Simple and rapid method for the assessment of the oxygen affinity of haemoglobin

The affinity of haemoglobin for oxygen may be expressed as the oxygen tension at 50 % saturation under standard conditions (P50). A rapid technique for the determination of P50 using a micro-tonometer with pH electrode and oximeter was evaluated. Equilibration time was found to be 15 minutes with no change in PCV, although plasma haemoglobin levels were slightly elevated. Estimation of P50 in blood from 32 non-smokers gave a mean of 26·4 ± 0·9 (SD) mm Hg (3·51 ± 0·12 kPa) with a precision of 0·3 (SD) mm Hg (0·04 kPa). The system was found to be accurate, precise, and simple in operation, allowing up to 16 P50 determinations an hour to be performed with 85 μl blood samples.