Arterial Blood Gases: Difference between revisions

No edit summary
No edit summary
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">Hough A. Physiotherapy in Respiratory Care. An evidence based-approach to respiratory and cardiac managemenmt. 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>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>
[[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">Hough A. Physiotherapy in Respiratory Care. An evidence based-approach to respiratory and cardiac managemenmt. 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>


To perform this test, blood is collected from a specific artery, usually the radial artery of the wrist. 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>ABGs give us information about the activity in both the [[Respiratory System|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|oxygen therapy]]<ref name=":0">Woodrow P. Arterial blood gas analysis. Nursing Standard (through 2013). 2004;18(21):45.</ref>.
To perform this test, blood is collected from a specific artery, usually the radial artery of the wrist. 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>.


== Uses ==
<br>Arterial blood gas test results can show if:
ABGs are very useful for detecting conditions that cause respiratory failure. Including: Asthma; Pulmonary fibrosis; Pulmonary edema; Hypoventilation; Hyperventilation; Sepsis; Renal metabolism disorder.<ref name=":4" />


== ABG Definitions  ==
* Lungs are getting enough oxygen.
* P<sup>H</sup>: The measure of hydrogen ions in the blood
* Lungs are removing enough carbon dioxide.
* PaC02: Partial pressure of Carbondioxide in the blood, the acidic element of the balance
* Kidneys are working properly.<ref name=":0" />
** Acidic component
** 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, et al. Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002). Pure and applied chemistry. 2002;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>  ==
== Uses ==
 
ABGs are very useful for detecting conditions that cause respiratory failure. Including: Asthma; Pulmonary fibrosis; Pulmonary edema; Hypoventilation; Hyperventilation; Sepsis; Renal metabolism disorder.<ref name=":4" />
{| width="600" cellspacing="1" cellpadding="1" border="1" align="left" summary="The normal values and reference ranges expected from a 'normal' ABG"
|+
|-
! scope="col" | Arterial Blood Analysis
! scope="col" | Reference Ranges
! scope="col" | Venous Blood analysis
! scope="col" | Reference Ranges
|-
| pH
| 7.35 - 7.45
| pH
| 7.31&nbsp; - 7.41
|-
| PaO<sub>2</sub>
|
10.7 - 13.3 kPa
 
| PO<sub>2</sub>
|
5.0 - 5.6 kPa
 
|-
| PaCO<sub>2</sub>
| 4.7 - 6.0 kPa
| PCO<sub>2</sub>
| 5.6 - 6.7 kPa
|-
|
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 BJ,Taghavi SM, Amidon GL, Amidon GE. [http://onlinelibrary.wiley.com/doi/10.1002/jps.24108/abstract In Vivo Pre dictive Dissolution: Transport Analysis of the CO2, Bicarbonate In Vivo Buffer System]. Journal of Pharmaceutical Sciences. 2014;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 by 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. Neurologic presentations of acid-base imbalance, electrolyte abnormalities, and endocrine emergencies. Neurol Clin. 2010; 28 (1): 1–16</ref>
* Decreased pH
* Increased PaCO2
* '''Causes'''
** Hypoventilation
** Acute Lung Injury
*** Upper airway obstruction
*** Lower airway obstruction
*** Impaired alveolar filling
** Chronic Lung Disease
** [[Neuromuscular Disorders|Neuromuscular disorders]]
** [[Obesity]]
** CNS Depression
* '''Symptoms'''
** [[Headache]]
** Anxiety
** Blurred vision
** Restlessness
** Drowsiness
** Tremors
** Delirium
** [[Coma Recovery Scale (Revised)|Coma]]<ref name=":0" />
 
Image: Overview of the respiratory system<ref >Overview of the respiratory system image - © Kenhub Overview of the respiratory system</ref>  


== Metabolic Acidosis ==
== Measurements ==
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. 
The key components to an ABG are:
* Decreased pH
* Decreased HCO3
* '''Causes'''
*** Renal disease
*** Liver disease
*** Lactic acidosis
*** Prolonged lack of oxygen
*** Shock
*** Poisioning
*** Medications
*** Dehydration
*** Diarrhoea
* '''Symptoms'''
** Rapid breathing
** Confusion
** Lethargy
** Cold, clammy skin
** Tachycardia and arrhythmia<ref name=":0" />


== Respiratory Alkalosis ==
# pH - This measures the balance of acids and bases in your blood.
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">Hadjiliadis D. 2020. [https://www.nlm.nih.gov/medlineplus/ency/article/000111.htm Respiratory alkalosis: MedlinePlus Medical Encyclopedia].  Available from:https://medlineplus.gov/ency/article/000111.htm (accessed 24 May 2021) </ref>
# Partial pressure of oxygen (PaO2) - This measures the pressure of oxygen dissolved in your blood.
* Increased pH
# Partial pressure of carbon dioxide (PaCO2) - This measures the amount of carbon dioxide in your blood and how well carbon dioxide can move out of your body.
* Decreased PaCO2
# Bicarbonate (HCO3) - This is calculated using the measured values of pH and PaCO2 to determine the amount of the basic compound made from carbon dioxide (CO2.)
* '''Causes'''
# Oxygen saturation (O2 Sat) - This measures how much hemoglobin in your blood is carrying oxygen.
** Hyperventilation
# Oxygen content (O2CT) - This measures the amount of oxygen in your blood.
** Acute [[asthma]]
# Hemoglobin - This measures the amount of hemoglobin in your blood.
** CNS disturbance
** High altitude
** [[Pneumonia]]
** Drugs
** [[Fever]]
** [[Sepsis]]
* '''Symptoms'''
** Diziness
** Peripheral paraesthesia
** Confusion
** Dry mouth
** Bloating<ref name=":1" />


== Metabolic Alkalosis ==
== Normative Values ==
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, editors. Decision Making in Medicine: An Algorithmic Approach. 3rd edition. Philadelphia, PA: Mosby Elsevier; 2010. 374-5.</ref>  
According to the National Institute of Health, typical normal values are:
* Increased pH
* Increased HCO3
* '''Causes'''
** Excess alkali administration
** Hyperkalaemia
** IV penicillin
** Re-feeding syndrome
** Massive blood transfusion
** [[Diuretics|Diuretic therapy]]
** Vomitting
* '''Symptoms'''
** Weakness
** Myalgia
** Polyuria
** Cardiac arrhythmias
** Hypoventilation<ref name=":0" /><ref name=":2" />


== Respiratory Failure ==
* pH: 7.35-7.45
[[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. Physiopedia.  Available from: https://www.physio-pedia.com/index.php?title=Respiratory_Failure&oldid=179534. (accessed 24 May 2021)</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. Journal of crit care. 2016; 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, et al. [https://pubmed.ncbi.nlm.nih.gov/26102313/ Pre-hospital invasive ventilation for acute respiratory failure: a systematic review and cost effectiveness evaluation]. Health Technol Assess. 2015; 19(42):v-vi, 1-102. Doi: 10.3310/hta19420.</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" />
* Partial pressure of oxygen (PaO2): 75 to 100 mmHg
 
* Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg
It is the inability to perform adequately the fundamental functions of respiration:
* Bicarbonate (HCO3): 22-26 mEq/L
# To deliver oxygen to the blood
* Oxygen saturation (O2 Sat): 94-100%
# To eliminate carbon dioxide from it


== Interpretation of ABGs ==
== Interpretation of ABGs ==
Line 189: Line 50:
#* Increased = Metabolic Alkalosis
#* Increased = Metabolic Alkalosis
#* Decreased = Metabolic Acidosis
#* Decreased = Metabolic Acidosis
# <u>Look at the O2</u>
# <u>Look at the O2</u><br>
 
=== Compensation ===
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.
 
If pH is NORMAL despite an abnormal PCO2 and HCO3 it must be compensated.
# Look at the pH - Which side of 7.4 is it?
# Look for the cause
#* PCO2 goes in the opposite direction to pH
#* HCO3 travels in the same direction as pH
# The other value is the compensator
Finding compensated, partially compensated, or uncompensated ABG problems:
* 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.
* 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.
* 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>Chegg Study. Uncompensated, Partially Compensated, Or Combined Abg Problems. Available from:https://www.chegg.com/homework-help/definitions/uncompensated-partially-compensated-or-combined-abg-problems-14 (accessed 24 May 2021)</ref>
 
<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>
 
<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.'''  
'''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.'''  


Line 218: Line 60:
<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  ==


Revision as of 02:16, 9 May 2022

Original Editor - Scott Buxton

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

Arterial Blood Gases[edit | edit source]

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[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 radial artery of the wrist. 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: Asthma; Pulmonary fibrosis; Pulmonary edema; Hypoventilation; Hyperventilation; Sepsis; Renal metabolism disorder.[3]

Measurements[edit | edit source]

The key components to an ABG are:

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

Interpretation of ABGs[edit | edit source]

[4]
  1. Look at the pH
    • Increased = Alkalosis
    • Decreased = Acidosis
  2. Look at the PaCO2
    1. Increased = Respiratory Acidosis
    2. Decreased = Respiratory Alkalosis
  3. Look at the HCO3
    • Increased = Metabolic Alkalosis
    • Decreased = Metabolic Acidosis
  4. Look at the O2

The results should always be read and compared in reference to the patients 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 be successful or not.

Tutorials[edit | edit source]

[5]
[6]
[7]

Useful Resources[edit | edit source]

ABG Calculator

ABG's at altitude

Acid-Base Questions

ABG Interpretation Quiz

Associated Topics[edit | edit source]

 References[edit | edit source]

  1. ↑ Hough A. Physiotherapy in Respiratory Care. An evidence based-approach to respiratory and cardiac managemenmt. 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. ↑ https://ed.ted.com/on/9q9pS35Z
  5. ↑ Arterial Blood Gas (ABG) Tic-Tac-Toe Examples. Available from: https://www.youtube.com/watch?v=_OpvyEIlFj8[last accessed 27/03/18]
  6. ↑ 6 Easy Steps to ABG Analysis. Available from: https://www.youtube.com/watch?v=WUf-cPpnrXw[last accessed 27/03/18]
  7. ↑ 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=304452"