NIF (also called MIP) measures how much inspiratory force a patient's respiratory muscles can generate, used alongside the RSBI to judge whether someone is strong enough to come off a ventilator.
Adequate inspiratory muscle strength for weaning.
Borderline — interpret with the rest of the picture.
Inadequate strength — weaning less likely to succeed.
The stronger the inspiratory pull, the more negative the pressure recorded.
NIF measures the vacuum pressure a patient can generate pulling air in against a blocked airway. A bigger negative number means more force was generated, so the inspiratory muscles are stronger.
A value more negative than about −20 to −25 cmH₂O is generally considered adequate. Values less negative than −20 suggest inadequate respiratory muscle strength.
Measured — it comes from a manometer while the patient inhales forcefully against an occluded airway. This page interprets a measured value rather than computing one.
RSBI captures the breathing pattern and load; NIF captures muscle strength. Together they give a fuller picture of whether a patient can sustain breathing off the ventilator.