Simultaneous monitoring of noninvasive hemodynamic profile and capnography for tissue perfusion evaluation.

To study the simultaneous variations of end-tidal CO2 pressure (PetCO2) and aortic blood flow (ABF) during modifications of tissue perfusion, continuous noninvasive hemodynamic monitoring and continuous recording of PetCO2 were performed on 30 patients under general anesthesia and artificial mechanical ventilation. The 30 patients underwent orthopedic surgery on one of the lower limbs using a hemostatic tourniquet. Deflation of the pneumatic tourniquet resulted in a rise of ABF up to 39% (P<0.001), a rise of PetCO2 up to 17% (P<0.001), and a drop of total vascular systemic resistance (TVSR) of 59% (P<0.001). In all cases, the gradient of Paco2-PetCO2 showed mean variations of 1.2±0.5 mmHg. According to these results, the observed variations can not be explained by an alteration of the Ventilation/Perfusion (Vo/Q) ratio alone. It may be suggested that tissue hypoperfusion produced by a tourniquet generates CO2 and other metabolic products accumulation in tissues, which are removed during reperfusion. This would be expected to produce parallel increases in ABF and PetCO2. If the results are confirmed with further studies, rapid variations of PetCO2 during anesthesia may provide a noninvasive means of assessing the quality of global tissue perfusion.