Association of body mass index with postoperative pulmonary complications and potential explanatory pathways in paediatric scoliosis correction surgery: a multicentre cohort study

At the completion of surgery, the incremental predictive value of BMI was assessed using an elastic-net model developed in centres 1 and 3 and externally validated in centre 2.</p> <p>PPCs occurred in 321 patients (27.55%). In the primary preoperative-adjusted model, each 1-kg/m² higher BMI was associated with lower odds of PPCs (aOR, 0.87; 95% CI, 0.83–0.91; <i>p</i> < 0.001). A secondary exploratory perioperative-adjusted model yielded a similar estimate (aOR, 0.85; 95% CI, 0.81–0.89; <i>p</i> < 0.001).

Compared with normal weight, thinness was associated with higher odds of PPCs (aOR, 4.26; 95% CI, 2.74–6.67; <i>p</i> < 0.001), whereas overweight was associated with lower odds (aOR, 0.57; 95% CI, 0.34–0.91; <i>p</i> = 0.022). The causal forest yielded an inverse average partial-effect estimate for BMI (−0.031; 95% CI, −0.037 to −0.025; <i>p</i> < 0.001). Exploratory pathway analyses suggested small indirect components through PNI, blood loss, and fusion levels.

Adding BMI increased the external-validation AUC from 0.658 to 0.703 (<i>p</i> < 0.001), representing a modest improvement in discrimination.</p> <p>Higher preoperative BMI was associated with lower odds of PPCs, with a concordant inverse causal-forest estimate under its identification assumptions. Low BMI or thinness may serve as a preoperative risk marker, while the examined pathways accounted for only small proportions of the association.

At the end-of-surgery prediction time point, adding BMI provided modest incremental predictive value, although the model’s external performance was modest and further prospective validation is required.</p>