The effects of different dose levels of peri-neural dexmedetomidine on the pharmacodynamic and side effect profiles of bupivacaine-induced ultrasound-guided femoral nerve block

Mohamed Ollaek, Mohamed Abdulatif, Maher Fawzy, Heba Nassar, Ahmed Hasanin, Hassan Mohamed

Background and Goal of Study: 
Dexmedetomidine extends the duration of brachial plexus block. The clinical use of dexmedetomidine as adjuvant for lower extremities nerve blocks was not adequately investigated. This study was designed to explore the effects of different dose levels of dexmedetomidine on the clinical and side effect profiles of femoral nerve block.

Materials and Methods:
This randomised, controlled double-blind study included 60 adult patients undergoing arthroscopic knee surgery. Ultrasound-guided femoral nerve block was performed 30 min before induction of anaesthesia using 25 ml of bupivacaine 0.5%. Bupivacaine was combined with normal saline, 25, 50, or 75μg dexmedetomidine (n= 15, each). All patients received a standard general anaesthetic. The onset and duration of sensory and
motor blocks, the time to first request to postoperative analgesic, sedation score, haemodynamic changes, and visual analogue pain scores, were recorded at predetermined intervals. Total postoperative 24-h morphine consumption was recorded. The primary outcome measure was the duration of sensory block.

Results and Discussion:
The onset of sensory block was shorter and its duration was extended with the use of 75μg dexmedetomidine: 21.6 (3.0), 23.3 (1.8), 30.8 (3.6), and 43.7 (4.3) h in the control, 25, 50, and 75μg groups, respectively. The onset of motor block was shorter in the 75μg group compared to the control and 25μg groups. The duration of motor block was longer in the 75μg group, 36.1 (6.4) h compared to the other three groups. The time to first
request to rescue analgesic was longer in the 75μg group, 10.8 (1.6), 11.0 (7.1) and 21.8 (3.0) and 28.6 (10.0) h, respectively. The total postoperative 24 hour morphine consumption was reduced in the 75μg group compared to the control and 25μg group: 1.8 (2.6), 7.6 (5.1), and 6.5 (3.5) mg, respectively. Postoperative sedation was comparable in all groups. The incidence of hypotension was higher in the 75μg group.

Conclusion:
Perineural dexmedetomidine reduces the onset and prolongs the duration of bupivacaine-induced femoral nerve block in a dose dependent manner. The best analgesic profile is achieved with the 75μg dose level, however, this dose is associated with higher incidence of hypotension.

The effects of different dose levels of peri-neural dexmedetomidine on the pharmacodynamic and side effect profiles of bupivacaine-induced ultrasound-guided femoral nerve block