Prevalence of low central venous oxygen saturation in the first hours of intensive care unit admission and associated mortality in septic shock patients: a prospective multicentre study

Abstract

Introduction: In septic shock patients, the prevalence of low (<70%) central venous oxygen saturation (ScvO2) on admission to the intensive care unit (ICU) and its relationship to outcome are unknown. The objectives of the present study were to estimate the prevalence of low ScvO2 in the first hours of ICU admission and to assess its potential association with mortality in patients with severe sepsis or septic shock.

Methods: This was a prospective, multicentre, observational study conducted over a one-year period in ten French ICUs. Clinicians were asked to include patients with severe sepsis or septic shock preferably within 6 hours of ICU admission and as soon as possible without changing routine practice. ScvO2 was measured at inclusion and 6 hours later (H6), by blood sampling.

Results: We included 363 patients. Initial ScvO2 below 70% was present in 111 patients and the pooled estimate for its prevalence was 27% (95% Confidence interval (95%CI): 18% to 37%). At time of inclusion, among 166 patients with normal lactate concentration (≤2 mmol/L), 55 (33%) had a low initial ScvO2 (<70%), and among 136 patients who had already reached the classic clinical endpoints for mean arterial pressure (≥65 mmHg), central venous pressure (≥8 mmHg), and urine output (≥0.5 mL/Kg of body weight), 43 (32%) had a low initial ScvO2 (<70%). Among them, 49% had lactate below 2 mmol/L. The day-28 mortality was higher in case of low initial ScvO2 (37.8% versus 27.4%; P = 0.049). When adjusted for confounders including the Simplified Acute Physiology Score and initial lactate concentration, a low initial ScvO2 (Odds ratio (OR) = 3.60, 95%CI: 1.76 to 7.36; P = 0.0004) and a low ScvO2 at H6 (OR = 2.18, 95%CI: 1.12 to 4.26; P = 0.022) were associated with day-28 mortality by logistic regression.

Conclusions: Low ScvO2 was common in the first hours of admission to the ICU for severe sepsis or septic shock even when clinical resuscitation endpoints were achieved and even when arterial lactate was normal. A ScvO2 below 70% in the first hours of ICU admission and six hours later was associated with day-28 mortality.

Figure 1

Flow diagram.

Figure 2

Forest plot for subgroup analysis. ^aAll cutoff values provided in the figure for demographic, clinical or laboratory variables are median values calculated on the whole study population. ^bSequential organ failure assessment (SOFA) score is the highest value during the first 24 hours after enrollment. ^cWith the use of a cutoff of 2 mmol/L for lactate, the odds ratio for day-28 death (OR) was 1.29 (0.54, 3.05) in the case of lactate >2 mmol/L, and 4.59 (1.79, 11.84) in the case of lactate ≤2 mmol/L. ^dVasopressor dose = continuous intravenous (iv) norepinephrine dose plus continuous iv epinephrine dose. ^eLeft ventricular ejection fraction assessed by transthoracic echocardiography before 24 hours after enrollment. ^fHaemoglobin concentration was taken into account only if measured between 6 hours before and 6 hours after enrollment. SAPSII, Simplified acute physiology score; ScvO2, central venous oxygen saturation.

Figure 3

Survival curve and death rate (%) at day 28 according to initial lactate level and central venous oxygen saturation (S _cv O ₂ ). The left part of the figure shows survival curves in four patients’ subgroups according to their initial zero hours (H0) lactate concentration and S_cvO₂. The right part of the figure shows the day-28 death rate in each subgroup. Numbers inside the bars are number of non survivors/total number of patients in each subgroup. ^aUnadjusted pair comparison of survival curves between the different subgroups were not statistically significant on log-rank test. ^bThere was no significant difference in crude death rate at day-28 among the four groups (chi-squared test). However, there was a significant global trend towards higher death rate from the condition with normal lactate and S_cvO₂ to the condition with high lactate and low S_cvO₂ (P <0.001, Cochran-Armitage test).