Compared with the Henderson-Hasselbalch approach, the Stewart approach may better describe the mechanisms of acid-base physiology and disorders. We prospectively examined the acid-base disorders of 100 routine blood samples from critically ill patients using Stewart's physical chemistry analysis. The median results were pH 7.45, PaCO2 5.5 kPa, bicarbonate 27.2 mmol.l-1 and base excess 3 mmol.l-1. The median reference strong ion difference was 46.0 meq.1-1 and the measured median was 45.5 meq.l-1. The median reference total weak-acid concentration was 11.1 mmol.l-1. The measured median total weak-acid concentration was 6.8 mmol.l-1. From Stewart's approach, the most likely explanation for the overall alkalosis was decreased total weak-acid concentration resulting from decreased plasma albumin concentration.
- Critical illness: acidosis; alkalosis