respiratory failure may require intubation of the trachea and breathing support through mechanical ventilation, generally on an intensive care unit. the need for ventilatory support can be anticipated by measurement of two spirometry-based breathing tests: the forced vital capacity (fvc) and the negative inspiratory force (nif). an fvc of less than 15 ml per kilogram body weight or an nif of less than 60 cmho are considered markers of severe respiratory failure.