Prolonged hypoxemia and acidemia in anesthetized pigs: a model for research on extracorporeal organ support in an intensive care setting

Adverse influence of mixed acidemia on the biocompatibility of continuous veno-venous hemofiltration with respect to the lungs

Experimental data indicate that hypercapnic adidosis has anti-inflammatory effects. These anti-inflammatory effects may even be a beneficial property in case of low tidal volume ventilation with consecutive hypercapnic acidosis. It is unclear whether these anti-inflammatory effects predominate in critically ill patients who suffer from multiple pro- and anti-inflammatory insults like extracorporeal organ support (pro-inflammatory), metabolic acidosis (pro- and anti-inflammatory), as well as hypoxia (pro-inflammatory). Eighteen pigs were randomized into three groups, mechanically ventilated and connected to a continuous veno-venous hemofiltration (CVVH) as pro-inflammatory insult. A reference group with normal acid-base state obtained normoventilation; a normoxemic acidemia group obtained normoxemic, mixed acidemia due to infusion of lactic and hyperchloremic acid and low tidal volume ventilation, and in a hypoxemic acidemia group the mixed acidemia was paralleled by hypoxemia. Lung histology including pulmonary leukocyte invasion, blood gases, blood cell counts, and hemodynamics were examined. The histological examination of the lungs of acidemic pigs showed a suppressed invasion of leukocytes and thinner alveolar walls compared with normoventilated and with hypoxemic pigs. Enhanced congestion and alveolar red blood cells (RBCs) combined with an increase of the pulmonary artery pressure were observed in acidemic pigs in comparison with the reference group. Normoxemic acidemia reduced the pro-inflammatory reaction to the CVVH and mechanical ventilation in the ventilated lung areas in the form of pulmonary leukocyte invasion. However, this did not result in reduced scores for lung injury. Instead, an increased score for criteria which represent lung injury (congestion and alveolar RBCs) was observed in acidemic pigs.

In a porcine model of mixed acidemia HES 130/0.4 may support more stable hemodynamics during CVVH when compared to gelatine

PURPOSE

Continuous veno-venous hemofiltration (CVVH) and mixed acidemia often occur simultaneously in critically ill patients. In a previous study in non-acidemic pigs we found that colloids and CVVH interact specifically with respect to hemodynamic stability, with favorable effects for 6% HES 130/0.4 versus 4% gelatine (GEL) infusion. In a porcine model, we investigated whether these colloid-type associated differences are still dominant under acidemic conditions.

METHODS

We utilized 5 groups, a non-acidemic reference group receiving HES130 and CVVH; two acidemic groups receiving HES130 infusion (one with and one without CVVH); and two acidemic groups receiving GEL infusion (one with and one without CVVH). Mixed acidemia (pH ~7.20) was established by low tidal volume ventilation and acid infusion. Stable acidemia/CVVH application was maintained for 3 hours. Hemodynamics and blood gases were recorded.

RESULTS

Mixed acidemia led to a significant decrease in MAP and increase in MPAP in all groups. CVVH led to a further decrease in MAP but improved MPAP. During CVVH, HES130 ensured significantly higher MAP, Hb, and DO2 values than GEL infusion. In the groups without CVVH these differences between HES 130/0.4 and GEL were not observed.

CONCLUSIONS

As in a previous study in non-acidemic pigs, we found a colloid-specific influence of HES130 versus GEL on hemodynamics during CVVH under acidemia. Again, HES130 infusion may lead to favorable effects. In contrast, acidemia without CVVH application was dominant over the impact of a respective colloid. The application of a CVVH seems to be an important trigger for the overall circulatory response to a particular colloid.