A double blind comparison of the variability of block levels assessed using a hand help Neurotip™ or a Neuropen® at elective caesarean section under spinal anaesthesia

BackgroundWe previously noted that when two experienced anaesthetists assessed the level of spinal block to touch at caesarean section, one with a hand held device (Neurotip™), and the other with a very similar spring loaded device (Neuropen®), the median difference between the assessed levels of block was zero but there were some wide individual paired differences between the anaesthetists. We theorised that differences in the applied pressure of the stimulus may have contributed to this variation. We wished to investigate whether compared to the Neurotip™, the Neuropen® would reduce the variability of assessed block levels between anaesthetists of varying experience.MethodsThe levels of block to touch and sharp pinprick were assessed by paired anaesthetists using both the Neurotip™ and Neuropen®. The anaesthetists were blind to each other’s assessments. To ensure comparability of dermatome identification, the patient’s torso was marked before surgery.ResultsIn 44 cases, managed by 35 different pairs of anaesthetists, there was no statistically significant difference in the variability of differences in assessed levels of block between anaesthetists (P=0.23) whether the Neurotip™ or Neuropen® or touch or sharp pinprick were used. The median dermatomal difference [upper quartile, lower quartile] was 0 [1, -1] for both instruments with both touch and sharp pinprick.ConclusionCompared to the Neurotip™, the Neuropen® did not result in a reduction of the variability in the differences in spinal block levels when assessed by 35 different pairs of anaesthetists.