Critical evaluation of the 'heated-hand-technique' for obtaining 'arterialized' venous blood: incomplete arterialization and alterations in glucagon responses

In order to test the degree of 'arterialization' and the occurrence of arterio- (or capillary-) venous differences in glucose concentrations for commonly used blood sampling sites (including the retrogradely cannulated dorsal hand vein with application of dry heat to this hand/arm--the 'heated-hand-technique'), oxygen partial pressure (oxygen saturation) and plasma glucose was determined in blood drawn from different venous sites before and after an oral glucose load (75 g). Experiments with and without heating (hot air 68 degrees C) were compared in nine healthy volunteers. Basal pO2 (and oxygen saturation) increased in the order cubital fossa vein less than superficial forearm vein less than dorsal hand vein. Heating raised pO2 by approximately 20 mmHg; P = 0.008) and oxygen saturation (P = 0.008-0.02) at all sites, including those on the contralateral arm. Capillary-venous glucose differences after the glucose challenge were significantly related to the sampling site (P less than 0.0001). They were reduced by approximately 50% in response to heat exposure (P = 0.008-0.011) and could be correlated to pO2-values (r = 0.92; P = 0.01). The lowest capillary-venous glucose concentration difference was measured with the 'heated-hand-technique' (0.4 +/- 0.1 mmol l-1). Heating did not alter integrated incremental glucose (capillary values), insulin, and C-peptide-responses and late, counter-regulatory responses (120-240 min after glucose) of cortisol, growth hormone, and adrenalin. However, the late glucagon response was enhanced (P = 0.011) by heating, concomitant with a significantly reduced 'reactive' decrement in glucose concentrations. In conclusion, the 'heated-hand-technique' provides blood more similar to arterial blood that can be obtained from other venous sampling sites. However, significant residual differences in pO2 and glucose concentrations remain. In addition, altered counter-regulatory hormone responses may occur with heating.