Six-Point Risk Factor Score Predicts Hypoxemia During Tracheal Intubation

Oxygen saturation at induction and acute hypoxemic respiratory failure were the risk factors most strongly associated with lower oxygen saturation.

A simplified 6-point score may identify patients at risk for hypoxemia during intubation according to the results of a study published in the Annals of the American Thoracic Society.

In critically ill adults undergoing tracheal intubation, hypoxemia is a common complication. It is associated with cardiac arrest and is often used as an end point in airway management research. Identifying individuals likely to experience hypoxemia during tracheal intubation may improve patient outcomes by allowing changes in modifiable risk factors.

Researchers analyzed data on 426 intubations from 2 randomized trials and developed linear and logistic regression models to identify preprocedural risk factors for lower arterial oxygen saturation levels and severe hypoxemia between induction and 2 minutes after intubation.

The mean lowest oxygen saturation was 88% and the median was 93%. Hypoxemic respiratory failure as an indication for intubation had an odds ratio (OR) of 2.70 for severe hypoxemia, whereas lower oxygen saturation at induction had an OR of 0.92 per 1% increase.

Other independent predictors included younger age (OR 0.97 per 1-year increase), higher body mass index (OR 1.03 per 1 kg/m2), race (OR 4.58 for white vs black; OR 4.47 for other vs black), and operator with fewer than 100 prior intubations (OR 2.83). This 6-point score predicted severe hypoxemia with an area under the receiver-operating curve of 0.714.

Oxygen saturation at induction and acute hypoxemic respiratory failure were the risk factors most strongly associated with lower oxygen saturation. Provider training level was another important risk factor. The strongest independent predictor of severe hypoxemia was blood oxygen saturation at induction. The results suggested that even in patients with a blood oxygen saturation above 95%, higher levels may be better, although the researchers cautioned that the benefits of extending the preoxygenation period should be weighed against possible deterioration in some patients.

Another modifiable variable is the operator’s previous intubation experience. The researchers contended that race as a factor appears to have no physiologic rationale and may be related to incomplete knowledge of comorbidities that confound that variable. They also noted that the association between older age and lower risk for hypoxemia seems to be counterintuitive and may result from clinicians being more likely to intubate older patients and in contrast, waiting to intubate until less physiologic reserves remain in younger patients.

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The researchers concluded that a simple bedside risk score that stratifies patients according to their risk for hypoxemia during intubation may help target use of preventive interventions.


McKown AC, Casey JD, Russell DW, et al. Risk factors for and prediction of hypoxemia during tracheal intubation of critically ill adults [published online August 15, 2018]. Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201802-118OC