Canadian Journal of Anesthesia, Vol 32, 491-498, Copyright © 1985 by Canadian Anesthesiologists' Society

Responses of EEG, Cerebral Oxygen Consumption and Blood Flow to Peripheral Nerve Stimulation During Thiopentone Anaesthesia in the Dog

¹ Department of Anesthesiology, Yamaguchi University School of Medicine, Ube, Yamaguchi, Japan

Address correspondence to: Yoshitoyo Miyauchi, Department of Anesthesiology, Yamaguchi University School of Medicine, 1144 Kogushi, Nishi-ku, Ube, Yamaguchi, 755, Japan.

The effects of sciatic nerve stimulation on the electroencephalogram (EEG), cerebral metabolic rate for oxygen (CMRO₂) and cerebral blood flow (CBF) were investigated during thiopentone anaesthesia in dogs. Anaesthetic levels at 15, 35, 65, 95 and 125 minutes after the start of thiopentone infusion (23 mg·kg^-1·hr^-1) were designated levels I, II, III, IV and V, respectively. The effects of stimulation for 5 min were tested at each level. At level I (plasma thiopentone concentration; 15 ± 2 µg·ml^-1), the EEG was activated with stimulation and CMRO₂ and CBF increased by a maximum of 16 and 15 per cent, respectively. The increase in CMRO₂ and CBF was significant for five and four minutes, respectively, though the increase became less with time. At level II (27 ± 3 µg·ml^-1), the CMRO₂ and CBF increased at one minute by eight and nine per cent, the increase being accompanied by transient EEG activation. At the three deepest levels III, TV and V (37 ± 6, 42 ± 6, 49 ± 6 µg·ml^-1), the EEG, CMRO₂ and CBF remained unchanged with stimulation. The results suggest the existence of the tight coupling between the EEG, CMRO₂ and CBF and of a threshold level of thiopentone to block the response to peripheral stimulation during thiopentone anaesthesia.

Key Words: ANAESTHETICS, INTRAVENOUS: thiopentone. BRAIN: electroencephalogram • stimulation, BRAIN: blood flow, metabolism