High-flow oxygen delivery system and oxygen reserve index-guided apnoeic oxygenation versus low-tidal-volume ventilation during robotic flexible ureteroscopy: A retrospective cohort study

Abstract

Background and Aims:

Robotic flexible ureteroscopy often requires intermittent apnoeic periods to minimise kidney movement and improve surgical conditions. This study evaluated the effectiveness of high-flow oxygenation (HFO) in maintaining oxygenation and preventing desaturation during retrograde flexible ureteroscopy (RFU).

Methods:

This retrospective cohort study included 62 male patients undergoing robotic RFU: 28 received HFO and 34 served as controls. The HFO group underwent repeated 5-minute apnoeic periods with 100% oxygen delivered at up to 80 L/min. Vital parameters were recorded before and after each apnoeic period. In the control group, the tidal volume was reduced to 250 mL with a respiratory rate of 20 cycles per minute during the robotic phase, and these settings were maintained throughout. Wilcoxon rank-sum test, T-tests, and Fisher’s exact test were used to compare the groups. Durbin–Conover test was used for pairwise comparisons.

Results:

Compared to the HFO group, overall, the control group had slightly higher median end-tidal carbon dioxide (EtCO2) levels (43.3 vs 41.6, P = 0.021), heart rate (71.6 vs 65.1, P = 0.001), mean arterial pressure (83 vs 70.6, P < 0.001), and temperature (36.5 vs 35.6, P < 0.001). No desaturation events or haemodynamic instability occurred in the HFO group. ORI and PI remained stable, and no postoperative complications were reported.

Conclusion:

HFO during robotic ureteroscopy appears effective in maintaining oxygenation and haemodynamic stability while providing a still surgical field. These findings support its integration into clinical practice for procedures requiring controlled apnoea.

INTRODUCTION

In recent years, minimally invasive surgical techniques have seen widespread adoption, largely driven by advancements in robotically controlled instruments.[1] These innovations have significantly enhanced surgical precision, reduced morbidity, and improved patient outcomes. In the management of renal and ureteric stones, minimally invasive procedures such as ureteroscopic lithotripsy, extracorporeal shock wave lithotripsy, and percutaneous nephrolithotomy are commonly employed.[2]

Robotic flexible ureteroscopy (RFU) has gained considerable popularity for renal and ureteric stone management. RFU offers several advantages, including reduced physical and mental fatigue for surgeons through automated procedural functions, lower radiation exposure, improved manoeuvrability, and enhanced visualisation.[3] However, one of the challenges during RFU is the potential for renal or ureteric stone migration, which can be exacerbated by increased respiratory rates. This affects the efficiency of stone fragmentation and increases the risk of kidney injury. Gadzhiev et al.[4] demonstrated that minimising renal movement through the use of general anaesthesia improved conditions for stone dusting and also contributed to higher surgeon satisfaction.

To reduce kidney movement during RFU, several techniques have been explored, such as periodic apnoea, high-frequency ventilation, a combination of high-frequency jet ventilation with small mechanical ventilation, and spinal anaesthesia.[5] At our institute, we utilise intermittent periodic apnoea during RFU to optimise surgical conditions by minimising kidney movement. To extend the apnoeic window and prevent desaturation, the high-flow oxygen (HFO) delivery system is employed. This system delivers heated and humidified oxygen at flow rates up to 120 L/min.[6,7]

The mechanisms of HFO include the flushing of anatomical dead space, reducing the work of breathing, decreasing metabolic demand and nasopharyngeal resistance, and promoting alveolar recruitment.[8] While the use of HFO is well established in critical care and anaesthesia settings, its application for intraoperative apnoeic oxygenation during RFU has not been previously documented in the literature.

This study aimed to address this gap by evaluating the effectiveness of HFO and Oxygen Reserve Index (ORI)-guided apnoeic oxygenation as an intraoperative oxygen-delivery technique compared to conventional low tidal volume (TV) ventilation. The secondary objective was to assess intraoperative haemodynamic changes associated with apnoeic oxygenation and assess the feasibility of incorporating HFO into routine RFU practice.

METHODS

Ethical approval was obtained from the Medical Research Centre (MRC-01-24-764) on 24 November 2024. Written informed consent for surgery and anaesthesia was obtained from all patients. As this was a retrospective study using de-identified data, additional patient consent was waived in accordance with local guidelines. The study adhered to the Declaration of Helsinki and was conducted between November 2024 and August 2025.

Data were collected from the medical records of eligible patients undergoing RFU under general anaesthesia (GA) between 1 June 2023 and 1 October 2024. This study included all patients aged above 18 years of American Society of Anesthesiologists (ASA) class I, II, and III. Patients were excluded if they were under 18 years, ASA class IV, had respiratory or cardiovascular diseases, received regional anaesthesia, had a surgery duration longer than 3 hours, or for whom Roboflex was planned but not applied during surgery. The eligible participants were divided into two cohorts according to the anaesthetic technique documented. The study group included patients who had received HFO and ORI-guided apnoeic oxygenation during surgery. The control group included patients who had received low TV ventilation.

Data were collected from the electronic medical records after approval from the institutional review board. Key variables included 1) demographic information (age, body mass index, smoking status); 2) preoperative assessment parameters such as ASA physical status classification, Mallampati score, and comorbidities; 3) intraoperative data including surgery duration, apnoeic window duration, electrocardiogram (ECG), peripheral oxygen saturation (SpO₂), end-tidal carbon dioxide (EtCO₂) levels, heart rate, mean arterial pressure (MAP), temperature, and bispectral index (BIS). Baseline recordings were documented prior to anaesthesia induction. Capnography and oropharyngeal temperature monitoring were initiated after anaesthesia induction. In the HFO group, ORI and Perfusion Index (PI) monitoring were started before apnoea.

According to institutional practices, all patients were pre-oxygenated using a face mask with 15 L/min of 100% oxygen until the EtCO₂ reached 90%. Lactated Ringer’s solution was usually administered as the initial intravenous fluid. GA was induced using target-controlled infusion of remifentanil and propofol. The Schnider model was used for propofol administration (1% target concentration), while the Minto model was applied for remifentanil infusion at a target concentration of 1 µg/kg/min. Infusions were continued throughout surgery and discontinued at the end of the procedure to allow emergence. Remifentanil was stopped at the end of procedure; propofol was discontinued when surgical stimulation ceased. Tracheal intubation was facilitated with rocuronium at a dose of 0.6 mg/kg, and a 7.5-mm cuffed endotracheal tube was placed. Mechanical ventilation was initiated in the volume-controlled mode with a TV of 6–8 mL/kg using a Drager Primus anaesthesia machine (Dragerwerk AG and Co Lubeck, Germany). EtCO₂ was maintained between 30 and 40 mmHg by adjusting the respiratory rate. Anaesthesia was maintained with a 50:50 oxygen–air mixture, along with continuous propofol and remifentanil infusion.

Control Group Protocol: In this group, the documentation indicated that once the surgery commenced, the TV was reduced to 250 mL, and the respiratory rate was increased to 20 breaths/min. Patients were ventilated using these parameters throughout the robotic procedure. All the parameters were compared with the first time point (T1), except for BIS and EtCO₂, for which T2 was used as baseline. T1 values were recorded as baseline parameters before anaesthesia induction. T2 parameters were recorded 10 minutes after induction, T3 at the end of the first hour of anaesthesia, T4 at the second hour, and T5 at the end of the third hour.

Study Group Protocol: During RFU, intraoperative documentation indicated that 5-minute periods of apnoeic oxygenation were implemented. ORI monitoring was initiated beforehand, and insufflation with 100% oxygen was applied until the ORI value exceeded 0.50. Apnoeic oxygenation was repeated up to seven times based on intraoperative requirements. During planned apnoeic periods, flow was increased if ORI decreased to 0 or showed a sustained fall >0.10 absolute, if SpO₂ fell to ≤96% or decreased >3% from baseline, or if the anaesthetist judged there was an impending safety concern. The maximum flow used was 80 L/min. PI was derived from the pulse-oximetry plethysmogram and was recorded continuously on the same monitor. PI values reported in the analysis are the baseline values immediately prior to apnoea and the mean of values sampled every 30 seconds during each apnoeic window.

During apnoea, mechanical ventilation was paused. The tracheal tube was connected to the Optiflow HFO delivery system (Armstrong Medical Limited, London, UK) with flow titration starting at 30 L/min and increasing to 80 L/min using 100% oxygen. Vital parameters were recorded at the beginning and end of each apnoeic period. Baseline values for each apnoea period were labelled as T1b to T7b, while values at the end of each apnoea period were labelled as T1a to T7a. All parameters were compared with the first time point. At the end of the 5-minute interval measured with a chronometer, mechanical ventilation was resumed using pre-apnoea settings. Following each apnoeic period, a gradual CO₂ washout was achieved, reducing EtCO₂ to approximately 36 mmHg before initiating another apnoeic period. Re-initiation of the next apnoeic period was permitted once EtCO₂ had fallen to 36 mmHg. EtCO₂ was recorded continuously, and washout time was measured from the first breath after apnoea to the time EtCO₂ reached ~36 mmHg.

As part of a multimodal analgesic approach, patients received intravenous morphine (1 mg/kg), paracetamol (1 g), and ketorolac (30 mg) intraoperatively. At the end of the surgery, patients were extubated. Following extubation, neurological assessments, including the Michigan Sedation Score and pupillary light reflex, were performed to confirm normal function. Patients were transferred to the post anaesthesia care unit for further monitoring once they were awake, cooperative, pain-free, and responsive to commands. Postoperative complications were recorded.

Continuous variables were assessed for normality using histograms. Normally distributed variables (i.e., age, body mass index (BMI), PI, ORI) were reported as mean and standard deviation (SD), while non-normally distributed variables (i.e., heart rate, MAP, SpO₂, EtCO₂, temperature, BIS, duration of surgery, and apnoeic window) were reported as median interquartile range (IQR). Group comparisons used t-tests for normally distributed variables and Wilcoxon rank-sum tests for non-normal variables. Categorical variables were compared using Fisher’s exact test. Changes over time in heart rate, MAP, temperature, SpO₂, and EtCO₂ were analysed using the Friedman test. Durbin–Conover test was used for pairwise comparisons. Exact P values were reported and interpreted as evidence against the null hypothesis. P value less than 0.05 was considered statistically significant.

RESULTS

Table 1 presents the baseline characteristics of all eligible participants included in the study. A total of 62 male participants with a median age of 37 years (IQR 30–45.75) were enroled and divided into two groups: 34 in the control group and 28 in the study group. The mean BMI was 26.6 kg/m² in the control group and 27 kg/m² in the study group. Smokers comprised 15 participants (44.1%) in the control group and 9 (32.1%) in the study group. At least two comorbidities were present in 5 participants (14.7%) in the control group and 6 (21.4%) in the study group. ASA physical status classification II was observed in 94.1% (n = 32) of the control group and 78.6% (n = 22) of the study group, while a Mallampati score of 2 was noted in 79.4% (n = 27) of the control group and 64.3% (n = 18) of the study group cases.

Table 1.

Baseline characteristics of participants

Variable	Level	Control Group	Study Group	P
N		34	28
Age (years)		38.56 (12.04)	40.214 (11.76)	0.588
BMI (kg/m2)		26.62 (3.06)	27 (3.02)	0.624
Smoking	Yes	15 (44.1%)	9 (32.1%)	0.434
	No	19 (55.9%)	19 (67.9%)
Comorbidities	0	7 (20.6%)	12 (42.9%)	0.104
	1	22 (64.7%)	10 (35.7%)
	≥2	5 (14.7%)	6 (21.4%)
ASA class	1	1 (2.9%)	5 (17.9%)	0.082
	2	32 (94.1%)	22 (78.6%)
	3	1 (2.9%)	1 (3.6%)
Mallampati class	1	3 (8.8%)	3 (10.7%)	0.351
	2	27 (79.4%)	18 (64.3%)
	3	4 (11.8%)	7 (25%)

Data are presented as mean (standard deviation) or number of patients (percentages). BMI=body mass index; ASA=American Society of Anesthesiologists; N=number of patients

Table 2 summarises the intra-operative monitoring data for all participants. The control group demonstrated slightly higher median values of EtCO₂ (43.3 vs 41.6, P = 0.021), heart rate (71.6 vs 65.1, P = 0.001), MAP (83 vs 70.6, P =<0.001), and temperature (36.5 vs 35.6, P =<0.001) compared to the HFO group. No statistically significant differences were observed in terms of SpO₂, BIS, and duration of surgery.

Table 2.

Intraoperative monitoring

Variable	Control Group	Study Group	P
n	34	28
Heart rate (bpm)	71.6 (66.7-76.5)	65.1 (57.2-70.4)	0.001
Mean arterial pressure (mmHg)	84 (73.3-87.8)	70.6 (68.7-73.7)	<0.001
SpO2 (%)	98.8 (98.6-99.2)	99.3 (98-99.5)	0.263
End-tidal (mmHg)	43.3 (41.3-46.7)	41.6 (41-42.8)	0.021
Temperature (°C)	36.5 (36.5-36.6)	35.6 (35.6-35.6)	<0.001
Bispectral Index	42.9 (40.5-44.7)	43.8 (42.1-50)	0.068
Perfusion Index	-	6.35 (1.96)	-
Oxygen Reserve Index	-	0.42 (0.15)	-
Duration of Surgery (minutes)	88 (70-105)	77.5 (55-104.25)	0.116
Duration of apnoeic window (minutes)	-	20 (15-35)	0.334

Data are presented as mean (standard deviation) or median (interquartile range). SpO₂=peripheral oxygen saturation; CO₂=carbon dioxide; bpm=beats per minute

Table 3 presents the changes in monitored parameters over time within the control group, comparing each time point to baseline measurement at T1, except for BIS and EtCO₂ for which T2 was used as a baseline. A statistically significant decrease in SpO₂ was observed at T2, T4, and T5 compared to baseline. Heart rate values were statistically significantly lower at T3 and T4 relative to T1. For MAP, all subsequent measurements showed a statistically significantly reduction compared to baseline values. The BIS values were statistically significantly higher at T5 compared to its value at T2. Additionally, EtCO₂ values at T4 and T5 were statistically significant relative to baseline at T2.

Table 3.

Parameter changes over time in the control group

	T1	T2	T3	T4	T5	P
SpO2 (%)	99.5 (98.3-100)	100.0 (99.0–100.0)	99.0 (99.0–100.0)	99.0 (98.0–99.0)	98.0 (97.0–99.0)	<0.001
Heart rate (beats/min)	77 (69-84.8)	70.5 (63.5–79.0)	65.0 (59.3–72.8)	72.0 (62.0–78.0)	77.5 (63.5–85.0)	<0.001
Temperature (°C)	36.5 (36.4-36.8)	36.5 (36.5–36.7)	36.5 (36.4–36.7)	36.5 (36.4–36.7)	36.5 (36.4–36.7)	0.589
Mean arterial pressure (mmHg)	99 (95.5-105)	72.0 (70.0–79.0)	79.0 (72.8–82.8)	72.0 (69.3–79.0)	91.0 (80.5–101.0)	<0.001
Bispectral index	-	41.5 (38.0–48.3)	41.5 (36.0–45.5)	39.5 (34.0–45.0)	46.5 (42.5–52.0)	0.014
End-tidal CO2 (mmHg)	-	36.0 (34.3–37.8)	35.0 (32.3–37.0)	51.0 (47.3–57.5)	52.0 (47.3–54.8)	<0.001

Data are presented as median (interquartile range). SpO₂=peripheral oxygen saturation; CO₂=carbon dioxide

Table 4 presents the changes in monitored parameters over time within the study group, comparing each time point to baseline measurement at T1b. MAP values were consistently statistically significantly lower than baseline at all time points. In terms of heart rate, only the measurement at T5b showed a statistically significant decrease compared to baseline. For EtCO₂, values during the robotic intervention phases were statistically significantly higher than baseline. Importantly, no episodes of desaturation or significant haemodynamic instability were observed during the apnoeic periods. Furthermore, no postoperative complications were recorded in the study group.

Table 4.

Parameter changes over time in the study group

	T1b	T1a	T2b	T2a	T3b	T3a		T4b
SpO2 (%)	100.0 (99.0–100.0)	99.0 (96.8–100.0)	100.0 (99.0–100.0)	99.0 (96.0–99.0)	99.0 (99.0–100.0)	99.0 (98.0–99.0)		99.0 (99.0–100.0)
Mean arterial pressure (mmHg)	73.0 (69.8–78.0)	72.0 (66.8–76.3)	72.0 (65.5–75.5)	69.0 (65.5–72.0)	71.0 (66.5–72.5)	69.0 (66.0–72.0)		69.0 (67.0–72.5)
Heart rate (beats/min)	61.0 (56.0–70.0)	65.5 (57.3–70.3)	64.0 (56.5–69.0)	66.0 (60.0–72.0)	62.0 (57.0–68.0)	60.0 (58.0–68.5)		63.0 (57.5–67.0)
End-tial CO2 (mmHg)	33.0 (32.0–33.3)	48.0 (44.8–51.0)	34.0 (34.0–35.0)	48.0 (47.0–51.0)	44.5 (40.3–48.0)	41.0 (40.0–43.8)		35.0 (34.0–35.0)
Bispectral index	45.0 (41.0–50.3)	44.0 (41.0–48.3)	44.0 (40.5–46.5)	44.0 (40.0–49.0)	35.6 (35.6–35.6)	35.6 (35.6–35.6)		40.0 (39.0–46.0)
Temperature (°C)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	34.0 (34.0–34.0)	35.6 (35.6–35.6)		35.6 (35.6–35.6)
Perfusion index	5.6 (4.66–6.85)	6.6 (5.1–8.4)	5.82 (4.73–7.84)	6.92 (5.14–8.88)	5.14 (4.62–6.61)	6.72 (5.45–8.65)		6.30 (4.60–7.73)
Oxygen reserve index	0.56 (0.48–0.63)	0.25 (0.0–0.47)	0.57 (0.49–0.62)	0.29 (0.0–0.47)	0.56 (0.52–0.61)	0.43 (0.19–0.50)		0.52 (0.48–0.62)
	T4a	T5b	T5a	T6b	T6a	T7b	T7a	P
SpO2 (%)	99.0 (99.0–100.0)	99.0 (99.0–100.0)	99.0 (99.0–99.5)	99.0 (99.0–99.0)	99.0 (99.0–99.0)	99.0 (99.0–99.0)	9.0 (99.0–99.0)	0.054
Mean arterial pressure (mmHg)	68.0 (67.0–72.0)	68.0 (66.0–73.0)	68.0 (66.0–71.5)	68.0 (67.0–70.0)	67.0 (65.5–69.0)	69.0 (67.0–69.0)	69.0 (68.0–71.0)	0.001
Heart rate (beats/min)	65.0 (58.0–69.5)	57.0 (54.0–65.5)	66.0 (59.0–69.5)	64.0 (60.0–69.0)	65.0 (63.0–68.5)	59.0 (57.0–64.0)	58.0 (54.0–61.0)	0.027
End-tial CO2 (mmHg)	50.0 (47.0–52.0)	35.0 (34.5–35.0)	51.0 (49.5–56.0)	35.0 (35.0–35.5)	51.0 (49.5–55.0)	35.0 (35.0–36.0)	52.0 (51.0–53.0)	<0.001
Bispectral index	44.0 (40.0–47.0)	42.0 (40.0–47.0)	42.0 (41.0–46.5)	45.0 (41.0–45.5)	43.0 (40.0–47.5)	45.0 (43.0–47.0)	44.0 (40.0–48.0)	0.354
Temperature (°C)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	35.6 (35.6–35.6)	0.425
Perfusion index	5.87 (4.59–7.53)	6.42 (5.28–7.02)	6.47 (5.14–7.82)	5.24 (3.86–6.73)	6.39 (3.73–7.31)	6.77 (1.93–6.78)	5.52 (4.07–6.37)	0.015
Oxygen reserve index	0.46 (0.29–0.54)	0.52 (0.45–0.54)	0.42 (0.11–0.46)	0.52 (0.43–0.57)	0.33 (0.25–0.47)	0.50 (0.35–0.57)	0.32 (0.30–0.45)	<0.001

Data are presented as median (IQR). SpO₂=peripheral oxygen saturation; CO₂=carbon dioxide

DISCUSSION

This retrospective cohort study compared HFO with ORI-guided apnoeic oxygenation to conventional low-TV ventilation during RFU, demonstrating HFO’s potential to optimise oxygenation and maintain haemodynamic stability during apnoeic periods.

Patients in the study group exhibited significantly lower MAP and heart rate, suggesting a more stable perioperative course without added haemodynamic stress. HFO also maintains airway humidity and temperature, enhancing comfort and reducing airway irritation.

Patients in the study group had significantly lower EtCO₂ than the control group. Respiratory and diaphragmatic motion can displace the kidney, increasing the risk of papillary or urothelial injury[9]; therefore, apnoea was used to provide a stable surgical field. Each apnoeic period was limited to 5 minutes, sufficient for surgical precision while minimising hypercapnia. During apnoea, EtCO₂ rose to 52.0 mmHg in the study group and decreased after ventilation resumed. This alternating apnoea–ventilation strategy maintained physiological anaesthesia and minimised atelectasis.

In the control group, TV reduction at the start of surgery resulted in progressive EtCO₂ elevation, which persisted until the third hour, exposing patients to at least 1 hour of sustained hypercapnia. Prolonged hypercapnia can adversely affect cerebral blood flow, haemoglobin oxygen affinity, haemodynamics, and cardiac output.[10,11] Despite these differences, no postoperative complications were observed, likely because most patients were of ASA physical status classification I or II.

Patel and Nouraei first described “Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE)” as a technique that extends apnoea tolerance during airway management.[12] They increased the apnoeic window in 25 patients with difficult airway. An apnoea time of 65 minutes was reached in one patient. There was no desaturation with SpO₂ under 90%, although EtCO₂ exceeded 450 mmHg. Consistent with prior studies, high-flow oxygenation prolongs the apnoeic window by generating low-level positive airway pressure and facilitating oxygen diffusion.[13,14,15] In our study, apnoea was limited to 5 min to avoid hypercarbia, which was successfully achieved.

Although high-frequency jet ventilation (HFJV) has been proposed as an alternative technique—delivering low TVs at rates of 100–160 breaths per minute—it carries notable risks.[3] These include pneumothorax, surgical emphysema, and pneumomediastinum[16] and requires a dedicated ventilation device.

Complete cessation of respiration provided optimal surgical conditions during RFU, with surgeon feedback confirming excellent targeting and no renal tissue injury. Emiliani et al.[17] described an apnoea protocol during ureteroscopy without supplemental oxygen allowing SpO₂ to fall to 93% before resuming ventilation; in contrast, our approach prioritised safety using HFO. The physiological benefits of HFO—including dead space washout, reduced work of breathing, alveolar recruitment, and improved oxygen delivery—were evident.[18]

HFO effectiveness was confirmed using ORI and PI monitoring. Although ORI does not measure PaO₂ directly, values >0.24 correlate with partial pressure of oxygen (PaO₂) ≥100 mmHg.[19] Patients were pre-oxygenated with 100% oxygen to achieve ORI >0.5 before apnoea, and no desaturation occurred. This proactive measure established a safety buffer and helped maintain adequate oxygen reserves throughout the apnoeic periods. PI, an indicator of peripheral perfusion,[20] remained stable, supporting adequate tissue perfusion throughout apnoeic periods underscoring its contribution to optimising patient outcomes.

To reduce barotrauma risk, the tracheal tube cuff was deflated, an oropharyngeal airway inserted, and the oxygen flow titrated from 30 L/min to 80–90 L/min. This approach aligns with prior evidence, including our previously published case report demonstrating the safety of intraoperative HFO during apnoeic oxygenation.[21]

This study has several limitations. Its retrospective design limits causal inference and is prone to incomplete data, highlighting the need for future randomised controlled trials. As a single-centre study, generalisability is limited, and multicentre studies with larger, diverse populations are required. Long-term and patient-reported outcomes were not assessed and should be included in future research. Although HFO may reduce atelectasis through alveolar recruitment, this was not confirmed with imaging; future studies should incorporate perioperative imaging. Finally, surgeon-reported renal tissue outcomes were not formally evaluated using validated scoring systems, underscoring the need for standardised renal outcome assessment.

CONCLUSION

The effectiveness of HFO was demonstrated by consistently stable ORI and PI readings. During RFU, HFO provided a motionless surgical field, enhanced intraoperative oxygenation, and maintained perioperative stability without adding haemodynamic stress. These findings support the feasibility of integrating HFO into routine practice, particularly for procedures involving prolonged apnoeic periods. Future research should focus on well-designed randomised controlled trials to confirm these benefits and further explore the long-term outcomes and broader clinical implications of HFO in this setting.

Presentation at conferences/CMEs and abstract publication

The abstract of this study was presented at the World Airway Management Meeting 2025 held in Florence, Italy from 5^th-8^th November.

Study data availability

De-identified data may be requested with reasonable justification from the authors (email to the corresponding author) and shall be shared upon request.

Disclosure of use of artificial intelligence (AI)-assistive or generative tools

AI tools or language models have not been utilised in the manuscript, except that software has been used for grammar corrections.

Declaration of use of permitted tools

Not used.

Supplementary material

None.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.