Generalized hypoxia is a medical condition in which the tissues of the body are deprived of the necessary levels of oxygen due to an insufficient supply of oxygen, which may be due to the composition or pressure of the breathing gas, decreased lung ventilation, or respiratory disease, any of which may cause a lower than normal oxygen content in the arterial blood, and consequently a reduced supply of oxygen to all tissues perfused by the arterial blood. This usage is in contradistinction to

localized hypoxia Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue (biology), tissue level. Hypoxia may be classified as either ''Generalized hypoxia, generalized'', affecting the whole body, or '' ...

, in which only an associated group of tissues, usually with a common blood supply, are affected, usually due to an insufficient or reduced blood supply to those tissues. Genralized hypoxia is also used as a synonym for hypoxic hypoxia This is not to be confused with

hypoxemia Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the bod ...

, which refers to low levels of oxygen in the blood, although the two conditions often occur simultaneously, since a decrease in blood oxygen typically corresponds to a decrease in oxygen in the surrounding tissue. However, hypoxia may be present without hypoxemia, and vice versa, as in the case of

infarction Infarction is tissue death ( necrosis) due to inadequate blood supply to the affected area. It may be caused by artery blockages, rupture, mechanical compression, or vasoconstriction. The resulting lesion is referred to as an infarct (from th ...

. Several other classes of medical hypoxia exist.

Causes

Hypoxia can result from various causes which can be categorised as: anemic hypoxia, cellular hypoxia, generalised, or hypoxic hypoxia, pulmonary hypoxia, stagnant hypoxia, increased oxygen consumption due to a hypermetabolic state, or any combination of these. The three fundamental causes of hypoxia at the tissue level are low oxygen content in the blood (hypoxemia), low perfusion of the tissue, and inability of the tissue to extraxt and use the oxygen in the blood. Generalised, or hypoxic hypoxia may be caused by: *

Hypoventilation Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapni ...

– failure of the respiratory pump due to any cause (fatigue, barbiturate poisoning,

pneumothorax A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve i ...

, etc.) *Low-inspired oxygen partial pressure, which may be caused by breathing air at low ambient pressures due to altitude, by breathing hypoxic

breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed ...

at an unsuitable depth, by breathing inadequately re-oxygenated recycled breathing gas from a

rebreather A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen i ...

life support system A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...

, or anesthetic machine, or

hypoxia of ascent Freediving blackout, breath-hold blackout or apnea blackout is a class of hypoxic blackout, a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold ( freedive or dynamic apnea) dive, when the swimmer does not necessarily ...

freediving Freediving, free-diving, free diving, breath-hold diving, or skin diving is a form of underwater diving that relies on breath-holding until resurfacing rather than the use of breathing apparatus such as scuba gear. Besides the limits of breath- ...

. *

Airway obstruction Airway obstruction is a blockage of respiration in the airway that hinders the free flow of air. It can be broadly classified into being either in the upper airway (UPA) or lower airway (LOA). Airway obstruction is a life-threatening condition ...

choking Choking, also known as foreign body airway obstruction (FBAO), is a phenomenon that occurs when breathing is impeded by a blockage inside of the respiratory tract. An obstruction that prevents oxygen from entering the lungs results in oxygen dep ...

drowning Drowning is a type of suffocation induced by the submersion of the mouth and nose in a liquid. Most instances of fatal drowning occur alone or in situations where others present are either unaware of the victim's situation or unable to offer as ...

. *Abnormal

pulmonary The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...

function **

Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

(COPD) **Neuromuscular diseases or interstitial lung disease *Malformed vascular system such as an anomalous coronary artery

Altitude effects

When breathing the ambient air at high altitudes (above 3048 metres/10,000 feet), the human body experiences

altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...

and hypoxemia due to a low

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

of oxygen, decreasing the carriage of oxygen by hemoglobin. * Above 3000 metres (10,000 feet) - ambient pressure 69.7kPa, about 14.6kPa partial pressure of oxygen – enough hypoxic stimulation to cause increased ventilation * Above 3700 metres (12,000 feet) - 64.4kPa, about 13.52kPa P_O₂ – first irritability appears * Above 5500 metres (18,000 feet) - 50.6kPa, about 10.6kPa P_O₂ – severe symptoms * Above 7600 metres (25,000 feet) - ambient pressure 37.6kPa absolute, 7.9kPa partial pressure of oxygen – consciousness lost While breathing pure oxygen at ambient pressure, from an oxygen cylinder or other source, the maximum altitude a human can tolerate while their body is at atmospheric pressure is 13,700 metres (45,000 feet), , where atmospheric pressure is about 14.7kPa. This is a function of the partial pressure of oxygen in the breathing gas, and is also dependent on level of exertion which affects the oxygen requirements of metabolism, cardiovascular fitness, and acclimatization to altitude which affects the available hemoglobin and can vary significantly between individuals.

Signs and symptoms

Cyanosis Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...

Headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

* Decreased reaction time, disorientation, and uncoordinated movement. * Impaired judgment, confusion, memory loss and cognitive problems. *

Euphoria Euphoria ( ) is the experience (or affect) of pleasure or excitement and intense feelings of well-being and happiness. Certain natural rewards and social activities, such as aerobic exercise, laughter, listening to or making music and d ...

or dissociation *

Visual impairment Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

* Lightheaded or dizzy sensation,

vertigo Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...

Fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

, Drowsiness or tiredness *

Shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...

Palpitations Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. Symptoms include a rap ...

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

Nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...

and vomiting * Initially raised

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure ...

followed by lowered blood pressure as the condition progresses. * 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. * Tingling in fingers and toes * Numbness

Treatment

Generalized hypoxia is an effect of a lack of oxygen, and in many cases of a one-time event can be reversed simply by eliminating the lack. Where there is no underlying pathology, provision of oxygen at normobaric partial pressure (about 0.21 bar) is usually sufficient to reverse minor symptoms. Where there is a pathology causing the hypoxia, treatment of the underlying pathology is often effective. *

Oxygen therapy Oxygen therapy, also known as supplemental oxygen, is the use of oxygen as medical treatment. Acute indications for therapy include hypoxemia (low blood oxygen levels), carbon monoxide toxicity and cluster headache. It may also be prophylactic ...

and hyperbaric medicine can improve saturation of oxygen in the blood which will stop hypoxia if it is caused by hypoxemia, i.e. low levels of oxygen in the blood. *

Artificial ventilation Artificial ventilation (also called artificial respiration) is a means of assisting or stimulating respiration, a metabolic process referring to the overall exchange of gases in the body by pulmonary ventilation, external respiration, and intern ...

may be required where the person is unable to breathe sufficiently unaided. *

Continuous positive airway pressure Continuous positive airway pressure (CPAP) is a form of positive airway pressure (PAP) ventilation in which a constant level of pressure greater than atmospheric pressure is continuously applied to the upper respiratory tract of a person. The ...

(CPAP) mask may be used to treat

sleep apnea Sleep apnea, also spelled sleep apnoea, is a sleep disorder in which pauses in breathing or periods of shallow breathing during sleep occur more often than normal. Each pause can last for a few seconds to a few minutes and they happen many tim ...

. * Bilevel positive airway pressure (BIPAP) may be used to treat

chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

(COPD), and some kinds of sleep apnea. * Supplemental oxygen by mask or nasal tubes may be provided to treat chronic hypoxia. *Inhaled

steroids A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and ...

that can dilate the airways may be used to treat

asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...

or other lung disease. * Diuretics may be used to reduce

edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

in and around the lungs.

Other types of medical hypoxia

*Hypoxemic hypoxia is a low oxygen tension in the arterial blood, due to the inability of the lungs to sufficiently oxygenate the blood. Causes include hypoventilation, impaired alveolar diffusion, and pulmonary shunting. This definition overlaps considerably with that of hypoxic hypoxia. * Pulmonary hypoxia occurs when the lungs receive adequately oxygenated gas which does not reach the blood in sufficient quantities. It may be caused by: **

Ventilation perfusion mismatch Ventilation perfusion mismatch or V/Q defects are defects in the total lung ventilation/perfusion ratio (V/Q ratio). It is a condition in which one or more areas of the lung receive oxygen but no blood flow, or they receive blood flow but no oxy ...

, ** Pulmonary shunt *

Circulatory hypoxia The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, t ...

ischemic hypoxia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...

or stagnant hypoxia may be caused by abnormally low blood flow to the lungs, which can occur during

shock Shock may refer to: Common uses Collective noun *Shock, a historic commercial term for a group of 60, see English numerals#Special names * Stook, or shock of grain, stacked sheaves Healthcare * Shock (circulatory), circulatory medical emerge ...

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...

, severe

congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...

, or

abdominal compartment syndrome Abdominal compartment syndrome (ACS) occurs when the abdomen becomes subject to increased pressure reaching past the point of intra-abdominal hypertension (IAH). ACS is present when intra-abdominal pressure rises and is sustained at > 20 mmHg and ...

, 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. *

Anemic Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

hypoxia or hypemic hypoxia is the lack of capacity of the blood to carry the normal level of oxygen. It can be caused by anemia or: **

Carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...

Methemoglobinemia Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications ...

* Cellular hypoxia occurs when the cells are unable to extract sufficient oxygen from normally oxygenated hemoglobin. *

Histotoxic hypoxia Histotoxic hypoxia (also called histoxic hypoxia) is the inability of cells to take up or use oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues. Histotoxic hypoxia results from tissue poisonin ...

(Dysoxia) occurs when oxygen is transported to the tissues but they cannot use it effectively because the cells cannot extract oxygen from the blood. This is seen in cyanide poisoning.

References

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Causes

Altitude effects

Signs and symptoms

Treatment

Other types of medical hypoxia

See also

References