Hadzic's Regional Anesthesia > Part XI. Neurologic Complications of Regional Anesthesia > Chapter 69. Neurologic Complications of Peripheral Nerve Blocks: Mechanisms & Management Peripheral Nerve Blocks in Anesthetized Patients Steven Deschner, MD, Alain Borgeat, MD, Admir Hadzic, MD

Normal versus Abnormal Discomfort/Pain on Injection

"Injection of local anesthetic in close proximity to the nerves is often associated with discomfort.^26,81 This is thought to result from mechanical irritation of the nerves or plexi as local anesthetic is injected in the immediate vicinity. Based on his studies of brachial plexus anesthesia, Winnie²⁶ coined the term "pressure paresthesia" to describe the discomfort patients feel during local anesthetic injection and implied that this was a desirable sign of impending successful blockade. In actual clinical practice, however, the variability of patients' pain thresholds, their ability to verbalize a sensation pain during a procedure, and an anesthesiologist's subjective interpretation of any such response make it very difficult to recommend where a "line" could be drawn between normal and abnormal pain or paresthesia on injection. In fact, a number of published case reports demonstrate that patients' complaints of pain during PNB may not be helpful in preventing the development of the neurologic complication. For instance, Barutell et al.²⁷published a report in which a patient communicated discomfort on injection that was perceived as "normal pressure paresthesia" by the anesthesia team. When the injection was carried out, the patient went on to develop permanent neurologic damage. Similarly, in the report by Kaufman et al.,⁸⁹ seven patients had discomfort at some point during block injection; however, this information could not be used to prevent the development of permanent neurologic injury,..."