Independent lung ventilation ilv allows each lung to

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Independentlung ventilation (ILV) allows each lung to be ventilatedseparately, thus controlling the amount of flow, volume, andpressure each lung receives.The presence of abnormal substances in the airways and alveolias a result of aspiration is misleadingly called aspiration pneumonia.-p528Gastric contents and oropharyngeal bacteria (see Pneumonia earlier in this chapter) arethe most common aspirates of the critically ill patient.If the pH is less than 2.5, the patient willdevelop a severe chemical pneumonitis resulting in hypoxemiaThe aspiration of acid (pH less than 2.5) liquid gastric contentsresults in the development of bronchospasm and atelectasisalmost immediately. Over the next 4 hours, tracheal damage,bronchitis, bronchiolitis, alveolar-capillary breakdown, interstitialedema, and alveolar congestion and hemorrhage occur.64Severe hypoxemia develops as a result of intrapulmonary shuntingand V/Q mismatchingrisk factors for aspiration and aspiration related pneumonia-p529Nonacid Food ParticlesThe aspiration of nonacid (pH greater than 2.5) nonobstructingfood particles is similar to acid aspiration initially, withsignificant edema and hemorrhage occurring within 6 hours.After the initial reaction, the response changes to a foreignbody-type reaction with granuloma formation occurring around the food particles within 1 to 5 days.64 In addition tohypoxemia, hypercapnia and acidosis occur as a result ofhypoventilation.Bronchoalveolarlavage is not recommended because this practice disseminatesthe aspirate in lungs and increases damage.p530A pulmonary embolism (PE) occurs when a clot (thromboticembolus) or other matter (nonthrombotic embolus) lodges inthe pulmonary arterial system, disrupting the blood flow to aregion of the lungsThe majority of thromboticemboli arise from the deep leg veins, particularly the iliac,femoral, and popliteal veinsinjury tovascular endothelium, and venous stasis [Virchow’s triad]),p531endothelial injury appears to be the most significantrisk factors of pe-p533Theeffects on the pulmonary system are increased alveolar deadspace, bronchoconstriction, and compensatory shunting.p531 Thehemodynamic effects include an increase in pulmonary vascularresistance and right ventricular workloadp531Alveolar hypocarbiaoccurs as a consequence of decreased carbon dioxide in theaffected area and leads to constriction of the local airways,increased airway resistance, and redistribution of ventilation toperfused areas of the lungsBronchoconstriction promotes the development ofatelectasis
The major hemodynamic consequence of a PE is the developmentof pulmonary hypertension, which is part of the effect ofa mechanical obstruction when more than 50% of the vascularbed is occluded.As the pulmonary vascular resistance increases, so does theworkload of the right ventricle as reflected by a rise in pulmonaryartery (PA) pressures. Consequently, right ventricularfailure occurs, which can lead to decreases in left ventricularpreload, CO, and blood pressure, and shock.p531

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