Anaesthesia and intensive care
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Recent modes of ventilatory support aim to facilitate weaning and minimise the physiological disadvantages of intermittent positive pressure ventilation (IPPV). Intermittent mandatory ventilation (IMV) allows the patient to breathe spontaneously in between ventilator breaths. ⋯ Other modes or refinements of IPPV include high frequency ventilation, expiratory retard, differential lung ventilation, inversed ratio ventilation, 'sighs', varied inspiratory flow waveforms and extracorporeal membrane oxygenation. While these techniques have useful applications in selective situations, IPPV remains the mainstay of managing respiratory failure for most patients.
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Desirable features of new generation intensive care ventilators include the ability to ventilate a wide range of patient sizes, an uncomplicated control panel, an appropriate but not excessive variety of ventilatory patterns, adequate patient monitoring and alarm functions, and simplicity of cleaning and routine maintenance. Examples of currently available ventilators include the Servo 900-C, CPU-1, Engstrom Erica, Bear 5, Drager EV-A and Hamilton Veolar. ⋯ Current trends in ventilator design include further refinement of computer control and the provision of graphic displays showing the results of continuous sophisticated analysis of respiratory function. The extent to which these developments will prove clinically useful will require careful evaluation.
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In this paper, a number of reported systems for classifying ventilators are considered and their usefulness commented on. Most omit the concept of power, which is an important factor in how the ventilator will perform. It is recommended that a system of classification should be backed by bench tests and clinical trials. Not enough is known about high frequency ventilation to permit reasonable evaluation of the classifications proposed in this area.