The role of thoracic ultrasonography in the assessment of extravascular lung water and breathlessness

Patients with respiratory failure and breathlessness frequently present clinicians with a unique diagnostic and therapeutic challenge. These patients may be acutely unwell and in need of rapid intervention with limited information available to guide the responsible clinician. The range of different conditions that can present with breathlessness is broad, and differentiating one from another may be extremely difficult in a patient with multiple overlapping co-morbidities. Even when the cause of a patient’s breathlessness appears obvious, as can be the case with malignant pleural disease, identifying the best treatment option for that individual may not always be a straightforward process.
The use of bedside, or point-of-care ultrasound has become increasingly common over the past decade; moving away from a traditional home in the radiology department and entering the hands of clinicians who are responsible for diagnosing and treating patients on a day-to-day basis. The most widely accepted role for thoracic ultrasound is as an adjunct to pleural procedures, but as clinicians have become more familiar with its use the ways in which thoracic ultrasound is utilized have begun to diversify. As a result, there is growing interest in how thoracic ultrasonography might be used as a diagnostic tool in patients who are breathless, and in turn have a positive impact on their treatment and key clinical outcomes.
The purpose of this thesis is to evaluate some of the differing roles that thoracic ultrasonography might have in the clinical assessment and management of the patient with breathlessness and respiratory failure, and to focus on areas that are outside what is currently regarded as conventional practice. This thesis will begin to answer, through a series of clinical studies, specific questions that have the potential to change the way clinicians use bedside thoracic ultrasound examination to diagnose and treat their patients.
Malignant pleural effusion is an increasingly common problem, traditionally managed by chest tube drainage and intrapleural administration of a chemical sclerosant such as talc with the aim of achieving pleurodesis and preventing fluid recurrence. This treatment strategy is however unsuccessful in up to 30% of patients. The first study presented in this thesis examined the ability of thoracic ultrasound to predict long-term pleurodesis success in the immediate aftermath of talc slurry administration via an intercostal chest tube to treat recurrent symptomatic malignant pleural effusion, recognizing the ability of thoracic ultrasound to identify the presence of pleural adhesions in other clinical scenarios through the loss of the normal “lung sliding” artefact. 18 participants were recruited to a prospective observational cohort feasibility study, undergoing a standardised nine-point thoracic ultrasound examination immediately before, and 24 hours after talc slurry administration in order to derive a pleural adherence score for the affected hemithorax at each of these timepoints. The ultrasound scans were reported by the primary bedside operator and two independent assessors blinded to the participant’s clinical status. Study participants who went on to suffer pleurodesis failure had a lower pleural adherence score at 24 hours post-talc instillation than those who were successful. This novel association between a thoracic ultrasound-derived pleural adherence score and long-term pleurodesis success and failure should now be evaluated in further research to assess its utility in supporting decision making in the treatment of patients with malignant pleural effusion.
The second study looked at whether thoracic ultrasound examination prior to any intervention for a symptomatic pleural effusion could predict the presence of unexpandable lung and the subsequent relief of breathlessness; two clinical outcomes that are of great relevance to both patients and clinicians in determining longer-term management strategies, such as a decision to proceed with an attempt at chemical pleurodesis. 92 participants were recruited to this prospective observational study assessing whether any parameters included in a standardised in-depth thoracic ultrasound examination were associated with the outcomes of interest described above. A reduction in the excursion of atelectatic lung with cardiac pulse transmission, as measured by motion (M-) mode ultrasound, was associated with the presence of unexpandable lung; as were the presence of anechoic pleural fluid and pleural fluid septations in a subsequent exploratory regression model. Future studies should explore these candidate parameters in greater depth with a view to validating an ultrasound-based model that can predict the presence of unexpandable lung prior to any pleural intervention, with potential implications for personalized care of patients with symptomatic pleural effusion.
The presence of extravascular lung water, for example in the form of pulmonary oedema secondary to congestive cardiac failure, is among the most common causes of breathlessness that may result in a patient presenting for medical treatment. The third study presented in this thesis assessed the ability of thoracic ultrasound to detect the presence of, and identify real-time changes in extravascular lung water in patients with end-stage renal failure undergoing haemodialysis. Computed tomography was utilized to provide a gold-standard radiologic reference test to correlate with the findings on thoracic ultrasound in this patient population. 30 participants were recruited to this prospective observational study, undergoing a standardised 20-point thoracic ultrasound examination to derive a total lung ultrasound B-line score before, during and after haemodialysis. The ultrasound scans were reported by the primary bedside operator and two independent assessors blinded to the participant’s clinical status. The results suggest an association between a reduction in total B-line score and an increasing volume of fluid removed during haemodialysis, with potentially greater sensitivity to this physiological change in total body fluid status and extravascular lung water than computed tomography. Further research is needed to further evaluate the potential capability of thoracic ultrasound in both this controlled setting and other relevant clinical scenarios as a point-of-care diagnostic tool, with a view to how this might influence the management of acutely breathless patients and/or those with excess lung water.

Keywords: extravascular lung water
thoracic ultrasound
malignant pleural effusion
Advisor: Rahman, N
Gleeson, F