Why the study?
Preoperative spirometry and CPET may stratify respiratory complication risk, but whether CPET-measured cardiopulmonary fitness confounds the associations between spirometry and postoperative outcomes remained unexamined.
Does preoperative spirometry predict respiratory complications after accounting for cardiopulmonary fitness in patients undergoing major non-cardiac surgery?
Does preoperative spirometry predict respiratory complications after accounting for cardiopulmonary fitness in patients undergoing major non-cardiac surgery?
Preoperative FEV1 is not strongly predictive of postoperative respiratory complications when accounting for cardiopulmonary fitness, suggesting prior associations may be confounded by peak oxygen consumption.
Spirometry-respiratory outcome links may reflect fitness rather than lung function alone; leaves open incremental value of spirometry beyond CPET.
Background Preoperative spirometry and cardiopulmonary exercise testing (CPET) may stratify risk for respiratory complications. This secondary analysis of the Measurement of Exercise Tolerance before Surgery (METS) study examined whether CPET performance (i.e., cardiopulmonary fitness) confounds associations of spirometry with outcomes. Methods The analysis included 1200 participants having major non-cardiac surgery at 25 hospitals in Canada, Australia, New Zealand and UK. Forced expiratory volume in 1 s (FEV 1 ), and ratio of FEV 1 to forced vital capacity (FVC) were measured during preoperative spirometry, and peak oxygen consumption and ventilatory efficiency during preoperative CPET. Outcomes were respiratory morbidity (Postoperative Morbidity Survey) and pulmonary complications (pneumonia or respiratory failure). We used multivariable logistic regression models to estimate associations of FEV 1 with outcomes after adjustment for risk factors and either peak oxygen consumption or ventilatory efficiency. Findings 128 participants (11%) developed respiratory morbidity, and 48 (4%) developed pulmonary complications. There was no strong evidence that FEV 1 predicted respiratory morbidity after adjustment for peak oxygen consumption ( p = 0·80) or ventilatory efficiency ( p = 0·76), or FEV 1 predicted pulmonary complications after adjustment for ventilatory efficiency ( p = 0·37). Peak oxygen consumption (odds ratio 0·66 per 5 mL/kg/min increase; 95% CI, 0·54–0·82) was associated with respiratory morbidity. Ventilatory efficiency was associated with respiratory morbidity ( p = 0·04) and pulmonary complications ( p = 0·02). Peak oxygen consumption also confounded the association between FEV 1 and respiratory morbidity. Interpretation After accounting for fitness and clinical factors, FEV 1 was not strongly predictive of respiratory complications. Prior associations between FEV 1 and respiratory morbidity may be explained by confounding by peak oxygen consumption. Funding Canadian Institutes of Health Research, Heart and Stroke Foundation of Canada, Ontario Ministry of Health and Long-Term Care, Ontario Ministry of Research, Innovation and Science, UK National Institute of Academic Anaesthesia, UK Clinical Research Collaboration, Australian and New Zealand College of Anaesthetists, and Monash University.
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Sankar et al. (2020) studied this question.
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