Editing Generalized hypoxia

{{Short description|Medical condition of oxygen deprivation}}
{{redirect|Hypoxic hypoxia|other uses of the term "hypoxia"|Hypoxia (disambiguation)}}
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| synonym         = Arterial hypoxia{{cn|date=December 2022}}
| image           = Bulletin CS-632 Hypoxia warning system p3 2012 002 5253 w6634419k.tiff

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| caption         = [[Oxygen sensor]] for [[hypoxia warning system]], 1963

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| specialty       = pulmonology
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'''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 distinct from [[localized hypoxia]], 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. '''Generalized hypoxia''' is also used as a synonym for '''hypoxic hypoxia'''<ref name="Mandal" /><ref name="Manninen and Unger 2016" /> This is not to be confused with [[hypoxemia]], which refers to low levels of [[Oxygen saturation (medicine)|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]]. Several other classes of [[Hypoxia (medical)|medical hypoxia]] exist.<ref name="Manninen and Unger 2016" /><ref name="Mandal" />

== 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.<ref name="Manninen and Unger 2016" /> 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 extract and use the oxygen in the blood.<ref name="Bhutta et al 2022" /> Generalised, or hypoxic hypoxia may be caused by:
*[[Hypoventilation]]<ref name="Manninen and Unger 2016" />  – failure of the respiratory pump due to any cause (fatigue, [[Barbiturate overdose|barbiturate poisoning]], [[pneumothorax]], etc.)
*Low-inspired oxygen partial pressure, which may be caused by breathing air at low ambient pressures due to altitude,<ref name="Manninen and Unger 2016" /><ref name="Bhutta et al 2022" /> by breathing hypoxic [[Breathing gas#Classification by oxygen fraction|breathing gas]] at an unsuitable depth, by breathing inadequately re-oxygenated recycled breathing gas from a [[rebreather]],<ref name="Elliott 1997" /> [[life support system]], or [[anesthetic machine]], or [[hypoxia of ascent]] in [[freediving]].<ref name="Lindholm 2006" />
*[[Airway obstruction]], [[choking]],<ref name="Manninen and Unger 2016" /> [[drowning]].
*Abnormal [[pulmonary]] function{{cn|date=November 2022}}<!-- plausible but no ref -->
**[[Chronic obstructive pulmonary disease]] (COPD)<ref name="Cleveland" />
**Neuromuscular diseases or [[interstitial lung disease]]<!-- plausible but no ref -->
*Malformed vascular system such as an [[Anomalous left coronary artery from the pulmonary artery|anomalous coronary artery]]{{cn|date=November 2022}}

===Altitude effects===
{{see also|Altitude sickness}}
When breathing the ambient air at high altitudes (above 3048 metres/10,000 feet), the human body experiences [[altitude sickness]] and hypoxemia due to a low [[partial pressure]] 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<sub>O<sub>2</sub></sub> – first irritability appears
* Above 5500 metres (18,000 feet) - 50.6kPa, about 10.6kPa P<sub>O<sub>2</sub></sub> – severe symptoms
* Above 7600 metres (25,000 feet) - ambient pressure 37.6kPa absolute, 7.9kPa partial pressure of oxygen – consciousness lost{{cn|date=November 2022}}

While breathing pure oxygen at ambient pressure, from an oxygen cylinder or other source, the maximum altitude a human can tolerate{{clarify|Is this stable for long term exposure, or only tolerable for limited periods? At what level of exertion?|date=November 2022}} while their body is at atmospheric pressure is 13,700 metres (45,000 feet),{{cn|date=October 2022}} , where atmospheric pressure is about 14.7kPa.<!-- plausible PPO2 to remain conscious for long periods--> 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. {{clarify|This altitude is possibly better expressed as a value for ambient pressure|date=November 2022}}

==Signs and symptoms==

* [[Cyanosis]]<ref name="Mandal b" />
* [[Headache]]<ref name="Mandal b" /><ref name="FAA" />
* Decreased reaction time,<ref name="Rochester" /> disorientation, and uncoordinated movement.<ref name="Mandal b" />
* Impaired judgment, confusion, memory loss and cognitive problems.<ref name="Mandal b" /><ref name="FAA" />
* [[Euphoria]] or dissociation<ref name="Mandal b" />
* [[Visual impairment]]<ref name="FAA" />
* Lightheaded or dizzy sensation, [[vertigo]]<ref name="Mandal b" />
* [[Fatigue]], [[Drowsiness]] or tiredness<ref name="Mandal b" />
* [[Shortness of breath]]<ref name="Mandal b" />
* [[Palpitations]] may occur in the initial phases. Later, the heart rate may reduce significantly degree. In severe cases, abnormal heart rhythms may develop.
* [[Nausea]] and vomiting<ref name="Mandal b" />
* Initially raised [[blood pressure]] followed by lowered blood pressure as the condition progresses.<ref name="Mandal b" />
* 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.<ref name="Mandal b" />
* Tingling in fingers and toes<ref name="FAA" />
* Numbness<ref name="FAA" />

==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.<ref name="Cleveland" /> 
*[[Oxygen therapy]] 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.<ref name="Choudhury 2018" /> 
*[[Artificial ventilation]] may be required where the person is unable to breathe sufficiently unaided.<ref name="Cleveland" />
*[[Continuous positive airway pressure]] (CPAP) mask may be used to treat [[sleep apnea]].<ref name="Cleveland" />
*[[Bilevel positive airway pressure]] (BIPAP) may be used to treat [[chronic obstructive pulmonary disease]] (COPD), and some kinds of sleep apnea.<ref name="Cleveland" />
*[[Supplemental oxygen]] by mask or nasal tubes may be provided to treat chronic hypoxia.<ref name="Cleveland" />
*Inhaled [[steroids]] that can dilate the airways may be used to treat [[asthma]] or other lung disease.<ref name="Cleveland" />
*[[Diuretics]] may be used to reduce [[edema]] in and around the lungs.<ref name="Cleveland" />

==Other types of medical hypoxia==
<!--ordered by progression of oxygen into the body-->
*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.<ref name="Bhutta et al 2022" /> 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:<ref name="Manninen and Unger 2016" />
**[[Ventilation perfusion mismatch]],
**[[Pulmonary shunt]]
*[[Circulatory hypoxia]],<ref name="Bhutta et al 2022" /> [[ischemic hypoxia]] or [[stagnant hypoxia]] may be caused by abnormally low blood flow to the lungs, which can occur during [[shock (circulatory)|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.<ref name="Manninen and Unger 2016" /><ref name="Cleveland" />
*[[Anemia|Anemic]] hypoxia or hypemic hypoxia is the lack of capacity of the blood to carry the normal level of oxygen.<ref name="Bhutta et al 2022" /> It can be caused by anemia or:<ref name="Manninen and Unger 2016" />
**[[Carbon monoxide poisoning]]
**[[Methemoglobinemia]]
*[[Cellular hypoxia]] occurs when the cells are unable to extract sufficient oxygen from normally oxygenated hemoglobin.<ref name="Manninen and Unger 2016" />
*[[Histotoxic hypoxia]] (Dysoxia)<ref name="Bhutta et al 2022" /> 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.<ref name="Mandal" />

{{expand section|date=November 2022}}

== See also ==
* {{annotated link|Hypoxemia}}
* {{annotated link|Hypoxia (medical)}}
* {{annotated link|Pulmonology}}
* {{annotated link|Oxygen}}

== References ==
{{Reflist|refs=

<ref name="Bhutta et al 2022" >{{cite web |last1=Bhutta |first1=B.S. |last2=Alghoula |first2=F. |last3=Berim |first3=I. |title=Hypoxia. |date=9 August 2022 |publisher= StatPearls [Internet] |location=Treasure Island, FL |pmid=29493941 |url=https://www.ncbi.nlm.nih.gov/books/NBK482316/ }}</ref>

<ref name="Choudhury 2018" >{{cite journal|last=Choudhury |first=R. |title=Hypoxia and hyperbaric oxygen therapy: a review. |journal=Int J Gen Med |date=20 November 2018 |volume=11 |pages=431–442 |doi=10.2147/IJGM.S172460 |pmid=30538529 |pmc=6251354 |doi-access=free }}</ref>

<ref name="Cleveland" >{{cite web|url=https://my.clevelandclinic.org/health/diseases/23063-hypoxia |title=Hypoxia: Management and Treatment |website=my.clevelandclinic.org |access-date=27 November 2022 }}</ref>

<ref name="Elliott 1997" >{{cite journal |last=Elliott |first=David
 |title=Some limitations of semi-closed rebreathers
 |journal=South Pacific Underwater Medicine Society Journal |volume=27 |issue=1 |year=1997 |issn=0813-1988 |oclc=16986801
 |url=http://archive.rubicon-foundation.org/6039 |archive-url=https://web.archive.org/web/20090808203812/http://archive.rubicon-foundation.org/6039 |url-status=usurped |archive-date=August 8, 2009 |access-date=2008-06-14}}</ref>

<ref name="FAA" >{{cite book |title=Pilot's Handbook of Aeronautical Knowledge: FAA Manual H-8083-25 |publisher=Flight Standards Service. Federal Aviation Administration, U.S. Dept. of Transportation |location=Washington, DC |date=2001 |isbn=1-56027-540-5 |chapter=17: Aeromedical Factors |url=https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak }}</ref>

<ref name="Lindholm 2006" >{{cite conference|url=https://www.diversalertnetwork.org/files/UHMS_DAN_2006_Breath-hold_Workshop_Proceedings.pdf|last=Lindholm |first=Peter |title=Physiological mechanisms involved in the risk of loss of consciousness during breath-hold diving |editor1-last=Lindholm |editor1-first=P. |editor2-last=Pollock |editor2-first=N. W. |editor3-last=Lundgren |editor3-first=C. E. G.|year=2006|work=Breath-hold diving. Proceedings of the Undersea and Hyperbaric Medical Society/Divers Alert Network 2006 June 20–21 Workshop.|publisher=Divers Alert Network |page=26 |access-date=24 January 2017|location=Durham, NC |isbn=978-1-930536-36-4 }}</ref>

<ref name="Mandal" >{{cite web |url=https://www.news-medical.net/health/Hypoxia-Types.aspx |title=Hypoxia Types |first=Ananya |last=Mandal |website=www.news-medical.net |date=17 February 2010 |access-date=27 November 2022 }}</ref>

<ref name="Mandal b" >{{cite web |url=https://www.news-medical.net/health/Hypoxia-Symptoms.aspx |title=Hypoxia Symptoms |first=Ananya |last=Mandal |website=www.news-medical.net |date=17 February 2010 |access-date=27 November 2022 }}</ref>

<ref name="Manninen and Unger 2016" > {{cite book|url=https://www.sciencedirect.com/topics/medicine-and-dentistry/hypoxic-hypoxia |chapter=Hypoxia |first1=Pirjo H. |last1=Manninen |first2=Zoe M. |last2=Unger |title=Complications in Neuroanesthesia |date=2016|isbn=978-0-12-804075-1 |editor-first=Hemanshu |editor-last=Prabhakar |publisher=Academic Press (Elsevier) |doi=10.1016/C2015-0-00811-5 }}</ref>

<ref name="Rochester" >{{cite web | url=https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=1&ContentID=562 | title=A Quick Look at Reflexes - Health Encyclopedia - University of Rochester Medical Center }}</ref> 

}}

[[Category:Respiratory diseases]]