Rabbits Treated with Chronic Isepamicin Are Resistant to Mivacurium and Rocuronium

Measurement of blood-oxygen saturation using a photoacoustic technique in the rabbit hypoxemia model

The golden standard method to obtain accurate blood oxygen saturation is blood gas analysis that needs invasive procedure of blood sampling. Photoacoustic technique enables us to measure real-time blood oxygen saturation without invasive procedure. The aim of this study is to use the photoacoustic technique, an optical method, for accurately determining oxygen saturation in vivo. We measured induced photoacoustic signals of arterial blood in the rabbit model of stable hypoxemia after irradiation at 750 and 800 nm. Oxygen saturation was calculated from the photoacoustic signals using two calibration curves. Calibration curve 1 is a conventional curve derived from the absorbance coefficient of hemoglobin, whereas calibration curve 2 is derived from the photoacoustic signals obtained from the original blood vessel model. Simultaneously, blood-gas analysis was performed to obtain the reference standard of oxygen saturation. Regression analysis and Bland-Altman analysis were performed to assess the accuracy of oxygen saturation obtained using the two methods. The oxygen saturation calculated using calibration curves 1 and 2 showed strong correlations with the reference standard in regression analysis (R = 0.965, 0.964, respectively). The Bland-Altman analysis revealed better agreement and precision with calibration curve 2, whereas there was significant underestimation of values obtained using calibration curve 1. Photoacoustic measurement of oxygen saturation using calibration curve 2 provided an accurate estimate of oxygen saturation, which was similar to that obtained using a portable blood-gas analyzer.

Reversal with sugammadex for rocuronium-induced deep neuromuscular block after pretreatment of magnesium sulfate in rabbits

Background

Magnesium sulfate (MgSO₄) has been used in the treatment of pre-eclampsia, hypertension and arrhythmia. Magnesium enhances the neuromuscular block of rocuronium. This study has been conducted to evaluate the reversal efficacy of sugammadex from deep rocuronium-induced neuromuscular block (NMB) during consistent pretreatment of MgSO₄ in rabbits.

Methods

Twenty-eight rabbits were randomly assigned to four groups, a control group or study groups (50% MgSO₄ 150–200 mg/kg and 25 mg/kg/h IV), and received rocuronium 0.6 mg/kg. When post-tetanic count 1–2 appeared, sugammadex 2, 4, and 8 mg/kg was administered in the 2-mg group, control and 4-mg group, and 8-mg group, respectively. The recovery course after reversal of sugammadex administration was evaluated in each group.

Results

The mean serum concentration of magnesium was maintained at more than 2 mmol/L in the study groups, and the total dose of MgSO₄ was more than 590 mg. The reversal effect of sugammadex on rocuronium-induced NMB in pretreated MgSO₄ was not different from that in the group without MgSO₄. The recovery time to train-of-four ratio 0.9 after sugammadex administration in the 2-mg group was longer than in the other groups (P < 0.001); there were no other significant differences among the groups.

Conclusions

The reversal of sugammadex from a deep rocuronium-induced NMB during large pretreatment of MgSO₄ was not affected. However, we should consider that the reversal effect of sugammadex varied depending on the dose.

Rocuronium-induced neuromuscular block after long pretreatment of clonidine in rabbits

Background

Clonidine, an α-2 adrenergic agonist, is used in the perioperative period and in intensive care for the management of hypertension. The in vivo and in vitro effects of clonidine on the actions of nondepolarizing neuromuscular blocking drugs are conflicting. We evaluated the potency and time course of rocuronium-induced neuromuscular block after prolonged pretreatment with clonidine in rabbits.

Methods

Sixty rabbits were randomly assigned to three groups; control (C) group: normal saline 0.1 ml/kg daily subcutaneous for 6 weeks; S3 group: clonidine 4 µg/kg daily subcutaneous for 3 weeks; S6 group: clonidine 4 µg/kg daily subcutaneous for 6 weeks. The dose-response relations of rocuronium were tested in 30 rabbits (10 from each of the three groups) during ketamine-thiopental anesthesia, while the time course of rocuronium 0.6 mg/kg was examined in 10 rabbits each from the three groups.

Results

There was no difference in mean arterial pressure and pulse rate among the experimental groups. The calculated ED₅₀ for rocuronium decreased significantly from 64.1 µg/kg (C group) to 50.3 µg/kg (S3 group) and 47.8µg/kg (S6 group) (P < 0.001). There was no difference in the onset and the recovery times after rocuronium.

Conclusions

Rocuronium after pretreatment with clonidine for three or six weeks may have an increased effect, but no difference in the duration of action compared with control group.

The duration of immobilization causes the changing pharmacodynamics of mivacurium and rocuronium in rabbits

In the clinical setting, in patients with a cast, it is not known whether the monitoring of the neuromuscular paralysis induced by either mivacurium or rocuronium in the contralateral limb is the correct interpretation. We compared the dose-response relationships and the neuromuscular blocking effects of mivacurium and rocuronium in 56 anesthetized rabbits immobilized in a plaster cast for 2, 4, and 6 wk. Train-of-four stimuli were simultaneously applied every 10 s to both common peroneal nerves, and the force of contraction of both tibialis anterior muscles was measured. Immobilization was associated with a rightward shift of the mivacurium and rocuronium dose-response curves after the duration of the immobilized limb, whereas no shift occurred in the contralateral limb. The 50% effective dose values for 0, 2, 4, and 6 wk of immobilization in the immobilized limb of mivacurium were 15.1 +/- 1.4, 18.2 +/- 1.5, 21.5 +/- 1.9, and 27.8 +/- 2.5 microg/kg, respectively, and they were unchanged in the contralateral limb. The calculated 50% effective dose values for the correspondence of rocuronium were 48.1 +/- 4.1, 56.2 +/- 4.2, 64.8 +/- 4.9, and 75.1 +/- 5.5 microg/kg, respectively, and they were unchanged in the contralateral limb. The rabbits receiving mivacurium and rocuronium had a significantly accelerated recovery from neuromuscular blockade compared with the placebo group in the immobilized limb after the immobilized duration, whereas there were no differences in the contralateral limb. The results of the present study showed that immobilization disuse atrophy produced by casting led to the development of resistance to both mivacurium and rocuronium; however, no resistance was shown in the contralateral limb. The peripheral nerve stimulator could be applied on the nonimmobilized limb, which might be associated with a normal recording if either mivacurium or rocuronium was used as neuromuscular relaxants.