Diuretic response to Ringer's solution is normal shortly after awakening from general anaesthesia: a retrospective kinetic analysis

BACKGROUND: The elimination of Ringer's solution is severely depressed during general anaesthesia, but the degree to which this continues postoperatively is poorly established. METHODS: An intravenous infusion of Ringer's acetate solution 20 ml kg(−1) was administered over 60 min in 12 patients undergoing laparoscopic cholecystectomy. Population kinetic analysis was performed based on repeated measurements of blood haemoglobin concentration and urinary excretion over 240 min regardless of when the operations were finished. The analysis contrasted the periods before and after awakening from general anaesthesia and compared them with data from 18 volunteers who received the same fluid at the same rate. RESULTS: Patients were monitored for approximately 2 h after awakening from general anaesthesia. The rate constant for redistribution of fluid from the extravascular space to the plasma (k(21)) and the rate constant for urinary excretion (k(10)) were significantly higher postoperatively than during the surgical period. Computer simulations indicated that urinary excretion after surgery was almost restored to the rate found in the volunteers. In contrast, the redistribution of fluid from the extravascular space to the plasma, which was almost nil during the surgery, showed only limited recovery during the postoperative phase, and was only approximately 10% of the flow rate found in the volunteers. The combination of nearly normalised urinary excretion and lack of adequate return of distributed fluid to the plasma promoted postoperative hypovolaemia. CONCLUSION: The kinetic analysis indicates that plasma volume support should be given during the first 2 h after laparoscopic cholecystectomy.