Ultrasound has particular usefulness in the critical care setting, with well-established applications for line placement and echocardiography. Questions remain regarding the validity of replacing traditional adjuncts with ultrasound. A previous Concise Critical Appraisal noted that thoracic ultrasound has been shown to be comparable to chest radiographs. In this review by Ashton-Cleary from Royal Cornwall Hospital in the United Kingdom, evidence is reviewed to evaluate the usefulness of thoracic ultrasound in the ICU.
MEDLINE, EMBASE, and Cochrane’s CENTRAL databases were searched as well as the International Standard Randomized Controlled Trial Number Register for relevant articles between 1995 and 2012. Eighty-eight articles of relevance were identified. The review specifically focused on ultrasound and comparative ability to detect or quantitate four common thoracic conditions in critical care: pleural effusion, consolidation, pulmonary edema, and pneumothorax. In each of the included studies, ultrasound was performed by physicians who were described explicitly or implicitly as having training and experience in the skill. Diagnostic measures for the four conditions were tabulated and included sensitivity, specificity, positive predictive value, negative predictive value, diagnostic accuracy, and area under the curve (AUC).
In studies comparing ultrasound to computed tomography (CT) or conventional chest radiograph (CXR), high sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy were noted with ultrasound. In all the included studies, ultrasound was noted to be superior to CXR in terms of sensitivity and NPV for detecting the presence and volume of pleural effusions. For consolidation and atelectasis, a combination of sonographic features was shown to have comparable diagnostic accuracy to CT, but these data were from a single author and were only repeated by one other group (though results were comparable). Ultrasound outperformed CXR and was similar to CT for the diagnosis of consolidation. In terms of evaluating extravascular lung water, sensitivity and specificity remained high when US was compared to pulmonary artery wedge pressure, CXR, and CT. For the differentiation between pulmonary edema from pneumonia, evidence was heterogeneous and further research is required. Whilst there are limited data available, based on the author’s review of diagnostic performance measures, ultrasound appears to be comparable and may possibly be superior for the early diagnosis of pneumothorax. However, the pneumothorax literature highlights the challenge of comparing ultrasound against CXR and other modalities for what is otherwise a relatively rare condition outside of trauma ICUs.
The data compiled by Ashton-Cleary suggest that in the hands of experts, thoracic ultrasound performance is equivalent to CT and surpasses CXR in many cases. Evidence suggesting that ultrasound has actually decreased the need for conventional imaging or replace it is essentially absent. Challenges that must be overcome before thoracic US is widely adopted include different US machines with varying resolution and recording capabilities as well as the lack of an agreed credentialing system since thoracic ultrasound is a new skill for many intensivists.
This Concise Critical Appraisal was authored by Jacob Glaser, MD, fellow in surgical critical care at the University of Maryland, R Adams Cowley Shock Trauma Center.
Samuel M. Galvagno Jr., DO, PhD, is editor of Concise Critical Care Appraisal. An assistant professor at the University of Maryland, R Adams Cowley Shock Trauma Center, he is board certified in anesthesiology, critical care medicine, and public health.