IS ALPHA-CHLORALOSE PLUS HALOTHANE INDUCTION A SUITABLE ANESTHETIC REGIMEN FOR CEREBROVASCULAR RESEARCH

The aim of this study was to determine whether alpha-chloralose, when associated with an initial period of halothane, is a suitable anesthet ic regimen for cerebrovascular studies. For this purpose, rats anesthe tized with alpha-chloralose plus halothane induction were first subjec ted to noxious stimuli, and the behavior, EEG and systemic variables w ere recorded. During a second step, cortical blood flow was measured w ith laser-Doppler flowmetry and the time-course of the cerebrovascular reactivity to hypercapnia were measured in artificially ventilated ra ts anesthetized with either alpha-chloralose (40 mg.kg(-1), s.c.) plus halothane induction (1.5% given during the first 45-60 min) or haloth ane alone (1.5%). Finally, an experimental paradigm was developed that allowed the comparison of the hypercapnic reactivity, both in awake a nd anesthetized conditions in the same animal. Our results show that t he association of alpha-chloralose with halothane leads to stable card iovascurar parameters and immobility of ventilated rats, placed in ear bars without curare, for 3 h without any sign of discomfort. Based on EEG criteria, we found that halothane induction lengthens the duratio n of alpha-chloralose anesthesia (253 +/- 19 vs. 200 +/- 15 min, P < 0 .01). Under alpha-chloralose alone or in association with halothane in duction, the vascular reactivity to hypercapnia was considerably impai red (-85% compared to the awake state, P < 0.01), but this impairment was transient, since a control reactivity was restored 150-190 min aft er induction of anesthesia. Under halothane alone, the vascular reacti vity remained reduced throughout the experiment. These results provide evidence that alpha-chloralose plus halothane induction is a suitable anesthetic regimen which displays a temporal window of normal cerebro vascular reactivity.