COVID-19-associated hypoxemia: Difference between revisions

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==Pathophysiology==
==Pathophysiology==


* [[COVID-19]] is caused by the novel [[Coronavirus]]. It binds to ACE-2 receptors in the lower respiratory tract which causes pulmonary manifestations.  
* [[COVID-19]] is caused by the novel [[Coronavirus]]. It binds to [[Angiotensin-converting enzyme|ACE]]-2 receptors in the lower respiratory tract which causes pulmonary manifestations.
* The virus causes alveolar injury which stimulates an [[inflammatory|inflammation]] response in the host tissue.
* The [[Virus (biology)|virus]] causes [[Alveolus|alveolar]] injury which stimulates an [[inflammatory]] response in the host tissue.
* Mononuclear inflammatory cells are recruited at the site of injury which release cytokines e.g Interleukin-6 and activate procoagulants
*[[Mononuclear cells|Mononuclear]] inflammatory [[Cells (biology)|cells]] are recruited at the site of injury which release [[cytokines]] e.g [[Interleukin-6]] and activate procoagulants
* As a result of this insult, the alveolar epithelium and capillary endothelium are damaged.
* As a result of this insult, the [[Alveolar-capillary barrier|alveolar epithelium]] and [[Capillary bed|capillary endothelium]] are damaged.
* Alveoli collapse occurs due to fluid accumulation and loss of surfactant.
* Alveoli collapse occurs due to fluid accumulation and loss of [[Pulmonary surfactant|surfactant]]
* Simultaneously, the activation of [[Coagulation cascade]] by [[cytokines]] leads to widespread [[thrombosis]] in multiple organs of the body, including [[lungs]].
* Simultaneously, the activation of [[Coagulation cascade]] by [[cytokines]] leads to widespread [[thrombosis]] in multiple organs of the body, including [[lungs]].
* It has also been suggested that there is down-regulation of the Hemostatic Oxygen Sensing system of the body (e.g Carotid bodies) through alteration of expression of mitochondrial proteins by the Coronavirus, occurring at a cellular level.
* It has also been suggested that there is down-regulation of the Hemostatic Oxygen Sensing system of the body (e.g [[Carotid bodies]]) through alteration of expression of [[Mitochondrial|mitochondrial proteins]] by the [[Coronavirus, SARS associated|Coronavirus,]] occurring at a cellular level.
* The above mechanism supports the lack of dyspnea in proportion to the severity of hypoxemia, on clinical presentation, a phenomenon known as "happy hypoxemia".
* The above mechanism supports the lack of [[dyspnea]] in proportion to the severity of [[hypoxemia]], on clinical presentation, a phenomenon known as "happy hypoxemia".


===Mechanisms of Hypoxemia in COVID-19===
===Mechanisms of Hypoxemia in COVID-19===


* [[Hypoxemia]] in [[COVID-19]] is marked by an increased A-a gradient.  
* [[Hypoxemia]] in [[COVID-19]] is marked by an increased [[Alveolar-arterial gradient|A-a gradient.]]


====Ventilation Perfusion Mismatch====
====Ventilation Perfusion Mismatch====


* V/Q mismatch is typically seen due to [[ARDS]].
*[[Ventilation-perfusion mismatch|V/Q mismatch]] is typically seen due to [[ARDS]].
* Initially the [[lungs]] have good [[compliance]] but there is marked [[hypoxemia]].
* Initially the [[lungs]] have good [[compliance]] but there is marked [[hypoxemia]].
* This can be explained by abnormal [[vasoregulation]] which disrupts the physiological, hypoxic pulmonary vasoconstriction response to [[hypoxemia]].<ref name="pmid32291463">{{cite journal |vauthors=Gattinoni L, Chiumello D, Caironi P, Busana M, Romitti F, Brazzi L, Camporota L |title=COVID-19 pneumonia: different respiratory treatments for different phenotypes? |journal=Intensive Care Med |volume=46 |issue=6 |pages=1099–1102 |date=June 2020 |pmid=32291463 |pmc=7154064 |doi=10.1007/s00134-020-06033-2 |url=}}</ref>
* This can be explained by abnormal [[vasoregulation]] which disrupts the physiological, hypoxic pulmonary [[vasoconstriction]] response to [[hypoxemia]].<ref name="pmid32291463">{{cite journal |vauthors=Gattinoni L, Chiumello D, Caironi P, Busana M, Romitti F, Brazzi L, Camporota L |title=COVID-19 pneumonia: different respiratory treatments for different phenotypes? |journal=Intensive Care Med |volume=46 |issue=6 |pages=1099–1102 |date=June 2020 |pmid=32291463 |pmc=7154064 |doi=10.1007/s00134-020-06033-2 |url=}}</ref>
* If [[hypoxemia]] is not addressed early, the patient increases inspiratory efforts which exerts more [[pressure]] on the tissues, causing a rise in the transpulmonary pressure.
* If [[hypoxemia]] is not addressed early, the patient increases inspiratory efforts which exerts more [[pressure]] on the [[tissues]], causing a rise in the [[Transpulmonary pressure|transpulmonary]] pressure.
* These changes in lung dynamics promote capillary leakage which further increases alveolar exudates and the lungs become poorly compliant.
* These changes in lung dynamics promote [[Capillary leak|capillary leakage]] which further increases alveolar [[Exudate|exudates]] and the [[lungs]] become poorly compliant.
* The ventilation-perfusion mismatch, therefore, progresses from a high Va/Q ratio to a low Va/Q ratio.
* The [[Ventilation-perfusion mismatch pathophysiology|ventilation-perfusion mismatch]], therefore, progresses from a high [[Ventilation/perfusion ratio|Va/Q ratio]] to a low [[Ventilation/perfusion ratio|Va/Q ratio]].
* Pulmonary vascular thrombi also contribute to Va/Q mismatch.
* Pulmonary vascular [[thrombi]] also contribute to [[Ventilation-perfusion mismatch|Va/Q mismatch]].
* Both acute pulmonary embolism and small vessel thrombosis are seen on autopsy.
* Both acute [[pulmonary embolism]] and small vessel [[thrombosis]] are seen on autopsy.
* This increases the alveolar dead space causing Va/Q mismatch.
* This increases the alveolar [[dead space]] causing [[Ventilation-perfusion mismatch pathophysiology|Va/Q mismatch]].


====Intrapulmonary Shunt====
====Intrapulmonary Shunt====
* Blood is shunted from the poorly ventilated alveoli to well-aerated lung regions.
*[[Blood]] is shunted from the poorly [[Ventilation|ventilated]] [[Pulmonary alveolus|alveoli]] to well-aerated [[lung]] regions.
* Intra-cardiac shunts can be detected in 20% of the patients being treated for ARDS. Patent foramen ovale opens due to positive pressure ventilation.<ref name="Mekontso DessapBoissier2010">{{cite journal|last1=Mekontso Dessap|first1=Armand|last2=Boissier|first2=Florence|last3=Leon|first3=Rusel|last4=Carreira|first4=Serge|last5=Roche Campo|first5=Ferran|last6=Lemaire|first6=François|last7=Brochard|first7=Laurent|title=Prevalence and prognosis of shunting across patent foramen ovale during acute respiratory distress syndrome*|journal=Critical Care Medicine|volume=38|issue=9|year=2010|pages=1786–1792|issn=0090-3493|doi=10.1097/CCM.0b013e3181eaa9c8}}</ref><ref name="pmid32634734">{{cite journal |vauthors=Fisher HK |title=Hypoxemia in COVID-19 patients: An hypothesis |journal=Med. Hypotheses |volume=143 |issue= |pages=110022 |date=June 2020 |pmid=32634734 |pmc=7308039 |doi=10.1016/j.mehy.2020.110022 |url=}}</ref>
* Intra-cardiac shunts can be detected in 20% of the patients being treated for [[Acute respiratory distress syndrome|ARDS]]. [[Patent foramen ovale]] opens due to [[positive pressure ventilation]].<ref name="Mekontso DessapBoissier2010">{{cite journal|last1=Mekontso Dessap|first1=Armand|last2=Boissier|first2=Florence|last3=Leon|first3=Rusel|last4=Carreira|first4=Serge|last5=Roche Campo|first5=Ferran|last6=Lemaire|first6=François|last7=Brochard|first7=Laurent|title=Prevalence and prognosis of shunting across patent foramen ovale during acute respiratory distress syndrome*|journal=Critical Care Medicine|volume=38|issue=9|year=2010|pages=1786–1792|issn=0090-3493|doi=10.1097/CCM.0b013e3181eaa9c8}}</ref><ref name="pmid32634734">{{cite journal |vauthors=Fisher HK |title=Hypoxemia in COVID-19 patients: An hypothesis |journal=Med. Hypotheses |volume=143 |issue= |pages=110022 |date=June 2020 |pmid=32634734 |pmc=7308039 |doi=10.1016/j.mehy.2020.110022 |url=}}</ref>
* Shunt can be differentiated from Va/Q mismatch due to the lack of response to supplemental oxygen.
* Shunt can be differentiated from [[Ventilation-perfusion mismatch|Va/Q mismatch]] due to the lack of response to supplemental [[oxygen]].


====Diffusion Impairment====
====Diffusion Impairment====
* Persistent hypoxemia has been seen in recovered patients, due to postviral fibrosis.<ref name="GeorgeWells2020">{{cite journal|last1=George|first1=Peter M|last2=Wells|first2=Athol U|last3=Jenkins|first3=R Gisli|title=Pulmonary fibrosis and COVID-19: the potential role for antifibrotic therapy|journal=The Lancet Respiratory Medicine|year=2020|issn=22132600|doi=10.1016/S2213-2600(20)30225-3}}</ref>
* Persistent [[hypoxemia]] has been seen in recovered patients, due to postviral [[fibrosis]].<ref name="GeorgeWells2020">{{cite journal|last1=George|first1=Peter M|last2=Wells|first2=Athol U|last3=Jenkins|first3=R Gisli|title=Pulmonary fibrosis and COVID-19: the potential role for antifibrotic therapy|journal=The Lancet Respiratory Medicine|year=2020|issn=22132600|doi=10.1016/S2213-2600(20)30225-3}}</ref>


* A study was conducted in China to measure DLCO of discharged patients. The researchers concluded that the decrease in DLCO correlated with the severity of pneumonia on admission.<ref name="MoJian2020">{{cite journal|last1=Mo|first1=Xiaoneng|last2=Jian|first2=Wenhua|last3=Su|first3=Zhuquan|last4=Chen|first4=Mu|last5=Peng|first5=Hui|last6=Peng|first6=Ping|last7=Lei|first7=Chunliang|last8=Chen|first8=Ruchong|last9=Zhong|first9=Nanshan|last10=Li|first10=Shiyue|title=Abnormal pulmonary function in COVID-19 patients at time of hospital discharge|journal=European Respiratory Journal|volume=55|issue=6|year=2020|pages=2001217|issn=0903-1936|doi=10.1183/13993003.01217-2020}}</ref>
* A study was conducted in China to measure [[DLCO]] of discharged patients. The researchers concluded that the decrease in [[DLCO]] correlated with the severity of [[pneumonia]] on admission.<ref name="MoJian2020">{{cite journal|last1=Mo|first1=Xiaoneng|last2=Jian|first2=Wenhua|last3=Su|first3=Zhuquan|last4=Chen|first4=Mu|last5=Peng|first5=Hui|last6=Peng|first6=Ping|last7=Lei|first7=Chunliang|last8=Chen|first8=Ruchong|last9=Zhong|first9=Nanshan|last10=Li|first10=Shiyue|title=Abnormal pulmonary function in COVID-19 patients at time of hospital discharge|journal=European Respiratory Journal|volume=55|issue=6|year=2020|pages=2001217|issn=0903-1936|doi=10.1183/13993003.01217-2020}}</ref>


==Causes==
==Causes==
*Hypoxemia in COVID-19 patients is associated with the development of the following:
*[[Hypoxemia]] in COVID-19 patients is associated with the development of the following:
** Acute Respiratory Distress Syndrome
**[[Acute respiratory distress syndrome|Acute Respiratory Distress Syndrome]]
** Microvascular Thrombi<ref>{{cite journal|doi=10.1016/ S1473-3099(20)30367-4}}</ref>
** Microvascular [[Thrombi]]<ref>{{cite journal|doi=10.1016/ S1473-3099(20)30367-4}}</ref>
** COVID-19 Pneumonia
** COVID-19 Pneumonia (see [[COVID-19-associated pneumonia|Covid-19-associated pneumonia]])


==Differentiating COVID-19-associated hypoxemia from other Diseases==
==Differentiating COVID-19-associated hypoxemia from other Diseases==
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==Epidemiology and Demographics==
==Epidemiology and Demographics==
* COVID-19 is seen more commonly in men.
*[[COVID-19]] is seen more commonly in men.
* 80% of patients with Coronavirus disease develop a respiratory infection.<ref>{{cite journal|doi=10.1161/CIRCULATIONAHA.120.047915Circulation}}</ref>
* 80% of patients with [[Coronavirus]] disease develop a respiratory infection.<ref>{{cite journal|doi=10.1161/CIRCULATIONAHA.120.047915Circulation}}</ref>
* According to a study conducted in Hubei, China, 5%-25% of patients admitted in hospital for COVID-19 needed ICU admission. Of the patients admitted in ICU, 60%-70% developed ARDS.<ref name="GreenlandMichelow2020">{{cite journal|last1=Greenland|first1=John R.|last2=Michelow|first2=Marilyn D.|last3=Wang|first3=Linlin|last4=London|first4=Martin J.|title=COVID-19 Infection|journal=Anesthesiology|volume=132|issue=6|year=2020|pages=1346–1361|issn=0003-3022|doi=10.1097/ALN.0000000000003303}}</ref>
* According to a study conducted in Hubei, China, 5%-25% of patients admitted in hospital for COVID-19 needed ICU admission. Of the patients admitted in ICU, 60%-70% developed [[Acute respiratory distress syndrome|ARDS.]]<ref name="GreenlandMichelow2020">{{cite journal|last1=Greenland|first1=John R.|last2=Michelow|first2=Marilyn D.|last3=Wang|first3=Linlin|last4=London|first4=Martin J.|title=COVID-19 Infection|journal=Anesthesiology|volume=132|issue=6|year=2020|pages=1346–1361|issn=0003-3022|doi=10.1097/ALN.0000000000003303}}</ref>
* There is no geographical association of hypoxemia in COVID-19.
* There is no geographical association of [[hypoxemia]] in [[COVID-19|COVID-19.]]


==Risk Factors==
==Risk Factors==
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*The [[diagnosis]] of [[COVID-19]] associated [[hypoxemia]] can be established by the following investigations:
*The [[diagnosis]] of [[COVID-19]] associated [[hypoxemia]] can be established by the following investigations:
**Reverse Transcriptase- Polymerase Chain Reaction from nasal or throat swab sample positive for [[COVID-19]]
**[[Polymerase chain reaction|Reverse Transcriptase- Polymerase Chain Reaction]] from nasal or throat swab sample positive for [[COVID-19]]
**Chest Tomography images showing peripheral and bilateral ground-glass opacities
**[[CT-scans|Chest Tomography]] images showing peripheral and bilateral ground-glass opacities
**[[Arterial Blood gas]] showing Pa02 (Partial Pressure of oxygen) below 60mmHg
**[[Arterial blood gases|Arterial Blood gas]] showing Pa02 (Partial Pressure of oxygen) below 60mmHg
**Oxygen Saturation below 90% on Pulse oximeter
**Oxygen Saturation below 90% on Pulse oximeter


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===Imaging Studies===
===Imaging Studies===
* Computed Tomography shows consolidation and bilateral ground glass opacities located peripherally.
*[[Ct scan|Computed Tomography]] shows consolidation and bilateral ground glass opacities located peripherally.


==Treatment==
==Treatment==
===Treatment of Hypoxemia due to COVID-19===
===Treatment of Hypoxemia due to COVID-19===
====Overview====
====Overview====
* Oxygen target should be Spo2>90%
*[[Oxygen]] target should be Spo2>90%
* Some centres have suggested to restrict [[oxygen]] supplementation by [[High Flow Nasal Cannula]](HFNC) and [[Non Invasive Ventilation]]( Bipap, CPAP) as they generate [[aerosol]] and pose a threat to the healthcare workers<ref name="pmid32291505">{{cite journal |vauthors=Kluge S, Janssens U, Welte T, Weber-Carstens S, Marx G, Karagiannidis C |title=German recommendations for critically ill patients with COVID‑19 |journal=Med Klin Intensivmed Notfmed |volume= |issue= |pages= |date=April 2020 |pmid=32291505 |pmc=7155395 |doi=10.1007/s00063-020-00689-w |url=}}</ref>
* Some centres have suggested to restrict [[oxygen]] supplementation by [[High Flow Nasal Cannula]](HFNC) and [[Non Invasive Ventilation]]( Bipap, CPAP) as they generate [[aerosol]] and pose a threat to the healthcare workers<ref name="pmid32291505">{{cite journal |vauthors=Kluge S, Janssens U, Welte T, Weber-Carstens S, Marx G, Karagiannidis C |title=German recommendations for critically ill patients with COVID‑19 |journal=Med Klin Intensivmed Notfmed |volume= |issue= |pages= |date=April 2020 |pmid=32291505 |pmc=7155395 |doi=10.1007/s00063-020-00689-w |url=}}</ref>
* Invasive mechanical Ventilation by early intubation is recommended for [[hypoxemia]] not responding to [[Non Invasive Ventilation]]
* Invasive mechanical Ventilation by early [[intubation]] is recommended for [[hypoxemia]] not responding to [[Non Invasive Ventilation]]


====Venturi Mask====
====Venturi Mask====
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====High Flow Nasal Oxygenation(HFNO)====
====High Flow Nasal Oxygenation(HFNO)====
* Use is recommended in negative pressure environment due to aerosol generation
* Use is recommended in negative pressure environment due to [[Aerosols|aerosol]] generation
* Apply if SpO2< 92%
* Apply if SpO2< 92%
* No response to [[Oxygen]] delivery is observed via [[nasal cannula]], face mask or [[Venturi mask]]
* No response to [[Oxygen]] delivery is observed via [[nasal cannula]], face mask or [[Venturi mask]]
* Use [[Oxygen]] flow of 30-50L/min
* Use [[Oxygen]] flow of 30-50L/min
* Keep FiO2 between 50%-70%
* Keep [[FiO2]] between 50%-70%


====Non Invasive Ventilation====
====Non Invasive Ventilation====
* Used when [[dyspnea]]/ [[hypoxemia]] does not improve within 1 hour of HFNO used at 50L/min and FiO2>70%  
* Used when [[dyspnea]]/ [[hypoxemia]] does not improve within 1 hour of HFNO used at 50L/min and FiO2>70%  
* Recommended to use pressure setting of 8-10cm Hg and [[FiO2]]of 60%
* Recommended to use pressure setting of 8-10cm Hg and [[FiO2]]of 60%
* Monitor with hourly [[Arterial Blood Gas]] sampling
* Monitor with hourly [[Arterial blood gas|Arterial Blood Gas]] sampling
* Use for 4-6 hours, allowing 1 hour break for feeding
* Use for 4-6 hours, allowing 1 hour break for feeding


====Invasive Mechanical ventilation====
====Invasive Mechanical ventilation====
* Performed in patients with severe [[hypoxemia]] ( Pa02/FiO2 <200) and failure of NIV
* Performed in patients with severe [[hypoxemia]] ( Pa02/FiO2 <200) and failure of NIV
* Rapid Sequence intubation is preferred to avoid aerosolisation by Bag mask ventilation
* Rapid Sequence [[intubation]] is preferred to avoid [[Aerosols|aerosolisation]] by Bag mask ventilation
* Lung protective Ventilation is used in patients with severe ARDS
* Lung protective Ventilation is used in patients with severe [[Acute respiratory distress syndrome|ARDS]]
* [[Tidal Volume]] at 4-6ml/kg of body weight
*[[Tidal volume|Tidal Volume]] at 4-6ml/kg of body weight
* [[Plateau Pressure]](Pplat) < 30cm H2O
* Plateau Pressure(Pplat) < 30cm H2O
* [[High Positive End Expiratory Pressure]] (PEEP) is recommended to keep [[driving pressure]](Pplat-PEEP)<14cm H2O
* High [[Positive-end expiratory pressure|Positive End Expiratory Pressure]] (PEEP) is recommended to keep [[driving pressure]](Pplat-PEEP)<14cm H2O


====Prone Position====
====Prone Position====
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* Recommended for total duration of 12-16 hours daily
* Recommended for total duration of 12-16 hours daily
* Not recommended for infants less than 6 months of age
* Not recommended for infants less than 6 months of age
* It decreases Va/Q mismatch by eliminating gravitational forces exerted on lung portion by [[mediastinal]] structures, allowing maximum [[lung]] recruitment when positive pressure mechanical ventilation is applied<ref name="pmid32484966">{{cite journal |vauthors=Lindahl SGE |title=Using the prone position could help to combat the development of fast hypoxia in some patients with COVID-19 |journal=Acta Paediatr. |volume=109 |issue=8 |pages=1539–1544 |date=August 2020 |pmid=32484966 |pmc=7301016 |doi=10.1111/apa.15382 |url=}}</ref>
* It decreases [[Ventilation-perfusion mismatch|Va/Q mismatch]] by eliminating gravitational forces exerted on [[lung]] portion by [[mediastinal]] structures, allowing maximum [[lung]] recruitment when positive pressure mechanical ventilation is applied<ref name="pmid32484966">{{cite journal |vauthors=Lindahl SGE |title=Using the prone position could help to combat the development of fast hypoxia in some patients with COVID-19 |journal=Acta Paediatr. |volume=109 |issue=8 |pages=1539–1544 |date=August 2020 |pmid=32484966 |pmc=7301016 |doi=10.1111/apa.15382 |url=}}</ref>
* Meta analysis have shown that Prone positioning can decrease mortality when used for long duration within intial 48hours in severe ARDS.<ref name="Mora-ArteagaBernal-Ramírez2015">{{cite journal|last1=Mora-Arteaga|first1=J.A.|last2=Bernal-Ramírez|first2=O.J.|last3=Rodríguez|first3=S.J.|title=The effects of prone position ventilation in patients with acute respiratory distress syndrome. A systematic review and metaanalysis|journal=Medicina Intensiva (English Edition)|volume=39|issue=6|year=2015|pages=359–372|issn=21735727|doi=10.1016/j.medine.2014.11.004}}</ref>
* Meta analysis have shown that [[Prone position|Prone positioning]] can decrease [[mortality]] when used for long duration within intial 48hours in severe [[Acute respiratory distress syndrome|ARDS]].<ref name="Mora-ArteagaBernal-Ramírez2015">{{cite journal|last1=Mora-Arteaga|first1=J.A.|last2=Bernal-Ramírez|first2=O.J.|last3=Rodríguez|first3=S.J.|title=The effects of prone position ventilation in patients with acute respiratory distress syndrome. A systematic review and metaanalysis|journal=Medicina Intensiva (English Edition)|volume=39|issue=6|year=2015|pages=359–372|issn=21735727|doi=10.1016/j.medine.2014.11.004}}</ref>
* In a pilot study performed in New York emergency, awake proning was associated with improved oxygen saturations in non intubated patients.<ref name="pmid32320506">{{cite journal |vauthors=Caputo ND, Strayer RJ, Levitan R |title=Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED's Experience During the COVID-19 Pandemic |journal=Acad Emerg Med |volume=27 |issue=5 |pages=375–378 |date=May 2020 |pmid=32320506 |pmc=7264594 |doi=10.1111/acem.13994 |url=}}</ref>
* In a pilot study performed in New York emergency, awake [[Prone position|proning]] was associated with improved [[Oxygen-16|oxygen]] saturations in non intubated patients.<ref name="pmid32320506">{{cite journal |vauthors=Caputo ND, Strayer RJ, Levitan R |title=Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED's Experience During the COVID-19 Pandemic |journal=Acad Emerg Med |volume=27 |issue=5 |pages=375–378 |date=May 2020 |pmid=32320506 |pmc=7264594 |doi=10.1111/acem.13994 |url=}}</ref>
* Position should be changed every 2 hours to prevent pressure ulcer formation
* Position should be changed every 2 hours to prevent pressure ulcer formation


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* PaO2/Fio2 < 50mmHg for more than 1 hour
* PaO2/Fio2 < 50mmHg for more than 1 hour
* PaO2/FiO2 < 80mmHg for more than 2 hours
* PaO2/FiO2 < 80mmHg for more than 2 hours
* [[Arterial Blood Gas]] indicating pH<7.2 persisting for more than 1 hour, due to uncompensated [[respiratory acidosis]]
*[[Arterial blood gases|Arterial Blood Gas]] indicating pH<7.2 persisting for more than 1 hour, due to uncompensated [[respiratory acidosis]]
* It is has shown improved clinical outcome in severe COVID-19<ref name="pmid32243266">{{cite journal |vauthors=Li X, Guo Z, Li B, Zhang X, Tian R, Wu W, Zhang Z, Lu Y, Chen N, Clifford SP, Huang J |title=Extracorporeal Membrane Oxygenation for Coronavirus Disease 2019 in Shanghai, China |journal=ASAIO J. |volume=66 |issue=5 |pages=475–481 |date=May 2020 |pmid=32243266 |pmc=7273861 |doi=10.1097/MAT.0000000000001172 |url=}}</ref>
* It is has shown improved clinical outcome in severe COVID-19<ref name="pmid32243266">{{cite journal |vauthors=Li X, Guo Z, Li B, Zhang X, Tian R, Wu W, Zhang Z, Lu Y, Chen N, Clifford SP, Huang J |title=Extracorporeal Membrane Oxygenation for Coronavirus Disease 2019 in Shanghai, China |journal=ASAIO J. |volume=66 |issue=5 |pages=475–481 |date=May 2020 |pmid=32243266 |pmc=7273861 |doi=10.1097/MAT.0000000000001172 |url=}}</ref>


Revision as of 20:51, 13 July 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rija Gul, M.B.B.S.

Synonyms and keywords:

Overview

COVID-19 emerged as a pandemic, after its outbreak in Wuhan, China in December 2019. It is caused by a new type of Coronavirus (novel Coronavirus), based on its genomic study. The virus binds to ACE-2 receptors on Type 2 pneumocytes in the lower respiratory tract. Its clinical presentation varies from asymptomatic disease to severe acute respiratory distress syndrome (ARDS).Hypoxemia is present with an increased A-a gradient. Hypoxemia is diagnosed by Pa02<60mmHg in a sample of Arterial Blood Gas. Mechanisms involved in hypoxemia are widely reported to be due to ventilation perfusion mismatch and intrapulmonary shunting. Diffusion impairment can cause hypoxemia during recovery period due to fibrosis in the lung. Older age, male sex, hypertension and dyspnea have been identified as risk factors for development of hypoxemia in COVID-19. Complications of hypoxemia include acute respiratory failure and multi-organ failure. Treatment is based on oxygen supplementation to keep target Spo2> 90%.

Historical Perspective

  • In December 2019, novel coronavirus outbreak occurred in Wuhan, China[1]
  • On 11th March 2020, it was declared as Pandemic by WHO.

Classification

  • There is no established system for the classification of COVID-19 associated hypoxemia.

Pathophysiology

Mechanisms of Hypoxemia in COVID-19

Ventilation Perfusion Mismatch

Intrapulmonary Shunt

Diffusion Impairment

  • A study was conducted in China to measure DLCO of discharged patients. The researchers concluded that the decrease in DLCO correlated with the severity of pneumonia on admission.[6]

Causes

Differentiating COVID-19-associated hypoxemia from other Diseases

Dyspnea is not a prominent feature of hypoxemia due to COVID-19 in contrast to other diseases causing hypoxemia[4]

Epidemiology and Demographics

  • COVID-19 is seen more commonly in men.
  • 80% of patients with Coronavirus disease develop a respiratory infection.[8]
  • According to a study conducted in Hubei, China, 5%-25% of patients admitted in hospital for COVID-19 needed ICU admission. Of the patients admitted in ICU, 60%-70% developed ARDS.[9]
  • There is no geographical association of hypoxemia in COVID-19.

Risk Factors

  • According to a study conducted in Wuhan, China, the following risk factors were identified in patients presenting with hypoxemia(Spo2< 90%):[10]

Natural History, Complications, and Prognosis

Diagnosis

Diagnostic Study of Choice

History and Symptoms

Laboratory Findings

Imaging Studies

  • Computed Tomography shows consolidation and bilateral ground glass opacities located peripherally.

Treatment

Treatment of Hypoxemia due to COVID-19

Overview

Venturi Mask

  • SpO2< 93%-94%
  • Respiratory rate > 28-30 breaths per minute
  • Deliver oxygen via 40% Venturi mask
  • If response is seen in 5-10 minutes, continue treatment for the next 6 hours
  • NIV is recommended if there is no improvement

High Flow Nasal Oxygenation(HFNO)

  • Use is recommended in negative pressure environment due to aerosol generation
  • Apply if SpO2< 92%
  • No response to Oxygen delivery is observed via nasal cannula, face mask or Venturi mask
  • Use Oxygen flow of 30-50L/min
  • Keep FiO2 between 50%-70%

Non Invasive Ventilation

  • Used when dyspnea/ hypoxemia does not improve within 1 hour of HFNO used at 50L/min and FiO2>70%
  • Recommended to use pressure setting of 8-10cm Hg and FiO2of 60%
  • Monitor with hourly Arterial Blood Gas sampling
  • Use for 4-6 hours, allowing 1 hour break for feeding

Invasive Mechanical ventilation

Prone Position

  • Recommended in severe ARDS(PaO2/FiO2<150) along with Invasive Mechanical ventilation
  • Recommended for total duration of 12-16 hours daily
  • Not recommended for infants less than 6 months of age
  • It decreases Va/Q mismatch by eliminating gravitational forces exerted on lung portion by mediastinal structures, allowing maximum lung recruitment when positive pressure mechanical ventilation is applied[16]
  • Meta analysis have shown that Prone positioning can decrease mortality when used for long duration within intial 48hours in severe ARDS.[17]
  • In a pilot study performed in New York emergency, awake proning was associated with improved oxygen saturations in non intubated patients.[18]
  • Position should be changed every 2 hours to prevent pressure ulcer formation

Extra Corporeal Membrane Oxygenation

  • Used in refractory hypoxemic respiratory failure
  • PaO2/Fio2 < 50mmHg for more than 1 hour
  • PaO2/FiO2 < 80mmHg for more than 2 hours
  • Arterial Blood Gas indicating pH<7.2 persisting for more than 1 hour, due to uncompensated respiratory acidosis
  • It is has shown improved clinical outcome in severe COVID-19[19]

Prevention

Primary Prevention

  • Infection with COVID-19 can be prevented by practicing the following:
    • Social distancing
    • Frequent hand washing
    • Personal Hygiene
    • Wearing mask

References

  1. ↑ Wu YC, Chen CS, Chan YJ (March 2020). "The outbreak of COVID-19: An overview". J Chin Med Assoc. 83 (3): 217–220. doi:10.1097/JCMA.0000000000000270. PMC 7153464 Check |pmc= value (help). PMID 32134861 Check |pmid= value (help).
  2. ↑ Gattinoni L, Chiumello D, Caironi P, Busana M, Romitti F, Brazzi L, Camporota L (June 2020). "COVID-19 pneumonia: different respiratory treatments for different phenotypes?". Intensive Care Med. 46 (6): 1099–1102. doi:10.1007/s00134-020-06033-2. PMC 7154064 Check |pmc= value (help). PMID 32291463 Check |pmid= value (help).
  3. ↑ Mekontso Dessap, Armand; Boissier, Florence; Leon, Rusel; Carreira, Serge; Roche Campo, Ferran; Lemaire, François; Brochard, Laurent (2010). "Prevalence and prognosis of shunting across patent foramen ovale during acute respiratory distress syndrome*". Critical Care Medicine. 38 (9): 1786–1792. doi:10.1097/CCM.0b013e3181eaa9c8. ISSN 0090-3493.
  4. ↑ 4.0 4.1 Fisher HK (June 2020). "Hypoxemia in COVID-19 patients: An hypothesis". Med. Hypotheses. 143: 110022. doi:10.1016/j.mehy.2020.110022. PMC 7308039 Check |pmc= value (help). PMID 32634734 Check |pmid= value (help).
  5. ↑ George, Peter M; Wells, Athol U; Jenkins, R Gisli (2020). "Pulmonary fibrosis and COVID-19: the potential role for antifibrotic therapy". The Lancet Respiratory Medicine. doi:10.1016/S2213-2600(20)30225-3. ISSN 2213-2600.
  6. ↑ Mo, Xiaoneng; Jian, Wenhua; Su, Zhuquan; Chen, Mu; Peng, Hui; Peng, Ping; Lei, Chunliang; Chen, Ruchong; Zhong, Nanshan; Li, Shiyue (2020). "Abnormal pulmonary function in COVID-19 patients at time of hospital discharge". European Respiratory Journal. 55 (6): 2001217. doi:10.1183/13993003.01217-2020. ISSN 0903-1936.
  7. ↑ . doi:10.1016/ S1473-3099(20)30367-4 Check |doi= value (help). Missing or empty |title= (help)
  8. ↑ . doi:10.1161/CIRCULATIONAHA.120.047915Circulation. Missing or empty |title= (help)
  9. ↑ Greenland, John R.; Michelow, Marilyn D.; Wang, Linlin; London, Martin J. (2020). "COVID-19 Infection". Anesthesiology. 132 (6): 1346–1361. doi:10.1097/ALN.0000000000003303. ISSN 0003-3022.
  10. ↑ Xie, Jiang; Covassin, Naima; Fan, Zhengyang; Singh, Prachi; Gao, Wei; Li, Guangxi; Kara, Tomas; Somers, Virend K. (2020). "Association Between Hypoxemia and Mortality in Patients With COVID-19". Mayo Clinic Proceedings. 95 (6): 1138–1147. doi:10.1016/j.mayocp.2020.04.006. ISSN 0025-6196.
  11. ↑ Greenland JR, Michelow MD, Wang L, London MJ (June 2020). "COVID-19 Infection: Implications for Perioperative and Critical Care Physicians". Anesthesiology. 132 (6): 1346–1361. doi:10.1097/ALN.0000000000003303. PMC 7155909 Check |pmc= value (help). PMID 32195698 Check |pmid= value (help).
  12. ↑ Yang X, Yu Y, Xu J, Shu H, Xia J, Liu H, Wu Y, Zhang L, Yu Z, Fang M, Yu T, Wang Y, Pan S, Zou X, Yuan S, Shang Y (May 2020). "Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study". Lancet Respir Med. 8 (5): 475–481. doi:10.1016/S2213-2600(20)30079-5. PMC 7102538 Check |pmc= value (help). PMID 32105632 Check |pmid= value (help).
  13. ↑ Pan F, Yang L, Li Y, Liang B, Li L, Ye T, Li L, Liu D, Gui S, Hu Y, Zheng C (2020). "Factors associated with death outcome in patients with severe coronavirus disease-19 (COVID-19): a case-control study". Int J Med Sci. 17 (9): 1281–1292. doi:10.7150/ijms.46614. PMC 7294915 Check |pmc= value (help). PMID 32547323 Check |pmid= value (help).
  14. ↑ Zhou F, Yu T, Du R, Fan G, Liu Y, Liu Z, Xiang J, Wang Y, Song B, Gu X, Guan L, Wei Y, Li H, Wu X, Xu J, Tu S, Zhang Y, Chen H, Cao B (March 2020). "Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study". Lancet. 395 (10229): 1054–1062. doi:10.1016/S0140-6736(20)30566-3. PMC 7270627 Check |pmc= value (help). PMID 32171076 Check |pmid= value (help).
  15. ↑ Kluge S, Janssens U, Welte T, Weber-Carstens S, Marx G, Karagiannidis C (April 2020). "German recommendations for critically ill patients with COVID‑19". Med Klin Intensivmed Notfmed. doi:10.1007/s00063-020-00689-w. PMC 7155395 Check |pmc= value (help). PMID 32291505 Check |pmid= value (help).
  16. ↑ Lindahl S (August 2020). "Using the prone position could help to combat the development of fast hypoxia in some patients with COVID-19". Acta Paediatr. 109 (8): 1539–1544. doi:10.1111/apa.15382. PMC 7301016 Check |pmc= value (help). PMID 32484966 Check |pmid= value (help). Vancouver style error: initials (help)
  17. ↑ Mora-Arteaga, J.A.; Bernal-Ramírez, O.J.; Rodríguez, S.J. (2015). "The effects of prone position ventilation in patients with acute respiratory distress syndrome. A systematic review and metaanalysis". Medicina Intensiva (English Edition). 39 (6): 359–372. doi:10.1016/j.medine.2014.11.004. ISSN 2173-5727.
  18. ↑ Caputo ND, Strayer RJ, Levitan R (May 2020). "Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED's Experience During the COVID-19 Pandemic". Acad Emerg Med. 27 (5): 375–378. doi:10.1111/acem.13994. PMC 7264594 Check |pmc= value (help). PMID 32320506 Check |pmid= value (help).
  19. ↑ Li X, Guo Z, Li B, Zhang X, Tian R, Wu W, Zhang Z, Lu Y, Chen N, Clifford SP, Huang J (May 2020). "Extracorporeal Membrane Oxygenation for Coronavirus Disease 2019 in Shanghai, China". ASAIO J. 66 (5): 475–481. doi:10.1097/MAT.0000000000001172. PMC 7273861 Check |pmc= value (help). PMID 32243266 Check |pmid= value (help).


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