[Evaluation of urine specific gravity as an index of hypotension after spinal anesthesia for cesarean section]

Although most cesarean sections are done under spinal anesthesia, we often experience severe hypotension. Fluid resuscitation is usually carried out for prevention of hypotension, but it is difficult to assess the suitable infusion volume. We examined whether the urine specific gravity can predict hypotension after spinal anesthesia for cesarean section.

Ninety nine patients (ASA 1 or 2) undergoing elective cesarean section were recruited. After dural puncture, we collected the cerebrospinal fluid and injected 2 ml of hyperbaric 0.5% bupivacaine. Thereafter urethral catheters were inserted, and then we collected the urine sample. The specific gravity of each sample was measured by using refractometer after the operation.

There was a good correlation between the urinary output and the urine specific gravity. The minimum systolic blood pressure until delivery, the total dose of ephedrine, and the maximum sensory block level showed a significant, but not particularly strong correlation with the urine specific gravity.

We concluded that it was difficult to predict hypotension by using urine specific gravity because the correlation was too weak.