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

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.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0609-7) contains supplementary material, which is available to authorized users.

Early fluid resuscitation

Solid evidence exists that fluid therapy must be started as a first-line treatment in all patients with septic shock as soon as hypotension is detected, with the goal of rapidly restoring tissue perfusion. Crystalloids or colloids can be used for initial fluid therapy, and albumin should be reserved for patients with patent or supposed hypoalbuminemia. Once fluid administration is started, its effect must be carefully monitored. In the early stages, appropriate monitoring should ensure that fluid resuscitation actually increases cardiac preload, mean arterial pressure, and tissue oxygenation. In later stages, monitoring should help to avoid fluid overload. For this purpose, the end-point of fluid therapy should not be the static values of preload indicators, but rather the disappearance of indicators of preload responsiveness. Finally, the risk of fluid overload must always be kept in mind, especially in case of lung injury.