Background: When an anesthetized patient is turned to the prone position using the Wilson frame, dynamic compliance (Cdyn) decreases and peak airway pressure (Ppeak) increases. As pressure-controlled ventilation (PCV) decreases the Ppeak, this prospective, randomized study was designed to compare the effect of PCV and volume-controlled ventilation (VCV) on lung mechanics in the prone position using the Wilson frame during posterior lumbar spine surgery.
Methods: Forty patients scheduled for posterior lumbar spine surgery were randomly allocated to receive mechanical ventilation using either the VCV (n=20) or PCV (n=20) mode. Respiratory variables (including Ppeak and Cdyn) and oxygenation parameters were recorded at the supine position (Tsupine) and 30 minutes after prone positioning (Tprone).
Results: During the study period, tidal volume, minute volume, end-tidal carbon dioxide tension, and positive end-expiratory pressure were comparable between the 2 groups. The Ppeak in the PCV group was lower than that in the VCV group throughout the study period (P=0.007 and 0.003 at Tsupine and Tprone, respectively) and was increased at Tprone compared with Tsupine in both groups. Cdyn was decreased from Tsupine to Tprone in both groups. However, the Cdyn in the PCV group was higher than that in the VCV group during the study period. The arterial oxygen tension was comparable between the 2 groups during the study period.
Conclusions: PCV provides lower Ppeak compared with VCV when the ventilator is set to deliver the same tidal volume and variable respiratory rate to maintain a constant end-tidal carbon dioxide tension in patients undergoing posterior lumbar spine surgery in the prone position using the Wilson frame.