Comparison of hypertonic saline (5%), isotonic saline and Ringer's lactate solutions for fluid preloading before lumbar extradural anaesthesia

Abstract

We have compared the haemodynamic effects of fluid preloading performed before lumbar extradural anaesthesia with isotonic saline (NS), 5% hypertonic saline (HS) and Ringer's lactate (RL) solutions in 30 ASA I patients undergoing minor orthopaedic surgery, allocated randomly to the three groups. All patients received an equal amount of sodium (2 mmol kg-1). After fluid preloading, lumber extradural anaesthesia was performed (2% lignocaine 6 mg kg-1) and ephedrine was administered in order to maintain mean arterial pressure (MAP) > 80% of its control value. Both volume and duration of fluid preload were significantly less in group HS (160 (SD 25) ml, 8.8 (SD 2.9) min) than in the two other groups (NS: 903 (144) ml, 17.7 (3.3) min; RL: 932 (166) ml, 212 (6.0) min) (P < 0.05). The number of blocked segments and the total amount of ephedrine administered were similar in the three groups. Heart rate increased significantly in all groups immediately after the fluid preload and remained increased until the end of the study (90 min). MAP was not affected by any fluid preload and its maximal decrease after lumbar extradural anaesthesia was similar in all groups. Infusion of 5% HS 2.3 ml kg-1 was tolerated well and produced a significant (P < 0.05) but moderate hypernatraemia lasting 90 min after the end of fluid preloading. We conclude that HS may be useful when rapid fluid preloading is desired, in situations where excess free water administration is not desired.