Acute respiratory distress syndrome laboratory tests: Difference between revisions
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==Overview== | ==Overview== | ||
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>)]] 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 mmHg) by the FIO<sub>2</sub> (as a decimal rather than a percentage). | |||
==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>)]] 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 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 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 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'']]) | *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'']]) | ||
== | ==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 [[Sepsis|septic patient]] or an elevated [[lipase]] in a patient with [[acute pancreatitis]]). | 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: | ||
*[[Chest X-ray]] | *[[Chest X-ray]] | ||
*[[Arterial blood gas|Arterial blood gas analysis]] | *[[Arterial blood gas|Arterial blood gas analysis]] | ||
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*[[Lactic acidosis|Serum lactate level]] | *[[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]] | *[[Lipase|Serum lipase level]] | ||
*Urine or blood [[toxicology]] tests | *Urine or blood [[toxicology]] tests | ||
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[[Category:Pulmonology]] | [[Category:Pulmonology]] | ||
[[Category:FinalQCRequired]] | |||
{{WikiDoc Help Menu}} | {{WikiDoc Help Menu}} | ||
{{WikiDoc Sources}} | {{WikiDoc Sources}} | ||
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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 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) 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 mmHg) by the FIO2 (as a decimal rather than a percentage).
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) 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 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:
- 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)
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:
- 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
Further testing should be guided by clinical suspicion and the patient's medical history. These laboratory tests include:
- 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