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Measurement of cerebral blood flow and volume with positron emission tomography during isoflurane administration in the hypocapnic baboon.

Using positron emission tomography, cerebral blood flow (CBF) and cerebral blood volume (CBV) were measured after the addition of isoflurane (1.3 vols %, end-tidal concentration) to neuroleptanesthesia (fentanyl/droperidol) in hypocapnic baboons. The study was designed to determine whether isoflurane, when administered during hypocapnia, acted as a cerebral vasodilator to increase either CBF or CBV. Mean arterial pressure was maintained within 10% of preisoflurane levels with an angiotensin infusion. In the first protocol (A), CBF and CBV were measured as close together in time as possible in order to detect divergent effects of isoflurane on these variables. When PaCO2 was reduced from 40 mmHg to 25 mmHg, CBF decreased from 44 +/- 4 to 31 +/- 4 ml.100 g-1.min-1 (P less than 0.05) and CBV decreased from 3.1 +/- 0.3 to 2.6 +/- 0.3 ml/100 g (P less than .05). Neither CBF nor CBV was significantly changed by the addition of isoflurane. In the second protocol (B), serial CBV scans were performed frequently during the addition of isoflurane in a fashion designed to detect transient changes in CBV at the time isoflurane was first added to the breathing circuit. Induction of hypocapnia again reduced CBV from 3.1 +/- .3 to 2.7 +/- .2 ml/100 g, (P less than .05) and addition of isoflurane did not change CBV. From these results the authors conclude that in the normal hypocapnic baboon the addition of 1.3% isoflurane does not significantly change cerebral blood flow or volume.