Intensive Care Unit Admission Parameters Improve the Accuracy of Operative Mortality Predictive Models in Cardiac Surgery

BACKGROUND: Operative mortality risk in cardiac surgery is usually assessed using preoperative risk models. However, intraoperative factors may change the risk profile of the patients, and parameters at the admission in the intensive care unit may be relevant in determining the operative mortality. This study investigates the association between a number of parameters at the admission in the intensive care unit and the operative mortality, and verifies the hypothesis that including these parameters into the preoperative risk models may increase the accuracy of prediction of the operative mortality. METHODOLOGY: 929 adult patients who underwent cardiac surgery were admitted to the study. The preoperative risk profile was assessed using the logistic EuroSCORE and the ACEF score. A number of parameters recorded at the admission in the intensive care unit were explored for univariate and multivariable association with the operative mortality. PRINCIPAL FINDINGS: A heart rate higher than 120 beats per minute and a blood lactate value higher than 4 mmol/L at the admission in the intensive care unit were independent predictors of operative mortality, with odds ratio of 6.7 and 13.4 respectively. Including these parameters into the logistic EuroSCORE and the ACEF score increased their accuracy (area under the curve 0.85 to 0.88 for the logistic EuroSCORE and 0.81 to 0.86 for the ACEF score). CONCLUSIONS: A double-stage assessment of operative mortality risk provides a higher accuracy of the prediction. Elevated blood lactates and tachycardia reflect a condition of inadequate cardiac output. Their inclusion in the assessment of the severity of the clinical conditions after cardiac surgery may offer a useful tool to introduce more sophisticated hemodynamic monitoring techniques. Comparison between the predicted operative mortality risk before and after the operation may offer an assessment of the operative performance

Predictive power of the models.

<p>Receiver operating characteristics analysis with area under the curve (AUC) for the logistic EuroSCORE (LES) and the ACEF score, before and after correction for the parameters at the admission in the intensive care unit (ICU).</p

Independent predictors of operative mortality at the admission in the Intensive Care Unit.

<p>Multivariable logistic regression analysis (stepwise forward). Variables dichotomized according to the values in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013551#pone-0013551-g001" target="_blank">figure 1</a>.</p

Parameters at the admission in the Intensive Care Unit in survivors and non-survivors.

<p>Data are expressed as mean ± standard deviation. P values according to Mann-Whitney U test.</p

Patient population profile (survivors and non-survivors).

<p>Data are expressed as mean ± standard deviation of the mean or number (%). P values according to Mann-Whitney U test. CPB: cardiopulmonary bypass.</p

Heart rate and operative mortality.

<p>Association between heart rate at the admission in the intensive care unit for relevant categories, with parameters for the identified cut-off value.</p

Blood lactates and operative mortality.

<p>Association between blood lactates at the admission in the intensive care unit for relevant categories, with parameters for the identified cut-off value.</p