Relationship among cardiac index, inspiration/expiration ratio, and perfluorocarbon dose during partial liquid ventilation in an oleic acid model of acute lung injury in sheep.

BACKGROUND: The aim of this study was to demonstrate the influence of different inspiration/expiration (I/E) ratios on cardiac index (CI) and hemodynamics during partial liquid ventilation (PLV) using a large animal model of acute respiratory failure in a prospective, randomized controlled animal laboratory trial. METHODS: After induction of respiratory failure by right atrial injection of 0.09 mL/kg oleic acid, (1) determination of agreement between reversed Fick and pulmonary artery thermodilution (QTD) techniques with progressive doses of perflubron (LiquiVent, Alliance Pharmaceutical Corp, San Diego, Calif) (n = 7 sheep) and (2) comparison of 4 groups with I/E ratios of 3.4:1, 2:1, 1:1, and 1:2 were performed, applying identical ventilatory patterns in all I/E groups (n = 28 sheep). PLV was established with intratracheal instillation of 25 mL/kg perflubron. Cardiac index was assessed at 15-minute intervals for a 120-minute experimental period by QTD. RESULTS: During progressive doses of PLV, the correlation (r) between Fick and QTD techniques was 0.82. Thermodilution deteriorated after induction of lung injury and recovered after PLV start. Regarding QTD, no significant changes after PLV onset (within-group comparison) and between I/E groups were observed (P < .05). CONCLUSION: The QTD technique is a satisfactory reflector of CI during PLV, and I/E ratio has no significant influence on CI, even using extreme inverse ratio ventilation.

Comparison of static airway pressures during total liquid ventilation while applying different expiratory modes and time patterns.

To compare pump driven (active) and gravity-siphon (passive) expiration modes during perfluorocarbon total liquid ventilation (TLV), a liquid ventilator was developed capable of providing either expiration mode. In a prospective, controlled laboratory study, 90 rabbits (3.2 +/- 0.1 kg) were anesthetized, tracheotomized, killed. After prefill with 12 ml/kg perflubron and TLV for 90 minutes (tidal volume 12 ml/kg, I:E ratio 1:2), randomly using passive (height 40 or 80 cm) or active expiration, respiratory rates were 4, 8, or 12/min. Static peak inspiratory and end-expiratory intratracheal pressures were measured at 5 minute intervals. Peak inspiratory and end-expiratory were constant in active groups, and increases in all 40 cm and 80 cm passive groups were significant. Differences between groups were significant for expiratory mode but not for respiratory rates. Only passive groups showed significant increases in body weight after TLV. Percentage of fluorothoraces was 10% using active and 85% using passive expiration. Based upon the stability of intrapulmonary pressures and volumes and a reduced rate of fluorothoraces, active expiration is more efficient than passive drainage during TLV.

Thrombogenicity is not reduced when heparin and phospholipid bonded circuits are used in a rabbit model of extracorporeal circulation.

In an effort to better mimic the thromboresistive nature of vascular endothelium, extracorporeal circuits bonded with heparin or phospholipids were developed. Using no systemic heparinization, these circuits were compared with standard poly(vinyl)chloride (PVC) (Tygon) in a rabbit model of extracorporeal circulation (ECC). Control circuits were run with and without systemic heparinization and used as comparison groups against the test circuits. Two New Zealand White rabbits were used per study: One was used as the platelet donor for 111Indium platelet labeling; the other animal was placed on bicaval ECC for 4 hours. Circuits (heparin coated n = 6, phospholipid coated n = 8, nonheparinized controls n = 14, heparinized controls n = 18) consisted of 1 m of tubing, two downsizing connectors, and two venous cannulae. ECC blood flow was at least 75 ml/min. Platelet and fibrinogen measurements were made hourly, and circuit dosimetry was performed at the end of the study or on circuit thrombosis. Thrombosis of the circuit occurred in one heparin coated, two phospholipid coated, and eight nonheparinized control circuits. None of the heparinized control circuits thrombosed. There was no significant difference between the groups with regard to platelet count or platelet adhesion. Test circuits exhibited preservation of fibrinogen levels. In this rabbit model of ECC, circuits coated with heparin or phospholipids appeared to preserve fibrinogen levels but did not reduce platelet adhesion or consumption.