Comparison of four objective methods of monitoring digital venous congestion.

This study sought to determine which of the four most commonly used objective monitoring modalities--pulse oximetry, laser Doppler flowmetry, skin surface temperature measurement, and skin surface fluorescence--is best able to detect early digital venous congestion. Digital venous congestion was induced in 12 hands by inflating a digital cuff to 5 mm Hg above the resting diastolic pressure. The cuff remained inflated for 1 hour while monitoring was done at 10-minute intervals. The baseline and experimental laser Doppler indices differed by at least 30% in each subject, and the laser Doppler index was always less than 40% during venous congestion. Skin surface fluorescence gave falsely normal results in three of eight hands, while pulse oximetry failed to detect venous congestion in any hand. The difference in temperature between the control and experimental fingers almost always exceeded the threshold of 2.5 degrees C. The results indicate that both laser Doppler flowmetry and skin surface temperature measurement are highly accurate methods of monitoring early digital venous congestion that are noninvasive and easy to use. Skin surface temperature measurement has further advantages in that thermometers are less expensive and easier to transport than laser Doppler devices. In contrast, skin surface fluorescence is invasive and cumbersome in addition to being less sensitive to experimentally induced early digital venous congestion than either laser Doppler flowmetry or skin surface temperature measurement. Pulse oximetry is unreliable in detecting early digital venous congestion.