The influence of BMI on optimal PEEP titrated by electrical impedance tomography in ARDS patients

Abstract

Background Obese patients with acute respiratory distress syndrome (ARDS) may require higher positive end-expiratory pressure (PEEP), but the dose-response relationship between body mass index (BMI) and PEEP remains undetermined. This study aimed to investigate the relationship between BMI and the optimal PEEP titrated by electrical impedance tomography (EIT) in ARDS patients. Methods ARDS patients who underwent EIT-guided PEEP titration were analyzed retrospectively. Patients were classified as obese (BMI ≥ 28 kg/m²) and non-obese (BMI < 28 kg/m²). All patients received a decremental PEEP trial from 18 to 3 cmH₂O, and the optimal PEEP was determined by the lowest sum of EIT-based regional overdistension and collapse. Results Among 115 ARDS patients reviewed, average BMI was 25.1 (22.4–28.0) kg/m², ranging from 16.0 to 38.1 kg/m², with 29 (25.2%) patients being obese. Compared to non-obese patients, the titrated PEEP was higher in obese patients (12 [12–15] cmH₂O vs 9 [6–12] cmH₂O, p < 0.001). At the PEEP level of 3 cmH₂O, the proportion of collapse in obese group was higher than in the non-obese group (39.0 [31.0-48.2] % vs 27.5 [18.3–40.7] %, p = 0.004). At the PEEP level of 18 cmH₂O, overdistension was lower in obese group (18.0 [14.0-26.6] % vs 25.4 [18.0–35.0] %, p = 0.023). A positive linear correlation was found between BMI and EIT-derived best PEEP (Spearman R = 0.46, p < 0.001). For detecting the optimal PEEP ≥ 12 cmH₂O, a cutoff of BMI > 30 kg/m² would provide a specificity of 96.4% and a positive predictive value of 88.2%. Conclusion A lower PEEP resulted in more collapse and a higher PEEP resulted in less overdistension in obese ARDS patients. The findings provided evidence to consider BMI in setting PEEP for this patient group.