The effects of hemodilution during pulmonary edema in dogs

The effects of hemodilution on acute inflammatory responses in a bleomycin-induced lung injury model

Acute normovolemic hemodilution (ANH) can be used in acute lung injury (ALI) patients who refuse blood transfusions. To investigate the effects of hemodilution on the acute inflammatory response in lung injury, the authors studied the effects of ANH in a rat model of bleomycin-induced lung injury. Bleomycin (10 mg/kg) was used to induce lung injury in 2 groups of rats. The treatment groups included a lung injury group with hemodilution (HI), a lung injury group without hemodilution (NHI), and a control group. Hemodilution was performed by removing blood and substituting the same amount of hydroxyethyl starch solution targeted to 7.0 g/dL via the right and left internal jugular veins. At day 3 after bleomycin instillation, systemic hemoglobin concentration was 9.5 +/- 1.1 g/dL. Tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 levels measured in the bronchoalveolar lavage fluid (BALF), blood, and lung tissue were not significantly different between the HI and NHI groups 3 days after lung injury. Microscopic findings showed fibrosis and inflammation in the HI and NHI groups 28 days after lung injury, but no significant differences were found between the 2 groups. Hemodilution after bleomycin administration did not further affect the acute inflammatory response or lung injury.

Mechanisms of improvement in pulmonary gas exchange during isovolemic hemodilution

Severe anemia is associated with remarkable stability of pulmonary gas exchange (S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson. J. Appl. Physiol. 83: 240-246, 1997), although the factors that contribute to this stability have not been studied in detail. In the present study, 10 Flemish Giant rabbits were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Serial hemodilution was performed in five rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; five rabbits were followed over a comparable time. Ventilation-perfusion (VA/Q) relationships were studied by using the multiple inert-gas-elimination technique, and pulmonary blood flow distribution was assessed by using fluorescent microspheres. Expired nitric oxide (NO) was measured by chemiluminescence. Hemodilution resulted in a linear fall in hematocrit over time, from 30 +/- 1.6 to 11 +/- 1%. Anemia was associated with an increase in arterial PO(2) in comparison with controls (P < 0.01 between groups). The improvement in O(2) exchange was associated with reduced VA/Q heterogeneity, a reduction in the fractal dimension of pulmonary blood flow (P = 0.04), and a relative increase in the spatial correlation of pulmonary blood flow (P = 0. 04). Expired NO increased with anemia, whereas it remained stable in control animals (P < 0.0001 between groups). Anemia results in improved gas exchange in the normal lung as a result of an improvement in overall VA/Q matching. In turn, this may be a result of favorable changes in pulmonary blood flow distribution, as assessed by the fractal dimension and spatial correlation of blood flow and as a result of increased NO availability.

A new experimental model of ARDS and pulmonary hypertension in the dog

The aim of this study was to establish a stable and reproducible model of pulmonary artery hypertension with concomitant ARDS-like changes of lung function and lung morphology. In eight anesthetized and ventilated dogs, 0.01 ml/kg oleic acid (OA) was given i.v. followed by repetitive injections of 100 microns glass beads (GB) into the right atrium until a mean pulmonary artery pressure of 35-40 mmHg was reached. Mean right ventricular (RVP) and pulmonary artery (PAP) pressures, pulmonary vascular resistance (PVR), lung compliance and resistance, PaO2, intrapulmonary shunt and colloidosmotic pressure (COP) were closely monitored for 150 min. PAP, RVP, and PVR considerably increased subsequent to OA/GB injection, and stabilized at a high level within 70 min, showing only a minimal decrease (PAP, RVP) or no change (PVR) during the following 80 min. A significant decrease of PaO2 and pulmonary compliance as well as an increase of resistance and intrapulmonary shunt were found as early as 30 min after the last embolization and they remained unchanged for 120 min. Reduction of COP suggested transcapillary leakage of macromolecules. Histology revealed an interstitial and intraalveolar edema. We conclude that the combined injection of oleic acid and glass beads provokes microvascular lung injury and results in stable pulmonary artery hypertension with concomitant ARDS-like changes of lung function. Thus, an acute model is provided in the dog allowing for the study of cardiac function in ARDS complicated by pulmonary artery hypertension.