Thoracic blood drainage debt: what amount should be expected as normal in the first postoperative hours of cardiac surgery?

Background

Data on the normal pattern of thoracic blood drainage in the first postoperative hours may be found in the literature, and values below 1 ml/kg per hour have been considered markers of good outcome.

Objectives

To assess, in our population, the normality threshold of the blood drainage index (BDI) in the first postoperative hours of cardiac surgery (CS), and to correlate this index with the clinical variables that may predict a worse outcome and a longer intensive care unit (ICU) stay.

Case series and methods

A classic cohort study was carried out with data of 1458 patients consecutively collected from June 2000 to January 2001 (593 patients, group B) and from January 2001 to February 2003 (865 patients, group A). All variables were previously defined according to the literature. The results underwent statistical analysis with the following tests: univariate analysis with the chi-square test, the Student t test, Pearson correlation, the Mann–Whitney test, Yates correction, and the McNemar test.

Results

With data obtained in the sample, a histogram of postoperative thoracic blood drainage was made. Adjusting through the likelihood ratio and distributing in the exponential form, its 95th percentile was determined, and the value of 0.97 ml/kg per hour was obtained in the postoperative period. When the BDI was correlated with the variables studied, greater drainage values were found in the following conditions: valve replacement associated with myocardial revascularization and surgery of the aorta (P = 0.0000 and P = 0.00002, respectively); patients with left atrium > 4.5 (P = 0.003); longer extracorporeal circulation (P = 0.0001); platelet count lower than 100,000 (P = 0.001); multiple organ dysfunction syndrome score greater than 4 (P = 0.00000); Sepsis-related Organ Failure Assessment score > 4 (P = 0.00000); longer length of stay in the ICU (P = 0.001); and a greater death index (P = 0.00000). No statistical difference between the results of the two hospitals was found.

Conclusions

A normal BDI of 0.97 ml/kg per hour was established in our population in the postoperative period of CS, and a poorer outcome and longer length of stay in the ICU were observed in patients with drainage greater than the BDI found. The following clinical variables can predict greater BDI in the postoperative period of CS: the type of CS; left atrium > 4.5; prolonged extracorporeal circulation; platelet count < 100,000; and greater multiple organ dysfunction syndrome and Sepsis-related Organ Failure Assessment scores.