Articles: ventilators.
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Critical care medicine · Jun 1986
Determinants of alveolar ventilation during high-frequency transtracheal jet ventilation in dogs.
The effectiveness of transtracheal jet ventilation is a function of gas delivery pressure (drive pressure), duty cycle (insufflation time/total cycle time), and respiratory frequency. Nine dogs, anesthetized with sodium pentobarbital, were ventilated through a cricothyrotomy cannula using a controller that allowed separate setting of drive pressure, duty cycle, and frequency. PaO2 and PaCO2 were measured after achieving steady-state gas exchange at 15 to 22 different combinations of drive pressure, duty cycle, and frequency in each dog. ⋯ The distribution of air flow between alveolar and physiologic dead space, upper airway leakage, and entrainment was determined for each set of conditions. Changes in alveolar ventilation corresponding to the blood gas changes resulted from interaction of dead-space ventilation and upper airway leakage, which varied with breath duration. Decreases in leakage during short breaths tended to compensate for the increased fractional dead-space ventilation at high frequency, thus minimizing the effects of frequency changes on gas exchange.
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An artificial patient capable of spontaneous and artificial ventilation has been used for bench testing of the Ohmeda CPU-1. This ventilator has an extensive capacity for interaction with the spontaneous breathing of the patient, and provides a wide variety of operating modes. These include spontaneous breathing with or without continuous positive pressure, volume-cycled and pressure-cycled artificial ventilation, with or without positive end-expiratory pressure or synchronization. ⋯ The synchronization permits adaptation of the ventilator to spontaneous respiration according to a wide range of harmonics. In any mode, artificial ventilation is initiated if spontaneous respiration is inadequate. The mandatory minute volume mode is based on a complicated program of a cautious nature which reacts instantly to inadequate spontaneous breathing, but is slow to discontinue artificial ventilation.
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Thirteen commercially available ventilator monitoring alarms supplied by the distributors were evaluated. It was decided that devices with no power failure precautions or unprotected variable controls could not be recommended for general use. By these criteria only two devices could be recommended for general use as ventilator alarms and a further three as disconnect alarms; in each instance these recommendations are subject to certain reservations and suggested modifications. A ventilator alarm should be regularly serviced and checked before use and should be not used by anyone unfamiliar with the applications or limitations of that particular device.
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Recent reports linking serious tracheal injuries to various forms of high-frequency ventilation prompted this study. We compared the tracheal histopathology seen following standard-frequency, conventional mechanical ventilation with that seen following high-frequency, conventional mechanical ventilation, and two different forms of high-frequency jet ventilation. Twenty-six adult cats were examined. ⋯ Of all of the ventilators examined, the BLP, the ventilator operating at the fastest rate, produced the greatest loss of surface cilia and depletion of intracellular mucus. IDC high-frequency jet ventilation and high-frequency, conventional mechanical ventilation produced nearly identical histologic injuries. In this study, significant tracheal damage occurred with all forms of high-frequency ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)