View source for Arterial blood gas test

{{Short description|A test of blood taken from an artery that measures the amounts of certain dissolved gases}}
{{Infobox diagnostic
|  Name        = Arterial-blood gas test
|  Image       = Davenport fig 10.jpg
|  Width       = 300px
|  Caption     =
|  ICD10       =
|  ICD9        =
|  MeshID      = D001784
|  MedlinePlus = 003855
|  LOINC       = {{LOINC|24336-0}}
|  OtherCodes  =
}}

An '''arterial blood gas''' ('''ABG''') '''test''', or '''arterial blood gas analysis''' ('''ABGA''') measures the amounts of arterial gases, such as [[oxygen]] and [[carbon dioxide]]. An ABG test requires that a small volume of blood be drawn from the [[radial artery]] with a [[syringe]] and a thin [[hypodermic needle|needle]],<ref>{{cite web|url=http://www.patient.info/doctor/Arterial-Blood-Gases-Indications-and-Interpretation.htm |title=Arterial Blood Gases - Indications and Interpretation |author=Dr Colin Tidy |date=26 Jan 2015 |others=Reviewed by Dr Adrian Bonsall |website=Patient |access-date=2017-01-02}}</ref> but sometimes the [[femoral artery]] in the [[groin]] or another site is used. The blood can also be drawn from an [[arterial catheter]].

An ABG test measures the [[blood gas tension]] values of the [[Oxygen#Partial pressure|arterial partial pressure of oxygen]] (PaO2), and the [[PaCO2|arterial partial pressure of carbon dioxide]] (PaCO2), and the [[pH#Living systems|blood's pH]]. In addition, the arterial [[oxygen saturation (medicine)|oxygen saturation]] (SaO2) can be determined. Such information is vital when caring for patients with critical illnesses or respiratory disease. Therefore, the ABG test is one of the most common tests performed on patients in [[intensive-care unit]]s. In other [[therapy#Levels of care|levels of care]], [[pulse oximetry]] plus transcutaneous carbon-dioxide measurement is a less invasive, alternative method of obtaining similar information.{{cn|date=April 2022}}

An ABG test can indirectly measure the level of [[bicarbonate]] in the blood.  The bicarbonate level is calculated using the Henderson-Hasselbalch equation. Many blood-gas analyzers will also report concentrations of [[lactic acid|lactate]], [[hemoglobin]], several [[electrolyte]]s, [[oxyhemoglobin]], [[carboxyhemoglobin]], and [[methemoglobin]]. ABG testing is mainly used in [[pulmonology]] and critical-care medicine to determine [[gas exchange]] across the alveolar-capillary membrane.  ABG testing also has a variety of applications in other areas of medicine. Combinations of disorders can be complex and difficult to interpret, so calculators,<ref name="ABG interpreter">{{cite web| author=Baillie K| title=Arterial Blood Gas Interpreter| url=http://www.prognosis.org/arterial_blood_gas_calculator.php| publisher=prognosis.org| access-date=2007-07-05| archive-date=2013-03-12| archive-url=https://web.archive.org/web/20130312041312/http://www.prognosis.org/arterial_blood_gas_calculator.php| url-status=dead}} - Online arterial blood gas analysis</ref> [[nomograms]], and rules of thumb<ref>{{cite journal |last=Baillie |first=JK |title=Simple, easily memorised 'rules of thumb' for the rapid assessment of physiological compensation for acid-base disorders |journal=Thorax |volume=63 |issue=3 |pages=289–90 |year=2008 |pmid=18308967 |doi=10.1136/thx.2007.091223|doi-access=free }}</ref> are commonly used.

ABG [[Sampling (medicine)|samples]] originally were sent from the clinic to the [[medical laboratory]] for analysis. Newer equipment lets the analysis be done also as [[point-of-care testing]], depending on the equipment available in each clinic.

==Sampling and analysis==
[[File:Arterial blood gas device.jpg|thumb| Bench top analyzer ABL800 FLEX - [[Radiometer (company)|Radiometer Medical]]]]
[[File:Cobas221A.png|thumb|Modern, blood gas analyzer. This device is capable of reporting pH, [[PCO2|pCO<sub>2</sub>]], pO<sub>2</sub>, SatO<sub>2</sub>, Na<sup>+</sup>, K<sup>+</sup>, Cl<sup>−</sup>, Ca<sup>2+</sup>, Hemoglobin (total and derivatives: O<sub>2</sub>Hb, MetHb, COHb, HHb, CNHb, SHb ), Hematocrit, Total bilirubin, Glucose, Lactate and Urea. (Cobas b 221 - [[Roche Diagnostics]]).]]
Arterial blood for [[blood gas test|blood-gas analysis]] is usually drawn by a [[respiratory therapist]] and sometimes a [[phlebotomist]], a [[nurse]], a [[paramedic]] or a doctor.<ref>{{cite journal |vauthors=Aaron SD, Vandemheen KL, Naftel SA, Lewis MJ, Rodger MA |title=Topical tetracaine prior to arterial puncture: a randomized, placebo-controlled, clinical trial |journal=Respir. Med. |volume=97 |issue=11 |pages=1195–1199 |year=2003 |pmid=14635973 |doi=10.1016/S0954-6111(03)00226-9 |doi-access=free }}</ref> Blood is most commonly drawn from the [[radial artery]] because it is easily accessible, can be compressed to control bleeding, and has less risk for [[vascular occlusion]]. The selection of which radial artery to draw from is based on the outcome of an [[Allen's test]]. The [[brachial artery]] (or less often, the [[femoral artery]]) is also used, especially during emergency situations or with children. Blood can also be taken from an arterial catheter already placed in one of these arteries.<ref>{{Citation |last=Hager |first=Heather H. |title=Artery Cannulation |date=2024 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK482242/ |access-date=2024-06-28 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29489243 |last2=Burns |first2=Bracken}}</ref>

There are plastic and glass syringes used for blood gas samples.<ref name="nano.2006.1.2.223">{{cite journal |last1=Wiwanitkit |first1=Viroj |title=Glass syringes are better than plastic for preserving arterial blood gas for oxygen partial pressure determination: an explanation based on nanomaterial composition |journal=International Journal of Nanomedicine |date=January 2006 |volume=1 |issue=2 |pages=223–224 |doi=10.2147/nano.2006.1.2.223 |pmid=17722540 |pmc=2426785 |doi-access=free }}</ref>  Most syringes come pre-packaged and contain a small amount of [[heparin]], to prevent [[coagulation]]. Other syringes may need to be heparinised, by drawing up a small amount of liquid heparin and squirting it out again to remove air bubbles. Once the sample is obtained,<ref name="geekymedics/agbS">{{cite web |last1=Potter |first1=Lewis |title=How to take an Arterial Blood Gas (ABG) - OSCE Guide |url=https://geekymedics.com/arterial-blood-gas-sampling/ |website=Geeky Medics |access-date=24 February 2023 |date=7 January 2014}}</ref> care is taken to eliminate visible gas bubbles, as these bubbles can dissolve into the sample and cause inaccurate results.  The sealed syringe is taken to a '''blood gas analyzer'''.<ref name="Horn">{{cite journal |last1=Horn |first1=Klaus |last2=Gruber |first2=Rudolf |last3=Ugele |first3=Bernhard |last4=Küster |first4=Helmut |last5=Rolinski |first5=Boris |title=Total Bilirubin Measurement by Photometry on a Blood Gas Analyzer: Potential for Use in Neonatal Testing at the Point of Care |issue=10 |url=http://clinchem.aaccjnls.org/content/47/10/1845.long |journal=Clinical Chemistry |volume=47 |pages=1845–1847 |language=en |date=1 October 2001|doi=10.1093/clinchem/47.10.1845 |pmid=11568098 |doi-access=free }}</ref>  If a plastic blood gas syringe is used, the sample should be transported and kept at room temperature and analyzed within 30 min.  If prolonged time delays are expected (i.e., greater than 30 min) prior to analysis, the sample should be drawn in a glass syringe and immediately placed on ice.<ref>{{Cite book | isbn = 978-1-56238-545-3 | title = Procedures for the Collection of Arterial Blood Specimens; Approved Standard—Fourth Edition (Procedures for the Collection of Arterial Blood Specimens; Approved Standard—Fourth Edition ) | year = 2004 | publisher = Clinical and Laboratory Standards Institute | url = http://shop.clsi.org/general-lab-documents/GP43-A4.html | access-date = 2015-04-27 | archive-url = https://web.archive.org/web/20150511082620/http://shop.clsi.org/general-lab-documents/GP43-A4.html | archive-date = 2015-05-11 | url-status = dead }}</ref>  Standard blood tests can also be performed on arterial blood, such as measuring [[glucose]], [[lactic acid|lactate]], [[hemoglobins]], dyshemoglobins, [[bilirubin]] and  [[electrolyte]]s.{{cn|date=November 2021}}

Derived parameters include bicarbonate concentration, SaO2, and base excess.  Bicarbonate concentration is calculated from the measured pH and PCO2 using the Henderson-Hasselbalch equation.  SaO2 is derived from the measured PO2 and calculated based on the assumption that all measured hemoglobin is normal (oxy- or deoxy-) hemoglobin.<ref name=":0" />

===Calculations===
[[File:Cobas b 121 Measurement Chamber (detail).jpg|thumb|Detail of measurement chamber of a modern blood gas analyzer showing the measurement electrodes. (Cobas b 121 - Roche Diagnostics)]]
The machine used for analysis aspirates this blood from the syringe and measures the [[pH]] and the [[partial pressure]]s of oxygen and carbon dioxide. The bicarbonate concentration is also calculated. These results are usually available for interpretation within five minutes.{{cn|date=November 2021}}

Two methods have been used in medicine in the management of blood gases  of patients in [[hypothermia]]: pH-stat method and alpha-stat method. Recent studies suggest that the α-stat method is superior.{{cn|date=November 2021}}
* pH-stat: The pH and other ABG results are measured at the patient's actual temperature. The goal is to maintain a pH of 7.40 and the arterial carbon dioxide tension (paCO<sub>2</sub>) at 5.3 kPa (40 mmHg) at the actual patient temperature. It is necessary to add CO<sub>2</sub> to the oxygenator to accomplish this goal.
* α-stat (alpha-stat): The pH and other ABG results are measured at 37&nbsp;°C, despite the patient's actual temperature. The goal is to maintain the arterial carbon dioxide tension at 5.3 kPa (40mmHg) and the pH at 7.40 when measured at +37&nbsp;°C.

Both the pH-stat and alpha-stat strategies have theoretical disadvantages. α-stat method is the method of choice for optimal myocardial function. The pH-stat method may result in loss of autoregulation in the brain (coupling of the cerebral blood flow with the metabolic rate in the brain). By increasing the cerebral blood flow beyond the metabolic requirements, the pH-stat method may lead to cerebral microembolisation and intracranial hypertension.<ref name=":0">{{cite journal |author=Kofstad J |title=Blood Gases and Hypothermia: Some Theoretical and Practical Considerations |journal=Scand J Clin Lab Invest Suppl |year=1996 |volume=224 |pages=21–26 |pmid=8865418|doi=10.3109/00365519609088622 }}</ref>

===Guidelines===
# A 1 mmHg change in PaCO<sub>2</sub> above or below 40 mmHg results in 0.008 unit change in pH in the opposite direction.<ref>Stoelting: Basics of Anesthesia, 5th ed. p 321.</ref>
# The PaCO<sub>2</sub> will decrease by about 1 mmHg for every 1 mEq/L reduction in [{{chem|HCO|3|-}}] below 24 mEq/L
# A change in [{{chem|HCO|3|-}}] of 10 mEq/L will result in a change in pH of approximately 0.15 pH units in the same direction.
# Assess relation of pCO<sub>2</sub> with pH: If pCO<sub>2</sub> & pH are moving in opposite directions i.e., pCO<sub>2</sub> ↑ when pH is <7.4 or pCO<sub>2</sub> ↓ when pH > 7.4, it is a primary respiratory disorder. If pCO<sub>2</sub> & pH are moving in same direction i.e., pCO<sub>2</sub> ↑when pH is >7.4 or pCO<sub>2</sub> ↓ when pH < 7.4, it is a primary metabolic disorder.<ref name="EduLanche">{{cite web|url=https://edulanche.com/arterial-blood-gas-abg-4-steps|title=Arterial Blood Gas (ABG) In 4 Steps|website=www.edulanche.com/|publisher=EduLanche|access-date=2016-05-13}}</ref>

==Parameters and reference ranges==
{{also|Reference ranges for blood tests#Acid–base and blood gases}}
These are typical [[reference ranges]], although various analysers and laboratories may employ different ranges.
{| class="wikitable"
|-
! Analyte
! style="width: 8em;" | Range
! Interpretation
|-
| pH
| 7.34–7.44<ref name=southwest>[https://web.archive.org/web/19980424232639/http://pathcuric1.swmed.edu/PathDemo/NRRT.htm Normal Reference Range Table] from The University of Texas Southwestern Medical Center at Dallas. Used in Interactive Case Study Companion to Pathologic basis of disease.</ref>
| rowspan=2 | The [[pH]] or H<sup>+</sup> indicates if a person is acidemic (pH < 7.35; H<sup>+</sup> >45) or alkalemic (pH > 7.45; H<sup>+</sup> < 35).
|-
| H<sup>+</sup>
| 35–45 n[[Mole (unit)|mol]]/[[litre|L]] (n[[Concentration#Molality|M]])
|-
| {{anchor|oxygen}}Arterial [[oxygen partial pressure]] (P<sub>a</sub>O<sub>2</sub>)
| {{cvt|75-100|mmHg|kPa|sigfig=2|order=flip|disp=br}}<ref name=southwest/>
| A low PaO<sub>2</sub> indicates abnormal oxygenation of blood and a person is known as having hypoxemia. (Note that a low PaO<sub>2</sub> is not required for the person to have [[Hypoxia (medical)|hypoxia]] as in cases of [[Ischemia]], a lack of oxygen in tissues or organs as opposed to arterial blood.) At a P<sub>a</sub>O<sub>2</sub> of less than 60&nbsp;mm Hg, [[supplemental oxygen]] should be administered.
|-
| {{anchor|carbon dioxide}}Arterial [[carbon dioxide partial pressure]] (P<sub>a</sub>CO<sub>2</sub>)
| {{cvt|35-45|mmHg|kPa|sigfig=2|order=flip|disp=br}}<ref name=southwest/>
| The carbon dioxide partial pressure (Pa[[carbon dioxide|CO<sub>2</sub>]]) is an indicator of CO<sub>2</sub> production and elimination: for a constant metabolic rate, the Pa[[carbon dioxide|CO<sub>2</sub>]] is determined entirely by its elimination through [[Ventilation (physiology)|ventilation]].<ref name="O2_calc">{{cite web | vauthors=Baillie K, Simpson A | title=Altitude oxygen calculator | url=http://www.altitude.org/oxygen_levels.php | publisher=Apex (Altitude Physiology Expeditions) | access-date=2006-08-10 | archive-url=https://web.archive.org/web/20170611073650/http://www.altitude.org/oxygen_levels.php | archive-date=2017-06-11 | url-status=dead }} - Online interactive oxygen delivery calculator</ref> A high Pa[[carbon dioxide|CO<sub>2</sub>]] ([[respiratory acidosis]], alternatively [[hypercapnia]]) indicates underventilation (or, more rarely, a [[Malignant hyperthermia|hypermetabolic disorder]]), a low Pa[[carbon dioxide|CO<sub>2</sub>]] ([[respiratory alkalosis]], alternatively [[hypocapnia]]) hyper- or overventilation.
|-
| {{chem2|link=bicarbonate|HCO3–}}
| 22–26&nbsp;mEq/L
| The {{chem2|HCO3-}} ion indicates whether a [[metabolism|metabolic]] problem is present (such as [[ketoacidosis]]). A low {{chem2|HCO3-}} indicates [[metabolic acidosis]], a high {{chem2|HCO3-}} indicates [[metabolic alkalosis]]. As this value when given with blood gas results is often calculated by the analyzer, correlation should be checked with [[Carbon dioxide#Human physiology|total CO<sub>2</sub> levels]] as directly measured (see below).
|-
| [[Standard bicarbonate concentration|SBC<sub>e</sub>]]
| 21 to 27&nbsp;mmol/L
| the bicarbonate concentration in the blood at a [[carbon dioxide|CO<sub>2</sub>]] of 5.33 kPa, full [[oxygen saturation]] and 37 Celsius.<ref>{{Cite web|url=http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_03.htm|title=Acid Base Balance (page 3)|date=June 13, 2002|archive-url=https://web.archive.org/web/20020613020114/http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_03.htm|archive-date=2002-06-13}}</ref>
|-
| [[Base excess]]
| −2 to +2&nbsp;mmol/L
| The base excess is used for the assessment of the metabolic component of [[Acid-base imbalance|acid-base disorders]], and indicates whether the person has metabolic acidosis or metabolic alkalosis. Contrasted with the bicarbonate levels, the base excess is a calculated value intended to completely isolate the non-respiratory portion of the pH change.<ref>{{Cite web|url=http://www.rcpamanual.edu.au/sections/pathologytest.asp?s=33&i=410|title=RCPA Manual: Base Excess (arterial blood)}}</ref>
There are two calculations for base excess (extra cellular fluid - BE(ecf); blood - BE(b)).  The calculation used for the BE(ecf) = [<nowiki/>{{chem2|HCO3-}}]− 24.8 + 16.2 × (pH − 7.4). The calculation used for BE(b) = (1 − 0.014 × [[Mean corpuscular hemoglobin concentration|Hgb]]) × ([<nowiki/>{{chem2|HCO3-}}]− 24.8 + (1.43 × Hgb + 7.7) × (pH − 7.4).
 |-
 | ''total'' CO<sub>2</sub> (tCO<sub>2</sub> (P)<sub>c</sub>)
 | 23–30&nbsp;mmol/L<ref name=brookside>{{cite web |url=http://www.brooksidepress.org/Products/OperationalMedicine/DATA/operationalmed/Lab/ABG_ArterialBloodGas.htm |website=Brookside Associates |title=ABG (Arterial Blood Gas) |access-date=2017-01-02}}</ref><br />100–132&nbsp;mg/dL<ref name=co2-molar>Derived from molar values using molar mass of 44.010 g/mol</ref>
 | This is the total amount of CO<sub>2</sub>, and is the sum of {{chem2|HCO3-}} and [[PCO2|PCO<sub>2</sub>]] by the formula: tCO<sub>2</sub> = <nowiki>[</nowiki>{{chem2|HCO3-}}<nowiki>]</nowiki> + ''α''×PCO<sub>2</sub>, where α=0.226 mM/kPa, {{chem2|HCO3-}} is expressed in [[Concentration#Molality|millimolar concentration]] (mM) (mmol/L) and PCO<sub>2</sub> is expressed in kPa
 |-
 | O<sub>2</sub> Content (C<sub>a</sub>O<sub>2</sub>, C<sub>v</sub>O<sub>2</sub>, C<sub>c</sub>O<sub>2</sub>)
 | 94-100%<ref>{{cite web|url=https://www.mountsinai.org/health-library/tests/blood-gases | title = Blood Gases | access-date=2023-04-18}}</ref><br />(mL O<sub>2</sub>/dL blood)
 | This is the sum of oxygen dissolved in plasma and chemically bound to [[hemoglobin]] as determined by the calculation: C<sub>a</sub>O<sub>2</sub> = (PaO<sub>2</sub> × 0.003) + (SaO<sub>2</sub> × 1.34 × Hgb) where hemoglobin concentration is expressed in g/dL.<ref>{{Cite web|url=http://www.meddean.luc.edu/lumen/MedEd/MEDICINE/pulmonar/physio/pf10.htm|title=Hemoglobin and Oxygen Transport Charles L|website=www.meddean.luc.edu}}</ref>
|}

Contamination of the sample with room air will result in abnormally low carbon dioxide and possibly elevated oxygen levels, and a concurrent elevation in pH.  Delaying analysis (without chilling the sample) may result in inaccurately low oxygen and high carbon dioxide levels as a result of ongoing cellular respiration.

===pH===
{{Blood test sample values|align=right}}
The normal range for pH is 7.35–7.45. As the pH decreases (< 7.35), it implies [[acidosis]], while if the pH increases (> 7.45) it implies [[alkalosis]]. In the context of arterial blood gases, the most common occurrence will be that of [[respiratory acidosis]].  Carbon dioxide is dissolved in the blood as carbonic acid, a weak acid; however, in large concentrations, it can affect the pH drastically. Whenever there is poor pulmonary ventilation, the carbon dioxide levels in the blood are expected to rise. This leads to a rise of carbonic acid, leading to a decrease in pH. The first buffer of pH will be the plasma proteins, since these can accept some H<sup>+</sup> ions to try to maintain [[acid-base homeostasis]]. As carbon dioxide concentrations continue to increase (''Pa''CO<sub>2</sub> > 45 mmHg), a condition known as respiratory acidosis occurs. The body tries to maintain homeostasis by increasing the respiratory rate, a condition known as tachypnea. This allows much more carbon dioxide to escape the body through the lungs, thus increasing the pH by having less carbonic acid. If a person is in a critical setting and intubated, one must increase the number of breaths mechanically.{{citation needed|date=July 2020}}

[[Respiratory alkalosis]] (''Pa'' CO<sub>2</sub> < 35 mmHg) occurs when there is too little carbon dioxide in the blood. This may be due to hyperventilation or else excessive breaths given via a [[mechanical ventilator]] in a critical care setting. The action to be taken is to calm the person and try to reduce the number of breaths being taken to normalize the pH. The respiratory pathway tries to compensate for the change in pH in a matter of 2–4 hours. If this is not enough, the metabolic pathway takes place.{{cn|date=November 2021}}

Under normal conditions, the [[Henderson–Hasselbalch equation]] will give the blood pH

:<math chem> \ce{pH} = 6.1 + \log_{10}  \left ( \frac{[\ce{HCO3^-}]}{0.03 \times Pa\ce{CO2}} \right )</math>
where:
* 6.1 is the [[acid dissociation constant]] (p''K''<sub>a</sub>) of [[carbonic acid]] ({{chem2|H2CO3}}) at normal body temperature
* [{{chem2|HCO3-}}] is the concentration of [[bicarbonate]] in the blood in mEq/L
* ''Pa''CO<sub>2</sub> is the partial pressure of carbon dioxide in the arterial blood in mmHg

The kidney and the lung are two main organs responsible for the metabolic homeostasis of pH. Bicarbonate is a base that helps to accept excess hydrogen ions whenever there is acidaemia. However, this mechanism is slower than the respiratory pathway and may take from a few hours to 3 days to take effect. In acidaemia, the bicarbonate levels rise, so that they can neutralize the excess acid, while the contrary happens when there is alkalaemia. Thus when an arterial blood gas test reveals, for example, an elevated bicarbonate, the problem has been present for a couple of days, and metabolic compensation took place over a blood acidaemia problem.{{citation needed|date=July 2020}}

In general, it is much easier to correct acute pH derangement by adjusting respiration. Metabolic compensations take place at a much later stage. However, in a critical setting, a person with a normal pH, a high CO<sub>2</sub>, and a high bicarbonate means that, although there is a high carbon dioxide level, there is metabolic compensation. As a result, one must be careful as to not artificially adjust breaths to lower the carbon dioxide. In such case, lowering the carbon dioxide abruptly means that the bicarbonate will be in excess and will cause a metabolic alkalosis. In such a case, carbon dioxide levels should be slowly diminished.{{citation needed|date=July 2020}}

==Arterial versus venous blood==

Since the advent of [[pulse oximetry]] which measures oxygen saturation transcutaneously and is non-invasive, arterial blood is seldom used for the determination of oxygenation outside the ICU. Acid base status can be determined with [[venous blood]]  precluding the pain and inconvenience of arterial blood sampling in most cases. When an indwelling arterial line [[catheter]] is present, arterial blood is easy to obtain and still used. [[Venous blood]] is generally used otherwise, usually from a [[ Peripheral vascular system | peripheral ]] vein, such as a forearm vein. 
The values of pH and HCO3 of venous blood are close enough to arterial blood for direct comparison. The pCO2 of [[venous blood]] is less reliably compared to arterial blood but may be used in some cases. The PO2 level of venous blood is always significantly lower than arterial and should be reported, labeled and interpreted as venous PO2.
<ref>{{Cite journal |last=Byrne |first=Anthony L |last2=Bennett |first2=Michael |last3=Chatterji |first3=Robindro |last4=Symons |first4=Rebecca |last5=Pace |first5=Nathan L |last6=Thomas |first6=Paul S |date=January 2014 |title=Peripheral venous and arterial blood gas analysis in adults: are they comparable? A systematic review and meta‐analysis |url=https://onlinelibrary.wiley.com/doi/10.1111/resp.12225 |journal=Respirology |language=en |volume=19 |issue=2 |pages=168–175 |doi=10.1111/resp.12225 |issn=1323-7799|url-access=subscription }}</ref>

==See also==
* [[Anion gap]]
* [[Radial artery puncture]]
* [[Chemical equilibrium]]
* [[Hemoximetry]]
* [[Arteriovenous oxygen difference]]

==References==
{{Reflist}}

==External links==
{{Wikiversity|Arterial blood gasses}}
* [http://www.prognosis.org/arterial_blood_gas_calculator.php Online arterial blood gas calculator] {{Webarchive|url=https://web.archive.org/web/20130312041312/http://www.prognosis.org/arterial_blood_gas_calculator.php |date=2013-03-12 }}

{{Blood tests}}
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[[Category:Blood tests]]
[[Category:Diagnostic emergency medicine]]
[[Category:Diagnostic intensive care medicine]]
[[Category:Respiratory physiology]]
[[Category:Respiratory therapy]]