New gas-liquid equilibration method: syringe tonometer.

This new apparatus for gas-liquid equilibration (tonometry) in a transportable vessel is designed for tonometry of blood or buffer solution in a specially designed syringe. Gas enters the syringe chamber through small holes in the tip of the syringe plunger and bubbles upward through the sample. The syringe plunger is a second chamber, which is used for warming and humidifying the gas before it enters the tonometer chamber. The entire syringe is housed in a transparent, temperature-controlled environment during equilibration. After equilibration, the sample is easily entered into a blood-gas analyzer. At most, gas-liquid O2/CO2 equilibration for 2.5 mL of buffer or blood requires less than 13 min. Comparisons with a standard thin-film tonometer show good agreement for pO2 and pCO2 over the range 0-93 kPa (0-700 mmHg) and 2-20 kPa (14-150 mmHg), respectively. The syringe tonometer eliminates contamination of the sample during transfer and transport to the analyzer, thus making tonometry more technique-independent. The apparatus is simple and easy to use, with definite advantages over existing methods of tonometry.