Respiratory Failure Workup
- Author: Ata Murat Kaynar, MD; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, MCCM more...
Respiratory failure may be associated with a variety of clinical manifestations. However, these are nonspecific, and very significant respiratory failure may be present without dramatic signs or symptoms. This emphasizes the importance of measuring arterial blood gases in all patients who are seriously ill or in whom respiratory failure is suspected.
Chest radiography is essential. Echocardiography is not routinely done but is sometimes useful. Pulmonary functions tests (PFTs), if feasible, may be helpful. Electrocardiography (ECG) should be performed to evaluate the possibility of a cardiovascular cause of respiratory failure; it also may detect dysrhythmias resulting from severe hypoxemia or acidosis. Right-sided heart catheterization is controversial.
Once respiratory failure is suspected on clinical grounds, arterial blood gas analysis should be performed to confirm the diagnosis and to assist in the distinction between acute and chronic forms. This helps assess the severity of respiratory failure and helps guide management.
A complete blood count (CBC) may indicate anemia, which can contribute to tissue hypoxia, whereas polycythemia may indicate chronic hypoxemic respiratory failure.
A chemistry panel may be helpful in the evaluation and management of a patient in respiratory failure. Abnormalities in renal and hepatic function may either provide clues to the etiology of respiratory failure or alert the clinician to complications associated with respiratory failure. Abnormalities in electrolytes such as potassium, magnesium, and phosphate may aggravate respiratory failure and other organ function.
Measuring serum creatine kinase with fractionation and troponin I helps exclude recent myocardial infarction in a patient with respiratory failure. An elevated creatine kinase level with a normal troponin I level may indicate myositis, which occasionally can cause respiratory failure.
In chronic hypercapnic respiratory failure, serum levels of thyroid-stimulating hormone (TSH) should be measured to evaluate the possibility of hypothyroidism, a potentially reversible cause of respiratory failure.
Chest radiography is essential in the evaluation of respiratory failure because it frequently reveals the cause (see the images below). However, distinguishing between cardiogenic and noncardiogenic pulmonary edema is often difficult. Increased heart size, vascular redistribution, peribronchial cuffing, pleural effusions, septal lines, and perihilar bat-wing distribution of infiltrates suggest hydrostatic edema; the lack of these findings suggests acute respiratory distress syndrome (ARDS).
Echocardiography need not be performed routinely in all patients with respiratory failure. However, it is a useful test when a cardiac cause of acute respiratory failure is suspected.
The findings of left ventricular dilatation, regional or global wall motion abnormalities, or severe mitral regurgitation support the diagnosis of cardiogenic pulmonary edema. A normal heart size and normal systolic and diastolic function in a patient with pulmonary edema would suggest ARDS.
Echocardiography provides an estimate of right ventricular function and pulmonary artery pressure in patients with chronic hypercapnic respiratory failure.
Pulmonary Function Tests
Patients with acute respiratory failure generally are unable to perform PFTs; however, these tests are useful in the evaluation of chronic respiratory failure.
Normal values for forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) suggest a disturbance in respiratory control. A decrease in the FEV1 -to-FVC ratio (FEV1/FVC) indicates airflow obstruction, whereas a reduction in both FEV1 and FVC and maintenance of FEV1/FVC suggest restrictive lung disease.
Respiratory failure is uncommon in obstructive diseases when FEV1 is greater than 1 L and in restrictive diseases when FVC is greater than 1 L.
See Pulmonary Function Testing for further details.
Right-Sided Heart Catheterization
Right-sided heart catheterization (also known as pulmonary artery catheterization or Swan-Ganz catheterization) remains a controversial issue in the management of critically ill patients. Invasive monitoring probably is not routinely needed in patients with acute hypoxemic respiratory failure, but when significant uncertainty about cardiac function, adequacy of volume resuscitation, and systemic oxygen delivery remain, right-sided heart catheterization should be considered.
Measurement of pulmonary capillary wedge pressure may be helpful in distinguishing cardiogenic from noncardiogenic edema. The pulmonary capillary wedge pressure should be interpreted in the context of serum oncotic pressure and cardiac function.
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