A 55-year-old man with a history of hypertension and obesity is evaluated in the recovery room for hypoxemia after undergoing a sleeve gastrectomy several hours ago. Although the endotracheal intubation was difficult, the procedure was completed without intraoperative complications. The patient was then extubated and transferred to the postanesthesia recovery unit. He was initially stable on ambient air but soon became hypoxemic. Despite the use of oxygen by nasal cannula, his condition has not improved. Other issues include gastroesophageal reflux and generalized anxiety disorder. The patient's medications include omeprazole, paroxetine, chlorthalidone, and lisinopril. He drinks 3 or 4 beers on most days but does not use tobacco or illicit drugs. His last alcoholic drink was the night prior to surgery. The patient's preoperative testing was significant only for a mildly elevated serum bicarbonate at 30 mEq/L. Temperature is 37.2 C (99 F), blood pressure is 140/80 mm Hg, pulse is 108/min, and respirations are 12/min. The patient's pulse oximetry shows 84% on room air. BMI is 39 kg/m². Examination shows an obtunded patient who is minimally responsive to stimuli. Physical findings include 3-mm reactive pupils, moist mucous membranes, normal jugular venous pressure, coarse breath sounds over the lung fields without stridor or wheezing, and normal S1 and S2. The abdomen is soft and nontender. Examination shows no edema. Laboratory results are as follows: ECG shows sinus tachycardia, and chest x-ray reveals bibasilar atelectasis. Which of the following is the most likely cause of this patient's clinical deterioration?

Question

Quizplus · Accepted Answer

Explanation: This patient has acute perioperative hypercapnic and hypoxic respiratory failure, most likely due to underlying obstructive sleep apnea (OSA). Male sex and obesity (defined as BMI >30 kg/m²) are risk factors for OSA. In addition, this patient's elevated baseline serum bicarbonate (>27 mEq/L) suggests compensation for chronic respiratory acidosis, which is a clue to comorbid obesity hypoventilation syndrome, a disorder that OSA typically accompanies. Approximately 50% of patients with OSA are undiagnosed at the time of preoperative screening; identification of these patients is important because they are at increased risk of respiratory complications from procedures involving sedation, neuromuscular blockers, opioid analgesia, and/or anesthesia. In addition to causing a depressed state of arousal, these medications likely decrease pharyngeal dilator muscle tone and predispose patients with OSA to apneic or hypopneic events. Acute respiratory failure due to OSA results from hypoventilation (evidenced by bibasilar atelectasis on chest x-ray), and typically leads to hypercapnic, hypoxic respiratory failure (acute on chronic hypercapnic, hypoxic respiratory failure in this patient) with respiratory acidosis. (Choice A) Perioperative myocardial infarction can cause acute systolic heart failure and consequent respiratory failure due to pulmonary edema. However, bibasilar crackles and jugular venous distension would be expected on physical examination. In addition, respiratory alkalosis (due to tachypnea and hyperventilation) is expected in the acute setting; hypercapnic respiratory failure is not typical initially. (Choice B) Acute ischemic stroke affecting the medulla or pons can lead to impaired respiratory drive and acute hypercapnic respiratory failure; however, hypoventilation due to airway obstruction is more likely in this patient with evidence of OSA. (Choice C) In heavy alcohol users, alcohol withdrawal may occur within 48-96 hours of last alcohol ingestion; however, typical findings include agitation and other manifestations of sympathetic nervous system activation (eg, tachycardia, tachypnea). Somnolence and hypoventilation are not typical. (Choice E) Pulmonary embolism can lead to acute hypoxic respiratory failure, but, like respiratory failure due to pulmonary edema, respiratory alkalosis is expected initially. Acute hypercapnic respiratory failure is not typical of pulmonary embolism in the absence of significant underlying chronic obstructive pulmonary disease. Educational objective: Patients with obstructive sleep apnea are at increased risk of perioperative respiratory failure from procedures involving sedation, neuromuscular blocker, opioids, or anesthesia. When respiratory failure occurs, it results from hypoventilation and typically presents with hypercapnia and hypoxia.

A 55-Year-Old Man with a History of Hypertension and Obesity