Anaesthetic management of a patient with a sacral nerve stimulator or sacral neuromodulation.

Sir,

Sacral nerve stimulation (SNS) or sacral nerve neuromodulation is being increasingly used for the treatment of overactive bladder, voiding dysfunction and urge incontinence. Initially used to treat urinary incontinence, SNS was first reported for the treatment of faecal incontinence by Matzel and colleagues.[1] They described an approach of using intraoperative peripheral nerve evaluation (PNE) to identify the most efficient spinal nerve for stimulation, followed by a temporary (subchronic) stimulation period of 1 to several weeks. If faecal incontinence improves during this evaluation period, patients are then offered permanent (chronic) electrode implantation. This staged approach is widely accepted as the standard of care.[2]

It's not uncommon for an anaesthesiologist to encounter a patient with SNS in his day-to-day practice. We report anaesthetic management of a young ASA 1 patient for lower body lift under general anaesthesia.

A 38-year-old female patient was scheduled for a lower body lift. Lower body lift involves an incision along the waist to remove an apron of excess skin and fat, with or without liposuction to reposition and tighten the tissues.

She gave a history of SNS (Interstim™, Medtronic Inc.) inserted for faecal incontinence 12 years previously under local anaesthesia. As per the patient, she was continent even without the device. [Figure 1] The rest of her history, examination and laboratory investigations were unremarkable. With the patient's written consent, the device was turned off and it was decided to disconnect leads from pulse generator as it was in the way of the proposed surgical field. The primary treating surgeon was also consulted preoperatively. The SNS company personnel were present at the time of switching the implant off.

Figure 1

Radiographs showing the location of leads and pulse generator

After applying standard monitors, general anaesthesia was induced with intravenous (IV) propofol and rocuronium. The trachea was intubated with the number 7 flexometallic tube. With the patient under prone position, the previous scar was explored and the pulse generator removed. Anaesthesia was maintained with sevoflurane (1.2–1.5 MAC) in a mixture of oxygen and air (50:50) with low flows. The rest of the procedure and anaesthetic were uneventful. She received postoperative regular IV paracetamol, IV parecoxib and PRN oral oxycodone.

The implant of SNS is a minimally invasive surgical procedure and consists of (1) a testing evaluation interval and (2) a second stage with permanent stimulator implantation, provided the testing interval results are clinically successful. The first stage, also termed percutaneous nerve evaluation (PNE), is of most relevance to determine the feasibility of electrode implantation into the sacral foramina and to demonstrate clinical benefits worth pursuing with permanent SNS. Two technical options are available for PNE: A temporary, percutaneously placed, unipolar stimulation lead to be removed later, or the surgical placement of a quadripolar lead next to a target nerve. Both types of leads are then connected to an external pulse generator to be substituted by a permanent pulse generator implanted subcutaneously in case of a positive outcome. The permanent implant is the size of a coin (diameter 24.26 mm, thickness 1.75 mm), is usually placed in the gluteal area and can be managed by a small handheld device. It is thought that SNS works via complex neuromodulation of sacral reflexes to regulate rectal sensitivity and anorectal motility.[3]

There is a paucity of literature regarding anaesthetic implications in patients, particularly with SNS. There is a case report of spinal anaesthesia in a parturient with a sacral nerve stimulator.[4] We believe anaesthetic considerations and perioperative management of such cases can be like patients with spinal cord stimulators (SCS). Harned et al. recommend turning the amplitude of the SCS to the lowest possible setting and turning off prior to any procedure. This ensures if the device is inadvertently turned on, stimulation would be very low and likely be unnoticed. Turning off the device also reduces the risk of accidental reprogramming via electromagnetic interference (EMI).[5] Monopolar electrocautery should be avoided. If unavoidable, monopolar electrocautery should be used in the lowest effective setting and the grounding pad should be placed as far away as possible from the SNS and on the contralateral side of the pulse generator. Bipolar cautery is favoured. SNS may interfere with ECG monitoring resulting in high-frequency artefacts in multiple leads. SNS may present potentially dangerous interactions with cardiovascular implanted electronic devices (CIEDs) such as permanent pacemakers (PPM) and internal cardiac defibrillators (ICD). While manufacturers recommend against the simultaneous use of SCS and CIEDs, there are numerous examples of safe concomitant use in the literature.[5] By setting the CIEDs at maximum sensitivity and SCS at maximally tolerated stimulation, any interaction or interference under typical clinical settings would be observed. The implantation of the pulse generator on the contralateral side of the CIED is recommended.[5]

Adequate precautions need to be taken regarding confirming the position of the lead by reviewing the previous X-rays and reviewing the operation notes of insertion of the SCS/SNS may also be helpful.

Compared to SCS, SNS is unlikely to interfere with spinal or lumbar/thoracic epidural anaesthesia as leads are in the vicinity of sacral nerve roots. One needs to weigh potential risks and benefits when considering caudal analgesia. Ultrasound may be useful for identifying the correct level of lumbar interspace more definitively rather than relying on anatomical landmarks.[4]

It would be reasonable to first determine the brand and model of SNS, and then obtain the appropriate manual to review magnetic resonance imaging (MRI) compatibility before scheduling these patients for MRI studies.[5]

It is recommended that the SNS be interrogated postoperatively; however, this does not need to be done in the immediate postoperative setting.[5] In our case, the patient was referred to the primary treating urologist for further management.

To conclude, SNS is being used increasingly in patients with bowel and bladder voiding dysfunctions. The anaesthesia care team should be aware of the functionality of the device and potential risks posed to the patient and the device. The involvement of anaesthesia team early in the care improves the patient outcome.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.