A randomised comparison of a hand-held Neurotip and the Neuropen for assessing loss of touch sensation during spinal anaesthesia for caesarean section.

Background: With spinal anaesthesia various methods may be used to assess the block to touch. We wished to compare the levels of block assessed using a non-standardised, assessor-dependent touch stimulus with those assessed when the same stimulus was applied in a standardised manner independent of the assessor.

Methods: In a double-blind, randomised study the levels of block to touch were assessed by two investigators, one using a hand-held Neurotip tester pin and the other using the same tester pin mounted in a spring loaded system (Neuropen). Both the testing device and the order of testing were randomised between the two observers. The dermatomes were marked on patients' torsos before surgery.

Results: Whole group data analysis in a Bland Altman plot demonstrated a median difference of 0 dermatomes between the two methods: the 5th, 25th, 75th, and 95th centiles of agreement being -2, -1, +1, and +2 dermatomes respectively. There were occasional wide differences in levels of block to touch with the Neuropen varying between seven dermatomes rostral to and four dermatomes caudal to the Neurotip. These differences were short-lived and did not affect clinical management.

Conclusion: When comparing two very similar touch stimuli, one standardised and user-independent and one non-standardised, we observed occasional wide but short lived differences in the assessed levels of block to touch. Although these differences did not affect clinical management, whether more dissimilar touch testing methods might affect clinical management remains to be seen.