Evaluation of cardiac output variations with the peripheral pulse pressure to mean arterial pressure ratio

Cardiac output (CO) optimisation during surgery reduces post-operative morbidity. Various methods based on pulse pressure analysis have been developed to overcome difficulties to measure accurate CO variations in standard anaesthetic settings. Several of these methods include, among other parameters, the ratio of pulse pressure to mean arterial pressure (PP/MAP). The aim of this study was to evaluate whether the ratio of radial pulse pressure to mean arterial pressure (PPrad/MAP) could track CO variations (CO) induced by various therapeutic interventions such as fluid infusions and vasopressors boluses [phenylephrine (PE), norepinephrine (NA) or ephedrine (EP)] in the operating room. Trans-oesophageal Doppler signal and pressure waveforms were recorded in patients undergoing neurosurgery. CO and PPrad/MAP were recorded before and after fluid challenges, PE, NA and EP bolus infusions as medically required during their anaesthesia. One hundred and three patients (mean age: 52 +/- 12years old, 38 men) have been included with a total of 636 sets of measurement. During fluids challenges (n=188), a positive correlation was found between PPrad/MAP and CO (r=0.22, p=0.003). After PE (n=256) and NA (n=121) boluses, PPrad/MAP positively tracked CO (r=0.53 and 0.41 respectively, p<0.001). By contrast, there was no relation between PPrad/MAP and CO after EP boluses (r=0.10, p=0.39). PPrad/MAP tracked CO variations during PE and NA vasopressor challenges. However, after positive fluid challenge or EP boluses, PPrad/MAP was not as performant to track CO which could make the use of this ratio difficult in current clinical practice.