Cardiac output by arterial pulse contour: reliability under hemodynamic derangements

Pulse contour methods (PCM) for the measurements of cardiac output (CO) are gaining popularity in intensive care settings but their reliability during hemodynamic instability has been questioned. Pressure-recording-analytical-method (PRAM) is a newly developed uncalibrated hemodynamic monitor and its capability in measuring CO during hemodynamic instability is still under investigation. Dobutamine (2.5 and 5 microg/kg/min), vasoconstriction (arginine-vasopressin 4, 8 and 16 IU/h), hemorrhage (-10%, -20%, -35%, and -50% of the theoretical volemia), and volume resuscitation were induced in eight swine. CO by means of thermodilution (CO(ThD)), transesophageal echocardiography (CO(TEE)) and PRAM (CO(PRAM)) were contemporarily registered. R(2), bias, and percentage error were used to compare the methods. Comparison between CO(PRAM) and CO(ThD) resulted in: r(2)=0.87; bias=-0.006 l/min; precision=+/-0.87 l/min; percentage error=22.8%. Comparison between CO(PRAM) and CO(TEE) resulted in: r(2)=0.85; bias=-0.007 l/min; precision=+/-0.86 l/min; percentage error=22%. Sub-group analysis revealed disagreement between methods only during the last two steps of hemorrhage: CO(PRAM) vs. CO(ThD): r(2)=0.67, bias=-0.37 l/min, precision=+/-1.04 l/min, limits of agreement=-1.39+0.66 l/min, and percentage error=45%; CO(PRAM) vs. CO(TEE): r(2)=0.38, bias=0.4 l/min, precision=+/-1.42 l/min, limits of agreement=-0.99+1.79 l/min, and percentage error=62%. PRAM resulted to be accurate in measuring CO during hemodynamic stability, tachycardia, and vasoconstriction. When volemia was reduced by >35%, disagreement between methods was observed.