A 34-year-old man is brought to the emergency department after a severe industrial fire. H… — USMLE Step 2 CK

A $34$ -year-old man is brought to the emergency department after a severe industrial fire. He sustained deep, full-thickness circumferential burns to his anterior and posterior torso, as well as his bilateral lower extremities. The total body surface area burned is estimated at $55\%$ . Due to marked oropharyngeal edema and carbonaceous sputum, he was intubated at the scene. Intravenous fluid resuscitation with lactated Ringer solution was initiated based on standard weight-based formulas.

Upon arrival, his temperature is $36.7^\circ\text{C}$ ( $98.1^\circ\text{F}$ ), blood pressure is $112/68 \text{ mm Hg}$ , and heart rate is $110/\text{min}$ .

Four hours later, the patient's urine output has decreased to $10 \text{ mL/hr}$ . Repeat vital signs show a blood pressure of $78/48 \text{ mm Hg}$ and a heart rate of $142/\text{min}$ . The mechanical ventilator frequently alarms for high airway pressures.

Current ventilator parameters and central line measurements are as follows:
- Peak inspiratory pressure: $65 \text{ cm H}_2\text{O}$
- Plateau pressure: $55 \text{ cm H}_2\text{O}$
- Central venous pressure: $18 \text{ mm Hg}$

Bedside echocardiography demonstrates a small, underfilled, and hyperdynamic left ventricle. There is no evidence of pericardial effusion. An arterial blood gas analysis reveals a pH of $7.18$ , $p\text{CO}_2$ of $72 \text{ mm Hg}$ , and $p\text{O}_2$ of $62 \text{ mm Hg}$ .

Which of the following is the most appropriate next step in the management of this patient?

A
Immediate transport for computed tomography angiography of the chest
B
Intravenous administration of furosemide
C
Intravenous administration of broad-spectrum antibiotics
Bedside incision of the anterior chest wall burn escharAnswer
E
Intravenous administration of sodium bicarbonate

Answer

Bedside incision of the anterior chest wall burn eschar

The correct answer is bedside incision of the anterior chest wall burn eschar (escharotomy). This patient is experiencing thoracic compartment syndrome due to circumferential full-thickness burns of the torso. As massive fluid resuscitation progresses, profound tissue edema develops beneath the rigid, inelastic burn eschar. The eschar acts like a tourniquet and severely restricts outward chest wall expansion. This mechanically reduces chest wall compliance, leading to markedly elevated peak and plateau airway pressures on the ventilator, which results in severe hypoventilation (hypercapnia and respiratory acidosis). The massively elevated intrathoracic pressure also physically compresses the intrathoracic great vessels (superior and inferior vena cava), profoundly impairing venous return to the right heart. This manifests as an obstructive shock pattern, characterized by hypotension, tachycardia, oliguria, and a small, underfilled left ventricle on echocardiography. The central venous pressure is falsely elevated because the intravascular transducer is measuring the high external pressure transmitted to the central veins. The definitive, life-saving treatment is an immediate bedside escharotomy (incising the burn eschar) to release the mechanical restriction, which will acutely restore both pulmonary compliance and venous return.

Step-by-Step Solution

Identify the cause of the mechanical ventilation failure.

Elevated peak (

65 \text{ cm H}_2\text{O}

) and plateau (

55 \text{ cm H}_2\text{O}

) pressures indicate severely decreased compliance of the respiratory system.

Differentiating between airway resistance issues (e.g., bronchospasm) and compliance issues (e.g., rigid chest wall) is the first step in troubleshooting ventilator alarms.

Analyze the hemodynamic profile.

The patient exhibits hypotension, tachycardia, and a small, underfilled left ventricle combined with a falsely elevated central venous pressure (

18 \text{ mm Hg}

These findings point to obstructive shock caused by elevated intrathoracic pressure physically compressing venous return.

Synthesize the clinical data with the physical presentation.

The patient has circumferential torso burns that have formed a rigid eschar. Ongoing fluid resuscitation causes underlying tissue edema, which is restricted from expanding outwardly. This creates thoracic compartment syndrome.

Establishing the definitive diagnosis connects the pathophysiology to the required physical intervention.

Determine the most appropriate definitive intervention.

Immediate bedside escharotomy of the chest wall is required.

Incision of the eschar will mechanically release the restriction, acutely improving both pulmonary compliance and venous return.

Key Concept

Thoracic compartment syndrome secondary to circumferential chest burns

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