The Acutely Burned Patient
Fluid management of the acutely burned patient focuses on restoration
of plasma volume and a shift of the ECF volume into the burned but viable tissue,
accompanied by increased losses caused by loss of the normal barrier function of
the skin. The tissue injury produced by the
burn leads to an abrupt disruption of the capillary bed, manifested by local vasodilation,
increased permeability, and presumably, decreased reflection coefficient to proteins.
Vasodilation increases the surface area for filtration and tends to increase capillary
pressure. The lowered reflection coefficient diminishes the ability of colloids
to retain fluid in the capillaries. Water, electrolytes, and protein enter the burned
tissue at the expense of the intravascular volume. Fluid is mobilized from uninjured
tissues by a variety of processes, with a net result of transfer of fluid from normal
tissue into the injured tissue and intravascular hypovolemia. Capillary permeability
was formerly thought to increase in all tissues after a serious burn injury, but
this is not the currently held view.[135]
In addition
to the tissue edema, there is a marked increase in loss of water by evaporation from
the wound surface, and the metabolic rate increases dramatically, leading to proportionate
increases in fluid requirements.
Several formulas have been developed to aid in writing the initial
fluid prescription. The key to success is close hemodynamic monitoring with titration
of therapy to the individual patient's physiology. For example, if urine output
increases progressively or if filling pressures increase, fluid administration must
be decreased. The Parkland formula[136]
prescribes
fluids based on the percentage of the body surface area (BSA) burned (percent BSA-burned):
2 mL/kg/percent BSA-burned during the first 8 hours and 2 mL/kg/percent BSA-burned
during the next 16 hours. The formula prescribes the following regimen of fluids:
- Lactated Ringer's solution at [(0.25 mL/kg)/(percent BSA-burned)]/hour
for 8 hours
- Lactated Ringer's solution at [(0.125 mL/kg)/(percent BSA-burned)]/hour
for 16 hours
- 5% dextrose in water at [(0.8 mL/kg)/(percent BSA-burned)]/hour plus 5%
albumin at [(0.015 mL/kg)/(percent BSA-burned)]/hour for 24 hours
For example, a 50-kg person with 50% BSA burn should receive fluids
equal to (50 kg) × (0.25 mL/kg) × (50% BSA-burned),
or 625 mL/hour for 8 hours. This is followed by fluids equal to (50 kg)
× (0.125 mL/kg) × (50% BSA-burned), or 310 mL/hour for 16
hours. During the second 24 hours, fluids administered equal (50 kg) ×
(0.08 mL/kg) × (50% BSA-burned), or 200 mL/hour of 5% dextrose in
water, plus (50 kg) × (0.015 mL/kg) × (50% BSA-burned),
or 37.5 mL/hour of 5% albumin. Colloids are not contraindicated, even during the
acute phase of fluid resuscitation. Although they pass into the injured tissue at
an accelerated rate, they have a more sustained effect on plasma volume than crystalloid
alone.
