CURRENT Essentials of Critical Care.pdf

Chapter 8 Respiratory Failure 109■■■Respiratory Failure: HypoxemiaEssentials of Diagnosis• Arterial PO 2 (PaO 2 ) 60 mm Hg, equivalent to arterial O 2 saturation92%• If PaO 2 is less than expected when breathing supplemental O 2(FIO 2 21%), should also consider as hypoxemia• May have tachycardia, tachypnea, diaphoresis, anxiety,cyanosis, arrhythmias• If severe, may have confusion, lethargy, or coma• May coexist with respiratory acidosis (PaCO 2 45 mm Hg withpH 7.35); may have respiratory depression, impaired level ofconsciousness• Any pulmonary disease, pneumonia, COPD, asthma, pulmonaryembolism, ARDS, atelectasis, interstitial lung diseases; alsopleural effusions, pulmonary edema, extrapulmonary right-toleftshuntDifferential Diagnosis• Decreased O 2 delivery—low cardiac output, shock, anemia—without arterial hypoxemia (i.e. normal PaO 2 )• CarboxyhemoglobinemiaTreatment• Establish airway (positioning, suctioning, artificial airway)• Measure PaCO 2 to assess ventilation status• Supplemental O 2 ; amount based on likely disease and mechanismof hypoxemia; goal PaO 2 60 mm Hg or O 2 saturation92%• Asthma, COPD, pulmonary embolism, mild pneumonia and atelectasisrespond to FIO 2 0.24–0.4 (usually caused by V /Q mismatching)• ARDS, severe pneumonia or atelectasis, and extracardiac rightto-leftshunts require FIO 2 0.4–1.0 (due to hypoxemia from rightto-leftshunts)• Endotracheal intubation, PEEP and mechanical ventilationneeded if severe■ PearlYou cannot predict the new PaO 2 when you change the FIO 2 becausePaO 2 depends on the mechanism of hypoxemia.ReferenceHenig NR et al: Mechanisms of hypoxemia. Respir Care Clin N Am2000;6:501. [PMID: 11172576]