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American Journal of Critical Care. 2004;13: 59-64
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Comparison of 3 Methods of Detecting Acute Respiratory Distress Syndrome: Clinical Screening, Chart Review, and Diagnostic Coding

By April E. Howard, RN, CCRN, CCRC, Carrie Courtney-Shapiro, MD, Lynn A. Kelso, RN, ARNP, BC, Michele Goltz, BS and Peter E. Morris, MD. From Wake Forest University School of Medicine, Winston-Salem, NC.


   Abstract
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 Abstract
Subjects and Methods
 Results
 Discussion
 References
 
• Background Although the incidence of acute respiratory distress syndrome has been studied, few researchers have prospectively assessed the search tool used to identify cases.

• Methods For 5 months, all patients admitted to a medical intensive care unit in a teaching hospital were evaluated daily to determine whether criteria for acute respiratory distress syndrome were met, and physicians’ progress notes and discharge summaries for these prospectively identified patients were reviewed for mention of the syndrome. Discharge forms were reviewed for the codes (International Classification of Diseases, Ninth Revision) specific to acute respiratory distress syndrome (518.82 or 518.85).

• Results Of 314 patients admitted, 65 prospectively met the criteria for acute respiratory distress syndrome. Of these 65 patients, 31 had acute respiratory distress syndrome mentioned in their progress notes, and 4 of the 31 were subsequently assigned a code of 518.82 or 518.85. Patients with a physician’s notation for acute respiratory distress syndrome in their charts had a higher mortality (22/31 [71%]) than did the patients with no such notation (10/34 [29%]). This difference could not be accounted for by differences in length of stay, mean age, score on Acute Physiology and Chronic Health Evaluation III, or number of days in the unit before meeting the criteria.

• Conclusions The incidence of acute respiratory distress syndrome is underestimated when based on either diagnostic coding or physicians’ notes without testing of the accuracy of coding. Both physicians and medical record coding specialists may require training in use of terms related to acute respiratory distress syndrome.

Despite the publication of many articles on acute respiratory distress syndrome (ARDS), the estimated range of incidence is wide. Many review articles have offered critiques of these studies, citing limitations such as few patients studied and retrospective methods of estimation used.1,2 Since the appearance of the American European Consensus Conference (AECC) definition of ARDS in 1992,3 clinical trials have regularly been designed on the basis of the AECC criteria for ARDS. Consequently, criteria for including patients have become more uniform across ARDS clinical trials. Despite use of the AECC criteria for 10 years in clinical trials, it is unclear how vigorously these criteria are applied to routine review of patients’ records.

We attempted to quantify 2 suspected problems at our institution. First, we suspected that physicians do not describe all ARDS cases with appropriate notation in the medical record. Therefore, ARDS is not referred to in the medical records of some patients who meet the AECC criteria for this syndrome. Second, specialists in coding medical records may be less likely to use the codes from the International Classification of Diseases, Ninth Revision (ICD-9) associated with ARDS (518.82 and 518.85) if ARDS is not mentioned in patients’ progress notes. Thus, if appropriate ICD-9 codes are not assigned accurately, large-scale reporting of ARDS incidence based on retrieval of ICD-9 codes may yield underestimates. In this study, we determined how likely our intensive care unit (ICU) physicians (pulmonary and critical care trained attending physicians, pulmonary fellows, and internal medicine residents) were to use the AECC terminology in patients’ daily progress notes. Then, within the group of patients whose prospective diagnosis met AECC criteria for ARDS, we determined whether or not a physician’s chart notation of ARDS correlated with assignment of an ICD-9 code for ARDS at discharge.


ARDS includes a PaO2-FIO2 ratio less than 200 and noncardiogenic bilateral pulmonary infiltrates.

 


   Subjects and Methods
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 Abstract
 Subjects and Methods
Results
 Discussion
 References
 
Approval from the institutional review board was obtained for expedited consent. All patients admitted to the medical ICU (MICU) from January 1 through May 31, 1999, at the University of Kentucky were evaluated on each of their days in the MICU to determine whether AECC criteria had been met within the preceding 24 hours. The AECC criteria were a ratio of PaO2 to fraction of inspired oxygen (FIO2) less than 200, evidence of bilateral infiltrates on chest radiographs, and no reason to suspect that the pulmonary edema was cardiogenic.1

Attending and house-staff physicians were unaware of the aims of this study. Both were accustomed to investigators evaluating patients daily for potential inclusion in clinical trials, but they were not aware of the specifics of this investigation.

Patients were considered to have fulfilled the AECC criteria for ARDS if all criteria were met within a 24-hour period. We evaluated all patients admitted to the MICU for the development of ARDS not only upon admission to the ICU but on every day during their MICU stay. The chart of each patient was reviewed for any mention of the term ARDS in the physicians’ progress notes. Additionally, each patient’s discharge summary was reviewed for any mention of ARDS. Discharge ICD-9 codes were collected for each patient.

Codes for patients who met the AECC criteria for ARDS were considered appropriate if the discharge ICD-9 codes included 518.82 and 518.85.4 Table 1Go denotes which diagnoses are specifically included in each of these ICD-9 codes.


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  		Table 1 Codes from the International Classification of Diseases, Ninth Revision, specific to acute respiratory distress syndrome
 
In order to determine whether the frequency of diagnosis of ARDS varied from month to month, the number of patients admitted per month and the frequency of patients’ meeting AECC criteria were measured. A {chi}2 test was used to determine differences in mortality rates between groups.


   Results
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 Abstract
 Subjects and Methods
 Results
Discussion
 References
 
A total of 314 patients were admitted to the MICU between January 1 and May 31, 1999. Of these, 65 met AECC criteria for ARDS. For all patients who met AECC criteria, data from either a pulmonary artery catheter or an echocardiogram were available to exclude cardiogenic pulmonary edema.

Among the 314 patients admitted, demographic data on male-female ratio and age were similar between patients who met the AECC criteria for ARDS and the remainder of the MICU population. Of the 314 patients admitted, the patients with ARDS had a higher mortality rate (51%) than did the other MICU patients (15%) admitted during this period (P < .001; Table 2Go). The mean and median qualifying PaO2/FIO2 ratio for the 65 ARDS patients were 126 and 114, respectively.


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  		Table 2 Demographic information
 
The term ARDS was mentioned in the progress notes for 31 of the 65 who met the AECC criteria for ARDS. Only 4 of those 31 patients, on discharge, received an ICD-9 code for ARDS. Additionally, review of all 314 MICU patients’ discharge sheets indicated that only those 4 patients and no others were assigned an ICD-9 code specific for ARDS. That is, an ICD-9 code for ARDS was never randomly assigned to a MICU patient who had not been determined by the investigators to meet the AECC criteria for ARDS.

During the study period, attending and house-staff physicians were rotated on the first of each month. No single month accounted for a preponderance of the number of patients admitted to the MICU (Table 3Go). No one month accounted for an excessive number of prospectively identified cases of ARDS or patients with a chart notation of ARDS.


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  		Table 3 Monthly distribution of the frequency of ARDS diagnosis*
 

In cases of ARDS, the term "ARDS" was found in only 48% of progress notes, and only 6% were assigned the ARDS ICD-9 code. Instead, the code for respiratory failure, which actually excludes ARDS, was used most often.

 

Within our study period, nearly 21% of the patients admitted to the MICU met the AECC criteria for ARDS. Only half of those patients ever had ARDS mentioned within the progress notes by attending or house staff physicians, and only 6% of those patients had an ICD-9 code for ARDS on their discharge sheets.

Table 4Go shows the comparison between patients who met the AECC criteria for ARDS according to whether or not the term ARDS was mentioned in the progress notes. Mean age (49 years for both), number of days in the MICU before meeting AECC criteria (1.1 vs 0.9 days), MICU length of stay (7.0 vs 6.9 days), and score on the Acute Physiology and Chronic Health Evaluation (APACHE) III (78 vs 79) did not differ significantly between the 2 groups.


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  		Table 4 Patients who met the criteria of the American European Consensus Conference for acute respiratory distress syndrome (ARDS): differences between patients with and patients without ARDS mentioned in their chart
 
Patients with a physician’s notation for ARDS in their charts had a higher mortality (22/31 [71%]) than did the patients with no such notation (10/34 [29%]).

From review of the discharge sheets, the most frequently occurring ICD-9 code among the 65 patients who met AECC criteria was 518.81 (ie, respiratory failure). This code specifically excludes ARDS and pneumonia. The next most frequent codes, in order, were 486 (pneumonia) and 571.2 (alcoholic cirrhosis). Consequently, identification of ARDS patients by either retrieval of specific ICD-9 codes or by retrospective chart review for the mention of the term ARDS would have yielded underestimates of the incidence of ARDS in this group of patients.

Within the 314 MICU patients, retrieval of ARDS-specific ICD-9 codes had a specificity of 99.6% and a sensitivity of 6.2% for identifying cases of ARDS.


   Discussion
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 Abstract
 Subjects and Methods
 Results
 Discussion
References
 
Among the patients who met the AECC criteria for ARDS, the mortality rate was higher for those who had the term ARDS mentioned in their chart than for those who did not. It appeared that patients with ARDS with possibly higher perceived mortality risks were more frequently given a chart notation of ARDS by the attending physician or house staff. However, the 2 subgroups did not differ with respect to age, MICU length of stay, APACHE III score, or number of days in the MICU before meeting the AECC criteria. So despite similar baseline characteristics, the group who had ARDS noted in the medical records also had a higher mortality rate.

Many reasons may account for the failure to use ICD-9 codes for ARDS for patients who met the AECC criteria for the syndrome. A coding error may have resulted from misinterpretation of the patient’s chart. Alternatively, the absence of a specific mention of ARDS in the physician’s notes may have led medical coding specialists away from assigning an ARDS-specific ICD-9 code.

In 1972, an estimate by the National Institutes of Health concluded that the incidence of ARDS was approximately 75 cases per 100 000 US population.5 Published estimates since then have ranged from 1.5 to 15 cases per 100 000.2 The numbers of cases may have been overestimated in the 1972 study because of the broad definition of patients to be included, such as patients with lung injury associated with renal failure and volume overload.

Three years of ARDS data from the Canary Islands allowed a better estimation of incidence, because all patients requiring mechanical ventilation at one hospital were included.6 The study indicated that with a PaO2/FIO2 ratio of less than 110, the incidence was 1.5 cases per 100 000; with a PaO2/FIO2 of less than 150, the incidence was estimated at 3.5 cases per 100 000. This population differed from that of many North American or Northern European communities in that the mean age in the Canary Islands was only 32 years.

In 1995, Thomsen and Morris7 estimated that the incidence of ARDS in Utah was 8.3 per 100 000 residents. These investigators went to great lengths to assess their screening tools. Indeed, the investigators assessed the specificity and sensitivity of the ICD-9 documentation for several but not all of the study hospitals. In the primary hospital in this study, the sensitivity and specificity of ICD-9 codes for ARDS were 88% and 99%, respectively. (The Utah study used a PaO2/PAO2 of <0.2 to define ARDS patients.)


The true incidence of ARDS is underestimated, which dilutes the impact and burden of the syndrome.

 

In a 2-month prospective study in Germany, Lewandowski et al8 were able to prospectively survey 97% of the ICUs in the study area and reported an estimated incidence of 3 cases per 100 000.

In a separate study, during an 8-week period, investigators9 in Sweden, Denmark, and Iceland determined the incidence of and 90-day mortality associated with acute respiratory failure, acute lung injury, and ARDS. All patients more than 15 years old admitted to the ICU were assessed daily for AECC criteria for ARDS (n = 13 346). As in the study from Germany, no correction for migration in or out of the study area was possible. The population more than 15 years old in the 3 countries was 11.74 million. A total of 1231 patients with acute respiratory failure were found, among whom 287 had acute lung injury and 221 had ARDS. The annual incidence was 17.9 per 100 000 for acute lung injury and 13.5 per 100 000 for ARDS. Ninety-day mortality was 42.2% for acute lung injury and 41.2% for ARDS.

The preliminary findings of a study1 in the Seattle area in which the AECC definition was used indicated that the incidence of ARDS was 12.6 per 100 000.

Discharges from all acute care hospitals in Mary-land were reviewed by using a computer data base to search for ICD-9 codes for ARDS from the Health Services Cost Review Commission. Patients 12 years of age or older were included. Screening criteria consisted of ICD-9 codes 518.5 and 518.82 cross-referenced with procedural codes for ventilatory support (96.70, 96.71, and 96.72).10 Applying the ICD-9 ARDS criteria yielded lower and upper limits of 159 to 205, 439 to 568, 531 to 694, and 529 to 720 cases of ARDS for 1992, 1993, 1994, and 1995, respectively. Normalizing for a population of 5 million yields yearly lower and upper limit rates of 3.2 to 4.2 and 10.5 to 14.2 cases of ARDS per 100 000 persons. Upper and lower limits for mortality rates based on the same duration, admissions, and population were 38% to49%, 39% to 52%, 36% to 47%, and 36% to 49%, respectively. The incidence of ARDS in Maryland was estimated at 10 to 14 cases per 100 000 people. The ARDS mortality rate was 36% to 52%.

In a study of patients contracted to a for-profit health maintenance organization in Ohio, Arroliga et al11 reported on ARDS patients treated at the sole tertiary care center for the health maintenance organization. Patients were identified prospectively by AECC definitions within the ICUs. The denominator used in the incidence calculation was the number of adult members of the health maintenance organization. Estimated annual incidence of ARDS was 15.3 cases per 100000 persons.

Most recently, in a study in which all ICU admissions in a 2-month period in 3 Australian states were examined, Bersten et al12 estimated that the incidence of ARDS was 28 cases per 100000. Unlike earlier studies, these investigators observed each ICU patient daily for the length of the patient’s ICU stay to determine whether or not on any given day the patient had yet to meet the AECC definition. Thus, the greater annual incidence projection may reflect this feature of the study, including patients in whom ARDS developed more than 24 hours after admission to the ICU.

Few published studies describe factors that influence accurate assignments of ICD-9 codes. For example, Buchbinder et al13 found poor agreement between diagnostic labels recorded in the medical records and subsequent assignment of ICD-9 codes for patients with soft-tissue disorders of the neck and upper limb. In an unpublished study, Rubenfeld et al14 reviewed inappropriate use of ARDS-specific ICD-9 codes in Seattle. In reviewing 13 398 ICU admissions in a 1-year period, they found that ARDS (as defined by the AECC criteria) developed in 11% of admitted patients; however, incidence and mortality, estimated solely on the basis of ICD-9 codes, could be inaccurate by as much as 100%. A comparison of clinical screening with 3 different combinations of ICD-9 diagnostic and procedure codes revealed high specificity (97%–100%) but poor sensitivity (28%–74%). The lack of sensitivity for ARDS-specific ICD-9 coding in our ICU population is consistent with the Seattle data and supports the notion that this trend is not an isolated occurrence at a single institution.

Current estimates of hospital costs for a patient with ARDS range from $60 000 to $70 000 (SD $85 000).15 In general, the in-hospital costs of a patient with ARDS are much greater than the mean hospital costs for other ICU patients. Certainly, more accurate coding of the patients for whom most of the ICU dollars are allocated would aid in the management of ICU resources.

In conclusion, epidemiological studies of ARDS incidence generated through review of ICD-9 codes or chart review of physicians’ notes for the term ARDS may inaccurately represent the frequency of this syndrome. Future studies of the incidence of ARDS in which a prospective diagnosis of ARDS is used may foster an increased understanding of resource use in the ICU with regard to patients who have ARDS. For the patients in our study who met the AECC criteria for ARDS, both review of ICD-9 coding and chart review would have led to underestimation of the incidence of ARDS. Analyses based on retrieval of ICD-9 codes or retrospective chart review for mention of ARDS without a testing of the accuracy of the coding may misrepresent the incidence of ARDS. Underestimation of the incidence of ARDS therefore dilutes the impact and burden of ARDS on the number of patients and families affected, and it affects staffing of critical care units. Underestimating such a costly illness has strong financial implications for budgeting of allocated funds within hospitals, reimbursement, and research. In future studies, accurate coding of ARDS cases will improve the quality of estimates of the incidence of the syndrome.


   ACKNOWLEDGMENT
 
This study was funded in part by National Institutes of Health award M01 RR02602.

To purchase reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 809-2273 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, reprints{at}aacn.org.


   REFERENCES
Top
 Abstract
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Hudson LD, Steinberg KP. Epidemiology of acute lung injury and ARDS. Chest. 1999;116(1 suppl):74S–82S.[Free Full Text]
  2. Atabai K, Mathay MA. Acute lung injury and the acute respiratory distress syndrome: definitions and epidemiology. Thorax. 2002;57:452–458.[Abstract/Free Full Text]
  3. Bernard GR, Artigas A, Brigham KL, et al. The American-European Consensus Conference on ARDS: definitions, mechanism, relevant outcomes, and clinical trial coordination. Am J Respir Crit Care Med. 1994;149:818–824.[Abstract]
  4. American Medical Association. International Classification of Diseases, 9th Revision, Clinical Modification. Chicago, Ill: American Medical Association; 1999:116.
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  8. Lewandowski K, Metz J, Deutschmann C, et al. Incidence, severity and mortality of acute respiratory failure in Berlin, Germany. Am J Respir Crit Care Med. 1995;151:1121–1125.[Abstract]
  9. Luhr OR, Antonsen K, Karlsson M, et al. Incidence and mortality after acute respiratory failure and acute respiratory distress syndrome in Sweden, Denmark, and Iceland. The ARF Study Group. Am J Respir Crit Care Med. 1999;159:1849–1861.[Abstract/Free Full Text]
  10. Reynolds HN, McCunn M, Borg U, Habashi N, Cottingham C, Bar-Lavi Y. Acute respiratory distress syndrome: estimated incidence and mortality rate in a 5 million-person population base. Crit Care. 1998;2:29–34.[Medline]
  11. Arroliga A, Ghamra Z, Trepichio AP, et al. Incidence of ARDS in an adult population of northeast Ohio. Chest. 2002;121:1972–1976.[Abstract/Free Full Text]
  12. Bersten AD, Edibam C, Hunt T, et al. Incidence and mortality of acute lung injury and the acute respiratory distress syndrome in three Australian states. Am J Respir Crit Care Med. 2002;165:443–448.[Abstract/Free Full Text]
  13. Buchbinder R, Goel V, Bombardier C. Lack of concordance between the ICD-9 classification of soft tissue disorders of the neck and upper limb and chart review diagnosis: one steel mill’s experience. Am J Indust Med. 1996;29:171–182.[Medline]
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