We thank Dr. Shiber for his interest in the case report.

Because we were preparing for intubation, our goal was complete denitrogenation with 100% oxygen ; thus, the fraction of inspired oxygen for noninvasive positive-pressure ventilation was 100%. Although the patient had acute respiratory acidosis, you correctly point out that the terminology of acute on chronic respiratory acidosis is more accurate. It is debated whether the modest hypercapnia that is sometimes observed after oxygen administration to patients with acute exacerbations of chronic obstructive pulmonary disease is due to ventilation-perfusion mismatch, a modest decrease in minute ventilation, or both. Available evidence suggests that abrupt apnea from oxygen administration to a patient with acute chronic obstructive pulmonary disease exacerbation is very unlikely and, to our knowledge, has never been described, unlike ketamine-associated apnea.

Although we did not wait until the formal definition of apnea was achieved before intervening with bag-valve-mask ventilation, the patient’s total observed apnea time until the onset of pharmacologic paralysis was approximately 1 minute. We did not wait to observe further clinical deterioration such as hypoxemia or bradycardia, but rather sought to avoid these associated complications for this patient for whom we already had a plan of intubation.

Consistent with your described clinical experience with ketamine, this agent has a long history of safe use for procedural sedation with apnea as a rare complication. The use of the phrase “critically ill patients” was not meant to describe the physical location of patients, such as the ICU, but rather to describe patients undergoing active resuscitation, such as those with shock or impending respiratory failure. We believe that this patient population is likely to have higher apnea rates related to ketamine than more stable patients undergoing procedural sedation.

Regardless of the mechanism or rarity of ketamine-associated apnea, it is important to recognize that it can occur. Therefore, when performing delayed sequence intubation, physicians should remain at the bedside and be prepared to immediately manage the patient’s airway.