Acute lung injury at Baragwanath ICU. An eight-month audit and call for consensus for other organ failure in the adult respiratory distress syndrome

What is Acute Respiratory Distress Syndrome?

Acute respiratory distress syndrome (ARDS) is a form of acute lung injury which usually occurs within 24 hours of a major illness or injury. Unfortunately a clear definition of ARDS does not presently exist, and the variability in the diagnostic criteria may impact on the results of clinical trials for ARDS and our understanding of the epidemiology and pathogenesis of this syndrome. In this article the history of ARDS is reviewed and a few of the definitions that have evolved over wtime are explored in depth. In addition, several controversies with these existing defiitions are discussed.

The Berlin definition of ARDS: an expanded rationale, justification, and supplementary material

PURPOSE

Our objective was to revise the definition of acute respiratory distress syndrome (ARDS) using a conceptual model incorporating reliability and validity, and a novel iterative approach with formal evaluation of the definition.

METHODS

The European Society of Intensive Care Medicine identified three chairs with broad expertise in ARDS who selected the participants and created the agenda. After 2 days of consensus discussions a draft definition was developed, which then underwent empiric evaluation followed by consensus revision.

RESULTS

The Berlin Definition of ARDS maintains a link to prior definitions with diagnostic criteria of timing, chest imaging, origin of edema, and hypoxemia. Patients may have ARDS if the onset is within 1 week of a known clinical insult or new/worsening respiratory symptoms. For the bilateral opacities on chest radiograph criterion, a reference set of chest radiographs has been developed to enhance inter-observer reliability. The pulmonary artery wedge pressure criterion for hydrostatic edema was removed, and illustrative vignettes were created to guide judgments about the primary cause of respiratory failure. If no risk factor for ARDS is apparent, however, objective evaluation (e.g., echocardiography) is required to help rule out hydrostatic edema. A minimum level of positive end-expiratory pressure and mutually exclusive PaO(2)/FiO(2) thresholds were chosen for the different levels of ARDS severity (mild, moderate, severe) to better categorize patients with different outcomes and potential responses to therapy.

CONCLUSIONS

This panel addressed some of the limitations of the prior ARDS definition by incorporating current data, physiologic concepts, and clinical trials results to develop the Berlin definition, which should facilitate case recognition and better match treatment options to severity in both research trials and clinical practice.

Epidemiology of Acute Respiratory Failure and Mechanical Ventilation

Acute respiratory failure, and the need for mechanical ventilation, remains one of the most common reasons for admission to the intensive care unit (ICU). The burden of acute respiratory failure is high in terms of mortality and morbidity as well as the cost of its principal treatment, mechanical ventilation. Very few epidemiologic studies have evaluated the prevalence and outcome of acute respiratory failure and mechanical ventilation in general. Most of the published literature has focused on specific forms of acute respiratory failure, particularly acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In this chapter, we provide a brief review of the pathophysiology of acute respiratory failure, its definition and classification, and then present the incidence and outcomes of specific forms of acute respiratory failure from epidemiologic studies.

Epidemiology of Acute Respiratory Failure and Mechanical Ventilation

Acute respiratory failure, and the need for mechanical ventilation, remains one of the most common reasons for admission to the intensive care unit (ICU). The burden of acute respiratory failure is high in terms of mortality and morbidity as well as the cost of its principal treatment, mechanical ventilation. Very few epidemiologic studies have evaluated the prevalence and outcome of acute respiratory failure and mechanical ventilation in general. Most of the published literature has focused on specific forms of acute respiratory failure, particularly acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In this chapter, we provide a brief review of the pathophysiology of acute respiratory failure, its definition and classification, and then present the incidence and outcomes of specific forms of acute respiratory failure from epidemiologic studies.

The epidemiology of acute respiratory failure in critically ill patients(*)

STUDY OBJECTIVES

To describe the risk factors for the development of and mortality resulting from acute respiratory failure (ARF) in a large patient population.

DESIGN

A substudy of a prospective, multicenter, observational cohort study, which was designed to validate the sequential organ failure assessment score.

SETTING

Forty ICUs in 16 countries.

PATIENTS

All critically ill patients who were admitted to one of the participating ICUs during a 1-month period were observed until the end of their hospital course.

MEASUREMENTS AND RESULTS

Of the 1,449 patients who were enrolled into the study, 458 (32%) were admitted to an ICU with ARF, as defined by a PaO(2)/fraction of inspired oxygen ratio of < 200 mm Hg and the need for respiratory support. Patients who presented with ARF were older than the other patients (63 vs 57 years, respectively; p < 0.001) and more commonly had an infection (47% vs 20%, respectively; p < 0.001). The length of ICU stay was longer (6 vs 4 days, respectively; p < 0.001) and the ICU mortality rate was more than double (34% vs 16%, respectively; p < 0.001) in ARF patients compared to non-ARF patients. Of the 991 patients who were admitted to an ICU without ARF, 352 (35%) developed ARF later during the ICU stay. The independent risk factors for the development of ARF were infection developing in the ICU (odds ratio [OR], 7.59; 95% confidence interval [CI], 5.08 to 11.33) or present on ICU admission (OR, 2.3; 95% CI, 1.68 to 3.16), the presence of neurologic failure on ICU admission (OR, 2.73; 95% CI, 1.90 to 3.91), and older age (OR, 1.70; 95% CI, 1.30 to 2.22). Of all 810 patients with ARF, 253 (31%) died. The independent risk factors for death were multiple organ failure following ICU admission, history of hematologic malignancy, chronic renal failure or liver cirrhosis, the presence of circulatory shock on ICU admission, the presence of infection, and older age.

CONCLUSIONS

The present study stresses that ARF is common in the ICU (56% of all patients) and that a number of extrapulmonary factors are related to the risk of development of ARF and to mortality rate in these patients.

A 9-year, single-institution, retrospective review of death rate and prognostic factors in adult respiratory distress syndrome

OBJECTIVE

To evaluate, at a single institution, the adult respiratory distress syndrome (ARDS) death rate in critically ill ventilated surgical/trauma patients and to identify the factors predicting death in these patients.

SUMMARY BACKGROUND DATA

The prognostic features affecting mortality at the onset of ARDS have not been clearly defined. Defining rare characteristics would be valuable because it would allow for better stratification of patients in clinical trials and more appropriate utilization of constrained resources in ICU environments.

METHODS

A retrospective analysis of 980 ventilated surgical and trauma intensive care unit patients from January 1990 to December 1998 was performed at Rhode Island Hospital. One hundred eleven adult intensive care unit patients with ARDS were identified using the criteria of Lung Injury Score more than 2.50 and the definition from the American-European Consensus Conference. Slightly more than half were trauma patients, 57% were men, and the median age was 59 years. The overall death rate was 52%. Patients were segregated by admission date to the intensive care unit (before or after January 1, 1995). Severity of illness was measured by the Revised Trauma Score for trauma patients and the Acute Physiology and Chronic Health Evaluation III for surgical patients. The Multiple Organ Dysfunction Score was determined on the day of onset of ARDS for all patients. Other recorded variables were age, sex, intensive care unit length of stay, length and mode of ventilation, presence or absence of tracheostomy, ventilation variables of peak and mean airway pressures, lung injury scores, elective versus emergency surgery, and presence or absence of pneumonia.

RESULTS

There was a significant decrease in the ARDS death rate from the period 1990 to 1994 to the period 1995 to 1998. The major reason for the decline was a reduction in the posttraumatic ARDS death rate. Lung-protective ventilation strategies were used more frequently in the second period than in the first, and the death rate was significantly decreased in trauma patients in the second period when lung-protective ventilation modes were used. Predictors of death at the onset of ARDS were advanced age, Multiple Organ Dysfunction Score of 8 or more, and Lung Injury Score of 2.76 or more.

CONCLUSION

In this single-institution series, the death rate from ARDS declined from 1990 to 1998, primarily in posttraumatic patients, and the decrease is related to the use of lung-protective ventilation strategies. Based on this patient population, the authors developed a statistical model to evaluate important prognostic indicators (advanced age, organ system and pulmonary dysfunction measurements) at the onset of ARDS.

Incidence of acute respiratory distress syndrome: a comparison of two definitions

OBJECTIVES

To determine the incidence and outcome of acute respiratory distress syndrome (ARDS) in children by comparing two commonly used definitions: the lung injury score and the American-European Consensus Conference definition. The causes and risk for developing ARDS were also studied.

METHODS

Part prospective and retrospective analysis of 8100 consecutive hospital admissions from 1 June 1995 to 1 April 1997.

RESULTS

Twenty one patients fulfilled the criteria for ARDS. Both definitions identified the same group of patients. The incidence was 2.8/1000 hospital admissions or 4.2% of paediatric intensive care unit admissions. The main causes were sepsis and pneumonia. Mortality was 13 of 21. Factors predicting death were a high admission paediatric risk of mortality (PRISM) score (30.38 v 18.75) and the presence of multiple organ dysfunction syndrome (92% v 25%).

CONCLUSION

Both definitions identified similar groups of patients. The incidence in this population was higher than that reported elsewhere, but mortality and cause were similar to those in developed countries. Poor outcome was associated with sepsis, a high admission PRISM score, and simultaneous occurrence of other organ dysfunction.

The acute respiratory distress syndrome: definitions, severity and clinical outcome. An analysis of 101 clinical investigations

OBJECTIVE

To determine possible changes in outcome from acute respiratory distress syndrome (ARDS) and to compare severity of lung injury and methods of treatment from 1967 to 1994.

DATA SOURCES

Computerized (Medline, Current Contents) and manual (Cumulated Index Medicus) literature search using the key word and/or title ARDS.

STUDY SELECTION

Only clinical studies published as full papers reporting data on both patient mortality (survival) and oxygenation index (PaO2/FIO2) were included. Single case reports, abstracts, reviews and editorials were excluded from evaluation.

DATA EXTRACTION

Relevant data were extracted in duplicate, followed by quality checks on approximately 80% of data extracted.

DATA SYNTHESIS

101 papers reporting on 3264 patients were included: 48 studies (2207 patients) were performed in the USA, 43 studies (742 patients) in Europe and 10 studies (315 patients) elsewhere. Mortality reported in these studies was 53 +/- 22% (mean +/- SD), with no apparent trend towards a higher survival (1994: 22 studies, mortality 51 +/- 19%). The mean PaO2/FIO2 ratio remained unchanged throughout the observation period (118 +/- 47 mmHg). No correlation could be established between outcome and PaO2/FIO2 or lung injury score. Patients who underwent pressure-limited ventilation had a significantly lower mortality (35 +/- 20%) than patients on volume-cycled ventilation (54 +/- 22%) or patients for whom there was no precise information on ventilatory support (59 +/- 19%). Significantly lower PaO2/FIO2 ratios (61 +/- 17 mmHg) were observed in patients prior to extracorporeal lung assist, together with mortality rates in the range of those for conventionally treated patients (55 +/- 22%).

CONCLUSIONS

The mortality of ARDS patients remained constant throughout the period studied. Therefore, the standard for outcome in ARDS should be a mortality in the 50% range. Neither PaO2/FIO2 ratio nor lung injury score was a reliable predictor for outcome in ARDS. Patients might benefit from pressure-limited ventilatory support, as well as extracorporeal lung assist. Since crucial data were missing in most clinical studies, thus preventing direct comparison, we emphasize the importance of using standardized definitions and study entry criteria.

Predictors of mortality in severe malaria: a two year experience in a non-endemic area

Management of severe malaria is an increasing problem worldwide. This paper reviews the pathophysiology and management documenting two years' experience of admissions of severe malaria to an ICU in a non-endemic area. Clinical and laboratory features of severe malaria were analysed for predictors of mortality Twenty-eight patients had clinical or laboratory features compatible with the WHO criteria for severe malaria and, despite treatment with intravenous quinine and supportive ICU care, mortality was 28.5% (8/28). The three pregnant patients died with 100% foetal mortality and the four paediatric patients survived. Of the non-survivors, 8/8 developed ARDS (defined by worst ALI score > 2.5), 7/8 developed shock requiring inotropic support and 7/8 developed acute renal failure requiring CVVHD. Admission haemoglobin, platelet count, parasite count, and lowest Glasgow Coma Score in the first 24 hours were shown not to be predictors of mortality.

Interobserver variation in the chest radiograph component of the lung injury score

The lung injury score is a semi-quantitative system used in the definition and grading of the acute respiratory distress syndrome. It is composed of two, three or four equally weighted components. One component is derived from the chest radiograph, which may contribute up to 50% of the total score. A score of 1 is awarded for each quadrant on the chest radiograph which contains alveolar consolidation. We examined the interobserver variation between two anaesthetists, two radiologists and two critical care physicians who scored blindly 100 chest radiographs from patients with adult respiratory distress syndrome. There was very good agreement between the two radiologists in the total scores (kappa 0.97) and in individual scores in each of the 4 quadrants (kappa 0.97-1.0). The agreement between anaesthetists and radiologists was only fair for the total score (kappa 0.37-0.42), but moderate to good for individual quadrant scores (kappa 0.43-0.73). The agreement between the two anaesthetists was moderate for individual quadrant scores (kappa 0.44-0.60), but only fair for total score (kappa 0.34). There was poor agreement between the two critical care physicians for total score (kappa 0.05) and for individual quadrant scores (kappa 0.04-0.20). Agreement between the physicians and other observers was poor to fair for the total score (kappa 0.12-0.32) and poor to moderate for the individual quadrant scores (kappa 0.15-0.63). Both anaesthetists and physician 2 underestimated the overall chest scores (median scores 2, 3 and 1 respectively) in comparison to the radiologists (median scores 3.5). Physician 1 significantly overscored (median score 4). The chest radiograph component of the lung injury score can be consistently assessed by radiologists, but significant variations may be introduced when assessed by other clinicians. This has significant implications for the use of the lung injury score in studies of adult respiratory distress syndrome and other studies which incorporate radiographic appearances in the definition.

Establishing the relative accuracy of three new definitions of the adult respiratory distress syndrome

OBJECTIVES

Over the last few years, new definitions of the adult respiratory distress syndrome (ARDS) have been introduced that potentially identify patients earlier in their course of acute lung injury. However, these definitions have never been compared with any of the older and potentially stricter definitions of ARDS to determine if similar patients are eventually identified. We compared new definitions of ARDS--as represented by the Lung Injury Score, a modified Lung Injury Score, and the American-European Consensus Conference definition--against a stricter definition of ARDS to determine their accuracy.

DESIGN

Prospective.

SETTING

Intensive care unit (ICU) patients in a tertiary, university-affiliated city hospital.

PATIENTS

ICU patients with clearly defined at-risk diagnoses for ARDS (group 1, n = 111) and general medical ICU patients without clearly defined at-risk diagnoses for ARDS (group 2, n = 125).

MEASUREMENTS AND MAIN RESULTS

Measurements of hypoxemia, static respiratory system compliance, positive end-expiratory pressure, radiographic changes, and general demographic information were collected. The sensitivity, specificity, positive-predictive value, negative-predictive value, and accuracy of all three new definitions were determined. Accuracy was defined as the true-positive plus the true-negative results divided by the total number of patients. When compared with a stricter definition of ARDS, all three definitions maintained a high degree of accuracy in those patients with a clearly defined at-risk diagnosis (group 1): Lung Injury Score 90.0% (95% confidence interval 84-96); modified Lung Injury Score 97.3% (95% confidence interval 94-100), and the American-European Consensus Conference definition 97.3% (95% confidence interval 94-100). For these at-risk patients, the accuracy of the modified Lung Injury Score and the American-European Consensus Conference definition was significantly better than the Lung Injury Score when compared with the strict definition (p = .027 for both comparisons). Although all three definitions maintained an accuracy of > 90% for general medical ICU patients (group 2), the low frequency of ARDS in these patients (3.4%) produced a low positive-predictive value for all three definitions.

CONCLUSIONS

We conclude that the Lung Injury Score, the modified Lung Injury Score, and the American-European Consensus Conference definition identify similar patients, provided that these methods are applied to patients with clearly defined at-risk diagnoses for ARDS.