British Journal of Anaesthesia (2023), 130 (1): 103-110
John Schutzer-Weissmann, Thomas Wojcikiewicz et al
AIM OF STUDY
To explored the safe upper limit of apnoea in morbidly obese patients – a comparison between the effect of oxygen flow rate and proximity of fresh gas flow to the respiratory epithelium on the duration of apnoea.
DESIGN (& LOCATION)
Prospective physiological study in a tertiary centre in London
Patients undergoing bariatric surgery randomised into high flow nasal oxygen or face mask group. Standardised induction agent administered, and both groups pre oxygenated. Serial arterial blood gas samples taken and oxygen saturation measured from induction of anaesthesia. Patients were intubated when end point reached (defined as 18 minutes since onset of apnoea or arterial oxygen saturation reached below 92%.
The time to arterial haemoglobin oxygen desaturation to 92%.
The arterial oxygen and carbon dioxide tension during apnoea to determine whether higher oxygen flow rate promotes more efficient apnoeic oxygenation, ventilation, or both.
Mixed effect models for time measurements
Linear mixed effect models used with Poisson distribution for needle passes nos.
- The risk of desaturation was significantly lower in the HFNO group than in the FM group
- The median time to desaturation was 18min in both groups
(data are heavily right-censored, as most patients in both groups reached the 18 min endpoint without desaturating)
- No statistically significant findings
- Morbid obesity does not preclude apnoeic oxygenation.
- Desaturation risk decreased by oxygen delivery characteristic, but other factors play roles (?patient positioning at 45 degrees incline)
STATED LIMITATIONS FROM STUDY
- The findings may not transfer to other population
- Primary outcome is sensitive to study design ?better primary outcome
- Technical limitation: ABG not immediately processed
DISCUSSION FROM JOURNAL CLUB MEETING (? Change of practice)
- Consider using TIVA for patients living with morbidly obesity, if difficult ventilation/ airway predicted
- Carefully consider patient position prior to induction in patients living with morbid obesity
- Both HFNO/ FM effective at oxygenating patients
Summary by Dr SJ Park. Journal Club Meeting 16 March 2023.