Body mass index is negatively correlated with respiratory muscle weakness and interleukin-6 production after coronary artery bypass grafting

Purpose: The present study was performed to clarify the relationships between body mass index (BMI), interleukin-6 (IL-6) production, and respiratory muscle weakness in patients undergoing coronary artery bypass grafting (CABG). Materials and Methods: The correlations among BMI, changes in maximum inspiratory and expiratory pressure (ΔMIP, ΔMEP) on postoperative days (POD) 1 and 7, postoperative IL-6, and rapid turnover proteins (retinol-binding protein, prealbumin, and transferrin) on POD1 were assessed in 154 consecutive patients undergoing elective CABG. The patients were divided into quartiles of BMI, Q1 (BMI, <20.8 kg/m²) to Q4 (BMI, ≥25.25 kg/m²), and compared among groups. Results: There were significant correlations between ΔMIP and BMI (POD1, r = -0.369; POD7, r = -0.285) and IL-6 (POD1, r = 0.423; POD7, r = 0.431), and between ΔMEP and BMI (POD1, r = -0.252; POD7, r = -0.228) and IL-6 (POD1, r = 0.252; POD7, r = 0.384). Interleukin-6 showed a significant negative correlation with BMI (r = -0.374) and retinol-binding protein (r = -0.382). Interleukin-6 was highest in Q1 and lowest in Q4. Higher BMI indicated greater respiratory muscle strength than lower BMI. Conclusions: Preoperative BMI is correlated with respiratory muscle strength and cytokine production after CABG. The findings of this study suggest that BMI may be a valuable predictor for respiratory management in CABG patients.