Background: For some surgical procedures a higher sensory block is needed. However, it is complicated by a higher incidence of hypotension, more bradycardia and nausea and a higher use of vasoactive drugs. In elderly and obstetric population complications have been attributed to the decrease in cardiac output and systemic vascular resistance, especially in a high block (above Th6). The aim of our study was to find the incidence of hypotension and bradycardia after a spinal anaesthesia in young, healthy patients. As young patients compensate more, we aimed to find the difference in haemodynamic variables between the group with a high and the group with a low spinal block and the underlying mechanisms of hypotension.
Methods: in a prospective, randomized study 44 ASA 1 patients scheduled for knee arthroscopy under spinal anaesthesia were randomly distributed to a high (group H) and a low (group L) spinal block group. In a group H patients were placed into horizontal, whereas in a group L in 15-degree anti-Trendelenburg position immediately after the spinal block. Haemodynamic parameters were measured continuously noninvasively from 10 min before to 25 min after the spinal block using the CNAPTM device with the LiDCORapid monitor.
Results: The differences in haemodynamic parameters between the groups were not statistically significant at all measured times despite a significant difference in the spinal block level (18.5 vs 13.3 dermatomes above S5, p<0.001) and a significant difference in haemodynamic variables inside each group compared to the baseline value. With cardiac index (CI) as a dependent variable, a significant correlation between CI and stroke volume index (SVI) was found (β=0.849, p<0.001) and also between CI and heart rate (HR) (β=0.573, p<0.001). In group H the incidence of hypotension was 35%, whereas in group L it was 10%. The same difference was seen in the use of phenylephrine between the groups, however the difference was not significant.
Conclusion: In our study it was found that in young, healthy patients there are no significant differences in haemodynamic parameters and in incidence of hypotension between a high and low spinal block. Young, healthy patients compensate a decrease in systemic vascular resistance caused by the spinal anaesthesia with a compensatory increase in CI resulting from an increase in SVI and HR. However, a trend towards less hypotension, less bradycardia and less frequent phenylephrine use in a low spinal block was noted.
Keywords: spinal anaesthesia, hyperbaric bupivacaine, haemodynamic parameters, cardiac output, hypotension