Urine specific gravity during general anesthesia

BACKGROUND: The urine volume and urine specific gravity per unit time during a short operation under volume loading were examined to explore the possibility of urine specific gravity as an indirect index of fluid therapy. METHODS: After introducing anesthesia, under volume loading with acetic acid Ringer solution 10 ml x kg(-1) x hr(-1), urine volume and specific gravity per unit time at 30 min intervals from urination to 90 min later and the correlation between the urine volume and urine specific gravity were examined. A chronological increase of urine specific gravity was also confirmed. Therefore, the values of urine specific gravity of each 30 minute intervals were compared using Student's t-test. RESULTS: The urine volume and urine specific gravity per unit time showed no significant negative correlation until after 90 min. Increasing urine specific gravity even under volume loading became significant 90 min after urination. CONCLUSIONS: There is a possibility of employing urine specific gravity as an indirect index of fluid therapy.