Background & Goal of Study: The efficiency of lung gas exchange deteriorates after induction of general anaesthesia due to increased ventilation-perfusion (V/Q) scatter. Blood gas data from studies in the setting of one lung anaesthesia suggests that propofol TIVA may preserve V/Q matching better than inhalational agents. We compared V/Q matching in patients under relaxant general anaesthesia randomized to either propofol TIVA or sevoflurane maintenance anaesthesia, using both Bohr deadspace and shunt fraction measurements and the MIGET (Multiple Inert Gas Elimination Technique) for characterization of V/Q dstributions.
Materials & Methods: Patients with clinical evidence of underlying lung disease were excluded. Baseline arterial blood sampling and collection of mixed expired gas was done before induction and repeated after 1-2 hours of relaxant general anaesthesia, supine with controlled ventilation at an FiO2 of 0.3 and a target end-tidal PCO2 of 30-35 mmHg and bispectral index range of 40-60. Blood samples for MIGET were processed by headspace equilibration in 20mL gas tight glass syringes at 36C, with measurement of partial pressures in expired and headspace gas samples by gas chromatography. The primary endpoint was comparison of the two groups in the change from baseline of absolute difference between log standard deviation (dδlogSD) of ventilation and blood flow distributions.
Results & Discussion: Data from 20 patients (10 in each group) to date was suitable for analysis. There were no significant differences between the two groups in baseline demographics or lung function indices. Mean Bohr alveolar deadspace fraction (standard deviation SD) increased from baseline across both groups with
anaesthesia [11.7 (9.1)% to 24.7 (4.8)%, p < 0.001) and the PaO2/FIO2 decreased [468 to 400 mmHg, log transformed p = 0.023), but shunt fraction (SD) was
not significantly changed [13.1 (10.0)% to 10.5 (6.4)%, p = 0.37]. Primary endpoint: dδlogSD (SD) was not different between TIVA and sevoflurane groups (0.17 (0.29)
versus 0.17 (0.85), p = 0.99).
Conclusions: We found no evidence that TIVA preserved V/Q matching in patients with normal lung function undergoing anaesthesia with controlled ventilation compared with sevoflurane. 

03 / Intravenous versus inhalational anaesthesia and lung ventilation-perfusion matching