Temperature as a Test for Regional Anesthesia
Assessing the effectiveness of regional anesthesia is an essential part of perioperative care. Before surgery begins, the anesthesiologist must confirm that the targeted nerves are adequately blocked to ensure analgesia and patient comfort. Several methods have been established to test the success of the regional anesthesia block, including evaluation of sensory loss to pinprick, touch, and temperature.
Neurophysiology informs the reasoning for using temperature as a test for regional anesthesia. The nerve fibers responsible for transmitting temperature and pain sensations are small, thinly myelinated and unmyelinated fibers. They are particularly sensitive to local anesthetics and tend to be blocked earlier than larger, heavily myelinated fibers such as those controlling motor function. As a result, the loss of temperature sensation is often one of the earliest and most reliable indicators that a block is taking effect 1–3.
In clinical practice, temperature testing is simple and non-invasive. A cold stimulus is gently applied to the skin in the distribution of the targeted nerve. The patient is then asked to report whether the cold sensation feels diminished or absent compared to an unblocked area. In some cases, a warm object or the back of the examiner’s hand may be used to assess for altered heat sensation, although cold testing is more common 4,5.
Temperature testing offers several advantages. First, it is easy to perform at the bedside without specialized equipment or a risk of scarring, making it suitable for a wide range of clinical environments. It is also sensitive, often detecting block onset earlier than other modalities such as pinprick or light touch. Patients usually find the test intuitive and can easily compare sensations between blocked and unblocked areas. Since temperature sensation is mediated by fibers that are among the first to be affected, it provides a reassuring early marker of block success before surgical stimulation begins 6–8.
Despite its usefulness, temperature has a number of limitations as a test of regional anesthesia. It relies on patient cooperation and subjective reporting, which may be difficult in children, sedated patients, or those with communication barriers. The perception of cold can also vary between individuals, introducing variability in interpretation. Furthermore, temperature testing alone does not provide information about motor block or deeper analgesia, so it should be used in conjunction with other assessments. Environmental factors, such as a cold operating room, may also influence results if patients confuse ambient chill with the testing stimulus 4,9,10.
References
1. Borum, A. D., Voogd, K. L., Smith, M. A., Gerlif, C. & Jensen, H. I. Relationship between Temperature and Pain Sensation Following a Peripheral Ulnar Block: An Exploratory Pilot Study. DOI: 10.2174/0125896458335716241002075140.
2. Lenhardt, R. Chapter 37 – Body temperature regulation and anesthesia. in Handbook of Clinical Neurology (ed. Romanovsky, A. A.) vol. 157 635–644 (Elsevier, 2018).
3. Bissonnette, B. & Nebbia, S. P. Hypothermia during Anesthesia: Physiology and Effects of Anesthetics on Thermoregulation. Anesthesiology Clinics of North America 12, 409–424 (1994). DOI: 10.1016/S0889-8537(21)00685-4
4. Frank, S. M., Nguyen, J. M., Garcia, C. M. & Barnes, R. A. Temperature monitoring practices during regional anesthesia. Anesth Analg 88, 373–377 (1999). DOI: 10.1097/00000539-199902000-00003.
5. Hermanns, H., Werdehausen, R., Hollmann, M. W. & Stevens, M. F. Assessment of skin temperature during regional anaesthesia-What the anaesthesiologist should know. Acta Anaesthesiol Scand 62, 1280–1289 (2018). DOI: 10.1111/aas.13176
6. Hilgenhurst, G., Shafer, A. L. & Pharm, D. Temperature, Not Pain, Is Best for Assessing Regional Block. Reg Anesth 17, 239–240 (1992). DOI: 10.1136/rapm-00115550-199217040-00014
7. Sessler, D. I. Temperature Monitoring and Perioperative Thermoregulation. Anesthesiology 109, 318–338 (2008). DOI: 10.1097/ALN.0b013e31817f6d76
8. Bruins, A. A. et al. Thermographic skin temperature measurement compared with cold sensation in predicting the efficacy and distribution of epidural anesthesia. J Clin Monit Comput 32, 335–341 (2018). DOI: 10.1007/s10877-017-0026-y
9. Morris, R. H. Influence of ambient temperature on patient temperature during intraabdominal surgery. Ann Surg 173, 230–233 (1971). DOI: 10.1097/00000658-197102000-00008
10. Battistel, L., Vilardi, A., Zampini, M. & Parin, R. An investigation on humans’ sensitivity to environmental temperature. Sci Rep 13, 21353 (2023). DOI: 10.1038/s41598-023-47880-5