Evaluation of ventilatory responses in severe acidemia in diabetic ketoacidosis

Ventilatory response in patients with severe acidemia in diabetic ketoacidosis (DKA) was unresolved. Thus, 83 patients with uncomplicated DKA were studied for the relation between arterial blood pH, calculated bicarbonate concentration (HCO3) and carbon dioxide tension (PCO2). The equation for the PCO2/HCO3 pair was: PCO2 = 1.58 x HCO3 + 7.6 (SE 2.55, r = 0.95, p < 0.01); for the PCO2/pH pair was: PCO2 = 43.8 x pH-293 (SE 6.23, r = 0.66, p < 0.01). The correlation coefficient for the PCO2/HCO3 pair was significantly greater compared to the PCO2/pH pair (p < 0.001). Multiple regression analysis showed that severe acidemia (pH less than or equal to 7.10) per se was independently associated with PCO2 far the PCO2/HCO3 pair, but not for the PCO2/pH pair. Thus, our patients were divided into 2 groups for the PCO2/HCO3 pair: group 1 with pH less than or equal to 7.10 (n = 25) and group 2 with pH > 7.10 (n = 58). The equations were: group 1:PCO2 = 3.18 x HCO3 + 2.88 (SE 1.72, r = 0.87, p < 0.01); group 2:PCO2 = 1.65 x HCO3 + 6.6 (SE 2.6, r = 0.95, p < 0.01). There was a significant difference between these 2 equations (p < 0.01). Mathematical simulations with 10 sets of 25 or 58 random pH/PCO2 pairs (and calculated HCO3) for 'group 1' and 'group 2' also showed similar results, albeit with less precision. Hence, ventilatory response in DKA varies between patients with severe acidemia and those with moderate acidemia by the PCO2/HCO3 pair, but not by the PCO2/pH pair.