VENTILATOR TERMS

1. Volume-targeted modes: Volume constant, inspiration terminates when preset VT delivered. Peak airway pressure is variable and increases as needed to deliver prescribed VT. This is generally represented by a constant flow waveform.
2. Pressure-targeted modes: Volume variable and dependent on pulmonary compliance. The vent terminates flow of air when the pressure is met. Peak airway pressure is fixed, determined by set pressure level. This is generally represented by a decelerating flow waveform.
3. Tidal volume (VT): Is the volume of gas, exchanged during a breath and commonly expressed in milliliters. VT is generally set between 4-8 ml/kg ideal body weight (IBW), to prevent lung over distension and barotrauma.
4. Frequency (f): Is the rate, per minute, of breathing (patient or ventilator). Known as respiratory rate (RR).
5. Minute Ventilation (Ve): Is the average volume of gas entering, or leaving, the lungs per minute, commonly expressed in liters per minute. The product of VT and RR (respiratory rate). Normal Ve is 5 – 10 L/min.
6. Inspiratory (I) and Expiratory (E) time and I:E ratio: Is the period of time over which the VT is delivered. Setting a shorter inspiratory time (I) results in a faster inspiratory flow rate in volume cycled ventilation. Average adult inspiratory time is 0.7 to 1 second. I:E ratio is usually 1:2.
7. Positive end-expiratory pressure (PEEP): Is the amount of positive pressure that is maintained at end-expiration. It is expressed in centimeters of water (cmH2O). The purpose of PEEP is to increase end-expiratory lung volume and reduce air-space closure at end-expiration. Normal physiologic PEEP is 5 cmH2O.
8. Pressure Support (PS): Delivers flow at a set pressure, generally to overcome resistance of the airway and ventilator circuit. PS can also be used to support a spontaneously breathing patient, such as with Bi-PAP.
9. Flow: Is the velocity at which gas is delivered to the patient, expressed in liters per minute. When the flow rate is set higher, the speed of gas delivery is faster and inspiratory time is shorter.
10. Peak Inspiratory Pressure (PIP): Represents the total pressure that is required to deliver the VT and depends upon various airway resistance, lung compliance, and chest wall factors. It is expressed in centimeters of water (cmH2O).
11. Sensitivity or trigger sensitivity: Effort, or negative pressure, required by the patient to trigger a machine breath, commonly set so that minimal effort (-1 to -2 cmH2O) is required to trigger a breath.1,3