Respiratory failure

Respiratory failure is a serious medical condition where the respiratory system cannot perform adequate gas exchange. To stay healthy, the body must maintain specific levels of oxygen and carbon dioxide in the blood. In a healthy person, oxygen levels (PaO2) are usually above 80 mmHg (11 kPa). Carbon dioxide levels (PaCO2) are typically less than 45 mmHg (6.0 kPa). When these levels fall out of balance, the body enters respiratory failure. This condition can be acute, meaning it happens suddenly, or chronic, meaning it lasts a long time.

The mechanism of respiratory failure involves the failure to move gases between the air in the lungs and the blood. If oxygen levels in the blood drop, the condition is called hypoxemia. If carbon dioxide levels rise too high, it is called hypercapnia. When the brain does not receive enough oxygen, it can lead to ischemia. This lack of blood flow to the brain can cause an altered state of consciousness, such as confusion or lethargy.

Medical professionals classify respiratory failure into several distinct types. Type 1 respiratory failure is characterized by hypoxemia with normal or low carbon dioxide levels. This type occurs when oxygenation fails. Causes include low ambient oxygen at high altitudes or a ventilation-perfusion mismatch. In a mismatch, parts of the lung receive oxygen but lack enough blood to absorb it. This can be caused by a pulmonary embolism or congestive heart failure. Other causes include diffusion problems from pneumonia or a right-to-left shunt.

Type 2 respiratory failure involves both hypoxemia and hypercapnia. In this type, the body cannot eliminate the carbon dioxide it produces. This is often due to inadequate alveolar ventilation. Common causes include increased airway resistance from asthma or COPD. It can also result from reduced breathing effort due to drug effects or brain stem lesions. Neuromuscular problems, such as Guillain–Barré syndrome, can also prevent the muscles from breathing effectively.

There are also specialized categories known as Type 3 and Type 4. Type 3 is a specific form of Type 1 failure called peri-operative respiratory failure. It is specifically associated with surgery or medical procedures. This often happens because of atelectasis, which is the collapsing of the functional units of the lung. Type 4 respiratory failure occurs when the body's metabolic oxygen demands exceed what the heart and lungs can provide. This often happens during shock, such as cardiogenic or hypovolemic shock.

Doctors use several methods to diagnose the specific cause of the failure. The gold standard is the arterial blood gas (ABG) assessment. This test measures the exact levels of oxygen and carbon dioxide in the blood. Other tools include capnometry, which measures exhaled carbon dioxide, and pulse oximetry. Pulse oximetry measures the fraction of hemoglobin saturated with oxygen. Doctors also look for physical signs like tachypnea, which is a fast breathing rate. They may also notice cyanosis, a bluish color in the fingers or lips, or clubbing of the fingertips.

Treatment focuses on addressing the underlying cause whenever possible. If an infection is the cause, doctors may use antibiotics. If the failure is caused by an opioid overdose, the antidote naloxone is used. For many patients, respiratory therapy is necessary to support breathing. Type 1 failure might require high-flow nasal oxygen or continuous positive airway pressure. Type 2 failure often requires non-invasive ventilation (NIV). In severe cases, doctors use endotracheal intubation and a mechanical ventilator.

The prognosis for respiratory failure varies greatly depending on the cause and how quickly treatment begins. Because the condition can be so severe, it is a major focus of intensive care medicine. One in three hospitalized cases of acute respiratory failure is fatal. Understanding the specific type of failure helps medical teams choose the right tools to restore the balance of gases in the body.