Bilevel positive airway pressure reduces anaesthesiologist workload and turnover time in electroconvulsive therapy: a randomized controlled trial

Abstract

Background

The increasing clinical demand for electroconvulsive therapy (ECT) highlights specific challenges in anaesthetic management, particularly the reliance on continuous mask ventilation. Bilevel positive airway pressure (BPAP) provides automated, hands-free ventilatory support and may enhance efficiency. This study aims to compare the impact of BPAP versus face mask ventilation on procedural turnover time during ECT.

Methods

In this single-blind, randomized controlled trial, 110 patients were enrolled with a history of at least two prior ECT sessions. Participants were randomly allocated to receive either BPAP or face mask ventilation. The primary outcome was the turnover time, defined as the duration from anaesthesia induction to entry into the post-anaesthesia care unit (PACU). Secondary outcomes included the total ECT duration, breathing and consciousness recovery times, incidence of hypoxemia (SpO2 < 94% for > 5 s), adverse events and operator-centered measures, including upper limb discomfort, anxiety and satisfaction scores.

Results

The BPAP group demonstrated a significantly shorter median turnover time ccompared to the face mask group (332 [286–415] s vs. 426 [348–472] s; median difference 84 s, 95% CI 44–119, P < 0.001). No significant differences in the total ECT duration, breathing recovery time, consciousness recovery time, or incidence of hypoxemia. The incidence of anaesthesiologist-reported upper limb discomfort was lower in the BPAP group (P < 0.001), and operator satisfaction scores were higher (P < 0.001).

Conclusions

In patients with prior ECT experience, BPAP safely reduced procedural turnover time and significantly decreased the physical burden on anaesthesiologists compared to face mask ventilation. BPAP represents a viable strategy to improve workflow efficiency and operator comfort in high-volume ECT settings.

Trial registration

ChiCTR2100051837, the Chinese Clinical Trial, 20-211-006.

Research registration number: ChiCTR2100051837, the Chinese Clinical Trial Registry.

IRB number: [2021] 02-203-01, the Research Ethics Committee of the Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12871-026-04067-5.

Background

Electroconvulsive therapy (ECT) is a well-established therapeutic modality for severe psychiatric conditions [1]. Its application has increased consistently across Asia during the last twenty years, with particularly significant growth observed in China [2–4]. This rising clinical demand adds to the substantial workload pressures already faced by anaesthesiologists [5–8]. A core task during ECT involves providing face mask ventilation, which frequently requires the anaesthesiologist to pause ventilatory support to allow the psychiatrist to work, a process that can jeopardize consistent airway patency and gas exchange [9]. Therefore, identifying an alternative airway management technique that is both efficacious and safe is crucial, as it would permit anaesthesiologists to dedicate greater attention to comprehensive patient monitoring.

Bilevel positive airway pressure (BPAP) is a promising approach to address this need. This non-invasive ventilatory modality, which has demonstrated utility in various perioperative contexts, delivers automated and sustained ventilation during periods of sedation and transient apnoea [10–16]. A principal advantage is its hands-free operation, which eliminates the need for sustained manual effort, thereby freeing the anaesthesiologist’s hands. This may decrease the time dedicated to active airway intervention, reduce operator fatigue, and limit procedural disruptions. Furthermore, the portability of BPAP devices facilitates continuous mechanical ventilation during patient transport to the post-anaesthesia care unit (PACU), unlike stationary conventional anaesthesia machines. Collectively, these features indicate that BPAP could enhance procedural workflow in ECT by providing more reliable ventilatory support.

Although BPAP has been adopted for other short procedural sedation [10–17], its specific applicability and advantages in the setting of ECT have not been thoroughly evaluated. To address this knowledge deficit, we conducted a randomised controlled trial. Our primary objective was to compare procedural efficiency—measured as turnover time—between BPAP and conventional face mask ventilation during ECT. We hypothesised that the automated, hands-free support delivered by BPAP would significantly lessen the time required for operator-managed airway control and the associated physical strain on the anaesthesiologist. This, in turn, was expected to reduce turnover time and enhance workflow efficiency while maintaining patient safety.

Methods

Ethics

This study is a randomized, controlled, single-blind trial, and its report adheres to the Consolidated Standards of Reporting Trials (CONSORT) guidelines. The trial was carried out at the Third Affiliated Hospital of Sun Yat‑sen University between October 2021 and May 2022. The study adheres to the ethical principles of the Declaration of Helsinki and received ethical approval from the Research Ethics Committee of the Third Affiliated Hospital of Sun Yat-sen University (Approval No. [2021]02‑203‑01). Written informed consent to participate was obtained from all patients (or their legally authorised representatives) before enrolment.

Inclusion and exclusion criteria

Eligible participants were adults (≥ 18 years) with an American Society of Anaesthesiologists (ASA) physical status I or II who had undergone at least two prior ECT sessions. Exclusion criteria comprised facial anatomical abnormalities, active respiratory tract infection within the preceding two weeks, elevated risk of upper airway obstruction or aspiration, and inability to cooperate due to extreme anxiety. We selectively recruited patients who had already undergone at least two ECT sessions to ensure the safety and homogeneity of the study population, given the novelty of the ventilation technique in this setting. The first two treatments were not part of this study.

Randomisation and blinding

Using a computer-generated random sequence, participants were allocated in a 1:1 ratio to either the bilevel positive airway pressure (BPAP) group or the face mask ventilation (FM) group. Allocation concealment was maintained with sequentially numbered, sealed, opaque envelopes. Before induction, a study nurse opened the envelope and disclosed the assignment to the attending anesthesiology. Due to the nature of the intervention, the anaesthesiologists performing the ventilation could not be blinded to the group assignment. However, to minimize observer bias, the researchers responsible for data collection were not involved in the intraoperative management. To maintain blinding and facilitate rapid application of the nasal mask in the BPAP group, the horizontal strap of the headgear was placed loosely under the occiput of all patients (including those in the FM group) before induction (Fig. 1). All study interventions were administered post-induction, ensuring patients were blinded to group assignments.

Fig. 1.

Placement of nasal mask and headgear strap relative to bitemporal ECT electrodes. a The headgear strap was placed loosely under the occiput in all patients before induction to enable blinding. b The strap is positioned below, leaving the temporal areas free for ECT electrode placement. The nasal mask is secured over the nose without interfering with the electrodes

Study protocol

In our institution, ECT sessions were conducted three times per week, with approximately 30 patients treated per session. Prior to each procedure, the patient’s psychotropic medication regimen was carefully reviewed in consultation between psychiatrists and anaesthesiologists. For each ECT treatment, the anaesthesia team consisted of one attending anaesthesiologist (with ≥ 8 years of clinical anaesthesia experience and ≥ 3 years of ECT anaesthesia experience) and one resident anaesthesiologist (≥ 3 years of anaethesia experience) in the treatment room, plus one attending anaesthesiologist in the PACU. Standard monitoring, including electrocardiography, non-invasive blood pressure, and pulse oximetry (SpO2), was established before anaesthesia induction. To reduce airway secretions, atropine was administered intravenously at a dose of 0.007 mg/kg.

All patients received 1.5 mg/kg propofol followed by 0.7 mg/kg succinylcholine while in the supine position. In the FM group, two-hand mask ventilation was initiated post-induction with pure oxygen at 5 L/min. Ventilation was provided in pressure-control mode with a peak airway pressure of 15 cmH₂O and a respiratory rate of 12 breaths/min. Anaesthetic depth was confirmed by loss of consciousness (unresponsiveness to verbal commands and loss of eyelash reflex) after propofol administration. After confirming the absence of the eyelash reflex in the patient, the psychiatrist places the bitemporal electrodes and an oral bite block.

ECT stimulus parameters included a pulse width of 0.5 ms, with the stimulus dose based on the quality of previous seizures and treatment response. Seizure activity was monitored by visual observation of the patient’s physical activity and EEG. Following the seizure, oropharyngeal suction was performed, and mask ventilation was resumed until spontaneous breathing was well re-established, defined as a tidal volume ≥ 6 ml/kg. Patients were then transferred to the PACU, where supplemental oxygen was delivered via nasal cannula at 2 L/min.

In the BPAP group (Fig. 1), after loss of consciousness, a nasal mask (BMC-NM4, BMC Medical Co., Ltd., Beijing, China) was applied and connected to a BPAP ventilator (AtmoIvory 8CPE50 Bilevel ST30, HOFFRICHTER GmbH, Schwerin, Germany). The ventilator was set to deliver bilevel pressure support in spontaneous/timed (S/T) mode, with an inspiratory positive airway pressure (IPAP) of 13 cmH₂O, an expiratory positive airway pressure (EPAP) of 6 cmH₂O, and a backup respiratory rate of 15 breaths/min. Ventilation was monitored in real-time via the device display (pressure, tidal volume) and by observation of adequate chest wall excursion. The IPAP could be titrated based on thoracic movement, delivered tidal volume, and SpO2, but was not permitted to exceed 20 cmH₂O to minimize the risk of gastric insufflation and aspiration [18, 19]. Following seizure termination and oropharyngeal suction, patients were transferred to the PACU with BPAP support continuing uninterrupted. In the PACU, BPAP was maintained until the return of sufficient spontaneous respiration, at which point supplemental oxygen was provided via nasal cannula at 2 L/min. Hypoxemia was defined as an SpO2 < 94% lasting > 5 s. A sustained decline in SpO2 exceeding 1 min triggered immediate jaw-thrust manoeuvre and rescue mask ventilation; laryngeal mask insertion or tracheal intubation were reserved for emergency airway rescue. A schematic timeline comparing the procedural phases between the two ventilation groups is presented in Fig. 2.

Fig. 2.

Schematic timeline comparing procedural phases between ventilation groups during electroconvulsive therapy. The horizontal bar indicates common procedural stages. The blue shaded area represents the period of Bilevel Positive Airway Pressure (BPAP) ventilation. The green shaded area represents the period of required Face Mask (FM) ventilation. A key distinction is that in the FM group, ventilation necessarily extended beyond the patient’s entry into the Post-anaesthesia Care Unit (PACU) until the return of adequate spontaneous breathing, as indicated by the triangle symbol within the orange area. In contrast, BPAP provided continuous ventilatory support through this transition. The primary outcome, turnover time, was defined as the interval from anaesthesia induction (Induction Start) to PACU entry (PACU Entry). The schematic visually explains the source of time savings (Δ) with BPAP, which reduced the duration of hands-on airway management

Upon arrival in the procedure room, baseline vital signs—including SpO2, heart rate (HR), and mean arterial pressure (MAP)—were recorded. SpO2 was subsequently measured at four predefined time points [20]: at baseline (T0), one minute after seizure termination (T1), three minutes after the resumption of spontaneous respiration (T2), and upon full awakening (T3). Several time‑related outcomes were prospectively defined and documented: total ECT duration (from entry into the treatment room to discharge from the PACU), breathing recovery time (from administration of neuromuscular blocking agent to onset of spontaneous respiration), and consciousness recovery time (from loss of consciousness until the patient could follow simple commands). Following each procedure, the anaesthesiologist performing ventilation was asked about any upper‑limb discomfort and asked to rate their satisfaction and anxiety levels using a 100‑mm visual analogue scale (VAS). The treating psychiatrist recorded ECT treatment parameters, including seizure duration, stimulus intensity, and delivered current. All adverse events—such as requirement for rescue mask ventilation, laryngeal mask insertion, tracheal intubation, or aspiration—were systematically documented.

The primary outcome was turnover time, prospectively defined as the interval from the start of anaesthesia induction (administration of propofol) to entry into PACU. This measure was selected to reflect the period during which the patient occupied the procedure room and required continuous airway management during ECT by the anaesthesiologist, distinguishing it from the inter-case turnover time typically used in operating room efficiency metrics.

Secondary outcomes encompassed: (1) total ECT duration (from treatment-room entry to PACU discharge), (2) breathing recovery time (from neuromuscular blocker administration to onset of spontaneous respiration), (3) consciousness recovery time (from loss of consciousness until following simple commands), (4) incidence of intraoperative hypoxemia (SpO2 < 94% for > 5 s but < 60 s), (5) average SpO2 at four time points (T0–T3), (6) incidence of operator-reported upper-limb discomfort, (7) anaesthesiologist satisfaction and anxiety scores (assessed by VAS), and (8) adverse events (including rescue ventilation, advanced airway intervention, aspiration, etc.).

Sample size calculation

Considering the findings from a preliminary study, it was observed that the turnover time for the BPAP group amounted to 346 ± 66 s. In contrast, the FM group recorded the turnover time of 401 ± 98 s. Type 1 error was set to 5%, and type 2 error was set to 10%. A minimum of 100 samples were determined through PASS15 software. Given the impact of the drop a sample size of 110 patients was needed.

Statistical analysis

Statistical analysis was performed with the SPSS software (version 26). The primary analytical strategy followed a modified intention-to-treat principle. Continuous variables were assessed for normal distribution via the Kolmogorov–Smirnov test. Normally distributed data are presented as mean ± SD, while non-normally distributed data are summarized as median [IQR, range]. Between-group comparisons for continuous outcomes employed the student’s t-test or the Mann-Whitney U test. Categorical data are expressed as patient counts and percentages and were compared using the Chi-square test or Fisher’s exact test. For primary outcome, the pseudo median difference and its 95% confidence interval were calculated with the use of the Hodges-Lehmann estimate based on the Mann-Whitney U test [21]. The P values was two-sided and less than 0.05 were considered to indicate statistical significance.

Results

A total of 110 patients were randomized in this trial. Following the exclusion of 3 individuals from the final analysis, 54 patients comprised the FM group and 53 were allocated to the BPAP group. Participant flow is detailed in Fig. 3. Demographic and baseline clinical characteristics are summarized in Table 1, with no significant differences observed between the two groups.

Fig. 3.

CONSORT diagram

Table 1.

Demographic and baseline characteristics for the patients undergoing electroconvulsive therapy

	Face mask n = 54	Bilevel-positive airway pressure n = 53
Age; yr	27.8 ± 8.4	29.6 ± 11.5
Sex
Female	24(44.4%)	31(58.5%)
Male	30(55.6%)	22(41.5%)
BMI; kg/m2	22.3(2.7)	22(2.9)
ASA
I	41(75.9%)	44(83%)
II	13(24.1%)	9(17%)
History of smoking	6(11.1%)	3(5.7%)
History of hypertension	1(1.9%)	3(5.7%)
Baseline SpO2	99[98 to 100,96 to 100]	99[99 to 100, 97 to 100]
Baseline MAP; mmHg	89 ± 10.4	86.7 ± 9.7
Dosage of propofol; mg	100[90 to 120, 60 to 150]	100[80 to 107.5, 7 0 to 150]
Dosage of succinylcholine; mg	50[42 to 50, 25 to 100]	45[40 to 50, 30 to 100]

Values are mean ± SD or median [IQR, range] or number (proportion)

Primary and secondary outcome measures are presented in Table 2. Turnover time was significantly reduced in the BPAP group (332 s [IQR 286 to 415]) compared to the FM group (426 s [IQR 348 to 472]), yielding a mean difference of 84 s (95% CI 44 to 119; P < 0.001). The total duration of the ECT session, along with times to breathing recovery and consciousness recovery, did not differ significantly between cohorts. The groups were also comparable in terms of average peri-procedural SpO2. While two patients in the FM group and four in the BPAP group experienced transient SpO2 readings below 94% (minimum 89% in both groups), the overall incidence of periprocedural hypoxemia did not differ statistically (Table 3). A marked reduction in the incidence of operator-reported upper-limb discomfort was noted in the BPAP group (P < 0.001), and anaesthesiologist satisfaction scores were significantly higher in this group (P < 0.001). In contrast, no between-group difference was found in anaesthesiologist anxiety scores.

Table 2.

Primary outcome and secondary outcomes

	Face mask n = 54	Bilevel-positive airway pressure n = 53	P value
ECT turnover time; s	426[348 to 472, 257 to 740]	332[286 to 415, 162 to 591]	<0.001
Total ECT duration; s	1104[924 to 1354, 580 to 2095]	1114[969 to 1274, 441 to 2434]	0.985
Breathing recovery time; s	261[238 to 311, 203 to 604]	271[235 to 303, 168 to 373]	0.876
Consciousness Recovery time; s	580[494 to 684, 310 to 1318]	633[544 to741, 237 to 1266]	0.078
Average SpO2	99[98 to 99, 96 to 100]	99[98 to 99, 95 to 100]	0.475
T0	99[98 to 100, 96 to 100]	99[99 to 100, 97 to 100]
T1	100[99 to 100, 97 to 100]	99[99 to 100, 95 to 100]
T2	99[97 to 99, 92 to 100]	98[98 to 99, 93 to 100]
T3	98[97 to 99, 95 to 100]	99[98 to 100, 95 to 100]
Incidence of Hypoxemia	2(3.7%)	4(7.5%)	0.657
Incidence of upper Limb discomfort among anaesthetists	19(35.2%)	0(0%)	<0.001
Satisfaction scores of anaesthetists	7[7 to 8, 5 to 10]	9[8 to 10, 5 to 10]	<0.001
Anxiety scores of anaesthetists	2[1 to 3, 0 to 6]	2[1 to 3, 0 to 7]	0.480

T0 The baseline, T1 One minute following seizure cessation, T2 Three minutes after the resumption of spontaneous respiration, T3 Upon full awakening. Values are mean ± SD or median [IQR, range] or number (proportion)

Table 3.

Information for the hypoxemia patients undergoing electroconvulsive therapy

Group	Age	Sex	BMI	ASA	Time	Baseline SpO2	Minimum SpO2	Treatment
FM	30–35	F	20–25	2	ECT	97	92	Mask ventilation
FM	25–30	M	25–30	2	ECT	98	89	Mask ventilation
BPAP	30–35	F	20–25	2	ECT	100	89	Adjusting ventilator
BPAP	20–25	F	15–20	2	ECT	99	89	Adjusting ventilator
BPAP	20–25	M	20–25	2	ECT	100	93	Adjusting ventilator
BPAP	20–25	M	20–25	2	ECT	99	92	Adjusting ventilator

FM Face mask group, BPAP Bilevel-positive airway pressure group, F Female, M Male, ECT Electroconvulsive therapy

Adverse events are summarized in Table 4. The safety profile was similar between the FM and BPAP groups, with no patient requiring additional pharmacological rescue or advanced airway intervention.

Table 4.

Adverse events for the patients undergoing electroconvulsive therapy in the face mask group and the bilevel-positive airway pressure group

	Face mask n = 54	Bilevel-positive airway pressure n = 53	P value
Intraoperative tachycardia	19(35.2%)	10(18.9%)	0.058
Intraoperative bradycardia	2(3.7%)	2(3.8%)	1.000
Intraoperative hypotension	21(38.9%)	13(24.5%)	0.111
Additional mask ventilation	0	0
Laryngeal mask	0	0
Tracheal intubation	0	0
Pneumonia	0	0

Intraoperative tachycardia: HR>100 bpm min^− 1 at T1; Intraoperative bradycardia: HR<100 bpm/min at T1; Intraoperative hypotension: MAP increased more than 20% baseline MAP at T1; T1: 1 min following seizure cessation. Values are number (proportion)

Discussion

In this trial, BPAP shortened the hands-on ventilation time by approximately one minute compared to face mask ventilation during ECT. While the absolute reduction per procedure is modest, it consistently decreases the period of active airway manipulation. Importantly, this gain in efficiency did not compromise safety, with both groups showing similar hypoxemia rates and recovery times.

The approximately 90-second reduction in turnover time observed with BPAP, albeit seemingly modest in isolation, corresponds to a consistent decrease in the duration of required hands-on airway management. In the context of a high-volume ECT service performing multiple sessions daily, such time saving per procedure can accumulate substantially, potentially increasing treatment capacity or reducing staff overtime. Importantly, this gain in efficiency is achieved by BPAP’s capability to provide continuous mechanical ventilation during transport and early recovery, thereby reducing the dependency on the patient’s spontaneous breathing resumption compared to mask ventilation. We acknowledge that BPAP shifts – rather than eliminates – airway support from the treatment room to the PACU, but the key advantage lies in reducing the hands-on period (the most labour-intensive part) and allowing the anaesthesiologist to focus on other tasks while the device runs automatically. Beyond time savings, a further key advantage lies in the reduction of physical fatigue for the practitioner, which may mitigate work-related strain and improve long-term performance and job satisfaction.

Notably, despite turnover time was significantly shorter in the BPAP group, the overall ECT duration was similar between groups. This suggests that the time saved by BPAP is largely confined to the core procedural interval. In contrast, other relatively fixed components—including pre-procedural preparation (monitor attachment, IV access, and equipment setup, with the BPAP group additionally requiring ventilator circuit preparation), PACU monitoring to meet discharge criteria, and transfer logistics—remained consistent between groups and accounted for a greater proportion of the total time.

A further notable finding was that BPAP significantly alleviated physical strain, particularly upper-limb fatigue, as positively reported by the anaesthesiologists. Prolonged hand-on mask ventilation is known to induce muscle fatigue and shoulder discomfort, an experience that can contribute to operator weariness [22]. Contrary to our initial expectations, however, we observed no significant difference in self-reported anxiety scores between the two groups. This may be attributed to the high level of experience and confidence among the participating anaesthesiologists, for whom proficient airway management and emergency response are core professional competencies, likely reinforcing their perceived control over patient safety during ECT.

To our knowledge, this study provides the first systematic evaluation of BPAP specifically within the ECT setting, and it includes a larger patient cohort than prior feasibility reports. Our study demonstrated the safe use of BPAP in S/T mode to maintain oxygenation during the apnoeic phase of ECT. This extends earlier evidence demonstrating the utility of non-invasive ventilation for managing post-induction apnoea. For instance, Hiroshi Iwama et al. reported the satisfactory ventilation in non-obese patients using BPAP with a pressure support level of 10 cmH₂O, while Mike Fogarty et al. demonstrated its feasibility during induction with setting 12 cmH₂O pressure support in 30 selected surgery patients [11, 12]. Steven Grant et al. reported using BPAP before intubation in eight emergency patients [15]. Our ventilation parameters (IPAP 13 cmH₂O, EPAP 6 cmH₂O) are closely aligned with these precedents. Moreover, the physiological state following ECT induction parallels that of routine general anaesthesia, further supporting the translatability of NIV strategies to this context.

This study has several limitations. First, due to the visible nature of the intervention, only a single-blind design was practical; the unblinded anaesthesiologist performing the procedure may have introduced performance or assessment bias. Additionally, ventilation adequacy was judged clinically by chest wall movement and SpO₂, without direct monitoring of tidal volume, end-tidal carbon dioxide (EtCO₂), or leak percentage. While the BPAP device provided real-time tidal volume readings (with limited accuracy), these data were not systematically recorded, and EtCO₂ monitoring was not available. This limits the precision of our ventilatory efficacy evaluation. Future studies should incorporate quantitative monitoring of tidal volume, EtCO₂, and leak fraction to allow a more robust assessment of ventilatory effectiveness during BPAP application in ECT. Second, the exclusion of first-time ECT patients, while intended to enhance safety, creates a selection bias and restricts the generalizability of our results to this often more physiologically variable population. Third, the cohort included very few patients with obesity (BMI >28 kg/m²), precluding meaningful conclusions about BPAP in this higher-risk group where airway management is more challenging [14]. Fourth, the assessment of upper limb discomfort was subjective and could have been influenced by the time of day or cumulative caseload; the anaesthesiologist could not be blinded to group assignment. Fifth, in high-volume ECT centres, adopting BPAP would require multiple devices and consumables to maintain parallel workflow; in our study, we had two BPAP devices available, which sufficed for the protocol but may not represent real-world scalability. Sixth, the headgear strap was placed in all patients before induction (to maintain blinding and facilitate rapid BPAP application) and took approximately 10–15 s to secure after loss of consciousness – a minor time investment not required in the FM group. Finally, although prospectively defined, the term “turnover time” may be interpreted inconsistently across different clinical contexts; future studies might consider more specific descriptors, such as active airway management time, for enhanced clarity.

Conclusions

This randomized trial demonstrates that BPAP safely shortens turnover time and decreases anaesthesiologist physical discomfort during ECT relative to face mask ventilation. BPAP thus represents a practical strategy to enhance workflow efficiency and mitigate operator strain in busy ECT services. Future research should examine its generalizability to first-time ECT patients and its performance under quantitative ventilation monitoring.

Abbreviations

ECT

Electroconvulsive therapy

BPAP

Bilevel positive airway pressure

PACU

Post-anaesthesia care unit

ASA

American Society of Anaesthesiologists physical status

FM

Face mask

IPAP

Inspiratory positive airway pressure

EPAP

Expiratory positive airway pressure

SpO₂

Pulse oximetry

HR

Heart rate

MAP

Mean arterial pressure

VAS

Visual analogue scale

BMI

Body mass index

EtCO₂

End tidal carbon dioxide

Authors’ contributions

YYL: Methodology; Writing - Original Draft. XYL: Formal analysis; Writing - Review & Editing. JRY: Investigation. TJR: Investigation. JYX: Visualization. NS: Methodology; Writing - Review & Editing; Project administration. PJH: Conceptualization; Methodology; Writing - Review & Editing; Supervision.

Funding

This study was supported by the following funding sources:

The Key Medical Disciplines and Specialities Program of Huadu District People’s Hospital of Guangzhou(Grant No. YNZDXK202501).

Huadu District Basic and Applied Basic Research Joint Funding Project (District-Hospital Collaboration), Guangzhou (Grant No. 23HDQYLH05).

Data availability

The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Research Ethics Committee of the Third Affiliated Hospital of Sun Yat‑sen University (Approval No. [2021]02‑203‑01). Written informed consent to participate was obtained from all patients (or their legally authorised representatives) before enrolment.

Consent for publication

Written informed consent for publication of the photographs presented in Fig. 1 was obtained from the patients’ legally authorised representatives. The corresponding author retains copies of the signed consent forms and will make them available to the journal upon request.

Competing interests

The authors declare no competing interests.