BEST PEEP DURING ONE-LUNG VENTILATION

Eight patients were studied under general anaesthesia for elective pul monary lobectomy to see if intrinsic positive end-expired pressure (PE EPi) would appear or increase in the dependent lung during one-lung ve ntilation (OLV) or if application of external PEEP equal to individual ly measured PEEPi would produce better arterial oxygenation, haemodyna mic state and oxygen delivery than either zero PEEP (ZEEP) or an exter nal PEEP 5 cm H2O greater than PEEPi. Patients were non-obese, without obstructive airways disease, aged 53-76 yr and ASA < III. They receiv ed standardized anaesthesia with fentanyl, 50% nitrous oxide in oxygen and isoflurane; monitoring included radial and fibreoptic pulmonary a rterial catheters and intermittent positive pressure ventilation with a tidal volume of 8 ml kg(-1), 16 bpm, and an I:E ratio of 1:2. PEEPi was measured during two-lung ventilation (TLV) and OLV, using rapid ai rway occlusion at end-expiration. There was no PEEPi during TLV, but 2 -6 mm Hg of PEEPi appeared during OLV. Applying external PEEP equal to individually measured PEEPi reduced venous admixture and increased Pa -o2 without a decrease in cardiac index (thus increasing oxygen delive ry) compared with ZEEP, but the improvement in pulmonary gas exchange was lost and an additional penalty of reduced cardiac output was impos ed when external PEEP was increased to 5 mm Hg above PEEPi.