To B or not to B - IS that the question?

Abstract

B lines are at best a simple tool, and require intelligent use to perform at test characteristics reported by the more favourable meta-analyses. B lines are an evanescent phenomenon. Their exact physical cause is uncertain. They came to light in the 1980s, and will probably become extinct in the next 5 years, as rapid improvement of transducer resolution replaces this mysterious artefact with real time depiction of the pleura and subpleural lung. The use of the B line is further threatened by automatic optimisation of machine settings - which aim to minimise artefact. B lines are just such artefacts, created by disease processes that affect the pleura - but modified by machines, settings and operators. Their integration into care has staunch supporters and vocal detractors. Belief in B lines suffered when the defining reference test crept from the radiological process (‘interstitial syndrome’) to the more specific ‘pulmonary oedema’. Intelligent use of the B line phenomenon requires a reversal of this process. B lines appear when the peripheral air/interstitial ratio of the lung drops below 99%. Picano divides them usefully into ‘wet’ and ‘dry’ B lines, the one due to transudate from the pulmonary capillary bed - rapidly evolving and amenable to fluid management, the second due to fixed deformity of the lung surface from less reversible inflammation or fibrosis. B lines lose sensitivity with conditions that begin at the hilum and are slow to affect the pleura, and this may be one reason for less utility in conditions such as ARDS and hyper-acute pulmonary oedema. The aim of this talk is to discuss literature investigating B lines, and combine it with our own experience of the traps and caveats of B lines, to illustrate how best to protect their reputation and optimise use.