Burn Resuscitation

Introduction

Burns in excess of about 20% of the total body surface area (TBSA) cause shock, manifested by decreased circulating blood volume, decreased cardiac output (CO), and inadequate end-organ perfusion. Fluid resuscitation to address burn shock is one of the key lifesaving interventions in the early care of burn patients. Inadequate or delayed fluid resuscitation causes organ failure and death. On the other hand, provision of excessive amounts of fluid (overresuscitation), by augmenting edema formation and engendering complications such as compartment syndromes, also increases morbidity and mortality. Thus the overarching goal of fluid resuscitation is to achieve a careful balance between the two extremes of over- and underresuscitation; in other words, “to maintain vital organ function at the least immediate or delayed physiologic cost.”

The primary cause of burn shock is a reduction in the circulating blood volume due to loss of fluid similar in composition to plasma across the microvasculature. Thus burn shock is hypovolemic shock. Such fluid loss occurs primarily in burned tissues but also, for larger burns, in unburned tissues as well. The term “leaky capillaries” is often used to describe this complex process (for details, see Chapter 8, Pathophysiology of Burn Shock and Burn Edema ). Other factors that contribute to burn shock include intense vasoconstriction during the immediate postburn hours, causing increased afterload, and a decrease in intrinsic myocardial contractility. These three factors—hypovolemia, vasoconstriction, and decreased myocardial contractility—contribute to decreased CO. The aims of fluid resuscitation are simultaneously (1) to counteract the loss of circulating blood volume with intravenous fluids; (2) to monitor the physiologic response frequently and diligently; (3) to alter treatment strategy based on physiologic response (e.g., by titrating the fluid infusion rate hourly); and (4) to anticipate, guard against, and correct the effects of edema formation. This could be summarized as follows: burn shock mandates simultaneous fluid resuscitation and edema management strategies .

Early Approaches to Fluid Resuscitation

A wide variety of resuscitation formulas dominates much of the discussion on the treatment of burn shock ( Table 9.1 ). Knowledge of how these formulas came about is helpful to understanding their advantages and limitations. Intravenous fluid resuscitation for the treatment of burns owes much to early investigations of the pathophysiology and treatment of cholera. In 1831, O'Shaughnessy, an Irish physician, performed studies of the chemical and microscopic features of the blood in cholera patients. Based on these studies, he proposed “the injection into the veins of tepid water holding a solution of the normal salts of the blood.” He did canine experiments of this novel therapy but did not apply it to humans. One year later, Thomas Latta, a Scottish physician, read about O'Shaughnessy's work and treated patients with cholera using rectal, oral, and then intravenous saline solutions. In 1906, Dr. Haldor Sneve of St. Paul, Minnesota, described the use of saline solutions, including enemas, for the treatment of burns. His common-sense recommendations were not followed for years because the prevailing point of view at the time was that the main cause of death in patients with extensive burns was not hypovolemia but the absorption of toxic substances from the burned skin (“toxemia”). This belief led to the widespread adoption of tanning agents such as tannic acid, the purpose of which was to “fix” the toxins and prevent them from entering the bloodstream.

Table 9.1

Common Burn Resuscitation Formulas

From Hansen SL. From cholera to “fluid creep”: a historical review of fluid resuscitation of the burn trauma patient. Wounds 2008;20(7): 206–213. For earlier version of the Cincinnati formula, see Merrell SW, Saffle JR, Sullivan JJ, et al. Fluid resuscitation in ther­mally injured children. Am J Surg . 1986;152(6):664–669. For earlier version of the Galveston formula, see Carvajal HF. Fluid resuscitation of pediatric burn victims: a critical appraisal. Pediatr Nephrol . 1994;8(3):357–366.

Formula	First 24 Hours Post Burn	Next 24 Hours Post Burn
Evans Formula	NS: 1 mL/kg/%TBSA burn	NS: 0.5 mL/kg/%TBSA burn
	Colloid: 1 mL/kg/%TBSA burn	Colloid: 0.5 mL/kg/%TBSA burn
	D5W: 2000 mL	D5W: 2000 mL
Brooke Formula	NS: 1.5 mL/kg/%TBSA burn	NS: 0.5 mL/kg/%TBSA burn
	Colloid: 0.5 mL/kg/%TBSA burn	Colloid: 0.25 mL/kg/%TBSA burn
	D5W: 2000 mL	D5W: 2000 mL
Modified Brooke Formula	LR: 2 mL/kg/%TBSA burn	LR: None
	Colloid: None	Colloid: 0.3–0.5 mL/kg/%TBSA burn
Parkland Formula	LR: 4 mL/kg/%TBSA burn	LR: None
	Colloid: None	Colloid: 5% albumin given at 0.3–1 mL/kg/%TBSA burn/16 per hour
Shriner's Cincinnati (For Children)	LR: 4 mL/kg/%TBSA burn + 1500 mL/m 2 , given over first 8 h and the remaining over the next 16 h (older children)
	LR: 4 mL/kg/%TBSA burn + 1500 mL/m 2 + 50 mEq sodium bicarbonate for the first 8 h, followed by LR alone in second 8 h, followed by 5% albumin in LR in third 8 h (younger children)
Galveston Formula (For Children)	LR: 5000 mL/m 2 burn + 2000 mL/m 2 total, volume in first 8 h, followed by remainder in 16 h.

D5W, 5% Dextrose in water; LR, lactated Ringer's solution; NS, normal saline; UO, urinary output; TBSA, total body surface area.

Subsequent mass-casualty disasters and armed conflict both contributed to resuscitation advances. On November 27, 1921, the Rialto Theatre in New Haven, Connecticut, caught fire, killing 6 and injuring 80. Dr. Frank Underhill examined 21 survivors who were admitted following the fire. Underhill was a veteran of World War I and had previously reported on the effects of chemical warfare agents on the lungs. He drew a parallel between the process whereby the lungs are flooded with fluid following inhalation of toxic gases and that by which edema forms in wounds following thermal injury. He reported that the more severe the burn, the more severe the hemoconcentration (increased hemoglobin), and that fluid replacement must be rapid and is of paramount importance in survival. Additionally he reported that blister fluid was similar in composition to plasma and that the fluid lost could be replaced with an intravenous physiologic salt solution, supplemented rectally, orally, and subdermally. Oral and rectal infusions were de-emphasized until recently, when their utility in austere and combat-casualty-care scenarios was revisited.

In 1931, Alfred Blalock built on Underhill's reports by performing experiments in which anesthetized dogs sustained burns of approximately one-third of the TBSA, localized to one-half of the body (right or left). The animals were not resuscitated. After a period of observation (6–26 hours), the animals were euthanized, bisected, and the carcasses weighed. Thus he quantified the amount of fluid lost across the burn wounds, which averaged 3.34% of the total body weight. This fluid loss was accompanied by a mean increase in the hemoglobin level of 48%. Blalock speculated that this process, rather than toxemia, was sufficient to explain the resultant postburn hypotension. Further experiments involving excision of the burn wound as well as cross-transfusion (of burned to unburned dogs) supported his hypothesis.

With World War II on the horizon, and following battles such as the Battle of Britain in 1940 and the attack on Pearl Harbor in 1941, there was great urgency to develop effective methods to care for wartime burn casualties. Meanwhile plasma now became available for intravenous administration. Several formulas were developed for burn-shock resuscitation using plasma. One recommended enough plasma to maintain the peripheral circulation, evidenced by the ease with which blood could be drawn by a needle prick. Others were based on calculations that incorporated the hematocrit and/or the protein levels in the blood. The burn-size-based formulas we use today originated from a conference on January 7, 1942, of the National Research Council (NRC). This committee stated that a burn patient should receive 500 mL of plasma initially, followed by 100 mL of plasma per TBSA burned during the first 24 h post burn. Other fluids (normal saline or dextrose) should not normally exceed the plasma dose. Interestingly, Harkins (who participated in the NRC meeting) described a First Aid Formula at the same time that recommended half this amount, or 50 mL/TBSA of plasma. In addition, patients should receive about 1000 mL of normal saline solution and “large amounts” of dextrose, preferably by mouth.

These preparations were tested when, on November 28, 1942, the Cocoanut Grove nightclub in Boston caught fire, killing 492 people and injuring hundreds more in the deadliest nightclub fire in U.S. history. Patients were resuscitated with plasma, which, however, was provided by the blood bank diluted with equal volumes of normal saline. Dr. Cope at the Massachusetts General Hospital provided in the first 24 hours 50 mL of plasma plus 50 mL saline for every 1% TBSA burned, followed by adjustments based on hemoconcentration. Dr. Lund at the Boston City Hospital did not use a formula to guide resuscitation, but rather clinical parameters such as heart rate, blood pressure, and hematocrit.

Later, Cope and Moore reported the first burn formula based on burn surface area for fluid therapy, recommending that 75 mL plasma and 75 mL noncolloid isotonic fluid be administered for every 1% TBSA burned in the first 24 hours, with one-half being given in the first 8 hours and the remaining being given in the next 16 hours. This practice of providing half of the fluid needs within the first 8 hours remains a feature of nearly all modern burn resuscitation formulas. Additionally, 2000 mL fluid was to be given on each day to maintain urine flow, preferably by mouth.

These formulas were based on a normal-sized adult and could be unfavorable at the extremes of weight. Thus formulas based on both weight and TBSA were developed.

Dr. Everett Evans developed one such formula. This formula predicts infusion of 1 mL/kg per TBSA of normal saline and an equal part colloid, plus 2000 mL of 5% dextrose in water (D5W), in the first 24 hours. This is followed by 0.5 mL/kg per TBSA of saline and an equal part colloid and of D5W in the second 24 hours.

Children

Formulas have been developed specifically for resuscitation of children. Graves et al. at the USAISR performed a retrospective review of children weighing less than 25 kg who were resuscitated with the pediatric modified Brooke formula. This formula estimates 3 mL/kg per TBSA of LR for the first 24 hours, with half given over the first 8 hours; LR is then titrated based on urine output (UO; target UO, 0.5–1.5 mL/kg per hour). Children are also given 5% dextrose in one-half normal saline (D5W NS) at a maintenance rate, which is not titrated. The actual volume of LR infused was, on average, 3.91 mL/kg per TBSA (3.78 in those whose UO was within the target range). Maintenance fluids added an additional 2.39 mL/kg per TBSA to the total. The 2011 Advanced Burn Life Support manual recommends the use of this 3 mL/kg per TBSA burned formula for children, with the addition of maintenance fluid of D5WLR.

The Shriner's Cincinnati and Galveston pediatric formulas account for the larger body surface area-to-weight ratio of children. For the first 24 hours post burn, the Cincinnati formula provides 4 mL/kg per TBSA (with half given in the first 8 hours), plus maintenance needs (MN), plus evaporative losses (EL). Here, MN = (1500 mL) × (body surface area in m ² ), and EL = 35 + (TBSA burned in %) × (body surface area in m ² ).

For the first 24 h post burn, the Galveston formula provides 5000 mL × (TBSA burned in m ² ) + 2000 mL × (body surface area in m ² ), with half given in the first 8 hours post burn.