Patient characteristics
After reviewing 166,355 first ICU stays in eICU-CRD, we finally included 6,049 fulfilling the inclusion and exclusion criteria (Fig.1). The baseline characteristics between survivors and non-survivors are shown in Table 1. Though there was no significant difference in the use of sedatives and the history of tachyarrhythmia, the survivors were, on average, younger, predominantly male and lower in BMI. Non-survivors were significantly complicated with more comorbidities, more severe in diseases (higher SOFA score and OASIS), needing more support (mechanical ventilation and vasopressors), less use of antihypertensive drug, higher incidence of AKI and sepsis and lower MPP compared with survivors. More non-survivors had tachyarrhythmia history and less use of sedatives, but the difference did not reach statistical significance. Other information about hospitals, initial diagnosis, comorbidities and MPP data of the whole cohort were listed in supplementary Table 2.
The median of the four MPPV parameters were 7.8 mmHg (SD), 12.3% (CV), 2.8 mmHg (ARV) and 0.40 units (VIM) in the whole cohort. The 10th percentile and 90th percentile for the four MPPV parameters were 5.1 mmHg and 12.2 mmHg for SD, 8.2% and 12.2% for CV, 1.6 mmHg and 5.6 mmHg for ARV, 0.27 units and 0.62 units for VIM, respectively. The survivors had higher CV (13.0% vs 12.2%, p<0.001) and VIM (0.42 units vs 0.40 units, p<0.001), lower ARV (2.7mmHg vs 2.8 mmHg, p=0.014) and similar SD (7.9 mmHg vs 7.8 mmHg, p=0.269) as compared with non-survivors.
Association with MPP and other BPV
The scatter plots and the fitting curves of time-weighted average MPP (TWA-MPP) and MPPV showed us the relationship intuitively. The SD and ARV increased with the increase of the TWA-MPP. In the contrast, CV had a downward trend with the increase of the TWA-MPP. VIM did not change with the TWA-MPP (supplementary Fig.1). The correlation coefficient for CV and VIM was 0.98, which was the strongest (supplementary Fig.2).
There was also a strong correlation between MPPV and other BPV like MAP, systolic BP (SBP) and diastolic BP (supplementary Fig.3), among which the correlation coefficients of ARV were higher.
Association with hospital mortality
After adjusting for age, gender, BMI, ethnicity, Charlson score, SOFA score, OASIS, history of tachyarrhythmia, sepsis, incidence of AKI in the first day of ICU admission, the need for mechanical ventilation, the use of vasopressor, antihypertensive drug and sedatives, we found a ‘U’ shaped curve between variability with dimension indicators (SD and ARV) and hospital mortality using general additive models (Fig. 2A, 2C). However, hospital mortality simply increased with the dimensionless variability (CV and VIM) increasing (Fig. 2B, 2D).
After grouping in deciles (Fig. 3), multiple logistic regression revealed that both higher and lower MPPV with dimension were related to an increase in the risk of hospital mortality compared with the fifth and sixth decile (SD: adjusted odds ratio [OR] in the first decile: 1.64, 95% confidence interval [Cl]:1.25-2.15, adjusted OR in the tenth decile: 1.83, 95% Cl: 1.40-2.40; ARV: adjusted OR in the first decile: 2.10, 95% Cl:1.62-2.73, adjusted OR in the tenth decile: 1.74, 95% Cl: 1.33-2.27). But in dimensionless variability indicators, only higher MPPV (Fig. 3B, 3D) were associated with increased risk of hospital mortality compared with the fifth and sixth decile (CV: adjusted OR in the tenth decile: 1.50, 95% Cl: 1.16-1.93; VIM: adjusted OR in the tenth decile: 1.51, 95% Cl: 1.17-1.96). These results were consistent with the changing trend of general additive models.
Sensitivity and subgroup analyses
For the sensitivity analyses, we analyzed the association between MPPV and ICU mortality. We observed similar trends in each variability index (supplementary Fig.5). Multiple logistic regression also confirmed our findings (supplementary Fig.6). Higher MPPV increases the risk of ICU mortality without exception (adjusted OR in the tenth decile: SD: 1.90, 95% Cl: 1.39-2.58; CV: 1.57, 95% Cl: 1.18-2.09; ARV: 1.78, 95% Cl: 1.32-2.39; VIM: 1.47, 95% Cl: 1.10-1.96). In two MPPV with dimension indicators, lower variability also increased the risk of ICU mortality. (adjusted OR in the first decile: SD: 1.64, 95% Cl: 1.20-2.22; ARV: 2.25, 95% Cl: 1.69-3.00).
Since there was time interval in the calculation of daytime or nighttime ARV, we chose SD and CV representatively to analyze the association between day and night MPPV and hospital mortality. The results still showed good consistency (supplementary Fig.7, supplementary Fig.8).
The association of high MPPV and in-hospital mortality was analyzed across patients who were male or female, elderly (age ≥ 65 years) or not, with or without hypertension, sepsis, median SOFA score on the first day of ICU admission (Fig. 4). In patients who had SOFA score of ≥ eight or had hypertension history, higher variability is associated with higher risk of death in hospital. Surprisingly, sepsis patients with high variability did not increase hospital death risk.