Accuracy of Daily Lung Ultrasound for the Detection of Pulmonary Edema Following Subarachnoid Hemorrhage

Neurogenic pulmonary edema in subarachnoid hemorrhage: relevant clinical concepts

BACKGROUND

Subarachnoid hemorrhage (SAH) continues to be a condition that carries high rates of morbidity, mortality, and disability around the world. One of its complications is neurogenic pulmonary edema (NPE), which is mainly caused by sympathetic hyperactivity. Due to the complexity of the pathophysiological process and the unspecificity of the clinical presentation, it is little known by general practitioners, medical students and other health care workers not directly related to the neurological part, making the management of this chaotic condition difficult. This review aims to present recent evidence on clinical concepts relevant to the identification and management of NPE secondary to SAH.

MAIN BODY OF THE ABSTRACT

NPE is defined as a syndrome of acute onset following significant central nervous system (CNS) injury. Its etiology has been proposed to stem from the release of catecholamines that produce cardiopulmonary dysfunction, with this syndrome being associated with spinal cord injury, cerebrovascular disorders, traumatic brain injury, status epilepticus, and meningitis. NPE has long been considered a rare event; but it may occur more frequently, mainly in patients with SAH. There are two clinical presentations of NPE: the early form develops in the first hours/minutes after injury, while the late form presents 12-24 h after neurological injury. Clinical manifestations consist of non-specific signs of respiratory distress: dyspnea, tachypnea, hypoxia, pink expectoration, crackles on auscultation, which usually resolve within 24-48 h in 50% of patients. Unfortunately, there are no tools to make the specific diagnosis, so the diagnosis is by exclusion. The therapeutic approach consists of two interventions: treatment of the underlying neurological injury to reduce intracranial pressure and control sympathetic hyperactivity related to the lung injury, and supportive treatment for pulmonary edema.

SHORT CONCLUSION

SAH is a severe condition that represents a risk to the life of the affected patient due to the possible complications that may develop. NPE is one of these complications, which due to the common manifestation of a respiratory syndrome, does not allow early and accurate diagnosis, being a diagnosis of exclusion. Therefore, in any case of CNS lesion with pulmonary involvement, NPE should be suspected immediately.

Optimizing B-lines on lung ultrasound: an in-vitro to in-vivo pilot study with clinical implications

B-lines on lung ultrasound (US) are the hallmark of pulmonary edema. It is unknown if ultrasound machine settings or probe type matter. We created an in-vitro gelatin model. Using lung presets as baseline, five blinded investigators assessed the impact of 32 distinct settings on B-line visibility based on a Likert-Scale (LS) from 0 to10 (< 5 worse, > 5 better) separately for two probes. The experiment was then repeated in-vivo in a patient with known pulmonary edema. Based on a multivariable regression LS-ratings were similar when comparing the in-vitro versus in-vivo experiment (P = 0.16; partial R² = 0.2%) and when using the curvilinear versus linear probe (P = 0.69; partial R² = 0.02%) but significantly different across machine settings (P < 0.0001; partial R² = 34.4%). Limited by its pilot character, our study suggests that (1) certain US-machine settings heavily impact B-line visibility, with no clear difference between probes; (2) in-vitro models are a valid and practical alternative to more challenging patient-based research; (3) there is significant potential to improve B-line visibility and thus diagnostic yield in the clinical setting by using lung presets, centering the focal zone at the pleural line and increasing the distal time gain compensation, most of which are (in our experience) rarely done.

Correlation of B-Lines on Ultrasonography With Interstitial Lung Disease on Chest Radiography and CT Imaging

BACKGROUND

We prospectively identified B-lines in patients undergoing ultrasonographic (US) examinations following liver transplantation who also had chest radiography (CXR) or chest CT imaging, or both, on the same day to determine if an association between the presence of B-lines from the thorax on US images correlates with the presence of lung abnormalities on CXR.

METHODS

Following institutional review board (IRB) approval, patients who received liver transplants and underwent routine US examinations and chest radiography or CT imaging, or both, on the same day between January 1, 2015 through July 1, 2016 were prospectively identified. Two readers who were blinded to chest films and CT images and reports independently reviewed the US interreader agreement for the presence or absence of B-lines and performed an evaluation for the presence or absence of diffuse parenchymal lung disease (DPLD) on chest films and CT images as well as from clinical evaluation. Receiver operating characteristic (ROC) curves were constructed.

RESULTS

There was good agreement between the two readers on the presence of absence of B-lines (kappa = 0.94). The area under the ROC curve for discriminating between positive DPLD and negative DPLD for both readers was 0.79 (95% CI, 0.71-0.87).

CONCLUSIONS

There is an association between the presence of extensive B-lines to the point of confluence and "dirty shadowing" on US examinations of the chest and associated findings on chest radiographs and CT scans of DPLD. Conversely, isolated B-lines do not always correlate with abnormalities on chest films and in fact sometimes appear to be a normal variant.