BACKGROUND: Cisatracurium unlike atracurium is devoid of histamine-induced cardiovascular effects and this alone would be the greatest advantage in replacing atracurium for the facilitation of tracheal intubation. On the other hand, 2 ED(95) doses of cisatracurium (100 micro g/kg) do not yield satisfactory intubating conditions such as those seen with equipotent doses of atracurium and therefore the recommended intubating dose of cisatracurium is 3 ED(95). To understand this discrepancy better, we evaluated the potency and onset of atracurium and cisatracurium directly at the larynx adductors in humans. METHODS: The study was conducted in 54 patients (ASA class I or II) undergoing peripheral surgery requiring general anesthesia. Cisatracurium 25-150 micro g/kg or atracurium 120-500 micro g/kg intravenous (i.v.) boluses doses were administered during anesthesia with propofol, nitrous oxide, oxygen and fentanyl. Neuromuscular block was measured by electromyography (single twitch stimulation every 10 s) at the larynx and the adductor pollicis. The dose-response effect measured at both muscles included maximum neuromuscular blockade achieved (Emax), the time to maximum depression of twitch height (onset) and time to spontaneous recovery of the twitch height to 25%, 75% and 90% (T25, T75, T90) of control value. RESULT: The onset at the larynx was of 196 +/- 28 s after the 100 micro g/kg cisatracurium dose compared with 140 +/- 14 s after the 500 micro g/kg atracurium dose (P < 0.05). Emax at the larynx was 92 +/- 1% and 98 +/- 1% after 100 micro g/kg cisatracurium and 500 micro g/kg atracurium, respectively (P < 0.05). The time to onset of maximum suppression Emax = 100 +/- 0% after a 150 micro g/kg cisatracurium dose was 148 +/- 29 s. At the larynx, the ED(50) was 25 micro g/kg for cisatracurium and 180 micro g/kg for atracurium and the ED(95) was 87 micro g/kg for cisatracurium compared with 400 micro g/kg for atracurium. CONCLUSION: The slow onset time at the laryngeal muscles after cisatracurium can be explained by the higher potency as compared with atracurium.
BACKGROUND:Cisatracurium unlike atracurium is devoid of histamine-induced cardiovascular effects and this alone would be the greatest advantage in replacing atracurium for the facilitation of tracheal intubation. On the other hand, 2 ED(95) doses of cisatracurium (100 micro g/kg) do not yield satisfactory intubating conditions such as those seen with equipotent doses of atracurium and therefore the recommended intubating dose of cisatracurium is 3 ED(95). To understand this discrepancy better, we evaluated the potency and onset of atracurium and cisatracurium directly at the larynx adductors in humans. METHODS: The study was conducted in 54 patients (ASA class I or II) undergoing peripheral surgery requiring general anesthesia. Cisatracurium 25-150 micro g/kg or atracurium 120-500 micro g/kg intravenous (i.v.) boluses doses were administered during anesthesia with propofol, nitrous oxide, oxygen and fentanyl. Neuromuscular block was measured by electromyography (single twitch stimulation every 10 s) at the larynx and the adductor pollicis. The dose-response effect measured at both muscles included maximum neuromuscular blockade achieved (Emax), the time to maximum depression of twitch height (onset) and time to spontaneous recovery of the twitch height to 25%, 75% and 90% (T25, T75, T90) of control value. RESULT: The onset at the larynx was of 196 +/- 28 s after the 100 micro g/kg cisatracurium dose compared with 140 +/- 14 s after the 500 micro g/kg atracurium dose (P < 0.05). Emax at the larynx was 92 +/- 1% and 98 +/- 1% after 100 micro g/kg cisatracurium and 500 micro g/kg atracurium, respectively (P < 0.05). The time to onset of maximum suppression Emax = 100 +/- 0% after a 150 micro g/kg cisatracurium dose was 148 +/- 29 s. At the larynx, the ED(50) was 25 micro g/kg for cisatracurium and 180 micro g/kg for atracurium and the ED(95) was 87 micro g/kg for cisatracurium compared with 400 micro g/kg for atracurium. CONCLUSION: The slow onset time at the laryngeal muscles after cisatracurium can be explained by the higher potency as compared with atracurium.