DIAGNOSIS OF MIXED ACID-BASE-DISORDERS IN DIABETIC-KETOACIDOSIS

In diabetic ketoacidosis, a mixed acid-base disorder is suggested when the anion gap increase (DELTAAG) does not equal the bicarbonate decre ase (DELTAHCO3), or when the DELTAAG/DELTAHCO3 ratio does not equal 1. 0. It is widely assumed that DELTAAG/DELTAHCO3 is significantly differ ent from 1.0 when it is less than 0.8 or greater than 1.2. The validit y of these ratio limits were examined by analyzing a normal control gr oup of 68 subjects and 27 diabetic ketoacidosis admissions that had no evidence of mixed disorders. In the 27 ketoacidosis admissions, regre ssion analysis showed that DELTAAG was predicted to equal DELTAHCO3, a s expected in pure anion gap acidosis: DELTAAG = 1.0DELTAHCO3 (r = 0.7 44, p < 0.001). It was found that DELTAAG is significantly different f rom DELTAHCO3 when they differ by more than 8 mEq/L, and equivalently, DELTAAG/DELTAHCO3 is significantly different from 1.0 when it is less than (1.0 -8/DELTAHCO3) or greater than (1.0 + 8/DELTAHCO3). These cr iteria from regression analysis suggested that 4% of the 27 pure anion gap acidoses, and 3% of the control group, had mixed disorders. In co ntrast, the ratio limits of 0.8 and 1.2 suggested 56% of the pure anio n gap acidoses, and 94% of the control group, had mixed disorders. It was concluded that mixed disorders are overdiagnosed by the ratio limi ts of 0.8 and 1.2. Mixed disorders are more accurately detected by not ing whether DELTAAG and DELTAHCO3 differ by more than 8 mEq/L.