Anesth Analg 2007;104:741-742
© 2007 International Anesthesia Research Society
doi: 10.1213/01.ane.0000253919.20089.1e
LETTER TO THE EDITOR
Section Editor:
Lawrence Saidman
Further Evidence that Temperature Measurement Is a Useful Indicator of Regional Anesthesia Outcomes
Markus F. Stevens, MD, DEAA,
Robert Werdehausen,
Henning Hermanns, MD, and
Peter Lipfert, MD, PhD
Department of Anesthesiology; University of Düsseldorf; Düsseldorf, Germany; markus.stevens{at}med.uni-duesseldorf.de
In Response:
Drs. Galvin and Niehof (1) suggest that temperature increase after peripheral nerve block has a high sensitivity and specificity for a successful block. We agree (2,3). The differences in results are possibly linked to methodological differences. We defined a temperature difference of 1°C as clinically useful for two reasons. First, a temperature difference of 1°C is the least temperature difference which can be felt by a hand touching (4). Second, minute skin temperature increases can be induced by surroundings in a clinical situation outside the controlled conditions of study or by the low accuracy of most clinically used thermometers. Additionally, Galvin et al. (3) found a skin temperature difference of up to 0.8°C in patients with failed nerve blocks. This further demonstrates that only skin temperature increases more than 1°C can be interpreted as a sign of a successful block.
Drs. Galvin and Niehof correctly noted that in 63.2% of patients, the temperature increase ( 1°C) occurred at the same time or earlier than the loss of sensation, but only in 6.6% of our patients did the temperature increase precede the loss of sensation. What is the use, then, of temperature measurement as a predictor of successful block, if an increase in skin temperature occurs in one-third of patients (36.6%) after limb anesthesia is already complete?
Drs. Galvin and Niehof question why there was only a minor temperature increase at the site innervated by the femoral nerve. Because we were also astonished by this observation, we investigated the skin temperature of the lower extremities after combined femoral/sciatic nerve block, epidural and spinal anesthesia by video-thermography. We demonstrated a uniform pattern of skin temperature increase for all three blocks, i.e., a large temperature increase in the feet, but no significant temperature changes at the calf (5). Galvin et al. only measured temperature distally at the hand and not at the forearm. However, a successful block of the median nerve could lead to a temperature increase at the middle finger, but to no temperature increase in the skin innervated by the median nerve at the forearm, as shown for the sciatic nerve at the leg (5). Our most likely explanation for this phenomenon is that the capability of the skin to warm after regional anesthesia is predominantly determined by the abundance of subcutaneous skin vessels and the location of arterio-venous anastamoses (6).
REFERENCES
- Galvin EM, Niehof S. Further evidence that temperature measurement is a useful indicator of regional anesthesia outcomes. Anesth Analg 2007;104:740–1.[Free Full Text]
- Stevens MF, Werdehausen R, Hermanns H, Lipfert P. Skin temperature and sensory changes during regional anesthesia of the lower extremity. Anesth Analg 2006;102:1247–51.[Abstract/Free Full Text]
- Galvin EM, Niehof S, Medina HJ, et al. Thermographic temperature measurement compared with pinprick and cold sensation in predicting the effectiveness of regional blocks. Anesth Analg 2006;102:598–604.[Abstract/Free Full Text]
- Guyton AC, Hall JE. Somatic sensations: II. Pain, headache, and thermal sensations. In: Guyton AC, Hall JE, eds. Textbook of medical physiology. 9th ed. Philadelphia: Saunders, 1996:609–20.
- Werdehausen R, Braun S, Hermanns H, et al. Uniform distribution of skin temperature increase following different regional anesthesia techniques of the lower extremity. Reg Anesth Pain Med 2007; 32:73–8.[Web of Science][Medline]
- Johnson JM, Proppe DW. Cardiovascular adjustments to heat stress. In: Fregly MJ, Blatteis CM, eds. Handbook of physiology. New York: Oxford University Press, 1996:215–43.
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