Hypotension due to unexpected cardiac tamponade.

We report a case of profound hypotension, after induction of general anaesthesia, that resulted from unexpected cardiac tamponade. The differential diagnosis was complicated by the absence of any evidence to indicate that there was significant direct chest injury. Many of the recognised clinical signs of cardiac tamponade were absent, in particular, there was no compensatory tachycardia, and heart rate remained stable despite severe hypotension before surgical drainage of the pericardium. The possible aetiology and pathophysiology is discussed. It is suggested that after major trauma, cardiac tamponade should be considered as a possibility even in the absence of significantly abnormal cardiovascular signs, evidence of direct chest injury, or an abnormal chest X ray.