Pleural effusion in heart failure – on which side is it more common?
Conventionally it is considered that pleural effusion in heart failure is more common on the right side. If it is bilateral, it is likely to be more severe on the right side. In fact if it is more on the left side, the conventional teaching is that a cause other than heart failure is to be looked for. There have been several discussions on the sidedness of pleural effusion in heart failure one view is that the larger surface area of right lung permits more transudation into the right pleural cavity. Another technical aspect is that an enlarged heart on the left side may prevent the detection of minimal effusion on the left side clinically as well as on chest x-rays. But this does not apply to the detection of pleural effusion by an ultrasound examination. Another hypothesis which has been proposed is that individuals with heart failure prefer to lie in the right lateral position and hence it is a simple gravitational phenomenon to have larger effusions on the right side in heart failure. Recently Leung RS et al  evaluated 75 heart failure patients and 75 controls by nocturnal polysomnography with monitoring of body position. It was noted that patients with heart failure spent significantly less time in the left lateral position than in the right lateral position during sleep. No such difference was present in the controls. In the heart failure group, those with higher left ventricular end diastolic pressures, higher pulmonary capillary wedge pressure and lower cardiac output spent less time in left lateral position. This is presumed to be for avoiding the discomfort from the prominent apical heart beat or further hemodynamic derangement.
X-ray Chest PA showing pleural effusion in heart failure
In spite of all these considerations, a recent report by Woodring JH  has questioned this conventional wisdom. In a group of 120 patients with heart failure and pleural effusion demonstrated on chest x-ray at the time of admission, there were 207 effusions including both sides. There were 105 effusions on the right side and 102 on the left side. Isolated right sided effusion was seen in 18 while isolated left sided effusion was seen in 15. Bilateral effusions with right dominance was seen in 25, left dominance in 26 and co-dominance in 36. The difference was not statistically significant.
Mild degrees of pleural effusion in heart failure is often detected on echocardiography done for the evaluation of heart failure. Larger degrees of effusion can be detected on clinical evaluation or chest x-ray. Small pleural effusions are seen as echo free space above the hemidiaphragms when the echo transducer is being tilted in the subcostal view for imaging the heart. It one is specifically looking for pleural effusion, keeping the transducer on the lateral thoracic wall in the infra axillary region is useful to see pleural effusion as echo free regions, instead of the lung which gives dense white echoes.
Leung RS, Bowman ME, Parker JD, Newton GE, Bradley TD. Avoidance of the left lateral decubitus position during sleep in patients with heart failure: relationship to cardiac size and function. Am Coll Cardiol. 2003;41:227-30.
Woodring JH. Distribution of pleural effusion in congestive heart failure: what is atypical? South Med J. 2005 May;98(5):518-23.