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==Overview==
==Overview==
Laboratory findings consistent with the diagnosis of ARDS include severe [[hypoxemia]] (low PaO<sub>2</sub> with decreased P/F ratio) and [[hypercapnia]] (increased PaCO<sub>2</sub>) secondary to an increase in pulmonary dead space.


==Laboratory Findings==
==Laboratory Findings==
Laboratory findings consistent with the diagnosis of ARDS include an [[PaO2|arterial partial pressure of oxygen (PaO<sub>2</sub>)]] that is inappropriately low relative to the [[FiO2|fraction of inspired oxygen (FIO<sub>2</sub>)]]. This is referred to as the PaO<sub>2</sub>/FIO<sub>2</sub> ratio (sometimes abbreviated as ''P/F ratio'') and is calculated by dividing the PaO<sub>2</sub> (in mmHg) by the FIO<sub>2</sub> (as a decimal rather than a percentage). Below are three examples of P/F ratio calculations that correspond to the three different [[Acute respiratory distress syndrome classification|degrees of ARDS severity]]:
*A patient with a '''PaO<sub>2</sub> of 80 mm Hg''' who is [[mechanical ventilation|mechanically ventilated]] with an '''FIO<sub>2</sub> of 35%''' and a '''PEEP of 5 cm H<sub>2</sub>O''' has a '''PaO<sub>2</sub>/FIO<sub>2</sub> ratio of 80/0.35 = 229''' ([[Acute respiratory distress syndrome diagnostic criteria|''mild ARDS'']])
*A patient with a '''PaO<sub>2</sub> of 80 mm Hg''' who is [[mechanical ventilation|mechanically ventilated]] with an '''FIO<sub>2</sub> of 50%''' and a '''PEEP of 5 cm H<sub>2</sub>O''' has a '''PaO<sub>2</sub>/FIO<sub>2</sub> ratio of 80/0.40 = 160''' ([[Acute respiratory distress syndrome diagnostic criteria|''moderate ARDS'']])
*A patient with a '''PaO<sub>2</sub> of 80 mm Hg''' who is [[mechanical ventilation|mechanically ventilated]] with an '''FIO<sub>2</sub> of 80%''' and a '''PEEP of 5 cm H<sub>2</sub>O''' has a '''PaO<sub>2</sub>/FIO<sub>2</sub> ratio of 80/0.80 = 100''' ([[Acute respiratory distress syndrome diagnostic criteria|''severe ARDS'']])


Tests used to diagnose ARDS include:
In addition to severe [[hypoxemia]], [[hypercapnia]] (increased PaCO<sub>2</sub>) secondary to an increased pulmonary dead space may also be present.<ref>{{cite book | last = Kasper | first = Dennis | title = Harrison's principles of internal medicine | publisher = McGraw Hill Education | location = New York | year = 2015 | isbn = 978-0071802154 }}</ref>


* Arterial blood gas
==Additional Laboratory Tests==
* Bronchoscopy
Other notable diagnostic findings are those that support an underlying diagnosis that may have led to the development of ARDS (e.g., positive [[blood cultures]] and an elevated [[white blood cell]] count in a [[Sepsis|septic patient]] or an elevated [[lipase]] in a patient with [[acute pancreatitis]]). Additional laboratory tests that may be helpful in diagnosing the underlying cause of ARDS include:
* CBC and blood chemistries
*[[Arterial blood gas|Arterial blood gas analysis]]
* Chest x-ray
*[[CBC|Complete blood count (CBC) with differential]]
* Sputum cultures and analysis
*[[Comprehensive metabolic panel]] ([[BMP|serum electrolytes]], [[BUN|blood urea nitrogen]] and [[creatinine]], and [[LFT|tests of liver function]])
*Coagulation studies ([[partial thromboplastin time]] and [[prothrombin time]] with [[international normalized ratio]])
*[[Blood culture|Blood]], [[Sputum culture|sputum]], and [[Urine culture|urine cultures]]
*[[Lactic acidosis|Serum lactate level]]
 
Further testing should be guided by clinical suspicion and the patient's medical history. These laboratory tests include:
*[[Lipase|Serum lipase level]]
*Urine or blood [[toxicology]] tests
*[[Blood alcohol content|Blood alcohol level]]
*[[HIV|Human immunodeficiency virus (HIV)]] test
*[[Viral pneumonia|Respiratory virus]] screen (direct fluorescent antibody [DFA] or [[polymerase chain reaction]] [PCR] assay)
*[[Influenza virus]] testing
*[[Fungus|Fungal]] cultures
*Tests for [[Atypical pneumonia|atypical pathogens that may cause pneumonia]]:<ref name="pmidPMID: 30872586">{{cite journal| author=Matthay MA, Zemans RL, Zimmerman GA, Arabi YM, Beitler JR, Mercat A | display-authors=etal| title=Acute respiratory distress syndrome. | journal=Nat Rev Dis Primers | year= 2019 | volume= 5 | issue= 1 | pages= 18 | pmid=PMID: 30872586 | doi=10.1038/s41572-019-0069-0 | pmc=6709677 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=30872586  }} </ref>
:*[[Legionella pneumophila|''Legionella pneumophila'']] culture and urine [[antigen]] testing
:*[[Mycoplasma pneumoniae|''Mycoplasma pneumoniae'']] culture and [[antibody titers]]
:*[[Pneumocystis jirovecii|''Pneumocystis jirovecii'']] sputum [[silver stain]] and culture
:*[[Mycobacterium tuberculosis|''Mycobacterium tuberculosis'']] sputum smear for [[AFB|acid-fast bacilli (AFB)]] and culture


==References==
==References==
{{reflist|2}}


{{Reflist|2}}
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Latest revision as of 00:26, 14 October 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Brian Shaller, M.D. [2] Abiodun Akanmode,M.D.[3]

Overview

Laboratory findings consistent with the diagnosis of ARDS include severe hypoxemia (low PaO2 with decreased P/F ratio) and hypercapnia (increased PaCO2) secondary to an increase in pulmonary dead space.

Laboratory Findings

Laboratory findings consistent with the diagnosis of ARDS include an arterial partial pressure of oxygen (PaO2) that is inappropriately low relative to the fraction of inspired oxygen (FIO2). This is referred to as the PaO2/FIO2 ratio (sometimes abbreviated as P/F ratio) and is calculated by dividing the PaO2 (in mmHg) by the FIO2 (as a decimal rather than a percentage). Below are three examples of P/F ratio calculations that correspond to the three different degrees of ARDS severity:

In addition to severe hypoxemia, hypercapnia (increased PaCO2) secondary to an increased pulmonary dead space may also be present.[1]

Additional Laboratory Tests

Other notable diagnostic findings are those that support an underlying diagnosis that may have led to the development of ARDS (e.g., positive blood cultures and an elevated white blood cell count in a septic patient or an elevated lipase in a patient with acute pancreatitis). Additional laboratory tests that may be helpful in diagnosing the underlying cause of ARDS include:

Further testing should be guided by clinical suspicion and the patient's medical history. These laboratory tests include:

References

  1. ↑ Kasper, Dennis (2015). Harrison's principles of internal medicine. New York: McGraw Hill Education. ISBN 978-0071802154.
  2. ↑ Matthay MA, Zemans RL, Zimmerman GA, Arabi YM, Beitler JR, Mercat A; et al. (2019). "Acute respiratory distress syndrome". Nat Rev Dis Primers. 5 (1): 18. doi:10.1038/s41572-019-0069-0. PMC 6709677 Check |pmc= value (help). PMID 30872586 PMID: 30872586 Check |pmid= value (help).
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