Assessment of Validity and Reliability of a Neurophysiologic Evoked Potential Instrument

Abstract

The purpose of this study was to determine the validity of a step by step nonsimultaneous method for measuring somatosensory evoked potentials (SSEPs) and to determine reliability of a neurophysiologic evoked potential instrument, Bio-logic Evoked Potential System, on healthy, adult volunteers in a controlled environment. The neurophysiologic monitoring during anesthesia and surgery is used to optimize surgical outcomes and minimize neurologic morbidity. During surgery, the anesthetic regimen and subject variables can affect the electrical signals of neurophysiologic monitoring. The neurophysiologic instrument has an important role in the successful monitoring of the central nervous system. The research questions were: (1) What is the content validity of a research protocol that is a step by step method for measuring SSEPs (as assessed by a panel of experts)? (2) What is the precision of repeated measurements across five generators of SSEPs on the right and left median nerves using the Bio-logic Instrument? (3) What is the difference in the measurements of SSEPs on the median nerves between males and females? and (4) What is the relationship between the length of the arm from the wrist crease to Erb's point and the poststimulus latency? Content validity was determined by a panel of experts, who assessed the research protocol for measuring SSEPs. Using Lynn's (1986) Content Validity Index, a one hundred percent agreement was calculated from the content validity assessment results. The results of the assessment of the research protocol content demonstrated that the step by step methods for measuring SSEPs designed by the investigator was a content valid approach. This descriptive study used convenience sampling for a two group design of 52 healthy adult volunteers divided by gender. The t-test results of mean difference between the two groups was statistically significant $(p \le 0.05)$ for height, arm length, and stimulus. Data collection consisted of three nonsimultaneous somatosensory evoked potential measurements on each median nerve (right and left) and of three arm length measurements (nerve length) on each arm from the posterior wrist crease to Erb's point. The results of latency, interwave latency, and amplitude of the SSEP measurements across the five generators showed the Bio-logic Evoked Potential Instrument to be precise according to the consistency of the repeated measurements, the calculated R-Square Value, and the coefficients of variation. The study results showed a difference between males and females with statistical significance $(p \le 0.05)$ for the measurements of latency and amplitude. The mean latencies for the five generators were computed to be less for females as compared to males. Yet, the female group had greater mean log amplitudes for all five generators when compared to the male group. The results of the study supported the theory that as nerve length increased so does latency as measured at Erb's point (brachial plexus). But the results were not statistically significant $(p \ge 0.05)$, even when the gender variable was analyzed for an interaction with arm length. The findings of the study showed the step by step research protocol accurate for measurement of SSEPs and the Bio-logic Instrument precise for measurement of SSEPs.