Introduction: Biologic half life and pharmacokinetics of xenon are known fr
om application of xe(133) in nuclear medicine. In these investigations wash
out time constants were calculated after relatively short exposure times of
10-20 minutes. Investigations using xenon concentrations and exposure time
s as used in anaesthesia have not yet been carried out. We have investigate
d xenon uptake, distribution and elimination under conditions of experiment
al anaesthesia.
Materials and methods: 7 pigs were anaesthetized with a combination of intr
avenous pentobarbital and buprenorphine and an inspiratory concentration of
xenon 70%. Radioactive xenon(133) was used as tracer for inert xenon(134).
Washin and washout of xenon was observed under a gamma camera. Washin time
was 4 hours, washout time was 2 hours. Kinetic curves for all body compart
ments revealing different activity curves as the whole body were calculated
separately. Statistics were calculated using an empiric regression model.
Mean residence times (MRT), terminal half lives (t 1/2), biologic half live
s (t(50%)) and t(90%) were calculated for the compartments whole body, lung
, fatty tissue and bowel.
Results: As known from previous investigations, the fastest compartment was
the lung. The slowest compartments were fatty tissue and bowel, respective
ly. No other compartments revealed delays of excretion as compared to whole
body.
Discussion: Time constants like mean residence times and half lives were di
fferent as reported from investigations from nuclear medicine. The slowest
compartments were found to be fatty tissue and bowel. The reason for that f
inding is that in short exposures slow compartments are not saturated. Wash
out time constants calculated after short exposures cannot be easily transf
erred to conditions of xenon anaesthesia.