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Hypoxia (medicine)

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level.[1] Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body.[2] Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise.

Hypoxia

Hypoxiation, lack of oxygen, low blood oxygen (technically hypoxemia), oxygen starvation

Pulmonology, toxicology

Cyanosis, numbness or pins and needles feeling of the extremities

Gangrene, necrosis

Diabetes, coronary artery disease, heart attack, stroke, embolism, thrombosis, deep-vein thrombosis, tobacco smoking

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Hypoxia differs from hypoxemia and anoxemia, in that hypoxia refers to a state in which oxygen present in a tissue or the whole body is insufficient, whereas hypoxemia and anoxemia refer specifically to states that have low or no oxygen in the blood.[3] Hypoxia in which there is complete absence of oxygen supply is referred to as anoxia.


Hypoxia can be due to external causes, when the breathing gas is hypoxic, or internal causes, such as reduced effectiveness of gas transfer in the lungs, reduced capacity of the blood to carry oxygen, compromised general or local perfusion, or inability of the affected tissues to extract oxygen from, or metabolically process, an adequate supply of oxygen from an adequately oxygenated blood supply.


Generalized hypoxia occurs in healthy people when they ascend to high altitude, where it causes altitude sickness leading to potentially fatal complications: high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE).[4] Hypoxia also occurs in healthy individuals when breathing inappropriate mixtures of gases with a low oxygen content, e.g., while diving underwater, especially when using malfunctioning closed-circuit rebreather systems that control the amount of oxygen in the supplied air. Mild, non-damaging intermittent hypoxia is used intentionally during altitude training to develop an athletic performance adaptation at both the systemic and cellular level.[5]


Hypoxia is a common complication of preterm birth in newborn infants. Because the lungs develop late in pregnancy, premature infants frequently possess underdeveloped lungs. To improve blood oxygenation, infants at risk of hypoxia may be placed inside incubators that provide warmth, humidity, and supplemental oxygen. More serious cases are treated with continuous positive airway pressure (CPAP).

Hypoxic hypoxia

Hypoventilation

Hypoxemic hypoxia is a lack of oxygen caused by low oxygen tension in the arterial blood, due to the inability of the lungs to sufficiently oxygenate the blood. Causes include hypoventilation, impaired alveolar , and pulmonary shunting.[8] This definition overlaps considerably with that of hypoxic hypoxia.

diffusion

Pulmonary hypoxia

[7]

Circulatory hypoxia, also known as ischemic hypoxia or stagnant hypoxia, is caused by abnormally low blood flow to the lungs, which can occur during shock, cardiac arrest, severe congestive heart failure, or abdominal compartment syndrome, where the main dysfunction is in the cardiovascular system, causing a major reduction in perfusion. Arterial gas is adequately oygenated in the lungs, and the tissues are able to accept the oxygen available, but the flow rate to the tissues is insufficient. Venous oxygenation is particularly low.[7][11]

[8]

[8]

(Dysoxia)[8] or Cellular hypoxia occurs when the cells of the affected tissues are unable to use oxygen provided by normally oxygenated hemoglobin.[7] Examples include cyanide poisoning which inhibits cytochrome c oxidase, an enzyme required for cellular respiration in mitochondria. Methanol poisoning has a similar effect, as the metabolism of methanol produces formic acid which inhibits mitochondrial cytochrome oxidase.[7][13]

Histotoxic hypoxia

[52]

Cyanosis

[52][53][54]

Headache

Decreased reaction time, disorientation, and uncoordinated movement.[52]

[55]

Impaired judgment, confusion, memory loss and cognitive problems.[53]

[52]

or dissociation[52]

Euphoria

[53] A moderate level of hypoxia can cause a generalized partial loss of color vision affecting both red-green and blue-yellow discrimination at an altitude of 12,000 feet (3,700 m).[56]

Visual impairment

Lightheaded or dizzy sensation, [52]

vertigo

drowsiness, or tiredness[52]

Fatigue

[52]

Shortness of breath

may occur in the initial phases. Later, the heart rate may reduce significantly degree. In severe cases, abnormal heart rhythms may develop.

Palpitations

and vomiting[52]

Nausea

Initially raised followed by lowered blood pressure as the condition progresses.[52]

blood pressure

Severe hypoxia can cause loss of consciousness, seizures or convulsions, coma and eventually death. Breathing rate may slow down and become shallow and the pupils may not respond to light.

[52]

Tingling in fingers and toes

[53]

Numbness

[53]

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Diagnosis[edit]

Physical examination and history[edit]

Hypoxia can present as acute or chronic.


Acute presentation may include dyspnea (shortness of breath) and tachypnea (rapid, often shallow, breathing). Severity of symptom presentation is commonly an indication of severity of hypoxia. Tachycardia (rapid pulse) may develop to compensate for low arterial oxygen tension. Stridor may be heard in upper airway obstruction, and cyanosis may indicate severe hypoxia. Neurological symptoms and organ function deterioration occur when the oxygen delivery is severely compromised. In moderate hypoxia, restlessness, headache and confusion may occur, with coma and eventual death possible in severe cases.[8]


In chronic presentation, dyspnea following exertion is most commonly mentioned. Symptoms of the underlying condition that caused the hypoxia may be apparent, and can help with differential diagnosis. A productive cough and fever may be present with lung infection, and leg edema may suggest heart failure.[8]


Lung auscultation can provide useful information.[8]

Tests[edit]

An arterial blood gas test (ABG) may be done, which usually includes measurements of oxygen content, hemoglobin, oxygen saturation (how much of the hemoglobin is carrying oxygen), arterial partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), blood pH level, and bicarbonate (HCO3)[91]

 – Severely deficient supply of oxygen

Asphyxia

 – Oxygen shortage of the brain

Cerebral hypoxia

 – Intentional restriction of oxygen to the brain for sexual arousal

Erotic asphyxiation

also known as diffusion hypoxia – Changes of oxygen partial pressure in the pulmonary alveoli caused by a soluble anesthetic gas

Fink effect

 – Loss of consciousness due to sustained high acceleration

G-LOC

 – Medical condition in which cells cannot use oxygen

Histotoxic hypoxia

 – Exposure of tissues to abnormally high concentrations of oxygen.

Hyperoxia

 – Physical training method

Hypoventilation training

 – Abnormally low level of oxygen in the blood

Hypoxemia

 – Response of fish to environmental hypoxia

Hypoxia in fish

 – Protein that responds to low oxygen

Hypoxia-inducible factor

 – Medical condition of oxygen deprivation, a result of insufficient oxygen available to the lungs

Hypoxic hypoxia

 – Biological reaction to increased altitude

Hypoxic ventilatory response

 – Device for providing breathing air with reduced oxygen content a device intended for hypoxia acclimatisation in a controlled manner

Hypoxicator

 – Technique aimed at improving human performance by adaptation to reduced oxygen.

Intermittent hypoxic training

 – Medical condition when the fetus is deprived of sufficient oxygen, when a fetus is deprived of an adequate supply of oxygen

Intrauterine hypoxia

 – Lung gas and blood oxygen concentration sufficient to support consciousness only at depth

Latent hypoxia

increased cytosolic ratio of free NADH to NAD+ in cells

Pseudohypoxia

 – Method used in evaluation of respiratory function of the nasal cavity

Rhinomanometry

 – Disorder involving pauses in breathing during sleep

Sleep apnea

 – Duration of effective performance in a hypoxic environment

Time of useful consciousness

 – Situation where tumor cells have been deprived of oxygen

Tumor hypoxia

Vasculogenic Mimicry

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