Atropine sulfate for treatment of bradycardia in a patient with morbid obesity: what may happen when you least expect it

A 74-year-old morbidly obese man was scheduled for surgical repair of an incisional ventral hernia. Anaesthesia was induced with propofol and fentanyl, and maintained with desflurane. A second dose of fentanyl 0.2 mg, given before starting surgery, resulted in sinus bradycardia and mild decrease of arterial blood pressure. Atropine sulfate 0.5 mg was administered. One minute later, the ECG rhythm on the monitor changed to third degree atrioventricular block with a ventricular response rate of 40 beats/min associated with marked hypotension. Isoproterenol 0.02 mg reverted the atrioventricular block to sinus rhythm. Cardiac enzymes and ECG ruled out acute myocardial ischaemia. The surgical procedure and the recovery from anaesthesia were uneventful. The patient was discharged from the hospital on the fifth postoperative day. For the treatment of bradycardia atropine sulfate should be adjusted at least to lean body weight in order to avoid paradoxical heart rate response in patients with obesity.