A preliminary study evaluating cardiac output measurement using Pressure Recording Analytical Method (PRAM) in anaesthetized dogs

Abstract

Background: Haemodynamic variations normally occur in anaesthetized animals, in relation to the animal status, administered drugs, sympathetic and parasympathetic tone, fluid therapy and surgical stimulus. The possibility to measure some cardiovascular parameters, such as cardiac output (CO), during anaesthesia would be beneficial for both the anaesthesia management and its outcome. New techniques for the monitoring of CO are aimed at finding methods which are non invasive, accurate and with good trending ability, which can be used in a clinical setting. The aim of this study was to compare the Pressure Recording Analytical Method (PRAM) with the pulmonary artery thermodilution (TD) for the measurement of cardiac output in 6 anaesthetized critically ill dogs.

Results: Fifty-four pairs of CO measurements were obtained with a median (range) of 3.33 L/min (0.81-7.21) for PRAM-CO and 3.48 L/min (1.41-6.56) for TD-CO. The Bland-Altman analysis showed a mean bias of 0.17 L/min with limits of agreement (LoA) of - 0.46 to 0.81 L/min. The percentage error resulted 18.2%. The 4-quadrant plot analysis showed an acceptable concordance (93%) between the 2 methods. The polar plot showed a good trending ability with the mean angular bias of 3.9° and radial LoA ± 12.1°.

Conclusions: The PRAM resulted in good precision, acceptable concordance and good trending ability for the measure of CO in the anaesthetized dog, representing a promising alternative to thermodilution for the measurement of CO. Among all the pulse contour methods available on the market it is the only one that does not require any calibration or adjustment of the measurement. Further studies are required to verify the ability of this method to accurately measure cardiac output even during unstable hemodynamic conditions.

Keywords: Anaesthesia; Cardiac output; Dog; Pressure recording analytical method; Pulse contour.

Fig. 1

Plot of PRAM-CO values (y axis) and TD-CO values (x axis) with Spearman correlation test results

Fig. 2

Bland Altman plot for 54 pairs of CO measurements. Light grey line: mean bias; dashed lines: upper and lower limits of agreement

Fig. 3

Four-quadrant plot. Sequential percentage changes (∆CO) of PRAM-CO (Y axis) and of TD-CO (x axis). The central grey zone represents the exclusion area that contains ∆CO < 10%. Upper right and lower left quadrant contain concordant ∆CO, upper left and lower right quadrant contain discordant ∆CO

Fig. 4

Polar plot of ∆CO expressed as polar coordinates (radius and polar angle). The central grey circle represents the exclusion zone (mean ∆CO < 10%). The black dashed line represents the mean polar angle of 3.9° (mean angular bias), light gray dashed lines represent the radial LoA (± 12.1°). Sixteen data points were excluded from analysis because they fell in the exclusion zone