Home Health Acute Respiratory Distress Syndrome
Technical Advantages and Limitations
Chest X-ray represents an inexpensive imaging technique, routinely and ubiquitously applied. The role of chest radiography is still actual, radiological findings are integral part of the diagnostic process, and X-ray images are still useful to detect malposition of tubes, catheters, and associated complications . All patients admitted to an ICU receive at least one chest X-ray.
Nevertheless, the ICU features and the mandatory bedside application of radiography in these patients affect the quality of images. This technique has poor contrast diagnostic resolution, and in addition to this, the anterior-posterior view, the noncooperation of patients, and the presence of several lines in the field (e.g., endotracheal tube, arterial and central venous catheter, electrocardiogram monitoring, nasogastric tube, etc.) affect the quality of final imaging (Fig. 10.2).
Computed tomography represents the gold standard technique for the management of ARDS patients and provides several advantages: since from the 1980s, it has been used to study the inhomogeneous pattern of lung abnormalities in ARDS .
As described before, computed tomography allows to investigate the response to different types of ventilation in terms of lung morphology, lung recruitment, and overdistention.
Fig. 10.2 Bedside application of chest X-ray in intensive care unit patients
Moving from these considerations, the use of CT scan analysis has spread in spite of risks of transferring critically ill patients outside the ICU to radiological department and of the risk of X-ray radiation exposure.
The radiation dose applied to perform a CT exam is related to image definition; the higher the dose, the lower the image noise; nevertheless, it is known that exposure to radiation could be associated with an increased incidence of cancer [46-49]. Moreover, a dose-effect relationship was observed , and the exposure to radiation during CT scans even if not able to cause immediate damage could be associated with subsequent sequelae .
Currently, no consensus for optimal acquisition is available; in the literature, a wide range of radiation dose is reported (tube current-time products from 100 to 350 mAs). Since from the 1990s, the use of low-dose chest CT was described to underline the possibility to visualize lung parenchyma reducing the effective mAs . Recently Chiumello et al. aimed to evaluate the accuracy of quantitative analysis and the accuracy of visual anatomical analysis using low-dose chest CT to estimate lung recruitability in 45 ARDS patients . Of note, the reduction of radiation dose (up to 30 mAs of the applied tube current-time product) did not affect the accuracy of quantitative analysis, and visual anatomical evaluation of lung recruitability was sufficiently accurate (Fig. 10.3). This study can open the prospective to potentially monitor ARDS patients by CT scan with a substantial reduction of radiation exposure.
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