Effect of injection of air into the epidural space on subarachnoid puncture during combined spinal-epidural block

Abstract

Objective To investigate the effect of injection of air into the epidural space on the subarachnoid puncture during the combined spinal-epidural anesthesia (CSEA) .Methods Two hundred and ten ASA Ⅰ or Ⅱ parturients who were at full term with a singleton fetus, aged 20-42 yr, weighing 57-82 kg (height 152-170cm) , undergoing cesarean section under CSEA, were randomly divided into 3 groups ( n = 70 each) : hanging drop technique group (group Ⅰ ) and injection of small volume of air group (group Ⅱ ) and injection of large volume of air group ( group Ⅲ ) . The epidural space was indentified using hanging drop technique in group Ⅰ and using loss of resistance to air technique in Ⅱ and Ⅲ groups. Injection of air was stopped as soon as the clear loss of resistance identified the epidural space in group Ⅱ , whereas all 4 ml of air was injected in group Ⅲ . After the epidural space was confirmed at L3,4 interspace, a 25-gauge spinal needle protruding 14 mm beyond the 18-gauge epidural needle was introduced through the epidural needle. Subarachnoid placement was confirmed by backflow of cerebrospinal fluid (CSF) . If no backflow of CSF was observed, the spinal needle was withdrawn and an epidural catheter was inserted through the epidural needle to perform epidural anesthesia. Successful subarachnoid puncture, failures to observe backflow of CSF and adverse reactions were recorded. Results The three groups were comparable with respect to age, height, body weight and gestation weeks. The success rate of subarachnoid puncture was 91% ,93% and 79% in Ⅰ ,Ⅱ and Ⅲ groups respectively, and it was significantly higher in Ⅰ and Ⅱ groups than in group Ⅲ ( P 0.05) . Bilateral segmental analgesia presented in all cases who received only epidural anesthesia after no backflow of CSF was observed, and the expected analgesia also presented in all cases in whom back flow of CSF was observed. No adverse reactions occurred. Conclusion Injection of air into the epidural space is related to the success of subarachnoid puncture during CSEA and injection of a large volume of air lowers the success rate. Key words: Air; Injections, epidural; Anesthesia, spinal