Ventilation and Perfusion of Each Lung during Differential Ventilation with Selective PEEP

Open Access
Publisher Website
Google Scholar
Abstract
Lung perfusion was studied in 10 patients (mean age 48 yr) in the lateral position during enflurane anesthesia. They were ventilated through a double-lumen endotracheal catheter; by 1 ventilator with free distribution of ventilation between the lungs, with no (zero) end-expiratory pressure (ZEEP); as above but with a general positive end-expiratory pressure (PEEP) of 9 cmH2O; or by 2 ventilators with equal distribution of ventilation between the lungs and with a selective PEEP of 8 cmH2O to the dependent lung only. Total ventilation was on average 8 l/min (BTPS) throughout the study. During the 1st method, 34% of ventilation was distributed to the dependent and 66% to the nondependent lung. Cardiac output (thermodilution) was 4.5 l/min, 57% being distributed to the dependent lung as assessed by i.v. boli of 133Xe. During the 2nd method, ventilation was assumed to be distributed equally between the lungs. Cardiac output was decreased to 3.8 l/min, and the dependent lung received 81% of lung blood flow. During the 3rd method, cardiac output was significantly greater than during the 2nd method (4.1 l/min), 51% passing to the dependent lung. Peak and end-inspiratory airway pressures were 5-18 cmH2O lower during selective than during general PEEP. Arterial O2 tension was significantly greater during the 3rd method than during either of the other ventilator settings and the alveolar-arterial O2 tension difference was almost halved compared with the 1st method. Differential ventilation with selective PEEP evidently improves ventilation-perfusion matching and thus oxygenation.