EFFECT OF LOCAL LIMB TEMPERATURE ON PULSE OXIMETRY AND THE PLETHYSMOGRAPHIC PULSE-WAVE

We attempted to evaluate prospectively local thermoregulatory vasocons triction and vasodilatation in 15 volunteers by means of pulse oximetr y and plethysmography as measured by a finger tip-pulse oximeter. Rece nt studies [1] concluded that the plethysmo time interval (PTI) betwee n the QRS complex on ECG and the upstroke of the plethysmographic wave of the pulse oximeter is useful in evaluating the peripheral circulat ory status. Venous (both Vv cubitae) blood samples for determination o f SvO(2) were drawn, as well as pulse oximetry SpO(2) oxygen saturatio n measurements and calculation of PTI were performed under conditions of normothermia, hypothermia and hyperthermia, before and after immers ing the hands of the volunteers in a cold (15 degrees C) and warm (45 degrees C) waterbath. Two pulse oximeters simultaneously were used, on e for each hand, in order to check to which extent SpO(2), SvO(2) and PTI might be influenced by gross limb temperature changes. Our results show that during local hyperthermia SpO(2) significantly decreased an d during local hypothermia SpO(2) increased after immersing the one ha nd in a warm waterbath and the other hand in a cold waterbath at the s ame time. The peripheral SvO(2) significantly increased in the warm ha nd and decreased in the cold hand. PTI remained unchanged after exposu re to either a cold or a warm waterbath. The possibility of technical causes for the SpO(2) changes were eliminated. Finger-tip pulse oximet ry SpO(2) readings change with limb temperature. The change in venous oxygen saturation can be explained by temperature dependent arterioven ous shunts in the periphery. The observed change in SpO(2) probably re flects altered transmission of arterial pulsations to venous blood in the finger.