Abstract: The analysis included 24 trials reporting on 2226 participants of whom 239 developed TNS. Two studies are awaiting classification and one is ongoing. Included studies mostly had unclear to high risk of bias. The NMA included 24 studies and eight different local anaesthetics; the number of pair-wise comparisons was 32 and the number of different pair-wise comparisons was 11. This analysis showed that, compared to lidocaine, the risk ratio (RR) of TNS was lower for bupivacaine, levobupivacaine, prilocaine, procaine, and ropivacaine with RRs in the range of 0.10 to 0.23 while 2-chloroprocaine and mepivacaine did not differ in terms of RR of TNS development compared to lidocaine. Pair-wise meta-analysis showed that compared with lidocaine, most local anaesthetics were associated with a reduced risk of TNS development (except 2-chloroprocaine and mepivacaine) (bupivacaine: RR 0.16, 95% confidence interval (CI) 0.09 to 0.28; 12 studies; moderate-quality evidence; 2-chloroprocaine: RR 0.09, 95% CI 0.01 to 1.51; 2 studies; low-quality evidence; levobupivacaine: RR 0.13, 95% CI 0.02 to 0.69; 2 studies; low-quality evidence; mepivacaine: RR 1.01, 95% CI 0.18 to 5.82; 4 studies; very low-quality evidence; prilocaine: RR 0.18, 95% CI 0.07 to 0.49; 4 studies; moderate-quality evidence; procaine: RR 0.14, 95% CI 0.04 to 0.52; 2 studies; moderate-quality evidence; ropivacaine: RR 0.10, 95% CI 0.01 to 0.78; 2 studies; low-quality evidence). We were unable to perform any of our planned subgroup analyses due to the low number of TNS events. Results from both NMA and pair-wise meta-analysis indicate that the risk of developing TNS after spinal anaesthesia is lower when bupivacaine, levobupivacaine, prilocaine, procaine, and ropivacaine are used compared to lidocaine. The use of 2-chloroprocaine and mepivacaine had a similar risk to lidocaine in terms of TNS development after spinal anaesthesia. Patients should be informed of TNS as a possible adverse effect of local anaesthesia with lidocaine and the choice of anaesthetic agent should be based on the specific clinical context and parameters such as the expected duration of the procedure and the quality of anaesthesia. Due to the very low- to moderate-quality evidence (GRADE), future research efforts in this field are required to assess alternatives to lidocaine that would be able to provide high-quality anaesthesia without TNS development. The two studies awaiting classification and one ongoing study may alter the conclusions of the review once assessed.

Plain-language summary: We included all randomized trials and quasi-randomized trials comparing the frequency of TNS and neurological complications after spinal anaesthesia with lidocaine compared to other local anaesthetic agents. Randomized trials compare two or more treatments where the treatments are allocated to participants in a random manner that cannot be predicted by the study organizers. Quasi-randomized studies are similar but are not truly random, but carry a greater likelihood that the study organizer can predict which treatment the participants receive (e.g. based on date of birth or the order in which people were recruited). The evidence is current to 25 November 2018. We included 24 trials reporting on 2226 participants, 239 of whom developed TNS. There was no evidence TNS was associated with any specific neurological disease and symptoms disappeared spontaneously by the fifth postoperative day. The risk of developing TNS with lidocaine for spinal anaesthesia was increased compared to bupivacaine, prilocaine, or procaine; and similar compared to 2-chloroprocaine and mepivacaine. Specifically, when alternative local anaesthetics were compared directly to lidocaine, the risk of developing TNS was reduced by between 82% and 90% when bupivacaine, levobupivacaine, prilocaine, procaine, and ropivacaine were used rather than lidocaine. There were no clear differences in TNS between lidocaine and 2-chloroprocaine or mepivacaine. In the case of 2-chloroprocaine, TNS occurred in only one study and the results varied greatly for the small number of participants. Painful symptoms stopped by the fifth postoperative day in all participants. Among pregnant women undergoing surgery, only 3/310 women developed TNS; no conclusions could be drawn on whether symptoms were more likely with lidocaine. The authors also used the statistical method of network meta-analysis to compare the various local anaesthetics. This analysis similarly showed that the risk of TNS was lower for bupivacaine, levobupivacaine, prilocaine, procaine, and ropivacaine, while 2-chloroprocaine and mepivacaine did not differ in risk of TNS compared to lidocaine. Due to the very low- to moderate-quality of evidence among currently available studies, future research efforts in this field are needed to assess alternatives to lidocaine that can provide high-quality anaesthesia without TNS development. Lidocaine has been the drug of choice for inducing spinal anaesthesia in ambulatory surgery (or day surgery) because of its rapid onset of action, intense nerve blockade, and short duration of action. The present review shows that lidocaine is more likely to cause TNS than bupivacaine, prilocaine, and procaine. However, these drugs produce longer local anaesthetic effects and therefore are not desirable for ambulatory patients. Our results suggest that 2-chloroprocaine might be a viable alternative to lidocaine for day surgery of short duration and obstetric procedures since this local anaesthetic has a rapid onset of action, is quickly metabolized, and has low toxicity. However, this conclusion is based on only two studies and low-quality evidence.