Longitudinal Changes of Electrical Impedance tomography-based Best PEEP in Obese Patients Undergoing Laparoscopic Surgery: A Prospective Physiological Study

Background: During laparoscopic surgery, there is an increased tendency for lung collapse. Individualized PEEP has shown possible advantages in obese patients undergoing laparoscopic procedures, but the optimal timing for titration and the evolution of lung regional mechanics have not been extensively explored. Methods: Patients with Class I/II Obesity undergoing laparoscopic surgery for abdominal procedures were monitored using 16 electrodes Electrical Impedance Tomography (EIT) and underwent a decremental PEEP titration trial at 3 timepoints: after anesthesia induction (T1), after positioning and pneumoperitoneum (T2) and after laparoscopy (T3). EIT-derived lung regional collapse (EITCO) and overdistension (EITOD) were recorded, as well as respiratory mechanics, hemodynamic and surgical data. The best PEEP according to EIT (PEEPEIT) was calculated at each timepoint as the intersection between regional collapse and overdistention. Results: We enrolled 31 patients with a median age of 63 [49-74] years and a BMI of 36 [32-37] kg m-1. During surgery, PEEPEIT at T1 and T2 were respectively 10[9-11.5] and 13.9[12.6-15] cmH2O (p < 0.001), with a median increase of 3 [2-4] cmH2O, a range of increase of 0-7 cmH2O and a coefficient of increase variation of 60.8%. The difference in PEEPEIT between T2 and T1 did not correlate with intrabdominal pressure (r=-0.03, p = 0.88), while a significant association was found with trunk inclination (p = 0.018, r=0.42). Conclusions: EIT-based best PEEP changes dynamically and non-homogeneously during laparoscopic surgery in class I/II obese patients. PEEP reassessment is required to guarantee the application of protective mechanical ventilation throughout the entire course of anesthesia. Registration: ClinicalTrials.gov, registration number NCT05554536.