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== Hypoxaemia ==
== Introduction ==
 
[[File:Respiratory failure.jpg|right|frameless|599x599px]]
=== Introduction ===
Hypoxemia is defined as an abnormally low partial pressure of oxygen in the [[Blood Physiology|blood]] (normal arterial partial pressure of oxygen: 75 - 100mmHg). It is different from hypoxia, where the tissue [[oxygen]] delivery is inadequate to support normal the aerobic metabolism of the tissues.<ref>Scheufler KM. [https://scholar.google.com/scholar_url?url=https://www.sciencedirect.com/science/article/pii/S1473050204000916&hl=en&sa=T&oi=gsb&ct=res&cd=0&d=12826581058716236317&ei=TrVtZP7PJ5n5yATM9JTYDw&scisig=AGlGAw-8oym7_DKRvea5tI9WqKvk Tissue oxygenation and capacity to deliver O2 do the two go together?]. Transfusion and apheresis science. 2004 Aug 1;31(1):45-54.</ref> It is a common presentation in critically ill patients, with the potential for severe harm if not addressed appropriately. Hypoxaemia refers to a lower than normal [[Arterial Blood Gases|arterial blood oxygen]] level, measured either as oxygen saturation (SaO2) or partial pressure of oxygen (PaO2).<ref>Aronson LA. Hypoxemia. InComplications in Anesthesia 2007 Jan 1 (pp. 637-640). WB Saunders.</ref>  
Hypoxaemia is an abnormally low amount of oxygen in the blood, specifically arterial blood<ref name=":0">Pollak, Charles P.; Thorpy, Michael J.; Yager, Jan (2010). ''The encyclopedia of sleep and sleep disorders'' (3rd ed.). New York, NY. p. 104.</ref><ref name=":3">Eckman, Margaret (2010). ''Professional guide to pathophysiology'' (3rd ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins. p. 208. </ref>. Hypoxaemia is defined as the inability to maintain the PaO2 above 8kPa (see [[Arterial Blood Gases|ABGs]] for more details).<ref name=":2">Martin, Lawrence (1999). ''All you really need to know to interpret arterial blood gases'' (2nd ed.). Philadelphia: Lippincott Williams & Wilkins.</ref>  
* It is a common feature of acutely unwell hospitalised patients and can result in substantial morbidity and mortality if not treated rapidly and appropriately. Hypoxaemic patients may require admission to an intensive care unit, with more than 60% of those that do eventually requiring invasive [[Ventilation and Weaning|ventilation]].  
 
* The mortality of hypoxaemic critically ill patients is 27%, rising to as high as 50% in patients with severe hypoxaemia No specific threshold of SaO2 or PaO2 defines hypoxaemia.
It can cause hypoxia (low oxygen) in body tissues if unresolved, which can in turn lead to cell death of the peripheral then central tissues. Hypoxia is also known as type 1 [[Respiratory Failure|respiratory failure]].  
* Normal values for PaO2 are 10.5–13.5 kPa, and for SaO2 are 94–98%. Obtained via arterial blood gas (providing PaO2and SaO2) and pulse oximetry (providing peripheral capillary oxygen saturation; SpO2).  
 
* Normal values decline with age and are influenced by the presence of [[Multimorbidity|comorbidities]] such as [[Chronic Obstructive Pulmonary Disease Rehabilitation Class|chronic lung disease]]<ref name=":5">Flower L, Martin D. [https://www.magonlinelibrary.com/doi/full/10.12968/hmed.2019.0186?rfr_dat=cr_pub++0pubmed&url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org Management of hypoxaemia in the critically ill patient.] British Journal of Hospital Medicine. 2020 Jan 2:1-0.</ref>.
=== Type 1 Respiratory Failure  ===
[[Respiratory Failure]]:  a clinical condition that happens when the respiratory system fails to maintain its main function, which is gas exchange, in which PaO2 is lower '''i.e., hypoxemia''' than 60 mmHg and/or PaCO2 higher than 50 mmHg. Respiratory failure is divided into type I and type II.
[https://www.physio-pedia.com/Respiratory_Failure Respiratory failure] is characterised by a reduction in the function of the lungs due to lung disease, skeletal or neuromuscular disorder.
# Type I respiratory failure involves low oxygen, and normal or low carbon dioxide levels.
 
# Type II respiratory failure involves low oxygen, with high carbon dioxide.
It occurs when gas exchange in the lungs is significantly impaired causing a drop in the levels of oxygen in the blood: hypoxaemia or type 1 respiratory failure.<ref>Tulaimat A, Patel A, Wisniewski M, Gueret R. [https://europepmc.org/article/med/27288621 The validity and reliability of the clinical assessment of increased work of breathing in acutely ill patients.] Journal of critical care. 2016 Aug 1;34:111-5.</ref>
 
When there is a drop in oxygen and a rise in carbon dioxide levels this is known as: hypercapnia or type 2 respiratory failure.


Respiratory failure is demonstrated in [https://www.physio-pedia.com/Arterial_Blood_Gases arterial blood gas] (ABG). Type I respiratory failure is defined as PaO2 <8.0kPa with a normal or lowered PaCO2.<ref name=":0" />  
== Hypoxia and Hypoxemia ==
The term hypoxia and hypoxemia are not synonymous.
# Hypoxemia is defined as a decrease in the partial pressure of oxygen in the blood
# Hypoxia is defined by reduced level of tissue oxygenation. Severe hypoxia can affect the production of [[Adenosine triphosphate (ATP)|ATP]] by [[mitochondria]]<nowiki/>[[mitochondria|l]]<nowiki/>oxidative phosphorylation, threatening cellular integrity. Non-oxygen dependent bioenergetic pathways are referred to as [[Anaerobic Capacity|anaerobic]] metabolism; they are short-term inefficient systems that are unable to sustain life for prolonged periods of time in humans<ref name=":5" />.
== Mechanisms of Hypoxemia  ==
There are various mechanisms of hypoxemia. These are V/Q mismatch, right-to-left shunt, diffusion impairment, hypoventilation, and low inspired PO2<ref>Sarkar M, Niranjan N, Banyal PK. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5234199/ Mechanisms of hypoxemia]. Lung India: official organ of Indian Chest Society. 2017 Jan;34(1):47.</ref>.
[[File:Pulmonary-embolism-29.png|right|frameless|400x400px]]
'''Ventilation/perfusion (V/Q) mismatch''' Image 2: Positive study pulmonary embolism situated within the right middle lobe/anterior segment of the right upper lobe and the posterior basal segment of the right lower lobe.
* This is the most common type of hypoxemia. Ventilation refers to the oxygen supply in the lungs, while perfusion refers to the blood supply to the lungs.
* Ventilation and perfusion are measured in a ratio, called V/Q ratio. Normally, there’s a small degree of mismatch in this ratio, however if the mismatch becomes too great, problems can occur.
* There are two causes of ventilation perfusion mismatch:
*# The lungs are getting enough oxygen, but there’s not enough blood flow (increased V/Q ratio).
*# There is blood flow to the lungs, but not enough oxygen (decreased V/Q ratio).
'''Shunt'''
* Normally, deoxygenated blood enters the right side of the heart, travels to the lungs to receive oxygen, and then travels to the left side of the heart to be distributed to the rest of the body.
* In this type of hypoxemia, blood enters the left side of the heart without becoming oxygenated in the lungs.
'''Diffusion impairment'''
* When oxygen enters the lungs, it fills the [[alveoli]]. Capillaries surround the alveoli. Oxygen diffuses from the alveoli into the blood running through the capillaries.
* In this type of hypoxemia, the diffusion of oxygen into the bloodstream is impaired.
'''Hypoventilation'''
* Hypoventilation is when oxygen intake occurs at a slow rate. This can result in higher levels of carbon dioxide in the blood and lower levels of oxygen.
'''Low Inspired PO2'''
* This type of hypoxemia typically occurs at higher altitudes. Available oxygen in the air decreases with increasing altitude.
* Therefore, at higher altitudes each breath provides you with lower levels of oxygen than when you’re at sea level<ref name=":6">Healthline Hypoxemia Available:https://www.healthline.com/health/hypoxemia#types (accessed 19.4.2021)</ref>.


Type 1 respiratory failure is related to respiratory distress, with increased work of breathing and deranged gas exchange.<ref name=":1">Harden B, Cross J, Broad MA. Respiratory physiotherapy: An on-call survival guide. Elsevier Health Sciences; 2009.</ref> It may occur with or without the presence of excessive pulmonary secretions and/or sputum retention, and is not necessarily related to a primary respiratory problem, e.g. neurological problems may be related to respiratory depression, hypoventilation, reduced level of consciousness and inability to protect the airway<ref name=":1" />. Cough depression and risk of aspiration are a serious concern.
== Clinical Signs  ==
=== Classification and Causes of Hypoxaemia  ===
A patient with acute hypoxaemia will display some or all of the following symptoms<ref name=":1">Harden B, Cross J, Broad MA. Respiratory physiotherapy: An on-call survival guide. Elsevier Health Sciences; 2009.</ref><ref>Colledge NR, Walker BR, Ralston SH, eds. (2010). ''Davidson's principles and practice of medicine'' (21st ed.). Edinburgh: Churchill Livingstone/Elsevier.</ref>;
There are many causes of hypoxaemia, it is often due to respiratory disorders:<ref name=":2" />
{| class="wikitable"
!
!''Classification''
!''Cause''
|-
|'''Hypoxic hypoxaemia'''
|
* Occurs where blood flows through parts of the lung which are unventilated
* There is an inability to transfer oxygen across the pulmonary membrane (gas diffusion limitation)
* Acute bronchoconstriction: asthma (insufficient gas flow in and out of the lung)
* Insufficient inspired oxygen therapy (including faulty oxygen delivery equipment)
|
* Primary respiratory disease: [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]], pulmonary fibrosis, [[Cystic Fibrosis|CF]], [[pneumonia]], sputum retention, decreased gas transfer across thickened (fibrotic/ oedematous) membrane
* Primary cardiac disease: [[Heart Failure|heart failure]], congestive cardiac failure, pulmonary oedema (causing a diffusion limitation across the respiratory membrane)
|-
|'''Ischaemic hypoxaemia'''
|
* Usually due to inadequate blood flow through the lung
|
* Pulmonary embolus
* Destruction of the pulmonary vasculature (COPD, pulmonary trauma)
|-
|'''Anaemic hypoxaemia'''
|
* Reduction in the oxygen carrying capacity of the blood
|
* Shock (significant blood loss with a reduced Hb)
* Primary haematological diseases, e.g. sickle cell crisis, anaemia
|-
|'''Toxic hypoxaemia'''
|
* Difficulty in the utilisation of oxygen
* It is common in patients admitted with inhalation burns/ smoke inhalation injuries
|
* E.g. carbon monoxide poisoning, cyanide poisoning
|}
<ref name=":0" /><ref name=":1" /><ref name=":3" />
 
=== Clinical Signs ===
A patient with acute hypoxaemia will display some or all of the following symptoms<ref name=":1" /><ref>Colledge NR, Walker BR, Ralston SH, eds. (2010). ''Davidson's principles and practice of medicine'' (21st ed.). Edinburgh: Churchill Livingstone/Elsevier.</ref>;
{{#ev:youtube|v=Qj3xxNfWsH8}}<ref>marcophage. Signs and symptoms of hypoxemia. Available from: https://www.youtube.com/watch?v=Qj3xxNfWsH8 [last accessed 15/04/2017]</ref>
{{#ev:youtube|v=Qj3xxNfWsH8}}<ref>marcophage. Signs and symptoms of hypoxemia. Available from: https://www.youtube.com/watch?v=Qj3xxNfWsH8 [last accessed 15/04/2017]</ref>


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|-
|-
|Reduced mental state
|Reduced mental state
|Confused, agitated
|Confused, Agitated, Restlessness
|
|
|}
|}


Chronic hypoxaemia can occur from chronic lung conditions such as [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]] [[Sleep Apnea|or seep apnoea]], but it can also be caused by environmental factors such as frequent flying or living at high altitudes. which can be compensated or uncompensated. The compensation may result in the symptoms to be overlooked initially, however, further disease progression or mild illness such as a chest infection may increase oxygen demand and unmask the existing hypoxemia. <ref>Adde FV, Alvarez AE, Barbisan BN, Guimarães BR. [https://www.sciencedirect.com/science/article/pii/S0021755713000041 Recommendations for long-term home oxygen therapy in children and adolescents]. Jornal de pediatria. 2013 Feb;89(1):06-17. </ref>
Chronic hypoxaemia can occur from chronic lung conditions such as [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]] [[Sleep Apnea|or seep apnoea]], but it can also be caused by environmental factors such as frequent flying or living at high altitudes. which can be compensated or uncompensated<ref name=":4" />. The compensation may result in the symptoms to be overlooked initially, however, further disease progression or mild illness such as a chest infection may increase oxygen demand and unmask the existing hypoxaemia. <ref>Adde FV, Alvarez AE, Barbisan BN, Guimarães BR. [https://www.sciencedirect.com/science/article/pii/S0021755713000041 Recommendations for long-term home oxygen therapy in children and adolescents]. Jornal de pediatria. 2013 Feb;89(1):06-17. </ref>
 
== Causes of Hypoxaemia ==
== Aim of Physiotherapy ==
Some of the respiratory causes of hypoxaemia are:
The overall aim of physiotherapy is to identify and treat, if appropriate, the cause of the hypoxaemia, thus aiming to increase PaO2 >8kPa while administering appropriate [[Oxygen Therapy|oxygen therapy]]. <ref name=":1" />
* [[Anaemia]]: a condition in which there aren’t enough red blood cells to effectively carry oxygen. Because of this, a person with anemia may have low levels of oxygen in their blood.
 
* [[Asthma]]
== Treatment of Hypoxaemia ==
* [[Pulmonary Embolism|Pulmonary embolus]] (PE): is a blockage of an artery in the lungs by a clot that has moved from elsewhere in the body through the bloodstream (embolism).<ref>Dalen JE, Alpert JS. Natural history of pulmonary embolism. Progress in cardiovascular diseases. 1975 Jan 1;17(4):259-70.</ref> Symptoms of a PE may include shortness of breath and chest pain, particularly on inspiration.
The primary treatment for hypoxaemia is controlled oxygen therapy, alongside the identification and treatment of the underlying cause. Patients who are unable to maintain a SaO2 >90% with a face mask may require additional respiratory support. This might include either continuous positive airway pressure (CPAP) or intubation and mechanical ventilation. Patients presenting with a unilateral lung disease can be positioned in side-lying, with the unaffected lung down, to try to improve V/Q matching.<ref name=":1" />
* Collapsed lung ([[atelectasis]])
 
* Congenital heart defects or disease
==== [[Oxygen Therapy|Controlled Oxygen Therapy]] ====
* High altitudes
Controlled oxygen therapy is prescribed for hypoxaemic patients to increase alveolar oxygen tension and decrease their work of breathing.<ref>Hardinge M, Annandale J, Bourne S, Cooper B, Evans A, Freeman D, Green A, Hippolyte S, Knowles V, MacNee W, McDonnell L. British Thoracic Society guidelines for home oxygen use in adults: accredited by NICE. Thorax. 2015 Jun 1;70(Suppl 1):i1-43.</ref> It is important to remember that oxygen is a drug and should always be prescribed with the required percentage and/or flow rate. It is usually delivered at 24-60% and can be given by an oxygen mask. Lower requirements of 2-4L/min are commonly supplied via nasal cannulae; however, often a mask may be preferable if hypoxic and/or the patient is a mouth breather.<ref name=":1" /> If a patient is requiring over 60% oxygen with persistently low oxygen saturation (<90%) a non-rebreather mask should be used to administer constant flow of high concentration oxygen. CPAP is also useful with profound hypoxaemia once a pneumothorax has been excluded.<ref>Machado ML, Vollmer WM, Togeiro SM, Bilderback AL, Oliveira MC, Leitão FS, Queiroga F, Lorenzi-Filho G, Krishnan JA. CPAP and survival in moderate-to-severe obstructive sleep apnoea syndrome and hypoxaemic COPD. European Respiratory Journal. 2010 Jan 1;35(1):132-7.</ref>
* Interstitial lung disease eg [[Pulmonary Fibrosis|Pulmonary fibrosis]]: describes a collection of diseases which lead to interstitial lung damage and ultimately fibrosis and loss of the elasticity of the lungs. It is a chronic condition characterised by shortness of breath.<ref>Gribbin J, Hubbard RB, Le Jeune I, Smith CJ, West J, Tata LJ. [https://www.ncbi.nlm.nih.gov/pubmed/16844727 Incidence and mortality of idiopathic pulmonary fibrosis and sarcoidosis in the UK]. Thorax. 2006 Nov 1;61(11):980-5.</ref> The lung tissue becomes thickened, stiff and scarred over a period of time. The development of scar tissue is called fibrosis. As the lung tissue becomes scarred and thicker, the lungs start to lose their ability to transfer oxygen into the bloodstream.
 
* Medications that lower breathing rate eg some [[Opiod Use Disorder|opiods]] and anesthetics
==== Humidification ====
* [[Pneumonia]]: is caused by an infection which can start off as a lower respiratory tract infection, which when untreated can cause consolidation and significant sputum retention.<ref>Blaisdell FW. Pathophysiology of the respiratory distress syndrome. Arch Surg. 1974 Jan 1;108(1):44-9.
Oxygen therapy is known to dry out the airways. Humidifying oxygen is often used in an attempt to help prevent the drying of the upper respiratory tract. The BTS oxygen guidelines (2008) state that humidification is not required for the delivery of low flow oxygen (4L/minute and under) or short term use of high flow oxygen for short periods.<ref>O’driscoll BR, Howard LS, Davison AG. BTS guideline for emergency oxygen use in adult patients. Thorax. 2008 Oct 1;63(Suppl 6):vi1-68.</ref> In patients who are requiring high flow oxygen or oxygen for longer periods consider cold or heated humidification. Heated humidification is believed to be better for tenacious secretions or severe bronchospasm. <ref name=":1" />
</ref> Due to the lobe consolidation, the lungs are not adequately ventilated.
 
* [[Sleep Apnea-Hypopnea Syndrome|Sleep apnea]]
==== Treat the cause, e.g. bronchospasm, sputum retention, volume loss ====
* [[Pulmonary Oedema|Pulmonary oedema]]: occurs when fluid accumulates in the alveoli of the lungs causing an increased work of breathing. This fluid accumulation interferes with gas exchange and can cause respiratory failure.<ref>Masip J, Betbesé AJ, Páez J, Vecilla F, Cañizares R, Padró J, Paz MA, de Otero J, Ballús J. [https://www.ncbi.nlm.nih.gov/pubmed/11191538 Non-invasive pressure support ventilation versus conventional oxygen therapy in acute cardiogenic pulmonary oedema: a randomised trial.] The Lancet. 2000 Dec 23;356(9248):2126-32.</ref>
Whilst the delivery of oxygen therapy is the primary treatment for hypoxaemia it is essential to treat the cause. If it is a primary respiratory problem, treat this. If the primary problem is cardiac or renal in origin, discuss this with the medical team to help resolve the presenting issue.<ref name=":1" />
* Chronic respiratory conditions: such as [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]] ( flow of air in the lungs is obstructed. Destruction of the walls of alveoli and surrounding capillaries in COPD can lead to problems with oxygen exchange, which can lead to hypoxemia) or [[Cystic Fibrosis|CF]]
 
* Distended abdomen, e.g. pancreatitis, ascites. This prevents the [[Diaphragmatic Breathing Exercises|diaphragm]] from descending which reduces the surface area for gas exchange.
==== Increased work of breathing ====
* Hypoxemia can sometimes occur in newborns with congenital heart defects or disease. In fact, measuring the levels of oxygen in the blood is used to screen infants for congenital heart defects.
Patients will commonly present with an increased work of breathing. Positioning is essential to reduce breathlessness and improve ventilation perfusion matching<ref name=":1" />. Airway clearance techniques can also be useful if needed. IPPB may be considered (with a high flow rate) to rest the respiratory muscles and improve efficacy of other treatments.
* Preterm infants are also vulnerable to hypoxemia, particularly if they’ve been placed on a mechanical ventilator<ref name=":6" />
 
== Common Issues in Hypoxaemia ==
 
Unrecognised respiratory failure may lead to;
* respiratory muscle fatigue
* hypoventilation
* sputum retention
* Decreased O2 (hypoxaemia)<ref name=":1" />
* An acute assessment to establish the underlying cause is imperative as, if respiratory failure is left untreated, it may progress to one or all of the following;
** cardiac arrhytmia
** cerebral hypoxaemia
** respiratory acidosis
** coma
** cardiorespiratory arrest Thus, timely recognition and treatment of respiratory failure is of the utmost importance and a serious part of a patients care.<ref name=":1" />
==== Bronchopneumonia ====
Bronchopneumonia is a form of pneumonia, sometimes referred to as lobar pneumonia, that also causes inflammation in the bronchi. <ref>Blaisdell FW. Pathophysiology of the respiratory distress syndrome. Arch Surg. 1974 Jan 1;108(1):44-9.
</ref> A patient presenting with bronchopneumonia will present with troubled breathing due to airway constriction. Due to inflammation, their lungs are not adequately ventilated. Symptoms can range from mild to severe. Physiotherapy treatment can include;
* Ensure medication is optimised (oxygen, analgesia, bronchodilators, antibiotics, etc.)
* Positioning to decrease work of breathing
* Airway clearance techniques
* Humidification<ref name=":1" />
 
==== Acute lobar pneumonia ====
Lobar [[pneumonia]] is an acute exudative inflammation of an entire pulmonary lobe, produced in 95% of cases by Streptococcus pneumoniae (pneumococci). If not treated lobar pneumonia progresses in 4 stages; namely consolidation, red hepatization, grey hepatization and resolution.<ref>Pneumonia. (2018, January 9). ''Physiopedia,'' . Retrieved 11:29, March 31, 2018 from https://www.physio-pedia.com/index.php?title=Pneumonia&oldid=182184.</ref> Treatment is dependent on the severity of symptoms and may include some of the following techniques;
* During the unproductive phase advice on positioning may reduce WOB
* CPAP is useful for hypoxaemia
* Sputum clearance s only indicated if the patient becomes productive
 
==== Pulmonary embolus ====
Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism).<ref>Dalen JE, Alpert JS. Natural history of pulmonary embolism. Progress in cardiovascular diseases. 1975 Jan 1;17(4):259-70.</ref> Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing in, and coughing up blood. Physiotherapy is not indicated. CPAP may help with severe hypoxaemia.  


==== Pulmonary fibrosis ====
== Medical Treatment of Hypoxaemia ==
Pulmonary fibrosis describes a collection of diseases which lead to interstitial lung damage and ultimately fibrosis and loss of the elasticity of the lungs. It is a chronic condition characterised by shortness of breath.<ref>Gribbin J, Hubbard RB, Le Jeune I, Smith CJ, West J, Tata LJ. Incidence and mortality of idiopathic pulmonary fibrosis and sarcoidosis in the UK. Thorax. 2006 Nov 1;61(11):980-5.</ref> The lung tissue becomes thickened, stiff and scarred over a period of time. The development of scar tissue is called fibrosis. As the lung tissue becomes scarred and thicker, the lungs start to lose their ability to transfer oxygen into the bloodstream. Treatment of pulmonary fibrosis may involve;
[[File:Humidifier.jpeg|right|frameless]]
* Present with profound hypoxaemia. Humidified CPAP is effective
The primary treatment for hypoxaemia is controlled oxygen therapy, alongside the identification and treatment of the underlying cause. 
* Ensure sufficient oxygen is available when CPAP removed
# [[Oxygen Therapy|Controlled Oxygen Therapy]]:<br>Patients who are unable to maintain a SaO2 >90% with a face mask may require additional respiratory support. This might include either continuous positive airway pressure (CPAP), [[Non Invasive Ventilation|non-invasive ventilation]] or intubation with [[Ventilation and Weaning|mechanical ventilation]]<ref>Simon M, Braune S, Frings D, Wiontzek AK, Klose H, Kluge S. [https://link.springer.com/article/10.1186/s13054-014-0712-9 High-flow nasal cannula oxygen versus non-invasive ventilation in patients with acute hypoxaemic respiratory failure undergoing flexible bronchoscopy-a prospective randomised tria]l. Critical Care. 2014 Dec 1;18(6):712.</ref>. <br>Controlled oxygen therapy is prescribed for hypoxaemic patients to increase alveolar oxygen tension and decrease work of breathing.<ref>Hardinge M, Annandale J, Bourne S, Cooper B, Evans A, Freeman D, Green A, Hippolyte S, Knowles V, MacNee W, McDonnell L. British Thoracic Society guidelines for home oxygen use in adults: accredited by NICE. Thorax. 2015 Jun 1;70(Suppl 1):i1-43.</ref> It is important to remember that oxygen is a drug and should always be prescribed with the required percentage and/or flow rate.<ref name=":4">Bonsignore MR, Baiamonte P, Mazzuca E, Castrogiovanni A, Marrone O. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374907/ Obstructive sleep apnea and comorbidities: a dangerous liaison.] Multidisciplinary respiratory medicine. 2019 Dec;14(1):8.</ref>
# Humidification (image 3):<br>Oxygen therapy is known to dry out the airways. Humidifying oxygen is often used in an attempt to help prevent the drying of the upper respiratory tract. In patients who are requiring high flow oxygen or oxygen for longer periods consider cold or heated humidification.<ref>O'driscoll BR, Howard LS, Earis J, Mak V. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5531304/ BTS guideline for oxygen use in adults in healthcare and emergency settings]. Thorax. 2017 Jun 1;72(Suppl 1):ii1-90.</ref> Heated humidification is believed to be better for tenacious secretions or severe bronchospasm. <ref name=":1" />
# Treat the Cause:<br>Whilst the delivery of oxygen therapy is the primary treatment for hypoxaemia, it is essential to treat the cause ,e.g. bronchospasm, sputum retention, volume loss. There may be an acute primary respiratory problem, however, the respiratory failure could be due to compensation for another condition such as cardiac or renal. Multi-disciplinary team (MDT) working is vital in managing this.<ref name=":1" />
== Physiotherapy ==
[[File:NIV1.jpg|right|frameless]]
The overall aim of physiotherapy is to identify and treat the cause of the hypoxaemia, thus aiming to increase PaO2 >8kPa while administering appropriate [[Oxygen Therapy|oxygen therapy]]. <ref name=":1" /> The cause of hypoxaemia may be sputum retention and in this case various physiotherapy techniques can be used<ref>Derakhtanjani AS, Jaberi AA, Haydari S, Bonabi TN. [https://www.ncbi.nlm.nih.gov/pubmed/31903332 Comparison the Effect of Active Cyclic Breathing Technique and Routine Chest Physiotherapy on Pain and Respiratory Parameters After Coronary Artery Graft Surgery]: A Randomized Clinical Trial. Anesthesiology and Pain Medicine. 2019 Oct;9(5).</ref>:
* [[Respiratory Physiotherapy|Positioning]] - to improve V/Q matching<ref name=":1" />
* [[Active Cycle of Breathing Technique|Active cycle of breathing exercises]]
* [[Autogenic Drainage|Autogenic drainage]]
* Manual techniques: [[percussion]] or vibrations
* Bubble [[Positive Expiratory Pressure (PEP) Devices|PEP]] or other oscillating instruments: acapella, flutter
* Cough assist or IPPB
* [[Oxygen Therapy at Home|Home oxygen therapy]]


==== Pulmonary oedema ====
=== Relevance to Physiotherapy ===
Pulmonary oedema occurs when fluid accumulates in the alveoli of the lungs causing an increased work of breathing. This fluid accumulation interferes with gas exchange and can cause respiratory failure.<ref>Masip J, Betbesé AJ, Páez J, Vecilla F, Cañizares R, Padró J, Paz MA, de Otero J, Ballús J. Non-invasive pressure support ventilation versus conventional oxygen therapy in acute cardiogenic pulmonary oedema: a randomised trial. The Lancet. 2000 Dec 23;356(9248):2126-32.</ref> Treating a patient with pulmonary oedema may include;
Physiotherapists should be aware of the manifestations of hypoxemia which may occur in patients. The causes of hypoxemia may include [[Ventilation and Weaning|hypoventilation]], ventilation/perfusion mismatch, shunting, diffusion impairment, and low partial pressure of oxygen.<ref>Sarkar M, Niranjan N, Banyal PK. Mechanisms of hypoxemia. Lung India: official organ of Indian Chest Society. 2017 Jan;34(1):47.</ref> The use of [[Oxygen Therapy|supplemental oxygen]] may be indicated in patients who show signs of hypoxemia at rest, and or with activity, in combination with breathing exercises to optimize oxygen utilization and minimize breathlessness.<ref>Hillegass E, Fick A, Pawlik A, Crouch R, Perme C, Chandrashekar R, McNamara SB, Cahalin LP. Supplemental oxygen utilization during physical therapy interventions. Cardiopulmonary Physical Therapy Journal. 2014 Jun 1;25(2):38-49.</ref>
* CPAP is effective in the treatment of pulmonary oedema
* If hypotensive, check that BP does not drop with increased intrathoracic pressure.
* NIV (pressure support with EPAP) may be useful in the patient tiring on CPAP<ref name=":1" />


==== CO2 retention ====
== Complications with Hypoxaemia ==
Uncontrolled oxygen therapy, or receiving too much oxygen, can make people who usually have higher CO2 levels retain more until it reaches dangerous levels.
* Acute CO2 retention is not a reason to reduce FiO2 unless patients have evidence of acute-on-chronic CO2 retention secondary to chronic respiratory disease
* This can be diagnosed by interpretation of recent [[Arterial Blood Gases|blood gas]] results, assessing pH, in relation to PaCO2, standard bicarbonate and base excess. Only this group of patients require judicious oxygen administration )24-28%), which should be prescribed accordingly


==== Fatigue ====
If left untreated hypoxaemia can lead to type 1 [[Respiratory Failure|respiratory failure]]. This may result is further symptoms which can be life threatening:
* Hypoxaemic patients may start to fatigue. This is seen by a rising PaCO2 - type II respiratory failure failure. An important clinical sign requiring immediate attention
* Respiratory acidosis
* Cardiac arrhythmia
* Cerebral hypoxaemia
* Altered mental state including [[Coma Recovery Scale (Revised)|coma]]
* Cardiorespiratory arrest <ref name=":1" />


==== Chronic chest patients ====
== Resources ==
* Patients who have longstanding chest diseases may have a regular chest clearing routine they adhere to e.g. Bronchiectatic, CF patient
[[Respiratory Failure|Respiratory failure]]
* It is important to discuss this and mould your treatment plan so that it fits within their existing regimen and their current physiotherapy problems<ref name=":1" />


==== Renal failure ====
[[Respiratory System|Respiratory system]]
* Patient in renal failure may present with an increased work of breathing
* [[Arterial Blood Gases|ABGs]] will show metabolic acidosis, generally with some form of respiratory ompensation e.g. Decreased CO2
* Pulmonary oedema and pleural effusion may also be present<ref name=":1" />


==== Distended abdomen, e.g. pancreatitis, ascites ====
[[Arterial Blood Gases|Arterial blood gases]]
* Positioning in alternate side-lying or well supported high side-lying is useful
* Standing where possible<ref name=":1" />


== References  ==
== References  ==
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[[Category:Respiratory System - Assessment and Examination]]
[[Category:Respiratory System - Assessment and Examination]]
[[Category:Acute Respiratory Disorders - Conditions]]
[[Category:Acute Respiratory Disorders - Conditions]]
[[Category:Conditions]]

Latest revision as of 06:46, 27 October 2023

Original Editor - Adam Vallely Farrell

Top Contributors - Adam Vallely Farrell, Lucinda hampton, Abbey Wright, Kim Jackson, Rishika Babburu and Chelsea Mclene  

Introduction[edit | edit source]

Respiratory failure.jpg

Hypoxemia is defined as an abnormally low partial pressure of oxygen in the blood (normal arterial partial pressure of oxygen: 75 - 100mmHg). It is different from hypoxia, where the tissue oxygen delivery is inadequate to support normal the aerobic metabolism of the tissues.[1] It is a common presentation in critically ill patients, with the potential for severe harm if not addressed appropriately. Hypoxaemia refers to a lower than normal arterial blood oxygen level, measured either as oxygen saturation (SaO2) or partial pressure of oxygen (PaO2).[2]

  • It is a common feature of acutely unwell hospitalised patients and can result in substantial morbidity and mortality if not treated rapidly and appropriately. Hypoxaemic patients may require admission to an intensive care unit, with more than 60% of those that do eventually requiring invasive ventilation.
  • The mortality of hypoxaemic critically ill patients is 27%, rising to as high as 50% in patients with severe hypoxaemia No specific threshold of SaO2 or PaO2 defines hypoxaemia.
  • Normal values for PaO2 are 10.5–13.5 kPa, and for SaO2 are 94–98%. Obtained via arterial blood gas (providing PaO2and SaO2) and pulse oximetry (providing peripheral capillary oxygen saturation; SpO2).
  • Normal values decline with age and are influenced by the presence of comorbidities such as chronic lung disease[3].

Respiratory Failure: a clinical condition that happens when the respiratory system fails to maintain its main function, which is gas exchange, in which PaO2 is lower i.e., hypoxemia than 60 mmHg and/or PaCO2 higher than 50 mmHg. Respiratory failure is divided into type I and type II.

  1. Type I respiratory failure involves low oxygen, and normal or low carbon dioxide levels.
  2. Type II respiratory failure involves low oxygen, with high carbon dioxide.

Hypoxia and Hypoxemia[edit | edit source]

The term hypoxia and hypoxemia are not synonymous.

  1. Hypoxemia is defined as a decrease in the partial pressure of oxygen in the blood
  2. Hypoxia is defined by reduced level of tissue oxygenation. Severe hypoxia can affect the production of ATP by mitochondrialoxidative phosphorylation, threatening cellular integrity. Non-oxygen dependent bioenergetic pathways are referred to as anaerobic metabolism; they are short-term inefficient systems that are unable to sustain life for prolonged periods of time in humans[3].

Mechanisms of Hypoxemia[edit | edit source]

There are various mechanisms of hypoxemia. These are V/Q mismatch, right-to-left shunt, diffusion impairment, hypoventilation, and low inspired PO2[4].

Pulmonary-embolism-29.png

Ventilation/perfusion (V/Q) mismatch Image 2: Positive study pulmonary embolism situated within the right middle lobe/anterior segment of the right upper lobe and the posterior basal segment of the right lower lobe.

  • This is the most common type of hypoxemia. Ventilation refers to the oxygen supply in the lungs, while perfusion refers to the blood supply to the lungs.
  • Ventilation and perfusion are measured in a ratio, called V/Q ratio. Normally, there’s a small degree of mismatch in this ratio, however if the mismatch becomes too great, problems can occur.
  • There are two causes of ventilation perfusion mismatch:
    1. The lungs are getting enough oxygen, but there’s not enough blood flow (increased V/Q ratio).
    2. There is blood flow to the lungs, but not enough oxygen (decreased V/Q ratio).

Shunt

  • Normally, deoxygenated blood enters the right side of the heart, travels to the lungs to receive oxygen, and then travels to the left side of the heart to be distributed to the rest of the body.
  • In this type of hypoxemia, blood enters the left side of the heart without becoming oxygenated in the lungs.

Diffusion impairment

  • When oxygen enters the lungs, it fills the alveoli. Capillaries surround the alveoli. Oxygen diffuses from the alveoli into the blood running through the capillaries.
  • In this type of hypoxemia, the diffusion of oxygen into the bloodstream is impaired.

Hypoventilation

  • Hypoventilation is when oxygen intake occurs at a slow rate. This can result in higher levels of carbon dioxide in the blood and lower levels of oxygen.

Low Inspired PO2

  • This type of hypoxemia typically occurs at higher altitudes. Available oxygen in the air decreases with increasing altitude.
  • Therefore, at higher altitudes each breath provides you with lower levels of oxygen than when you’re at sea level[5].

Clinical Signs[edit | edit source]

A patient with acute hypoxaemia will display some or all of the following symptoms[6][7];

[8]

Sign Clinical feature Observation
Central cyanosis Blue-ish palor, blue lips Hypothermic <36.5 degrees C
Peripheral shut down Cool to touch, clammy Hypothermic <36.5 degrees C
Tachypnoea Increased respiratory rate >20 breaths per min, appears in distress with breathing
Low O2 Low O2 saturations <90%
Accessory muscle use Tracheal tug, flared nostrils, bracing through upper limbs
Reduced mental state Confused, Agitated, Restlessness

Chronic hypoxaemia can occur from chronic lung conditions such as COPD or seep apnoea, but it can also be caused by environmental factors such as frequent flying or living at high altitudes. which can be compensated or uncompensated[9]. The compensation may result in the symptoms to be overlooked initially, however, further disease progression or mild illness such as a chest infection may increase oxygen demand and unmask the existing hypoxaemia. [10]

Causes of Hypoxaemia[edit | edit source]

Some of the respiratory causes of hypoxaemia are:

  • Anaemia: a condition in which there aren’t enough red blood cells to effectively carry oxygen. Because of this, a person with anemia may have low levels of oxygen in their blood.
  • Asthma
  • Pulmonary embolus (PE): is a blockage of an artery in the lungs by a clot that has moved from elsewhere in the body through the bloodstream (embolism).[11] Symptoms of a PE may include shortness of breath and chest pain, particularly on inspiration.
  • Collapsed lung (atelectasis)
  • Congenital heart defects or disease
  • High altitudes
  • Interstitial lung disease eg Pulmonary fibrosis: describes a collection of diseases which lead to interstitial lung damage and ultimately fibrosis and loss of the elasticity of the lungs. It is a chronic condition characterised by shortness of breath.[12] The lung tissue becomes thickened, stiff and scarred over a period of time. The development of scar tissue is called fibrosis. As the lung tissue becomes scarred and thicker, the lungs start to lose their ability to transfer oxygen into the bloodstream.
  • Medications that lower breathing rate eg some opiods and anesthetics
  • Pneumonia: is caused by an infection which can start off as a lower respiratory tract infection, which when untreated can cause consolidation and significant sputum retention.[13] Due to the lobe consolidation, the lungs are not adequately ventilated.
  • Sleep apnea
  • Pulmonary oedema: occurs when fluid accumulates in the alveoli of the lungs causing an increased work of breathing. This fluid accumulation interferes with gas exchange and can cause respiratory failure.[14]
  • Chronic respiratory conditions: such as COPD ( flow of air in the lungs is obstructed. Destruction of the walls of alveoli and surrounding capillaries in COPD can lead to problems with oxygen exchange, which can lead to hypoxemia) or CF
  • Distended abdomen, e.g. pancreatitis, ascites. This prevents the diaphragm from descending which reduces the surface area for gas exchange.
  • Hypoxemia can sometimes occur in newborns with congenital heart defects or disease. In fact, measuring the levels of oxygen in the blood is used to screen infants for congenital heart defects.
  • Preterm infants are also vulnerable to hypoxemia, particularly if they’ve been placed on a mechanical ventilator[5]

Medical Treatment of Hypoxaemia[edit | edit source]

Humidifier.jpeg

The primary treatment for hypoxaemia is controlled oxygen therapy, alongside the identification and treatment of the underlying cause.

  1. Controlled Oxygen Therapy:
    Patients who are unable to maintain a SaO2 >90% with a face mask may require additional respiratory support. This might include either continuous positive airway pressure (CPAP), non-invasive ventilation or intubation with mechanical ventilation[15].
    Controlled oxygen therapy is prescribed for hypoxaemic patients to increase alveolar oxygen tension and decrease work of breathing.[16] It is important to remember that oxygen is a drug and should always be prescribed with the required percentage and/or flow rate.[9]
  2. Humidification (image 3):
    Oxygen therapy is known to dry out the airways. Humidifying oxygen is often used in an attempt to help prevent the drying of the upper respiratory tract. In patients who are requiring high flow oxygen or oxygen for longer periods consider cold or heated humidification.[17] Heated humidification is believed to be better for tenacious secretions or severe bronchospasm. [6]
  3. Treat the Cause:
    Whilst the delivery of oxygen therapy is the primary treatment for hypoxaemia, it is essential to treat the cause ,e.g. bronchospasm, sputum retention, volume loss. There may be an acute primary respiratory problem, however, the respiratory failure could be due to compensation for another condition such as cardiac or renal. Multi-disciplinary team (MDT) working is vital in managing this.[6]

Physiotherapy[edit | edit source]

NIV1.jpg

The overall aim of physiotherapy is to identify and treat the cause of the hypoxaemia, thus aiming to increase PaO2 >8kPa while administering appropriate oxygen therapy. [6] The cause of hypoxaemia may be sputum retention and in this case various physiotherapy techniques can be used[18]:

Relevance to Physiotherapy[edit | edit source]

Physiotherapists should be aware of the manifestations of hypoxemia which may occur in patients. The causes of hypoxemia may include hypoventilation, ventilation/perfusion mismatch, shunting, diffusion impairment, and low partial pressure of oxygen.[19] The use of supplemental oxygen may be indicated in patients who show signs of hypoxemia at rest, and or with activity, in combination with breathing exercises to optimize oxygen utilization and minimize breathlessness.[20]

Complications with Hypoxaemia[edit | edit source]

If left untreated hypoxaemia can lead to type 1 respiratory failure. This may result is further symptoms which can be life threatening:

  • Respiratory acidosis
  • Cardiac arrhythmia
  • Cerebral hypoxaemia
  • Altered mental state including coma
  • Cardiorespiratory arrest [6]

Resources[edit | edit source]

Respiratory failure

Respiratory system

Arterial blood gases

References[edit | edit source]

  1. ↑ Scheufler KM. Tissue oxygenation and capacity to deliver O2 do the two go together?. Transfusion and apheresis science. 2004 Aug 1;31(1):45-54.
  2. ↑ Aronson LA. Hypoxemia. InComplications in Anesthesia 2007 Jan 1 (pp. 637-640). WB Saunders.
  3. ↑ 3.0 3.1 Flower L, Martin D. Management of hypoxaemia in the critically ill patient. British Journal of Hospital Medicine. 2020 Jan 2:1-0.
  4. ↑ Sarkar M, Niranjan N, Banyal PK. Mechanisms of hypoxemia. Lung India: official organ of Indian Chest Society. 2017 Jan;34(1):47.
  5. ↑ 5.0 5.1 Healthline Hypoxemia Available:https://www.healthline.com/health/hypoxemia#types (accessed 19.4.2021)
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Harden B, Cross J, Broad MA. Respiratory physiotherapy: An on-call survival guide. Elsevier Health Sciences; 2009.
  7. ↑ Colledge NR, Walker BR, Ralston SH, eds. (2010). Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier.
  8. ↑ marcophage. Signs and symptoms of hypoxemia. Available from: https://www.youtube.com/watch?v=Qj3xxNfWsH8 [last accessed 15/04/2017]
  9. ↑ 9.0 9.1 Bonsignore MR, Baiamonte P, Mazzuca E, Castrogiovanni A, Marrone O. Obstructive sleep apnea and comorbidities: a dangerous liaison. Multidisciplinary respiratory medicine. 2019 Dec;14(1):8.
  10. ↑ Adde FV, Alvarez AE, Barbisan BN, Guimarães BR. Recommendations for long-term home oxygen therapy in children and adolescents. Jornal de pediatria. 2013 Feb;89(1):06-17. 
  11. ↑ Dalen JE, Alpert JS. Natural history of pulmonary embolism. Progress in cardiovascular diseases. 1975 Jan 1;17(4):259-70.
  12. ↑ Gribbin J, Hubbard RB, Le Jeune I, Smith CJ, West J, Tata LJ. Incidence and mortality of idiopathic pulmonary fibrosis and sarcoidosis in the UK. Thorax. 2006 Nov 1;61(11):980-5.
  13. ↑ Blaisdell FW. Pathophysiology of the respiratory distress syndrome. Arch Surg. 1974 Jan 1;108(1):44-9.
  14. ↑ Masip J, Betbesé AJ, Páez J, Vecilla F, Cañizares R, Padró J, Paz MA, de Otero J, Ballús J. Non-invasive pressure support ventilation versus conventional oxygen therapy in acute cardiogenic pulmonary oedema: a randomised trial. The Lancet. 2000 Dec 23;356(9248):2126-32.
  15. ↑ Simon M, Braune S, Frings D, Wiontzek AK, Klose H, Kluge S. High-flow nasal cannula oxygen versus non-invasive ventilation in patients with acute hypoxaemic respiratory failure undergoing flexible bronchoscopy-a prospective randomised trial. Critical Care. 2014 Dec 1;18(6):712.
  16. ↑ Hardinge M, Annandale J, Bourne S, Cooper B, Evans A, Freeman D, Green A, Hippolyte S, Knowles V, MacNee W, McDonnell L. British Thoracic Society guidelines for home oxygen use in adults: accredited by NICE. Thorax. 2015 Jun 1;70(Suppl 1):i1-43.
  17. ↑ O'driscoll BR, Howard LS, Earis J, Mak V. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017 Jun 1;72(Suppl 1):ii1-90.
  18. ↑ Derakhtanjani AS, Jaberi AA, Haydari S, Bonabi TN. Comparison the Effect of Active Cyclic Breathing Technique and Routine Chest Physiotherapy on Pain and Respiratory Parameters After Coronary Artery Graft Surgery: A Randomized Clinical Trial. Anesthesiology and Pain Medicine. 2019 Oct;9(5).
  19. ↑ Sarkar M, Niranjan N, Banyal PK. Mechanisms of hypoxemia. Lung India: official organ of Indian Chest Society. 2017 Jan;34(1):47.
  20. ↑ Hillegass E, Fick A, Pawlik A, Crouch R, Perme C, Chandrashekar R, McNamara SB, Cahalin LP. Supplemental oxygen utilization during physical therapy interventions. Cardiopulmonary Physical Therapy Journal. 2014 Jun 1;25(2):38-49.
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