Carbon Dioxide Changes during High-flow Nasal Oxygenation in Apneic Patients: A Single-center Randomized Controlled Noninferiority Trial

Background: Anesthesia studies using high-flow, humidified, heated oxygen delivered via nasal cannulas at flow rates of more than 50 l center dot min(-1) postulated a ventilatory effect because carbon dioxide increased at lower levels as reported earlier. This study investigated the increase of arterial partial pressure of carbon dioxide between different flow rates of 100% oxygen in elective anesthetized and paralyzed surgical adults before intubation. Methods: After preoxygenation and standardized anesthesia induction with nondepolarizing neuromuscular blockade, all patients received 100% oxygen (via high-flow nasal oxygenation system or circuit of the anesthesia machine), and continuous jaw thrust/laryngoscopy was applied throughout the 15-min period. In this single-center noninferiority trial, 25 patients each, were randomized to five groups: (1) minimal flow: 0.25 l center dot min(-1), endotracheal tube; (2) low flow: 2 l center dot min(-1), continuous jaw thrust; (3) medium flow: 10 l center dot min(-1), continuous jaw thrust; (4) high flow: 70 l center dot min(-1), continuous jaw thrust; and (5) control: 70 l center dot min(-1), continuous laryngoscopy. Immediately after anesthesia induction, the 15-min apnea period started with oxygen delivered according to the randomized flow rate. Serial arterial blood gas analyses were drawn every 2 min. The study was terminated if either oxygen saturation measured by pulse oximetry was less than 92%, transcutaneous carbon dioxide was greater than 100 mmHg, pH was less than 7.1, potassium level was greater than 6 mmol center dot l(-1), or apnea time was 15 min. The primary outcome was the linear rate of mean increase of arterial carbon dioxide during the 15-min apnea period computed from linear regressions. Results: In total, 125 patients completed the study. Noninferiority with a predefined noninferiority margin of 0.3 mmHg center dot min(-1) could be declared for all treatments with the following mean and 95% CI for the mean differences in the linear rate of arterial partial pressure of carbon dioxide with associated P values regarding noninferiority: high flow versus control, -0.0 mmHg center dot min(-1) (-0.3, 0.3 mmHg center dot min(-1), P = 0.030); medium flow versus control, -0.1 mmHg center dot min(-1) (-0.4, 0.2 mmHg center dot min(-1), P = 0.002); low flow versus control, -0.1 mmHg center dot min(-1) (-0.4, 0.2 mmHg center dot min(-1), P = 0.003); and minimal flow versus control, -0.1 mmHg center dot min(-1) (-0.4, 0.2 mmHg center dot min(-1), P = 0.004). Conclusions: Widely differing flow rates of humidified 100% oxygen during apnea resulted in comparable increases of arterial partial pressure of carbon dioxide, which does not support an additional ventilatory effect of high-flow nasal oxygenation.

Automated summary

This study investigated the effects of different flow rates of humidified 100% oxygen on the increase of arterial partial pressure of carbon dioxide. The results showed that different flow rates resulted in comparable increases in arterial partial pressure of carbon dioxide, suggesting no additional ventilatory effect of high-flow nasal oxygenation.