Neostigmine or β-blockers? A pharmacologic conundrum

Abstract

T HE CONTROL OF heart rate and rhythm under anesthesia may present difficulty in the presence of coincident valvular heart disease, poor ventricular function, or pressure-dependent organ perfusion; particularly when currently available antiarrhythmic drugs, such as betablockers and calcium antagonists, may have undesirable negative inotropic or vasodilator effects in addition to their desired chronotropic effects. Neostigmine is used routinely in anesthetic practice as an anticholinesterase to provide “reversal” of nicotinic cholinergic blockade at the neuromuscular junction. Concurrent administration of anticholinergic drugs, (atropine or glycopyrronium) is usual to prevent troublesome muscarinic side effects, such as bradycardia. Both neostigmine and edrophonium have been used by bolus injection and by continuous infusion, in the case of edrophonium, to treat supraventricular arrhythmias in awake patients, making specific use of such side effects.‘” The use of low-dose neostigmine as a negative chronotrope in an anesthetized patient is described, in whom conventional agents were thought to be more likely to cause undesirable effects than the deliberate use of the muscarinic side effects of neostigmine. left axillo-bifemoral conduit was established to provide distal perfusion. A total of 12 L of blood was lost. Warmed whole blood, crystalloid and colloid solutions were used to maintain filling pressures as nearly as possible at preincision levels. During siting of the axillo-bifemoral graft, the heart rate rose from 85 to 112 beats/min (sinus rhythm), the blood pressure from 190/100 to 2101120 mmHg, and the pulmonary artery diastolic pressure from 21 to 31 mmHg. A further dose of fentanyl(6 kg/kg) was administered, with no effect on heart rate. It is believed that, in the presence of aortic stenosis and poor ventricular function, associated with massive blood transfusion, the rise in heart rate was leading to cardiac decompensation. The heart rate had to be lowered with minimum reduction of contractility and peripheral resistance. Accordingly, vecuronium, 8 mg, was given to maintain nicotinic blockade, followed by neostigmine in 100 kg aliquots to a total of 400 pg. Over the next 5 minutes reductions occurred in the heart rate from 112 to 65 beats/min, in the PA diastolic pressure from 31 mmHg to 22 mmHg, and in the blood pressure from 2101120 to 1701110 mmHg. Subsequently, anesthesia and surgery were uneventful and the patient was returned to intensive care where she was ventilated postoperatively for 36 hours. The patient left the hospital 15 days later, with no additional changes in her ECG to suggest any acquired myocardial damage.