A 68-year-old woman with HIV is admitted to the ICU with respiratory failure secondary to pneumocystis pneumonia, requiring intubation and mechanical ventilation. A chest CT scan was performed before intubation and demonstrated cystic changes throughout the lungs, thought to be a sequela of past pneumocystis infection, with superimposed diffuse ground glass opacities. Her ventilator is set on:
On day 2 of her critical illness, her ventilator suddenly alarms for elevated peak pressures. She is observed to be deeply sedated and breathing passively on the ventilator. The peak pressure has risen from 25 cm H2O several hours before 50 cm H2O. The patient has simultaneously experienced oxygen desaturation from 95% to 90%. She is otherwise hemodynamically stable. A chest radiograph is ordered. An inspiratory hold maneuver is performed and her plateau pressure is 20 cm H2O.
Which of the following is the MOST LIKELY explanation for this acute event?
A. Rupture of a cyst leading to pneumothorax and acute decrease in lung compliance
Correct Answer: B
The ventilator mechanics reported here describe an acute increase in peak airway pressure with a normal plateau pressure. This indicates that the peak airway pressure is reflective of an acute increase in resistance within the respiratory system or endotracheal tube. Potential causes of this include biting or other kinking of the endotracheal tube, mucous within the endotracheal tube or airway without complete obstruction, bronchospasm, or airway edema/inflammation (answer B is correct). An increase in peak airway pressure, with a corresponding increase in plateau pressure, represents decrease in respiratory system compliance. This may be secondary to lobar collapse, mainstem intubation, pulmonary edema, pneumonia, ARDS, pleural effusion, pneumothorax, elevated intraabdominal pressure, or elevated chest wall pressure (answers A, C and E are incorrect). Given that the patient is deeply sedated, biting on the endotracheal tube is not a likely explanation for the increase in airway resistance (answer D is incorrect).