P0453 - Asthma, obesity and post-operative pneumonia in children

Background: Childhood obesity and asthma have reached national epidemic proportions and an increasing number of children requiring anesthesia and surgery would be either obese or asthmatic. Obesity and asthma have a clear proclivity for disturbing pulmonary physiology; and they have both been shown to be risk factors for acute perioperative respiratory adverse events. What is currently unknown is whether the separate or joint presence of obesity and asthma increases the risk of postoperative pneumonia. Our objective was to examine the association of obesity and asthma with postoperative pneumonia in a cohort of children who underwent inpatient surgical procedures between 2012 and 2017.

Methods: This is retrospective cohort study of children (2-18 years of age) who underwent inpatient surgery between 2012 and 2017, in hospitals participating in the National Surgical Quality Improvement Program-Pediatric. We used the CDC criteria to categorize children into four groups according to BMI z-scores: underweight (< -1.89), normal weight (-1.89 to 1.04), overweight (1.05 to 1.64), and obese (≥ 1.65). Our primary outcome was the time to post-operative pneumonia and secondary outcome was time to unplanned postoperative intubation (UPI). We conducted a stratified analysis to estimate the hazard-ratios (HR) of postoperative pneumonia and UPI, across the strata of BMI. We assessed interaction on the multiplicative scale, between BMI and asthma by modeling the time to pneumonia on asthma, BMI and interaction terms between asthma and BMI. We used propensity score weighting to limit the effects of imbalance, across asthma groups, due to potential confounders.

Results: Our final sample comprised of 203,950 children, of whom 12.1% (n=19,236) were underweight, 54.3% (n=86,654) normal weight, and 33.6% (n=53,607) obese. The cumulative incidence of postoperative pneumonia was 1.0% (n=196) among underweight children, 0.6% (n=482) among normal weight children, and 0.5% (n=263) among obese children. Overall, asthma was associated with a relative greater risk of pneumonia following surgery. Compared to children with normal weight, the association between BMI group and asthma was weaker among overweight children (HR: 1.58 vs. 2.22). In addition, asthma had a weaker association with pneumonia among obese children, relative to underweight children (HR: 1.58 vs 1.82). We found that children with asthma were more likely to require UPI, and this association was stronger among obese children, compared to normal weight children (HR: 1.63 vs. 1.54)However, the test of interaction between BMI and asthma was not statistically significant at the alpha level of 0.05.

Conclusion: The variation in the association between asthma and post-operative pneumonia were consistent with the obesity paradox, in that obesity appeared to counterintuitively buffer the impact of asthma on pneumonia. The association between asthma and unplanned reintubation appeared to be strongest among obese children. However, these findings were not found to be statistically significant.