Respiratory failure: current status of experimental therapies

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.

Airway pressure release ventilation and pediatrics: theory and practice

Airway pressure release ventilation (APRV) facilitates oxygenation and ventilation by maintaining an elevated baseline airway pressure similar to continuous positive airway pressure (CPAP). APRV differs from CPAP only by the addition of regular, brief release of airway pressure to facilitate carbon dioxide removal. The baseline pressure maintains a near continuous airway pressure to facilitate recruitment, improving ventilation and oxygenation. Pediatric patients who have recruitable lung disease may be well suited to the application of APRV.

Real-time visualization of partial liquid ventilation in a model of acute lung injury

BACKGROUND

To clarify the effects of partial liquid ventilation, we visualized and morphologically analyzed real-time alveolar recruitment in a model of acute lung injury.

METHODS

Male Wistar rats were divided into 3 groups: a group that underwent hydrochloric acid aspiration and mechanical gas ventilation (ALI group, n = 15), a group that underwent acid aspiration and partial liquid ventilation beginning 90 minutes after acid aspiration (PLV group, n = 15), and a group that underwent mechanical ventilation without acid aspiration (control group, n = 5). The number of ventilated alveoli and the diameter of the largest ventilated alveolus in each of 10 high-power fields observed on fluorescence micrographs with a tracer of labeled albumin were determined and averaged from 90 to 210 minutes after acid aspiration.

RESULTS

The number of alveoli in the PLV group significantly increased in comparison to that in the ALI group. The diameter of the largest alveolus in the PLV group decreased from 103.7 +/- 16.3 microm to 76.3 +/- 6.5 microm until the end of the experiment. This diameter was equivalent to that in the control group.

CONCLUSIONS

The excellent alveolar recruitment suggests that liquid ventilation ameliorates ventilator-associated lung injury.

Noninvasive motion ventilation (NIMV): a novel approach to ventilatory support

A motion platform was developed that oscillates an animal in a foot-to-head direction (z-plane). The platform varies the frequency and intensity of acceleration, imparting periodic sinusoidal inertial forces (pG(z)) to the body. The aim of the study was to characterize ventilation produced by the noninvasive motion ventilator (NIMV) in animals with healthy and diseased lungs. Incremental increases in pG(z) (acceleration) with the frequency held constant (f = 4 Hz) produced almost linear increases in minute ventilation (VE). Frequencies of 2-4 Hz produced the greatest VE and tidal volume (VT) for any given acceleration between +/-0.2 and +/-0.8 G. Increasing the force due to acceleration produced proportional increases in both transpulmonary and transdiaphragmatic pressures. Increasing transpulmonary pressure by increasing pG(z) produced linear increases in VT, similar to spontaneous breathing. NIMV reversed deliberately induced hypoventilation and normalized the changes in arterial blood gases induced by meconium aspiration. In conclusion, a novel motion platform is described that imparts periodic sinusoidal acceleration forces at moderate frequencies (4 Hz) to the whole body in the z-plane. These forces, when properly adjusted, are capable of highly effective ventilation of normal and diseased lungs. Such noninvasive ventilation is accomplished at airway pressures equivalent to atmospheric or continuous positive airway pressure, with acceleration forces less than +/-1 G(z).