[Vasomotor tone and CBP : monitoring components, pratical and therapeutic approaches].

The vasomotor tone is an essential determinant of blood pressure. Vascular resistance is the result of a calculation including vasomotor tone, blood flow and blood viscosity. The vascular tone is modulated by the sympathetic system and the direct actions of drugs (patient's pathology, anaesthesia). The pressure and flow allow the vascular tone apprehension. A decrease in vasomotor tone lowers the mean arterial pressure and may cause an intense vasoplegia with arterial vascular resistance below than 800 dyn/s/cm(5) leading to a lack of tissue oxygenation. Vasomotor paralysis can be caused by the patient medications or an intense inflammatory reaction starting at the extracorporeal circulation onset. Monitoring parameters of extracorporeal circulation such as pressure, flow, arterial and venous oxygen saturation, blood level in the venous reservoir, and extensively blood gases, haemoglobin, CO(2) partial pressure level of the oxygenator vent, bispectral index, and oxygen saturation of cerebral tissue are reviewed. They will know the vasoplegia consequences and bear an indication of adequate tissue oxygenation. It may be obtained by using vasopressors (ephedrine, norepinephrine, terbutalin and vasopressin) methylene blue, increasing blood viscosity (erythrocytes) and blood flow, even by inducing hypothermia.
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