Acute respiratory distress syndrome laboratory tests: Difference between revisions
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__NOTOC__ | __NOTOC__ | ||
{{Acute respiratory distress syndrome}} | {{Acute respiratory distress syndrome}} | ||
{{CMG}} | {{CMG}}, {{AE}} {{BShaller}} | ||
==Overview== | ==Overview== | ||
==Laboratory Findings== | ==Laboratory Findings== | ||
The most important laboratory finding in ARDS is an [[PaO2|arterial partial pressure of oxygen (PaO<sub>2</sub>)]] that is inappropriately low relative to the [[FiO2fraction of inspired oxygen (FIO<sub>2</sub>)]] that is being breathed by the patient. 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 mm Hg) 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'']]) | |||
==Other Useful Diagnostic 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 [[Sepsis|septic patient]] or an elevated [[lipase]] in a patient with [[acute pancreatitis]]). Some lab tests that may be helpful in diagnosing the underlying cause of ARDS include: | |||
*[[Chest X-ray]] | |||
*[[Arterial blood gas|Arterial blood gas analysis]] | |||
*[[CBC|Complete blood count (CBC) with differential]] | |||
*[[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]] | |||
* | Additional testing should be guided by clinical suspicion and the patient's medical history. These may include such tests as: | ||
* | *[[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]]: | |||
:*[[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== | ||
Revision as of 18:22, 26 June 2016
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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]
Overview
Laboratory Findings
The most important laboratory finding in ARDS is an arterial partial pressure of oxygen (PaO2) that is inappropriately low relative to the [[FiO2fraction of inspired oxygen (FIO2)]] that is being breathed by the patient. This is referred to as the PaO2/FIO2 ratio (sometimes abbreviated as P/F ratio) and is calculated by dividing the PaO2 (in mm Hg) 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:
- A patient with a PaO2 of 80 mm Hg who is mechanically ventilated with an FIO2 of 35% and a PEEP of 5 cm H2O has a PaO2/FIO2 ratio of 80/0.35 = 229 (mild ARDS)
- A patient with a PaO2 of 80 mm Hg who is mechanically ventilated with an FIO2 of 50% and a PEEP of 5 cm H2O has a PaO2/FIO2 ratio of 80/0.40 = 160 (moderate ARDS)
- A patient with a PaO2 of 80 mm Hg who is mechanically ventilated with an FIO2 of 80% and a PEEP of 5 cm H2O has a PaO2/FIO2 ratio of 80/0.80 = 100 (severe ARDS)
Other Useful Diagnostic 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). Some lab tests that may be helpful in diagnosing the underlying cause of ARDS include:
- Chest X-ray
- Arterial blood gas analysis
- Complete blood count (CBC) with differential
- Comprehensive metabolic panel (serum electrolytes, blood urea nitrogen and creatinine, and tests of liver function)
- Coagulation studies (partial thromboplastin time and prothrombin time with international normalized ratio)
- Blood, sputum, and urine cultures
- Serum lactate level
Additional testing should be guided by clinical suspicion and the patient's medical history. These may include such tests as:
- Serum lipase level
- Urine or blood toxicology tests
- Blood alcohol level
- Human immunodeficiency virus (HIV) test
- Respiratory virus screen (direct fluorescent antibody [DFA] or polymerase chain reaction [PCR] assay)
- Influenza virus testing
- Fungal cultures
- Tests for atypical pathogens that may cause pneumonia:
- Legionella pneumophila culture and urine antigen testing
- Mycoplasma pneumoniae culture and antibody titers
- Pneumocystis jirovecii sputum silver stain and culture
- Mycobacterium tuberculosis sputum smear for acid-fast bacilli (AFB) and culture