Table 2

Summary of technical characteristics of NIV ventilators and their influence on traces semiology

Normal semiological aspect
Ventilatory modality
 Volume targetSquared flow
Increasing pressure
 Pressure targetSquared pressure
Decreasing flow
 HybridsVariable (depends on modality of volume targeting)
Inspiratory trigger function
 SpontaneousNegative deflection in pressure and flow curves
 AssistedNegative deflection in pressure and flow curves
 Assisted/controlledNegative deflection in pressure and flow curves (only in a patient-triggered cycle)
 Rise time
  FixedInspiratory slope until reaching the pressure target
Ability to sustain inspiratory plateauMaintain constant pressure and/or flow level
I to E cycling
 Time cycledFixed inspiratory time
 Flow cycled
  FixedVariable inspiratory time
  Adjustable (% of peak flow)
  ‘Intelligent’ algorithms
PEEP levelLevel of expiratory pressure
Type of exhalation
 Single or double limb with expiratory valveExpiratory slope reflects expired Vt*
 Single limb with calibrated leakExpiratory 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.