Technical tips: methods of warming and maintaining limb temperature during nerve conduction studies

Many physiologic and nonphysiologic factors contribute to performing correct or incorrect nerve conduction studies. Nonphysiologic factors such as filter settings, averaging techniques, stimulus artifact, and supramaximal stimulation are just a few of the ones encountered during the nerve conduction study examination. Physiologic factors such as muscle atrophy, tremors and spasticity, edema, and profuse sweating are physical conditions that may pose technical problems during the study. Other general physiologic conditions such as height, aging and nerve maturation, variation between various nerve segments, and temperature may also contribute to the obtaining an accurate and correct nerve conduction study, as well as the electromyogram (EMG) itself. Obtaining and keeping the patient's surface temperature between 31 to 34 or 33 to 34 degrees Celsius, depending on which literature you read, is essential to obtaining and presenting correct nerve conduction studies. Cold limb temperature results in discrepancies in basic nerve conduction values such as amplitude, distal latency, conduction velocity, and duration in both motor and sensory studies. Cold to cool temperature also adversely affects the EMG. Repetitive stimulation studies for neuromuscular junction disease are greatly affected by decreasing the limb temperature. How to warm these patients and maintain a desirable temperature throughout the examination is vitally important. Methods of warming patients may vary from inexpensive to expensive in cost and simple to complex in nature.