What are the causes of respiratory acidosis?

Respiratory acidosis is a serious medical condition that occurs when the lungs can't remove all of the carbon dioxide produced by the body through normal metabolism. The blood becomes acidified, leading to increasingly serious symptoms, from sleepiness to coma.

Respiratory acidosis is a medical emergency, requiring a prompt diagnosis. Treatment can include breathing machines and long-term management to address underlying contributions. This condition is also called primary hypercapnia.

As carbon dioxide levels increase, the brain experiences increased blood flow and volume, leading to specific impairment and associated symptoms. The release of catecholamines—hormones produced by your adrenal glands during stressful periods—may additionally lead to other symptoms such as skin flushing, sweating, and heart dysfunction.

These are the most common symptoms associated with respiratory acidosis:

• Sleepiness
• Fatigue
• Lethargy
• Confusion
• Coma
• Anxiety
• Psychosis
• Headaches
• Shortness of breath
• Tremors (manifest as shaking or jerking muscle movements)
• Asterixis (an inability to maintain posture of part of the body)
• Seizures
• Warm and flushed skin
• Sweating

Not all of these symptoms must be present for the diagnosis of respiratory acidosis, and some occur earlier while others may develop if the condition progresses. For example, someone may at first seem sleepy before becoming more lethargic and eventually becoming unresponsive and slipping into a comatose state.

Respiratory acidosis occurs when breathing becomes impaired to the degree that the ability to expel carbon dioxide is compromised. This hypoventilation increases the concentration of carbon dioxide in the blood and decreases the blood’s pH level. These changes may occur acutely in sudden illness or be due to chronic, long-term diseases.

Carbon dioxide is combined with water in the lungs to produce carbonic acid. This dissociates into bicarbonate and a hydrogen ion, effectively decreasing the pH level of the blood, making it more acidic.

The body’s acid-base balance normally results in a pH level between 7.35 to 7.45. When it falls below 7.35, this is known as acidosis (or acidemia, referring to acidity in the blood). If the level exceeds 7.45, it's called alkalosis (or alkalemia, referring to alkalinity in the blood). The balance can be shifted by breathing (and the degree of expiring, or breathing off, carbon dioxide). It can also be affected by changes in metabolism that impact carbon dioxide or acid production, or bicarbonate excretion through the kidneys. There are two types of respiratory acidosis:

• Acute respiratory acidosis—Carbon dioxide levels may build up very quickly due to an acute illness that disrupts the acid-base balance, like that stemming from a drug overdose, stroke, aspiration (such as choking on vomit), or pneumonia.
• Chronic respiratory acidosis—Over a longer period of time, the kidneys work to stabilize the situation by increasing bicarbonate production to restore the body’s acid-base balance. While the stabilization may help for a while, there may come a point when this compensation is simply inadequate. This can be caused by chronic obstructive pulmonary disease (COPD), muscular disorders, or severe thoracic skeletal defects.

Respiratory acidosis may occur for multiple reasons. If the brainstem fails to prompt normal breathing, the airway is blocked, lung tissue is inadequately ventilated with air or inadequately perfused with blood, or the diaphragm and musculoskeletal support of breathing fails, respiratory acidosis may develop.

Within the brainstem, the respiratory center generates a signal that causes the lungs to inflate or deflate through activation of the respiratory muscles (especially the diaphragm). As the diaphragm contracts, it's drawn down and the lungs are filled with air, and as it relaxes, the lungs passively empty. If the respiratory center in the brainstem is damaged, breathing may be compromised. Possible impairment may occur in the setting of:

• Medicines that suppress breathing (narcotics, benzodiazepines, and alcohol)
• Drug overdose
• Spinal cord injury
• Stroke
• Tumor
• Trauma

These abnormalities typically cause other symptoms, often affecting consciousness and contributing to unresponsiveness or coma in more severe cases.

The delivery of air to the lungs may become blocked at various points. The passageway that connects the nose and mouth to the lungs (extending from the throat to the trachea and bronchi) may be obstructed. Alternatively, the smaller grape-like sacs within the lungs—called alveoli—may become stiff or filled with mucus. Respiratory failure and respiratory acidosis may gradually develop due to these blockages that affect air exchange. Contributions include:

• Aspiration (such as choking on vomit)
• Asthma
• COPD

These conditions may be associated with wheezing, shortness of breath, coughing, and other signs of breathing problems.

To rid the body of carbon dioxide, the blood must deliver it to functioning alveoli well-ventilated by air. Compromised blood flow, or lung tissue that cannot be adequately filled with air, both affect function. When there is a mismatch between airflow (ventilation) and blood flow (perfusion), this leads to a condition called dead space ventilation. This loss of function can contribute to respiratory acidosis and may be due to:

Many of these problems lead to breathing difficulties that may become evident due to decreased oxygen levels.

The diaphragm is primarily responsible for the expansion and filling of the lungs. If this muscle fails (often due to phrenic nerve damage), breathing may be compromised. Disorders that restrict lung expansion or weaken the muscles that aid breathing may gradually cause respiratory acidosis. Consider these potential causes:

These conditions may require testing to identify the degree that they may be contributing to the development of respiratory acidosis.

Respiratory acidosis typically comes to attention because the affected individual shows signs of difficulty breathing, often associated with changes in consciousness. Depending on the acuity, this may require emergency evaluation. If the symptoms come on more gradually, assessment may occur in a clinical or hospital setting.

A physician will perform a physical examination, listening to the heart and lungs, assessing circulation, and ensuring there is not a blockage affecting the airway. Risk factors for respiratory acidosis will be identified. If deemed to be unstable, blood tests will be quickly obtained to measure the carbon dioxide and pH levels of the blood.

The most important test for the diagnosis of respiratory acidosis is the arterial blood gas measurement. This test measures the oxygen and carbon dioxide levels in the blood by taking a sample from a peripheral artery, typically from an extremity. The measurement of carbon dioxide—called the arterial CO2 tension, or PaCO2—is above 45 millimeters of mercury in simple respiratory acidosis (as measured at rest and at sea level).

The acidity of the blood is measured with the pH level. Respiratory acidosis occurs when an increase in PaCO2 develops secondary to impairments in breathing that result in a pH of less than 7.35, as measured in blood taken from an artery.

In chronic respiratory acidosis, the PaC02 may be elevated with a normal blood pH (in the range of 7.35 to 7.45). It may also be in a near-normal range. This occurs due to the kidneys compensating for the acidosis with an elevation of neutralizing bicarbonate levels within the blood.

Further testing to identify the causes of respiratory acidosis may include:

• Basic metabolic panel (blood test)
• Chest X-ray
• CT scan of the chest
• Pulmonary function testing (to measure breathing and how well the lungs are functioning)

Depending on the suspected cause, especially if it's due to an abnormality affecting the brain or musculoskeletal system, additional testing may prove necessary.

In acute respiratory acidosis, the body initially attempts to compensate. This response, called metabolic compensation, occurs if the acidosis persists for more than 12 hours. The kidneys will increase the release of hydrogen ions, through ammonium, reducing the acidity of the blood. Generating and reabsorbing bicarbonate also helps to restore the pH balance of the body toward normal values. This process occurs over three to five days. Unfortunately, it may not be enough.

Ultimately, treatment to correct respiratory acidosis may only be successful by artificially supporting breathing to avoid complete respiratory failure and addressing the underlying cause. This may require the use of the following treatments.

These supportive devices include continuous positive airway pressure (CPAP) or bilevel (BiPAP) therapy. Pressurized air is delivered through a face mask, often through the nose or nose and mouth, allowing improvement in the ability of the lungs to expel carbon dioxide. These interventions are especially useful in obstructive sleep apnea, obesity hypoventilation syndrome, and neuromuscular failure. They may be used acutely to avoid the need for intubation and placement on a ventilator.

If the blood oxygen level is detected to be low, additional oxygen may be provided to alleviate this problem. Oxygen alone is not an appropriate treatment, as it may suppress breathing in some circumstances, leading to even higher carbon dioxide levels.

If breathing difficulties progress, it may be necessary to place a tube within the airway for more direct access to ventilate the lungs. The affected person will be sedated and restrained to avoid removal of the tube. It will be connected to a ventilator and proper settings will optimize the ability of the lungs to obtain oxygen and expel carbon dioxide. This requires observation in the intensive care unit.

Further interventions are dependent on the contributing factors. These may include the following.

• Medications: Bronchodilator medicines and corticosteroids may be used to reverse some types of airway obstruction, such as those associated with asthma or COPD.
• Smoking cessation: Smokers will be encouraged to quit. Smoking contributes to airway dysfunction, and avoiding additional damage may prevent future problems.
• Weight loss: In the case of obesity hypoventilation syndrome, significant weight loss may be necessary to reduce abnormal compression of the lungs. This may be accomplished with dieting and exercise, but in the case of morbid obesity, surgical weight loss interventions may be needed.
• Avoiding sedatives: Be careful about taking sedating medicines. These may include both narcotic (or opioid) pain medication and benzodiazepines used to treat anxiety and other conditions. Never combine prescription medications with alcohol to avoid side effects that may affect breathing.
• Sleep apnea treatment: Disordered breathing during sleep may predispose toward daytime problems. Sleep apnea is the most common condition that affects nighttime breathing. It may be associated with other symptoms, such as snoring and daytime sleepiness, and testing is highly recommended if this condition is suspected. Treatment with the use of an oral appliance or CPAP machine may provide long-term benefits. If you have been prescribed treatment, such as CPAP, make certain that you use it nightly.

The long-term prognosis of respiratory acidosis depends on the underlying abnormality that's causing the problem. Some contributors are chronic and progressive, whether others would be expected to resolve fairly quickly. It's important to work with a physician to identify what might be contributing and resolve as many evocative factors as possible.

If you suspect someone of having difficulty breathing, leading to symptoms suggestive of respiratory acidosis, it's important to have them checked out by a doctor immediately: bring them to the emergency room or call 911. By seeking prompt medical evaluation, interventions may be pursued to resolve the breathing difficulty and restore the body to normal function.