Local anaesthesia - adjuncts

Adjuncts to local anaesthesia for prolongation of effective postoperative analgesia

Local anaesthesia is not only effective during surgery but is also an important part of early postoperative multi-modal analgesia. Also the local anaesthetics with the longest duration have however a limited duration of analgesic action. Several adjuncts to local anaesthesia have been tested in order to prolong the duration of effective anaesthesia.

Lee at al presented in October issue of Can J Anesth their findings from a study of 66 patients undergoing arthroscopic rotator cuff repair. The interscalene nerve block was performed with 0.5% bupivacaine 20 mL with epinephrine (1:200,000) plus either 10% magnesium sulphate 2 mL (Magnesium Group) or normal saline 2 mL (Saline Group). The following data were recorded for 24 first postoperative hours: onset times and durations of sensory and motor blocks, analgesic duration, the pain numeric rating scale (NRS), postoperative fentanyl consumption, and complications. A significant differences was found but the clinical value may be argued; the duration of analgesia was longer in the Magnesium Group than in the Saline Group [mean and (standard deviation) 664 (188) min vs. 553 (155) min, respectively; P = 0.017]. Patients in the Magnesium Group had significantly reduced pain NRS scores at 12 hr (P = 0.012), but the cumulative fentanyl consumption was similar in both groups. The onset times and durations of sensory and motor blocks were not significantly different between the two groups.

A meta-analysis of the effects of clonidine in addition to local anaesthesia for caudal block in children by Schnabel et al was presented in the December issue of Paediatric Anaesthesia. Twenty randomized controlled trials (published between 1994 and 2010) including 993 patients met the inclusion criteria for the analysis. The results, both with regard to effective analgesia and need for rescue analgesia, seems to be of more clinical relevance as compared to the 100 minute difference found with magnesium. There was a longer duration of postoperative analgesia in children receiving clonidine in addition to local anesthetic, mean different: 3.98 h; 95% CI: 2.84-5.13; P < 0.00001. Furthermore, there was a lower number of patients requiring rescue analgesics in the clonidine group (RR: 0.72; 95% CI: 0.57-0.90; P = 0.003). The incidence of complications (e.g., respiratory depression) remained very low and was not different to caudal local anaesthetics alone.

Even more exiting are the results with the addition of dexmedetomidine in a study by Anand published Indian J Anaesth July issue. They performed a randomised, prospective, parallel group, double-blinded study in 60 children allocated into two groups: Group RD (n=30) received 0.25% ropivacaine 1 ml/kg with dexmedetomidine 2 μg/kg, making the volume to 0.5 ml and Group R (n=30) received 0.25% ropivacaine 1 ml/kg + 0.5 ml normal saline. They found an impressing increase in effective analgesia. The duration of postoperative analgesia recorded a median of 5.5 hours in Group R compared with 14.5 hours in Group RD, with a P value of <0.001. Group R patients achieved a statistically significant higher FLACC score compared with Group RD patients. The difference between the means of mean sedation score, emergence behaviour score, mean emergence time was statistically highly significant (P<0.001).

Positive effects, prolonged duration of spinal anaesthesia/analgesia has also been shown with the addition of low 5 microgram dose dexmedetomidine to ropivacain for spinal anaesthesia. Gupta et al randomly allocated 60 patients to receive intrathecally either 3 ml of 0.75% isobaric ropivacaine + 0.5 ml normal saline (Group R) or 3 ml of 0.75% isobaric ropivacaine + 5 μg dexmedetomidine in 0.5 ml of normal saline (Group D). They found dexmeditomidine to prolong and improve the analgesic effect. The mean time of sensory regression to S2 was 468.3±36.78 minutes in group D and 239.33±16.8 minutes in group R. Duration of analgesia (time to requirement of first rescue analgesic) was significantly prolonged in group D (478.4±20.9 minutes) as compared to group R (241.67±21.67 minutes). The maximum visual analogue scale score for pain was less in group D (4.4±1.4) as compared to group R (6.8±2.2).
Further studies are warranted evaluating the benefit vs. risk from the use of dexmeditomidine as adjunct to local anaesthesia for the prolongation of effective postoperative analgesia.

References:
Lee AR, Yi HW, Chung IS, Ko JS, Ahn HJ, Gwak MS, Choi DH, Choi SJ. Magnesium added to bupivacaine prolongs the duration of analgesia after interscalene nerve block. Can J Anaesth. 2011 Oct 20. [Epub ahead of print]

Schnabel A, Poepping DM, Pogatzki-Zahn EM, Zahn PK. Efficacy and safety of clonidine as additive for caudal regional anesthesia: a quantitative systematic review of randomized controlled trials. Paediatr Anaesth. 2011 Dec;21(12):1219-30.

Anand VG, Kannan M, Thavamani A, Bridgit MJ. Effects of dexmedetomidine added to caudal ropivacaine in paediatric lower abdominal surgeries.Indian J Anaesth. 2011 Jul;55(4):340-6.

Gupta R, Bogra J, Verma R, Kohli M, Kushwaha JK, Kumar S. Dexmedetomidine as an intrathecal adjuvant for postoperative analgesia. Indian J Anaesth. 2011 Jul;55(4):347-51.