V

Fig. 2 Schematic representation of airway pressure (Paw) changes with (a) PC-IRV and (b) HFJV in central and peripheral airways. In pressure-controlled inverse ratio ventilation, intrinsic PEEP can be harnessed with or without extrinsic PEEP. The increase in minimium alveolar pressure (by extrapolation) for a given Paw will depend on the level of intrinsic PEEP. Of note is the difference in maximum alveolar pressures; essentially the alveolus is exposed to the central peak inspiratory pressure in pressure-controlled inverse ratio ventilation, whereas peak inspiratory pressure is markedly attenuated in HFJV. (Reproduced with permission from Keogh (19.96,).)

In addition, aggressive lung volume recruitment with PC-IRV commonly mandates the practice of permissive hypercapnia. While hypercapnia is now widely applied, concerns remain about its adverse effects, particularly in certain patient groups. The application of effective HFJV, in which hypercapnia is not necessary and Paco2 levels can be effectively controlled, may be more appropriate than pressure-controlled inverse ratio ventilation in patients with renal failure, metabolic acidosis, cardiac insufficiency, or neurological pathology.

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