Influence of protective lung ventilation on arterial-to-end tidal carbon dioxide gradient during one lung ventilation: A prospective observational study

Abstract

Background: One lung ventilation (OLV) results in a ventilation-perfusion (V/Q) mismatch. Protective lung ventilation (PLV) reduces postoperative pulmonary complications following OLV. However, PLV predisposes to areas of atelectasis in the ventilated lung and worsens the V/Q mismatch. Aim of Study: To evaluate the gradient between arterial carbon dioxide tension (PaCO2) and partial pressure of end-tidal carbon dioxide gas (ETCO2) during OLV using PLV. The second objective was to see if a high gradient could be predicted based on preoperative pulmonary function tests (PFTs), American Society of Anesthesiologists Physical Status (ASA-PS) or intraoperative haemodynamic changes. Patients and Methods: The PaCO2 and ETCO2 during two lung ventilation (TLV) and OLV were noted with patient in the lateral position. The PaCO2-ETCO2 gradients during TLV and OLV were calculated. The mean values of PaCO2, ETCO2 and PaCO2-ETCO2 gradient were compared for OLV and TLV. For gradients above 8 mm Hg, PFT, ASA-PS grade and blood pressure were assessed to identify any clinical association. Results: Sixty patients were enrolled in the study. The mean values of PaCO2 were 38.17 and 44.02 mm Hg during TLV and OLV respectively. The mean values of ETCO2 were 31.31 and 34.53 mm Hg during TLV and OLV respectively. The mean PaCO2-ETCO2 gradient was 6.74 and 9.71 mm Hg during TLV and OLV respectively. These values were significantly lower during TLV than OLV. Conclusion: ETCO2 does not correspond with PaCO2 during OLV using PLV. It is not possible to predict which patients will show a higher PaCO2-ETCO2 gradient. This study could not find any clinical association between the preoperative PFT, ASA-PS grade or intraoperative haemodynamics when PaCO2-ETCO2 gradient was greater than 8 mm Hg.