The effects of inhalation anaesthetics on common clinical pathology parameters in laboratory rats

Effects of common anaesthetics such as ether, methoxyflurane, isoflurane, carbon dioxide (at 100%, 80% or 60% admixed with O 2) on toxicity and clinical pathology parameters in rats were investigated. Ether, methoxyflurane and 100% CO 2 induced toxicity in some animals. Erythrocyte, haemoglobin and haematocrit were reduced in females by 100% CO 2, methoxyflurane and isoflurane. Glucose was increased by 60% CO 2, 80% CO 2, ether, isoflurane and methoxyflurane in males. Chloride was reduced by isoflurane and all CO 2 concentrations in females. Serum proteins were reduced by isoflurane and methoxyflurane. Sodium, inorganic phosphate, calcium and magnesium were reduced by methoxyflurane and isoflurane, but increased by all CO 2 concentrations. Potassium was reduced by ether, methoxyflurane or isoflurane. Triiodothyronine and thyroxine were reduced by all anaesthetics. Prolactin was reduced by methoxyflurane, but raised by ether and isoflurane. Erythrocyte cholinesterase (E-ChE) activity is markedly reduced (20–40%) after anaesthesia with all CO 2 concentrations in both sexes. E-ChE was unaffected by ether, methoxyflurane, or isoflurane. Serum and brain cholinesterase activities were not affected. E-ChE inhibition correlated with decreased blood pH, suggesting that this was caused by acidosis. This is of practical relevance in the risk assessment of cholinesterase inhibitors. Conclusions: Clinical pathology data were affected by all anaesthetics. CO 2/O 2 (80%/20%) and isoflurane are the most suitable anaesthetics. If E-ChE activity is to be determined, isoflurane is the anaesthetic of choice.