Cardiac Output and Perfusion Efficacy Monitoring

After an urgent surgical revascularization, the patient is often hemodynamically unstable and is in life-threatening clinical situations. Circulation efficacy is monitored as macrocirculation and microcirculation (tissue perfusion). Traditionally macrocirculation monitoring focused on clinical examination, arterial blood pressure, urine output, serum lactate and base deficit measurements, cardiac output, and mixed venous oxygen saturation. However, several studies have shown that there is a discrepancy between macrocirculation and microcirculation in critically ill patients and macrocirculation cannot always guaranty the adequacy of tissue perfusion. New techniques that allow direct monitoring the microcirculation had being incorporated into the clinical management. Cardiac output (CO) monitoring plays an essential role in macrocirculation monitoring and it can be measured or estimated by many clinical methods. Patient status dictates the type of required CO monitoring. Tissue microcirculation can be explored by monitoring the end result of perfusion, tissue oxygenation, metabolic markers, and tissue blood flow. Global oxygenation and respiration (CO2 a by-product of cellular respiration) can be monitored globally in blood, either intermittently through blood gas analysis, or continuously with specialized catheters. Tissue oxygenation can be directly monitored locally through invasive electrodes or non-invasively using light absorbance. Likewise, CO2 and PCO2 can be measured locally in accessible mucosal tissues (sublingual, gastric) by 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 microscopic imaging.