A 68-year-old woman is evaluated in the intensive care unit due to high-pressure ventilato… — USMLE Step 2 CK

A $68$ -year-old woman is evaluated in the intensive care unit due to high-pressure ventilator alarms. She is on postoperative day $3$ following an exploratory laparotomy for a perforated diverticulum. Her past medical history includes severe chronic obstructive pulmonary disease, heart failure with preserved ejection fraction, and chronic kidney disease. She has been heavily sedated and on volume assist-control mechanical ventilation since surgery.

She is currently receiving targeted intravenous ceftriaxone, as peritoneal fluid cultures from the surgery are growing pan-sensitive *Escherichia coli*.

Current vital signs:
Temperature: $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ )
Blood pressure: $105/65\text{ mmHg}$
Heart rate: $118/\text{min}$
Oxygen saturation: $93\%$ on an $\text{FiO}_2$ of $0.40$

Current ventilator settings:
Tidal volume: $400\text{ mL}$ ( $6\text{ mL/kg}$ predicted body weight)
Respiratory rate: $16/\text{min}$
PEEP: $8\text{ cm H}_2\text{O}$

The peak inspiratory pressure has abruptly increased to $58\text{ cm H}_2\text{O}$ (was $28\text{ cm H}_2\text{O}$ four hours ago).
The physician performs an end-inspiratory hold maneuver, which reveals a plateau pressure of $24\text{ cm H}_2\text{O}$ (unchanged from four hours ago).

Arterial blood gas analysis reveals:
pH: $7.21$
$\text{PaCO}_2$ : $66\text{ mmHg}$
$\text{PaO}_2$ : $68\text{ mmHg}$
$\text{HCO}_3^-$ : $26\text{ mEq/L}$

Physical examination reveals scattered wheezes bilaterally and a prolonged expiratory phase. Cardiac examination shows tachycardia with a regular rhythm. The abdomen is tender but without surgical site erythema.

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

A
Increase the set respiratory rate to $26/\text{min}$
B
Administer intravenous furosemide
Administer an in-line inhaled bronchodilator and suction the endotracheal tubeAnswer
D
Broaden the current antibiotic regimen to include vancomycin and cefepime
E
Obtain venous duplex ultrasonography of the lower extremities

Answer

Administer an in-line inhaled bronchodilator and suction the endotracheal tube

This patient presents with a sudden increase in peak inspiratory pressure (

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

) but a normal, unchanged plateau pressure (

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

). The gradient between peak and plateau pressure represents airway resistance. When peak pressure is elevated but plateau pressure remains normal, the pathology is exclusively related to increased resistance in the conducting airways (e.g., severe bronchospasm, mucus plugging, or an obstructed endotracheal tube). In contrast, processes that decrease alveolar compliance (e.g., acute respiratory distress syndrome, cardiogenic pulmonary edema, or pneumothorax) would elevate *both* the peak and plateau pressures. Given her history of COPD and physical exam showing wheezing, acute bronchospasm or secretion retention is the cause. The most appropriate immediate intervention is to clear the airway obstruction via suctioning and bronchodilator administration.

Step-by-Step Solution

Analyze the mechanical ventilator pressure parameters.

The peak inspiratory pressure (PIP) is markedly elevated at

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

, while the plateau pressure (Pplat) is normal and unchanged at

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

Differentiating between elevated PIP and Pplat is the critical first step in determining the etiology of ventilator alarms.

Determine the pathophysiologic mechanism.

An elevated PIP with a normal Pplat (a widened transairway pressure gradient) indicates high airway resistance, not decreased lung compliance.

Elastic processes (ARDS, pulmonary edema, pneumothorax) elevate BOTH PIP and Pplat. Resistive processes (bronchospasm, mucus plugging, tube obstruction) elevate ONLY the PIP.

Integrate clinical findings to formulate a treatment plan.

The patient has a history of COPD and diffuse wheezing, suggesting acute bronchospasm or secretion retention.

Administering bronchodilators and suctioning directly addresses the mechanical obstruction causing the respiratory acidosis and ventilator alarms.

Key Concept

Differentiating resistive versus elastic work of breathing on mechanical ventilation using peak and plateau pressures to diagnose the cause of acute respiratory deterioration.

Alternative Method

Advanced mechanical ventilators continuously calculate and display dynamic airway resistance (Raw) and static compliance (Cstat) beat-to-beat, which can instantly identify resistance issues without requiring the physician to manually perform an end-inspiratory hold maneuver.

Estimated Time:2m 0s

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