Evaluating tissue hypoxia and the response to fluid administration in septic shock patients: a metabolic cluster analysis.

BACKGROUND: The selection of adequate indicators of tissue hypoxia for guiding the resuscitation process of septic patients is a highly relevant issue. Current guidelines advocate for the use of lactate as sole metabolic marker, which may be markedly limited, and the integration of different variables seems more adequate. In this study, we explored the metabolic profile and its implications in the response to the administration of a fluid challenge in early septic shock patients. METHODS: Observational study including septic shock patients within 24 h of ICU admission, monitored with a cardiac output estimation system, with ongoing resuscitation. Hemodynamic and metabolic variables were measured before and after a fluid challenge (FC). A two-step cluster analysis was used to define the baseline metabolic profile, including lactate, central venous oxygen saturation (ScvO2), central venous-to-arterial carbon dioxide difference (PcvaCO2), and PcvaCO2 corrected by the difference in arterial-to-venous oxygen content (PcvaCO2/CavO2). RESULTS: Seventy-seven fluid challenges were analyzed. Cluster analysis revealed two distinct metabolic profiles at baseline. Cluster A exhibited lower ScvO2, higher PcvaCO2, and lower PcvaCO2/CavO2. Increases in cardiac output (CO) were associated with increases in VO2 exclusively in cluster A. Baseline isolated metabolic variables did not correlate with VO2 response, and changes in ScvO2 and PcvaCO2 were associated to VO2 increase only in cluster A. CONCLUSIONS: In a population of early septic shock patients, two distinct metabolic profiles were identified, suggesting tissue hypoxia or dysoxia. Integrating metabolic variables enhances the ability to detect those patients whose VO2 might increase as results of fluid administration.

Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care.

The detection of levels of impairment in microvascular oxygen consumption and reactive hyperemia is vital in critical care. However, there are no practical means for a robust and quantitative evaluation. This paper describes a protocol to evaluate these impairments using a hybrid near-infrared diffuse optical device. The device contains modules for near-infrared time-resolved and diffuse correlation spectroscopies and pulse-oximetry. These modules allow the non-invasive, continuous, and real-time measurement of the absolute, microvascular blood/tissue oxygen saturation (StO2) and the blood flow index (BFI) along with the peripheral arterial oxygen saturation (SpO2). This device uses an integrated, computer-controlled tourniquet system to execute a standardized protocol with optical data acquisition from the brachioradialis muscle. The standardized vascular occlusion test (VOT) takes care of the variations in the occlusion duration and pressure reported in the literature, while the automation minimizes inter-operator differences. The protocol we describe focuses on a 3-min occlusion period but the details described in this paper can readily be adapted to other durations and cuff pressures, as well as other muscles. The inclusion of an extended baseline and post-occlusion recovery period measurement allows the quantification of the baseline values for all the parameters and the blood/tissue deoxygenation rate that corresponds to the metabolic rate of oxygen consumption. Once the cuff is released, we characterize the tissue reoxygenation rate, magnitude, and duration of the hyperemic response in BFI and StO2. These latter parameters correspond to the quantification of the reactive hyperemia, which provides information about the endothelial function. Furthermore, the above-mentioned measurements of the absolute concentration of oxygenated and deoxygenated hemoglobin, BFI, the derived metabolic rate of oxygen consumption, StO2, and SpO2 provide a yet-to-be-explored rich data set that can exhibit disease severity, personalized therapeutics, and management interventions.

[Haemodynamic monitoring in sepsis and septic shock]. / Monitorización hemodinámica en la sepsis y el shock séptico.

Cardiovascular disturbances associated with sepsis cause hypoperfusion situations, which will negatively impact these patients' prognosis. The aim of haemodynamic monitoring is to guide the detection and correction of this hypoperfusion, and assist in decision making in optimising oxygen transport to tissues, primarily by manipulating cardiac output. This review seeks to summarise the different parameters of haemodynamic monitoring, the objectives of resuscitation, the physiological parameters, and the tools available to us for appropriate cardiac output manipulation.