Skin temperature measured by infrared thermography after specific ultrasound-guided blocking of the musculocutaneous, radial, ulnar, and median nerves in the upper extremity

Background. Sympathetic block causes vasodilatation and increases in skin temperature (T(s)). However, the T(s) response after specific nerve blocking is unknown. In this study, we hypothesized that T(s) would increase after specific blocking of the nerve innervating that area. Methods. Forty-six patients undergoing hand surgery were included. We performed ultrasound-guided, specific nerve blocking of either the musculocutaneous, radial, ulnar, or median nerve in each patient and analysed T(s) in the forearm and hand at 2 min intervals in the following 22 min by the use of infrared thermography. Areas of interest corresponding to the cutaneous innervation area of each of the four nerves were defined and the mean T(s) in each area was analysed. Results. Specific blocking of the ulnar and median nerves caused a substantial increase in mean (SD) T(s) in the areas innervated by these nerves [5.2 (3.2)degrees C and 5.1 (2.5)degrees C, respectively; both P < 0.0001]. The increase was even larger at the fingertips. Median nerve blocking also increased T(s) in the area of the hand innervated by the radial nerve (P < 0.0001). However, T(s) did not increase in any area after either musculocutaneous or radial nerve blocking. Conclusions. Specific blocking of the ulnar and median nerve causes substantial increases in T(s) in specific areas of the hand. In contrast, the specific blocking of the musculocutaneous or radial nerve does not increase T(s). Further studies are needed to clarify if these findings can be used to objectively evaluate brachial plexus block success.