DIURETIC EFFECT OF CLONIDINE DURING ISOFLURANE, NITROUS-OXIDE, AND OXYGEN ANESTHESIA

Background: Because clonidine, a relative selective alpha(2)-agonist, inhibits the action of arginine vasopressin (AVP), the authors examine d whether clonidine as an oral preanesthetic medication would induce d iuresis and also would affect AVP release and its action during genera l anesthesia. Methods: Fifty-seven patients (aged 18-65 yr) randomly r eceived oral clonidine either approximately 5 mu g.kg(-1) (n = 19), ap proximately 2.5 mu g.kg(-1) (n = 19), or none (n = 19) in addition to oral famotidine 20 mg, 90 min before arrival at operating room. Urine volume, urine osmolality, and amount of sodium and potassium excreted into urine were examined every hour for 3 h during minor surgery under general anesthesia with isoflurane and nitrous oxide in oxygen. For 5 patients of each group, plasma AVP and atrial natriuretic peptide con centrations and urine cyclic adenosine monophosphate concentrations as an index of AVP action were also assayed. Results: Urine output indic es (calculated as hourly urine output [milliliters per hour] divided b y body weight [kilograms]) were significantly greater in the all perio ds (P less than or equal to 0.035) after the initiation of anesthesia in the patients receiving clonidine 5 mu g.kg(-1) and only in the 3rd h in those receiving clonidine 2.5 mu g.kg(-1) (P = 0.047) as compared with those in the patients given famotidine alone. The peak effects o f diuresis and natriuresis induced by oral clonidine 5 mu g.kg(-1) wer e both observed at the 2nd h (mean +/- SEM, 2.4 +/- 0.4 ml.kg(-1).h(-1 ) and 5.7 +/- 1.5 mEq.h(-1) vs. 0.6 +/- 0.1 ml.kg(-1).h(-1) and 2.2 +/ - 0.5 mEq.h(-1) in the control subjects; P = 0.001 and P = 0.049). Kal iuresis also increased in the patients receiving clonidine 5 mu g.kg(- 1) in the 2nd and 3rd h (P less than or equal to 0.003). Urine osmolal ity showed a significant reduction over time in patients given clonidi ne but not in the control subjects. However, plasma AVP and atrial nat riuretic peptide levels, and urine cyclic adenosine monophosphate conc entrations did not significantly differ among the three groups. Conclu sions: Oral preanesthetic medication of clonidine 2.5 or 5 mu g.kg(-1) caused a significant diuretic effect during surgery under general ane sthesia, though it did not apparently relate to AVP action. This effec t of clonidine could be related to its pharmacological action as an al pha(2)-adrenoceptor agonist not necessarily restricted to the kidney. The diuretic effect of clonidine implicates its clinical importance in the management of patients during anesthesia.