How to diagnose Respiratory Failure ?
Your doctor will diagnose respiratory failure based on your medical history, a physical exam, and test results. Once respiratory failure is diagnosed, your doctor will look for its underlying cause.
                
Medical History
                
Your doctor will ask whether you might have or have recently had diseases or conditions that could lead to respiratory failure.
                
Examples include disorders that affect the muscles, nerves, bones, or tissues that support breathing. Lung diseases and conditions also can cause respiratory failure.
                
For more information, go to "What Causes Respiratory Failure?"
                
Physical Exam
                
During the physical exam, your doctor will look for signs of respiratory failure and its underlying cause.
                
Respiratory failure can cause shortness of breath, rapid breathing, and air hunger (feeling like you can't breathe in enough air). Using a stethoscope, your doctor can listen to your lungs for abnormal sounds, such as crackling.
                
Your doctor also may listen to your heart for signs of an arrhythmia (irregular heartbeat). An arrhythmia can occur if your heart doesn't get enough oxygen.
                
Your doctor might look for a bluish color on your skin, lips, and fingernails. A bluish color means your blood has a low oxygen level.
                
Respiratory failure also can cause extreme sleepiness and confusion, so your doctor might check how alert you are.
                
Diagnostic Tests
                
To check the oxygen and carbon dioxide levels in your blood, you may have: 
                
Pulse oximetry. For this test, a small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood.
                
Arterial blood gas test. This test measures the oxygen and carbon dioxide levels in your blood. A blood sample is taken from an artery, usually in your wrist. The sample is then sent to a laboratory, where its oxygen and carbon dioxide levels are measured.
                
A low level of oxygen or a high level of carbon dioxide in the blood (or both) is a possible sign of respiratory failure.
                
Your doctor may recommend other tests, such as a chest x ray, to help find the underlying cause of respiratory failure. A chest x ray is a painless test that takes pictures of the structures inside your chest, such as your heart, lungs, and blood vessels.
                
If your doctor thinks that you have an arrhythmia as a result of respiratory failure, he or she may recommend an EKG (electrocardiogram). An EKG is a simple, painless test that detects and records the heart's electrical activity.