To the Editor:
The analysis, by Sakaguchi et al., of the role of high-flow nasal oxygen administered postoperatively in those diagnosed with obstructive sleep apnea (OSA) in lieu of conventional continuous positive airway pressure therapy is interesting. We would welcome further commentary from the authors on a few points, however.
First, although we agree that high-flow nasal oxygen improves sleep time and oxygenation compared with simple oxygen therapy and overcomes upper airway obstruction in OSA via a continuous positive airway pressure–like effect, the institution of 30-degree head-of-bed elevation can also increase pulmonary functional residual capacity and reduce pharyngeal critical closing pressure. These are known to improve oxygenation and relieve upper airway obstruction postoperatively. Surprisingly, this was not observed here. Conversely, oxygenation in the 30-degree head-of-bed elevation group was inferior to that in the supine position (table 21 ). Curiously, although the combination of high-flow nasal oxygen and 30-degree head-of-bed elevation showed additive or even synergistic effects, neither alone showed much impact on the apnea-hypopnea index. This seems hard to understand, and we would welcome the authors’ thoughts on the point.
Second, most patients in this study were not particularly obese, and none were morbidly so. In severe obesity, airway obstruction is a major problem. Although a greater number of patients in the second group had moderate OSA, more in the first group had higher apnea-hypopnea indices and more desaturation. This seems surprising. Most patients with OSA have associated chronic obstructive pulmonary disease. Thus, it seems counterintuitive to initiate postoperative delivery of 40% oxygen in the high-flow nasal oxygen group, itself a cause of hypopnea and apnea as is evident table 2. We wonder why the oxygen therapy was not titrated to peripheral oxygen saturation or arterial blood gas analysis?
We thank the authors for their insightful study on combined high-flow nasal oxygen and 30-degree head-of-bed elevation in OSA. However, we would invite further comment on the points mentioned earlier.
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