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Difficulty: Very hardPulmonary and Critical Care

A 66-year-old man is admitted to the intensive care unit after sustaining right-sided rib fractures in a motor vehicle collision. He has a history of severe chronic obstructive pulmonary disease (COPD). On hospital day 2, he develops increasing respiratory distress and is intubated for mechanical ventilation. He is deeply sedated with a continuous propofol infusion and paralyzed with rocuronium.

Ten minutes after intubation, the ventilator's high-pressure alarm sounds. His blood pressure precipitously drops from 145/88 mm Hg to 72/40 mm Hg, and his heart rate increases to 132/min. Oxygen saturation is 93% on a fraction of inspired oxygen (FiO2FiO_2) of 1.0.

An arterial blood gas reveals:
- pH: 7.18
- PaCO2PaCO_2: 74 mm Hg
- PaO2PaO_2: 68 mm Hg
- HCO3−HCO_3^-: 27 mEq/L

Bedside evaluation of ventilator mechanics reveals a peak airway pressure of 68 cm H2OH_2O and a plateau airway pressure of 22 cm H2OH_2O (measured during an end-inspiratory breath hold).

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

  1. Disconnect the patient from the mechanical ventilatorAnswer
  2. B
    Transport the patient for an emergent computed tomography scan of the chest
  3. C
    Administer intravenous sodium bicarbonate
  4. D
    Escalate empiric antibiotics to intravenous meropenem
  5. E
    Administer intravenous furosemide

Answer

Disconnect the patient from the mechanical ventilator
The correct action is to disconnect the patient from the mechanical ventilator. This patient has developed severe hypotension shortly after intubation. The ventilator mechanics show a highly elevated peak airway pressure (68 cm H2OH_2O) with a normal plateau pressure (22 cm H2OH_2O; normal is < 30 cm H2OH_2O). A high peak-to-plateau pressure gradient indicates a purely resistive problem, such as severe bronchospasm, mucus plugging, or endotracheal tube obstruction. In a patient with severe COPD, high airway resistance combined with inadequate expiratory time prevents complete exhalation before the next ventilator breath is delivered. This leads to progressive air trapping, known as dynamic hyperinflation or auto-PEEP. The accumulated intrathoracic pressure compresses the inferior vena cava, drastically reducing right ventricular preload and causing acute obstructive shock. Temporarily disconnecting the patient from the ventilator circuit allows for a prolonged expiratory phase, letting the trapped air escape and rapidly restoring venous return and blood pressure. Afterward, ventilator settings must be adjusted (e.g., decreasing the respiratory rate, increasing inspiratory flow rate) to maximize expiratory time.

Step-by-Step Solution

1
Analyze the ventilator airway pressures.
The peak airway pressure is severely elevated (68 cm H2O), but the plateau airway pressure is normal (22 cm H2O).
A high peak-to-plateau pressure gradient (here, 46 cm H2O) isolates the problem to increased airway resistance (e.g., bronchospasm) rather than decreased lung compliance.
2
Correlate the airway resistance with the patient's underlying disease and current hemodynamics.
The patient has severe COPD. High airway resistance prevents full exhalation during the set respiratory cycle, leading to air trapping (auto-PEEP or dynamic hyperinflation).
Trapped air progressively increases intrathoracic pressure.
3
Determine the cause of the sudden hypotension.
The severely elevated intrathoracic pressure from auto-PEEP compresses the vena cava, causing a massive drop in right ventricular preload and subsequent obstructive shock.
The sudden drop in blood pressure immediately post-intubation in a highly resistant airway is the classic presentation of auto-PEEP-induced hemodynamic collapse.
4
Select the immediate life-saving intervention.
Disconnecting the ventilator circuit allows the trapped air to escape passively.
This immediately relieves the intrathoracic pressure, restoring venous return and normalizing the blood pressure.

Key Concept

In mechanically ventilated patients with severe obstructive lung disease, dynamic hyperinflation (auto-PEEP) can cause obstructive shock; the immediate life-saving treatment is temporary disconnection from the ventilator to allow for prolonged exhalation.
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Topics

Pulmonary and Critical Care

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