A comparison of a Neuropen monofilament and ethyl chloride for assessing loss of touch sensation during combined spinal–epidural anaesthesia for caesarean section

BackgroundBefore caesarean section is performed under regional anaesthesia the block should be assessed, preferably using a touch stimulus. What constitutes a touch stimulus remains unclear. The aim of this study was to compare a Neuropen monofilament with ethyl chloride in the assessment of touch.MethodsForty women undergoing elective caesarean section received combined spinal–epidural anaesthesia. The upper dermatome spread was assessed using touch to a monofilament and ethyl chloride and cold to ethyl chloride at 5, 10, 15 and 20 min after intrathecal injection and again at the end of surgery. Visual analogue pain scores and Apgar scores were collected.ResultsTwo one-sided test analysis demonstrated equivalence for Neuropen touch and ethyl chloride touch within one dermatome (P < 0.0001). Wilcoxon post tests showed that Neuropen touch was marginally lower than ethyl chloride touch (P = 0.0056). The median level of block to touch using both stimuli was below T5 at all time points. Pain scores had a median value of 0 cm and Apgar scores were 10 in all infants at 10 min.ConclusionData from this study suggest that a Neuropen monofilament and ethyl chloride are equivalent when used to assess a block to touch. However, subtle differences in the level of block to touch indicate that sensory level assessments should state the stimulus used. As the block to touch was below T5 at all time points, when opioids are added to local anaesthetics, T5 might no longer represent a necessary goal to ensure the absence of pain during caesarean section.