II. Definitions
- Negative Inspiratory Flow (NIF) or Maximal Inspiratory Pressure (MIP)
- Maximal inspiratory effort measured as the pressure generated against an occluded airway
- Maximal Inspiratory Pressure (MIP) and Negative Inspiratory Flow (NIF) represent the same measure
- MIP is typically reported as positive, while NIF is reported as negative
III. Indications
- Progressive Neuromuscular Disease (e.g. Guillain Barre Syndrome, Myasthenia Gravis)
- Ventilator Weaning
IV. Interpretation: Findings of Impending Respiratory Failure
- Physical findings
- Quantitative Tests
- Single Breath Counting <10 to 15
- Vital Capacity <15-20 ml/kg
- Tidal Volume <5 ml/kg
- Maximum expiratory force <40 cm H2O (normal may be as high as 100 cm H2O)
- Negative Inspiratory Flow (NIF) less negative than -20 to -30 cm H2O (normal may be < -100 cm H2O)
- NIF less negative than-25 cmH2O may predict Ventilator Weaning failure