Which is the best finger

Dr. Krishan Chugh

Pulse Oximetry

Thumb/Any Finger Can Be Used But Which Is The Best ?

In a survey of health care workers for monitoring pulse oximetry, index finger was selected by 80 % for SpO2 measurement



Dr. Krishan Chugh



Principle of optical plethysmography & photospectrometry

The diode emits red and infra-red light which passes through the pulsatile vascular bed. Oxygenated and Deoxygenated hemoglobin absorb these 2 wave lengths differentially. Ratio between the 2 wave lengths absorbed gives the SpO2

Emitting diode

Finger

  

Photo-detector

• Technology is designed to recognize peaks and troughs

• Pulsatile flow essential
Pulse oximeters with wave form are better





Dr. Krishan Chugh

 

Hence, finger which has the best blood supply is likely to give the highest reading

Dr. Krishan Chugh

Arterial Supply of Hand & Finger

Index finger is dominantly fed from deep palmar arch created from radial artery. But middle finger receives both ulnar and radial artery blood supply.

  

Picture Courtesy Dr. Amitava Gupta

Picture Courtesy Dr. Amitava Gupta

Dr. Krishan Chugh



Hence, Middle Finger is the Best site for SpO2 measurement



There may be some exceptions due to individual anatomical variations

Dr. Krishan Chugh