A 74-year-old male patient weighing 80 kg with a history of essential hypertension and known subglottic laryngeal cancer is scheduled for elective surgery. He presents with dyspnea (respiratory rate of 45 breaths/min), hypoxemia (SpO2 80% in ambient air), and a highpitched stridor that can be easily localized to the neck. Respiratory sounds are barely heard bilaterally on lung auscultation. A fiberoptic examination shows no space for nasotracheal or orotracheal intubation, so an emergency percutaneous tracheostomy is performed. Invasive mechanical ventilation initiated with assist control volume control ventilation (tidal volume of 600 mL and a PEEP of 8 cm H2O). However, the patient remains hypoxemic with a PO2 of 69 mm Hg despite an FiO2 of 80%. An x-ray shows bilateral infiltrates.
What would be the MOST appropriate first intervention on this patient?
A. Switch to protective ventilationCorrect Answer: A
The respiratory failure developing during severe upper airway obstruction typically originates from a negative-pressure pulmonary edema caused by the repeated negative airway pressure that the patient develops in order to overcome the resistance. This causes trans-vascular fluid extravasation and thereby interstitial and alveolar edema. This condition is purely hydrostatic and is generally relieved in 24 to 48 hours if positive pressure ventilation is ensured, and airway resistance is eliminated. The rate of alveolar fluid clearance in this condition is between 14% and 17% per hour, approaching physiological values, while in the presence of lung injury it may be as low as 0% to 3%/h. For this reason, the main intervention to take in this situation is to limit and prevent lung injury by guaranteeing a protective ventilation strategy (6 mL/kg of tidal volume with plateau pressure below 30 cm H2O). Diuretics can accelerate the rate of fluid uptake, but their efficacy is limited in the presence of lung injury. Fiberoptic bronchoscopy may only reveal the presence of pink frothy transudate which may also present by simply performing a tracheal aspiration. The immediate execution of a CT scan is not indicated until the effects of positive pressure ventilation, PEEP, and alveolar clearance clarify the actual damage accumulated by the lung tissue, if any exists.
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