Previous authors highlighted that replacing HME with HH decreases dead space, promotes CO 2 clearance and allows V T and plateau pressure reduction during ARDS : however, no data clarify to what extent ∆ P is reduced by this approach and whether this is safe in patients with concomitant brain injury, for whom tight control of PaCO 2 is mandatory and any intervention has to be evaluated also from the perspective of cerebral hemodynamics. Although they are simpler to use, HMEs carry relevant instrumental dead space and decrease the proportion of V T contributing to alveolar ventilation. Heat and moisture exchangers (HME) and heated humidifiers (HH) are used for gas conditioning during invasive mechanical ventilation. In clinical practice, patients with acute brain injury and ARDS often receive V T exceeding 6 ml/kg of predicted body weight (PBW). The optimal balance between brain and lung protection during mechanical ventilation is not well established, and no recommendation exists on ventilatory management of these patients. Ĭonsequently, in brain-injured patients with ARDS, two competing priorities arise: use of low V T for lung protection and tight PaCO 2 control to maintain proper cerebral blood flow and prevent undue intracranial pressure increases. Nonetheless, lower V T yield increased risk of hypercapnia, which is deleterious, especially in patients with brain injury: In this particular subset of patients, tight control of arterial partial pressure of carbon dioxide (PaCO 2) is needed to prevent any secondary brain injury due to increases in cerebral blood flow and intracranial pressure. The use of low tidal volume ( V T) to limit plateau pressure and driving pressure (i.e., plateau pressure–positive end-expiratory pressure, ∆ P) reduces ventilator-induced lung injury (VILI) and improves survival in ARDS patients.
Acute respiratory distress syndrome (ARDS) affects up to 30% of critically ill patients with acute brain injury, representing an independent predictor of worse clinical outcome.
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