Succinylcholine-induced phase II block and pharmacodynamics in rat diaphragm

BACKGROUND: Succinylcholine causes phase II block by a large dose or a prolonged exposure. There are rare data in a pharmacodynamics of phase II block. The purpose of this study was to investigate a concentration-response relationship, the occurrence and recovery of phase II block, and to clarify whether pretreatment of succinylcholine potentiates muscle relaxation caused by rocuronium. METHODS: Hemidiaphragm-phrenic nerve preparations were dissected from male Sprague-Dawley rats (150-250 g). Preparations were bathed in Krebs' solution, then maintained at 32oC, and saturated with a mixture of 95% O2 and 5% CO2. Isometric forces made with supramaximal stimulations (0.1 Hz, and 50 Hz for 1.9 s) to the phrenic nerve, were measured with a force transducer, before and after each treatment. Succinylcholine, 10, 20, 40, 60 and 80microM were cumulatively added to the bath. Succinylcholine 80microM (for 100 min) or succinylcholine 300microM (for 20 min) was washed out. After succinylcholine 300microM (for 20 min), or 0microM as pretreatment was washed out, rocuronium, 2, 4, 8, 12, 16, 20microM were cumulatively added to the bath. RESULTS: The potencies of single twitch, peak tetanic tension and tetanic fade for succinylcholine were 36.1, 26.0, 20.7microM. Irrespective of dose or exposure duration, the recovery of muscle relaxation caused by succinylcholine was almost complete around 20 min after succinylcholine was washed out. CONCLUSIONS: Tetanic fade occurred at a lower concentration of succinylcholine than single twitch. The recovery from phase II block was relatively rapid if the concentration of succinylcholine is sufficiently low.

Unusual Prolonged Recovery of Succinylcholine - induced Neuromuscular Block Following Neostigmin / 대한마취과학회지

We report a case of slow recovery of the neuromuscular block induced by succinylcholine (SCC) immediately after administration of neostigmine for the reversal of pancuronium. Left hemithyroidectomy was performed in a 4l kg female patient under general endotracheal inhalation anesthesia with 50%-nitrous oxide and 2.0%-enflurane. Four mg of pancuronium was used for muscular relaxation to facilitate the controlled ventilaion on the anesthesia ventilator. At the end of the operation, one and a half hours from the injection of pancuronium, 10 mg of pyridostigmine was administered to reverse the neuromuscular blockade. Five minutes later, 25 mg of succinylcholine was given for reintubation. Following this event, train-of-four stimuli was applied under the uncalibrated mode with Datex Relaxograph because apnea followed by SCC appeared for more than 30 minutes. Neuromuscular monitoring revealed fade to less than 50% of the T, ratio. The ventilator was applied for the recovery of neuromuscular blockade for one hour. There was no more late complications after transfer to the ward. The literature relating to this iatrogenic complication and phase II block after SCC is reviewed and discussed.