Radiologic Considerations in the Adult Respiratory Distress Syndrome

Overview of current lung imaging in acute respiratory distress syndrome

Imaging plays a key role in the diagnosis and follow-up of acute respiratory distress syndrome (ARDS). Chest radiography, bedside lung ultrasonography and computed tomography scans can provide useful information for the management of patients and detection of prognostic factors. However, imaging findings are not specific and several possible differential diagnoses should be taken into account. Herein we will review the role of radiological techniques in ARDS, highlight the plain radiological and computed tomography findings according to the pathological stage of the disease (exudative, inflammatory and fibroproliferative), and summarise the main points for the differential diagnosis with cardiogenic oedema, which is still challenging in the acute stage.

Adult respiratory distress syndrome

ARDS or acute respiratory distress syndrome continues to be a considerable critical care challenge. Mortality has not decreased significantly over the last more than 30 years. This article presents an overview of origin, evaluation, and treatment of ARDS. Recent findings relative to onset and precipitators of ARDS have led to changes in evaluation and treatment plans. Clinical and radiologic descriptors in assessment of the patient with ARDS are discussed. Ventilatory modes and nursing interventions to optimize patient outcomes are identified. The challenges of outcomes issues presented offer opportunities for further study.

Radiologic determination of intravascular volume status using portable, digital chest radiography: a prospective investigation in 100 patients

OBJECTIVE

To answer the following questions: Can the digital chest roentgenogram (CXR) be used to differentiate patients' volume status? Do clinical data alter radiologists' accuracy in interpreting the digital CXR?

DESIGN

Prospective cohort study.

SETTING

Nine adult intensive care units of a tertiary care medical center.

PATIENTS

One hundred thirty-five consecutive patients with pulmonary artery catheters, of whom 35 were excluded because of unacceptable pulmonary artery occlusion pressure (PAOP) tracings.

METHODS

Each patient had a portable, anteroposterior, supine digital CXR. Clinicians evaluated volume status and then measured hemodynamic data within 1 hr of the CXR. Digital CXRs were independently interpreted on two separate occasions (with and without clinical information) by three experienced chest radiologists, and these interpretations were compared with hemodynamic data.

RESULTS

Of the 100 patients, 39 had PAOP >18 mm Hg, whereas 61 had PAOP <18 mm Hg. Radiologists' accuracy in differentiating volume status increased with incorporation of clinical data (56% without vs. 65% with clinical data, p =.009). Using objective receiver operating characteristic-derived cutoffs of 70 mm for vascular pedicle width and 0.55 for cardiothoracic ratio, radiologists' accuracy in differentiating PAOP >18 mm Hg from PAOP <18 mm Hg was 70%. The intrareader and the inter-reader correlation coefficients were very high. The likelihood ratio of the CXR in determining volume status using the objective vascular pedicle width and cardiothoracic ratio measures was 3.1 (95% confidence interval, 1.9-6.0), significantly higher than subjective CXR interpretations with and without clinical data (p <.001).

CONCLUSIONS

Differentiating intravascular volume status with portable, supine, digital CXRs may be improved by using objective cutoffs of vascular pedicle width >70 mm and cardiothoracic ratio >0.55 or by incorporating clinical data.

Radiographic findings in patients with acute respiratory distress syndrome

Since its description in 1967, acute respiratory distress syndrome (ARDS) has become a widely recognized, if somewhat imperfectly understood, entity. This article reviews the imaging characteristics of ARDS as demonstrated on plain chest radiography, CT scan, radionuclide imaging, and MR imaging. The abnormalities displayed on these modalities are well understood even though there may be some dispute as to their relative importance in diagnosing and managing patients.

Estudo de crianças com síndrome do desconforto respiratório agudo: correlação anatomoclínica radiológica

Estudo retrospectivo com revisão dos casos clínicos de Síndrome do Desconforto Respiratório Agudo, realizado no período de out/88 a dez/90 na Unidade de Pacientes Graves do Instituto Fernandes Figueira. Os autores estudaram as características clínicas, radiológicas e histopatológicas de acordo com o estágio evolutivo da doença. Dentre 459 casos estudados, foram selecionados 49 (11%). Onze casos tiveram exame anatomopatologico [biopsia (4), necropsia (8)] e foram classificados de acordo com o estágio evolutivo em: fase exsudativa inicial, fase proliferativa celular e fase proliferativa fibrótica. Houve correlação clínica radiológica e anatomopatológica nos casos confirmados com exame histológico. Os autores consideram importante estudos futuros em que a interação entre a pesquisa clínica e experimental permita o melhor conhecimento desta Síndrome na população pediátrica.

Appraising pulmonary edema using supine chest roentgenograms in ventilated patients

The role of portable, anteroposterior, supine chest X-rays (CXRs) in distinguishing hydrostatic pulmonary edema (HPE) from permeability pulmonary edema (PPE) in mechanically ventilated patients is controversial. We prospectively obtained and evaluated such CXRs in 33 supine, mechanically ventilated intensive-care-unit patients with pulmonary artery catheters. Three chest radiologists independently reviewed CXRs without clinical information and recorded the cardiothoracic (CT) ratio, vascular pedicle width (VPW), and other radiographic features commonly used to evaluate pulmonary edema. Hydrostatic pulmonary edema was associated with a larger CT ratio (p < 0.001), subjective impressions of cardiomegaly (p < 0.01), and increased VPW (p = 0.02). There was a significant correlation between the pulmonary artery occlusion pressure and the VPW (r = 0.45, p = 0.0076) and CT ratio (r = 0.52, p = 0.0016), as well as between the VPW and CT ratio (r = 0.49, p = 0.0032). Despite this detailed evaluation of the CXRs, the mean accuracy of the radiologists' clinical diagnosis of HPE versus PPE was 41%, and 15 of 19 (79%) of PPE patients showed one or more roentgenographic signs of volume overload. Receiver-operating-characteristic curves were constructed to determine optimum cut-off values of VPW and CT ratio associated with HPE. Hydrostatic pulmonary edema was found to correlate best using a VPW > 63 mm coupled to a CT ratio > 0.52 (p = 0.027). With this combination of objective criteria, radiologists' diagnostic accuracy could have been increased to 73%. We therefore conclude that measurements of CT ratio and VPW correlate with pulmonary artery occlusion pressure in supine, mechanically ventilated patients. Distinction of hydrostatic from permeability pulmonary edema is difficult using portable, supine CXRs, but readily assessed radiologic signs may contribute to the correct diagnosis.

Acute respiratory distress syndrome: diagnosis and management

This review will attempt to put together the voluminous studies and concepts that have been published during the past 25 years following the description of the acute respiratory distress syndrome (ARDS) regarding diagnosis and management. The initial discussion will focus on how to clinically diagnose ARDS based recommendations. This also gives the current definition of acute lung injury and when to call it ARDS. The radiographic and hemodynamic characteristics are discussed including oxygenation parameters. The management outlines the conventional as well as new therapies intended to improve survival of this devastating disease.

Computed tomography in established adult respiratory distress syndrome. Correlation with lung injury score

STUDY OBJECTIVES

To identify serial changes in the appearances of the lungs on computed tomography (CT) in patients with established adult respiratory distress syndrome (ARDS). Second, to evaluate any relationship between the extent of morphologic abnormalities on CT anatomic and physiologic derangement using a numeric score of the severity of lung injury.

DESIGN

Retrospective, descriptive.

SETTING

Adult intensive care unit, Department of Radiology, and outpatient department of a national tertiary referral center.

PATIENTS

Eight patients meeting diagnostic criteria for ARDS able to tolerate CT scanning during the acute phase of their illness and who survived to be reevaluated during convalescence.

INTERVENTIONS

Mechanical ventilatory support. Conventional intensive care support of other failed systems a appropriate.

MEASUREMENTS AND RESULTS

Thin-section CT scans of the lungs categorized as to extent (calculated percent volume of abnormal lung), distribution, and dominant disease pattern. Concurrent lung injury score (LIS) was recorded at the time of the CT during the acute phase of illness (mean, 26 days; range, 3 to 48 days after precipitating event) and at follow-up (96; 17 to 187 days). On initial CT scans, disease patterns included ground-glass opacification (8/8), parenchymal distortion (8/8), multifocal areas of consolidation (6/8), reticular opacities (6/8), and linear opacities (5/8). On follow-up scans, there was clearing of consolidation in all patients, but ground-glass opacification persisted in four of eight patients. The reticular pattern persisted unchanged in five of eight patients, became more extensive in two of eight, and developed in one. A reticular pattern was most pronounced in areas that had been densely consolidated previously. Evidence of parenchymal distortion, present on the initial scan in all patients, persisted in six of eight patients. Computed tomographic features suggestive of emphysema developed in one patient. The LIS revealed moderate to severe ARDS in all patients initially; this decreased to a mild or zero LIS at follow-up. Overall, there was 76.9% +/- 5.3% abnormal lung on the initial CT scan and 34.5 +/- 9.3% on the follow-up CT scan. There was a significant correlation between the extent of abnormalities on CT and LIS (r = 0.75, p < 0.01).

CONCLUSIONS

The CT appearances of patients with ARDS who survive are variable and relate to the pattern of disease in the acute phase. Furthermore, the extent of CT abnormalities correlates strongly with LIS in both the acute phase and at follow-up.

Adult respiratory distress syndrome in children

In spite of modern technological advances, ARDS continues to be an important cause of morbidity and mortality from a diverse group of disorders such as sepsis, trauma, and aspiration. ARDS represents a target organ injury resulting from activation of the host's inflammatory cells and uncontrolled liberation of inflammatory mediators. In most instances, therefore, ARDS is a localized manifestation of a widespread onslaught characteristic of SIRS. At this time, there are no proven interventions to prevent ARDS, and the management is mainly supportive. Modulation of the host's inflammatory response seems to hold the most promise for prevention and treatment of ARDS. Such strategies need to be explored with well-controlled clinical trials.