Is 4% articaine suitable for spinal anaesthesia?

This Invited Commentary accompanies the following article: Bachmann M, Pere P, Kairaluoma P, et al. Randomized comparison of hyperbaric articaine and hyperbaric low-dose bupivacaine along with fentanyl in spinal anaesthesia for day-case inguinal herniorrhaphy. Eur J Anaesthesiol 2012; 29:22–27. Concerns regarding neurotoxicity with lidocaine have prompted efforts to find an alternative local anaesthetic for short-acting spinal anaesthesia. Current practice for ambulatory spinal anaesthesia involves low doses of bupivacaine or ropivacaine to which a lipid-soluble opioid is added. Articaine is not a new local anaesthetics but in common with lidocaine, it has a profile that includes a short duration, suggesting that it may be suitable for ambulatory spinal anaesthesia.1 In support of this, Bachmann et al.2 compared 84 mg of intrathecal 4% articaine with a combination of 7 mg of bupivacaine and 10 μg of fentanyl for the repair of inguinal hernia in 80 ambulatory patients. They chose 84 mg of articaine for this study because a previous study showed that it was as efficient as 108 mg for day-case surgery.3 They found that cephalad spread of anaesthesia was higher and the duration of anaesthesia shorter with articaine than with a bupivacaine–fentanyl combination. There was no significant difference between the two groups in the time that the anaesthesia block height rose to T10; however, despite this, three patients required general anaesthesia because the duration of anaesthesia was too short. Two of these patients had received articaine, and the third had an inadequate block after bupivacaine–fentanyl. The authors found that 84 mg of articaine was equivalent to the 7 mg of bupivacaine and 10 μg of fentanyl combination and felt that it was suitable for ambulatory spinal anaesthesia. They came to this view in the knowledge that two patients in the articaine group had unilateral transient radicular symptoms identical to those associated with spinal anaesthesia, and one patient in the bupivacaine–fentanyl group had sciatica related to the prolapse of an intervertebral disk. No other radicular signs were reported by patients during telephone interviews on postoperative days 1 and 7. Some 56% of patients in the articaine group reported satisfaction with their spinal anaesthesia compared with 44% in the bupivacaine–fentanyl group.2 Articaine has a reputation for low systemic toxicity due to its rapid breakdown into an inactive metabolite,4,5 but little is known about its potential for local neurotoxicity. When all this is taken into account, should we use articaine in our routine practice? Although lidocaine has a long history of use in spinal anaesthesia, local neurological toxicity was not reported until the 1990s.6–9 After the development of cauda equina syndromes following its use by the intrathecal route, and the reporting of transient radicular irritation, further experiments went on to prove the toxic effects of lidocaine on nervous tissue.10–13 We have understood for a long time that all local anaesthetics are potentially neurotoxic, but the severity of the toxicity varies according to the local anaesthetic used.14 We know that bupivacaine and ropivacaine are less neurotoxic than lidocaine,13,15 but information regarding the potential neurotoxicity of articaine is currently unavailable. Studies that fail to demonstrate clinical signs of neurotoxicity are not sufficient to draw firm conclusions about safety for intrathecal use. There are no published data about the potential neurotoxic effects of articaine, but because it is a short-acting local anaesthetic much used in dentistry it does have a track record. Residual paraesthesia or dysaesthesia is reported after dental anaesthesia with local anaesthetics in general, mainly lidocaine, prilocaine and articaine. In a survey of the incidence of paraesthesia occurring after dental surgery, Haas and Lennon,16 in the province of Ontario, showed a dramatic rise in this complication in 2000, coincident with the introduction of 4% articaine. Garisto et al.17 showed that reports of paraesthesia with 4% articaine were 3.6 times greater than expected on the basis of its use by US dentists. Pedlar18 at the Leeds Dental Institute made similar observation. The incidence of paraesthesia was higher after mandibular nerve blocks than that after inferior alveolar block.19 A neurotoxic effect cannot be ruled out because the site of local anaesthetic injection is closer to the mandibular nerve. Paraesthesiae were also reported in the present study in two patients, and by Hendriks et al.20 in another study. Recently, Hillerup et al.,21 in an electrophysiological and histological study on the rat sciatic nerve, showed concentration-dependent neurotoxic injuries after injection of articaine that were significantly different between the 2 and 4% formulations. The concentration of articaine used in dental anaesthesia and for spinal anaesthesia was the 4% solution. Before promoting the use of 4% articaine for spinal anaesthesia in routine practice, we must first establish its neurological safety in the experimental laboratory. Acknowledgement This article was checked and accepted by the editors, but was not sent for external peer review.

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