Pressure preset ventilators

If flow is measured and used to deliver a preset volume, then a ventilator is considered to be a flow controller (1). In most of the cases, volume preset ventilation is provided by ventilators that actually measure flow and use flow over time to deliver a preset volume. These machines maintain an approximately constant volume in the face of varying lung mechanics. The most common flow-controlled ventilators are listed in Table 2. As indicated in the table, most of these machines can also provide pressure ventilation. 

In pressure ventilation, most ventilators cycle from inspiration to expiration when inspiratory flow decreases to a predetermined percent of its peak flow or when a preset inspiratory time is reached. It has become increasingly clear that cycling plays an important role in assuring patient-ventilator synchrony (11). This has been quite well studied in pressure support ventilation and several authors have shown that a fixed cycle value can lead to premature cycling in patients with restrictive diseases and delayed cycling in those with obstructive disease (12,13). 

Regardless of whether a ventilator uses positive pressure or negative pressure, the trans-pulmonary pressure gradient determines the tidal volume. A ventilator that is a pressure controller delivers a preset pressure and this variable is unaffected by changes in limg compliance or resistance. A positive pressure ventilator applies pressure inside the chest to expand it using a noninvasive interface, or an artificial airway. 

Care providers play a crucial role in HMV in most countries. The Eurovent survey showed that, in Europe, ventilator servicing, such as maintenance, repair, delivery of spare parts, and regular surveillance, was carried out mainly by private companies. In some countries like Sweden, ventilator servicing was carried out directly by hospitals. The interaction between servicing companies and the prescriber was poor (14). Another problem was the variety of ventilators that exist in the market, with more than 70 models in Europe for 70% preset pressure and 30% volume ventilation. 

Pressure-generating and cycled devices are not suitable for ventilation in toxic trauma. Because of their construction, these devices will cycle once a preset pressure has been released. Therefore, if there is airway resistance and reduced lung... 

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