Abstract PR631

Abstract

Background & Objectives: Atelectasis is aggravated on induction of anesthesia and pneumoperitoneum in the morbidly obese. Currently employed per-operative ventilation strategy, based on lung protection strategy, require recruitment maneuver (RM) for optimal gas exchange. Lower tidal volume (VT) is recommended in patients with acute lung injury for positive pressure ventilation (PPV). There is no evidence to the premise of using a lower VT in morbidly obese patients. Parameter on which to base tidal volume (VT) in these patients is still not validated. During anaesthesia, appropriate VT is required to minimize obligate aggravation of atelectasis. Abdominal obesity (AO) is a better predictor of severity of obesity than body mass index (BMI). Waist circumference (WC) is a fair measure of AO and may be used for setting VT for PPV strategy for the obese. Ideal body weight (IBW) was also analyzed for VT calculation and its impact on gas exchange and pulmonary morbidity (if any). Materials & Methods: A prospective cohort of sixty morbidly obese patients (BMI>35 kg m-2), randomized into two groups, received PPV determined by IBW and AO-based VT calculation. Anaesthesia technique was standardized for the two groups. In AO group, VT was calculated by formula WC in cm × 6.0 ml and in IBW group by equation IBW (kg) × 13ml. We applied a PEEP of 5 cm H2O PEEP in AO group and 10 cm H2O in IBW group. Respiratory rate (13/min) and I:E (1:2) ratio were similar for both groups. Primary outcome variable was PaCO2 < 45 mmHg and PaO2 > 80 mmHg which were determined by taking serial ABG samples. Postoperative pulmonary morbidity was sought in all the participants. Results: All patients returned satisfactory oxygen saturation and arterial partial pressure of oxygen (PaO2) (Figure. 1). In the AO group, after creation of pneumoperitoneum with the exception of three patients who had hypocapnia, rest all maintained partial pressure of carbon dioxide (PaCO2) within the normal range (Figure.2). Three patients had hypercarbia (range: 52-54 mmHg) one hour after the first ABG measurement. Largely, the acid base balance was within the normal range in most patients. One patient was excluded from study, as he required RM for ABG optimization. IBW group patients were hypocapnic, but maintained oxygenation. No patient in the IBW group was excluded from study. Intraoperative haemodynamics were maintained within normal range in all the patients. Both ventilation strategies resulted in satisfactory oxygenation. AO based regimen gave satisfactory gas exchange in majority of patients. Ventilation regimen using IBW resulted in hyperventilation. No patient had pulmonary shortcoming. Conclusion: The ventilation strategy based on waist circumference returned superior gas exchange (no hyperventilation), it holds promise for being proposed as safe and effective alternative to conventional ventilation option. Disclosure of Interest: None declared