Hypocalcemia and nephrogenous cyclic AMP production in critically ill or injured patients

Critically ill or injured patients often have impaired cardiovascular function. Since low ionized calcium levels can cause such changes, serum calcium and urine calcium were measured in a prospective study involving 28 criticially ill or injured patients and 16 normal controls. Serum protein levels were also measured to calculate "corrected" total calcium levels. Ionized calcium levels are difficult to measure. Since ionic hypocalcemia is thought to increase the "nephrogenous production" of cyclic AMP, cyclic AMP levels were measured in the blood and urine of these patients and the "nephrogenous" cyclic AMP calculated from the creatinine clearance. The mean total serum calcium in these patients was 7.7 +/- 0.8 mg/dl (S.D.). This was significantly lower (p less than 0.001) than our controls (9.6 +/- 0.6). When corrected for hypoproteinemia, the mean serum calcium (8.7 +/- 0.8) was still significantly lower (p less than 0.005) than control (9.4 +/- 0.5). The mean urine calcium excretion in the patients (56 +/- 66 mg/100 ml G.F.R.) was lower, but not significantly so, than in the controls (84 +/- 44 mg/100 ml G.F.R.). The "apparent nephrogenous" cyclic AMP in the study group was 2,731 +/1 1,451 pm/ml/100 ml G.F.R. The nephrogenous cyclic AMP had a negative correlation (r =-0.45) with "corrected" total calcium levels. Thus "total," "corrected" total, and "ionized" calcium levels appear to be reduced in the majority of critically ill or injured patients studied. The clinical implications of these findings and the potential value of serial cyclic AMP determinations in blood and urine will be discussed.