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Latest revision as of 03:50, 20 July 2016

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

Overview

Acute respiratory distress syndrome (ARDS), originally known as adult respiratory distress syndrome (to contrast with neonatal respiratory distress syndrome) is a serious and potentially life-threatening inflammatory lung condition that develops rapidly (usually within 24 to 48 hours) in the setting of sepsis, toxic exposures, adverse drug reactions, trauma, or other critical illnesses. ARDS is characterized by inflammation of the lung parenchyma resulting in increased permeability of the alveolar-capillary membrane, non-cardiogenic pulmonary edema, impaired gas exchange, and decreased lung compliance.

The vast majority of patients with ARDS are managed in an intensive care unit (ICU), where many will require mechanical ventilation at some point during the course of their illness and recovery. ARDS may be categorized as mild, moderate, or severe based on the degree to which oxygenation is impaired; however, all levels of severity carry a high mortality rate if appropriate measures to improve oxygenation and minimize the risk of further lung injury are not taken.^[1]

Historical Perspective

Although the pathologic features of ARDS were first documented in the 19th century, the modern definition of ARDS did not arise until the 1960s. In 2012, the Berlin Definition of ARDS became the standard diagnostic criteria and definition of the syndrome.

Classification

ARDS may be classified according to 2012 Berlin Definition into three subtypes: mild, moderate, and severe. These levels of severity are based on the degree to which oxygenation relative to the amount of supplemental oxygen is being delivered to the patient via positive pressure ventilation.^[1]

Pathophysiology

ARDS is a syndrome of inflammation and increased permeability with the lung parenchyma that leads to loss of type I pneumocytes, impaired gas exchange, inappropriate cell proliferation within alveoli, and, in survivors, fibrosis.

Causes

ARDS may be caused by either direct or indirect insults to the lung. Common causes of ARDS include sepsis, aspiration pneumonitis, and transfusion-related acute lung injury (TRALI).^[2]

Differentiating ARDS from Other Diseases

ARDS must be differentiated from other diseases that cause hypoxemia and pulmonary infiltrates, such as pneumonia, pulmonary contusion, pulmonary edema, and pulmonary hemorrhage. Prior to the development of the Berlin Definition in 2012, a greater emphasis was placed on excluding other potential illnesses prior to making a diagnosis of ARDS. While it is important to recognize and treat and underlying cause of the patient's impaired ventilation and hypoxemia, this search for potential etiologies should not delay any focused efforts to improve oxygenation and ventilation.

Epidemiology and Demographics

The incidence of ARDS in the United States is estimated at approximately 75 cases per 100,000 individuals, which amounts to roughly 150,000 new cases annually.^[3] There is substantial variance in the rates of ARDS between different countries and geographic regions due to factors such as mean life expectancy, prevalence of different risk factors and comorbidities, and access to healthcare.

Risk Factors

The most potent risk factor in the development of ARDS is chronic alcoholism.^[4]^[5] Other risk factors include advanced age, cigarette smoke exposure, and chronic liver disease.

Screening

There are no screening tools for ARDS. The best way to make an early diagnosis of ARDS is to apply the diagnostic criteria to any patient with bilateral pulmonary infiltrates on chest x ray, and new/worsening hypoxemia with an increasing supplemental oxygen requirement in whom a potential cause or risk factor for ARDS exists.

Natural History, Complications, and Prognosis

If left untreated, 70% of patients with ARDS may progress to mortality.^[6] Common complications to ARDS include weakness, impaired lung function, and brain death. Prognosis for patients with ARDS is generally poor and varies based on the severity of illness, the precipitating insult, and medical comorbidities.

Diagnosis

Diagnostic Criteria

Established by the ARDS Definition Task Force in 2012, the Berlin Definition is the most current set of diagnostic criteria for ARDS.

History and Symptoms

The history of a patient with ARDS varies according to the underlying cause. The symptoms of ARDS are fairly nonspecific and typically include rapid breathing, shortness of breath, and rapid heartbeat.

Physical Examination

There are no physical exam findings specific to or pathognomonic of ARDS. The most notable physical exam findings tend to be those of the underlying illness or injury, as well as those of respiratory distress, critical illness, shock, and end organ damage.

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).

Imaging Findings

Electrocardiogram

There are no EKG findings associated with ARDS.

X Ray

X ray is the imaging modality of choice for ARDS. By definition, findings of ARDS on x ray include bilateral airspace opacities.

CT

There are no findings on computed tomography (CT) that are diagnostic of ARDS. CT scan may be used to better define the extent of lung injury or identify potential underlying causes of ARDS.

Echocardiogram

Echocardiography is not especially useful in the diagnosis of ARDS, except under circumstances where cardiogenic pulmonary edema has not yet been excluded.

Other Diagnostic Studies

There are no additional diagnostic studies that are especially useful in the diagnosis and management of ARDS.

Treatment

Medical Therapy

The majority of medical therapies for ARDS are aimed at treating its underlying cause (e.g., antimicrobials for infection).

Mechanical Ventilation Therapy

Most patients with ARDS will require endotracheal intubation and mechanical ventilation at some point during the course of their illness and recovery. A mechanical ventilation strategy using lower tidal volumes of 6 mL/kg predicted body weight and higher levels of positive end-expiratory pressure (PEEP) has been shown to be most effective at improving oxygenation and minimizing volutrauma (injury to stiff lungs resulting from overdistention).

Surgery

Surgical intervention is not recommended for the management of ARDS, except when a procedure might be recommended to treat the underlying cause.

Prevention

There are no primary preventive measures available for ARDS. The only prevention strategy for ARDS is early recognition and treatment of medical conditions that have the potential to cause ARDS.

Secondary prevention strategies for ARDS include aggressive treatment of the underlying cause and the early application of noninvasive methods of oxygenation to slow or prevent the worsening of ARDS and potentially reduce the need for intubation and mechanical ventilation.

References

↑ ^1.0 ^1.1 ARDS Definition Task Force. Ranieri VM, Rubenfeld GD, Thompson BT, Ferguson ND, Caldwell E; et al. (2012). "Acute respiratory distress syndrome: the Berlin Definition". JAMA. 307 (23): 2526–33. doi:10.1001/jama.2012.5669. PMID 22797452.
↑ Pepe PE, Potkin RT, Reus DH, Hudson LD, Carrico CJ (1982). "Clinical predictors of the adult respiratory distress syndrome". Am J Surg. 144 (1): 124–30. PMID 7091520.
↑ Lucas AC (1988). "The future of radiological instrumentation". Health Phys. 55 (2): 191–5. PMID 3410685.
↑ Moss M, Bucher B, Moore FA, Moore EE, Parsons PE (1996). "The role of chronic alcohol abuse in the development of acute respiratory distress syndrome in adults". JAMA. 275 (1): 50–4. PMID 8531287.
↑ Moss M, Burnham EL (2003). "Chronic alcohol abuse, acute respiratory distress syndrome, and multiple organ dysfunction". Crit Care Med. 31 (4 Suppl): S207–12. doi:10.1097/01.CCM.0000057845.77458.25. PMID 12682442.
↑ Reynolds HN, McCunn M, Borg U, Habashi N, Cottingham C, Bar-Lavi Y (1998). "Acute respiratory distress syndrome: estimated incidence and mortality rate in a 5 million-person population base". Crit Care. 2 (1): 29–34. doi:10.1186/cc121. PMC 28999. PMID 11056707.

[pmid22797452-1] 1.0 ^1.1 ARDS Definition Task Force. Ranieri VM, Rubenfeld GD, Thompson BT, Ferguson ND, Caldwell E; et al. (2012). "Acute respiratory distress syndrome: the Berlin Definition". JAMA. 307 (23): 2526–33. doi:10.1001/jama.2012.5669. PMID 22797452.

[pmid7091520-2] Pepe PE, Potkin RT, Reus DH, Hudson LD, Carrico CJ (1982). "Clinical predictors of the adult respiratory distress syndrome". Am J Surg. 144 (1): 124–30. PMID 7091520.

[pmid3410685-3] Lucas AC (1988). "The future of radiological instrumentation". Health Phys. 55 (2): 191–5. PMID 3410685.

[pmid8531287-4] Moss M, Bucher B, Moore FA, Moore EE, Parsons PE (1996). "The role of chronic alcohol abuse in the development of acute respiratory distress syndrome in adults". JAMA. 275 (1): 50–4. PMID 8531287.

[pmid12682442-5] Moss M, Burnham EL (2003). "Chronic alcohol abuse, acute respiratory distress syndrome, and multiple organ dysfunction". Crit Care Med. 31 (4 Suppl): S207–12. doi:10.1097/01.CCM.0000057845.77458.25. PMID 12682442.

[pmid11056707-6] Reynolds HN, McCunn M, Borg U, Habashi N, Cottingham C, Bar-Lavi Y (1998). "Acute respiratory distress syndrome: estimated incidence and mortality rate in a 5 million-person population base". Crit Care. 2 (1): 29–34. doi:10.1186/cc121. PMC 28999. PMID 11056707.

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@@ Line 1: / Line 1: @@
+__NOTOC__
 {{Acute respiratory distress syndrome}}
-{{CMG}}
+{{CMG}} {{AE}} {{BShaller}}
 ==Overview==
-'''Acute respiratory distress syndrome''' ('''ARDS'''), also known as '''respiratory distress syndrome''' ('''RDS''') or '''adult respiratory distress syndrome''' (in contrast with [[infant respiratory distress syndrome]], or [[infant respiratory distress syndrome|IRDS]]) is a serious and potentially life-threatening inflammatory lung condition that may occur in the setting of infection, toxic exposure, adverse drug reactions, trauma, or overall critical illness. ARDS is characterized by inflammation of the lung parenchyma resulting in increased permeability of the [[Alveolar-capillary barrier|alveolar-capillary membrane]], non-cardiogenic [[pulmonary edema]], impaired gas exchange, and decreased lung [[Compliance (physiology)|compliance]].
+'''Acute respiratory distress syndrome''' ('''ARDS'''), originally known as '''adult respiratory distress syndrome''' (to contrast with [[infant respiratory distress syndrome|''neonatal respiratory distress syndrome'']]) is a serious and potentially life-threatening [[inflammation|inflammatory]] lung condition that develops rapidly (usually within 24 to 48 hours) in the setting of [[sepsis]], [[toxin|toxic exposures]], [[adverse drug reaction|adverse drug reactions]], [[trauma]], or other critical illnesses. ARDS is characterized by [[inflammation]] of the lung [[parenchyma]] resulting in increased [[permeability]] of the [[Alveolar-capillary barrier|alveolar-capillary membrane]], non-cardiogenic [[pulmonary edema]], impaired [[gas exchange]], and decreased lung [[Compliance (physiology)|compliance]].
-ARDS may be categorized as ''mild'', ''moderate'', or ''severe'' based on the magnitude of impaired oxygenation; however, even mild ARDS may progress to [[multiple organ failure]] if appropriate measures to improve oxygenation are not taken. The vast majority of patients diagnosed with ARDS are managed in an [[intensive care unit]], and most will require [[Mechanical ventilation indications for use|mechanical ventilation]] at some point during the course of their illness and recovery.
+The vast majority of patients with ARDS are managed in an [[intensive care unit|intensive care unit (ICU)]], where many will require [[Mechanical ventilation indications for use|mechanical ventilation]] at some point during the course of their illness and recovery. ARDS may be categorized as ''mild'', ''moderate'', or ''severe'' based on the degree to which [[oxygenation]] is impaired; however, all levels of severity carry a high [[mortality rate]] if appropriate measures to improve oxygenation and minimize the risk of further lung injury are not taken.<ref name="pmid22797452">{{cite journal| author=ARDS Definition Task Force. Ranieri VM, Rubenfeld GD, Thompson BT, Ferguson ND, Caldwell E et al.| title=Acute respiratory distress syndrome: the Berlin Definition. | journal=JAMA | year= 2012 | volume= 307 | issue= 23 | pages= 2526-33 | pmid=22797452 | doi=10.1001/jama.2012.5669 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22797452  }} </ref>
-Below is a table showing The Berlin definition of Acute Respiratory Distress Syndrome:<ref name="Ranieri-2012">{{Cite journal  | last1 = Ranieri | first1 = VM. | last2 = Rubenfeld | first2 = GD. | last3 = Thompson | first3 = BT. | last4 = Ferguson | first4 = ND. | last5 = Caldwell | first5 = E. | last6 = Fan | first6 = E. | last7 = Camporota | first7 = L. | last8 = Slutsky | first8 = AS. | last9 = Ranieri | first9 = V. | title = Acute respiratory distress syndrome: the Berlin Definition. | journal = JAMA | volume = 307 | issue = 23 | pages = 2526-33 | month = Jun | year = 2012 | doi = 10.1001/jama.2012.5669 | PMID = 22797452 }}</ref>
+==Historical Perspective==
+Although the pathologic features of ARDS were first documented in the 19th century, the modern definition of ARDS did not arise until the 1960s. In 2012, the Berlin Definition of ARDS became the standard diagnostic criteria and definition of the syndrome.
-{| class="wikitable"
+==Classification==
-!
+ARDS may be classified according to [[Acute respiratory distress syndrome diagnostic criteria|2012 Berlin Definition]] into three subtypes: ''mild'', ''moderate'', and ''severe''. These levels of severity are based on the degree to which [[oxygenation]] relative to the amount of [[supplemental oxygen]] is being delivered to the patient via [[positive pressure ventilation]].<ref name="pmid22797452">{{cite journal| author=ARDS Definition Task Force. Ranieri VM, Rubenfeld GD, Thompson BT, Ferguson ND, Caldwell E et al.| title=Acute respiratory distress syndrome: the Berlin Definition. | journal=JAMA | year= 2012 | volume= 307 | issue= 23 | pages= 2526-33 | pmid=22797452 | doi=10.1001/jama.2012.5669 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22797452  }} </ref>
-! '''Acute Respiratory Distress Syndrome'''
-|-
-| '''Timing'''
-| ❑ Within 1 week of a known clinical insult or new or worsening respiratory symptoms
-|-
-| '''Chest imaging''' <br>i.e., [[CXR]] or [[CT]]
-| ❑ Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or
-nodules
-|-
-| '''Origin of edema'''
-| ❑ Respiratory failure not fully explained by cardiac failure or fluid overload<br>❑ Need objective assessment (e.g., echocardiography) to exclude hydrostatic edema<br> if no risk factor present
-|-
-| '''Oxygenation'''<br> (Corrected for altitude)
-|
-|-
-| Mild
-|❑ 200 mm Hg < PaO2/FiO2 ≤ 300 mmHg with PEEP or CPAP > 5 cm H2O
-|-
-| Moderate
-| ❑ 100 mm Hg < PaO2/FIO2 ≤ 200 mm Hg with PEEP ≥ 5 cm H2O
-|-
-| Severe
-| ❑ PaO2/FiO2 ≤ 100 mm Hg with PEEP ≥ 5 cm H2O
-|}
-ARDS usually occurs within 24 to 48 hours of the initial injury or illness. The patient usually presents with [[shortness of breath]], [[tachypnea]], and symptoms related to the underlying cause, i.e. [[Shock (medical)|shock]].
+==Pathophysiology==
+ARDS is a syndrome of [[inflammation]] and increased [[permeability]] with the lung parenchyma that leads to loss of [[pneumocyte|type I pneumocytes]], impaired [[gas exchange]], inappropriate [[cell proliferation]] within [[alveolus|alveoli]], and, in survivors, [[fibrosis]].
-An [[arterial blood gas]] analysis and [[chest X-ray]] allow formal diagnosis by inference using the aforementioned criteria. Although severe hypoxemia is generally included, the appropriate threshold defining abnormal PaO<sub>2</sub> has never been systematically studied.
+==Causes==
+ARDS may be caused by either direct or indirect insults to the lung. Common causes of ARDS include [[sepsis]], [[aspiration pneumonia|aspiration pneumonitis]], and [[transfusion-related acute lung injury|transfusion-related acute lung injury (TRALI)]].<ref name="pmid7091520">{{cite journal| author=Pepe PE, Potkin RT, Reus DH, Hudson LD, Carrico CJ| title=Clinical predictors of the adult respiratory distress syndrome. | journal=Am J Surg | year= 1982 | volume= 144 | issue= 1 | pages= 124-30 | pmid=7091520 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7091520  }} </ref>
-Any cardiogenic cause of pulmonary edema should be excluded. This can be done by placing a [[pulmonary artery catheter]] for measuring the pulmonary artery wedge pressure. However, this is not necessary and is now rarely done as abundant evidence has emerged demonstrating that the use of pulmonary artery catheters does not lead to improved patient outcomes in critical illness including ARDS.
+==Differentiating ARDS from Other Diseases==
+ARDS must be differentiated from other diseases that cause [[hypoxemia]] and pulmonary infiltrates, such as [[pneumonia]], [[pulmonary contusion]], [[pulmonary edema]], and [[pulmonary hemorrhage]]. Prior to the development of the [[Acute respiratory distress syndrome diagnostic criteria|Berlin Definition]] in 2012, a greater emphasis was placed on excluding other potential illnesses prior to making a diagnosis of ARDS. While it is important to recognize and treat and underlying cause of the patient's impaired [[ventilation]] and [[hypoxemia]], this search for potential etiologies should not delay any focused efforts to improve [[oxygenation]] and [[ventilation]].
-While CT scanning leads to more accurate images of the pulmonary parenchyma in ARDS, its has little utility in the clinical management of patients with ARDS, and remains largely a research tool.  Plain Chest X-rays are sufficient to document bilateral alveolar infiltrates in the majority of cases
+==Epidemiology and Demographics==
+The incidence of ARDS in the United States is estimated at approximately 75 cases per 100,000 individuals, which amounts to roughly 150,000 new cases annually.<ref name="pmid3410685">{{cite journal| author=Lucas AC| title=The future of radiological instrumentation. | journal=Health Phys | year= 1988 | volume= 55 | issue= 2 | pages= 191-5 | pmid=3410685 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3410685  }} </ref> There is substantial variance in the rates of ARDS between different countries and geographic regions due to factors such as mean [[life expectancy]], prevalence of different [[risk factors]] and [[comorbidities]], and access to [[healthcare]].
-==Historical Perspective==
+==Risk Factors==
-Although the first pathologic descriptions of what was likely ARDS date back to the 19th century, our understanding of the distinct pathophysiologic features of ARDS evolved alongside the development of medical technologies that facilitated a more in-depth study of the syndrome. The advent of [[projectional radiography|radiography]] permitted visualization of the bilateral pulmonary infiltrates (originally termed ''double [[pneumonia]]''), while the development of [[ABG|arterial blood gas measurement]] and [[mechanical ventilation|positive-pressure mechanical ventilation]] allowed for identification of the impaired oxygenation and reduced lung compliance that are now recognized as central features of ARDS.<ref name="pmid16020801">{{cite journal| author=Bernard GR| title=Acute respiratory distress syndrome: a historical perspective. | journal=Am J Respir Crit Care Med | year= 2005 | volume= 172 | issue= 7 | pages= 798-806 | pmid=16020801 | doi=10.1164/rccm.200504-663OE | pmc=2718401 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16020801  }} </ref>
+The most potent risk factor in the development of ARDS is [[chronic alcoholism]].<ref name="pmid8531287">{{cite journal| author=Moss M, Bucher B, Moore FA, Moore EE, Parsons PE| title=The role of chronic alcohol abuse in the development of acute respiratory distress syndrome in adults. | journal=JAMA | year= 1996 | volume= 275 | issue= 1 | pages= 50-4 | pmid=8531287 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8531287  }} </ref><ref name="pmid12682442">{{cite journal| author=Moss M, Burnham EL| title=Chronic alcohol abuse, acute respiratory distress syndrome, and multiple organ dysfunction. | journal=Crit Care Med | year= 2003 | volume= 31 | issue= 4 Suppl | pages= S207-12 | pmid=12682442 | doi=10.1097/01.CCM.0000057845.77458.25 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12682442  }} </ref> Other risk factors include [[elderly|advanced age]], [[smoking|cigarette smoke exposure]], and [[chronic liver disease]].
-Ashbaugh and colleagues published he first description of what is now widely recognized as ARDS in a case series of 12 patients with rapidly progressive respiratory failure with bilateral pulmonary infiltrates and profound hypoxemia following trauma or infection in "The Lancet" in 1967.<ref name="pmid4143721">{{cite journal| author=Ashbaugh DG, Bigelow DB, Petty TL, Levine BE| title=Acute respiratory distress in adults. | journal=Lancet | year= 1967 | volume= 2 | issue= 7511 | pages= 319-23 | pmid=4143721 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=4143721  }} </ref> The clinical syndrome was called the "adult respiratory distress syndrome" (ARDS) to distinguish it from the respiratory distress syndrome of infancy due to [[hyaline membrane disease]], although the nomenclature was later changed from "acute" to "adult" once it was recognized that ARDS could also present in infants as a distinct entity from hyaline membrane disease.
+==Screening==
+There are no screening tools for ARDS. The best way to make an early diagnosis of ARDS is to apply the [[Acute respiratory distress syndrome diagnostic criteria|diagnostic criteria]] to any patient with bilateral pulmonary infiltrates on [[chest x ray]], and new/worsening [[hypoxemia]] with an increasing [[Oxygen therapy|supplemental oxygen]] requirement in whom a [[Acute respiratory distress syndrome causes|potential cause]] or [[Acute respiratory distress syndrome risk factors|risk factor]] for ARDS exists.
-==Classification==
-The current ARDS diagnostic criteria (commonly referred to as the ''Berlin Criteria'' or ''Berlin Definition'') were established by the ARDS Definition Task Force in 2012. [[#Diagnostic Criteria|The Berlin Criteria]] classify ARDS as ''mild'', ''moderate'', and ''severe'' based on the degree of oxygenation impairment and serve as a means of risk-stratifying patients.<ref name="pmid22797452">{{cite journal| author=ARDS Definition Task Force. Ranieri VM, Rubenfeld GD, Thompson BT, Ferguson ND, Caldwell E et al.| title=Acute respiratory distress syndrome: the Berlin Definition. | journal=JAMA | year= 2012 | volume= 307 | issue= 23 | pages= 2526-33 | pmid=22797452 | doi=10.1001/jama.2012.5669 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22797452  }} </ref>
-==Pathophysiology==
+==Natural History, Complications, and Prognosis==
-ARDS typically develops within 24 to 48 hours of the provoking illness or injury and is classically divided into three phases:<br>
+If left untreated, 70% of patients with ARDS may progress to [[mortality]].<ref name="pmid11056707">{{cite journal| author=Reynolds HN, McCunn M, Borg U, Habashi N, Cottingham C, Bar-Lavi Y| title=Acute respiratory distress syndrome: estimated incidence and mortality rate in a 5 million-person population base. | journal=Crit Care | year= 1998 | volume= 2 | issue= 1 | pages= 29-34 | pmid=11056707 | doi=10.1186/cc121 | pmc=28999 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11056707  }} </ref> Common complications to ARDS include [[weakness]], impaired [[spirometry|lung function]], and [[brain death]]. Prognosis for patients with ARDS is generally poor and varies based on the severity of illness, the precipitating insult, and medical comorbidities.
-*'''Exudative phase (''within 24-48 hours'')''': Systemic inflammation results in increased alveolar capillary permeability and leads to the formation of hyaline membranes along alveolar walls, accumulation of proteinaceous exudate within the alveolar air spaces (''non-cardiogenic pulmonary edema''), and extravasation of inflammatory cells (predominantly [[neutrophils|neutrophils]] and [[macrophages|macrophages]]) into the lung parenchyma, leading to extensive alveolar damage and sometimes hemorrhage into alveoli
-*'''Proliferative phase (''within 5-7 days'')''': Fibroblast proliferation, collagen deposition, and early fibrotic changes are observed within the pulmonary interstitium as alveolar exudate and hyaline membranes begin to be absorbed
-*'''Fibrotic phase (''within several weeks'')''': Most patients with ARDS will develop some degree of pulmonary fibrosis, of which at least one-quarter will go on to develop a restrictive ventilatory defect on pulmonary function tests<ref name="pmid23520315">{{cite journal| author=Burnham EL, Janssen WJ, Riches DW, Moss M, Downey GP| title=The fibroproliferative response in acute respiratory distress syndrome: mechanisms and clinical significance. | journal=Eur Respir J | year= 2014 | volume= 43 | issue= 1 | pages= 276-85 | pmid=23520315 | doi=10.1183/09031936.00196412 | pmc=4015132 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23520315  }} </ref>; the development and extent of pulmonary fibrosis in ARDS correlates with an increased mortality risk<ref name="pmid7813276">{{cite journal| author=Martin C, Papazian L, Payan MJ, Saux P, Gouin F| title=Pulmonary fibrosis correlates with outcome in adult respiratory distress syndrome. A study in mechanically ventilated patients. | journal=Chest | year= 1995 | volume= 107 | issue= 1 | pages= 196-200 | pmid=7813276 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7813276  }} </ref>
-===Genetic Susceptibility===
+==Diagnosis==
-The role of genetics in the development of ARDS is an ongoing area of research. While studies have demonstrated associations between certain genetic factors (including [[single-nucleotide polymorphisms|single-nucleotide polymorphisms]] and allelic variants of [[angiotensin-converting enzyme|angiotensin-converting enzyme]]<ref name="pmid16484896">{{cite journal| author=Jerng JS, Yu CJ, Wang HC, Chen KY, Cheng SL, Yang PC| title=Polymorphism of the angiotensin-converting enzyme gene affects the outcome of acute respiratory distress syndrome. | journal=Crit Care Med | year= 2006 | volume= 34 | issue= 4 | pages= 1001-6 | pmid=16484896 | doi=10.1097/01.CCM.0000206107.92476.39 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16484896  }} </ref><sup>,</sup><ref name="pmid23364437">{{cite journal| author=Cardinal-Fernández P, Ferruelo A, El-Assar M, Santiago C, Gómez-Gallego F, Martín-Pellicer A et al.| title=Genetic predisposition to acute respiratory distress syndrome in patients with severe sepsis. | journal=Shock | year= 2013 | volume= 39 | issue= 3 | pages= 255-60 | pmid=23364437 | doi=10.1097/SHK.0b013e3182866ff9 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23364437  }} </ref>) and increased susceptibility to developing ARDS, the nature and implications of these relationships remain uncertain.<ref name="pmid23048207">{{cite journal| author=Tejera P, Meyer NJ, Chen F, Feng R, Zhao Y, O'Mahony DS et al.| title=Distinct and replicable genetic risk factors for acute respiratory distress syndrome of pulmonary or extrapulmonary origin. | journal=J Med Genet | year= 2012 | volume= 49 | issue= 11 | pages= 671-80 | pmid=23048207 | doi=10.1136/jmedgenet-2012-100972 | pmc=3654537 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23048207  }} </ref>
+===Diagnostic Criteria===
+Established by the ARDS Definition Task Force in 2012, the Berlin Definition is the most current set of diagnostic criteria for ARDS.
-===Pathology===
+===History and Symptoms===
-*On gross pathology, the lungs are firm, boggy, and dusky, and they typically weigh more than healthy lungs due to edema
+The history of a patient with ARDS varies according to the underlying cause. The symptoms of ARDS are fairly nonspecific and typically include [[Tachypnea|rapid breathing]], [[shortness of breath]], and [[Tachycardia|rapid heartbeat]].
-*On microscopic histopathological analysis, the lung parenchyma demonstrates hyaline membranes lining the alveolar air spaces, edema fluid within alveoli and the interstitium, shedding of type I pneumocytes and proliferation of type II pneumocytes, infiltration of polymorphonuclear and other inflammatory cells into the interstitial and alveolar compartments, thrombosis and obliteration of pulmonary capillaries, and occasionally hemorrhage into alveoli
-:*Features specific to the underlying disease process (e.g., [[pneumonia|bacterial pneumonia]] or [[aspiration pneumonitis|aspiration pneumonitis]]) are often seen as well
-:*As ARDS progresses, alveolar infiltrates are reabsorbed and the inflammatory milieu is replaced by increased collagen deposition and proliferating fibroblasts, culminating in interstitial fibrosis
-[[File:Hyaline membranes - very high mag.jpg|thumb|Hyaline membranes - very high magnification]]
+===Physical Examination===
+There are no physical exam findings specific to or [[pathognomonic]] of ARDS. The most notable physical exam findings tend to be those of the underlying illness or injury, as well as those of [[respiratory distress]], [[critical illness]], [[shock]], and [[end organ damage]].
-==Causes==
+===Laboratory Findings===
-* [Disease name] may be caused by either [cause1], [cause2], or [cause3].
+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).
-* [Disease name] is caused by a mutation in the [gene1], [gene2], or [gene3] gene[s].
-* There are no established causes for [disease name].
-==Differentiating [disease name] from other Diseases==
-*[Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as:
-:*[Differential dx1]
-:*[Differential dx2]
-:*[Differential dx3]
-==Epidemiology and Demographics==
-* The prevalence of [disease name] is approximately [number or range] per 100,000 individuals worldwide.
-* In [year], the incidence of [disease name] was estimated to be [number or range] cases per 100,000 individuals in [location].
-===Age===
-*Patients of all age groups may develop [disease name].
-*[Disease name] is more commonly observed among patients aged [age range] years old.
-*[Disease name] is more commonly observed among [elderly patients/young patients/children].
-===Gender===
-*[Disease name] affects men and women equally.
-*[Gender 1] are more commonly affected with [disease name] than [gender 2].
-* The [gender 1] to [Gender 2] ratio is approximately [number > 1] to 1.
-===Race===
-*There is no racial predilection for [disease name].
-*[Disease name] usually affects individuals of the [race 1] race.
-*[Race 2] individuals are less likely to develop [disease name].
-==Risk Factors==
-*Common risk factors in the development of [disease name] are [risk factor 1], [risk factor 2], [risk factor 3], and [risk factor 4].
-== Natural History, Complications and Prognosis==
-*The majority of patients with [disease name] remain asymptomatic for [duration/years].
-*Early clinical features include [manifestation 1], [manifestation 2], and [manifestation 3].
-*If left untreated, [#%] of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].
-*Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].
-*Prognosis is generally [excellent/good/poor], and the [1/5/10year mortality/survival rate] of patients with [disease name] is approximately [#%].
-== Diagnosis ==
-===Diagnostic Criteria===
-The diagnosis of [disease name] is made when at least [number] of the following [number] diagnostic criteria are met:
-:*[criterion 1]
-:*[criterion 2]
-:*[criterion 3]
-:*[criterion 4]
-=== Symptoms ===
-*[Disease name] is usually asymptomatic.
-*Symptoms of [disease name] may include the following:
-:*[symptom 1]
-:*[symptom 2]
-:*[symptom 3]
-:*[symptom 4]
-:*[symptom 5]
-:*[symptom 6]
-=== Physical Examination ===
-*Patients with [disease name] usually appear [general appearance].
-*Physical examination may be remarkable for:
-:*[finding 1]
-:*[finding 2]
-:*[finding 3]
-:*[finding 4]
-:*[finding 5]
-:*[finding 6]
-=== Laboratory Findings ===
-*There are no specific laboratory findings associated with [disease name].
-*A  [positive/negative] [test name] is diagnostic of [disease name].
-*An [elevated/reduced] concentration of [serum/blood/urinary/CSF/other] [lab test] is diagnostic of [disease name].
-*Other laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].
 ===Imaging Findings===
-*There are no [imaging study] findings associated with [disease name].
+====Electrocardiogram====
+There are no [[EKG]] findings associated with ARDS.
-*[Imaging study 1] is the imaging modality of choice for [disease name].
-*On [imaging study 1], [disease name] is characterized by [finding 1], [finding 2], and [finding 3].
+====X Ray====
-*[Imaging study 2] may demonstrate [finding 1], [finding 2], and [finding 3].
+X ray is the imaging modality of choice for ARDS. By definition, findings of ARDS on x ray include [[bilateral]] [[Pulmonary consolidation|airspace opacities]].
-=== Other Diagnostic Studies ===
+====CT====
-*[Disease name] may also be diagnosed using [diagnostic study name].
+There are no findings on [[computed tomography|computed tomography (CT)]] that are diagnostic of ARDS. CT scan may be used to better define the extent of lung injury or identify potential underlying causes of ARDS.
-*Findings on [diagnostic study name] include [finding 1], [finding 2], and [finding 3].
-== Treatment ==
-=== Medical Therapy ===
-*There is no treatment for [disease name]; the mainstay of therapy is supportive care.
-*The mainstay of therapy for [disease name] is [medical therapy 1] and [medical therapy 2].
-*[Medical therapy 1] acts by [mechanism of action 1].
-*Response to [medical therapy 1] can be monitored with [test/physical finding/imaging] every [frequency/duration].
-=== Surgery ===
-*Surgery is the mainstay of therapy for [disease name].
-*[Surgical procedure] in conjunction with [chemotherapy/radiation] is the most common approach to the treatment of [disease name].
-*[Surgical procedure] can only be performed for patients with [disease stage] [disease name].
-=== Prevention ===
-*There are no primary preventive measures available for [disease name].
-*Effective measures for the primary prevention of [disease name] include [measure1], [measure2], and [measure3].
-*Once diagnosed and successfully treated, patients with [disease name] are followed-up every [duration]. Follow-up testing includes [test 1], [test 2], and [test 3].
+====Echocardiogram====
+[[Echocardiogram|Echocardiography]] is not especially useful in the diagnosis of ARDS, except under circumstances where [[cardiogenic pulmonary edema]] has not yet been excluded.
+===Other Diagnostic Studies===
+There are no additional diagnostic studies that are especially useful in the diagnosis and management of ARDS.
+==Treatment==
+===Medical Therapy===
+The majority of medical therapies for ARDS are aimed at treating its underlying cause (e.g., [[antimicrobials]] for [[infection]]).
+====Mechanical Ventilation Therapy====
+Most patients with ARDS will require [[endotracheal intubation]] and [[mechanical ventilation]] at some point during the course of their illness and recovery. A mechanical ventilation strategy using lower [[Lung volumes|tidal volumes]] of 6 mL/kg predicted body weight and higher levels of [[PEEP|positive end-expiratory pressure (PEEP)]] has been shown to be most effective at improving oxygenation and minimizing [[barotrauma|volutrauma]] (injury to stiff lungs resulting from overdistention).
+===Surgery===
+Surgical intervention is not recommended for the management of ARDS, except when a procedure might be recommended to treat the underlying cause.
+===Prevention===
+There are no primary preventive measures available for ARDS. The only prevention strategy for ARDS is early recognition and treatment of medical conditions that have the potential to cause ARDS.
+Secondary prevention strategies for ARDS include aggressive treatment of the underlying cause and the early application of [[Acute respiratory distress syndrome mechanical ventilation therapy#Non-Invasive Positive Pressure Ventilation|noninvasive methods of oxygenation]] to slow or prevent the worsening of ARDS and potentially reduce the need for [[tracheal intubation|intubation]] and [[mechanical ventilation]].
 ==References==
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 [[Category:Pulmonology]]
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