ABSTRACT
The Henderson-Hasselbalch equation can be considered as the backbone of acid base physiology. This is conventionally represented using two dimensional plots. Although two dimensional plots are simple to use, the equation in reality represents a surface in three dimensional space. Any combination of PaCO2, [HCO3 ] and blood pH values representing acid base disorders is restricted to this surface. Two models depicting the three dimensional surface generated by the Henderson-Hasselbalch equation were constructed from easily available materials. The first model was constructed using coloured beads, thin metal rods and plywood. This model depicted the Henderson-Hasselbalch surface as a collection of discreet points. The second model depicted the Henderson-Hasselbalch equation as a continuous surface using polystyrene sheets and white cement. The models were presented to undergraduate and post-graduate medical students along with other conventional two dimensional nomograms. Three dimensional models of the Henderson-Hasselbalch equation can serve as supplementary teaching material to ensure a deeper understanding of acid base physiology.
