Does pulse pressure variation correlate with conventional measures of preload?

Objective: Systolic pressure variation (SPV) and pulse pressure variation (PPV) are sensitive and specific predictors of cardiovascular response to fluid challenge, with PPV being slightly more accurate. SPV does not correlate well with conventional measure of preload such as pulmonary artery occlusion pressure (P_PAO), central venous pressure (CVP) or echocardiographic measures such as end-diastolic area (EDA), especially in patients with decreased left ventricular (LV) function. Because PPV is a more sensitive and specific predictor of preload responsiveness, we questioned whether PPV would correlate with conventional measures of preload. Design: Prospective repeat measures series. Setting: University teaching hospital cardiac operating theatre. Patients: Eight anesthetized cardiac surgery patients before and after cardiopulmonary bypass. Interventions: Positive pressure ventilation with tidal volumes of 8-10 ml/kg. Measurements: P_PAO, CVP, arterial pressure and 2-dimensional LV mid-axis cross-sectional areas with transesophageal echocardiography were measured both before and after bypass during a brief apneic period followed by a mechanical breath. All measures were performed with the chest closed. Main Results: Using linear regression modeling, neither SPV nor PPV correlated with P_PAO, CVP or EDA. Conclusions: PPV does not correlate with conventional measures of preload such as CVP, P_PAO, and EDA. This suggests that preload responsiveness and estimates of LV end-diastolic volume reflect different physiologic concepts.