Fiber-optic chemical sensors (Gas-Stat®) for blood gas monitoring during hypothermic extracorporeal circulation

Abstract

Measurements of pO₂, pCO₂ and pH by optical fluorescence microsensing technology has recently become available for monitoring blood gases during extracorporeal circulation (ECC). We have compared simultaneous measurements with fiber-optic sensors (Gas-Stat®, Bentley) and electrochemical sensors (ABL-4®, Radiometer) on discrete samples.

In 10 patients undergoing coronary artery bypass grafting during hypothermic (25 °C) ECC and hemodilution (hemoglobin concentration 4 mmol · 1^-1) arterial and venous pO₂, pCO₂ and pH were measured in-line in the extracorporeal circuit at the actual blood temperature. Simultaneous and anaerobically collected blood samples in glass syringes were analyzed within five minutes at 37 °C in the ABL-4.

Linear regression analysis of the values at actual temperature shows the following equations: Gas-Stat = Y, ABL-4 = X: pO₂ (kPa): Y=1.04 X+0.5 r = 0.95 n = 136 pCO₂(kPa): Y=0.71 X + 1.5 r = 0.79 n = 136 pH: Y = 0.788 Y + 1.590 r = 0.76 n = 136

The advantage of the Gas-Stat is continuous monitoring of blood gas parameters during ECC. The present study shows that measurements of pO₂, pCO₂ and pH with fiber-optic chemical sensors may be reliable. The differences between the two principles of measurement may be due to unknown factors interfering with the in-line measurements or to variations in sensitivity and stability of the individual sensor.

Key-words:

• Carbon dioxide
• electrochemical sensors
• hydrogen ion
• optical fluorescence sensors
• oxygen