A low-cost transmittance transducer for measurement of blood oxygen saturation in extracorporeal circuits

Designs for a for low-cost dual wavelength transducer based on light transmittance and a disposable cuvette for monitoring oxygen saturation (SO ₂) in extracorporeal arterial and venous blood are presented. The transducer utilizes red and infrared light-emitting diodes and a large photodiode; it is designed to attach to a flow-through curvette modified from 3/8-in×3/8-in bypass-circuit connectors. A mock extracorporeal circulation system was assembled to evaluate operation of the transducer at a controlled blood SO ₂ and the relationship between light transmittance and hemodilution. SO ₂ was calculated based on multiple linear regression analyses. The results show a high correlation between the SO ₂ obtained with the equipment designed and values measured with commercial gasometric equipment in the range of 50% to 100% (r ²=0.976, error <2%). The method presented allows continuous and real time measurement of whole blood SO ₂ with a low-cost transmittance transducer.