Abstract
PURPOSE
To analyze the association between the defining characteristics of decreased cardiac output (DCO), identified by noninvasive methods, and the cardiac index (CI), obtained by thermodilution.
METHODS
DCO was defined as cardiac indices ≤2.5 L/min/m2. Univariate statistical tests were applied to analyze the association between defining characteristics and DCO. The first phase of the study consisted of a literature search for defining characteristics of DCO, formulation of operational definitions for each characteristic, and selection of the characteristics to be clinically studied. In the second phase, the selected defining characteristics were assessed in 49 postoperative heart surgery patients (X̄= 63.4 years; 59% female, 72% had undergone coronary artery bypass graft). On all surgical days one of the authors, a critical care nurse, identified the patients who met the inclusion criteria (>18 years; submitted to cardiopulmonary bypass; with pulmonary artery catheter emplaced for a maximum period of 72 hours), assessed them according to the selected defining characteristics, measured the CI by thermodilution, assessed other parameters depending on the presence of a pulmonary artery catheter, and collected information about drugs the patient was receiving.
FINDINGS
Eighty-seven defining characteristics were identified. After a detailed analyses, 42 were selected for study. Of these, 10, depending on whether they had a pulmonary artery catheter, served either as a dependent variable (CI) or as a descriptive variable; 32 were the independent variable. Twenty-four patients had DCO and 25 did not. The range of cardiac output readings in patients with DCO was 2.0–3.9 L/min; in patients without DCO it was 4.0–8.9 L/min. The correlation coefficient between DCO and CI was 0.928 (p<0.00), as expected. From the total of 32 independent variables, 8 were not assessed: restlessness, dilated pupils, jugular vein distention, altered heart sounds, superficial breathing, use of accessory muscles for breath, hepatic congestion, and ascites. Level of consciousness could not be assessed in 44 patients because they were intubated. From the remaining 23 variables, 6 had frequencies >80% in patients with DCO: altered central venous pressure, altered hemoglobin/hematocrit, hyperglycemia, altered cardiac enzymes, decreased peripheral perfusion, and slow intestinal peristalsis. Five variables had frequencies between 50% and 80%: decreased peripheral pulses, dysrhythmia, altered chest radiography, blood pressure variations, and edema. Only two variables were associated with DCO: decreased peripheral pulse (p= 0.00) and decreased peripheral perfusion (p= 0.00) because they were more frequent in patients with DCO. Oliguria/anuria was identified in 1 patient with DCO and in 2 without. There was statistical association between oliguria/anuria and diuretics (p= 0.01). There was no association between other drugs (vasoactive, sedatives) and selected defining characteristics.
DISCUSSION
The variables with frequencies >80% in patients with DCO are typical findings after heart surgery. The results of association tests suggest that decreased peripheral pulses and decreased peripheral perfusion, of all the independent variables studied, are good indicators of DCO. However, they also occurred in patients without DCO. Although there was no association between oliguria/anuria and DCO, the use of diuretics masked identification. Considering that intensive care patients are promptly treated at the first sign of oliguria, it is difficult to use this variable to diagnose DCO in the clinical context.
CONCLUSIONS
Decreased peripheral pulses and decreased peripheral perfusion must be kept as defining characteristics of DCO. A practical application of the results of this study is that the peripheral perfusion is an important parameter to assess the hemodynamic state of postoperative heart surgery patients. The introduction of ever-more sophisticated and potentially more accurate technologies that are not always indicated or available poses the risk of neglecting noninvasive clinical assessment techniques. Proper nursing education should include the teaching of noninvasive assessment of patients and the development of perceptual and cognitive skills necessary to make the professional able to obtain and interpret, as accurately as possible, the data observed.
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