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Potential of Venous Ionized Calcium for Identification of High Risk Critical Care Patients
*Peter Bendix, *James Whedon, Kenneth Burchard
Darmouth-Hitchcock Medical Center, Lebanon, NH
Background
Low arterial ionized calcium (AIC) is associated with increased mortality risk for patients admitted to the ICU or trauma bay. We sought to determine if central venous ionized calcium (CVIC) is similar to AIC for risk categorization.
Methods
We performed a convenience retrospective cross sectional analysis of medical records data from our tertiary medical center’s ICU. 529 ICU patients were sampled. 471 consecutive, paired laboratory values for AIC and CVIC derived from < 30 minutes apart sampling of venous and arterial blood. We dichotomized values for AIC as high risk (<1.0 mmol/L) and low risk (1.01-1.33 mmol/L). We used linear regression to establish the point of dichotomization for CVIC and model the effect of CVIC on AIC. We analyzed for correlation between all measured values of AIC and CVIC and tested for correlation between AIC and CVIC values within high risk and low risk categories. Our main outcome measure was binary sensitivity and specificity of CVIC for detection of high risk values of AIC.
Results
We found strong positive correlation between AIC and CVIC (Spearman's rho = 0.70; p<.001) (Figure 1). CVIC for detection of high-risk AIC has sensitivity of 79% and specificity of 84% (Figure 2). The positive predictive value of CVIC for high risk AIC (PPV) = 69%, and negative predictive value (NPV) = 91%.
Conclusions
CVIC is moderately sensitive and highly specific for prediction of values of AIC in critically ill patients. This may mean that CVIC or peripheral iCa could be used to assess mortality risk in critically ill patients at admission to the ICU or trauma bay, eliminating the need for arterial or central venous puncture/catheterization.
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