Volumetargeted ventilation

On many ventilators in current use, the waveform of the inspiratory flow can be altered. There are four alternatives.

1. Square waveform: the flow rises rapidly to a peak that is maintained during the length of inspiration, and the volume-time waveform is an ascending ramp. Patients who are breathing spontaneously (e.g. assist-control mode or synchronized intermittent mandatory ventilation) find this waveform comfortable.

2. Sinusoidal waveform: the flow-time and volume-time waveforms are both sinusoidal but are out of phase with each other. In clinical use, this waveform is very similar to the square waveform.

3. Ascending waveform: the flow rises constantly through inspiration and the volume-time waveform ascends exponentially. There is no evidence to support the use of this waveform (Slutsky 1994).

4. Descending waveform: the flow rises rapidly to a peak and then falls constantly or exponentially through inspiration. The mean airway pressure is higher and the peak airway pressure lower than a corresponding cycle using the ascending waveform. Therefore it can be used (sometimes together with inverse ratio ventilation) to improve oxygenation by alveolar recruitment.

Sleep Apnea

Sleep Apnea

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