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Cerebral normoxia in the rhesus monkey during isofluraneor propofol‐induced hypotension and hypocapnia, despite disparate blood‐flow patterns
Author(s) -
ENLUND M.,
ANDERSSON J.,
HARTVIG P.,
VALTYSSON J.,
WIKLUND L.
Publication year - 1997
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1997.tb04827.x
Subject(s) - hypocapnia , isoflurane , propofol , medicine , anesthesia , cerebral blood flow , oxygenation , blood pressure , hypercapnia , acidosis
Background: Due to a few reports of cerebral dysfunction in connection with isoflurane‐induced hypotension and concomitant hypocapnia, positron emission tomography (PET) was used to measure cerebral oxygenation and blood flow during similar conditions with isoflurane or propofol. Methods: The short‐lived radionuclide 15 O was used for measurement of cerebralmetabolic rate of oxygen (CMRO 2 ), cerebral blood flow (CBF) and oxygen extraction ratio (OER) regionally in rhesus monkeys during normotensive/normocapnic and hypotensive/hypocapnic conditions, mean arterial pressure 100–110 and 50–65 mmHg and P a CO 2 4.4–5.4 and 3.4‐4.4 kPa, respectively. Isoflurane or propofol anaesthesia was given (n=4 in both groups), supported with 70% nitrous oxide and preceded by ketamine anaesthesia (baseline). Results: PET revealed wide variations in CBF between regions during isoflurane anaesthesia, particularly in comparison with propofol anaesthesia, while rCMRO 2 decreased globally in a dose‐dependent manner during both isoflurane and propofol anaesthesia. The metabolism‐flow coupling was intact during propofol but not during isoflurane anaesthesia. Hypotension reduced rCBF, and rOER increased globally with both study drugs when changing from normo‐ to hypotension. However, this rOER increase was not significant when using PaCO 2 as a co‐variate, and rOER was never above an arbitrary limit for hypoxia of 70%. Thus, hypocapnia, rather than hypotension, was responsible for the somewhat higher rOER measured. Conclusion: PET indicated adequate cerebral oxygenation during isoflurane and propofol anaesthesia, despite disparate blood‐flow patterns. Hypotension and concomitant moderate hyperventilation reduced rCBF, but did not result in hypoxia.