PERIPHERAL NERVE STIMULATION IN DIABETIC PATIENT

The prevalence of diabetes mellitus (DM) in industrialized countries is estimated to be about 7.3% and its incidence has been growing in recent years. The prevalence of diabetic neuropathy in the diabetic patient population is up to 50%. When limb surgery is necessary, it is reasonable to assume that diabetic patients will benefit from a regional anesthetic because of the severe comorbidities associated with DM. On the other hand, the use of regional anesthesia (RA) has generally not been recommended in patients with preexisting neuropathies mainly because of medical liability issues, as worsening neuropathy could be attributed to nerve damage caused by the regional anesthetic. The current state of the art of peripheral regional anesthesia for the identification of correct placement of an injection needle suitably close to the target nerve is to elicit a motor response by current injection through the needle. Constant reduction of the current as the nerve is approached ensures close proximity so that an effective nerve block is obtained when the local anesthetic is delivered through the needle, and absence of a motor response at 0.3 mA is generally accepted as a safety marker to avoid harmful intraneural injection. An important deficit in our understanding is whether diabetic neuropathy influences the stimulation parameters for peripheral nerve stimulation (PNS), possibly decreasing safety. The currently proposed research is guided by the hypothesis that nerves in patients with DM are resistant to stimulation and, as a consequence, the current thresholds for PNS have to be set much higher to prevent injections from occurring within the epineurium. We will examine this the effect of DM on nerve excitability in a blinded, prospective, observational case control trial. Accordingly, we have defined following aims: Aim 1: To characterize the required stimulation current in patients with and without diabetes mellitus. Aim 2: Follow-up to examine if the rate of adverse neurologic events is higher in diabetic patients. Aim 3: Guided by the results, formulate recommendations for the performance of regional anesthesia in patients with a history of DM. These experiments will provide better understanding of the needle-current-nerve relationship during peripheral nerve stimulation. Findings from this proposed study will have a major impact on patient safety, especially in the subgroup with preexisting neuropathy, undergoing regional anesthesia.

The main goal of this project was to gain fundamental knowledge on the area of regional anesthesia. The authors hope to contribute to improved patient safety for this specific anesthetic technique for all patients and specifically for those with pre-existing damage of peripheral nerves, especially for patients with diabetes mellitus. Based on the collected data the main result of this study is that the sole use of a nerve stimulator for the location of peripheral nerves during regional anesthetic procedures is not reliable and may even be harmful for patients with pre-existing neurological damage. This is due to the high variability of the stimulation current necessary for eliciting a motor response. There was no statistically significant difference between patients with diabetes and the healthy control group, however the variability in the diabetic group was considerably higher. In this group high stimulation currents were frequently observed, which puts patients at risk for suffering neurologic injuries by the sole use of a nerve stimulator during regional anesthesia. With the additional use of an ultrasound machine the position of the injection needle in relation to the nerve that should be blocked can be determined better. The results of this study show that the electric current thresholds which are current standard of care are not suitable for all patients.