Clonidine premedication for isoflurane-induced hypotension. Sympathoadrenal responses and a computer-controlled assessment of the vapour requirement.
The effect of single-dose clonidine premedication on the vapour requirement for isoflurane-induced hypotension in patients undergoing middle ear or nasal surgery was evaluated in an open, controlled, randomized study. Inspired isoflurane concentration was regulated by a microcomputer-based, self-tuning control program when hypotension was required. Patients given clonidine 0.6 mg by mouth 2 h before operation required a mean inspired isoflurane concentration of 2.0% to induce hypotension (mean intra-arterial pressure 50 mm Hg) compared with 3.01% in the control group (P less than 0.05). Five out of 10 patients in the control group required a supplementary dose of labetalol 5 mg i.v. to achieve satisfactory hypotension, compared with one of 10 patients given clonidine premedication (Fisher's exact probability, 0.07). A mean concentration of 1.4% isoflurane was required to maintain hypotension in the clonidine group, compared with 2.3% in the control group (P less than 0.01). Plasma adrenaline and noradrenaline concentrations did not increase during induced hypotension in each group.
Woodcock
T E
TE
Sir Humphry Davy Department of Anaesthesia, University of Bristol, Bristol Royal Infirmary.
Millard
R K
RK
Dixon
J
J
Prys-Roberts
C
C
D000293:Adolescent; D000328:Adult; D001794:Blood Pressure; D002986:Clinical Trials as Topic; D003000:Clonidine; D004432:Ear, Middle / Q000601:surgery; D004837:Epinephrine / Q000097:blood; D005260:Female; D006801:Humans; D007023:Hypotension, Controlled; D007530:Isoflurane / Q000008:administration & dosage*; D008297:Male; D008838:Microcomputers; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D009666:Nose / Q000601:surgery; D011229:Preanesthetic Medication; D011897:Random Allocation
D007530:Isoflurane; D003000:Clonidine; D009638:Norepinephrine; D004837:Epinephrine