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Tissue perfusion monitoring in the ICU 

Tissue perfusion monitoring in the ICU
Chapter:
Tissue perfusion monitoring in the ICU
Author(s):

Eric Kipnis

and Benoit Vallet

DOI:
10.1093/med/9780199600830.003.0138
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date: 08 December 2021

Resuscitation endpoints have shifted away from restoring normal values of routinely assessed haemodynamic parameters (central venous pressure, mean arterial pressure, cardiac output) towards optimizing parameters that reflect adequate tissue perfusion. Tissue perfusion-based endpoints have changed outcomes, particularly in sepsis. Tissue perfusion can be explored by monitoring the end result of perfusion, namely tissue oxygenation, metabolic markers, and tissue blood flow. Tissue oxygenation can be directly monitored locally through invasive electrodes or non-invasively using light absorbance (pulse oximetry (SpO2) or tissue (StO2)). Global oxygenation may be monitored in blood, either intermittently through blood gas analysis, or continuously with specialized catheters. Central venous saturation (ScvO2) indirectly assesses tissue oxygenation as the net balance between global O2 delivery and uptake, decreasing when delivery does not meet demand. Lactate, a by-product of anaerobic glycolysis, increases when oxygenation is inadequate, and can be measured either globally in blood, or locally in tissues by microdialysis. Likewise, CO2 (a by-product of cellular respiration) and PCO2 can be measured globally in blood or locally in accessible mucosal tissues (sublingual, gastric) by capnography or tonometry. Increasing PCO2 gradients, either tissue-to-arterial or venous-to-arterial, are due to inadequate perfusion. Metabolically, the oxidoreductive status of mitochondria can be assessed locally through NADH fluorescence, which increases in situations of inadequate oxygenation/perfusion. Finally, local tissue blood flow may be measured by laser-Doppler or visualized through intravital microscopic imaging. These perfusion/oxygenation resuscitation endpoints are increasingly used and studied in critical care.

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