ADAPTIVE LUNG VENTILATION (ALV) DURING ANESTHESIA FOR PULMONARY SURGERY - AUTOMATIC RESPONSE TO TRANSITIONS TO AND FROM ONE-LUNG VENTILATION

Adaptive lung ventilation is a novel closed-loop-controlled ventilatio n system. Based upon instantaneous breath-to-breath analyses, the ALV controller adjusts ventilation patterns automatically to momentary res piratory mechanics. Its goal is to provide a preset alveolar ventilati on (V'A) and, at the same time, minimize the work of breathing. Aims o f our study were (1) to investigate changes in respiratory mechanics d uring transition to and from one-lung ventilation (OLV), (2) to descri be the automated adaptation of the ventilatory pattern. Methods. With institutional approval and informed consent, 9 patients (33-72 y, 66-8 8 kg) underwent ALV during total intravenous anesthesia for pulmonary surgery. The ALV controller uses a pressure controlled ventilation mod e. V'A is preset by the anesthesiologist. Flow, pressure, and CO2 are continuously measured at the DLT connector. The signals were read into a IBM compatible PC and processed using a linear one-compartment mode l of the lung to calculate breath-by-breath resistance (R), compliance (C), respiratory time constant (TC), serial dead space (VdS) and V'A. Based upon the results, the controller optimizes respiratory rate (RR ) and tidal volume (VT) such as to achieve the preset V'A with the min imum work of breathing. In addition to V'A, only PEEP and FIO2 setting s are at the anesthesiologist's discretion. All patients were ventilat ed using FIO2 = 1,0 and PEEP = 3 cm H2O. Parameters of respiratory mec hanics, ventilation, and ABG were recorded during three 5-min periods: 10 min prior to OLV (I), 20 min after onset of OLV (II), and after ch est closure (III). Data analyses used nonparametric comparisons of pai red samples (Wilcoxon, Friedman) with Bonferroni's correction. Signifi cance was assumed at p < 0.05. Values are given as medians (range). Re sults. 20 min after onset of OLV (II), resistance had approximately do ubled compared with (I), compliance had decreased from 54 (36-81) to 5 0 (25-70) ml/cm H2O. TC remained stable at 1.4 (0.8-2.4) vs. 1.2 (0.9- 1.6) s. Institution of OLV was followed by a reproducible response of the ALV controller. The sudden changes in respiratory mechanics caused a transient reduction in VT by 42 (8-59) %, with IIR unaffected. In o rder to reestablish the preset V'A, the controller increased inspirato ry pressure in a stepwise fashion from 18 (14-23) to 27 (19-39) cm H2O , thereby increasing VT close to baseline (7.5 (6.6-9.0) ml/kg BW vs. 7.9 (5.4-11.7) ml/kg BW). The controller was, thus, effective in maint aining V'A. The minimum PaO2 during phase II was 101 mmHg. After chest closure, respiratory mechanics had returned to baseline. Conclusions. Respiratory mechanics during transition to and from OLV are character ized by marked changes in R and C into opposite directions, leaving TC unaffected. The ALV controller manages these transitions successfully , and maintaines V'A reliably without intervention by the anesthesiolo gist. VT during OLV was found to be consistently lower than recommende d in the literature.