Differential Sensory Block During Labor Epidural Analgesia: a Prospective Observational Study to Investigate the Relationship of Lower and Upper Sensory Block Levels to Cold With Sensory Block to Pinprick and Light Touch

Epidural analgesia remains the gold standard for pain control during labor and delivery. Proper assessment of an epidural's level of blockade is important for providing safe and effective analgesia. Previous studies have established that the most commonly tested modality for adequacy of epidural blockade is a patient's sensory blockade to cold temperature. In a study performed at our institution, Soares et. al. (publication pending) documented two thresholds of sensory block to ice: one defined as the lower sensory block level, in which the patient is able to notice the cold sensation but perceives that it is not as cold as a control dermatome; the other defined as the upper sensory block level, in which the patient perceives that the cold sensation is at approximately the same temperature as if it were applied to a non-anesthetized area such as the neck or face. Although this a known finding to nurses and physicians assessing the sensory block to ice, this phenomenon and its magnitude has not been previously reported in epidural anesthesia. The goal of this study is to examine patients with labour epidurals and to determine the dermatomal relationship between the lower and upper sensory block levels to cold when compared with sensory blockade to both pinprick and light touch.