Corticosteroid therapy in acute respiratory distress syndrome

The systemic inflammatory response syndrome

The systemic inflammatory response syndrome (SIRS) describes the clinical presentation of patients with systemic activation of the inflammatory response from any underlying cause. SIRS is a common problem in acute medical and surgical practice and an important cause of morbidity and mortality. As a consequence of SIRS, patients may develop multiple organ dysfunction syndrome and acute respiratory distress syndrome (ARDS). Over the recent years our understanding of the inflammatory response in SIRS has increased, but as yet specific immunomodulatory therapies have not proved useful. The mainstay of treatment for patients with SIRS and ARDS remains a general supportive care. It is in this area that more encouraging advances are being made, particularly in the management of invasive ventilation and nutrition. In this review we summarize the definitions, epidemiology and pathophysiology of SIRS, ARDS and related conditions. We then give a description of the clinical consequences and treatment of SIRS and ARDS with an emphasis on current aspects of supportive care.

Acute respiratory distress syndrome: update on the latest developments in basic and clinical research

PURPOSE OF REVIEW

Acute lung injury/acute respiratory distress syndrome is a common, serious condition affecting a heterogeneous population of critically ill patients. Other than low tidal volume ventilation, no specific therapy has improved survival. Understanding the epidemiology, pathogenesis, and lessons to be learned from previous clinical trials is necessary for the development of new therapies and the rational design of studies assessing their efficacy.

RECENT FINDINGS

Acute lung injury/acute respiratory distress syndrome occurs in 6-8% of the general intensive care unit population, with a mortality of 32-45%. A recent epidemiologic study found that multi-organ dysfunction, use of tidal volumes higher than 6 ml/kg, and high mean fluid balance were independent risks for mortality. Although high levels of inflammatory mediators are also markers for acute respiratory distress syndrome development and death, short courses of high-dose steroids are not effective in acute cases. The latest theory of biotrauma proposes cellular mechanisms by which mechanical ventilation incites a local and systemic inflammatory response; protective lung ventilation with low tidal volumes can attenuate this inflammation and injury to distal organs. Endogenous surfactant function is clearly impaired, but no commercially available surfactant preparation has been shown to reduce mortality. Results of trials to determine efficacy of steroids in late cases and optimal fluid management are pending.

SUMMARY

The results of recent clinical trials have raised more questions. Further study of the inflammatory response, surfactant regulation, and the cellular impact of mechanical ventilation should help to develop new therapies, target patients most likely to benefit, and identify appropriate timing of intervention.

Pharmacologic therapies for adults with acute lung injury and acute respiratory distress syndrome

BACKGROUND

Multiple pharmacologic treatments have been studied for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS).

OBJECTIVES

Our objective was to determine the effects of pharmacologic treatments on clinical outcomes in adults with ALI or ARDS.

SEARCH STRATEGY

We searched OVID versions of CENTRAL (The Cochrane Library Issue 3, 2003), MEDLINE (1966 to week 2, January 2004), EMBASE (1980 to week 4, 2004), CINAHL (1982 to week 2, January 2004), and HEALTHSTAR (1995 to December 2003); proceedings from four conferences (1994 to 2003); and bibliographies of review articles and included studies.

SELECTION CRITERIA

Randomized controlled trials of pharmacologic treatments compared to no therapy or placebo for established ALI or ARDS in adults admitted to an intensive care unit, with measurement of early mortality (primary outcome), late mortality, duration of mechanical ventilation, ventilator-free days to day 28, or adverse events. We excluded trials of nitric oxide, partial liquid ventilation, fluid and nutritional interventions, oxygen, and trials in other populations reporting outcomes in subgroups of patients with ALI or ARDS.

DATA COLLECTION AND ANALYSIS

Two reviewers independently screened titles and abstracts, rated studies for inclusion, extracted data and assessed methodologic quality of included studies. Disagreements were resolved by consensus in consultation with a third reviewer. For each pharmacologic therapy, we quantitatively pooled the results of studies using random effects models where permitted by the available data. We contacted study authors when clarification of the primary outcome was required.

MAIN RESULTS

Thirty three trials randomizing 3272 patients met our inclusion criteria. Pooling of results showed no effect on early mortality of prostaglandin E1 (seven trials randomizing 697 patients; relative risk [RR] 0.95, 95% confidence interval [CI] 0.77 to 1.17), N-acetylcysteine (five trials randomizing 239 patients; RR 0.89, 95% CI 0.65 to 1.21), early high-dose corticosteroids (two trials randomizing 187 patients; RR 1.12, 95% CI 0.72 to 1.74), or surfactant (nine trials randomizing 1441 patients; RR 0.93, 95% CI 0.77 to 1.12). Two interventions were beneficial in single small trials; corticosteroids given for late phase ARDS reduced hospital mortality (24 patients; RR 0.20, 95% CI 0.05 to 0.81), and pentoxifylline reduced one-month mortality (RR 0.67, 95% CI 0.47 to 0.95) in 30 patients with metastatic cancer and ARDS. Individual trials of nine additional interventions failed to show a beneficial effect on prespecified outcomes.

REVIEWERS' CONCLUSIONS

Effective pharmacotherapy for ALI and ARDS is extremely limited, with insufficient evidence to support any specific intervention.

Differential role for T cells in the development of fibrotic lesions associated with reovirus 1/L-induced bronchiolitis obliterans organizing pneumonia versus Acute Respiratory Distress Syndrome

Bronchiolitis obliterans organizing pneumonia (BOOP) and Acute Respiratory Distress Syndrome (ARDS) are two pulmonary diseases with fibrotic components. BOOP is characterized by perivascular/peribronchiolar leukocyte infiltration leading to the development of intra-alveolar fibrosis. ARDS is a biphasic disease that includes an acute phase, consisting of severe leukocyte infiltration, edema, hemorrhage, and the formation of hyaline membranes, and a chronic phase, which is characterized by persistent intra-alveolar and interstitial fibrosis. CBA/J mice infected with 1 x 10(6) plaque-forming units (pfu) reovirus 1/L develop follicular bronchiolitis and intra-alveolar fibrosis similar to BOOP. In contrast, CBA/J mice infected with 1 x 10(7) pfu reovirus 1/L develop histologic characteristics of ARDS including diffuse alveolar damage, hyaline membranes, and intra-alveolar fibrosis. In this report, we demonstrate a differential role for T lymphocytes in the development of fibrosis associated with BOOP versus ARDS. Neonatally thymectomized CBA/J mice infected with 1 x 10(7) pfu (ARDS) reovirus 1/L still develop the hallmark characteristics of ARDS, including a severe viral pneumonia with cellular infiltrates comprised mainly of macrophages and neutrophils, hyaline membrane formation, and hemorrhage during the acute phase of the disease and persistent intra-alveolar fibrosis during the chronic phase of the disease. In contrast, neonatally thymectomized CBA/J mice infected with 1 x 10(6) pfu (BOOP) reovirus 1/L do not develop intra-alveolar fibrosis associated with BOOP. Therefore, while T cells are necessary for the development of intraluminal fibrosis associated with BOOP, they are not necessary for the development of intraluminal fibrosis associated with ARDS. Furthermore, we suggest that interferon-gamma plays a key role in the fibrotic process and that elevated levels of interferon-gamma are associated with a continuum from least to more severe fibrosis.

Respiratory reovirus 1/L induction of diffuse alveolar damage: pulmonary fibrosis is not modulated by corticosteroids in acute respiratory distress syndrome in mice

Acute respiratory distress syndrome (ARDS) is a clinical syndrome characterized by diffuse alveolar damage (DAD) secondary to an intense host inflammatory response of the lung to a pulmonary or extrapulmonary infectious or noninfectious insult. We have previously described a unique animal model in which CBA/J mice infected with reovirus 1/L develop ARDS. This model recapitulates the histopathological changes observed in human ARDS, which consist of the overlapping phases of exudation, including the formation of hyaline membranes, regeneration, and healing via repair with fibrosis. In this report, we show that the development of DAD in the acute phase of the disease and intraalveolar fibrosis in the late phase of the disease was not modulated by treatment with methylprednisolone (MPS). In the presence or absence of MPS, the majority of cells infiltrating the lungs after reovirus 1/L infection were polymorphonuclear leukocytes and macrophages. A number of key proinflammatory and anti-inflammatory cytokines/chemokines that are observed in the BAL fluid of ARDS patients were also found in the lungs of mice after reovirus 1/L infection and were not modulated by MPS. These include interferon-gamma, interleukin-10, and monocyte chemoattractant protein. The histopathology, cytokine/chemokine expression, and response to corticosteroids in reovirus 1/L-induced ARDS are similar to what is observed in human patients, making this a clinically relevant model.