Hypoxaemia after preoxygenation

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, Orequirement

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

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