Hypoxemia is a lack of oxygen in the arterial blood, which can reduce the amount of oxygen reaching the body’s tissues and lead to symptoms such as rapid heartbeat, dizziness, and mental confusion.

This condition is most often caused by lung diseases like asthma, COPD, pneumonia, or pulmonary embolism, which can make it harder to breathe in air and prevent oxygen from reaching the bloodstream.

Hypoxemia is a medical emergency. If symptoms occur, it’s important to go to the emergency room right away to determine the cause and start appropriate treatment.

nurse placing pulse-ox on older woman's finger

Common symptoms

The main symptoms of hypoxemia include:

Rapid heartbeat;
Shortness of breath or difficulty breathing;
Cough, with or without mucus;
Wheezing while breathing;
Headache;
Mental confusion or fainting.

A person with hypoxemia may also develop cyanosis, which is when the skin, lips, or nails turn bluish or purplish. It’s essential to seek emergency medical care immediately if symptoms of hypoxemia appear, so that treatment can begin as soon as possible and complications can be avoided.

Hypoxemia vs hypoxia

Both hypoxemia and hypoxia are related to low oxygen levels. In hypoxemia, oxygen levels are low in the arterial blood. In hypoxia, there is a decrease in oxygen in a specific tissue, such as the heart or brain.

Confirming a diagnosis

A general practitioner or pulmonologist can diagnose hypoxemia in a hospital setting using tests like pulse oximetry or arterial blood gas (ABG). These exams measure the amount of oxygen in the body.

The doctor may also order lung function tests and imaging exams, such as a chest X-ray, to help determine the cause of hypoxemia.

Hypoxemia levels

Hypoxemia is defined by low oxygen saturation (SaO₂) and low partial pressure of arterial oxygen (PaO₂), as shown below:

Severity	SaO₂	PaO₂
Mild	90–94%	Around 80 mmHg
Moderate	85–89%	Around 60 mmHg
Severe	Below 85%	Below 50 mmHg

PaO₂ represents the partial pressure of oxygen dissolved in the blood, measured by arterial blood gas, while SaO₂ refers to the percentage of hemoglobin saturated with oxygen, measured by an oximeter.

Under normal conditions at sea level, PaO₂ is between 80 and 100 mmHg, and SaO₂ is above 95%. In older adults, slightly lower levels may still be considered normal.

Possible causes

The main causes of hypoxemia include:

Obstructive sleep apnea;
Asthma, bronchitis, or COPD;
Pneumonia or pneumothorax;
Emphysema or pulmonary edema;
Pulmonary fibrosis or pulmonary embolism;
Acute respiratory distress syndrome (ARDS);
Pulmonary hypertension.

These conditions can make it difficult to inhale or prevent oxygen from reaching the pulmonary capillaries, resulting in hypoxemia. Other causes may include anemia, congestive heart failure, and congenital heart defects.

Different types

1. Ventilation-perfusion (V/Q) mismatch

This is one of the most common causes of hypoxemia. It occurs when there is an imbalance between the amount of air reaching the lungs (ventilation) and the amount of blood flowing through the lungs (perfusion). The lungs may receive enough air, but blood flow may be insufficient to capture oxygen, or blood flow may be normal, but air intake is limited.

Common causes of this type of hypoxemia include COPD, pulmonary embolism, asthma, and pulmonary edema.

2. Hypoventilation

Hypoventilation-related hypoxemia occurs when the alveoli take in less oxygen, which reduces blood oxygen levels and raises carbon dioxide (CO₂) levels, a condition known as hypercapnia.

This type of hypoxemia can be caused by obstructive sleep apnea, COPD, use of sedative or opioid medications, alcohol consumption, or head trauma.

3. Right-to-left shunt

A right-to-left shunt happens when blood passes from the right side of the heart to the left without being oxygenated in the lungs. As a result, less oxygenated blood reaches the tissues.

This type of hypoxemia is mainly caused by congenital heart defects or abnormal connections between blood vessels in the lungs.

4. Diffusion limitation

This type of hypoxemia occurs when oxygen cannot effectively move (diffuse) from the alveoli into the blood vessels of the lungs, resulting in reduced oxygen in arterial blood.

Common causes include pulmonary fibrosis, emphysema, or interstitial lung disease.

5. Low ambient oxygen

At high altitudes, oxygen levels in the air are lower, which can cause hypoxemia since there is less oxygen available to breathe.

Treatment options

Treatment for hypoxemia should be managed by a general practitioner, pulmonologist, or cardiologist. The main goals are to raise oxygen levels in the blood and treat the underlying cause.

1. Oxygen therapy

Oxygen therapy helps increase blood oxygen levels using a nasal cannula, mask, or catheter. It can be administered in the hospital during emergencies or at home for several hours a day, or continuously in chronic cases such as COPD, pulmonary fibrosis, or sleep apnea.

There are different types of oxygen therapy that the doctor may recommend depending on the person’s specific needs.

2. Noninvasive ventilation

Noninvasive ventilation is used to deliver oxygen to the lungs through a mask or helmet and is often prescribed for conditions such as obstructive sleep apnea or pulmonary edema.

Common devices include CPAP and BiPAP machines.

3. Mechanical ventilation

Mechanical ventilation is performed in hospitals using specialized machines to assist breathing. It is typically used in severe cases, such as airway obstruction or acute respiratory failure caused by ARDS or pneumonia.

4. Medications for hypoxemia

Medications are used to treat the underlying condition that causes low blood oxygen levels.

For cases of asthma or COPD, inhaled bronchodilators or inhaled corticosteroids may be prescribed to open the airways and improve lung oxygenation.

For treatment of bacterial pneumonia, antibiotics are commonly used, while diuretics may be indicated in cases of pulmonary edema.

All medications for hypoxemia should be taken only under medical supervision.

5. Respiratory physiotherapy

Respiratory physiotherapy may be recommended to help clear the airways and improve oxygen flow to the tissues. It can be performed in hospitals, physical therapy clinics, or at home.

This type of therapy is generally used for conditions like asthma, bronchitis, COPD, pulmonary edema, emphysema, or pulmonary fibrosis.

6. Surgery

Surgery may be indicated for severe lung conditions or congenital heart malformations. It can involve removing damaged lung tissue or correcting a heart defect to improve blood oxygenation.

Possible complications

If hypoxemia is not treated quickly and properly, it can reduce oxygen delivery to the tissues and cause brain damage, respiratory acidosis, or cardiac arrhythmias.

Other possible complications include cardiorespiratory arrest or coma.

It is crucial to seek medical care immediately for any symptoms of hypoxemia in order to begin treatment as quickly as possible and prevent potentially life-threatening complications.

Hypoxemia: Symptoms, Causes, Types & Treatment