Intrathecal vs intravenous magnesium as an adjuvant to bupivacaine spinal anesthesia for total hip arthroplasty

Background
The aim of this study was to investigate the effect of intravenous infusion vs intrathecal magnesium sulfate during spinal anesthesia on postoperative pain, analgesic consumption, and intraoperative blood loss on patients undergoing total hip arthroplasty surgery.
Methods
In this prospective randomized controlled study, 75 adult patients, ASA physical status I and II scheduled for total hip arthroplasty, were included and randomized into three groups. Patients in Group I (control) received spinal anesthesia with hyperbaric bupivacaine and fentanyl. In Group II (IT Mg), 50 mg of magnesium sulfate was added to bupivacaine and fentanyl. In Group III (IV Mg), after induction of spinal anesthesia as in group I, a bolus dose of i.v. magnesium sulfate 40 mg kg was injected over 10 min, followed by continuous infusion of 15 mg kg h till the end of surgery. Arterial blood pressure, heart rate, electrocardiography, and O saturation were continuously monitored. Onset, duration of sensory and motor block, and postoperative pain scores were assessed. Serum magnesium concentrations were checked before induction of anesthesia, immediately after surgery, at 6 h and 24 h after surgery. Total analgesic consumption and intraoperative blood loss were calculated.
Results
There were no significant differences between the study groups in terms of onset time and maximum sensory level achieved, as well as onset and duration of motor block. Postoperative pain scores and 24 h analgesic consumption were lower in group II and III with insignificant differences between them. Intraoperative blood loss was significantly lower in group III. Postoperative Mg levels were higher in group III, without significant side effects.
Conclusions
Both i.v. infusion and intrathecal injection of Mg sulfate improved postoperative analgesia after total hip replacement. In addition, i.v. infusion of Mg sulfate reduced intraoperative blood loss.