Abstract
When used as an adjunct to local anaesthetic, opioid administered via the epidural route can improve the quality of analgesia. Reports of respiratory depression associated with epidural morphine use as a sole agent in the 1980s led to an increased use of lipophilic opioids, especially fentanyl. Although fentanyl is commonly used, controversy exists about its efficacy and site of action. It is possible that low-dose morphine may be more effective than fentanyl, without increasing the risk of respiratory depression.
A retrospective audit was conducted of 200 consecutive patients undergoing coronary artery bypass surgery who received high thoracic epidural analgesia.
One hundred patients who received fentanyl 2 μg/ml with 0.2% ropivacaine, prior to a change in our technique, were audited, followed by 100 patients who received 20 μg/ml morphine with 0.2% ropivacaine. Outcome measures included the incidence of Visual Analogue Score (VAS) ≥4/10; infusion rate adjustments; and side-effects. Patients receiving fentanyl were more likely to experience pain ≥4/10 (P'=0.002); the infusion rate was higher (P8=0.024); required more rate adjustments (P8=0.001); a greater need for noradrenaline (P'=0.001) and antiemetic drugs (P'=0.001). There were no significant differences between the groups for sedation scores or the incidence of respiratory depression.
This audit suggests morphine 20 μg/ml may be superior to fentanyl 2 μg/ml, as an adjunct to 0.2% ropivacaine. We found a reduced number of infusion interventions and less inadequate patient analgesia.