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Research

Effect of high flow nasal cannula oxygenation on incidence of hypoxia during sedated gastrointestinal endoscopy in patients with obesity: multicentre randomised controlled trial

BMJ 2025; 388 doi: https://doi.org/10.1136/bmj-2024-080795 (Published 11 February 2025) Cite this as: BMJ 2025;388:e080795

Linked Editorial

High flow nasal oxygenation in sedated gastrointestinal endoscopy for patients with obesity
  1. Leilei Wang, resident physician1,
  2. Yuanyuan Zhang, resident physician1,
  3. Dan Han, attending physician2,
  4. Mengyun Wei, attending physician3,
  5. Jie Zhang, attending physician1,
  6. Xiangyang Cheng, resident physician1,
  7. Yizhe Zhang, doctoral candidate1,
  8. Muyan Shi, resident physician1,
  9. Zijian Song, resident physician1,
  10. Xiangrui Wang, professor and chief physician2,
  11. Xiaoqing Zhang, professor and chief physician3,
  12. Diansan Su, professor and chief physician1 4
  1. 1Department of Anesthesiology, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
  2. 2Department of Anesthesiology, East Hospital, Tongji University School of Medicine, Shanghai, China,
  3. 3Department of Anesthesiology, Shanghai Tongji Hospital, Tongji University, Shanghai, China
  4. 4Department of Anesthesiology, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
  1. Correspondence to: D Su diansansu{at}yahoo.com
  • Accepted 21 January 2025

Abstract

Objective To determine whether high flow nasal cannula (HFNC) oxygenation can reduce the incidence of hypoxia during sedated gastrointestinal endoscopy in patients with obesity.

Design Multicentre, randomised, parallel group trial.

Setting Three tertiary hospitals in Shanghai, China.

Participants 1000 adult patients with obesity (body mass index ≥28) who were scheduled for gastrointestinal endoscopy.

Interventions Participants were randomly allocated to receive regular nasal cannula oxygenation or HFNC oxygenation during a sedated procedure with propofol and low dose sufentanil.

Main outcome measures The primary outcome was the incidence of hypoxia (75%≤SpO2<90% for <60 s) during the procedure. Secondary outcomes included the incidences of subclinical respiratory depression (90%≤SpO2<95% for any duration) and severe hypoxia (SpO2<75% for any duration or 75%≤SPO2<90% for >60 s) during the procedure.

Results From 6 May 2021 to 26 May 2023, 984 patients (mean age 49.2 years; 36.9% (n=363) female) completed the study and were analysed. Compared with regular nasal cannula oxygenation, HFNC oxygenation reduced the incidence of hypoxia from 21.2% (103/487) to 2.0% (10/497) (difference −19.14, 95% confidence interval −23.09 to −15.36; P<0.001), subclinical respiratory depression from 36.3% (177/487) to 5.6% (28/497) (difference −30.71, −35.40 to −25.92; P<0.001), and severe hypoxia from 4.1% (20/487) to 0% (0/497) (difference −4.11%, −6.26 to −2.48; P<0.001). Other sedation related adverse events did not differ between the two groups.

Conclusions In patients with obesity, oxygenation via HFNC during sedated gastrointestinal endoscopy significantly reduced the incidences of hypoxia, subclinical respiratory depression, and severe hypoxia without increasing other adverse events.

Trial registration ClinicalTrials.gov NCT04500392.

Introduction

Gastrointestinal cancers are increasing globally, with three quarters of cases occurring in developing countries, and deaths from these cancers are also high.12 According to the data of the International Agency for Research on Cancer in 2020, China as the largest developing country in the world ranks fourth and third worldwide in terms of the incidences of gastric and oesophageal cancers, respectively.12 The incidence of colorectal cancer is also increasing along with the increasing prevalence of obesity.345 With the advances in technology and operational skills, gastrointestinal endoscopic procedures have become the gold standard for diagnostic and therapeutic purposes in patients with various gastrointestinal diseases.6 Sedated gastrointestinal endoscopy increases patients’ comfort, reduces stress response, and eases the operation. Consequently, it has become the preferred treatment method for most patients. In China, the overall number of gastrointestinal endoscopies is high and is expected to increase in the future. Furthermore, the sedation rate is about 50%, which is much lower than in other countries, and varies by region and hospital.7

Hypoxia is the most common adverse event during sedated gastrointestinal endoscopy, with reported incidences from 1.8% to 69%.8910 It is mainly caused by factors including respiratory depression, airway obstruction, and decreased chest wall compliance.11 Prolonged and severe hypoxia can lead to myocardial hypoxia, arrhythmia, permanent neurological damage, and even death.1213 Patients with obesity have poor lung and chest wall compliance, low lung capacity and functional residual capacity, and imbalanced ventilation-to-perfusion ratio. Thus, patients with obesity are at a high risk of hypoxaemia and prone to hypoxaemia induced complications.14 The incidence of hypoxia during sedated gastrointestinal endoscopy is higher in patients with obesity than in those with normal weight and increases with increasing body mass index.15 Furthermore, mask ventilation is challenging and hypoxaemia is difficult to correct in patients with obesity.16 With the increasing number of patients with obesity, the proportion of this patient group undergoing sedated gastrointestinal endoscopy has also increased. Reducing the incidence of hypoxaemia in these patients during sedated gastrointestinal endoscopy is a challenging task.

According to our previous study,17 use of HFNC oxygenation significantly reduced the incidences of hypoxia and severe hypoxia during sedated gastroscopy in patients with American Society of Anesthesiologists (ASA) class I-II. However, patients enrolled in that trial had an average body mass index of approximately 22; only 6% had a body mass index ≥28. This small percentage was insufficient to show the effects of HFNC on the incidence of hypoxia in patients with obesity. Evidence on the effects of HFNC in patients with obesity is conflicting and weak. In a randomised trial of 379 patients at high risk (29.3% had body mass index ≥30), Nay and colleagues reported that use of HFNC significantly reduced the incidence of hypoxia during gastrointestinal endoscopy under sedation.14 However, the results came from a post hoc subgroup analysis. In a small sample size trial with 59 morbidly obese patients, HFNC oxygenation did not effectively reduce the incidence of hypoxia during colonoscopy under propofol sedation.18 Owing to the limited evidence, no recommendations were made in the American Society for Gastrointestinal Endoscopy and ASA guidelines about the use of HFNC for patients with obesity undergoing gastrointestinal endoscopy.619 Therefore, a large sample size trial is warranted to validate the effects of HFNC during sedated gastrointestinal endoscopy in patients with obesity.

Methods

Study design

This multicentre, randomised, parallel group trial with superiority design was conducted in three tertiary university hospitals in Shanghai, China: Renji Hospital (affiliated with Shanghai Jiao Tong University School of Medicine), Tongji Hospital (affiliated with Shanghai Tongji University School of Medicine), and East Hospital (affiliated with Shanghai Tongji University School of Medicine).

Participants

We enrolled patients aged 18-70 years who had obesity (body mass index ≥28) and ASA class ≤II and were scheduled for sedated gastrointestinal endoscopy (including sedated gastroscopy, sedated colonoscopy, and sedated gastroenteroscopy). We excluded patients who met any of the following criteria: history of coagulation disorders or a tendency of nose bleeding; diagnosed heart disease including heart failure, angina, myocardial infarction, or arrhythmia; diagnosed respiratory diseases including asthma, bronchitis, chronic obstructive pulmonary diseases, pulmonary bullae, pulmonary embolism, pulmonary oedema, lung cancer, or upper respiratory tract infection; pregnancy; current liver disease; current kidney disease; increased intracranial pressure; multiple trauma; emergent procedure or surgery; history of mental disorders; allergy to drugs used during the procedure; or unwillingness to participate in the study. Each participant provided written informed consent.

Randomisation and masking

A biostatistician who was not involved in data management and statistical analyses generated the random sequence by using the PROC PLAN programme in SAS (version 9.0). Randomisation was generated in a one-to-one allocation ratio with a block length of six and stratified by the participating centres. Randomisation results were sealed in sequentially numbered opaque envelopes which were opened immediately before sedation was started. In this way, the consecutively recruited patients were randomly assigned to the regular nasal cannula group or the HFNC group.

After peripheral intravenous access was established, each patient was given a regular nasal cannula covered with an HFNC (Airvo 2, Fisher, and Paykel, Panmure, New Zealand) to blind patients to the group assignment. The patients all had the procedure in the same room in each centre, and the HFNC oxygenation device was always at their bedside.

Trial procedure

In the gastroenteroscopy room, an anaesthesiologist who had been trained in the use of a regular nasal cannula and HFNC was designated for sedation during the procedure. Pre-oxygenation was provided for one minute before sedation started. Patients in both groups received oxygen inhalation through the regular nasal cannula at a rate of 3 L/min before being sedated with 0.5 mg/kg propofol. Subsequently, the oxygen flow rate was increased to 6 L/min in the control group; the HFNC was connected to the already set machine (oxygen flow rate 60 L/min; humidity 37°C; oxygen concentration 100%) in the HFNC group. The sufentanil dosage was predetermined on the basis of the routine practices of the three centres: 5 µg for patients undergoing gastroscopy or colonoscopy and 7.5 µg for those undergoing gastroenteroscopy. Subsequently, the anaesthesiologist intravenously administered 1-2 mg/kg propofol according to the recommendations of the Expert Consensus on Sedation/Anaesthesia in Chinese Digestive Endoscopy from the Chinese Society of Anesthesiology.

The anaesthesiologist closely observed the patients once the sedation started and continually evaluated the depth of sedation by using the Ramsay Sedation Scale. Once the Ramsay sedation score was ≥5, the endoscopist inserted the endoscope and started the procedure. To maintain intraoperative sedation (Ramsay sedation score ≥5), propofol was also intermittently administered at a dose of 0.2-0.5 mg/kg until the examination was completed.

Data collection and outcome measures

We recorded the patients’ basic information, including name, sex, age, ASA classification, height, weight and body mass index, airway examination (Mallampati classification, snoring mentioned by family, and polysomnography diagnosis of sleep apnoea syndrome), STOP-Bang questionnaire form, and perioperative adverse events. Total dose of propofol was also documented.

Patients’ heart rate, blood pressure, and arterial oxygen saturation (SpO2) were measured and recorded by the standard anaesthesia multiparameter monitors. During the research period, SpO2 at each centre was consistently monitored using the same monitor, which were different in the three centres (Philips IntelliVue MP40, Royal Dutch Philips Electronics, in Renji Hospital; Philips G40E, Royal Dutch Philips Electronics, in East Hospital; and Mindray ePM10, Mindray Medical International, China, in Tongji Hospital). An independent recorder manually recorded the data on a paper case report form. The recorder continuously monitored the SpO2 values and activated a stopwatch to record the duration of hypoxia when SpO2 dropped below 90%. When hypoxia occurred, the patient’s airway was opened using the jaw thrust manoeuvre. Mask ventilation and tracheal intubation were performed if severe hypoxia could not be corrected with airway opening.

The primary study endpoint was the incidence of hypoxia (75%≤SpO2<90% for <60 s). The secondary study endpoints included the incidences of subclinical respiratory depression (90%≤SpO2<95% for any duration), severe hypoxia (SpO2<75% for any duration or 75%≤SpO2<90% for >60 s), and other adverse events.

All the sedation related adverse events during the procedure were recorded using the reporting tool proposed by the World Society of Intravenous Anaesthesia International Sedation Task Force,20 which involved the following steps. Step 1: determine whether an adverse event occurred. Step 2: describe the adverse events, including respiratory and sedation related adverse events. Step 3: record the interventions used to correct the adverse events. Step 4: record the patient’s outcome.

HFNC oxygenation related adverse events, including xeromycteria, rhinalgia, pharyngalgia, headache, and barotrauma (for example, pneumothorax and subcutaneous emphysema) were recorded after recovery from anaesthesia. The patients were observed for at least one hour in the recovery area following the procedure. During this time, their oxygen saturation, presence of respiratory distress, chest pain, and crepitant rales were checked. If these symptoms were noted, barotrauma was suspected and advanced examinations, such as computed tomography of the chest, were ordered, if necessary.

Sample size estimation

According to relevant literature searches2122 and preliminary experimental results, the incidence of hypoxia during regular nasal cannula oxygenation in patients with obesity was approximately 20%. HFNC reduced the incidence of hypoxia from 8.4% to 0% in ASA class I-II patients having elective gastroscopy under propofol sedation.17 We anticipated that HFNC could also reduce the incidence of hypoxia by 8% in patients with obesity. Therefore, assuming that HFNC oxygenation can reduce the incidence of hypoxia to 12%, we set total class I error to α=0.05, the test efficacy power to 0.90, and the dropout rate to 10%. In the bilateral test, the patients were randomly allocated to groups in a one-to-one ratio, and the three components were calculated using the PASS software. Therefore, we estimated the sample size to be 972. Overall, we enrolled 1000 patients, 500 in the HFNC group and 500 in the control group, considering that the situation may vary.

Statistical analysis

All tests were two sided, and we considered a P value <0.05 to indicate statistical significance, unless otherwise stated. We used SAS software version 9.4 for all statistical analyses.

We did all analyses according to the intention-to-treat principle. We analysed patients who were randomised and received the study treatment as the full analysis set. The per protocol set, a subset of the full analysis set, included participants without major protocol deviations. We did analyses of the primary and secondary endpoints simultaneously in the full analysis set and per protocol set, but the primary analysis was based on the full analysis set. In cases lacking a primary outcome, we did complete case analysis if the missing proportion was ≤5%. Otherwise, we used multiple imputations as the primary analysis strategy. The safety analysis set included all patients who received the study intervention.

We expressed continuous variables as means (standard deviations) or medians (interquartile ranges) and categorical variables as numbers of cases and percentages. We used the χ2 test to analyse the primary endpoint, incidence of hypoxia. We calculated the difference between groups with 95% confidence intervals calculated using the Newcombe method. We also calculated relative risks and exact 95% confidence intervals. We did the same statistical analyses for all binary secondary outcomes. We analysed safety endpoints by using the χ2 test or Fisher’s exact test. The post hoc subgroups of interest included body mass index (<30 and ≥30), surgery type (gastroscopy or colonoscopy or gastroenteroscopy), initial dose of propofol (<1.5 and ≥1.5 mg/kg), and STOP-Bang score (low and high). We further explored the influence of body mass index and the initial dose of propofol on the effects of treatment by using splines through the R package interactionRCS (restricted cubic spline).

Patient and public involvement

Patients and members of the public were not directly involved in setting the research question, developing the study design, or contributing to the recruitment and implementation phases. This was primarily due to the lack of allocated funding for patient and public involvement activities and the fact that our team had not received specific training to effectively engage with the public in this context. However, we discussed the study with patients during its development to gain their perspectives. Additionally, after submission, we asked a member of the public to read our manuscript to ensure that it was clear and comprehensible from a lay perspective.

Results

Patient population

From 6 May 2021 to 26 May 2023 in the aforementioned hospitals, 1000 patients were enrolled and randomised into two groups. Of the enrolled patients, 10 in the control group and five in the HFNC group were excluded because of withdrawal of consent. Another patient in the control group was also excluded owing to cancellation of the procedure after randomisation. Finally, 984 patients were included in the full analysis set. Of these patients, 53 in the control group and 50 in the HFNC group were excluded from the per protocol set because the anaesthesia sedation was not consistent with the trial protocol (fig 1).

Fig 1
Fig 1

Study flow diagram. FAS=full analysis set; PPS=per-protocol set

Table 1 shows the patients’ baseline demographic, clinical, and procedural characteristics. The characteristics of the patients in the two groups, including age, sex, weight, body mass index, and ASA classification, matched well at baseline. Airway related variables, including Mallampati scores and snore mentioned by family, were also comparable between the groups (table 1). The total propofol doses were 184.0 (standard deviation 76.8) mg and 174.0 (67.1) mg for actual body weight in the HFNC group and control group, respectively (P=0.03).

Table 1

Baseline and procedural characteristics. Values are numbers (percentages) unless stated otherwise

View this table:

Efficacy outcomes

HFNC oxygenation significantly reduced the incidence of hypoxia. The incidences of hypoxia were 2.0% (10/497) and 21.2% (103/487) in the HFNC and control groups, respectively (risk ratio 0.10, 95% confidence interval (CI) 0.04 to 0.18; P<0.001) (table 2). In the per protocol set analysis, the incidences were 1.3% (6/447) and 18.4% (80/434), respectively (risk ratio 0.07, 95% CI 0.02 to 0.16; P<0.001) (table 2).

Table 2

Efficacy outcomes. Values are numbers (percentages) unless stated otherwise

View this table:

HFNC oxygenation reduced the incidence of subclinical respiratory depression. The incidences of subclinical respiratory depression were 5.6% (28/497) and 36.3% (177/487) in the HFNC and control groups, respectively (risk ratio 0.16, 95% CI 0.10 to 0.22; P<0.001) (table 2). In the per protocol set analysis, the incidences were 4.9% (22/447) and 37.8% (164/434), respectively (risk ratio 0.13, 95% CI 0.08 to 0.20; P<0.001) (table 2).

HFNC oxygenation reduced the incidence of severe hypoxia. The incidences of severe hypoxia were 0.0% (0/497) and 4.1% (20/487) in the HFNC and control groups, respectively (risk ratio 0.00, 95% CI 0.00 to 0.19; P<0.001) (table 2). In the per protocol set analysis, the incidences were 0.0% (0/447) and 3.9% (17/434), respectively (risk ratio 0.00, 95% CI 0.00 to 0.22; P<0.001) (table 2).

The above data show that HFNC oxygenation can completely eliminate the occurrence of severe hypoxia in patients with obesity but not the occurrence of hypoxia and subclinical respiratory depression. Table 3 shows the last method used to correcting hypoxia. Hypoxia was easier to correct in the HFNC group than in the control group. The number of patients in the HFNC group needing a jaw thrust manoeuvre to improve ventilation was only 11, which was significantly lower than that in the control group (103; P<0.001). Furthermore, in the control group, 24 patients needed mask ventilation to correct severe hypoxia. No patient was intubated in either group.

Table 3

Last method used to correct hypoxia. Values are numbers (percentages) unless stated otherwise

View this table:

Safety outcomes

Using the adverse event reporting tool proposed by the World Society of Intravenous Anaesthesia International Sedation Task Force,20 we recorded all adverse events. We observed no significant difference in the incidence of other sedation related adverse events between the two groups (table 4). The HFNC oxygenation related adverse events were mild and infrequent. The most common adverse event after awakening was xeromycteria, with an incidence rate of 2.8% (14/497). No other adverse events were observed in this study (table 5).

Table 4

Other sedation related adverse events (full analysis set). Values are numbers (percentages) unless stated otherwise

View this table:
Table 5

HFNC oxygenation related adverse events after awakening (full analysis set)

View this table:

Subgroup analysis

Figure 2 shows the results of the subgroup analysis. The results showed no significant subgroup interaction effects, indicating that the benefits of HFNC were consistent in different clinical settings. The restricted cubic spline analysis showed no significant interaction between treatment groups and body mass index or the initial propofol dose; the P values for interaction were 0.33 and 0.57, respectively.

Fig 2
Fig 2

Subgroup analysis of primary outcome. CI=confidence interval; HFNC=high flow nasal cannula

Discussion

This study shows that HFNC oxygenation can significantly reduce the incidences of hypoxia, subclinical respiratory depression, and severe hypoxia in patients with obesity undergoing elective gastrointestinal endoscopy. The incidences of adverse events were similar between patients receiving HFNC and those receiving regular nasal cannula oxygenation.

Comparison with other studies

We surmise that HFNC oxygenation reduces hypoxia during sedated gastrointestinal endoscopy through three mechanisms. Firstly, HFNC oxygenation provides variable oxygen concentrations from 21% to 100%.23 In this study, the oxygen concentration for HFNC oxygenation was set to the maximum value of 100% from beginning to end. In the control group, the patients had highest oxygen uptake concentrations of only up to 45%, respectively.24 The higher the intraoperative oxygen concentration, the more beneficial it is for maintaining oxygenation in patients with obesity and reducing the incidence of hypoxia. Secondly, HFNC oxygenation provides patients with an ultra-high oxygen flow rate (up to 60 L/min), clearing the anatomical dead space of the upper respiratory tract and establishing a fresh gas storage room in the upper airway for each breath.25 An ultra-high fresh gas flow rate can significantly reduce repeated inhalation of carbon dioxide. Thirdly, HFNC oxygenation provides a continuously variable low level positive end expiratory pressure, which increases the end of breath lung volume, reduces the work done by the ventilator, and lowers the respiratory rate, resulting in deeper and slower breathing.2627 HFNC oxygenation can still produce low positive end expiratory pressure levels even if the mouth is kept open.28 HFNC oxygenation can also generate positive pharyngeal pressure during expiration with a constant flow, with the pressure mainly determined by the patient’s flow volume and expiratory flow.29

Ricco and colleagues reported that HFNC oxygenation did not effectively reduce the incidence of hypoxia in patients with morbid obesity during colonoscopy under sedation with propofol.18 In that study, the oxygen flow rate of HFNC oxygenation was set to 60 L/min, with an oxygen concentration of 36-40%. Furthermore, only 28 of 59 patients were included in the HFNC group. A small sample size reduces the credibility of the research conclusion. The HFNC oxygen concentration was set to 100% in our study. These factors can lead to contrasting conclusions between previous research and our study.

We observed an extremely large effect size in the HFNC group. Several factors contributed to the beneficial effects. In addition to providing high concentration and high flow oxygen and generating positive end expiratory pressure as mentioned above,2627 HFNC extends the safe apnoea time to 20 minutes in ASA class I-II patients with normal body mass index.3031 Although these safe apnoea time extension effects would abate in patients with obesity, in this trial, with an average procedure duration of less than 11 minutes, even if patients experienced apnoea, HFNC would help them to maintain oxygenation. Therefore, the incidence of hypoxia in the HFNC group was only 2.0%.

The airway manoeuvres served as objective indicators. The results indicated that the occurrences of jaw thrust and mask ventilation were significantly lower in the HFNC group than in the control group. This further supports the positive effects of HFNC, reducing the need for a jaw thrust manoeuvre. This technique may also prevent the need for advanced airway intervention in patients with obesity.18 Mask ventilation can correct hypoxia in the control group, as it not only opens the airway but also increases ventilation. This suggests that a correlation exists between hypoxia, respiratory obstruction, and inadequate ventilation in patients with obesity in the control group. The jaw thrust manoeuvre could correct hypoxia without the need for mask ventilation in patients with obesity in the HFNC group. This indicates that the main cause of hypoxia in patients with obesity undergoing HFNC oxygenation is respiratory obstruction. Chen and colleagues highlighted the importance of ensuring airway openness during HFNC oxygenation.30

We observed no difference in the incidence of other sedation related adverse events between the two groups, indicating that HFNC reduces the incidence of hypoxia without increasing the risk of other sedation related adverse events. The incidence of hypotension in the HFNC group was slightly higher than that in the control group (21/497 (4.2%) patients in the HFNC group; 13/487 (2.6%) patients in the control group; P=0.181). HFNC itself cannot directly cause hypotension. Moreover, we observed that the body mass index of the HFNC group was higher than that of the control group (30.1 (2.2) v 29.9 (1.9)), and that the total dose of propofol administered was higher in the HFNC group (184.0 (76.8) v 174.0 (67.1) mg), which might have contributed to the higher incidence of hypotension in the HFNC group. Higher body mass index and higher propofol doses are generally correlated with a higher incidence of hypoxia. However, in this trial, despite the higher propofol dose and body mass index in the HFNC group, incidence of hypoxia was significantly lower in the HFNC group, showing the beneficial oxygenation effects of HFNC. Furthermore, the subgroup analysis results indicated that the initial dose of propofol (<1.5 and ≥1.5 mg/kg) did not affect the efficacy of HFNC on the reduction of hypoxia incidence. This suggests that regardless of whether the propofol dosage was higher or lower than 1.5 mg/kg, HFNC effectively reduced the incidence of hypoxia.

Systematic review and meta-analysis showed that the rates of major complications were similar in individual randomised controlled trials between patients receiving HFNC and those receiving usual care.32 Complications with HFNC are possible, but they are usually self-limited. In this study, the main HFNC oxygenation related complication was xeromycteria, which had a very low incidence; however, it usually disappears within half an hour. The results indicated that none of the patients had barotrauma after HFNC. Barotrauma often occurs after jet ventilation. Conversely, it is extremely rare after HFNC application, as HFNC is considered to be a gentle form of continuous positive airway pressure.

The duration of the three types of endoscopic procedures varied. The results of the subgroup analysis showed no interaction effects between surgery type and treatment group, indicating that the surgery type had no effect on the conclusion. HFNC can reduce the incidence of hypoxia in all three types of endoscopic procedures.

Meaning of findings

Previous studies have reported that patients with obesity have an increased risk of hypoxia during sedated gastrointestinal endoscopy.1522 Wani and colleagues showed that obesity is a factor in the occurrence of sedation related complications, including hypoxia, during sedated gastrointestinal endoscopy.15 A retrospective, observational cohort study that involved 1.38 million gastrointestinal endoscopic procedures reported a total severe adverse event rate of nearly 0.3%. The number of cases requiring cardiopulmonary resuscitation was approximately four per 100 000 procedures.33 Fortunately, no airway disasters occurred in our trial. However, the prevalence of obesity among patients had increased. From the Health Survey for England 2018, most men and women (67% and 60%, respectively) and more than a quarter of children aged 2-15 years (28%) live with obesity or excess body weight. The incidence of severe hypoxia increased by nearly sixfold in patients with obesity and 8.5-fold in patients with obesity categorised as class III compared with those with normal body mass index.22 Although no airway disasters occurred in our trial, that every patient experiencing severe hypoxia can be promptly rescued cannot be guaranteed. Patients at the highest risk for hypoxia should be carefully stratified and provided with adequate resources for a safe treatment. Standard oxygen therapy is recommended to prevent and treat hypoxia during gastrointestinal endoscopy.6 With the increase in obesity rates, a device that can reduce airway adverse events is clinically relevant. We consider that HFNC oxygenation is more beneficial for patients with obesity than regular nasal cannula oxygenation.

Limitations of study and future research

This study has several limitations. Firstly, HFNC is fundamentally different from a regular nasal cannula, making blinding of the anaesthesiologists extremely challenging. Thus, the anaesthesiologists were not blinded in this trial. However, SpO2 served as an objective observational indicator, which helped to minimise bias. Secondly, HFNC oxygenation provides ultra-high flow of fresh gas, which clears the anatomical dead space of the upper respiratory tract and reduces repeated inhalation of carbon dioxide. This makes monitoring of the patient’s end of breath carbon dioxide impossible. Thirdly, this study included only patients with obesity with ASA class ≤II and aged <70 years. Patients with obesity aged over 70 and with a history of heart disease, chronic obstructive pulmonary disease, and ASA classification ≥III were excluded. Although these patients generally have poor condition, they still need sedated gastrointestinal endoscopy. This requires further clinical research to determine whether HFNC oxygenation has advantages for such patients. Lastly, the patients included in this study were all Chinese. Thus, further research is warranted to determine whether this study is applicable to Europeans or Americans.

Conclusions

In patients with obesity, oxygenation via HFNC during sedated gastrointestinal endoscopy significantly reduced the incidences of hypoxia, subclinical respiratory depression, and severe hypoxia without increasing adverse events.

What is already known on this topic

  • Oxygenation via high flow nasal cannula (HFNC) significantly reduces the incidence of hypoxia during sedated gastrointestinal endoscopy in patients with normal weight

  • Findings on the use of HFNC oxygenation in patients with obesity are conflicting

What this study adds

  • Oxygenation via HFNC significantly reduced the incidence of hypoxia during sedated gastrointestinal endoscopy in patients with obesity without increasing adverse events

Ethics statements

Ethical approval

This study was approved by the ethics committee of Renji Hospital, Shanghai Jiao Tong University School of Medicine (KY2020-019).

Data availability statement

The data will be available to other researchers on request, with information shared after approval by the corresponding author (D-SS).

Acknowledgments

This trial was made possible by the collaborative efforts of doctors, nurses, and administrators at the recruiting hospitals. We are grateful for the cooperation and participation of the anaesthesiologists, nurse anaesthetists, gastroenterologists, endoscopy nurses, and patients with obesity in Renji Hospital, Tongji Hospital, and East Hospital. We thank Wei Zhang (Biomedical Informatics and Statistics Center, School of Public Health, Fudan University) and Xinyue Guo (Department of Biostatistics, School of Public Health, Fudan University) for providing assistance with the statistical analysis. We thank Dong-xin Wang (Departments of Anesthesiology, Peking University First Hospital) for helping to revise the manuscript.

Footnotes

  • Contributors: L-LW, Y-YZ, and DH contributed equally to this work. Y-YZ and D-SS conceived the study. L-LW, Y-YZ, and D-SS designed the study. L-LW, Y-YZ, DH, M-YW, JZ, X-YC, Y-ZZ, M-YS, and Z-JS conducted the study. X-RW, X-QZ, and D-SS coordinated and supervised the study. L-LW and Y-YZ did the analyses. L-LW and D-SS interpreted the results. L-LW and Y-YZ wrote the first draft of the manuscript. D-SS critically revised the manuscript. All authors approved the final version. L-LW and Y-YZ had full access to all the data and take responsibility for data integrity and accuracy of the data analysis. D-SS is the guarantor. The corresponding author attests that all listed authors meet authorship criteria, and that no others meeting the criteria have been omitted.

  • Funding: This study was supported by grants from the National Natural Science Foundation of China (grant numbers 82371193, 81771133, 81970995, U21A20357); Shanghai Municipal Science and Technology Commission Founding (grant number 21S31900100); Renji Hospital Clinical Innovation Foundation (grant numbers PYII20-09, RJTJ-JX-002, RJPY-DZX-007); Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Support (grant number 20191903); Shanghai Shenkang Founding (grant number SHDC22020208); Shanghai Municipal Health Commission Key Support Project (grant number 2023ZDFC0201); Key Specialty Construction Project of Pudong Health and Family Planning Commission of Shanghai (grant number PWZXQ2017-06); Shanghai Municipal Key Clinical Specialty (grant number shsiczdzk03601); and Shanghai Engineering Research Center of Peri-operative Organ Support and Function Preservation (grant number 20DZ2254200). The sponsors had no role in the design and conduct of the study; the collection, management, analysis and interpretation of the data; the preparation, review, and approval of the manuscript; and the decision to submit the manuscript for publication

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at https://www.icmje.org/disclosure-of-interest/ and declare: support from the National Natural Science Foundation of China, Shanghai Municipal Science and Technology Commission Founding, Renji Hospital Clinical Innovation Foundation, Shanghai municipal Education Commission-Gaofeng Clinical Medicine Support, Shanghai Shenkang Founding, Shanghai Municipal Health Commission Key Support Project, Key Specialty Construction Project of Pudong Health and Family Planning Commission of Shanghai, Shanghai Municipal Key Clinical Specialty, and Shanghai Engineering Research Center of Peri-operative Organ Support and Function Preservation; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.

  • Transparency: The lead author (the manuscript’s guarantor) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported, that no important aspects of the study have been omitted, and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

  • Dissemination to participants and related patient and public communities: We will share the findings broadly through social media platforms to reach both academic and non-academic audiences. The results will be presented at national and international conferences to inform the wider medical community. We believe that the publication of this research will contribute valuable evidence that may support the development of clinical guidelines and inform relevant policy decisions. We will organise sessions to share and explain the findings to relevant patient groups, ensuring that they can benefit from the insights of this research.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

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