Background: Pulse pressure variation (PPV) is an accepted measure of intravascular filling. It can now be estimated automatically. However, there is limited knowledge of the epidemiology and associations of such estimates in cardiac surgery patients.
Methods: We conducted a pilot prospective observational study of the epidemiology and associations of automatically estimated PPV in 30 cardiac surgery patients admitted to the intensive care unit of a tertiary hospital. The study was conducted in June and July 2010. We collected automated monitor-estimated PPV values every 15 minutes during mandatory ventilation in patients after cardiac surgery. We simultaneously collected data on all relevant haemodynamic values, hourly fluid balance, tidal volume (V(T)) and peak airway pressure. We made a total of 205 measurements on 30 patients. A PPV value ≥ 13% was selected as defining a likely fluid responsiveness (FR) state. Clinicians were not informed of the study.
Results: PPV values ≥ 13% were present in 38% of measurements, and the average duration of this physiological state was 38 minutes per patient. Higher PPV values correlated with negative fluid balance (P < 0.001), lower mean pulmonary arterial pressure (P = 0.018), lower cardiac index (P = 0.013), higher peak airway pressure (P < 0.001) and higher V(T) (P < 0.001).
Conclusions: In a tertiary ICU, among patients who had recently had cardiac surgery, automated PPV values in the likely FR range were present in over a third of measurements. Correlations with other haemodynamic and ventilation values were logical and expected.