Ionized hypocalcemia during out-of-hospital cardiac arrest and cardiopulmonary resuscitation is not due to binding by lactate.

OBJECTIVE

To determine the relationship between ionized calcium concentrations and blood lactate levels during cardiac arrest and cardiopulmonary resuscitation (CPR).

DESIGN

A prospective cohort study.

SETTING

Emergency department (ED) and general intensive care unit in a city hospital (tertiary care center).

PATIENTS AND PARTICIPANTS

32 patients with out-of-hospital cardiac arrest; 14 of the patients had a return of spontaneous circulation (ROSC) and 18 of the patients died.

INTERVENTIONS

Basic and advanced life support.

MEASUREMENTS AND RESULTS

Concentrations of ionized and total calcium, bicarbonate, lactate, and pyruvate and pH were simultaneously determined immediately upon arrival at the ED, and at 30 and 60 min. Upon arrival at the ED, all patients had ionized hypocalcemia (1.09 +/- 0.02 mmol/l). Ionized and total calcium concentrations progressively decreased during and after CPR, but pH and bicarbonate concentrations did not show any significant changes. In patients who had ROSC, a significant, but perhaps not clinically relevant, relationship was observed between the ionized calcium concentrations and pH (r2 = 0.152, p = 0.0117). In the patients who died, there were significant correlations between ionized calcium and pH (r2 = 0.382, p = 0.0001) and bicarbonate concentrations (r2 = 0.298, p = 0.0006). No definite correlations were demonstrated when comparing ionized calcium concentrations with lactate and pyruvate concentrations.

CONCLUSIONS

Ionized hypocalcemia during out-of-hospital cardiac arrest and CPR is not due to binding by both lactate and pyruvate, but may be partly due to complexing by bicarbonate, with some modifications due to variations in pH.