ABSTRACT
Patients with suspected respiratory failure or insufficiency require rapid evaluation and intervention to avoid subsequent clinical deterioration and respiratory arrest. An assessment of the airway should be performed immediately in order to ensure patency and air movement. Further assessments of vital signs, oxygen saturation, other signs and symptoms of acute respiratory failure, as well as the need for endotracheal intubation and mechanical ventilation are warranted. Assessing the need for endotracheal intubation and mechanical ventilation involves evaluation of several factors including the presence of and the patient’s ability to clear excessive pulmonary secretions, the patient’s current oxygenation status, the presence of airway obstruction or pending airway obstruction, the patient’s current mental status, and the patient’s ability to maintain adequate minute ventilation. If endotracheal intubation and mechanical ventilation are not required, supplemental oxygen should be supplied as the etiology of the respiratory failure is sought. Chest radiograph and arterial blood gas analysis should be performed as they will aid in the search for a cause of the respiratory dysfunction. Other helpful diagnostic tools include bronchoscopy (with or without bronchio-alveolar lavage and culture), CT angiography of the chest, toxicology screens, head CT, and echocardiogram.(4)
These mechanisms include decreased fraction of inspired oxygen (FiO
shunting of deoxygenated blood into the systemic circulation, and impaired diffusion of oxygen across the alveolar epithelium (Table 24.1). V/Q mismatch and physiologic shunt nearly always coexist and are the main causes of hypoxia (Figure 24.2). V/Q mismatch and physiologic shunt can be distinguished by assessing the PaO
mismatch is the main contributor to hypoxemia, significant corrections in PaO
minimal increases in FiO 2 . However, when physiologic shunt is
the main cause of hypoxemia, then small increases in FiO 2 have
little to no effect on PaO 2 levels, and oxygen saturations and even
large adjustments in FiO 2 result in only modest corrections of
PaO 2 levels and oxygen saturations.(3, 5)
Once acute respiratory failure or insufficiency is identified and urgent assessment has been completed, a dedicated search for a clinical cause should be undertaken. The five main sources of hypoxemia should be considered and a list of potential clinical diagnoses (differential diagnoses) should be generated. Clinical assessments and diagnostic tools are used to narrow the list of potential diagnoses. Finally, once the diagnostic field has been sufficiently narrowed, a treatment plan tailored to the final diagnosis should be expeditiously put into place.
