Respiratory care clinics of North America
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Partial ventilatory support techniques are intended for patients who are unable to maintain a normal alveolar ventilation, despite normal central control for respiration. Proportional assist ventilation (PAV) is a novel mode of partial ventilatory support in which the ventilator generates an instantaneous inspiratory pressure in proportion to the instantaneous effort of the patient. In theory, PAV should normalize the neuro-ventilatory coupling by making the ventilator an extension of patient's respiratory muscles, while leaving to the patient the entire control of all aspects of breathing. ⋯ In mechanically ventilated patients, the respiratory system impedance may change over time. These changes may impair the good matching between ventilator output and patient's ventilatory demand and lead to patient-ventilator asynchrony. To take full advantage of PAV, the authors believe that PAV should continuously and automatically adapt to the respiratory system passive mechanics, assessed by continuous noninvasive measurement of total elastance and resistance.
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Adaptive support ventilation (ASV) is a newer form of closed-loop ventilation control available on the Galileo ventilator (Hamilton Medical). ASV provides automated selection of initial ventilator parameters based on measurements of patient lung mechanics and breathing effort. ⋯ ASV may be thought of as an "electronic" ventilator management protocol that may improve the safety and efficacy of mechanical ventilation. Additional clinical investigations regarding the effect of ASV on outcome, ventilator days, and so forth are forthcoming.
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In this article automatic tube compensation (ATC) is described with respect to working principle, to technical realization, and to clinical experience. ATC, based on an indirect closed-loop working principle, compensates for the flow-dependent pressure drop across the tracheal tube during both inspiration and expiration. ATC reduces patient work of breathing, increases respiratory comfort, and allows prediction of successful extubation. ATC is not a stand-alone ventilatory mode, but rather a component of flow-proportional pressure support that can be combined with all conventional ventilatory modes.
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Adaptive lung ventilation (ALV) is a method of closed-loop mechanical ventilation analogous to modern closed-loop technology in aviation such as the autopilot and automatic landing system. The algorithm of the controller of ALV is designed to automatically provide pressure-controlled synchronized intermittent mandatory ventilation (P-SIMV) and weaning as individually required in any clinical situation. ⋯ The ease of application, efficiency, and safety of the first ALV controllers have been demonstrated in lung models, in patients with normal lungs undergoing general anesthesia, in patients requiring unusual positioning, in transition to and from one-lung anesthesia, and in long-term ventilation of patients with various lung pathologies and in weaning patients who have restrictive or obstructive pulmonary disease. Prospective comparative studies of ALV versus other currently used manually selected modes of mechanical ventilation, such as the one reported in this article, should confirm the safety and identify the benefits of this form of advanced closed-loop mechanical ventilation technology.
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Conventional mechanical ventilation modes fail to provide a setting for direct control of a patient's ventilatory effort; however, with all modes clinicians may manipulate conventional controls to modulate the spontaneous respiratory activity of the patient. For instance, during pressure support ventilation the spontaneous respiratory activity can be decreased by increasing the pressure support level to achieve an adequate residual load for the respiratory muscles of the patient, neither too high nor too low. This choice is based on the clinical observation. ⋯ Occlusion pressure at 0.1 second (P0.1) can be the ideal parameter for that purpose. The authors have designed a noninvasive method for breath-by-breath monitoring of P0.1, and then a closed-loop control mode that automatically adapts the pressure support level to reach and maintain a user-set P0.1 and alveolar volume. This article discusses features and performance of this P0.1 control mode, fields of application, known limits, and possible future improvements.