What Is Respiratory Depression (Hypoventilation)?

Respiratory depression, also known as hypoventilation or hypoventilatory syndrome, is the abnormal retention of carbon dioxide in the blood due to the poor exchange of carbon dioxide and oxygen within the lungs.

Slow and shallow breathing characterizes this breathing disorder, sometimes as low as 8 to 10 breaths per minute. The normal breathing rate is between 12 and 20 breaths per minute.

During normal breathing, the blood carries inhaled oxygen to all the tissues of the body while removing carbon dioxide through the lungs as a waste product.

Medical conditions that affect the brain and the functioning of the central nervous system can cause respiratory depression. Health conditions such as a stroke or sleep apnea can cause hypoventilation. It can also result from medication and other substances that impair brain function.

If a person does not receive medical treatment, severe respiratory depression can lead to reduced heart rate, heart attack, respiratory attack, brain damage, coma, or death.

Respiratory Depression Symptoms

The symptoms of hypoventilation vary depending on the severity of the condition. Early symptoms can be mild and unspecific such as:

• Lethargy and tiredness
• Daytime sleepiness
• Slow and shallow breathing 
• Depression
• Shortness of breath

If earlier symptoms are not addressed, then the severity of the condition can increase with the following symptoms:

• Confusion
• Disorientation
• Visual disturbance and headaches
• Labored breathing during activity and inactivity
• Bluish lips, fingers, and toes
• Increased daytime sleepiness and fatigue
• Difficulty staying awake and prolonged sleep at night
• Seizures
• Abnormally long pauses between breaths, known as apnea
• Nausea
• Abnormal breath sounds
• Diminished awareness and cognition

Diagnosis

It’s important to contact your doctor for a proper diagnosis of respiratory depression and to get treatment.

Your doctor will ask you questions about your symptoms and ask about any medications you're currently taking. The doctor will then make a further diagnosis with a physical examination and perform tests to determine the cause. These tests can include:

• Chest x-ray
• Lung function test
• Urine and serum drug screens
• Screening for alcohol and other toxins
• Blood gas test, which measures the amount of carbon dioxide and oxygen in the blood, along with the acid/base ratio
• Hematocrit and hemoglobin blood test which measures the number of red blood cells available to carry oxygen
• Pulse oximetry test measures the oxygen level in your bloodstream
• CT and MRI scans to check for stroke or tumors
• Sleep study to diagnose sleep-related disorders
• Thyroid function test to determine hypothyroidism, which is a potential cause of obesity and thus contributes to hypoventilation
• Electrocardiography (ECG) test to determine signs of heart strain and other disorders
• Electroencephalogram (EEG) test to check electrical patterns in the brain for conditions like seizures, head injuries, brain tumors, and epilepsy
• Ammonia levels test to determine levels of ammonia in the blood

Causes

Some health conditions can cause respiratory depression, which impacts breathing rate. When this occurs, the lungs cannot ventilate fully.

Neuromuscular Disorders

People with neuromuscular disorders can develop rapid, shallow breathing because of respiratory muscle weakness and poor muscle control, even though the neurological breathing impulse remains intact.

In neuromuscular disorders, ventilation decreases during sleep, especially REM sleep, causing hypoventilation to worsen.

Chest Wall Deformities

Chest wall deformities seen in conditions such as kyphoscoliosis and fibrothorax can interfere with normal respiration rate and lung function because of the physical limitations caused by the deformities. 

Obesity

Severe obesity in some people can lead to hypoventilation known as obesity-hypoventilation syndrome (OHS).

Excess weight around the neck, abdomen, and chest wall makes it harder for the body to breathe. This affects the brain’s breathing impulse and results in too much carbon dioxide in the blood, but not enough oxygen.

Brain Injury

Brain injuries can interfere with the brain’s ability to control basic functions like breathing. Impaired brainstem reflexes and consciousness after a brain injury can cause hypoventilation.

Sleep Apnea

People with obstructive sleep apnea (OSA) struggle to breathe as their airways become blocked or they collapse during the night, leading to hypoventilation.

For people with central sleep apnea (CSA), the airways are not blocked, but there is a pause in breathing caused by an abnormality in the shape of the chest wall, or their lungs become too stiff. This can lead to respiratory depression.

Chronic Lung Disease

Chronic lung disease such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis lead to blocked airways with severe obstruction and can cause hypoventilation.

Neurological Diseases

Underlying neurological diseases including conditions such as cerebrovascular accidents, trauma, head injuries, and abnormal growth of tissues can cause hypoventilation, known as central alveolar hypoventilation, which affects the central nervous system’s breathing function.

Elevated Ammonia Levels

Genetic problems or acquired liver disease such as cirrhosis disrupts the functioning of the liver and can elevate blood ammonia levels. This is also known as hyperammonemia, and it influences respiration and causes respiratory depression.

Medication and Drugs

Large doses of certain medications and substances can also cause respiratory depression or increase the risk of it. Some medications can lead to hypoventilation as a side effect.

Some substances interfere with brain function and depress the central nervous system which slows down the respiratory drive.

These medications and substances are:

• Sedatives
• Narcotics
• Opioids
• Alcohol
• Barbiturates
• Benzodiazepines

Respiratory Depression Treatment

The treatment of respiratory depression varies depending on the cause. The treatment options are mainly aimed at correcting the underlying disorder and improving ventilation.

Therapies and treatments commonly used to treat respiratory depressions are:

• Oxygen therapy, which delivers oxygen gas to support breathing
• Continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) machine to keep airways open while sleeping
• Surgery to correct chest deformity
• Weight loss including surgery and medication
• Inhaled medications to open airways and treat ongoing lung disease
• Mechanical ventilation
• Intravenous or oral fluid therapy
• If medication triggers hypoventilation, stopping the medication can often restore normal breathing.
• If an overdose of sedative drugs causes respiratory depression, then detoxification is necessary. Doctors will use medications to reverse the effect of the overdose.

Hypoventilation vs. Hyperventilation

Hypoventilation differs from hyperventilation. Hyperventilation is when you breathe too fast and exhale more than you take in.

This results in lower levels of carbon dioxide in the blood, which is the opposite of hypoventilation, during which your body cannot effectively remove carbon dioxide.

Prevention

Treatment is important if you have been diagnosed with respiratory depression. If left untreated, hypoventilation can lead to life-threatening health complications including death.

All causes of hypoventilation cannot be prevented, such as those caused by accidents or sudden disease. However, in some cases, there are ways to reduce the incidence of respiratory depression such as monitoring children taking prescription medication, monitoring those taking sedatives and narcotic medication, avoiding sedatives or narcotics, and avoiding excessive alcohol consumption.

Respiratory depression can interfere with your normal life. But with early detection and treatment, the condition can be managed to help prevent any further complications to your health.