Lung US Detects Asymptomatic Lung Congestion

Technique can detect congestion before symptoms arise


Highlights

• Lung ultrasound can detect asymptomatic lung congestion in dialysis patients and can predict their risk of dying prematurely or experiencing heart attacks or other cardiac events.

• Treating asymptomatic lung congestion may help improve cardiovascular health and prevent cardiovascular deaths in dialysis patients.

• Lung congestion is highly prevalent and often asymptomatic among patients with kidney failure.


Washington, DC (February 28, 2013) — Asymptomatic lung congestion increases dialysis patients' risks of dying prematurely or experiencing heart attacks or other cardiac events, according to a study appearing in an upcoming issue of the Journal of the American Society of Nephrology(JASN). The study also found that using lung ultrasound to detect this congestion helps identify patients at risk.

Lung congestion due to fluid accumulation is highly prevalent among kidney failure patients on dialysis, but it often doesn't cause any symptoms. To see whether such asymptomatic congestion affects dialysis patients' health, Carmine Zoccali, MD (Ospedali Riuniti, Reggio Calabria, Italy) and his colleagues measured the degree of lung congestion in 392 dialysis patients by using a very simple and inexpensive technique: lung ultrasound.

Among the major findings:

• Lung ultrasound revealed very severe congestion in 14% of patients and moderate-to-severe lung congestion in 45% of patients.

• Among those with moderate-to-severe lung congestion, 71% were asymptomatic.

• Compared with those having mild or no congestion, those with very severe congestion had a 4.2-fold increased risk of dying and a 3.2-fold increased risk of experiencing heart attacks or other cardiac events over a two-year follow-up period.

• Asymptomatic lung congestion detected by lung ultrasound was a better predictor of patients' risk of dying prematurely or experiencing cardiac events than symptoms of heart failure.

The findings indicate that assessing subclinical pulmonary edema can help determine dialysis patients' prognoses. "More importantly, our findings generate the hypothesis that targeting subclinical pulmonary congestion may improve cardiovascular health and reduce risk from cardiovascular death in the dialysis population, a population at an extremely high risk," said Dr. Zoccali. Fluid in the lungs may be reduced with longer and/or more frequent dialysis.

Investigators will soon start a clinical trial that will incorporate lung fluid measurements by ultrasound and will test whether dialysis intensification in patients with asymptomatic lung congestion can prevent premature death and reduce the risk of heart failure and cardiac events.

 

_________________________________________

 

Lung Ultrasound (LUS) examination

Methodology

LUS examination can be performed using any commercially available 2-D scanner, with any transducer (phased-array, linear-array, convex, microconvex). There is no need for a second harmonic or Doppler imaging mode. The examination can be performed with any type of echographic platform, from fully equipped machines to pocket size ones.^[15] Patients can be in the near-supine, supine or sitting position, as clinically indicated.^[16] All the chest can be easily scanned by ultrasound, just laying the probe along the intercostal spaces. However, some specific methods have been proposed: ultrasound scanning of the anterior and lateral chest may be obtained on the right and left hemithorax, from the second to the fourth (on the right side to the fifth) intercostal spaces, and from the parasternal to the axillary line, as previously described;^[7,17] (figure 2). Other approaches have been proposed, for instance by Volpicelli et al.,^[10] with evaluation of 8 scanning sites, 4 on the right and 4 on the left hemithorax. When assessing B-lines - the most informative LUS sign for the cardiologist - the sum of B-lines found on each scanning site yields a score, denoting the extent of extravascular fluid in the lung. In each scanning site, B-lines may be counted from zero to ten. Zero is defined as a complete absence of B-lines in the investigated area; the full white screen in a single scanning site is considered, when using a cardiac probe, as corresponding to 10 B-lines (figure 3). Sometimes B-lines can be easily enumerated, especially if they are a few; whereas, when they are more numerous, it is less easy to clearly enumerate them, since they tend to be confluent. In this situation, in order to obtain a semiquantification of the sign, one can consider the percentage of the scanning site occupied by B-lines (i.e. the percentage of white screen compared to black screen) and then divide it by ten (figure 3). For clinical purposes, B-lines may be categorized from mild to severe degree, similar to what is done for most echocardiographic parameters,^[16] (Table 1). B-lines have a very satisfactory intraobserver and interobserver variability, around 5% and 7%, respectively.^[7]

Limitations

LUS limitations are essentially patient dependent. Obese patients are frequently difficult to examine because of the thickness of their ribcage and soft tissues. The presence of subcutaneous emphysema or large thoracic dressings alters or precludes the propagation of ultrasound beams to the lung periphery.

The main limitation of B-lines is the lack of specificity. As already mentioned, they are a sign of interstitial syndrome, therefore they are a very sensitive but not specific sign of cardiogenic pulmonary edema. How to distinguish the different etiologies of B-lines has been discussed. However, it must be always reminded that all instrumental data should be evaluated within the clinical context and integrated with patient's history. No single test alone allows to establish the diagnosis.

 

From

Lung Ultrasound: A New Tool for the Cardiologist - Medscape

and Lung Ultrasound by L. Gargani 2011

Further reading : A-LINES, B-LINES and AIR ARTIFACTS