USE OF MAGNESIUM SULPHATE AS ADJUVANT TO BUPIVACAINE FOR SPINAL ANAESTHESIA FOR MYOMECTOMIES AT NNAMDI AZIKIWE UNIVERSITY TEACHING HOSPITAL, NNEWI

Abstract

BACKGROUND: Adequate analgesia following myomectomy decreases morbidity, hastens
ambulation and improves patient outcome. Central sensitization is an activity-dependent
increase in the excitability of spinal neurons. It is considered to be one of the mechanisms
implicated for development of pain. Intrathecal magnesium, an N-Methyl-D-Aspartate
receptor antagonist, inhibits central sensitization and has been shown to prolong analgesia
without significant side effects.
OBJECTIVES: To determine the effects of intrathecal magnesium sulphate in prolonging
the duration of spinal anaesthesia using hyperbaric bupivacaine for myomectomy.

METHODS: In this prospective, randomized, double-blinded study, 70 patients, aged 18-50
years of American Society of Anesthesiologists physical status I or II were randomly
assigned into two groups of 35 patients each to receive either intrathecal hyperbaric
bupivacaine 0.2mg/kg plus 50mg magnesium sulphate (group I) or intrathecal hyperbaric
bupivacaine 0.2mg/kg plus normal saline (group II). The outcome measures assessed were
the onset of sensory and motor bock, duration of sensory and motor block, duration of
analgesia, pain scores using Numerical Rating Scale, total postoperative analgesics consumed
in 24 hours, incidence of side effects and patients’ satisfaction.
RESULTS: Magnesium sulphate group had lower mean pain assessment scores throughout
the period of the study compared to the saline group (control group). The onset of sensory
block was prolonged in the magnesium sulphate group (3.42±0.08 minutes) compared to the
saline group (3.21±0.11 minutes) and it was statistically significant (p=0.001). The onset of
motor block was also prolonged in the magnesium sulphate group (7.75±0.76 minutes)
compared to the saline group (7.47±0.67 minutes) but was not statistically significant
(p=0.122). The duration of sensory block was prolonged in magnesium sulphate group
(144.38±9.14 minutes) compared to the saline group (124.69±9.67 minutes) and the observed
difference was statistically significant (p=0.001).The duration of motor block was also
prolonged in the magnesium sulphate group compared to the saline group (211.41±12.26
minutes vs 185.63±10.61 minutes) and the difference was statistically significant (p=0.001).
There was statistically significant difference between the duration of analgesia between the
magnesium sulphate group and saline group (253.50±5.90 min versus 199.00±4.19 minutes,
p= 0.001). The total amount of analgesics required 24 hour post-operatively was higher in the
saline group (443.43±29.25 mg) than in the magnesium group (374.22±19.56 mg) and the
difference was statistically significant (p=0.001).
Respiratory depression was not observed in any of the study groups. The incidence of
hypotension was 17.19% (11) in the magnesium sulphate group and 10.94% (7) in the saline
group but the difference was not statistically significant (p=0.266). Although, more patients
in the magnesium sulphate group (9.37%) had bradycardia compared to 6.25% among the
saline group, the observed difference was not statistically significant (p=0.491). One patient
vomited in the magnesium sulphate group, while two vomited in the saline group, (p=1.000).
No patient in the magnesium sulphate group experienced shivering while three patients
experienced shivering in the saline group and the difference was not statistically significant
(p=0.238).
The level of satisfaction between the two groups revealed that 21.2 % of the patients (7) in
the magnesium sulphate group reported their level of satisfaction as very satisfied compared
with 18.2% (6) in the saline group, (p=0.757). The proportion of patients that reported that
they were satisfied was 75.6 % (25) in the magnesium sulphate group while it was 69.7 %
(23) in the saline group, (p=0.069). The number of patients that reported being unsatisfied
was 3.0 % of the patients (1) in the magnesium sulphate group while it was 12.1 % (4) in the
saline group, (p= 0.852). The differences in the level of satisfaction between the two groups
were not statistically significant. There was no patient that reported not sure in either of the
groups.
CONCLUSION: This study therefore showed that the addition of 50mg magnesium sulphate to bupivacaine 0.2mg/kg for spinal anaesthesia resulted in superior quality of analgesia as
shown by lower mean pain assessment scores during the study compared with bupivacaine
alone, without increasing the incidence of side effects.
KEYWORDS: intrathecal, magnesium sulphate, myomectomy, spinal anaesthesia.