PVI during NIV
NIV has a solid base of evidence for its indications but deserves a considerable amount of attention to keeping the patient comfortable and the interface synchronous. NIV may be under-utilised secondary to suboptimal clinical use.
Potential causes of NIV failure include
- Poor patient selection
- Progression of underlying disease
- Patient-Ventilator-Asynchrony due to:
- Wrong interface (size, leak)
- Wrong ventilator (poor leak compensation)
- Suboptimal ventilator settings
- Clinician inexperience
An asynchrony index (AI) of > 10% is considered severe.
A large leak and a high amount of pressure support are associated with a high AI.
Patient-ventilator asynchrony (PVA) Definitions
Sharp decrease in expiratory flow followed by an increase in expiratory flow and a gradual decrease in flow till baseline with depression of Paw at end of inspiratory below baseline. Pes is in negative deflection at end of ventilatory cycle
Airway pressure end-inspiratory rise in pressure 2cmH2O above peak inspiratory pressure with concomitant flow pause before becoming negative. Flow waveform descending limb is decelerating without rise. Pes is rising from trough while ventilator is still in inspiration
Two consecutive ventilator cycles separated by a short expiratory time, half of the inspiratory time or less, of which the first had to be patient or ventilator triggered
Diaphragm contraction repeated in some cycle stimulated by previous passive ventilatory breath occuring during insufflation phase or at the transition from inspiration to expiration
Flow Asynchrony (Overshoot)
A rapid spike in flow at initiation of inspiration with initial Paw above plateau pressure, followed by a steep flow decrease with Pes that rises before end of inspiration
Flow Asynchrony (Starvation)
Mismatch between the ventilator flow and the patient’s demand on a patient triggered breath, and it was characterized by a concave appearance in the pressure waveform or concave in flow decelerating pattern with continued negative deflection of Pes during inspiratory flow
Response time of the ventilator longer than deemed "normal" --> trigger delay --> Ineffective trigger
Increase in flow, volume, and pressure without any signs of the patient’s effort to trigger the ventilator (i.e., without a negative deflection in the airway pressure waveform) and as being out of synchrony with the preset frequency of the ventilator without Pes negative drop 2cmH2O
Sudden increase in flow during inspiration or a decrease in expiration with a concomitant negative deflection in the airway pressure waveform without triggering the ventilator with concurrent Pes drop that exceeds 2cm H2O