Global Cerebral Hypoperfusion and Paco2

Abstract

We appreciate Olivé and Noquer’s comments regarding our article (1). From the data of our study, one may observe that of the three patients in the propofol group who had Paco2 values <31 mm Hg, all had a jugular bulb saturation Sjo2 <40%. Of the seven patients with Pco2 values >31 mm Hg, three had Sjo2 of 50% and lower, whereas two of these three patients had Paco2 values of 36 and 37 mm Hg. A broad range of Paco2 values that are clinically acceptable during neurosurgery, thus may be responsible for low Sjo2 values. The study by Schaffranietz and Heinke (2), quoted by Olivé and Noquer, shows that patients who underwent brain tumor surgery under propofol anesthesia and ventilated with oxygen in air at Paco2 levels of <31 mm Hg, had Sjo2 values <50%. From these results, the authors stated that the lower Paco2 limit from ventilation should be fixed at 32 mm Hg, tacidly implicating that low Sjo2 values, indicating global cerebral hypoperfusion, would not occur at Paco2 levels >32 mm Hg. However, in Schaffranietz and Heinke’s (2) study of 60 brain tumor patients, a certain number of patients were excluded from further study because of primary low jugular venous oxygen saturation of <50%, probably at relative normoventilation. These excluded patients might have been exactly those patients in our study who showed Sjo2 <50% at the higher Paco2 levels of 35 mm Hg and above. Of the isoflurane/nitrous oxide group in our study, all patients had Paco2 >31 mm Hg. No patients showed Sjo2 <50%. This is also confirmed by a study of Matta et al. (3) in 12 brain tumor patients anesthesized with isoflurane (0.5%–1.0%) in an O2-air mixture. At Paco2 values of 30 mm Hg and Pao2 values of 100 mm Hg, none of those patients had Sjo2 <50%. Thus, not only the results of our study, but also those of others, show data that suggest that during isoflurane/nitrous oxide anesthesia at Paco2 values >31 mm Hg, Sjo2 remains higher than 50%, although during propofol anesthesia, a certain number of patients consistently show Sjo2 values less than 50%. Whether these Sjo2 values under 50% will have any clinical consequences needs to be further investigated. Gerard F. A. Jansen MD Mohan B. Kedaria PhD MD Joseph A. Odoom PhD, MD Department of Anesthesiology Academic Medical Centre University of Amsterdam Amsterdam The Netherlands Bas H. van Praagh MD