MODIFICATIONS OF TISSULAR OXYGENATION AND SYSTEMIC HEMODYNAMICS AFTERTHE CORRECTION OF HYPOCAPNIA INDUCED BY MECHANICAL VENTILATION

The modifications of systemic hemodynamics, oxygen transport and tissu lar oxygenation in mechanically-ventilated critical ARF (acute respira tory failure) patients, after the correction of its hypocapnia by addi tion of dead space (VD) arc determined. The prospective and randomized study was carried out in a multidisciplinary ICU. Fifteen ARF patient s were studied within the first 48 hours of evolution. All the patient s were intubated and mechanically ventilated. Three stages were delimi ted: I) 30 min after the beginning of anesthesia; II) 30 min after add ing 30 cm of VD; III) 30 min after replacing the previous VD with a VD of 60 cm. Similar steady states had been reached when the measurement s were taken. Ventilation parameters and FiO2 were kept stable. In sta ge I the patients presented a pure respiratory alkalosis and, with res pect to hemodynamics, a hyperdynamic situation. In stage II the acid-b ase balance was normalized with a continuation of the hyperdynamic sit uation and an increase in mixed venous oxygen tension and saturation ( PvO2 and SvO2) (p<0.001). Stage III was characterized by a pure hyperc apnic acidosis and an increase in capillary wedge pressure (CWP) (p<0. 05), right atrial pressure (RAP) (p<0.001) and cardiac output (Qt) (p< 0.001); simultaneously, the systemic vascular resistances (SVR) decrea sed (p<0.01), the PvO2, SvO2 and oxygen delivery (DO,) increased (p<0. 001); oxygen utilization coefficient (OUC) decreased (p<0.01). The res ults suggest that the variations in PvO2 and SvO2 are a direct consequ ence of the modifications in blood flow. The hemodynamic response to n ormocapnia and moderate hypercapnia induced by the addition of VD, in situations of previous hypocapnia, might contribute to the evaluation of myocardial and capillary reserve and of tissular oxygenation in cri tical patients and might facilitate early therapeutic strategies.