The high-flow nasal oxygen (HFNO) has recently used as an alternative method for oxygenation to prolong the safe apnea time during anesthesia induction.1–3 Although a higher flow rate can theoretically extend the apnea time, it may result in gastric insufflation. We hypothesized on first principles that oxygenation with a higher flow rate might induce excessive pressure in the pharyngeal region, potentially allowing the leaking air to pass through the esophagus, and subsequently leading to gastric insufflation. Thus, this work was performed to explore the optimal flow of HFNO which can ensure adequate oxygenation while minimizing gastric insufflation during anesthesia induction.
METHODS
This single-center, randomized controlled study was approved by the Ethics Committee of the 1st Affiliated Hospital of Wenzhou Medical University, Zhejiang, China, and registered at the Chinese Clinical Trial Registry before patient enrollment. Additionally, the written informed consent was obtained from all subjects participating in the trial.
According to the flow rates of HFNO administered during 3-minute anesthesia induction, participants were assigned to one of the following 3 groups: 40 L.min−1 (Group H40), 60 L.min−1 (Group H60), and 80 L.min−1 (Group H80), respectively. High-flow humidified oxygen was warmed to 37 °C and delivered through a nasal cannula during anesthesia induction.
After the patient’s admission to the operating room, ultrasonic gastric monitoring was performed. Any preanesthesia gastric insufflation was excluded from the trial. Then anesthesia was induced using sufentanil (0.4 μg.kg−1), propofol (2 mg.kg−1), and rocuronium (0.6 mg.kg−1). After the eyelash reflex disappeared, the patients received different flow rates of HFNO according to the allocation for 3 minutes. Meanwhile, a catheter was inserted for real-time laryngopharyngeal pressure measurement. After the catheter placement (T0), the incidences of gastric insufflation were recorded at 1 minute (T1), 2 minutes (T2), and 3 minutes (T3) during anesthesia induction. Laryngopharyngeal pressures were also measured per 1 minute. An experienced anesthesiologist used a standard 2-handed jaw thrust maneuver to maintain the airway patency. The gastric antrum was detected to determine the presence of gastric insufflation, which was defined as the appearance of an acoustic shadow and/or a comet-tail artifact in the antrum.4,5 Moreover, the arterial Po2 (Pao2) and carbon dioxide (Paco2) at T0 and T3 were measured. Any other observed side effects were also collected.
RESULTS
A total of 302 patients from September 2023 to November 2023 were assessed for eligibility, and 238 patients (Group H40, n = 79; Group H60, n = 80; Group H80, n = 79) were analyzed as described in the flow diagram (Supplemental Digital Content 1, Supplemental Figure 1, https://links.lww.com/AA/F156). The demographic data and baseline characteristics among the 3 groups were summarized in Supplemental Digital Content 2, Supplemental Table 1, https://links.lww.com/AA/F157. The incidences of gastric insufflation under different flow rates over time are shown in the Figure. After 3-minute anesthesia induction (T3), Group H40 presented a lower incidence of gastric insufflation compared with the other 2 groups (Group H40: 1/79 [1.3%] vs Group H60: 10/80 [12.5%], odds ratio [OR] = 11.14, 95% confidence interval [CI], 1.39–89.26, P = .004; Group H40: 1/79 [1.3%] vs Group H80: 22/79 [27.8%], OR = 30.11, 95% CI, 3.94–229.89, P < .001). The comparisons for intergroup are presented in Supplemental Digital Content 3, Supplemental Table 2, https://links.lww.com/AA/F158.
Laryngopharyngeal pressure was increased dependently with the flow rate increased. None of the patients developed hypoxemia in our trial. There was no statistical difference in Pao2 (P = .075) and Paco2 (P = .597) after anesthesia induction among the 3 groups. In addition, the incidence of nausea in the postoperative anesthesia care unit did not show a significant difference (OR = 1.19, 95% CI, 0.67–2.12, P = .558). Nobody in each group experienced epistaxis.
DISCUSSION
To the best of our knowledge, this trial first suggested that HFNO with 40 L.min-1 could be safely used for oxygenation during anesthesia induction. Meanwhile, it presented the relatively lower laryngopharyngeal pressure and reduced incidence of gastric insufflation, compared with the ones with higher flow rates at 60 and 80 L.min−1.
HFNO can maintain oxygenation for patients with impaired pulmonary function.6 To avoid hypoxemia, nasal oxygenation with a relatively higher flow will be provided in clinical practice. Nowadays, HFNO has been increasingly applied in general anesthesia, including anesthesia induction and maintenance. Compared with the traditional mask ventilation, the HFNO was proven to decrease the extent of air influx entering the stomach.5 However, overabundant air flow by HFNO can still inflate the stomach. Severe gastric insufflation would lead to gastric distension and increase the probability of regurgitation, which theoretically promotes subsequent pulmonary aspiration.There is a conflict between adequate oxygenation provided by HFNO and gastric insufflation induced by high laryngopharyngeal pressure. Few studies have previously investigated the relationship between gastric insufflation and the flow rates of HFNO. Our findings indicated that excessive flow rates were more prone to gastric insufflation. Thus, caution is needed when using HFNO with inappropriate flow rates. Whether the threshold of laryngopharyngeal pressure to push lower esophageal sphincter and induce gastric insufflation needs to be further explored.
REFERENCES