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Abstract & Commentary
Source: El-Orbany MI, et al. The neuromuscular effects and tracheal intubation conditions after small doses of succinylcholine. Anesth Analg 2004;98:1680-1685.
All emergency physicians should be quite familiar with the use of succinylcholine for neuromuscular blockade to facilitate endotracheal intubation. Given for this purpose, succinylcholine generally provides excellent intubation conditions within 60 seconds. When given in full intubation doses, succinylcholine is not metabolized fast enough to allow recovery of spontaneous respiration before oxyhemoglobin desaturation occurs.
The authors point out that the effective dose for 95% of people (ED95) of succinylcholine is 0.3 mg/kg, less than one-third the typical dose used in rapid sequence intubation (RSI). This study examined whether succinylcholine given in doses smaller than 1.0 mg/kg can produce satisfactory intubation conditions quickly enough to be used for RSI, but with a shorter recovery time in the event that a cannot-intubate-cannot ventilate situation occurs.
The authors conducted this study in the operating suite. The subjects were American-Society- of-Anesthesiology (ASA) physical status I and II (essentially healthy) patients between the ages of 18 and 65 years scheduled for elective surgical procedures that require general anesthesia and endotracheal intubation. Exclusion criteria included patients with hepatic, renal, cardiac, pulmonary, or neuromuscular disease, and patients taking medications known or suspected to interfere with neuromuscular transmission. Pregnant women, obese patients (body mass index > 28 kg/m2 ), patients with a history of abnormal response to succinylcholine, patients with abnormal airway exams, and patients with a history of difficult intubation also were excluded.
One hundred-fifteen patients were assigned randomly to one of five groups (23 patients each) according to the dose of succinylcholine to be given. The dosages tested were 0.3 mg/kg, 0.4 mg/kg, 0.5 mg/kg, 0.6 mg/kg, and 1.0 mg/kg. Induction was performed using fentanyl and propofol, and maintained by propofol and N2O in oxygen.
After the induction, patients received the assigned dose of succinylcholine. Intubation conditions were graded at 60 seconds using a standardized scale. Time of onset of paralysis, maximal twitch depression, time to initial twitch detection after paralysis, and time to 10%, 25%, 50%, and 90% twitch height recovery were recorded. Time to initial diaphragmatic movement and time to resumption of spontaneous respiratory movement were calculated.
Onset times were decreased with increasing doses of succinylcholine, up to a dose of 0.6 mg/kg (from 82 seconds to 55 seconds), but the onset time using 0.6 mg/kg did not differ significantly from the onset time using 1.0 mg/kg (55 vs 52 seconds). The maximum twitch depression was similar after 0.5 mg/kg, 0.6 mg/kg, and 1.0 mg/kg doses. Intubation conditions often were graded as unacceptable after the 0.3 mg/kg and 0.4 mg/kg doses. Intubation conditions were acceptable in all patients receiving 0.5 mg/kg or more of succinylcholine, with the 0.6 mg/kg and 1.0 mg/kg doses receiving identical marks.
Time to 50% and 90% twitch height recovery was significantly shorter in the 0.6 mg/kg group than in the 1.0 mg/kg group, and the time to resumption of regular spontaneous respiratory movements was significantly shorter in the 0.6 mg/kg group than in the 1.0 mg/kg group (4.0 + 0.5 minutes vs 6.2 + 0.8 minutes). The authors conclude that 0.5 to 0.6 mg/kg of succinylcholine produces clinically satisfactory intubation conditions one minute after administration. They stated that the latter dose is similar to the 1.0 mg/kg dose in onset time, neuromuscular block intensity, and intubation conditions. The authors recommend using the smaller doses because the shorter apnea time of the smaller doses may avoid critical oxyhemoglobin desaturation in healthy adult patients in whom ventilation cannot be assisted.
Commentary by Jacob W. Ufberg, MD
Although this study is interesting food for thought, and might be a reasonable change in operating suite practice habits, it does nothing to suggest that we should be changing our emergency department dose of succinylcholine for RSI (which, by the way, is 1.5 mg/kg and not the max dose of 1.0 mg/kg used in this study).
Several limitations make this study impossible to translate to emergency patients requiring emergent intubation. First, this study had very limited inclusion criteria, including only healthy, non-obese patients without any history of major medical problems. Thus, they basically studied patients having little to nothing in common with ED patients requiring RSI. Second, patients had prior induction of general anesthesia prior to the administration of succinylcholine. When performed in the ED, the induction and paralytic agents are given essentially simultaneously, likely putting a greater onus on the paralytic agent in establishing favorable intubation conditions in the ED rather than in the operating suite. Finally, patients receiving succinylcholine in the ED for RSI are usually in a condition where there is little alternative to endotracheal intubation. There is no such option in the ED as there was in this study: to ventilate the patient, allow him to wake up, and postpone the elective operation. Thus, the likely next step for emergency physicians is to attempt to secure the airway using difficult airway adjuncts or cricothyrotomy.
EPs are able to intubate more than 95% of patients successfully. Most of the remaining 5% can be ventilated. I, for one, am not ready to let potentially unfavorable intubation conditions jeopardize the majority for the remote possibility that I may encounter a cannot-intubate, cannot-ventilate situation in the very small minority. This study is interesting fodder for future research, however, it is not applicable currently to the ED patient requiring RSI.
Dr. Ufberg, Assistant Professor of Emergency Medicine, Residency Program Director, Department of Emergency Medicine, Temple University School of Medicine, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.