Key messages

• Inspiratory time governs the inspiratory-to-expiratory (I:E) ratio and inspiratory flow rate. In mechanically ventilated patients, a 'standard' inspiratory time of 0.8 to 1.5 s should be adjusted according to the following.

Oxygenation: improvement in oxygenation may follow lengthening of the inspiratory time to increase mean airway pressure. Risk of ventilator-induced lung injury: shortening the expiratory time increases the possibility that auto-PEEP will develop. Cardiovascular stability: prolonged inspiration can cause hemodynamic instability by impeding venous return.

Level of spontaneous respiration and mode of ventilation: lengthened inspiratory time is usually poorly tolerated by patients who are breathing spontaneously or lightly sedated.

• Inspiratory waveform can only be adjusted in volume-targeted ventilation. The choice depends upon the following.

Patient comfort: square or sinusoidal waveforms are often well tolerated. Oxygenation: a descending waveform may improve Pao2.

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Sleep Apnea

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