Acute lung injury: is the intensive care unit the tip of the iceberg?

The Acute Respiratory Distress Syndrome: Role of Nutritional Modulation of Inflammation Through Dietary Lipids

The acute respiratory distress syndrome (ARDS) is the most serious form of acute hypoxic respiratory failure. ARDS represents the expression of an acute, diffuse, inflammatory process in the lungs consequent to a variety of infectious and noninfectious conditions. It is characterized pathologically by damage to pulmonary epithelial and endothelial cells, with subsequent alveolar-capillary leak and exudative pulmonary edema. The main clinical features of ARDS include rapid onset of dyspnea, severe defects in gas exchange, and imaging studies demonstrating diffuse pulmonary infiltrates. The role of nutrition in the management of ARDS has traditionally been supportive. Recent research has demonstrated the potential of certain dietary oils (eg, fish oil, borage oil) to modulate pulmonary inflammation, thereby improving lung compliance and oxygenation, and reducing time on mechanical ventilation. This article reviews the alterations in the immune response that underlie ARDS, discusses the physiology of dietary oils as immunonutrients, summarizes animal and human studies that explore the therapeutic effects of dietary oils, and provides clinical recommendations for their use.

Prevalence of acute lung injury among medical patients in the emergency department

BACKGROUND

Acute lung injury (ALI) affects an estimated 190,000 persons per year in U.S. intensive care units (ICUs), but little is known about its prevalence in the emergency department (ED).

OBJECTIVES

The objective was to describe the prevalence of ALI among mechanically ventilated adult nontrauma patients in the ED. The hypothesis was that the prevalence of ALI in adult ED patients would be low.

METHODS

This was a retrospective cohort study of admitted nontrauma patients presenting to an academic ED. Two trained investigators abstracted data from patient records using a standardized form. The use of mechanical ventilation in the ED was identified in two phases. First, all ED patients were screened for the current procedural terminology (CPT) code for endotracheal intubation (CPT 31500) from January 1, 2003, to December 31, 2006. Second, each patient record was reviewed to verify the use of mechanical ventilation. ALI was defined in accordance with a modified version of the American-European Consensus Conference criteria as: 1) hypoxemia defined as PaO(2) /FiO(2) ratio ≤300 mm Hg on all arterial blood gases (ABGs) in the ED and the first 24 hours of admission, 2) the presence of bilateral infiltrates on chest radiograph, and 3) the absence of left atrial hypertension. Data are presented in absolute numbers and percentages. Interobserver agreement was evaluated using the kappa statistic.

RESULTS

Of the 552 patients who received mechanical ventilation in the ED and were subsequently admitted, a total of 134 (24.3%, 95% confidence interval [CI] = 20.8% to 28.0%) met hypoxemia criteria. Of these, 34 had evidence of left atrial hypertension, 52 did not have chest radiograph findings consistent with ALI, and two did not have a chest radiograph performed; the remaining 46 met ALI criteria. An additional two patients who died in the ED had clinical evidence of ALI. Thus, 48 of 552, or 8.7% (95% CI = 6.6% to 11.3%), met criteria for ALI. The kappa value for determination of ALI was 0.84 (95% CI = 0.54 to 1.0).

CONCLUSIONS

The prevalence of ALI was nearly 9% in adult nontrauma patients receiving mechanical ventilation in the ED. Further study is required to determine which types of patients present to the ED with ALI, the extent to which lung protective ventilation is used, and the need for ED ventilator management algorithms.

Acute lung injury outside of the ICU: incidence in respiratory isolation on a general ward

BACKGROUND

Epidemiologic investigations of acute lung injury (ALI) and ARDS have focused on mechanically ventilated patients in ICUs, and have reported high mortality rates. We sought to determine the incidence and lethality of these syndromes in the respiratory isolation areas of general wards, a non-ICU setting that often serves patients with acute lung processes.

METHODS

We prospectively studied all patients who were admitted to respiratory isolation rooms on the general wards of a large tertiary care hospital over a 1-year period. Patients were classified as having ALI or ARDS if they met consensus definitions for the syndromes. Characteristics and outcomes were compared to those of other patients who had been admitted to a respiratory isolation room with infiltrating lung disease but lacking bilateral infiltrates, hypoxemia, or both.

RESULTS

Of 715 patients admitted to respiratory isolation rooms on general wards, 474 (66%) had acute infiltrates. ALI criteria were met by 9% of patients (62 of 715 patients), with 2% of patients (15 of 715) satisfying the criteria for ARDS. Respiratory distress was present in 71% of ALI patients (44 of 62 patients) and 32% of patients (130 of 412 patients) with acute infiltrates who did not have ALI (p < 0.001). However, the 90-day survival rates (ALI patients, 88%; patients with acute infiltrates who did not have ALI, 90%) was similar between the two groups (p > 0.50).

CONCLUSIONS

ALI and ARDS may be frequent among patients who are admitted to respiratory isolation beds outside of ICUs. Mortality rates are substantially lower than those typically reported from surveys of ventilated ICU patients with ALI and ARDS.

Clinical risk conditions for acute lung injury in the intensive care unit and hospital ward: a prospective observational study

BACKGROUND

Little is known about the development of acute lung injury outside the intensive care unit. We set out to document the following: the association between predefined clinical conditions and the development of acute lung injury by using the American-European consensus definition; the frequency of lung injury development outside the intensive care unit; and the temporal relationship between antecedent clinical risk conditions, intensive care admission, and diagnosis of lung injury.

METHODS

We conducted a 4-month prospective observational study in three Spanish teaching hospitals, enrolling consecutive patients who developed clinical conditions previously linked to lung injury, both inside and outside the intensive care unit. Patients were followed prospectively for outcomes, including the diagnosis of acute lung injury or acute respiratory distress syndrome.

RESULTS

A total 815 patients were identified with at least one clinical insult; the most common were sepsis, pneumonia, and pancreatitis. Pulmonary risk conditions were observed in 30% of cases. Fifty-three patients (6.5%) developed acute lung injury; 33 of these (4.0%) met criteria for acute respiratory distress syndrome. Lung injury occurred most commonly in the setting of sepsis (46/53; 86.7%), but shock (21/59; 36%) and pneumonia (20/211; 9.5%) portended the highest proportional risk; this risk was higher in patients with increasing numbers of clinical risk conditions (2.2%, 14%, and 21% (P < 0.001) in patients with one, two, and three conditions, respectively). Median days (interquartile range) from risk condition to diagnosis of lung injury was shorter with pulmonary (0 (0 to 2)) versus extrapulmonary (3 (1 to 5)) (P = 0.029) risk conditions. Admission to the intensive care unit was provided to 9/20 (45%) patients with acute lung injury and to 29/33 (88%) of those with acute respiratory distress syndrome. Lung injury patients had higher mortality than others (acute lung injury 25.0%; acute respiratory distress syndrome 45.5%; others 10.3%; P < 0.001).

CONCLUSION

The time course from clinical insult to diagnosis of lung injury was rapid, but may be longer for extrapulmonary cases. Some patients with lung injury receive care and die outside the intensive care unit; this observation needs further study.

Acute lung injury: an indicator of serious systemic illness

The history of the acute respiratory distress syndrome (ARDS) parallels that of critical care. Descriptive and colorful names for the condition such as "shock lung," "post perfusion lung," and "traumatic wet lung" clearly communicate the reality that the pulmonary tissue is involved in a pathologic process. It is not difficult to speculate that the focus on the lung originated from the dramatic chest radiographs and gas exchange abnormalities frequently observed in association with the syndrome. However, a named condition does not necessarily dictate the therapeutic approach to it, and a review of some pertinent studies suggests the condition is in fact systemic in nature. Concurrent with this recognition, the need for markers of severity of illness has become more important. Rather than a process needing primarily pulmonary approaches to management, it now seems that ARDS is the result of systemic events with noticeable pulmonary manifestations, which may suffice as a clinical marker for severity of systemic inflammation. Because the pathophysiology has been described elsewhere, this article will focus on the clinical trials that are shaping our perception and management of the syndrome.