Altered perceptions after upper and lower extremity blocks: An initial investigation

Background and Objectives: Nerve blocks frequently produce unusual altered perceptions in the extremities. We examined perceptual changes experienced after peripheral blocks. Methods: Fifty consecutive patients having an upper or lower extremity block for surgery participated in this prospective study. Patients were divided into 2 groups: upper extremity (n = 20) and lower extremity (n = 30). Each group was asked a list of questions about perceptions of limb sensation, length, weight, and location and given a detailed 2-point discrimination test over the V-1-V-3 divisions of the trigeminal nerve prior to block and sedation. While the extremity was still blocked, the exam was repeated before postanesthesia care unit discharge. Results: in both groups, 98% of patients described altered limb perception. The perceptions in the upper extremity were: heaviness, 60%; numbness, 50%; warmth, 40%; pain, 30%; full or fat, 20%; floating, 5%; shorter, 0%; or thinner, 10%. The perceptions in the lower extremity were: numbness, 75%; heaviness, 46%; warmth, 33%; pain, 32%; full or fat, 36%; floating, 25%; shorter, 18%, or thinner, 7%. Upper extremity block patients were more likely to describe the limb as lighter (P < .0001); the lower extremity group was more likely to describe the limb as numb (P = .01) or floating (P = .0002). There was no difference in the ability to correctly identify the location of the limb between the groups. There was no difference in 2-point discrimination between each assessment for either group. Conclusion: The results of this study confirm and quantify the perceptions experienced by patients undergoing upper and lower extremity blocks. These perceptions are prevalent. This knowledge is helpful in providing patients with accurate preoperative preparation. Further investigation is warranted to determine the neurologic etiology of these observations.