Effects of hypertonic 75 mg/ml (7.5%) saline on extracellular water volumewhen used for preloading before spinal anaesthesia

Background: Prevention of hypotension during spinal anaesthesia is commonly achieved using fluid preloading. This may result in a substantial amount o f excess free water retained in the body after spinal anaesthesia. We aimed to evaluate the effects of 7.5% hypertonic saline on extracellular water v olume and haemodynamics when used for fluid preloading before spinal anaest hesia. Methods: This randomised double-blind study evaluated the effects of 75 mg/ ml (7.5%) hypertonic saline (HS) on extracellular water volume and haematoc rit in patients undergoing arthroscopy or other lower limb surgery under sp inal anaesthesia. Amounts of 1.6 ml/kg of HS (20 patients) or 13 ml/kg of 9 mg/ml normal saline (20 patients) were administered for preloading before spinal anaesthesia with a 10 mg dose of 0.5% hyperbaric bupivacaine. Etilef rine was administered in order to maintain mean arterial pressure (MAP) at greater than or equal to 80% of its baseline value. Whole-body impedance ca rdiography-derived cardiac index (CI) and extracellular water (ECW) were me asured. Results: There were no significant differences in demographic data or in th e number of blocked segments. ECW remained similar in both groups despite t he much smaller amount of infused free water in the HS soup. There were no significant differences between the groups in CI values during the study Th e amount of etilefrine administered was similar in the treatment groups. Di lution of haematocrit was also similar in both groups. Conclusion: Hypertonic 75 mg/ml (7.5%) saline is an alternative for preload ing before spinal anaesthesia in situations where excess free water adminis tration is not desired. It is effective in small doses of 1.6 ml/kg, which increase the extracellular water, plasma volume and cardiac output, and thu s maintain haemodynamic stability during spinal anaesthesia.