Fluid Resuscitation in Burns

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Indications for Fluid Resuscitation

The American Burns Association state that "burns greater than 20% TBSA should undergo formal fluid resuscitation using estimates based on body size and surface area burned" (Pham et al, 2008).

More globally speaking, the following two are recommended guidelines for fluid resuscitation in a burn based on burn size.

1. Adults > 15% TBSA
2. Children >10% TBSA

The goal of fluid resuscitation is to prevent rather than treat burn shock. This goal is achieved in the following ways:

1. Restore circulating volume
2. Preserve tissue perfusion
3. Avoid ischemic extension of the burn wound

Pathophysiology of Burn Shock

Burn shock begins at a cellular level (Baxter 1968, Moyer 1965, Arturson 1979). It is a combination of distributive, cardiogenic, and hypovolemic shock.

Key components of the physiological changes during a burn are:

• Intracellular sodium shift contributes to hypovolemia and cellular oedema.
• Local vasoconstriction and systemic vasodilation form inflammatory and vasoactive mediators.
• A fluid shift from intravascular to interstitial spaces due to Increased vascular permeability from disrupted capillaries.

This pathophysiological response is compounded by a reduced cardiac output and increased systemic vascular resistance. It is also influenced by burn depth and total body surface area.

There are two main "fluid compartments".

• Intracellular: fluid inside the cell (the majority of fluid in the body)
• Extracellular: fluid outside the cell that consists of intravascular and interstitial fluid.

Types of Fluids

There is no absolute consensus on fluid formula or fluid type.

It is important to replace the fluid in the intravascular compartment to avoid end-organ hypoperfusion and ischemia. Isotonic crystalloids, hypertonic solutions and colloids can all be used to effectively restores plasma volume, but every solution has advantages and disadvantages.

Crystalloids

A crystalloid fluid is an aqueous solution of mineral salts and other small, water-soluble molecules.

Most commercially available crystalloid solutions are isotonic to human plasma.  Administration of large volumes of crystalloid during burn resuscitation decreases plasma protein concentration.

Commonly used crystalloids include:

• Saline: Normal Saline, Hypertonic Saline
• Ringer's Lactate (also called Haartman's solution)
• 5% Dextrose (used in paediatric burns)

Colloids

Several recent studies have suggested that colloid is useful in decreasing total fluid administration, thereby reducing the risk of “fluid creep,” and oedema formation.

There is little consensus with respect to indications or dosing (Eljaiek R et al, 2017). Colloid options available include:

• Albumin
• Dextran
• Hydroxyethyl

Albumin Replacement

Albumin should be replaced in a major burn. The Muir and Barclay formula calculates the volume of human albumin solution required in the first 36 hours:

• 0.5mL X kg X TBSA% to be infused in each time period
• Time periods are 3 x 4 hours, 2 x 6 hours, 1 x 12 hours.  

Formulas for Burn Resuscitation

There are a number of different formulas used to calculate fluid requirements in burn resuscitation. These include the commonly used Parkland formula and modified-Brooke formula.  

This is illustrated in the table below.  

Parkland Formula

4ml x %TBSA x kg

The Parkland formula (also known as the Baxter Formula) was developed in 1968 by Baxter and Shires. It remains one of the most widely used resuscitation crystalloid-only formulas. It is calculated as 4ml x %TBSA x kg. The first half is given in the first 8 hours, the second half is given in the next 16 hours.

First 24 hours after burn:

• 4ml x %TBSA x kg in the first 24 hours
• 1st half is in the first 8 hours, and 2nd half is in the next 16 hours.
• Increase fluids in deeper burns, delayed resus, & inhalation (Baxter 1974, 1978)

Second 24 hours after burn:

• There is less attention to colloid recommendations for the second 24 hours.
• Colloids are given as 20–60% of calculated plasma volume. No crystalloids.
• Glucose in water to maintain a urinary output of 0.5–1 ml/hr in adults & 1 ml/hr in children.

Variations

• The rate of fluid infusion should be adjusted to the physiological response
• The volume of fluid should be titrated to maintain a urine output of approximately 0.5–1.0 ml/ kg/hr in adults and 1.0–1.5 ml/kg/hr in children.
• Other variables, including the heart rate, blood pressure, lactate, base deficit, and mental status, must be considered simultaneously.

Modified-Brooke Formula

2ml x %TBSA x kg

The original Brooke formula proposed by Dr Artz at the Army Burn Center was composed of both crystalloid and colloid fluids.

Initial 24 hours:

• 2ml x %TBSA x kg in adults and 3ml x %TBSA x kg  in children
• No colloids.
• Ringer Lactate or Hartman's solution

Next 24 hours:

• Colloids at 0.3–0.5 ml/kg/% burn and no crystalloids are given.
• Glucose in water is added to maintain good urinary output.

Assessing Response to Fluids

The rate and volume of fluid resuscitation should be titrated and adapted to specific physiological responses.

Key parameters include

• Urine Output: >0.5mL/kg/hr in adults, >1mL/kg/hr in children.
• Vital Signs: pulse, blood pressure, respirator rate
• Temperature Core-peripheral temperature gradient
• Urine Osmolality
• Arterial Blood Gas: Lactate and Base Excess

Children and Elderly

Paediatrics

Maintenance fluid with 5% dextrose in addition to resuscitation fluid is required in the paediatric population. This is because

• Reduced physiological reserves
• Proportionally greater surface area than adults.

Glucose homeostasis is an important parameter in children.

• Hepatic glycogen stores in young children are depleted after ~12 hours
• Important to provide sufficient glucose substrates during the first 24 hours of re- suscitation.
• Achieved by adding dextrose to the maintenance fluid or early enteral nutrition

Elderly

The elderly population are compounded by medical comorbidities and a decreased baseline cardiac and pulmonary function. This results in an increased risk of volume overload complications. Hemodynamic monitoring should be used in concert with UOP to optimize perfusion and cardiac function‌             ‌

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Complications of Fluid Resuscitation

Precise titration of fluid rate is critical due to high morbidity of both under-resuscitation and over-resuscitation.

Complications of Under-resuscitation

• Uncontrolled burn shock
• Inadequate organ perfusion
• Organ failure

Complications of Over-resuscitation

• Increases the risk of massive oedema formation
• Elevated compartment pressures including the abdominal, ocular and extremity compartments
• Conversion of superficial to deep burn depth
• Acute respiratory distress syndrome (ARDS).

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