Comparison of SpO2 on different fingers of hands and effect of local temperature on SpO2 by pulse oximeter in healthy adults

Background: Pulse oximeter is a simple, cost effective and routinely used instrument to measure the peripheral oxygen saturation (SpO2). Aim and Objectives: To compare SpO2 values among all the fingers of both hands and also the effect of local change in temperature on SpO2 values. Material and Methods: Study was done on 40 healthy volunteers between the ages of 18 to 45 years. SpO2 was measured using same pulse oximeter from every finger of both hands after waiting for 1 minute and also after immersing the hands in 15oC and 45oC water bath for 5 minutes. A gap of 15 minutes was kept between cold and hot water bath immersion to bring back normal temperature. Results: There were significant differences (p < 0.05) in SpO2 values between middle finger and thumb and between ring finger and thumb in right hand, and between left middle finger and right thumb, between left little finger and right thumb and between right ring finger and left thumb. SpO2 values showed a significant decrease (p < 0.05) between normal temperature and cold in right index and middle fingers and left index, middle and little fingers and between normal temperature and hot in right index, middle, ring fingers and left middle finger. Conclusion: It can be hypothesized that difference in perfusion due to supply by different arteries may be one of the contributing factors for this variation in values between fingers. Vasoconstriction may be the reason for significant decrease in SpO2 when hand is immersed in cold water. Increased arterio- venous shunt resulting in increased pulsatile venous flow might have resulted in decrease in SpO2 on exposure to heat.