The Effect of Pressure Controlled Ventilation on Pulmonary Mechanics in Prone Patients Undergoing Elective Spine Surgeries: Comparative Study with Volume Controlled Ventilation

Abstract Background: As patients turned into prone position expe-rienced more decrease in lung compliance than those on supine position, this prospective, randomized study was designed to compare the effect of PCV and volume-controlled ventilation (VCV) on lung mechanics and heamodynamics in the prone position using the Wilson frame during elective lumbar spine surgery.
Patients and Methods: Sixty patients scheduled for elective lumbar spine surgery were randomly allocated to receive mechanical ventilation using either the VCV (n=30) or PCV (n=30) mode. Respiratory variables (peak airway pressure, mean airway pressure, shunt fraction, alveolar-arterial oxygen gradient). Dynamic compliance (Cdyn) of the respiratory system was calculated as VT/ (Ppeak-PEEP). The alveolar dead space-to-tidal volume ratio (VD/VT) will be estimated using the Hardman and Aitkenhead equation: VD/VT=1. 135– (PaCO2-ETCO2)/(PaCO2-0. 005). Results: The Ppeak in the PCV group was lower than that in the VCV group throughout the study period (p-value=0.961 and 0. 0.109 at supine position and prone position, respectively) and was increased at prone position compared with supine position in both groups. Cdyn was decreased from supine to prone position in both groups. However, the Cdyn in the PCV group was higher than that in the VCV group during the study period however it is only statistically significant after 1.5 and 2hrs. 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 pos-terior lumbar spine surgery in the prone position using the Wilson frame.