“Incidence and risk factors of hypoxaemia after preoxygenation at induction of anaesthesia” Baillard et al. British Journal of Anaesthesia, 122 (3): 388e394 (2019)
Background
- Hypoxaemia most common form cause of death at induction of anaesthesia
- 2010 retrospective study demonstrated hypoxaemia (SpO2≤ 90%) in 7.4% of patients at induction
- Hypoxaemia known to occur more quickly if preoxygenation omitted
Aim
To determine incidence of hypoxaemia during induction of anaesthesia, and its contributory factors in a large population after a standardised preoxygenation procedure
Methods
- Multicentre prospective analysis (France; 2 teaching hospitals and one DGH)
- 6 month inclusion period
- Orthopaedic, vascular, gynaecological, ENT and abdominal surgery; GI endoscopy
- Omitted: thoracic surgery, haemodynamic instability, O2 requirement
Preoxygenation technique:
- Supine EXCEPT obese patients (head-up 10-25°)
- O2flow 12L/min
- TV breathing 3-5 mins until FeO2≥ 90%
- Face mask adjusted according to capnograph
Outcomes
PRIMARY – Incidence of hypoxaemia (SpO2≤ 95%)
SECONDARY – Incidence of difficult preoxygenation (FeO2< 90%)
Results
2398 patients included in study
Hypoxaemia observed in 158 patients (6.6%)
Severe hypoxaemia observed in 34 patients (1.4%)
At 3 min, difficult preoxygenation in 1202 patients (50%)
At 5 min, difficult preoxygenation in 723 patients (30%)
5 independent risk factors for hypoxaemia: COPD, HTN, anticipated difficult FMV, anticipated difficult intubation, emergency
5 independent risk factors for difficult preoxygenation: male, COPD, HTN, emergency, anticipated difficult FMV
Can anticipate difficult MV/intubation with a high negative predictive value
Discussion
- Large patient cohort, representative of our patient population
- Significant incidence of difficult preoxygenation (30%)
- Significant incidence of hypoxaemia given strict preoxygenation regimen
- Anaesthetists need to become familiar with techniques to improve preoxygenation
Limitations
- Exclusion of haemodynamically unstable/O2requiring patients
- Likely underestimate of hypoxaemia due to preoxygenation
- Hypoxaemia definition SpO2≤ 95% – not powered for hypoxaemia ≤ 90%
- Vague definitions of difficult FM ventilation/intubation
- Data collected by anaesthetist
- No differentiation for starting SpO2of COPD patients
- Emergency surgery as a risk factor for hypoxaemia likely related to RSI
- Definition of RSI and variability of techniques unclear
Summary by Dr Adam Patrick