[A clinical study of the evaluation of hemodynamic status in mechanically ventilated critically ill patients by continuous non-invasive arterial pressure monitor]

Objective: To evaluate the difference and correlation between continuous non-invasive arterial pressure (CNAP) monitor and pulse indicated continuous cardiac output (PiCCO) monitor on determination of hemodynamic parameters in mechanically ventilated critically ill patients, and to assess the feasibility of non-invasive monitoring of hemodynamics with CNAP.

Methods: A prospective observation self-control study was conducted.The critically ill patients with mechanical ventilation who needed hemodynamics monitoring, and admitted to the fourth department of intensive care unit (ICU) of Fujian Provincial Hospital from June 2018 to March 2019 were enrolled. PiCCO catheter were inserted immediately after admission, the hemodynamic indexes were measured by thermodilution method, and mean arterial pressure (MAP_PiCCO), cardiac index (CI_PiCCO), pulse pressure variation rate (PPV_PiCCO) and systemic vascular resistance index (SVRI_PiCCO) were obtained at 0 hour and 24 hours respectively. Meanwhile, the above indexes (MAP_CNAP, CI_CNAP, PPV_CNAP and SVRI_CNAP) were measured with CNAP. All measurements were repeated thrice and average values were reported. The differences in above parameters between the two methods were evaluated. Pearson test was used for the correlation analysis and Bland-Altman analysis method was used for consistency test.

Results: Thirty-eight patients were enrolled into this study. One patient died within 24 hours was excluded, 2 patients were excluded due to withdrawing treatment within 24 hours, 2 patients were excluded because of atrial fibrillation, and 1 patient's data was lost due to technical problems. Thus, data from 32 patients were available for final analysis. There were 12 females and 20 males, aging 26-84 years old with the mean of (66.8±19.1) years old, body mass index (BMI) of (23.7±3.9) kg/m², acute physiology and chronic health evaluation II (APACHE II) score of 19.5±5.3, sepsis-related organ failure assessment (SOFA) score of 9.7±4.1. There were no significant differences in CI or PPV between CNAP and PiCCO groups [CI (mL×s^-1×m^-2): 59.8±12.6 vs. 58.5±14.2, PPV: (14.7±6.8)% vs. (14.0±6.8)%, both P > 0.05]. MAP and SVRI measured by CNAP were significantly higher than those measured by PiCCO [MAP (mmHg, 1 mmHg = 0.133 kPa): 65.6±9.4 vs. 60.1±9.2, SVRI (kPa×s×L^-1×m^-2): 206.2±53.9 vs. 179.5±57.8, both P < 0.01]. The correlation analysis showed that MAP, CI, PPV and SVRI measured by the two methods were significantly positively correlated (r value was 0.624, 0.864, 0.835 and 0.655 respectively, all P < 0.05). Bland-Altman analysis showed that CNAP and PiCCO had a good consistency for the measurement of CI and PPV, the average differences were 1.2 mL×s^-1×m^-2 and 0.5% respectively, while the 95% confidence interval (95%CI) were -12.8-15.3 mL×s^-1×m^-2 and -7.1%-8.2% respectively. However, the consistency of MAP and SVRI measured by those two methods was poor, the average differences were 5.5 mmHg and 26.8 kPa×s×L^-1×m^-2 respectively, while the 95%CI was -10.4-21.3 mmHg and -64.5-118.0 kPa×s×L^-1×m^-2 respectively.

Conclusions: CNAP was comparable with PiCCO when monitoring CI and PPV in mechanically ventilated critically ill patients; while the results of MAP and SVRI might be inaccurate, which should be interpreted correctly and carefully.