**5. Burn shock**

When burns cover <10% of the TBSA, the associated inflammatory response and vascular leakage tend to remain localized within the immediate proximity of the injured tissue. However, as the TBSA approaches 15–20%, the overall quantity of cytokines released systemically into the circulatory system increases dramatically, contributing to systemic inflammatory response whereby uninjured anatomically distant body regions experience various deleterious downstream manifestations such as vasoactive changes, increased capillary permeability, and tissue edema [3, 76, 77]. In the setting of such more severe burns, abrupt fluid shifts from vasculature into the interstitial space quickly lead to clinically apparent hypovolemic shock. In the setting of severe burn injury, this type of shock is appropriately termed "burn shock" [78, 79]. The state of hypovolemic shock during the acute, or "ebb," phase can be further exacerbated by the copresence of low cardiac output from decreased effective circulating blood volume, increased blood viscosity, and depressed cardiac contractility [77, 79, 80]. Most severely affected patients may experience multisystem organ failure (MOF) [81].

From a clinical management standpoint, the initiation of appropriate fluid resuscitation immediately upon the completion of BPE is imperative to providing (and maintaining) the necessary cardiovascular support. Every additional hour from time of injury that resuscitative fluid administration is delayed increases the risk of mortality [82]. Under resuscitation can lead to tissue hypoperfusion, acute renal injury, and death. Over-resuscitating, however, can cause increased tissue edema, compartment syndromes, acute respiratory distress syndrome (ARDS), infections (e.g., pneumonia), and MOF [83–85]. Therefore, proper resuscitation of burn patients requires individually tailored fluid administration and close monitoring in order to prevent secondary, mostly iatrogenic injuries.

Initiating appropriate intravenous fluid resuscitation requires establishing and maintaining dependable vascular access [3]. Short, large bore peripheral intravenous catheters placed through unburned skin are ideal because this approach avoids potentially thrombosed superficial veins underlying full thickness burn areas. That said, venous access through burned skin is preferred over no venous access, and in most situations may be more rapidly available then central venous access. Central venous access is reliable but comes with increased risk of complications compared to other available options such as saphenous venous cut-down or intraosseous route [86, 87]. Once adequate vascular access is established, fluid resuscitation should be initiated immediately. Optimally, a protocol-driven approach to fluid administration is preferred [88, 89].

The rate of clinical failure (defined as patient deterioration or mortality) with prompt and adequate resuscitation is relatively low (e.g., <5% even for patients with burned TBSA >85%) [90]. As a general guideline, patients who benefit the most from formula-based, calculated fluid resuscitation include adults between 15 and 50 years of age with ≥20% TBSA involving second and third degree burns; children ≤15 years old and adults ≥50 years of age with ≥ 10% TBSA involving second and third degree burns. In practice, many institutions will consider initiating resuscitative fluids when adult burn victim presents with injuries involving ≥15% TBSA [91]. A significant body of research regarding modern fluid resuscitation protocols

**149**

*Burn Shock and Resuscitation: Many Priorities, One Goal*

demonstrates that systemic capillary leakage during the initial 24-h period after injury permits movement of large molecules into the interstitial space [92, 93]. For this reason, colloids are generally considered to provide little added benefit to crystalloid administration in the first 24 h. The topic is somewhat controversial, however, as some researchers argue that capillary permeability may begin returning to normal as early as 6–8 h after injury [90, 94, 95]. Consequently, the latter group advocates that earlier colloid addition may reduce the total amount of fluid necessary to achieve hemodynamic resuscitation and intravascular volume restoration.

The Parkland formula is among the most widely used and studied burn patient resuscitation paradigms [91, 96–98]. When originally published, this resuscitation approach advocated total crystalloid infusion of 4 mL/kg for each percent of body surface area burned [96–98]. The equation estimates the total amount of Ringer's lactate to be given in the initial 24-h post-burn period. Half of the calculated total fluid amount is to be given in the first 8 h and the remaining over the following 16 h [91, 98]. At the same time, certain limitations inherent to formula-based resuscitative approaches do exist. For example, the Parkland formula has been noted to underestimate the total volume of Ringer's lactate needed during the first 24 h in severe burns (>40% TBSA) [91, 99]. This tendency to need larger than estimated fluid volume is referred to as "fluid creep" [84, 100]. Although the exact factors responsible for this phenomenon are still being debated, one effective way of addressing it involves frequent urine output monitoring with hourly adjustments in fluid rates [84]. Goal urine output for adults is 0.5 mL/kg/h and for children ≤30 kg is 1 mL/kg/h. Some institutions have developed protocols that incorporate hourly fluid infusion rate adjustments of 10–30% depending on whether urine output is above or below goal [84]. As an example, we will consider using an hourly rate adjustment of 20% in an adult burn victim. In such scenario, if urine output decreased to <0.5 mL/kg/h, then the current fluid rate would be increased by 20%. If urine output was maintained at 0.5–1 mL/kg/h, then no rate adjustments are made. Finally, if urine output was measured to be >1 mL/kg/h, then the current

Children have larger surface/volume ratios compared to adults, which translates to disproportionately higher infusion rates. The Galveston formula is designed to account for this difference, whereby during the first 24 h, patients receive fluids

daily maintenance [101]. Similar

× %TBSA +2000 mL/m2

to Parkland formula, half of the calculated total is given in the first 8 h and the rest over the remaining 16 h [102]. Children have lower glycogen stores than adults and consequently should have 5% dextrose added to the primary resuscitative crystalloid solution [103, 104]. As the formula indicates, children require greater amount of resuscitation fluid per kilogram than adults. Unfortunately, children also have lower physiologic reserves, which may predispose them to side effects of more aggressive fluid resuscitation approaches [105]. For example, it has been shown that the cardiac output of pediatric burn victims may not return to pre-burn levels for 24–48 h post-injury, even with complete intravascular status restoration. Furthermore, excessive secretion of antidiuretic hormone may lead to oliguria that extends beyond 48–72 h post-burn [105]. Taking the above parameters into consideration, it is recommended that urine output surveillance and fluid rate adjustments

*DOI: http://dx.doi.org/10.5772/intechopen.85646*

**5.1 The Parkland formula**

fluid rate would be reduced by 20%.

be made on a more frequent basis than adults.

**5.2 The Galveston formula**

based on 5000 mL/m2

*Burn Shock and Resuscitation: Many Priorities, One Goal DOI: http://dx.doi.org/10.5772/intechopen.85646*

demonstrates that systemic capillary leakage during the initial 24-h period after injury permits movement of large molecules into the interstitial space [92, 93]. For this reason, colloids are generally considered to provide little added benefit to crystalloid administration in the first 24 h. The topic is somewhat controversial, however, as some researchers argue that capillary permeability may begin returning to normal as early as 6–8 h after injury [90, 94, 95]. Consequently, the latter group advocates that earlier colloid addition may reduce the total amount of fluid necessary to achieve hemodynamic resuscitation and intravascular volume restoration.
