Burn Resuscitation: The Child Who Is Already Full of Fluid
An 8-year-old (30 kg, 120 cm) arrives 3 hours after a house fire with 45% total body surface area partial- and full-thickness burns involving the face and chest. He was intubated at the scene for increasing hoarseness and stridor; soot is visible in the oropharynx. He received 2.5 L of lactated Ringer's at the referring hospital. Now: HR 162, BP 88/52 mmHg, cool extremities, urine output 8 mL/h (a catheter was placed only an hour ago), and the abdomen is distended and firm. Peak inspiratory pressures have risen from 24 to 36 cm H2O over 45 minutes. Carboxyhemoglobin was 12% on arrival, roughly 2 hours after exposure.
1. Calculate a reasonable starting hourly fluid rate and explain how the fluid he has already received, and his current examination, change your interpretation of that number.
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Classic Parkland: 4 mL/kg/%TBSA = 4 x 30 x 45 = 5400 mL over 24 hours from the time of injury, half (2700 mL) in the first 8 hours. At 3 hours post-injury he should have received about 900-1000 mL/hour so far, meaning roughly 2700-3000 mL in total; he has received 2.5 L, which is close to but slightly behind that target. Pediatric practice usually adds maintenance fluid on top of the burn estimate, because children have small reserves.
The judgement issue is that the urine output of 8 mL/h looks like under-resuscitation but may not be. The catheter was only just placed, so the recorded volume may not reflect a full hour; target urine output is 1-2 mL/kg/h (30-60 mL/h). More importantly, the combination of a rising peak inspiratory pressure, a firm distended abdomen, and oliguria despite 2.5 L of crystalloid is the signature of over-resuscitation with capillary leak and rising intra-abdominal pressure, not of a child who simply needs more fluid. Measure intra-abdominal pressure via the bladder catheter before escalating the rate. If bladder pressure is elevated, the answer is decompression, not more volume.
2. What does the combination of rising peak pressures, a firm distended abdomen, and oliguria suggest, and how do you diagnose and treat it, including the chest wall?
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The picture suggests abdominal compartment syndrome with a contribution from chest wall non-compliance due to full-thickness eschar. Circumferential full-thickness burns of the torso produce a leathery, inelastic shell plus massive interstitial edema, so intra-abdominal pressure rises and the chest wall cannot expand.
Diagnosis: measure intra-abdominal pressure through the bladder with a standardized volume (about 1 mL/kg) and the patient supine and relaxed, ideally with neuromuscular blockade to remove abdominal wall muscle tone. Sustained pressure above 10 mmHg with new organ dysfunction suggests intra-abdominal hypertension; above 20 mmHg with oliguria or rising airway pressures is compartment syndrome. Correlate with the trend in peak pressures, bladder pressure, and urine output.
Treatment, in order: chest and abdominal escharotomy (this is a surgical emergency and is the single most effective maneuver for the rising peak pressure); decompress the gut with a nasogastric tube; ensure sedation and neuromuscular blockade; reduce the fluid infusion rate toward the low end of the target and consider colloid or hypertonic rescue; reverse Trendelenburg positioning. If bladder pressure remains high with organ dysfunction after escharotomy and medical measures, decompressive laparotomy with temporary closure is indicated, and it should be done before bowel ischemia or renal failure develops.
3. How does the inhalation injury and the carboxyhemoglobin result change your management, and what confounders affect that number?
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Airway and lungs: soot in the oropharynx with hoarseness and stridor is an indication for the early intubation already performed; a low threshold for bronchoscopy to assess and clear the airway; anticipate progressive edema and a rapidly rising oxygen requirement. If severe ARDS develops, this is a reasonable candidate for lung-protective ventilation and, if refractory, early ECMO consultation.
Carbon monoxide: treat with 100% oxygen, which shortens the half-life from roughly 4 hours to under an hour. The measured 12% is almost certainly an underestimate of the peak, because the sample was drawn hours after exposure and after oxygen was begun. Hyperbaric oxygen is reserved for severe poisoning (neurologic findings, syncope, COHb above 25%, acidosis, or pregnancy) and is rarely feasible in a ventilated child with extensive burns. Recognize that a normal COHb now does not exclude significant exposure.
Cyanide: enclosed-space fires cause cyanide toxicity, which presents as a high-anion-gap lactic acidosis with a normal PaO2 and an abnormally high venous oxygen saturation from impaired cellular oxygen utilization. Hydroxocobalamin 70 mg/kg is the antidote and should be given empirically if this pattern is present, without waiting for a level. Also watch for falsely reassuring pulse oximetry, since carboxyhemoglobin and methemoglobin both corrupt it.