Effect of Peripheral Vasoconstriction on Pulse Oximetry

Abstract

Objective. We tested the hypothesis that peripheral vasodilation has an effect on arterial oxygen saturation measurements by pulse oximetry, independent of temperature. Methods. Study 1 compared finger arterial oxygen saturation values (SpO₂), before and after peripheral vasoconstriction while temperature was kept constant. This was achieved by administering dexmedetomidine (peripheral vasoconstrictor) to 16 volunteers given general anesthesia. Study 2 compared SpO₂ before and after peripheral vasodilation (brachial plexus block) in a neurally denervated left hand and a neurally innervated right hand in ten awake volunteers. In both studies measurements were also made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmission through a finger (LTF), finger temperature and of hemodynamic variables. Results. In Study 1, systolic blood pressure, SpO₂ and LTF values increased (vasoconstriction) during dexmedetomidine infusion, (P<0.0001 for all) while there were no changes in finger temperature. In Study 2, in the left hand (axillary block), temperature increased by 1.9 ± 1.6 °C (P=0.004), SpO₂ decreased by 2.5 ± 1.0 % (P<0.0001) and LTF values decreased (vasodilation) by 42 ± 8 % (P<0.0001) after axillary block. Simultaneously, the axillary block did not induce any changes in temperature, SpO₂ or LTF values in the neurally innervated right hand. Conclusions. Our results demonstrate that finger pulse oximeter SpO₂ measurements can be affected by peripheral vascular tone independent of temperature. The mechanism for this effect remains speculative and unproven.