Hypoxemia is a health condition that occurs when there is a fall in the normal oxygen level in the blood. You may experience symptoms such as breathlessness, rapid breathing, bluish discolouration, chest pain, and confusion. It is usually a sign of some untreated heart or lung condition, but can also arise due to some external factors. 

What is hypoxemia?

Hypoxemia refers to low levels of oxygen in the blood. It commonly presents as shortness of breath or some breathing-related problem. Hypoxemia can occur due to a variety of reasons. The main aetiology is an underlying heart, lung, or blood disease, or some environmental factor. During inhalation, oxygen in the air enters the lungs, and the blood vessels (arteries) take up the oxygen, supplying it to the tissues. The normal level of oxygen in blood (oxygen saturation) is 94% to 99%.¹ Hypoxemia occurs when this level falls below 90%. Treatment mainly involves oxygen therapy or supplemental oxygen, and management of underlying medical conditions.

Causes of hypoxemia

Hypoxemia can occur due to any factor which influences the rate of air entering the lungs or the transfer of air from the lungs to blood. The main causes of hypoxemia are underlying respiratory, cardiac, hematologic, or neurologic diseases. Hypoxemia can also occur due to some environmental factors.

Respiratory causes

One of the main aetiologies of hypoxemia is hypoventilation, where there is too much carbon dioxide trapped in your blood and not enough oxygen can enter the blood. These include conditions like stroke, sleep apnea (gasping or choking in sleep), respiratory muscle weakness, and certain drugs like opioids and benzodiazepines that cause respiratory depression.

Hypoxemia also occurs due to underlying respiratory conditions which block the airflow from the lungs, like pneumonia, chronic obstructive pulmonary disease, asthma, and acute respiratory distress syndrome.² Conditions like pulmonary embolism and chronic bronchitis also cause hypoxemia, as there is a mismatch between ventilation (airflow in lungs) and perfusion (blood flow in lung vessels) leading to less oxygen in the blood exiting the lungs.

Cardiac causes

Factors that compromise the blood vessel integrity cause hypoxemia. These include cardiac conditions like congestive heart failure and cardiogenic shock, where your heart is unable to pump blood well, and congenital heart disease, where blood does not get oxygenated as it bypasses the lungs.³

Hematologic causes

These include blood disorders like anaemia, carbon monoxide poisoning, and methemoglobinemia.⁴ The number of healthy red blood cells which carry oxygen is reduced in anaemia, while in other disorders, the oxygen-carrying capacity of haemoglobin is reduced, all of which lead to hypoxemia. 

Neurologic causes

Stroke and certain CNS depressants like opioid pain relievers can lead to hypoxemia. This is because depression of CNS causes dysregulation of lung and heart functions.² 

Environmental causes

Oxygen saturation level decreases at high altitudes.⁵ Therefore traveling at high altitudes can predispose to hypoxemia. Air pollutants like ozone, nitrogen and sulfur oxides, and inhalation of smoke also cause hypoxemia by impairing lung structure and function.¹³

Symptoms of hypoxemia

Symptoms vary based on cause and severity. Hypoxemia usually occurs as a difficulty in breathing that becomes serious when accompanied by cough, rapid heartbeat, weakness at high altitudes, and sleep apnea.⁶ Symptoms in acute hypoxemia are similar to those seen in respiratory distress, mainly breathlessness and increased respiratory rate.

Initial symptoms

Hypoxemia initially presents as shortness of breath (dyspnea), rapid breathing (tachypnea), cyanosis (bluish discolouration), or headache.³ It may manifest as difficulty breathing or feeling breathless when doing some physical exercise. Due to low oxygen levels, the skin appears blue in colour. 

Advanced symptoms

Symptoms may further advance to confusion, increase or decrease in heart rate (bradycardia or tachycardia), hypotension, and loss of consciousness. Increased heart rate and shallow or rapid breathing are the body's response to a decrease in oxygen levels. The patient may reach a state of mental confusion and disorientation. 

Other symptoms

Hypoxemia also causes chest pain, coughing, and weakness when there is an underlying heart, lung, or blood disease.² Delayed growth, development, and sleep apnea are seen in children with chronic hypoxemia because the symptoms are noticed much later causing serious damage to the organs.⁷

Diagnosis

Diagnosis of hypoxemia is important to determine the proper management approach to be taken. The following methods may be included in the assessment.

• History taking to know the aetiology including any underlying heart, lung, or blood disease or environmental factors responsible for hypoxemia
• Physical examination includes observation and assessment of the signs and symptoms, risk factors, and general health of the patient. The healthcare provider measures the vital signs and checks skin colour for signs of cyanosis and respiratory distress. The examination also involves the auscultation of the lungs and heart
• Arterial blood gas(ABG) analysis is the gold standard for measuring oxygen saturation levels. It measures the haemoglobin oxygen saturation level in arteries⁸
• Pulse oximetry measures the ratio of oxygenated to deoxygenated haemoglobin in arterial blood. It is a standard diagnostic method used in hypoxemia¹ 
• Complete blood count (CBC) 
• Imaging studies reveal respiratory abnormalities and help to identify underlying medical conditions if any. These include chest X-rays, CT scans of the chest, and ventilation-perfusion scans which measure lung ventilation and blood perfusion
• Lung Function Tests (LFT) assess the function and capacity of the lungs and help to identify the respiratory condition responsible for hypoxemia⁹
• Polysomnography is used to diagnose sleep apnea in suspected patients¹⁰

Treatment of hypoxemia

Hypoxemia can be a once-in-a-lifetime occurrence or one might require medical care for a long time. Treatment of hypoxemia mainly involves oxygen therapy or supplemental oxygen. Any underlying health condition should be properly managed to maintain a safe oxygen level. 

Oxygen therapy or supplemental oxygen is the use of medicinal oxygen to treat hypoxemia. It is different from normal oxygen, it is tested for purity and content while manufacturing for the safety of the patient and is given to the patient in an inhalational form. Oxygen therapy is very effective in the treatment of hypoxemia. Medicinal oxygen is delivered to the patient through nasal prongs, nasal catheters, face masks, or mechanical ventilation. While it relieves symptoms of hypoxemia, there are some associated disadvantages to oxygen therapy including headaches, nosebleeds, and fatigue.¹⁴

In severe cases of hypoxemia, where there is a serious infection or anaemia, treatment involves the use of hyperbaric oxygen.¹¹ It consists of an oxygen therapy chamber with increased air pressure, which enables breathing much more air than normally possible. It also promotes the production of oxygen by tissues even after the treatment is stopped. There are associated risk factors with the treatment like possible injury to the middle ear, claustrophobia, and sinusitis.¹⁵

It is important to keep track of oxygen levels in patients with hypoxemia. This can reduce mortality due to pneumonia or other underlying illnesses. Oxygen levels can be easily monitored through the use of a pulse oximeter.

Any underlying cause should be properly managed to prevent the occurrence of hypoxemia. Appropriate medications should be taken. These include antibiotics for respiratory infections, anticoagulants for pulmonary embolism, and bronchodilators for asthma and COPD. 

Self-care is important to prevent the recurrence of hypoxemia. Quit smoking as smoking worsens any medical condition that causes hypoxemia.³ If you have difficulty breathing at high altitudes, take precautionary measures while travelling.

Supportive care includes fluid management, mechanical ventilation in respiratory failure, and management of complications if any.

Prevention

Regular exercise can increase strength and improve lung capacity. Quitting smoking is important as smoking worsens underlying medical conditions. Always keep track of oxygen levels using a pulse oximeter. Use supplemental oxygen when needed. If possible, avoid travelling. Regular vaccinations can prevent respiratory infections and associated hypoxemia. 

FAQs

When should I see a doctor?

The symptoms of hypoxemia are mainly due to some underlying heart or lung conditions. Consult a healthcare provider as early as possible when you begin to experience any of the symptoms like breathlessness, coughing, chest pain, increased heart rate, or confusion. 

How can I prevent hypoxemia?

Use supplemental oxygen when needed. Use a pulse oximeter at home and check oxygen saturation level at regular intervals. Regular exercise increases lung capacity and strength. Avoid smoking as it worsens the condition. Treat any underlying heart or lung disease to prevent further occurrence of hypoxemia. 

What are the potential complications of hypoxemia?

If untreated, hypoxemia can impair brain function and cause a state of mental confusion, irritability, and restlessness. You may have symptoms of respiratory distress like rapid and laboured breathing along with increased heart rate. A prolonged state of hypoxemia can lead to tissue damage.¹²

Summary

Hypoxemia is a condition that occurs when there is a low level of oxygen in the blood. People with underlying lung or heart conditions are at greater risk, though factors like smoking and high altitudes can also predispose them to hypoxemia. Patients should check oxygen levels at intervals possibly using a pulse oximeter. Treatment of hypoxemia involves oxygen therapy or supplemental oxygen and hyperbaric oxygen therapy in extreme cases. Any underlying medical condition should be treated to prevent the occurrence of hypoxemia. Consult a doctor immediately when symptoms like sleep apnea, mental confusion, and chest pain are noticed. Exercising, avoiding smoking, and taking necessary precautions can relieve the symptoms and improve the quality of life.