Inspiratory flow demand

The pressurization phase is the time the machine will use to reach inspiratory pressure. The ability of the ventilator to meet the patient s inspiratory flow demand has mainly been studied in the acute setting where a high-pressure rise time is known to decrease the inspiratory effort (7,8). A recent bench study showed that pressurization characteristics varied considerably among 10 home care ventilators (3). Battisti et al. concluded that some home care ventilators might be limited in patients with high inspiratory demand, those with marked obesity, or those with severe restriction. Depending on the type of home care ventilator, the pressure rise time can be individually adjusted or fixed. 

As home care ventilators become smaller in size, their pneumatic performance may be compromised. As rise time settings are often arbitrary numbers, clinicians should ask manufacturers for information on flow performance, as this information is easily available in the form of pressure flow graphs. One should look for the machine s ability to maintain inspiratory pressure stability. Breathing on the machine is also a very good way to evaluate a ventilator s ability to meet inspiratory flow demand. 

Sassoon CSH, Giron AE, Ely E, et al. Inspiratory work of breathing on flow-by and demand-flow continuos positive airway pressure. Crit Care Med 1989 17 1108-1114. 

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