For sacral neuromodulation (SNM), staged implant testing is considered to have the highest success rate in terms of progression to implantation of the implantable pulse generator (IPG) [1]. Stage 1 lead implantation (SNM I) is done in the operating room  under monitored anesthesia care (MAC), that is, intravenous sedation, or general anesthesia (GA). MAC allows for assessment of both sacral motor reflexes as well as sensory response to determine adequacy of lead implant, whereas GA allows for only motor response assessment. However, with MAC, patient discomfort can still be problematic resulting in patient movement that can make lead placement more challenging, whereas GA avoids this. There is evidence that relying on motor responses only is adequate for lead implantation [2]. Historically we have performed SNM I using MAC but more recently converted to using GA. Herein we report our results using both forms of anesthesia for SNM I for urge urinary incontinence (UUI), specifically assessing the rate of progression to IPG implantation (SNM II), to determine if the type of anesthesia used for SNM I impacts the outcome.

A retrospective chart review was performed on our patients undergoing staged SNM testing for UUI. Patients undergoing SNM testing for other indications were excluded, as were patients deemed to have inadequate information for review. Patients were divided into 2 groups based on the type of anesthesia used for SNM I, MAC vs GA. Clinical variables and the number of patients who progressed to SNM-II were compared between groups. Progression to SNM-II was based on ≥50% symptomatic improvement, as determined by a combination of subjective impression of improvement, as well as bladder diary and pad usage, during a 1-2 week trial period after SNM I.

One-hundred and forty-five patients were included in the study with 120 (83%) undergoing SNM I using MAC and 25 (17%) using GA. There were significantly more females in the MAC group (87% vs 72%, p=0.05) while a greater proportion of the GA patients had a diagnosis of multiple sclerosis (20% vs 4%, p<0.01). However, overall there was no statistically significant difference between the groups with respect to any neurologic diagnosis (MAC 33% vs GA 52%, p=0.08). Preoperative pad usage was greater in the GA group, although this was not statistically significant (MAC 3.0 pads vs GA 4.5 pads, p=0.06). There was no difference in the rate of progression to SNM II: MAC 86/120 (72%) vs GA 18/25 (72%), p=0.97.

Our findings of a similar rate of progression to stage 2 neurostimulator implantation between patients undergoing the SNM I under MAC vs GA suggests that the type of anesthetic used is not important, at least in the context of SNM for UUI. It also adds to the evidence in the literature that using motor responses for sacral lead placement is adequate and one may forgo the sensory responses, granted additional study with larger sample sizes is needed. A greater proportion of our GA patients had MS and this is a reflection of our recent conversion to using GA for SNM I combined with the newer SNM technology that is now MRI compatible. Despite this, similar rates of progression to SNM II were noted between groups.

We found that the rate of progression to IPG implantation after staged SNM testing for UUI was similar regardless of the type of anesthesia used for stage 1 testing.

Baxter C, Kim JH. Contrasting the percutaneous nerve evaluation versus staged implantation in sacral neuromodulation. Curr Urol Rep. 2010 Sep;11(5):310-4. doi: 10.1007/s11934-010-0128-2. PMID: 20535593; PMCID: PMC2908747.
Cohen BL, Tunuguntla HS, Gousse A. Predictors of success for first stage neuromodulation: motor versus sensory response. J Urol. 2006 Jun;175(6):2178-80; discussion 2180-1. doi: 10.1016/S0022-5347(06)00315-6. PMID: 16697833.