Introduction Morbid obesity and super obesity are associated with increasingly negative effects on respiratory parameters, but beyond BMI itself the physical predictors of difficult intraoperative ventilation have not been demonstrated. We performed a study to identify criteria for the prediction of difficult intraoperative mechanical ventilation in obesity patients.

Method We performed an observational study of 48 obese patients (BMI >35 kg/m²) undergoing laparoscopic surgery (bariatric, upper gastrointestinal and gynaecological). Patients with conditions likely to affect respiratory compliance, e.g. thoracic or spinal deformity were excluded.

We analysed biometric measurements such as age, sex, weight and BMI, waist, hip and neck circumferences, waist: hip ratio, STOP-BANG scores, presence of obstructive lung disease and pre-operative oxygen saturation measurements. Respiratory mechanics were assessed pre- and post-pneumoperitoneum using standard Pitot pneumotachograph measurements, including tidal volumes, peak pressures, positive end-expiratory pressure and dynamic respiratory compliance.

Differences in ventilator strategy (e.g. volume-control versus pressure-control and tidal volume delivered) were analysed post-hoc.

Results See Figures 1 and 2. Our study demonstrated a statistically significant correlation between BMI and increased peak pressures both pre- and post-pneumoperitoneum (p < 0.01, Figure 1). Additionally, BMI had a statistically significant negative correlation with respiratory compliance (p < 0.05, Figure 2).

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Abstract P109 Figure 1

Showing relationship between BMI and Peak Pressure. Peak Pressure: cmH₂O. BMI: kg/m². Our study demonstrated a statistically significant correlation between BMI and increased peak pressures both pre- and post-pneumoperitoneum (p < 0.01)

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Abstract P109 Figure 2

Showing relationship between BMI and Compliance. Compliance ml/cmH₂O and BMI kg/m²

Age, sex and absolute weight, neck, waist: hip ratio, waist and hip circumference had no correlation with intraoperative respiratory mechanics.

The difference between volume-controlled and pressure-controlled strategies were analysed and shown not to be significant.

Conclusion Our novel study shows increasing BMI has a negative influence on respiratory mechanics of the anaesthetised obese patient. It is important to stress that while BMI is the strongest predictor of increased peak pressure and reduced respiratory compliance, patient positioning and lung recruitment can have positive effects on respiratory mechanics. Further studies are needed to help identify predictors of difficult ventilation in obesity.