Background: Intrathecal morphine (IT) is commonly used for postoperative analgesia after caesarean section. The addition of intrathecal (IT) magnesium to spinal bupivacaine-fentanyl anaesthesia increases the duration of spinal analgesia for labour without additional side effects. In this prospective, randomized, double blind, controlled study, we evaluated whether adding intrathecal magnesium could prolong spinal morphine analgesia after caesarean section. PARTURIENT AND METHODS: After ethics committee approval and obtaining written consent, one hundred and five (ASA I or II) adult patients undergoing caesarean section were recruited. They were randomly allocated to one of three groups: (1) group Morphine (M): 10 mg of isobaric bupivacaine 0.5% (2 ml)+100 microg morphine (1 ml)+10 microg fentanyl (0.1 ml)+1 ml of isotonic saline solution, (2) group Magnesium (Mg): 10mg of isobaric bupivacaine 0.5% (2 ml)+100mg of magnesium sulphate 10% (1 ml)+10 microg fentanyl (0.1 ml)+1 ml of isotonic saline solution, (3) group Morphine+Magnesium (MMg): 10mg of isobaric bupivacaine 0.5% (2 ml)+100mg of magnesium sulphate 10% (1 ml)+100 microg morphine (1 ml)+10 microg fentanyl (0.1 ml). We recorded the following: time to the first analgesic request, pain scores with the visual analogic scale at rest and in movement at h0, h1, h2, h4 and then every 4h for the first 36 postoperative hours, the occurrence of adverse events and patients' satisfaction.
Results: Time of the first analgesic request was 28+/-8h in group MMg versus 19+/-6h in group M and 7+/-6h in group Mg (p<0.01). Pain scores were statistically lower in group MMg (9+/-7 and 17+/-9 mm respectively) compared to group M (16+/-9 and 28+/-11 mm respectively) and Mg (21+/-9 and 37+/-13 mm respectively) (p<0.01). There was no difference in adverse events among the three groups. Patients satisfaction was better in group MMg (p<0.01).
Conclusion: In patients undergoing caesarean section under spinal anaesthesia, the addition of IT magnesium sulphate (100mg) to morphine 100 microg improved the quality and the duration of postoperative analgesia without increasing the incidence of adverse effects.