Summary of technical characteristics of NIV ventilators and their influence on traces semiology
| Normal semiological aspect | |
| Ventilatory modality | |
| Volume target | Squared flow Increasing pressure |
| Pressure target | Squared pressure Decreasing flow |
| Hybrids | Variable (depends on modality of volume targeting) |
| Inspiratory trigger function | |
| Spontaneous | Negative deflection in pressure and flow curves |
| Assisted | Negative deflection in pressure and flow curves |
| Controlled | – |
| Assisted/controlled | Negative deflection in pressure and flow curves (only in a patient-triggered cycle) |
| Pressurisation | |
| Rise time | |
| Fixed | Inspiratory slope until reaching the pressure target |
| Adjustable | |
| Ability to sustain inspiratory plateau | Maintain constant pressure and/or flow level |
| I to E cycling | |
| Time cycled | Fixed inspiratory time |
| Flow cycled | |
| Fixed | Variable inspiratory time |
| Adjustable (% of peak flow) | |
| ‘Intelligent’ algorithms | |
| PEEP level | Level of expiratory pressure |
| Type of exhalation | |
| Single or double limb with expiratory valve | Expiratory slope reflects expired Vt* |
| Single limb with calibrated leak | Expiratory slope does not reflect expired Vt and may be absent* |
| Any level of positive expiratory pressure is recognised† | |
↵* Visual recognition of expiratory slope will depend on the position of the pneumotachograph with regard to the expiratory device. In this way the expiratory slope will reflect the expired volume only when the flow sensor is interposed between the mask and the exhalation device.
↵† As a mandatory PEEP level is needed to impede rebreathing.
NIV, non-invasive ventilation; PEEP, positive end expiration pressure; Vt, tidal volume.