To explore the relationship between the pulse pressure/central venous pressure (PP/CVP) ratio and the cardiac output (CO) of patients after cardiac surgery from the basic principles of hemodynamics, and to further evaluate the predictive value of PP/CVP ratio in patients with secondary low cardiac output syndrome (LCOS) after cardiac surgery.

A retrospective study was conducted, and patients who received pulse indicator continuous cardiac output (PiCCO) monitoring were enrolled at the department of critical care medicine of Peking Union Medical College Hospital from January 1, 2016, to September 1, 2021. Patients were divided into two groups: the LCOS group [cardiac index (CI) < 33.34 mL·s^-1·m^-2, 25 cases] and the non-LCOS group (CI ≥ 33.34 mL·s^-1·m^-2, 125 cases) according to the CI at 6 hours after surgery. The general clinical data and hemodynamic parameters were collected. Correlations between PP/CVP ratio and PiCCO monitoring indicators were performed with Pearson or Spearman correlation test. Receiver operator characteristic curve (ROC curve) analysis was carried out to evaluate the predictive value of the parameters in patients with LCOS after cardiac surgery.

A total of 150 patients with PiCCO monitoring after cardiac surgery were included. There were no differences in baseline characteristics between the two groups, while PP in the LCOS group was lower than that in the non-LCOS group [mmHg (1 mmHg ≈ 0.133 kPa): 40 (37, 44) vs. 55 (46, 64)], CVP was higher than that in the non-LCOS group [mmHg: 12 (11, 14) vs. 10 (8, 12)], and PP/CVP ratio in the LCOS group was lower than that in the non-LCOS group [3.3 (2.9, 3.7) vs. 5.5 (4.6, 6.8)], with significant differences (all P < 0.05). Correlation analysis results showed that PP/CVP ratio was positively correlated with CI, CO, and stroke volume index (SVI), respectively (r_s = 0.660, 0.592, 0.600, all P < 0.001). CI was negatively correlated with PP (r_s = 0.509, P < 0.001) and positively correlated with CVP (r_s = -0.297, P < 0.001). ROC curve analysis revealed that compared with PP, CVP, SVI and cardiac function index (CFI), PP/CVP ratio was the best predictor of LCOS after cardiac surgery [area under the ROC curve (AUC) was 0.94±0.02, P < 0.001], when the optimum cut-off value was 4.41, the sensitivity was 80.00%, and the specificity was 96.00%.

PP/CVP ratio was moderately positively correlated with CO after cardiac surgery, and PP/CVP ratio could be used as a prognostic predictor for LCOS after cardiac surgery.

Low cardiac output syndrome; Cardiac output; Pulse pressure; Central venous pressure