Comparing cardiac index and left ventricular ejection fraction in ICU patients with sepsis

BACKGROUND: The optimal parameter to assess cardiovascular function in sepsis is currently unknown. We investigated whether echocardiography-derived cardiac index offers superior haemodynamic monitoring and prognostic value compared to left ventricular ejection fraction (LVEF) in ICU patients with sepsis. METHODS: We conducted a retrospective, single-centre cohort study in ICU patients with sepsis admitted between April 2016 and December 2021 that received a transthoracic echocardiogram (TTE) within seven days of sepsis onset. Correlation between CI and LVEF was assessed using the Spearman rank test. The 90-day mortality rates of normal, low and high CI and LVEF subgroups were compared. Multivariable logistic regression analysis was performed to determine the association of CI and LVEF phenotypes with mortality. RESULTS: 1731 patients were included and were aged 62 years (IQR 47-72), with 21% (n = 367) having septic shock. Ninety-day mortality was 32.5% (n = 561). Although CI and LVEF demonstrated moderate correlation (r = 0.51 (0.47-0.54), one-third of patients in a given CI subgroup were classified into a discordant LVEF subgroup. The 90-day mortality rates of low and high CI (54%, 54%) and low and high LVEF subgroups (43%, 59%) were broadly comparable and were higher than their normal CI (20%) and LVEF (23%) counterparts respectively. After regression analysis, low and high CI independently associated with mortality (OR 2.6 (1.8-3.7; p < 0.001), (OR 3.4 (2.7-4.4; p < 0.001), as did low and high LVEF subgroups (OR 1.6 (1.2-2.3; p = 0.004), OR 3.2 (2.4-4.3; p < 0.001). Stratifying CI subgroups into low, normal and high LVEF (and vice-versa) was associated with significantly different mortality rates. CONCLUSIONS: Although CI and LVEF were modestly correlated, this association weakened when either parameter was abnormal, highlighting their non-equivalence as haemodynamic parameters. While both markers exhibited comparable associations with mortality, their combination substantially improved prognostic accuracy.