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Difference Between Hypoxia and Ischemia

What is Hypoxia?

Definition of Hypoxia:

Hypoxia is when the oxygen saturation of tissues falls below 90%. Hypoxia is thus also called oxygen desaturation. If the oxygen saturation falls below 88% then it is known as significant hypoxia.

Causes of Hypoxia:

Hypoxia can be caused by numerous medical conditions, for example: respiratory failure, or dyspnea (difficulty in breathing), pulmonary embolus, or pneumothorax (air trapped in the chest cavity outside the lungs). Hypoxia can also occur in patients with a history of cardiopulmonary disease who have a worsening of their condition, so for example someone in heart failure. In addition, hypoxia can be caused by environmental changes, for instance mountain climbers who can have high altitude sickness at extreme altitudes where atmospheric oxygen is very low. Another cause of hypoxia is carbon monoxide poisoning or smoke inhalation. Trauma such as a brain injury, can also cause hypoxia.

Testing and treatment of Hypoxia:

A pulse oximeter can be used to indicate the oxygen saturation of the blood. Chest X-rays and ECGs are also done to establish hypoxia and to help diagnose the cause of hypoxia. Once hypoxia is established patients can be given supplemental oxygen by face mask or nasal cannula. In cases of severe hypoventilation patients may need to be placed on a mechanical ventilator.

Consequences of Hypoxia:

If advanced enough, hypoxia can lead to cyanosis (bluish pallor to the skin), mental confusion, and rapid breathing. If not treated quickly, hypoxia can result in coma, seizures and brain death. The brain is very sensitive to lack of oxygen and cells die quickly once they reach a stage of having no oxygen (anoxia).


What is Ischemia?

Definition of Ischemia:

Ischemia is the interruption of blood flow to cells and tissues.

Causes of Ischemia:

Ischemia is caused by anything that blocks the blood supply. This blockage can be due to a clot or plaque in blood vessels or even an artery going into a spasm (e.g. coronary artery on the heart). Blood vessel spasms can be the result of high cholesterol and high blood pressure. Trauma in which tissues and vessels are damaged from an accident can also cause ischemia.

Testing and treatment of Ischemia:

Testing usually involves a physical exam first and then using X-rays or CT scans to confirm the location and cause of the ischemia. Clot busting drugs such as tissue plasminogen activator (TPA) can be used to treat an ischemic stroke if administered within the first few hours of the stroke beginning. The use of clot busting drugs is known as thrombolytic therapy. This therapy can also be used for clots in other blood vessels, including the coronary arteries of the heart. Angioplasty or coronary bypass surgery may be needed for people with blocked coronary arteries. Surgery is needed with intestinal ischemia to restore blood flow to the tissues and remove any dead tissue.

Consequences of Ischemia:

Ischemia cuts off the blood supply with the result that cells and tissues starve of nutrients and oxygen. This means that ischemia can cause hypoxia. Ischemia can thus lead to tissue death and organ failure. If intestines become ischemic (e.g. mesenteric ischemia) then gangrene, peritonitis and death can set in very rapidly. Ischemia can cause heart attacks if coronary vessels on the heart are blocked; and strokes if cerebral vessels in the brain are blocked. The blocked vessels cause infarction (tissue death).


Difference between Hypoxia and Ischemia

Definitions of Hypoxia and Ischemia

Hypoxia is when oxygen saturation is below 90% while ischemia is when blood flow is interrupted.

Causes of Hypoxia and Ischemia

Hypoxia is most often caused by respiratory failure or worsening of certain medical conditions, but can be caused by environment (high altitude sickness). Ischemia is most often caused by clots or spasms of blood vessels.

Substance that becomes limited

In hypoxia oxygen becomes limited while in ischemia oxygen and all nutrients usually carried by the blood supply become limited.

Testing for both Hypoxia and Ischemia

Hypoxia is first tested for using a pulse oximeter that measures oxygen saturation, then using X-rays and CT scans, while ischemia is tested for using a physical exam, X-rays and CT scans.

Treatment for both Hypoxia and Ischemia

Hypoxia is treated by provision of extra supplemental oxygen usually in the form of a nasal cannula or a face mask. If hypoxia becomes extreme, then a mechanical ventilator may be needed.

Ischemia is treated by medication such as clot-busting drugs, or else more invasive techniques such as angioplasty or surgery are used.

Part of body affected

Hypoxia usually affects the entire body (systemic), all organs and tissues, while ischemia is usually localized to one organ or tissue.

Complications from Hypoxia and Ischemia

Hypoxia can result in cyanosis (blue pallor) to the skin, mental confusion, seizures and can eventually cause brain death. Ischemia can result in organ failure, tissue death, gangrene, peritonitis and death.

Table comparing Hypoxia and Ischemia

Summary of Hypoxia Vs. Ischemia

  • Hypoxia is when oxygen saturation is below 90% while ischemia is when blood supply to tissue is interrupted.
  • Hypoxia can be caused by respiratory failure and many medical conditions, as well as environmental conditions.
  • Ischemia is caused by anything that blocks the blood supply, including the formation of clots, plaques, or blood vessels going into spasm.
  • During hypoxia only oxygen is in limited supply but in ischemia oxygen and all the nutrients carried by the blood is in limited supply.
  • Treatment of hypoxia involves supplemental oxygen or mechanical ventilators.
  • Treatment of ischemia involves medications such as clot busters, or surgery.
  • Hypoxia and ischemia are dangerous medical conditions that need to be treated quickly to avoid serious complications.

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References :

[0]Image credit: https://upload.wikimedia.org/wikipedia/commons/thumb/d/d7/MI_LBBB_%28CardioNetworks_ECGpedia%29.png/640px-MI_LBBB_%28CardioNetworks_ECGpedia%29.png

[1]Image credit: https://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Tumor_Hypoxia_and_Intracellular_pH.png/640px-Tumor_Hypoxia_and_Intracellular_pH.png

[2]Ansari, Parswa. ”Acute Mesenteric Ischemia”. Merckmanuals. Merck & Co., 2017, https://www.merckmanuals.com/en-pr/professional/gastrointestinal-disorders/acute-abdomen-and-surgical-gastroenterology/acute-mesenteric-ischemia

[3]Eachempati, Soumitra  R. “Oxygen desaturation”. Merckmanuals. Merck & Co., 2017, https://www.merckmanuals.com/en-pr/professional/critical-care-medicine/approach-to-the-critically-ill-patient/oxygen-desaturation

[4]WebMD. “What is ischemia?” WebMD, WebMD, 2018, https://www.webmd.com/heart-disease/what-is-ischemia#1

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