Initial Results Support the Efficacy of Transcutaneous Electrical Stimulation as a Noxious Stimulus for Neurological Assessments in Unresponsive Patients

Introduction: Serial neurological assessments are the foundation of clinical neuromonitoring for unresponsive patient with critical neurological illness. As such, noxious (i.e. painful) stimulation is a foundational skill for physicians and nurses who care for these patients. The current standard-of-care method of noxious stimulation is manual pressure, applied by hand. This practice is associated with significant variability, and manual stimulation has been implicated in the suboptimal reliability of neurological assessments in unresponsive patients. We hypothesized that transcutaneous electrical stimulation could produce similar exam responses as manual noxious stimulation in unresponsive patient admitted to the neuro ICU.

Methods: Patients admitted to the neuro ICU were screened based on unresponsive status and a neuro exam finding of either 1) localize or 2) withdraw in the upper extremity, or 3) withdraw in the lower extremity. There was n=5/group in this initial cohort. Consent was obtained from the patient’s medical decision maker. Immediately following a stable neuro exam, additional assessments were conducted on a single extremity with either manual noxious stimulation or varying levels of transcutaneous electrical stimulation in randomized order. Transcutaneous electrical stimulation was delivered at the supraorbital notch or the distal digit of the hand or foot using planar concentric electrodes at 20%, 40%, 60%, 80%, and 100% of levels corresponding to 7/10 pain in conscious subjects.

Results: For n=5 patients in each group we found equivalent exam responses for mechanical stimulation and transcutaneous electrical stimulation at both the 80% and 100% stimulation levels in 80% of participants per group. No adverse events occurred in this study.

Conclusion : To our knowledge, these findings represent the first use of an alternative to mechanical noxious stimulation for neuro assessments in unresponsive patients. These results suggest the potential for transcutaneous electrical stimulation to serve as an efficacious alternative to manual noxious stimulation, which may provide a more reliable and humane future method. Our next step is a dose escalation study to determine the optimal stimulation parameters for transcutaneous electrical stimulation across additional levels of consciousness.