Mechanical Ventilation of the Critically Ill Obese Patient-A Retrospective Cohort Study.

Abstract

Mechanical ventilation of severely ill obese patients can be difficult due to altered physiology, and clinical guidelines are lacking. This study aimed to investigate current practices for mechanical ventilation of obese patients in a Danish ICU. This retrospective study analyzed data from the Metabolomics Cohort, a single-centre ICU cohort of critically ill patients. We included patients receiving mechanical ventilation > 12 h and estimated the effect of body mass index (BMI) on ventilator settings, ventilator measurements, and ventilation blood gas parameters. We used linear and mixed-effects linear regression for admission and 5-day changes and adjusted for age, gender, Simplified Acute Physiology Score III, pneumonia, chronic obstructive pulmonary disease, diabetes, and chronic heart disease. Of the 577 patients included in the Metabolomics Cohort, 242 (41.9%) were included in this study. A one-unit increase in BMI resulted in an increase in admission positive end-expiratory pressure (PEEP) of 0.14 cmH₂O (95% CI: [0.07, 0.2], p < 0.01), minute volume of 0.08 L/min (95% CI: [0.03, 0.13], p < 0.01), peak inspiratory pressure of 0.23 cmH₂O (95% CI: [0.12, 0.34], p < 0.01), mean pressure of 0.18 cmH₂O (95% CI: [0.1, 0.27], p < 0.01) and a decrease in admission PaO₂/FiO₂ ratio of 0.38 (95% CI: [-0.64, -0.13], p < 0.01). During the first 5 days of mechanical ventilation, a one-unit increase in BMI resulted, on average, in an increase in PEEP of 0.14 cmH₂O (95% CI: [0.08, 0.2], p < 0.01), minute volume of 0.09 L/min (95% CI: [0.05, 0.12], p < 0.01), tidal volume/kg predicted body weight (PBW) of 0.08 mL/kg PBW (95% CI: [0.05, 0.1], p < 0.01), peak inspiratory pressure of 0.23 cmH₂O (95% CI: [0.13, 0.32], p < 0.01), mean pressure of 0.2 cmH₂O (95% CI: [0.12, 0.27], p < 0.01), PaCO₂ of 0.05 kPa (95% CI: [0.03, 0.07], p < 0.01) and a decrease in PaO₂ of 0.07 kPa (95% CI: [-0.12, -0.03], p < 0.01). In critically ill patients, an increasing BMI was associated with higher ventilator settings, increased airway pressures, and impaired gas exchange, resulting in hypoxia and hypercapnia. Future research should clarify the clinical impact of this and the potential for improved treatment of obese patients in critical care. This retrospective analysis, from a single center study cohort of critically ill obese patients requiring mechanical ventilatory support, and from the pre-pandemic period, characteristics of the cases and ventilatory parameters are presented. Patterns for ventilatory changes over time in the ICU are also shown.