One-lung ventilation in dogs. Effect of positive end-expiratory pressure on oxygen delivery with closed and open chest

Abstract

Selective ventilation of one lung (OLV) significantly decreases PaO2 and SaO2, and increases QS/QT. A rapid way to improve oxygenation during OLV is PEEP. The ultimate variable to evaluate oxygenation of peripheral tissues and vital organs is DO2. The objective of this research is to evaluate the effects of OLV and PEEP in dogs on DO2 with closed and open chest. Seven clinically normal adult dogs were anesthetized and catheters were inserted in the dorsal pedal and pulmonary arteries. Dogs were positioned in right lateral recumbency. After reaching baseline (PaCO2 of 35 to 45 mm Hg), data was collected for closed chest during TLV, and OLV with 0 PEEP, PEEP2.5 and PEEP5. Two-lung ventilation with 0 PEEP was resumed, and after a left thoracoscopic approach, the same set of data was retrieved for open chest. An equilibration period of 15 minutes was allowed before collection of data for each point. Statistical analysis was done with an ANOVA for repeated measures. During closed chest, OLV induced a significantly increased QS/QT (P = 0.002), and reduced PaO2 (P < 0.001), SaO2 (P = 0.002), and CaO2 (P < 0.001). Cardiac index was not altered, resulting in nonsignificant changes in DO2. Positive end-expiratory pressure during closed chest OLV significantly decreased QS/QT (P = 0.015) and increased SaO2 (P = 0.022). However, it failed to significantly affect CaO2 or CO. Thus, DO2 was not significantly affected. Interaction between OLV and closed-open chest was significant for QS/QT (P = 0.034), PaO2 (P = 0.006), CaO2 (P = 0.005), and PA-aO2 (P = 0.008), but not for SaO2 (P = 0.211). Other cardiopulmonary variables were not affected. As a net result DO2 was not significantly altered. Interaction between OLV-PEEP2.5-PEEP5 and closed-open chest was significant for PAWP (P = 0.010) and MPAP (P = 0.004), but it did not affect other variables. As a net result DO2 was not significantly changed. It was concluded that OLV and the use of PEEP2.5 and PEEP5 during OLV in anesthetized healthy dogs with a closed or open thoracic cavity does not affect DO2.