An In Vivo Study of Halothane Uptake and Elimination in the Rat Brain with Fluroine Nuclear Magnetic Resonance Spectroscopy

A recent NMR study reported the elimination of halothane from the brain of rabbits to be ten times slower than expected, based on known anesthetic solubility and cerebral blood flow. The authors conducted a study in five rats using fluorine nuclear magnetic resonance (NMR) spectroscopy to see if major pharmacokinetic discrepancies are associated with the uptake, maintenance, and elimination of halothane from the brain. The rats underwent a 60-min period of halothane anesthesia. They employed a spatially selective NMR spectroscopy technique known as surface coil “depth-pulsing” to assure that the fluorine NMR signals originated in brain tissue, and not in the scalp, muscle, adipose tissue, and bone marrow that surround the brain. After the inspired anesthetic concentration was decreased to zero, the amplitude of the fluorine NMR signal decreased to 40% of its maximum value within 34 ± 8.0 minutes (n = 5), rather than after 7 h as in the recent study, where the fluorine signal may have contained substantial contributions from metabolites tissues outside the brain. Fluorine was barely detectable in all of the animals 90 min after stopping the administration of halothane. The author's results are in agreement with model calculations the several other investigations.