy include increased blood volume, decreased hematocrit, increased cardiac output, increased heart rate, and decreased peripheral vascular resistance. Because of increased blood volume, an injured patient who is pregnant may lose a significant amount of blood before signs of maternal hypovolemia and shock develop. However, the fetus may be perfused inadequately during this time, even in the presence of normal maternal vital signs.¹⁸ Early aggressive fluid resuscitation is indicated. If blood products are required and the Rh-type of the mother is unknown, it is important to use Rh-negative components to avoid Rh sensitization. Also, these mothers should be treated with Rh immune globulin to minimize the risk of Rh sensitization attributable to fetomaternal transfusion. Unless a spinal injury is suspected, the patient who is pregnant should be maintained on her left side to relieve pressure of the uterus on the inferior vena cava because the pressure can compromise venous return to the heart. Adequate resuscitation of the mother will result in restoration of adequate placental blood flow to the fetus.

Burns

Patients sustaining 20% or more second and third degree body surface area burns require aggressive fluid resuscitation using isotonic crystalloid solutions. Initial resuscitation generally is based on the Parkland formula (4 mL of LR/kg/%BSA burn) as a guide for fluid requirements in the first 24 hours. One-half of the calculated 24-hour fluid requirement is given during the first 8 hours from the time of burn. The actual volume of fluid infused is guided by appropriate end points of resuscitation.

Head Injuries

Head injuries are the leading cause of death and disability in patients who are injured. Secondary brain injury attributable to hypotension (systolic BP < 90 mm Hg) and hypoxia (PaO₂ ≤ 60 mm Hg or apnea or cyanosis in field) is associated independently with significant increases in morbidity and mortality.¹⁰ The primary objective of fluid resuscitation in these patients is to minimize secondary brain injury related to hypotension by using aggressive fluid resuscitation and pharmacologic support directed at maintaining a normal cerebral perfusion pressure, while avoiding hypotonic solutions to minimize the risk of brain edema.

Spinal Cord Injuries

The most common cause of hypotension in patients with spinal cord injury is hemorrhage, especially in the presence of associated injuries. Once hemorrhage has been controlled or ruled out, hypotension may be attributed to neurogenic shock. Hypotension in this situation is caused by sudden loss of sympathetic vascular tone, and often is accompanied by bradycardia. Clinically, the patients seem warm and well perfused. Treatment consists of volume resuscitation with crystalloid solutions and low doses of vasopressors, such as phenylephrine, to restore vascular tone and correct the relative hypovolemia that resulted from venous pooling caused by the injury induced sympathectomy. It is unusual to require pressor therapy beyond the first several days of injury.

Controversies in Resuscitation

Crystalloid versus Colloids

Colloid solutions, such as those containing albumin, dextrans, or starches, increase the plasma oncotic pressure, which has the theoretical advantage of moving fluid from the interstitial space to the intravascular space, thereby minimizing total fluid of resuscitation and reducing the likelihood of peripheral and tissue edema.^11,34 Although there have been studies showing one type of fluid to be superior to another, systematic reviews of published studies have not shown any benefit of colloids over crystalloids in reducing mortality or pulmonary edema.^11,32 These studies, when combined with the increased cost of colloid solutions, underscore the continued advantage of crystalloid solutions as the initial resuscitation fluid of choice.

Hypotensive Resuscitation

The most universally accepted approach to hemorrhagic shock mandates aggressive fluid resuscitation to normalize various physiologic parameters. There are experimental and clinical data to suggest that this approach may worsen survival in small subsets of patients by increasing bleeding, especially when the source of hemorrhage is uncontrolled.^15,30 In a prospective randomized clinical trial, a small survival advantage was reported for patients who were hypotensive with penetrating injuries to the trunk and whose fluid resuscitation was delayed until after surgical control of hemorrhage was obtained.³ This area currently remains controversial and larger clinical trials are needed to answer this question definitively. Currently, however, resuscitation to normalize standard physiologic parameters remains the safest approach to care.

DISCUSSION

There is a large body of experimental and clinical research related to fluid resuscitation in patients with hemorrhagic shock. Experiments done on large and small animals have been invaluable in defining the pathophysiology of resuscitation. However, these models have certain shortcomings, which may restrict their application to clinical situations. These include a substantial variability from one laboratory to another, varying end points of resuscitation, arbitrary protocols not based on clinical experience, and differing anesthetic management.²³ There have been very few randomized clinical trials of resuscitation in patients with trauma, primarily because of logistic reasons surrounding the emergent nature of trauma, including the inability to obtain informed consent from patients. Attempts at meta-analysis have been limited because of methodologic differences among clinical trials.¹¹ Therefore, current practices of fluid resuscitation in patients with trauma, although based on sound physiology, seem to have evolved primarily based on clinical experience in military battlefields and civilian trauma centers.

Interestingly, despite five decades of extensive research, the fundamental principles of resuscitation have changed very little.²⁶ We have presented a review of those principles, and an update of more contemporary literature. Some recent developments that may profoundly impact current practices include the use of blood substitutes and hypertonic saline for resuscitation, and minimally invasive techniques for monitoring the end points of resuscitation. Blood substitutes refer to compounds or solutions that have oxygen-carrying capacity, but are not actually considered blood products. These substances fall into three categories: those based on hemoglobin, those based on perfluorocarbons, and liposome-encapsulated hemoglobin.³⁶ All of these are in different stages of development and clinical trials. None currently is available for clinical use but they are extremely promising for the future. The ultimate benefit of these products will be unlimited availability, prolonged shelf life, easy portability, and the nonexistent risk of transfusion-related blood-borne infections.

Hypertonic saline, generally supplied as 7.5% NaCl, with or without dextran, acts by rapidly shifting fluids from intracellular and interstitial spaces into the intravascular space, thereby restoring circulating blood volume with small volumes of resuscitation.²⁴ Published evidence of a survival benefit in resuscitation of patients with trauma has been equivocal, and a systematic review of literature published recently did not show any advantage of hypertonic crystalloid solutions over isotonic solutions for fluid resuscitation in patients who are critically ill.⁴ However, this product may have an application for patients with severe brain injury because it may expand the circulating blood volume with less risk of the patient having cerebral edema develop.

In the early hours after injury, basic noninvasive hemodynamic parameters, such as heart rate, blood pressure, capillary refill, and urine output, usually are adequate to guide the minute-to-minute progress of resuscitation. After the first 24–48 hours, especially in elderly patients or those patients with underlying cardiopulmonary or renal disease, invasive monitoring may be needed to guide ongoing resuscitation. Currently, hemodynamic monitoring with a pulmonary artery catheter is the standard of care. Recently, several minimally invasive techniques have been developed, such as esophageal Doppler monitoring, thoracic electrical impedance, transpulmonary cardiac output, pulse contour analysis, and lithium dilution cardiac output.⁹ Each has certain advantages and disadvantages, but experience is limited and the techniques are not yet widely available.

The assessment and management of the volume requirements of patients who are polytraumatized are not mysterious, and particularly are not shrouded in controversy. When presented with such a patient, a rapid assessment for the clinical parameters associated with acute hypovolemia, coupled by the aggressive infusion of warmed crystalloid solutions delivered through large bore catheters initially will serve the patient well. The use of warmed blood and blood products must be considered early on in a patient who is hypotensive and bleeding. They must be delivered in volumes that will correct past bleeding, and at a minimum, keep up with ongoing blood loss until it can be brought under control. Coagulopathy and hypothermia are to be expected and treated early with FFP, platelets, and advanced warming techniques. The combination of these few pearls and a large dose of common sense, will go far in the delivery of optimum care to patients who are injured.