Effects of magnesium chloride on rocuronium-induced neuromuscular blockade and sugammadex reversal in an isolated rat phrenic nerve–hemidiaphragm preparation: An in-vitro study

BACKGROUND Magnesium potentiates the effects of nondepolarising muscle relaxants. However, few studies have used magnesium chloride (MgCl2). Sugammadex reverses neuromuscular block by steroidal nondepolarising muscle relaxants. OBJECTIVES To assess the effects of MgCl2 on rocuronium-induced neuromuscular blockade and its reversal by sugammadex. DESIGN In-vitro experimental study. SETTING Animal laboratory, Asan Medical Center, Seoul, South Korea, from 20 March 2016 to 3 April 2016. ANIMALS Forty male Sprague Dawley rats. INTERVENTION Left phrenic nerve–hemidiaphragms from 40 Sprague Dawley rats were allocated randomly to four groups (1, 2, 3 and 4 mmol l-1 MgCl2 group, n = 10 each). Rocuronium was administered cumulatively until the first twitch of train-of-four (TOF) disappeared completely. Then, equimolar sugammadex was administered. MAIN OUTCOME MEASURES The effective concentration (EC) of rocuronium was obtained in each group. After administering sugammadex, recovery of the first twitch height and the TOF ratio were measured for 30 min. RESULTS EC50, EC90 and EC95 significantly decreased as the concentration of MgCl2 increased (all P ≤ 0.001), except the comparison between the 3 and 4 mmol l–1 MgCl2 groups. After administration of sugammadex, the maximal TOF ratio (%) was lower in the 4 mmol l-1 MgCl2 group than the 1 mmol l–1 MgCl2 group [median 91.7 interquartile range (83.4 to 95.8) vs. 98.3 interquartile range (92.2 to 103.4), P = 0.049]. The mean time (s) from sugammadex injection to achieving maximal first twitch was significantly prolonged in the 4 mmol l–1 MgCl2 group vs. the 1 mmol l–1 MgCl2 and 2 mmol l–1 MgCl2 groups [1483.9 (± 237.0) vs. 1039.0 (± 351.8) and 926.0 (± 278.1), P = 0.022 and 0.002, respectively]. CONCLUSION Increases in MgCl2 concentration reduce the ECs of rocuronium. In addition, administering sugammadex equimolar to the administered rocuronium shows limited efficacy as MgCl2 concentration is increased. TRIAL REGISTRATION The in-vitro study was not registered in a database.

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