Neuromuscular blocking drugs are used frequently during general anesthesia. The effects of neuromuscular blocking drugs are measured using a twitch monitor, that stimulates the ulnar nerve and measures the evoked response of the adductor pollicis muscle (thumb flexion), or other intrinsic hand muscle. When a series of 4 twitches is administered, the ratio of the first to the fourth twitch (train-of-four ratio) may be used to gauge the degree of muscle relaxation. A train-of-four ratio of 0.9 or greater is considered to represent adequate recovery from neuromuscular blockade. At the end of surgery, antagonists of neuromuscular blockade are commonly administered to reverse any remaining muscle relaxation. Sugammadex is a highly effective reversal agent of the aminosteroid neuromuscular blockings drugs rocuronium and vecuronium, which are the most commonly used neuromuscular blocking drugs. The recommended dose of sugammadex depends upon the degree of neuromuscular blockade. When at least 1 twitch of the train-of-four is present, the recommended dose of sugammadex is 2 mg/kg. When there are no twitches of the train-of-four present, but at least 1 count of the post tetanic count is present, the recommended dose of sugammadex is 4 mg/kg. However, in several dose ranging studies of sugammadex, and in using sugammadex clinically, we and others have determined that smaller doses of sugammadex, often much less than 2 mg/kg, may be effective producing a train-of-four ratio of 0.9 or greater. Sugammadex binds (encapsulates) aminosteroid neuromuscular blocking drugs tightly and the sugammadex-aminosteroid complex is subsequently cleared by the kidney. Therefore we do not expect that recurrence of neuromuscular blockade would occur, even after small doses of sugammadex, as long as the dose of sugammadex is adequate to produce a train-of-four ratio of 0.9. However, additional studies are needed to confirm that recurrence of neuromuscular blockade does not occur after small doses of sugammadex. The purpose of the proposed study is to test the hypothesis that when sugammadex is titrated in 50 mg increments until the train-of-four ratio is 0.9 or greater, that this train-of-four ratio is maintained and there is no recurrence of neuromuscular blockade.
Neuromuscular blockade will be monitored with EMG (electromyography)-based quantitative twitch monitoring (TwitchView). At the end of cardiac surgery, sugammadex will be administered to reverse neuromuscular blockade, as defined by a train-of-four ratio of 0.9 or greater. The patient will then transported asleep, intubated and ventilated to the intensive care unit where the train-of-four ratio of 0.9 or greater will be confirmed on arrival by the respiratory therapist.
Instead of administering a standard dose of sugammadex 2 mg/kg or 4 mg/kg, sugammadex will be titrated in 50 mg increments every 5 minutes until a train-of-four ratio of 0.9 or greater is reached. Train-of-four ratio will be measured on arrival in the intensive care unit and then hourly for 6 hours or until extubation if extubation occurs in \<6 hours. If the train-of-four ratio is less than 0.9 at any time, additional sugammadex will be administered until the train-of-four ratio is 0.9 or greater. The twitch monitoring results in the operating room just prior to reversal, following reversal and hourly in the intensive care unit will be recorded, along with sugammadex doses. The total dose of rocuronium or vecuronium and the time period of neuromuscular blocking drug will also be recorded. Data will either be recorded in real time by study assistants or retrieved from the electronic medical record. The patient's age, gender, and weight will be recorded.