Intrathecal opioids for hypotensive anaesthesia in children during posterior spinal fusion

Abstract

Intra-operative bleeding during spinal fusion is a serious problem. Factors influencing the amount of blood loss include extent of dissection, numbers of vertebrae fused, decortication, surgical technique and length of surgery. Hypotensive anaesthesia and haemodilution have been used to decrease blood loss during spinal fusion surgery. Two homogenous groups with 40 patients each (ASA I or II) undergoing posterior spinal fusion for idiopathic scoliosis were compared prospectively. After the induction of anaesthesia, group A received 20 μg kg−1 of morphine mixed with 50 μg of sufentanil diluted with 2 cc of normal saline intrathecally. Group B had standard anaesthesia with inhalation and narcotic technique. Intra-operative blood loss was determined by weighing sponges, measuring suction drainage, and estimating the amount of blood loss in the surgical field. Blood pressure was monitored continuously with an intra-arterial line. Group A had considerably less blood loss than group B (27.5% of blood volume vs. 53.5% in group B; P<0.001). Data regarding age, surgical procedure, weight, and sex were similar in both groups. Use of intrathecal opioids resulted in significantly reduced blood pressures in group A (mean 50-55 mmHg). Lower blood pressures were probably a result of the local-anaesthesia-type action of opioid drugs on the autonomic system [1] causing reduced vascular resistance. The mean arterial pressure (MAP) in group B ranged from 60-70 mmHg. Haemodynamic responses were less variable in group A, with fewer MAPs above 55 mmHg. Mean blood loss was 911.37 mL in group A and 1897.79 mL in group B. This study supports the concept that reduction in arterial blood pressure could be due to the localanaesthesia-type effect of intrathecal opioids. Studies have shown that the compound action potential of isolated nerve preparations can be blocked when exposed to high concentration of fentanyl or sufentanil [2]. In this study blockade of A and C fibres seemed to be concentration-dependent. In conclusion, we feel that intrathecal opioids are a safe choice for producing hypotensive anaesthesia to reduce blood loss and the number of homologous transfusions during spinal fusion surgery.