Arterial Blood Gases: Difference between revisions

m (Categorisation)
(Added Technology Category)
 
(24 intermediate revisions by 5 users not shown)
Line 6: Line 6:
== Arterial Blood Gases  ==
== Arterial Blood Gases  ==


[[Image:ABG.jpg|thumb|right|241x241px|Blood Gas Analyser]]Arterial blood gases (ABG's) is a blood test which is used to give an indication of ventilation, gas exchange and acid-base status and is taken from an arterial blood supply<ref name="Hough" />. It should be noted that it is not to be confused with venous blood gases which are used when arterial supply is not available or unreliable due to disease. The line in is usually inserted in the radial artery located at the wrist but is also&nbsp;sometimes used in the femoral artery in the groin<ref name="Hough">Hough A. Physiotherapy in Respiratory Care. An evidence based-approach to respiratory and cardiac managemenmt. 3rd ed. Cheltenham: Nelson Thomas Ltd. 2001</ref>.&nbsp;This is important to consider when moving and handling a patient as it is easy to catch a line on an object or clothing and care needs to be taken.  
[[Image:ABG.jpg|thumb|right|241x241px|Blood Gas Analyser]]Arterial blood gases (ABG's) is a blood test that is used to give an indication of ventilation, gas exchange, and acid-base status and is taken from an arterial blood supply<ref name="Hough">Hough A. Physiotherapy in Respiratory Care. An evidence-based approach to respiratory and cardiac management. 3rd ed. Cheltenham: Nelson Thomas Ltd. 2001</ref>. The arterial blood gas test is one of the most common tests performed on patients in intensive care units. At other levels of care, [[Pulse Oximeter|pulse oximetry]] plus transcutaneous carbon dioxide measurement is a less invasive alternative method of obtaining similar information.<ref name=":0">Scope health Arterial Gasometry: What is it? Why is it Necessary? Procedure, Compensation, Metabolic Disorders and Results Available: https://scopeheal.com/arterial-blood-gas/ (accessed 9.5.2022)</ref>


<br>It can be argued that&nbsp;one of the most important clinical uses of ABG analysis is to assess if&nbsp;a patient is in Type 1 ([[Hypoxaemia]]) or Type 2 [[Respiratory Failure|respiratory failure]] and it is important that as physiotherapists we able to quickly and correctly interpret&nbsp;this. &nbsp;
To perform this test, blood is collected from a specific artery, usually the wrist's radial artery. This blood sample allows an accurate determination of the amount of oxygen that passes from the lungs to the blood. This test is the one most commonly performed to diagnose cases of [[Respiratory Failure|respiratory failure]]<ref name=":4">Well being pole Gasometry Available:https://wellbeingpole.com/gasometry/ (accessed 9.5.2022)</ref>.<br>Arterial blood gas test results can show if:


ABGs give us information about the activity in both the respiratory system and the 'metabolic' system. If one system is disturbed, the other will try to restore the balance or compensate. Both systems work together in an attempt to keep pH in the normal range. They are commonly used to; identify acid/base disorders, identify gas exchange problems, monitor the effects of oxygen therapy<ref name=":0">Woodrow P. Arterial blood gas analysis. Nursing Standard (through 2013). 2004 Feb 4;18(21):45.</ref>.
* Lungs are getting enough oxygen.
* Lungs are removing enough carbon dioxide.
* Kidneys are working properly.<ref name=":0" />


== ABG Definitions  ==
== Uses ==
* PH: The measure of hydrogen ions in the blood
ABGs are very useful for detecting conditions that cause respiratory failure. Including: [[Respiratory Failure|Lung Failure]]; [[Acute Respiratory Distress Syndrome (ARDS)|Acute respiratory distress syndrome (ARDS)]]; [[Sepsis]]; Diabetic [[ketoacidosis]] (DKA); [[Cystic Fibrosis|Cystic fibrosis]]; [[Pneumonia]]; [[Emphysema]]; [[Shock|Hypovolemic shock]]; [[Heart Failure|Acute heart failure]]; [[Cardiac Arrest|Cardiac arrest]]; [[Chronic Kidney Disease|Kidney Failure]]; [[Sepsis|Septic Shock]]; [[Trauma-Informed Care|Trauma]]; Chronic vomiting; [[Diabetes|Uncontrolled diabetes]]; [[Asthma]] ; [[Chronic Obstructive Pulmonary Disease Rehabilitation Class|Chronic Obstructive Pulmonary Disease (COPD)]]; Hemorrhage; Drug Overdose; Metabolic Disease; Chemical Poisoning; To check if lung condition treatments are working.<ref name=":1" />
* PaC02: Partial pressure of Carbon Dioxide in the blood, the acidic element of the balance
[[File:Respiratory failure.jpg|center|frameless|599x599px]]
** Acidic component
<ref name=":4" />
** Indicator of respiratory function
** Changes rapidly to compensate
* Pa02: Partial pressure of oxygen in the blood.
* HCO3-: Bicarbonate ion concentration in the blood, the basic element of the balance
** Basic/Alkaline component
** Indicator of metabolic function
** Compensation is slower
* BE: Base Excess = quantity of strong acid or base that is required to restore pH to normal<ref>Buck RP, Rondinini S, Covington AK, Baucke FG, Brett CM, Camoes MF, Milton MJ, Mussini T, Naumann R, Pratt KW, Spitzer P. Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002). Pure and applied chemistry. 2002 Jan 1;74(11):2169-200.</ref>


== Normative Values<ref name=":0" /> <ref name="Kenyon">Kenyon K, Kenyon J. The Physiotherapist's Pocketbook. Essential Facts at your Fingertips. 2nd ed. London: Churchill Livingstone, Elsevier. 2009.</ref>  ==
== Measurements ==
The key components of an ABG are:


{| width="600" cellspacing="1" cellpadding="1" border="1" align="left" summary="The normal values and reference ranges expected from a 'normal' ABG"
# pH - This measures the balance of acids and bases in the blood.
|+
# Partial pressure of oxygen (PaO2) - This measures the pressure of oxygen dissolved in the blood.
|-
# Partial pressure of carbon dioxide (PaCO2) - This measures the amount of carbon dioxide in the blood and how well carbon dioxide can move out of the lungs.
! scope="col" | Arterial Blood Analysis
# Bicarbonate (HCO3) - This is calculated using the measured values of pH and PaCO2 to determine the amount of the primary compound made from carbon dioxide (CO2.)
! scope="col" | Reference Ranges
# Oxygen saturation (O2 Sat) - This measures how much hemoglobin in the blood is carrying oxygen.
! scope="col" | Venous Blood analysis
# Oxygen content (O2CT) - This measures the amount of oxygen in the blood.
! scope="col" | Reference Ranges
# Hemoglobin - This measures the amount of hemoglobin in the blood.
|-
| pH  
| 7.35 - 7.45
| pH
| 7.31&nbsp; - 7.41
|-
| PaO<sub>2</sub>
|
10.7 - 13.3 kPa


| PO<sub>2</sub>
== Normative Values ==
|
According to the National Institute of Health, typical normal values are:
5.0 - 5.6 kPa


|-
* pH: 7.35-7.45
| PaCO<sub>2</sub>
* Partial pressure of oxygen (PaO2): 75 to 100 mmHg
| 4.7 - 6.0 kPa
* Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg
| PCO<sub>2</sub>
* Bicarbonate (HCO3): 22-26 mEq/L
| 5.6 - 6.7 kPa
* Oxygen saturation (O2 Sat): 94-100%<ref name=":1">Nurse org. ABG test Available:https://nurse.org/articles/arterial-blood-gas-test/ (accessed 9.5.2022)</ref>
|-
|
Bicarbonate
 
(HCO<sub>3</sub><sup>-</sup>)
 
| 22 - 26 mmol/L
|
|
|-
| Base Excess
| -2 to +2
|
|
|}
 
== Acid-Base Balance ==
* '''pH'''
** Reflects acid-base balance and responds to metabolic and respiratory changes. Body cells and chemical reactions are acutely sensitive to the pH  of their environment.
*** Lower pH = Acidic
*** Higher pH= Alkaline
* '''Regulation'''
** Acid-base balance is disturbed if; CO2 removal by the lungs is abnormal, production of acid from tissues is abnormal, and removal of acid is abnormal.<ref name=":0" />
* '''Deviation from normal pH is resisted by 3 mechanisms;'''
# <u>The Buffering system</u>
#* Acts like a chemical sponge and neutralises acids and bases. It is an acid-base homeostatic mechanism involving the balance of carbonic acid (H2CO3), bicarbonate ion (HCO3), and carbon dioxide (CO2) that attempts to maintain the bloods pH. It also plays a role in the duodenum among other tissues, to support proper metabolic function. <ref>Krieg, Brian J.; Taghavi, Seyed Mohammad; Amidon, Gordon L.; Amidon, Gregory E. (2014-11-01). [http://onlinelibrary.wiley.com/doi/10.1002/jps.24108/abstract "In Vivo Predictive Dissolution: Transport Analysis of the CO2, Bicarbonate In Vivo Buffer System"]. ''Journal of Pharmaceutical Sciences''. '''103''' (11): 3473–3490. </ref>
# <u>The Lungs</u>
#* The respiratory component that reacts if the buffering system is not enough and the lungs help my regulating CO2.
# <u>The Kidneys</u>
#* The Metabolic component and is the last mechanism to work and begins to eliminate acid.
 
== Respiratory Acidosis ==
Respiratory acidosis is caused by inadequate alveolar ventilation leading to the retention of carbon dioxide and an increase in free hydrogen ions. It occurs when decreased ventilation (hypoventilation) increases the concentration of carbon dioxide in the blood and results in a decrease in the blood's pH. <ref>Yee AH, Rabinstein AA (February 2010). "Neurologic presentations of acid-base imbalance, electrolyte abnormalities, and endocrine emergencies". ''Neurol Clin''. '''28''' (1): 1–16</ref>
* Decreased pH
* Increased PaCO2
* '''Causes'''
** Hypoventilation
** Acute Lunge Injury
*** Upper airway obstruction
*** Lower airway obstruction
*** Impaired alveolar filling
** Chronic Lung Disease
** Neuromuscular disorders
** Obesity
** CNS Depression
* '''Symptoms'''
** Headache
** Anxiety
** Blurred vision
** Restlessness
** Drowsiness
** Tremors
** Delirium
** Coma<ref name=":0" />
 
== Metabolic Acidosis ==
Metabolic acidosis involves excess fixed acid production, i.e. lactate or loss of HCO<sub>3</sub>.It occurs when the body produces excess quantities of acid or the kidneys are not removing sufficient acid from the body. If left untreated, metabolic acidosis can lead to acidemia. Acidemia occurs when the bloods pH is low (<7.35) due to an increased production of hydrogen ions by the body or its inability to form bicarbonate (HCO3) in the kidneys. 
* Decreased pH
* Decreased HCO3
* '''Causes'''
*** Renal disease
*** Liver disease
*** Lactic acidosis
*** Prolonged lack of oxygen
*** Shock
*** Posioning
*** Medications
*** Dehydration
*** Diarrhoea
* '''Symptoms'''
** Rapid breathing
** Confusion
** Lethargy
** Cold, clammy skin
** Tachycardia and arrhythmia<ref name=":0" />
 
== Respiratory Alkalosis ==
Respiratory alkalosis is caused by over excretion of carbon dioxide (hyperventilation) resulting in more CO2 than normal being exhaled. Thus, leading to a reduction in free hydrogen ions and an alkalotic state.<ref name=":1">[https://www.nlm.nih.gov/medlineplus/ency/article/000111.htm "Respiratory alkalosis: MedlinePlus Medical Encyclopedia"]. ''www.nlm.nih.gov''. </ref>
* Increased pH
* Decreased PaCO2
* '''Causes'''
** Hyperventilation
** Acute asthma
** CNS disturbance
** High altitude
** Pneumonia
** Drugs
** Fever
** Sepsis
* '''Symptoms'''
** Diziness
** Peripheral paraesthesia
** Confusion
** Dry mouth
** Bloating<ref name=":1" />
 
== Metabolic Alkalosis ==
Metabolic alkalosis occurs as a result of decreased hydrogen ion concentration which leads to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations.<ref name=":2">Singh AK. Metabolic alkalosis. In: Mushlin SB, Greene HL II, eds. ''Decision Making in Medicine: An Algorithmic Approach''. 3rd ed. Philadelphia, PA: Mosby Elsevier; 2010. 374-5.</ref>  
* Increased pH
* Increased HCO3
* '''Causes'''
** Excess alkali administration
** Hyperkalaemia
** IV penicillin
** Re-feeding syndrome
** Massive blood transfusion
** Diuretic therapy
** Vomitting
* '''Symptoms'''
** Weakness
** Myalgia
** Polyuria
** Cardiac arrhythmias
** Hypoventilation<ref name=":0" /><ref name=":2" />
 
== Respiratory Failure ==
Respiratory failure is characterized by a reduction in function of the lungs due to lung disease or a skeletal or neuromuscular disorder.<ref name=":3">Respiratory Failure. (2017, October 5). ''Physiopedia,'' . Retrieved 10:12, March 27, 2018 from https://www.physio-pedia.com/index.php?title=Respiratory_Failure&oldid=179534.</ref> It occurs when gas exchange at the lungs is significantly impaired to cause a drop in blood levels of oxygen (hypoxemia) occurring with or without an increase in carbon dioxide levels(hypercapnia). It's usually defined in terms of the gas tensions in the arterial blood, respiratory rate and evidence of increased work of breathing<ref>Tulaimat A, Patel A, Wisniewski M, Gueret R. The validity and reliability of the clinical assessment of increased work of breathing in acutely ill patients. August 2016. Journal of crit care 34:111-5</ref>. Respiratory failure can be acute, chronic or acute on chronic.<ref>Pandor A, Thokala P, Goodacre S, Poku E, Stevens JW, Ren S, Cantrell A, Perkins GD, Ward M, Penn-Ashman J. Pre-hospital invasive ventilation for acute respiratory failure: a systematic review and cost effectiveness evaluation. Health Technol Assess 2015 June 19(42): 1-102.</ref> It's a major cause of mortality and morbidity and mortality rates increase with age and presence of co-morbidities. [[Respiratory Failure|Respiratory failure]] is not a disease but a consequence of the problems that interfere with the ability to breathe.<ref name=":3" />
 
It is the inability to perform adequately the fundamental functions of respiration:
# To deliver oxygen to the blood
# To eliminate carbon dioxide from it


== Interpretation of ABGs ==
== Interpretation of ABGs ==
Line 181: Line 45:
#* Decreased = Acidosis
#* Decreased = Acidosis
# <u>Look at the PaCO2</u>
# <u>Look at the PaCO2</u>
## Increased = Respiratory Acidosis
#* Increased = Respiratory Acidosis
## Decreased = Respiratory Alkalosis
#* Decreased = Respiratory Alkalosis
# <u>Look at the HCO3</u>
# <u>Look at the HCO3</u>
#* Increased = Metabolic Alkalosis
#* Increased = Metabolic Alkalosis
#* Decreased = Metabolic Acidosis
#* Decreased = Metabolic Acidosis
# <u>Look at the O2</u>
# <u>Identify if there is a compensation</u>
#* Full compensation if the pH is within the normal range
#* Partial compensation if either the PaCO2 or HCO3 value is wavering to compensate for the primary acid-base disturbance; but, the pH is still not within the normal physiologic range.
# <u>Look at the O2</u><br>
'''The results&nbsp; should always be read and compared&nbsp; in reference to the patient's previous ABG (if available)&nbsp; as you will then be able to assess a trend and make a more accurate assessment on whether you should treat or if your treatment has been successful or not.'''


=== Compensation ===
== Primary Acid-base disturbances ==
The bodies pH is closely controlled and this is done through various mechanisms to maintain it at a constant value. It is important to note that the body will never overcompensate as the drivers for compensation cease as the pH returns to normal. In practice, compensation for an acidosis will not cause an alkalosis or visa versa.
They are:


If pH is NORMAL despite an abnormal PCO2 and HCO3 it must be compensated.
# '''Uncompensated Respiratory Acidosis:''' This occurs when there is an increase in the PaCO2 level without a resultant alteration (increase) of  the HCO3 value. Thus, there will an acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
# Look at the pH - Which side of 7.4 is it?
# '''Partially compensated Respiratory Acidosis:''' This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; but, the pH is still not within the normal range. Thus, there will still be acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
# Look for the cause
# '''Fully compensated Respiratory Acidosis:''' This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs) with metabolic alkalosis.
#* PCO2 goes in the opposite direction to pH
# '''Uncompensated Respiratory Alkalosis:''' This occurs when there is  a decrease in the PaCO2 level without a resultant alteration (decrease) of  the HCO3 value. Thus, there will be an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
#* HCO3 travels in the same direction as pH
# '''Partially compensated Respiratory Alkalosis:''' This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; but, the pH is still not within the normal range. Thus, there will be an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
# The other value is the compensator
# '''Fully compensated Respiratory Alkalosis:''' This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood) with metabolic acidosis.
Finding compensated, partially compensated, or uncompensated ABG problems:
# '''Uncompensated Metabolic Acidosis:''' This occurs when there is  an decrease in the HCO3 level without a resultant alteration (decrease) of  the PaCO2 value. Thus, there will an acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
* When PaCO2 is high, but pH is normal instead of being acidic, and if HCO3 levels are also increased, then it means that the compensatory mechanism has retained more HCO3 to maintain the pH.
# '''Partially compensated Metabolic Acidosis:''' This occurs when there is a decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; but, the pH is still not within the normal range. Thus, there will still be acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
* When PaCO2 and HCO3 values are high but pH is acidic, then it indicates partial compensation. It means that the compensatory mechanism tried but failed to bring the pH to normal.
# '''Fully compensated Metabolic Acidosis:''' This occurs when there is a decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate) with respiratory alkalosis.
* If pH is abnormal and if the value of either PaCO2 or HCO3 is abnormal, it indicates that the system is uncompensated. This is probably because of either respiratory or metabolic acidosis.<ref>https://www.chegg.com/homework-help/definitions/uncompensated-partially-compensated-or-combined-abg-problems-14</ref>
# '''Uncompensated Metabolic  Alkalosis:''' This occurs when there is  a increase in the HCO3 level without a resultant alteration (increase) of the PaCO2 value. Thus, there will be an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
 
# '''Partially compensated Metabolic  Alkalosis:''' This occurs when there is an increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; but, the pH is still not within the normal range. Thus, there will be an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
<br>&nbsp;<u>'''Helpful guidelines<ref name="Stoeltin">Stoeltin RK, Miller RD. Basics of Anesthesia, 5th ed. Philadelphia: Churchill Livingstone, Elsevier. 2007.</ref>'''</u><br> 1.A 1mmHg change in PaCO2 above or below 40 mmHg results in 0.008 unit change in pH in the opposite direction.<br> 2.The PaCO2 will decrease by about 1 mmHg for every 1 mEq/L reduction in [HCO3-] below 24 mEq/L<br> 3.A change in [HCO3-] of 10 mEq/L will result in a change in pH of approximately 0.15 pH units in the same direction.<br>
# '''Fully compensated Metabolic Alkalosis:''' This occurs when there is an increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate) with respiratory acidosis.
 
# '''Mixed Acid-Base disturbances:''' This occurs when there is either both metabolic and respiratory acidosis present or metabolic and respiratory alkalosis present at the same time of analysing arterial blood gases
<br>
 
'''The results&nbsp;should always be read and compared&nbsp;in reference to the patients previous ABG (if available)&nbsp;as you will then be able to assess a trend and make a more accurate assessment on whether you should treat or if your treatment has be successful or not.'''  


== Tutorials  ==
== Tutorials  ==
Line 215: Line 80:
<div class="col-md-4">{{#ev:youtube|kfJws8NQW1k|250}} <div class="text-right"><ref>ABGs (Arterial Blood Gas). Available from: https://www.youtube.com/watch?v=kfJws8NQW1k[last accessed 27/03/18]</ref></div></div>
<div class="col-md-4">{{#ev:youtube|kfJws8NQW1k|250}} <div class="text-right"><ref>ABGs (Arterial Blood Gas). Available from: https://www.youtube.com/watch?v=kfJws8NQW1k[last accessed 27/03/18]</ref></div></div>
</div>
</div>
== Useful Resources  ==
== Useful Resources  ==


[http://www.prognosis.org/abg/arterial_blood_gas_calculator.php ABG Calculator]  
[http://www.prognosis.org/abg/arterial_blood_gas_calculator.php ABG Calculator]  
[http://www.altitude.org/oxygen_levels.php ABG's at altitude]


[https://sites.google.com/site/doctorkipp/ Acid-Base Questions]  
[https://sites.google.com/site/doctorkipp/ Acid-Base Questions]  


[http://www.adamw.org/med/apps/abg.cgi ABG Interpretation Quiz]  
[http://www.adamw.org/med/apps/abg.cgi ABG Interpretation Quiz]
 
== Associated Topics  ==
 
*[http://www.physio-pedia.com/Respiratory_Failure Respiratory Failure]
*[[Hypoxaemia]]
*[http://www.physio-pedia.com/Oxygen_Therapy Oxygen Therapy]
*Oxygen Dissociation Cure
*Anemia


[https://www.medistudents.com/osce-skills/arterial-blood-gases Steps to Perform an ABG Test]
== &nbsp;References  ==
== &nbsp;References  ==


Line 242: Line 96:
[[Category:Respiratory]]  
[[Category:Respiratory]]  
[[Category:Cardiopulmonary]]  
[[Category:Cardiopulmonary]]  
[[Category:Respiratory Examination]]  
[[Category:Cardiovascular System - Assessment and Examination]]
[[Category:Assessment and Examination - Cardiovascular System]]
[[Category:Respiratory System - Assessment and Examination]]
[[Category:Technology]]

Latest revision as of 15:47, 11 March 2024

Original Editor - Scott Buxton

Top Contributors - Adam Vallely Farrell, Kim Jackson, Uchechukwu Chukwuemeka, Scott Buxton, Lucinda hampton, Rachael Lowe, Admin, Joao Costa, 127.0.0.1, Laura Ritchie, Naomi O'Reilly, Abbey Wright and Angeliki Chorti  

Arterial Blood Gases[edit | edit source]

Blood Gas Analyser

Arterial blood gases (ABG's) is a blood test that is used to give an indication of ventilation, gas exchange, and acid-base status and is taken from an arterial blood supply[1]. The arterial blood gas test is one of the most common tests performed on patients in intensive care units. At other levels of care, pulse oximetry plus transcutaneous carbon dioxide measurement is a less invasive alternative method of obtaining similar information.[2]

To perform this test, blood is collected from a specific artery, usually the wrist's radial artery. This blood sample allows an accurate determination of the amount of oxygen that passes from the lungs to the blood. This test is the one most commonly performed to diagnose cases of respiratory failure[3].
Arterial blood gas test results can show if:

  • Lungs are getting enough oxygen.
  • Lungs are removing enough carbon dioxide.
  • Kidneys are working properly.[2]

Uses[edit | edit source]

ABGs are very useful for detecting conditions that cause respiratory failure. Including: Lung Failure; Acute respiratory distress syndrome (ARDS); Sepsis; Diabetic ketoacidosis (DKA); Cystic fibrosis; Pneumonia; Emphysema; Hypovolemic shock; Acute heart failure; Cardiac arrest; Kidney Failure; Septic Shock; Trauma; Chronic vomiting; Uncontrolled diabetes; Asthma ; Chronic Obstructive Pulmonary Disease (COPD); Hemorrhage; Drug Overdose; Metabolic Disease; Chemical Poisoning; To check if lung condition treatments are working.[4]

Respiratory failure.jpg

[3]

Measurements[edit | edit source]

The key components of an ABG are:

  1. pH - This measures the balance of acids and bases in the blood.
  2. Partial pressure of oxygen (PaO2) - This measures the pressure of oxygen dissolved in the blood.
  3. Partial pressure of carbon dioxide (PaCO2) - This measures the amount of carbon dioxide in the blood and how well carbon dioxide can move out of the lungs.
  4. Bicarbonate (HCO3) - This is calculated using the measured values of pH and PaCO2 to determine the amount of the primary compound made from carbon dioxide (CO2.)
  5. Oxygen saturation (O2 Sat) - This measures how much hemoglobin in the blood is carrying oxygen.
  6. Oxygen content (O2CT) - This measures the amount of oxygen in the blood.
  7. Hemoglobin - This measures the amount of hemoglobin in the blood.

Normative Values[edit | edit source]

According to the National Institute of Health, typical normal values are:

  • pH: 7.35-7.45
  • Partial pressure of oxygen (PaO2): 75 to 100 mmHg
  • Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg
  • Bicarbonate (HCO3): 22-26 mEq/L
  • Oxygen saturation (O2 Sat): 94-100%[4]

Interpretation of ABGs[edit | edit source]

[5]
  1. Look at the pH
    • Increased = Alkalosis
    • Decreased = Acidosis
  2. Look at the PaCO2
    • Increased = Respiratory Acidosis
    • Decreased = Respiratory Alkalosis
  3. Look at the HCO3
    • Increased = Metabolic Alkalosis
    • Decreased = Metabolic Acidosis
  4. Identify if there is a compensation
    • Full compensation if the pH is within the normal range
    • Partial compensation if either the PaCO2 or HCO3 value is wavering to compensate for the primary acid-base disturbance; but, the pH is still not within the normal physiologic range.
  5. Look at the O2

The results  should always be read and compared  in reference to the patient's previous ABG (if available)  as you will then be able to assess a trend and make a more accurate assessment on whether you should treat or if your treatment has been successful or not.

Primary Acid-base disturbances[edit | edit source]

They are:

  1. Uncompensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level without a resultant alteration (increase) of the HCO3 value. Thus, there will an acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
  2. Partially compensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; but, the pH is still not within the normal range. Thus, there will still be acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs).
  3. Fully compensated Respiratory Acidosis: This occurs when there is an increase in the PaCO2 level with a resultant alteration (increase) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the acidosis due to respiratory failure (inability to remove excess carbondioxide from the blood and the lungs) with metabolic alkalosis.
  4. Uncompensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level without a resultant alteration (decrease) of the HCO3 value. Thus, there will be an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
  5. Partially compensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; but, the pH is still not within the normal range. Thus, there will be an alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood).
  6. Fully compensated Respiratory Alkalosis: This occurs when there is a decrease in the PaCO2 level with a resultant alteration (decrease) of the HCO3 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the alkalosis due to respiratory failure (excess carbondioxide exhalation from the lungs and reduced carbondioxide tension in the blood) with metabolic acidosis.
  7. Uncompensated Metabolic Acidosis: This occurs when there is an decrease in the HCO3 level without a resultant alteration (decrease) of the PaCO2 value. Thus, there will an acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
  8. Partially compensated Metabolic Acidosis: This occurs when there is a decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; but, the pH is still not within the normal range. Thus, there will still be acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate).
  9. Fully compensated Metabolic Acidosis: This occurs when there is a decrease in the HCO3 level with a resultant alteration (decrease) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the acidosis due to metabolic failure (inability of the kidney to retain adequate bicarbonate) with respiratory alkalosis.
  10. Uncompensated Metabolic Alkalosis: This occurs when there is a increase in the HCO3 level without a resultant alteration (increase) of the PaCO2 value. Thus, there will be an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
  11. Partially compensated Metabolic Alkalosis: This occurs when there is an increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; but, the pH is still not within the normal range. Thus, there will be an alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate).
  12. Fully compensated Metabolic Alkalosis: This occurs when there is an increase in the HCO3 level with a resultant alteration (increase) of the PaCO2 value; thereby, balancing the pH within the normal range. Thus, there will be compensation for the alkalosis due to metabolic failure (inability of the kidney to excrete excess bicarbonate) with respiratory acidosis.
  13. Mixed Acid-Base disturbances: This occurs when there is either both metabolic and respiratory acidosis present or metabolic and respiratory alkalosis present at the same time of analysing arterial blood gases

Tutorials[edit | edit source]

[6]
[7]
[8]

Useful Resources[edit | edit source]

ABG Calculator

Acid-Base Questions

ABG Interpretation Quiz

Steps to Perform an ABG Test

 References[edit | edit source]

  1. ↑ Hough A. Physiotherapy in Respiratory Care. An evidence-based approach to respiratory and cardiac management. 3rd ed. Cheltenham: Nelson Thomas Ltd. 2001
  2. ↑ 2.0 2.1 Scope health Arterial Gasometry: What is it? Why is it Necessary? Procedure, Compensation, Metabolic Disorders and Results Available: https://scopeheal.com/arterial-blood-gas/ (accessed 9.5.2022)
  3. ↑ 3.0 3.1 Well being pole Gasometry Available:https://wellbeingpole.com/gasometry/ (accessed 9.5.2022)
  4. ↑ 4.0 4.1 Nurse org. ABG test Available:https://nurse.org/articles/arterial-blood-gas-test/ (accessed 9.5.2022)
  5. ↑ https://ed.ted.com/on/9q9pS35Z
  6. ↑ Arterial Blood Gas (ABG) Tic-Tac-Toe Examples. Available from: https://www.youtube.com/watch?v=_OpvyEIlFj8[last accessed 27/03/18]
  7. ↑ 6 Easy Steps to ABG Analysis. Available from: https://www.youtube.com/watch?v=WUf-cPpnrXw[last accessed 27/03/18]
  8. ↑ ABGs (Arterial Blood Gas). Available from: https://www.youtube.com/watch?v=kfJws8NQW1k[last accessed 27/03/18]
Retrieved from "https://www.physio-pedia.com/index.php?title=Arterial_Blood_Gases&oldid=351426"