Cutaneous blood flow responses to injection trauma measured by laser Doppler velocimetry

The question has been raised repeatedly: what is the effect of an intracutaneous injection on skin blood flow? This is particularly relevant where radioisotope clearance techniques are used for its measurement. This study was performed to measure these changes. Using the noninvasive technique of laser Doppler velocimetry to measure cutaneous blood flow, injections were made in the forearm skin with a needle alone, and with 20 microliter of saline, histamine or epinephrine. In each case, measurements were made of resting flow and elevated flow levels, the latter produced by heating the site to 44 degrees C for 5 min prior to the study. At resting flow levels, insertion of the needle or injection of saline produced approximately a sevenfold increase in flow over the base line; the flow increase remained elevated for periods of at least 20 min. Histamine produced a much smaller increase, and epinephrine a decrease as compared to the base line. In the heated sites, vasodilatation was already present, and flow levels decreased in all cases, slightly with the needle and saline, more with histamine, and most with epinephrine. It is concluded that there is a significant increase in skin blood flow caused by injections into the skin, but this response is progressively more masked as base line flow levels increase.