Physiologic effects of THRIVE versus facemask preoxygenation in obese patients undergoing bariatric surgery: A pilot...

Obesity reduces functional residual capacity (FRC) and promotes atelectasis during anesthetic induction. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) generates flow-dependent positive airway pressure and may preserve lung volume. This prospective observational pilot study compared THRIVE with facemask preoxygenation in obese patients undergoing bariatric surgery, focusing on regional ventilation distribution assessed by Electrical Impedance Tomography (EIT), respiratory mechanics, and gas exchange.

Adult patients (BMI ≥35 kg/m²) scheduled for elective laparoscopic sleeve gastrectomy received either THRIVE or facemask preoxygenation. EIT and arterial blood gases were collected at three time points: baseline, before induction, in room air (T1), intraoperatively, during pneumoperitoneum (T2), and at the end of surgery, with patients awake (T3); respiratory mechanics were assessed at T2. The primary outcome was regional ventilation distribution evaluated by predefined Regions of Interest (ROIs) and change in end-expiratory lung impedance (ΔEELI%), an impedance-derived surrogate of end-expiratory lung aeration. Secondary outcomes included lung mechanics (PEEPtot, static compliance, driving and plateau pressure) and gas exchange parameters.

Sixty-five patients were analyzed (33 THRIVE, 32 facemask). Baseline characteristics were comparable between groups. At T2, PEEPtot was significantly higher in the THRIVE group (6 ± 2.2 vs 4.9 ± 1.3 cmH₂O; p = 0.02), and PaO₂ values were significantly higher in the facemask group (132.4 ± 51.9 mmHg vs 119 ± 43.3 mmHg; p < 0.05), whereas at T3, PaCO₂ was slightly higher with THRIVE (42.2 ± 6.1 mmHg vs 40.2 ± 4.5 mmHg; p < 0.05). Overall, respiratory mechanics and gas exchange parameters were largely comparable between groups. EIT demonstrated greater dorsal ventilation (ROI4) in the THRIVE group both at T2 (32.4 ± 13.7% vs 18.1 ± 8.7%; p < 0.05) and at T3 (30.6 ± 11.7% vs 20 ± 8.9%; p < 0.05). Similarly, ΔEELI% values were significantly higher in THRIVE at both T2 (97.5 [395.7] vs 33 [285.4]; p < 0.05) and T3 (109 [479] vs -58.5 [346.2]; p < 0.05).

In this exploratory observational study, THRIVE was associated with greater dorsal ventilation distribution and higher impedance-derived end-expiratory lung aeration in obese patients undergoing bariatric surgery. These findings are hypothesis-generating and warrant confirmation in randomized trials.