Cardiac Index Validation Using the Pressure Recording Analytic Method in Unstable Patients

Objective

The authors investigated the accuracy and precision of the pressure recording analytic method (PRAM) in cardiac index measurement compared with thermodilution in unstable patients, a setting in which minimally invasive monitoring devices often fail.

Design

Criterion standard.

Setting

Intensive care unit.

Patients

Thirty-two consecutive patients with low cardiac output syndrome treated with an intra-aortic balloon pump and/or high doses of inotropic drugs but without atrial fibrillation were studied after cardiac surgery.

Interventions

None. Pulmonary and radial artery catheters were already in situ for clinical reasons.

Measurements and Main Results

Four patients (12.5%) were excluded from the study because of artifacts caused by under- or overdamping of the arterial pressure monitoring system. The authors performed 3 injections of the thermal indicator in 5 minutes through the pulmonary artery catheter. Mean cardiac index values of 12 consecutive beats were considered for the PRAM. A significant correlation was found between the cardiac index assessed by thermodilution and PRAM (r = 0.72, p < 0.001). The mean bias between the 2 techniques was 0.072 ± 0.41 L/min/m² with lower and upper 95% limits of confidence of −0.089 and 0.233 L/min/m², respectively. The percentage error was 30%. Sufficient agreement between the two techniques was evidenced by the Bland-Altman plot with only two points above the limits of agreement.

Conclusions

This study showed that PRAM, a minimally invasive method for cardiac index assessment, is clinically useful even in unstable patients such as those receiving intra-aortic balloon pump and/or ongoing high doses of a inotropic drugs because of a low cardiac output syndrome but without atrial fibrillation.

Key Words: pressure recording analytic method (PRAM), validation, cardiac index, hemodynamic monitoring, unstable patients, cardiac surgery, pulse contour analysis