Effect of intravenous magnesium sulphate on block characteristics and post operative analgesia for inguinal hernia surgeries under spinal anaesthesia

A prospective, randomized double blind clinical study was undertaken to evaluate the effects of intravenous magnesium sulphate on block characteristics and post operative analgesia for inguinal hernia surgeries under spinal anaesthesia.

Eighty patients were divided into two groups based on computer generated randomization code, each group consisting of forty patients. All the patients were given spinal anaesthesia with 10 mg of 0.5% hyperbaric bupivacaine (2ml) plus 25μg of fentanyl (0.5 ml).

Patients in Group A were administered a bolus dose of magnesium sulphate 30 mg/kg over 15 min, immediately after the administration of spinal drug and followed by an intravenous infusion 15 mg/kg/hr for 1 hour.

Patients in group B were administered a bolus of 50 ml of normal saline over 15 min, immediately after the administration of spinal drug followed by intravenous infusion of normal saline at the rate of 100 ml/hr for 1 hour.

All patients aged between 18 -55 years ,belonging to ASA class I and II posted for inguinal hernia surgery under spinal anesthesia were included in the study. Patients who had contraindication for spinal anaesthesia, history of allergy to test drugs, altered magnesium levels and significant cardiac, renal, respiratory, metabolic disorders were excluded from the study.

The parameters observed were

ï‚· Onset of sensory blockade

ï‚· Maximum level of sensory blockade.

ï‚· Onset of motor blockade.

ï‚· Duration of motor blockade.

ï‚· Duration of sensory blockade

ï‚· Duration of analgesia

ï‚· Haemodynamic parameters

It was found that there was no significant difference between the magnesium group and control group with regards to the onset of sensory and motor blockade, the maximum level of sensory blockade and the time taken to attain the maximum sensory level.

The duration of the sensory blockade was 192.45 ± 12.89 minutes in the magnesium group, and 167.37 ± 13.25 minutes in the control group. The difference of 25 minutes was statistically highly significant. The duration of analgesia was significantly prolonged being 267.37 ± 29.35 minutes in the magnesium group and 156.25 ± 14 minutes in the control group. The mean duration of the motor blockade was 161.72 ± 10.85 minutes in the magnesium group and 140.5 ± 11.36 minutes in the control group, which was highly statistically significant.

The serum magnesium levels were significantly higher in the magnesium group 24 hours after the surgery, being 0.86 ± 0.086 mmol/l and 0.82 ±0.076 mmol/l in the control group. But it may not be clinically significant as all the values were within the normal range.

The incidence of hypotension was comparatively more in the magnesium group but it was not statistically significant. Other adverse effects like respiratory depression, arrhythmias were not observed.