The Effect of Prolonged Inspiratory Time on Pulmonary Mechanics in Obese Patients

The area of aesthesia-induced atelectasis is much larger in the obese compared with the non-obese, but there may also be more airway closure and impaired matching of ventilation and lung blood flow. When an anesthetized patient is turned to the prone position, dynamic compliance (Cdyn) decreases and peak airway pressure increases unless the abdomen hangs freely to prevent the abdominal viscera from compromising the diaphragm movement. Although the Wilson frame is designed to allow the abdomen to hang, it partially compresses the anterior abdominal wall and therefore does not allow the abdomen to hang completely, especially in obese patients. This in turn increases peak airway pressure and decreases Cdyn, oxygenation. This study aimed to investigate the effects of a prolonged I:E ratio (i.e., 1:1) compared with the conventional I:E ratio of 1:2 on respiratory mechanics and hemodynamics during spine surgery in the prone position in obese patients. We hypothesized that, compared with an I:E ratio of 1:2, a ratio of 1:1 improve oxygenation without hemodynamic instability .