Division of Paediatric Intensive Care Medicine, Department of Paediatrics, University Children's Hospital, University of Bern, Bern, Switzerland.
Department of Anaesthesiology and Pain Medicine, Bern University Hospital, University of Bern, Bern, Switzerland.
PLoS One. 2022 Sep 28;17(9):e0273120. doi: 10.1371/journal.pone.0273120. eCollection 2022.
Previous studies concerning humidified, heated high-flow nasal oxygen delivered in spontaneously breathing patients postulated an increase in functional residual capacity as one of its physiological effects. It is unclear wheter this is also true for patients under general anesthesia.
The sincle-center noninferiority trial was registered at ClinicalTrials.gov (NCT NCT03478774). This secondary outcome analysis shows estimated differences in lung volume changes using electrical impedance tomography between different flow rates of 100% oxygen in apneic, anesthetized and paralyzed adults prior to intubation. One hundred and twenty five patients were randomized to five groups with different flow rates of 100% oxygen: i) minimal-flow: 0.25 l.min-1 via endotracheal tube; ii) low-flow: 2 l.min-1 + continuous jaw thrust; iii) medium-flow: 10 l.min-1 + continuous jaw thrust; iv) high-flow: 70l.min-1 + continuous jaw thrust; and v) control: 70 l.min-1 + continuous video-laryngoscopy. After standardized anesthesia induction with non-depolarizing neuromuscular blockade, the 15-minute apnea period and oxygen delivery was started according to the randomized flow rate. Continuous electrical impedance tomography measurements were performed during the 15-minute apnea period. Total change in lung impedance (an estimate of changes in lung volume) over the 15-minute apnea period and times to 25%, 50% and 75% of total impedance change were calculated.
One hundred and twenty five patients completed the original study. Six patients did not complete the 15-minute apnea period. Due to maloperation, malfunction and artefacts additional 54 measurements had to be excluded, resulting in 65 patients included into this secondary outcome analysis. We found no differences between groups with respect to decrease in lung impedance or curve progression over the observation period.
Different flow rates of humidified 100% oxygen during apnea result in comparable decreases in lung volumes. The demonstrated increase in functional residual capacity during spontaneous breathing with high-flow nasal oxygenation could not be replicated during apnea under general anesthesia with neuromuscular blockade.
先前关于自主呼吸患者接受湿化、加热高流量鼻氧疗的研究推测，其生理效应之一是功能残气量增加。但在全身麻醉下的患者中，这是否同样适用尚不清楚。
这项单中心非劣效性试验已在 ClinicalTrials.gov 注册（NCT NCT03478774）。本二次结果分析显示，在全身麻醉下进行气管插管前，使用电阻抗断层成像术测量不同氧流量（100%纯氧）对无自主呼吸、麻醉和肌松的成人的肺容积变化的估计差异。125 例患者被随机分为五组，接受不同氧流量（100%纯氧）：i）最小流量：通过气管内管输送 0.25 l.min-1；ii）低流量：2 l.min-1+持续下颌推力；iii）中流量：10 l.min-1+持续下颌推力；iv）高流量：70 l.min-1+持续下颌推力；和 v）对照组：70 l.min-1+持续视频喉镜。在非去极化神经肌肉阻滞下进行标准化麻醉诱导后，根据随机流量开始 15 分钟的无自主呼吸期和氧输送。在 15 分钟的无自主呼吸期间进行连续电阻抗断层成像测量。计算 15 分钟无自主呼吸期间肺阻抗的总变化（估计肺容积的变化）以及达到总阻抗变化的 25%、50%和 75%所需的时间。
125 例患者完成了原始研究。6 例患者未完成 15 分钟无自主呼吸期。由于操作失误、仪器故障和伪影，另外需要排除 54 次测量，因此有 65 例患者纳入本次二次结果分析。我们发现，在肺阻抗降低或曲线进展方面，各组之间没有差异。
在无自主呼吸期间，不同流量的湿化 100%氧气导致肺容积的降低相当。在自主呼吸时高流量鼻氧疗引起的功能残气量增加，在全身麻醉下使用神经肌肉阻滞剂进行无自主呼吸时无法复制。
