Assessing blocks after spinal anaesthesia for elective caesarean section: how different questions affect findings from the same stimulus

BackgroundA block to touch to T5 is widely used to indicate an adequate level of block for caesarean section with spinal anaesthesia. However, two studies using a “block to light touch” to T5 as their end-point, had a high requirement for intraoperative analgesia and their results cast doubt on the adequacy of a block to touch to T5. On enquiry, these two papers did not assess complete block to touch, but asked mothers when the touch sensation “was the same as” a control stimulus. The difference between these two assessment methods is unknown. The current study presents prospectively collected sensory block data which included both block to touch and the level when touch was the same as a control stimulus.MethodsThe levels of block were assessed using a Neurotip®. The mother was asked four questions to assess the block: first touch level, first sharp level, touch same as control and sharp same as control.ResultsThe first touch level was a median of two dermatomes lower than the touch same as a control level [IQR 0–3, range 0–6]. Block level assessment methods using first sharp and touch same as control were equivalent.ConclusionWhen describing a sensory block, not only is it necessary to indicate the exact stimulus used, but it is important to define the actual question asked of the patient. Clinically, block assessment using the first sharp level and touch same as control are equivalent.