Should we care if Mavis has crackles?

Presentations to the ED with acute dyspnoea are a bit of challenge.  History, examination and tests are used to decide if people have heart failure, pneumonia, COPD, or something else.  I think diagnosing heart failure in the ED is a particular challenge, as commonly used ED strategies aren’t particularly good tests for LVF.

In a pretty robust study of patients with no cardiovascular disease, normal hearts on ECHO, and normal BNP measurements in 2007 the incidence of bibasal creps in the 80-95 age group was 70%. (CI 58-92% p<0.001).  Incidence increases with age with 11% in 45-64, 34% in 65-79.  The auscultator was the same senior cardiologist who was blinded to patient diagnoses, so someone who is better than your or I at listening with a steth.

Right okay.  So I should get a CXR then right?

Well…. a meta-analysis in 1997 looked at this and pooled data from 29 studies.

Sign Sensitivity Specificity
Venous Redistribution 65% (95 % CI 55-75%) 67% (95% CI 53-79%)
Cardiomegaly 51% (95% CI 43 – 60%) 79%(95% CI 71-85%)

So it’s not an excellent test to rule in or rule out heart failure, however I couldn’t get at the full text for this one, so I don’t know how they were defining a true positive diagnosis of left ventricular failure.

In a subsequent retrospective analysis of the Acute Decompensated Heart Failure National Registry (85 376 patients), 15 937 had CXRs with no signs of congestion on the initial ED XR.  That’s a negative rate of 18.7% (CI 18.4-18.9%).  So nearly 1 in 5 heart failure patients don’t have obvious CXR signs.

Right.  So is there any collection of tests or investigations that have a high sensitivity and specificity for diagnosing say interstitial oedema versus consolidation?

Yup.  Well…maybe…Lung USS.

Comet tail artifact (aka B-lines) on USS appear in heart failure but not generally in COPD.  In 66 consecutive patients with dyspnoea and 80 patients without.  B-lines appeared in all 40 patients with pulmonary oedema.   That gives a sensitivity of 100% and a specificity of 92%.   (1 normal patient had them, and 2 COPD patients had ‘em).

However the gold standard test they were using to diagnose LVF or COPD was a CXR (blinded).  This means that they were not really using a great test to compare the new test to.  Also we’ve not got large trials of lung USS compared to any other tests, so the best I can say with any integrity is that it’s promising.

Really promising; The ETUDES study published in january 2009, compared B-lines and N-type BNP (blood test ‘for heart failure).  They did a prospective blinded, observational study for a convenience sample of patients (bias alert) presenting to the ED with dypsnoea.   They did an 8 zone lung USS, if all 8 zones were positive for B-lines the  positive LR ratio for pulmonary oedema was infinite (diagnostic).  Scanners were USS happy ED physicians or medical students who had had 2.5 hrs training .  USS performed better than BNP, but this was a single centre study, with inherent bias, and a small sample size.

So in summary –

Use the quiet time listening to the back of an old persons’ chest to think about what you are going to do.  The bases will be crackly.

You don’t need a CXR to diagnose LVF as 20% of the time your CXR is going to be clear.

Lung USS is promising.

References:

Kataoka H, Matsuno O. Age-Related Pulmonary Crackles (Rales) in Asymptomatic Cardiovascular Patients. Annals of Family Medicine. 2008;6(3):239-245. doi:10.1370/afm.834. 

 Badgett, Robert G., et al. “How well can the chest radiograph diagnose left ventricular dysfunction?.” Journal of general internal medicine 11.10 (1996): 625-634.

Collins, Sean P., et al. “Prevalence of negative chest radiography results in the emergency department patient with decompensated heart failure.” Annals of emergency medicine 47.1 (2006): 13-18.

 Lichtenstein D, Mezière G. A lung ultrasound sign allowing bedside distinction between pulmonary edema and COPD: The comet-tail artifact. Intensive Care Med. 1998 Dec;24(12):1331–4.

Liteplo, Andrew S., et al. “Emergency Thoracic Ultrasound in the Differentiation of the Etiology of Shortness of Breath (ETUDES): Sonographic B‐lines and N‐terminal Pro‐brain‐type Natriuretic Peptide in Diagnosing Congestive Heart Failure.” Academic Emergency Medicine 16.3 (2009): 201-210.