In oxygen therapy, the behavior and effectiveness of high airflow oxygen-entrainment systems depends to a great extent on the peak inspiratory flowrate (PIFR) of the patient. The formula reported here, PIFR = πVE(TI + TE)/2TI, provides a more accurate calculation of peak inspiratory flow than does the often-used clinical rule of thumb, PIFR = 3. VE, and may be used to predict inspiratory fresh-gas flow requirements for ventilators and nonrebreathing circuits. (Respir Care 1985;30:766-770.)
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