A Randomized Comparison of the Neuropen® and a Plastic Disposable Neurologic Wheel for Assessing Spinal Block at Caesarean Section Jessica A. Wolin MD, Tekuila R. Carter MD, Curtis L. Baysinger MD, John Downing MD STATISTICAL METHODS RESULTS INTRODUCTION AND HYPOTHESIS FIGURES REFERENCES Although there is general agreement as to the level of neuraxial block needed for caesarean section, there is controversy as to how to best assess the level of the block. The choice of sensory modality tested and the method of testing vary among practitioners and institutions. Inter-observer variability in assessed block level is a well- documented phenomenon. The optimal method for assessing blockade should minimize inter-observer variability while consistently predicting adequate surgical anesthesia. The Neuropen® is considered a user-independent and standardized method of providing a touch stimulus to assess peripheral nerve function and has been studied for assessment of spinal blockade. However, the Neuropen still exhibits inter- observer variability. The Wartenberg wheel has been used to asses spinal blockade and has the advantage of providing a relatively continuous stimulus. However, the device has the potential to spread infection if it is not sterilized between uses. A 3” plastic neurologic wheel (PDNW) is an inexpensive and disposable alternative to the Wartenberg wheel that could be included in epidural or spinal kits. In this study, we compared the 3” PDNW to the Neuropen, hypothesizing that the PDNW would produce identical results to the Neuropen Power analysis indicated that 40 patients would be required to have an 80% chance of detecting a dermatomal difference of ≥ 1 level 1 between devices. Mann-Whitney-U test was used to compare height of the block between devices at each assessed time. Bland Altman plot was used to assess device measurement agreement at each assessed time. To date, 29 patients have been enrolled. Four enrolled patients were excluded due to technical problems leaving 25 with sufficient data for analysis. 20 patients were assessed for differences in light and sharp touch by Neuropen testing. Primary endpoint: No significant differences emerged between mean assessments made with the Neuropen and the PDNW at any time. (Figure 1, below) There was frequent and often wide variability between individual assessments made with the two devices at each assessed time. The direction of this variability was inconsistent and changed at different time points. (Figure 2, above right) Secondary endpoints: Assessed spinal level rose over the 20 minute period with a significant difference in level compared to the level at prior assessed times using both devices. We also observed a difference between assessed level to sharp and light touch with the Neuropen with no fixed relationship between levels. The mean difference between assessed levels narrowed over time. (Figure 3, below right) METHODS DEPARTMENT OF ANESTHESIOLOGY Figure 1: Neuropen, Wartenberg Wheel, Plastic Neurologic Wheel DISCUSSION Our results support the hypothesis that the PDNW compares favorably with the Neuropen in assessing spinal block for CS. It has the advantage of being inexpensive, compact, convenient and disposable. There was variability between the individual measurements made with the devices and it is not clear from this study whether that variability is inherent to the devices, or due to the somewhat subjective nature of the measurement. Although we did not study it here, it is possible that the near continuous nature of the stimulus provided by the pinwheel could minimize inter-observer differences in measurements, which would make the pinwheel a superior measuring tool. In addition, an interesting divergence between perception of sharp vs. light touch that varied over time was observed. This phenomenon may explain apparent inconsistencies in the relationship between sharp and light touch reported in previous studies 3 and merits further investigation. Of particular interest is the difference between analysis with the Mann-Whitney–U test and Bland Altman analysis. The former shows that overall measurement of spinal level is similar with the two devices. The latter reveals that for individual measurements there is a large degree of variability between the devices with unpredictable direction of the variability. It is not clear from our study whether this variability is due to inter-observer technique or whether it is due to differences in patient perception of the stimulus. Inter- observer variability has been noted in previous studies of testing devices. 2 It has been hypothesized that these differences were due to different ways of using the devices, but these differences seem to persist, even when relatively constant stimulus delivery methods are used. Figure 2: Bland Altman plots of Neuropen vs. PDNW at 5, 10, 15 and 20 minutes Figure 3 Neuropen block to touch and sharp touch at 5 and 20 minutes IRB approval and written informed consent were obtained Spinal or CSE anesthesia were obtained with hyperbaric bupivacaine (12-15 mg), plus a combination of fentanyl (0 – 25 ug), clonidine (0 – 20 ug), and/or morphine (0 – 200ug ). Anesthetic and dose were determined by the attending anesthesiologist. A strip of tape was placed on the abdomen and marked with dermatomal levels T10-T-2. After IT injection, the highest level of the block until return of light touch and sharp touch sensation were assessed by 2 of 3 anesthesiologists (JW, CB, JD) who were blinded to each other’s findings, one using the Neuropen and the other using the PDNW. The instrument used and the order of testing were randomized according to a random number table. Assessments were done very 5 minutes for 20 minutes and at the end of the surgery Interval VAS scores and use of supplemental analgesics were recorded. The primary endpoint was height of the block to sharp touch at each assessed time. Secondary endpoints were height of block to light touch at each assessed time and the difference between levels assessed with light and sharp touch using the Neuropen. Neuropen,Wartenberg wheel, PDNW 1.Soundarararajan N, Russell I. A randomised comparison of hand-held Neurotip and the Neuropen for assessing loss of touch during spinal anaesthesia for cesarean section. In J Obstet Anesth 2007;16: Shirgaonkar AT, Purva M, Russell IF. A double blind comparison of the variability of block levels assessed using a hand held Neurotip or a Neuropen at elective caesarean section under spinal anesthesia. Int J Obstet Anesth 2010;19: Russell IF. A comparison of cold, pinprick, and touch for assessing the level of spinal block at caesarean section. Int J Obstet Anesth 2004;13: