Oxygenation

Improvement in oxygenation can sometimes be achieved by increasing the mean airway pressure. This is often the case where collapsed alveoli may be recruited by this increased pressure (e.g. acute lung injury) ( M§rcY„and„„M.§Ii,D.i 19.9.1). Prolonging the inspiratory time elevates the mean airway pressure and is often used for this effect. If the inspiratory time is lengthened sufficiently, the I:E ratio is reversed. This is termed 'inverse ratio ventilation'. Where the ventilation is pressure targeted, the square pressure waveform maintains mean airway pressure but limits peak alveolar pressure. With volume-targeted ventilation the mean airway pressure will be lower as the pressure waveform is not square, but it can be elevated by increasing the inspiratory plateau although care must be taken as the peak inspiratory pressure will rise (Marcy.and.Marini 1991). Although inverse ratio ventilation often increases Pao2, there is no conclusive evidence that it improves outcome (MaLCy.„,§.D.d.„,M§IiD.i

1.9.91,; Slutsky .1994). In addition, it has significant risks (see below).

Sleep Apnea

Sleep Apnea

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