Effects of anaesthesia, hypercarbia and hypocarbia on regional cerebral blood flow in the goat.

Abstract

Regional cerebral blood flow (rCBF) was evaluated by radioactive microsphere indicator technique in unanaesthetized goats and in goats anaesthetized with ketamine, pentobarbitone and halothane. In addition, rCBF was studied in goats anaesthetized with halothane associated with hypercarbia and hypocarbia. Microsphere distribution in unanaesthetized goats demonstrated significant differences in rCBF of the following order and magnitude: thalamus, 151 ± 11 per cent; cerebral gray matter, 111 ± 14 per cent; cerebellum, 92 ± 17 per cent; hypophysia, 75 ± 4 per cent; cerebral white matter, 47 ± 4 per cent (100 per cent = average flow per gm brain). Microsphere distribution following anaesthesia indicated significant changes in relative rCBF to various regions. Ketamine (10 mg/kg) produced a relative decrease in thalamic flow (75 ± 31 per cent ) while increasing gray matter flow (21 ± 10 per cent). Pentobarbitone (35 mg/kg) produced a relative decrease in thalamic (38 ± 19 per cent), gray matter (27 ± 18 per cent), and hypophysis (24 ± 15 per cent) flow, with substantially higher relative flow to white matter (61 ± 23 per cent). Halothane (1.5 per cent) at normocarbia decreased relative thalamic flow (65 ± 28 per cent) but had no effect on other regions. Halothane (1.5 per cent) with hypocarbia decreased relative thalamic flow 65 ± 15 per cent) while increasing relative gray matter flow (42 ± 27 per cent). Halothane (1.5 per cent) with hypercarbia caused a relative increase in thalamic ( 68 ± 28 per cent ) and gray matter (55 ± 34 per cent ) flow. Based on these observations, it was concluded that the goat brain is a heterogeneously perfused organ, and that anaesthesia causes significant shifts in regional cerebral blood flow.