Cardiac performance during unilateral lumbar spinal block after crystalloid preload

The haemodynamic effects of crystalloid preload were evaluated in a randomised blind study in 20 ASA status I-II, 50-80 yr-old patients, undergoing unilateral spinal anaesthesia for leg surgery produced with low doses of hyperbaric bupivacaine.

Baseline non-invasive blood pressure (oscillometry), heart rate, stroke volume and cardiac index (transthoracic electrical bioimpedance) were recorded. Then, patients were randomly allocated to receive 10 ml.kg-1 Ringer's Lactate solution over 20 min (preload group, n = 10) or no crystalloid infusion (no-preload group, n = 10). Spinal block was performed using 8 mg hyperbaric bupivacaine 0.5% injected slowly at the L2-L3 interspace (0.02 ml.sec-1 through a 25-gauge Whitacre needle) with patients lying on their operated side and with the needle opening directed towards the dependent side. Lateral decubitus position was maintained for up to 15 min after anaesthetic injection to facilitate hyperbaric bupivacaine distribution towards dependent regions of the subarachnoid space. Haemodynamic variables were recorded 5, 10, 15 and 30 min after spinal injection, while sensory level and motor block were evaluated 10, 15 and 30 min after anaesthetic injection on both operated and unoperated side.

No differences of upper sensory level and motor block were observed between the two groups on the operated and non-operated sides. Diastolic blood pressure was decreased compared with baseline in the no-preload group only (P = .0001). Systolic arterial pressure and heart rate did not change in either group. Stroke volume and cardiac index were decreased in the no-preload group compared with both baseline (P = .02; P = .001) and the preload group (P = .04; P = .02).

Crystalloid preload influences cardiovascular function during spinal block, and may be useful when very low bupivacaine doses and lateral decubitus are used to achieve unilateral spinal block.