Peep

The application of PEEP improves oxygenation by providing movement of fluid from the alveolar to the interstitial space, recruitment of small airways and collapsed alveoli, and an increase in functional residual capacity (FRC). In addition, cyclical collapse and low volume lung injury is attenuated. Increased Pao2 induced by PEEP was found to be correlated with the volume of lung recruited.26

In theory, setting PEEP above the lower inflection point may prevent derecruitment and low lung volume ventilator associated injury. As discussed above, adjusting the level of PEEP to 2 cm H2O above the lower inflection point was part of a lung ventilatory strategy that was advantageous.18 In a crossover study of 15 patients mechanically ventilated because of ALI, lung volume recruitment and Pao2 were increased with the combination of lower Vt (6 ml/kg) and increased PEEP at constant Pplat.27

It has been suggested that the effect of PEEP on recruitment in ARDS varies according to the regional distribution of consolidation. Hence, PEEP had little effect on lobar consolidation but induced the greatest reduction in non-aerated lung in patients with diffuse CT abnormalities.28 Current clinical practice in the absence of static PV curve measurement is to set PEEP at a relatively high level such as 15 cm H2O in patients with ARDS.

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