Incidence of post-induction hypoxemia in children and the effect of induction gas composition.

The clinical impact on oxygenation while using other gases with oxygen during an inhalational induction is unknown. The authors reviewed the effects of nitrous oxide, air and oxygen added to volatile during inhalational induction in children (under 18yrs old) retrospectively from an automated information management system.

The primary aim was to measure the incidence of hypoxaemia during induction, and the hypothesis was it would increase with decreasing FiO2. The secondary aim was to identify the impact of gas composition on the incidence of hypoxaemia.

The study was performed at a 219-bed tertiary paediatric teaching hospital. Data over a 10-year period was included. 66 035 case records were reviewed and 35 526 met the inclusion criteria.

Hypoxic episodes were defined as SpO2 <90% sustained for at least 120s, to help exclude pulse oximeter artifact.

The overall incidence of children with hypoxaemic episodes within 10 minutes of induction was 5.08% (95% CI 4.83%, 5.35%). There was a non-linear relationship between incidence of hypoxaemia, and FiO2 at the end of induction period. The odds ratio of a hypoxaemic episode was 1.2 if FiO2 was less than 0.6 and 2.4 if below 0.4. Hypoxaemia was, unsurprisingly, more likely in higher ASA and younger patients. They considered nitrous oxide and nitrogen with oxygen and were unable to find an effect from other gases.

The authors suggest during induction FiO2 should be above 0.6 to minimise hypoxaemia. By using 33% N2O and 66% oxygen, the benefits of N2O (second gas and concentration effect) can still be enjoyed. There was no clear evidence in this study for the beneficial effect of nitrogen immediately after induction on hypoxaemia (by reducing atelectasis).

The authors describe the reasons why they chose certain time limits, thresholds and definitions and these appear sensible to the reader. Their analysis did not include IV medications, airway issues like obstruction, anaesthetist experience, type of airway, or comorbidities. They noted this would not influence the more global nature of their findings. They did extrapolate 30s data to every second, which may have introduced inaccuracies. There does not seem to be inclusion of consideration of ventilation type post induction. For example: CPAP, PEEP, Pressure support, PPV. It is not mentioned, and may not be documented within the information management system used for this study.

They conclude with the statement “Our study suggests that the gas composition during inhalation induction should include at least 60% oxygen to minimise hypoxemia during airway management”.

Reviewed by Dr Anna Miedecke