Background: The use of low concentrations of volatile anaesthetics with avoidance of opioids may induce intraoperative awareness and adverse haemodynamic responses during Caesarean section. Magnesium is well known to reduce anaesthetic requirements and to block noxious stimuli. We investigated whether i.v. magnesium sulphate modulates anaesthetic depth and analgesic efficacy during Caesarean section.
Methods: Seventy-two patients undergoing Caesarean section were randomly assigned to receive i.v. saline (control group) or magnesium sulphate 30 mg kg(-1) bolus+10 mg kg(-1) h(-1) continuous infusion (Mg 30 group) or 45 mg kg(-1) bolus+15 mg kg(-1) h(-1) continuous infusion (Mg 45 group) after induction. Bispectral index (BIS) value, mean arterial pressure (MAP), and midazolam, fentanyl, and atracurium consumptions were recorded.
Results: BIS values [mean (sd)] at 7.5 and 10 min after surgery and before delivery in the control [64 (9), 66 (8), 67 (8), P<0.001] and the Mg 30 groups [62 (8), P<0.01; 64 (7), 63 (9), P<0.001] were higher than in the Mg 45 group [56 (8), 55 (8), 55 (7)]. MAP was greater in the control group (P<0.05) than in the Mg 30 and Mg 45 groups during the pre-delivery period. The magnesium groups required less midazolam (P<0.05), fentanyl (Mg 30, P<0.05; Mg 45, P<0.01), and atracurium (P<0.001) vs the control group.
Conclusions: Preoperative i.v. magnesium sulphate attenuated BIS and arterial pressure increases during the pre-delivery period. Magnesium sulphate can be recommended as an adjuvant during general anaesthesia for Caesarean section to avoid perioperative awareness and pressor response resulting from inadequate anaesthesia, analgesia, or both.