The effect of addition of magnesium sulfate or dexamethasone to bupivacaine on the post-operative analgesic duration of ultrasound-guided quadratus lumborum block in open abdominal surgeries: a comparative study

Background
The aim of this study was to assess the effect of addition of 500-mg magnesium sulfate (MgSo) or 8-mg dexamethasone to bupivacaine in bilateral ultrasound-guided quadratus lumborum block (QLB), on the duration of post-operative analgesia, the patient’s hemodynamic parameters, the severity of post-operative pain, number of patients who required rescue analgesia, the total dose of pethidine given, the number of patients who maintained post-operative analgesia for 36 h, and the time to first ambulation. Sixty-six patients, 18 to 65 years old, with body weight 60–90 kg, scheduled to undergo elective open abdominal surgeries under general anesthesia, were randomly divided into three equal groups: the Bupivacaine-Magnesium QLB group (BM) patients, the Bupivacaine-Dexamethasone QLB group (BD) patients, and the Bupivacaine-Saline QLB group (BS) patients.
Results
The post-operative visual analogue scale (VAS) at rest and with movement was comparable between patients in the three groups: upon arrival to the post-operative care unit (PACU), in the PACU, and in the post-operative 2, 4, 6, 8, 12, 24, and 36 h. At 30 post-operative hours, the VAS at rest and with movement was statistically significantly lower in group BD 2 (0–4) and 2.75 (2–4.5) than in group BM 2.25 (0–4) and 3 (0–4.5), than in group BS 3.25 (3–4) and 4 (3.5–5), respectively, with -value ˂ 0.001. Although 100% of patients in group BS received pethidine, versus 68.2% of patients in group BM and 63.6% of patients in group BD, with -value 0.007, the cumulative total pethidine doses given, the duration of post-operative analgesia, and the number of patients who maintained post-operative analgesia for 36 h were comparable between the three groups with -value 0.170, 0.239, and 0.231, respectively.
Conclusions
In bilateral ultrasound-guided QLB in open abdominal surgeries, the addition of dexamethasone or MgSo to bupivacaine reduced the VAS scores and the number of patients experiencing moderate pain at 30 post-operative hours, with fewer patients receiving pethidine and less cumulative total pethidine doses given, with dexamethasone showing better results.