Meta Analysis
Adult respiratory distress syndrome: a systemic overview of incidence and risk factors.
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Summary
Posted By: Gordon S. Doig
E-Mail: gdoig@med.usyd.edu.au
Posted Date: June 18, 2002
Title: Adult respiratory distress syndrome: a systemic overview of incidence and risk factors.
Authors: Garber BG, Hebert PC, Yelle JD, Hodder RV, McGowan J.
Reference: Crit Care Med 1996 Apr;24(4):687-95
Link: Click here for a direct link to the paper. A password may be required for access to fulltext.
Abstract: Objective: To determine the published incidence of adult respiratory distress syndrome (ARDS) as well as the clinical evidence supporting a causal association between ARDS and its major risk factors.
Data Sources: The National Library of Medicine MEDLINE database and the bibliographies of selected articles.
Study Selection: Clinical studies were selected from the English literature, if they pertained to either the incidence of ARDS or its association with one or more commonly identified risk factors.
Data Extraction: All relevant studies identified by the search were evaluated for strength of design, and risk factors were scored according to established criteria for the strength of causation.
Data Synthesis: A total of 83 articles were considered relevant: six on incidence and 77 on risk factors. Only 49% of the 83 articles provided a definition of ARDS; a definition of risk factors was given in 64%, and 23% had no definition for either ARDS or risk factors. The published, population-based incidence of ARDS ranges from 1.5 to 5.3/105 population/yr. The strongest clinical evidence supporting a cause-effect relationship was identified for sepsis, aspiration, trauma, and multiple transfusions. The weakest clinical evidence was identified for disseminated intravascular coagulation. The following study types were represented by the 77 articles on risk factors: observational case-series (56%); cohorts (23%); case-controls (12%); nonrandomized clinical trials (5%); and randomized clinical trials (3%). Only a single study reported an odds ratio.
Conclusions: The significant variation in the incidence of ARDS is attributed to differences in the type and strength of study designs, as well as definitions of ARDS. While a substantial body of evidence exists concerning a causal role for ARDS risk factors, such as sepsis, aspiration, and trauma, more than 60% of clinical studies employed weak designs. The lack of reproducible definitions for ARDS or its potential risk factors in 49% of studies raises concerns about the validity of the conclusions of these studies regarding the association between ARDS and the supposed risk factors.
 
Are the Results Valid?
1. Did the overview address a focused clinical question?
Yes. The authors begin by stating that their objective is to determine the published incidence of ARDS as well as to review the clinical evidence supporting a causal relationship between ARDS and its major risk factors.
2. Were the criteria used to select articles for inclusion appropriate?
Yes. The authors included all articles dealing with incidence and risk factors for ARDS.
3. Is it unlikely that important, relevant studies were missed?
A well documented Medline search was conducted combined with a manual inspection of references lists. It is unclear if 'experts' in the field were contacted. It is also of note that the search was restricted to English language papers and EMBASE was not searched.
4. Was the validity of the included studies appraised?
Yes. The assessment of the validity of the primary papers was very well done.
5. Were assessments of studies reproducible?
Although all studies were reviewed by two authors, a measure of their agreement with regards to methodological quality score was not provided. It was reported that differences in scores were resolved by consensus.
6. Were the results similar from study to study?
The incidence of ARDS differed depending upon the definition of ARDS and the population entered into the study.
Of the 79 risk factor papers reported, only one used an odds ratio as a measure of strengh of association which made it extremely difficult to determine if results were similar from study to study.
What are the Results?
1. What are the overall results of the overview?
Of 83 papers reviewed, only 49% of papers provided a definition of ARDS, only 64% provided a reproducible definition of the risk factor under study and 23% defined neither ARDS nor risk factors.
Four papers provided a population-based estimate of the incidience of ARDS, which ranged from 1.5 to 5.3 cases per 10,000 population per year.
77 papers were reviewed regarding causal risk factors for ARDS. Out of a maximum methods score of 18, the average score was 9.8 (range 8 to 11).
High quality (score > 9.8) papers suggested sepsis, trauma, mutiple transufions, aspiration of gastric contents, pulmonary contusion, pneumonia and smoke inhalation were risk factors for ARDS.
DIC, fat embolism and cardiopulmonary bypass were only identified as risk factors by the weakest (score <9.8) quality papers.
Overall, the majority of studies were very poorly conducted.
2. How precise were the results?
Will the Results Help Me In Caring For My Patients?
1. Can the results be applied to my patient care
Yes. This is an interesting methodologic review. Understanding the principles of causality outlined in this paper should help us identify and conduct better observational studies.
2. Were all clinically important outcomes considered?
N/A.
3. Are the benefits worth the harms and costs?
N/A

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