Critical care medicine
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Critical care medicine · Feb 1997
Unloadiing of the work of breathing by proportional assist ventilation in a lung model.
Proportional assist ventilation is devised to increase airway pressure in proportion to inspiratory effort. A systematic study of the performance of this new mode of ventilation has not been presented. We tested in the laboratory the capability of proportional assist ventilation to unload the work of breathing in proportion to ventilatory drive, under a variety of mechanical loads. ⋯ In a lung model, a prototype system delivering proportional assist ventilation provided uniform unloading of the work of breathing as the ventilatory drive was varied within a tidal volume range of 0.5 to 1.2 L. These findings confirm the theoretical modeling of proportional assist ventilation. This system, however, failed to properly unload low tidal volumes of 0.2 to 0.4 L.
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Critical care medicine · Feb 1997
Comparative StudyReduced airway resistance and work of breathing during mechanical ventilation with an ultra-thin, two-stage polyurethane endotracheal tube (the Kolobow tube).
To compare dynamic pulmonary function studies using the ultrathin walled Kolobow endotracheal tube, with conventional endotracheal tubes of similar external diameter on rabbits during mechanical ventilation. To test the hypothesis that the increased internal diameter of the Kolobow tube will result in decreased airway resistance and work of breathing. ⋯ The use of the ultrathin walled Kolobow endotracheal tube resulted in significant decreases in airway resistance and work of breathing, which has the potential for improving the ventilatory mechanics in very small premature newborns.
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Critical care medicine · Feb 1997
Comparative StudyHigh-frequency oscillatory ventilation with partial liquid ventilation in a model of acute respiratory failure.
To determine whether there is an improvement in oxygenation when partial liquid ventilation and high-frequency oscillatory ventilation are combined in the treatment of acute lung injury, compared with high-frequency oscillatory ventilation alone. ⋯ The combination of low-dose perflubron with high-frequency oscillatory ventilation leads to more rapid improvement in arterial oxygenation than high-frequency oscillatory ventilation alone, in a piglet model of acute lung injury. Although the group receiving high-frequency oscillatory ventilation alone eventually achieved PaO2 values that were equivalent to the group receiving high-frequency ventilation and perflubron, the combination of perflubron with high-frequency oscillatory ventilation may permit effective oxygenation and ventilation at lower mean airway pressures by facilitating alveolar expansion and decreasing intrapulmonary shunt.
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Critical care medicine · Feb 1997
Comparative StudyIntratracheal pressure monitoring during synchronized intermittent mandatory ventilation and pressure controlled-inverse ratio ventilation.
To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. ⋯ A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.
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Critical care medicine · Feb 1997
The unassisted respiratory rate/tidal volume ratio accurately predicts weaning outcome in postoperative patients.
To evaluate the accuracies of the respiratory rate/tidal volume ratio (rate/volume ratio), minute volume, and negative inspired force in predicting weaning outcome in postoperative mechanically ventilated patients. ⋯ The rate/volume ratio measured at the beginning and after 30 mins of weaning is more highly predictive of weaning outcome than the negative inspired force and minute volume. The principal weakness of the rate/volume ratio is false-positive results.