Ventilation Strategies: Tidal Volume and PEEP
Carmen Silvia Valente Barbas
Acute respiratory distress syndrome (ARDS), defined as an increment in the lung alveolar-capillary membrane permeability causing a pulmonary edema rich in proteins, has been recently reclassified as mild, moderate, and severe according to Berlin definition . It occurred in 1.8-10% of ICU admissions [1-3] and presents a progressively higher mortality ratio from its mild (34.9%) to the more severe form of presentation (46.1%) .
Respiratory System Structural Dysfunction After ARDS
After the initial lung insult, resulting from the exposition of a genetic predisposing patient to a risk factor (pulmonary infection, sepsis, acid-gastric lung aspiration, etc.), epithelial and endothelial lung barriers can be disrupted liberating, respectively, receptors for advanced glycation end products (RAGE) and angiopoietin-2. The extravasation of plasma inside the alveolar space turns an air-filled lung into a heavy high-osmotic pressure liquid-filled lungs. As a consequence, the higher weight of the lungs under the action of the gravity force predisposes the lowermost lung regions to collapse (Fig. 3.1) provoking a higher intrapulmonary shunt, a refractory hypoxemia, and a decrease in lung compliance. The functional alterations of the respiratory system are expressed by a decrease in the functional residual capacity (FRC) and a shift of the respiratory system pressure-volume curve down and to the right. The clinical manifestations are a dyspneic and hypoxemic patient with a high work of breathing that needs a high nasal flow oxygen system,
C.S.V. Barbas, MD, PhD
© Springer International Publishing Switzerland 2017 D. Chiumello (ed.), Acute Respiratory Distress Syndrome (ARDS), DOI 10.1007/978-3-319-41852-0_3
Fig. 3.1 Normal thoracic tomography versus ARDS thoracic tomography (Reprinted with permission from Medical Evidence Percorso Formativo 2015, yr. 8, n. 104, www.ati14.it)
noninvasive ventilation or intubation, and invasive mechanical ventilation to support the patient’s gas exchange and respiratory system mechanics while the clinical treatment and avoidance of the risk factors start [4, 5].