Oral clonidine prolongs lidocaine spinal anesthesia in human volunteers.
BACKGROUND
Premedication with oral clonidine may improve the quality and duration of lidocaine spinal anesthesia, but this effect has not been examined in a quantitative fashion.


METHODS
Eight volunteers received 50 mg lidocaine (1.5% dextrose free) both with and without 0.2 mg oral clonidine 1.5 h before spinal anesthesia in a randomized, double-blind, placebo-controlled, crossover fashion. Sensory block was assessed by pinprick, transcutaneous electric stimulation equivalent to surgical incision, and duration of tolerance to pneumatic thigh tourniquet. Motor block at the quadriceps and gastrocnemius muscles was assessed by isometric force dynamometry. Episodes of bradycardia, hypotension, and sedation were recorded.


RESULTS
Regression of pinprick was unchanged with clonidine. However, duration of tolerance to electric stimulation was increased at the knee (28 +/- 24 min) and ankle (31 +/- 28 min) with clonidine (P < 0.05). The duration of tolerance to tourniquet-induced pain was increased with clonidine (14 +/- 12 min; P < 0.05). The duration of motor block was increased at the quadriceps (20 +/- 13 min) and gastrocnemius (33 +/- 24 min) muscle groups with clonidine (P < 0.05). Although clonidine decreased systolic blood pressure (13 +/- 4 mmHg, P < 0.003) and heart rate (13 +/- 5 beats/min; P = 0.02), no subjects had hypotension or bradycardia. The incidence of sedation was greater with clonidine than with plain lidocaine (50% vs. 0%, P < 0.04).


CONCLUSIONS
Premedication with oral clonidine prolonged sensory and motor block from lidocaine spinal anesthesia. The exact mechanism whereby oral clonidine prolongs spinal anesthesia remains to be determined.
Liu
S
S
Department of Anesthesiology, Virginia Mason Medical Center, Seattle, Washington 98111, USA.
Chiu
A A
AA
Neal
J M
JM
Carpenter
R L
RL
Bainton
B G
BG
Gerancher
J C
JC
D000284:Administration, Oral; D000775:Anesthesia, Spinal; D003000:Clonidine / Q000494:pharmacology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D006801:Humans; D008012:Lidocaine / Q000494:pharmacology*; D011229:Preanesthetic Medication; D013997:Time Factors
D008012:Lidocaine; D003000:Clonidine