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Demo Question
A 55-year-old man is admitted to the Cardiac Intensive Care Unit from theatre following cardiac bypass surgery.
He has a history of diabetes and hypertension. An intra-aortic balloon pump is inserted for low cardiac output towards the end of surgery. His drains seem not to be draining much after 6 hours postoperatively. His blood pressure is low and urine output has tailed off.
Which of the following best describes the complications and management of this patient?
Enlarged cardiac shadow on the chest X ray is highly sensitive and specific in diagnosing a cardiac tamponade
Diastolic collapse of the right ventricle on a transoesophageal echo is a pathognomonic feature of tamponade
Low urine output is a very sensitive measure of cardiac output in the postoperative period
The intra-aortic balloon pump improves myocardial blood flow and oxygen delivery during systole
The presence of drains and lack of drainage precludes the cardiac tamponade
Key Learning Point
Characteristic echocardiographic features of a pericardial tamponade include abnormal septal movement with right atrial and ventricular diastolic collapse.
Explanation
Cardiac tamponade is the acute or chronic cardiac compression caused by the accumulation of pericardial fluid resulting in haemodynamic compromise. The classic Becks triad
of raised JVP, hypotension and quiet heart sounds.
The principal haemodynamic disturbance is a reduction in atrial filling with a fall in atrial diastolic volume. Trans-oesophageal echocardiography is the most reliable, non-invasive and convenient way of diagnosing the presence of an effusion, with or without thrombus and its haemodynamic effects. Characteristic features include abnormal septal movement with right atrial and ventricular diastolic collapse.
The chest X ray is not particularly sensitive, nor specific as it may be normal. Features suggestive of pericardial fluid include an enlarged globular cardiac shadow with a normal pulmonary vascular pattern.
Inflation of an intra-aortic balloon pump during diastole increases the pressure difference between aorta and left ventricle (diastolic pressure time index or DPTI). The haemodynamic consequence of this is an increase in coronary blood flow and, therefore, myocardial oxygen supply.
The urine output may fall as a result of a reduction of cardiac output and renal plasma flow. However, a fall in urine output may result from any changes in any of the Starling's forces acting across the glomerulus or nephrotoxic agents.
The presence of pericardial drains and lack of drainage does not rule out a pericardial effusion and cardiac tamponade.
