K. Kirov

Effects of an intubating dose of succinylcholine and rocuronium on the larynx and diaphragm: an electromyographic study in humans.

BACKGROUND Paralysis of the vocal cords is one objective of using relaxants to facilitate tracheal intubation. This study compares the neuromuscular blocking effect of succinylcholine and rocuronium on the larynx, the diaphragm, and the adductor pollicis muscle. METHODS Electromyographic response was used to compare the neuromuscular blocking effect of succinylcholine and rocuronium on the laryngeal adductor muscles, the diaphragm, and the adductor pollicis muscle. Sixteen patients undergoing elective surgery were anesthetized with propofol and fentanyl, and their tracheas were intubated without neuromuscular blocking agents. The recurrent laryngeal and phrenic nerves were stimulated at the neck. The electromyographic response was recorded from electrodes placed on the endotracheal tube and intercostally before and after administration of 1 mg/kg succinylcholine or 0.6 mg/kg rocuronium. RESULTS The maximum effect was greater at the adductor pollicis (100 and 99%) than at the larynx (96 and 97%) and the diaphragm (94 and 96%) after administration of succinylcholine and rocuronium, respectively (P < or = 0.05). Onset time was not different between the larynx (58+/-10 s), the diaphragm (57+/-8 s), and the adductor pollicis (54+/-13 s), after succinylcholine (all mean +/- SD). After rocuronium, onset time was 124+/-39 s at the larynx, 130+/-44 s at the diaphragm, and 115+/-21 s at the adductor pollicis. After succinylcholine administration, time to 90% recovery was 8.3+/-3.2, 7.2+/-3.5, and 9.1+/-3.0 min at the larynx, the diaphragm, and the adductor pollicis, respectively. Time to 90% recovery after rocuronium administration was 34.9+/-7.6, 30.4+/-4.2, and 49.1+/-11.4 min at the larynx, the diaphragm, and the adductor pollicis, respectively. CONCLUSION Neuromuscular blocking effect of muscle relaxants on the larynx can be measured noninvasively by electromyography. Although the larynx appears to be resistant to muscle relaxants, we could not demonstrate that its onset time differed from that of peripheral muscles.

Comparison between the Datex-Ohmeda M-NMT module and a force-displacement transducer for monitoring neuromuscular blockade.

Background and objective: The Datex‐Ohmeda neuromuscular transmission module (M‐NMT)® is a new monitor that is part of the AS/3® anaesthesia monitor. It incorporates a mechanosensor, which is a piezoelectric polymer attached to the hand. The module was compared with a force transducer in 30 patients requiring neuromuscular blockade. Methods: Anaesthesia was induced with fentanyl and propofol, and tracheal intubation was performed without muscle relaxants. Neuromuscular blockade was assessed by the test module on one arm and the force transducer on the other arm. When the response to train‐of‐four stimulation had been stable in both arms for 3 min, rocuronium 0.2 mg kg−1 was injected intravenously. During recovery from blockade, the train‐of‐four ratio was measured in 15 patients, and the ratio of response to double‐burst stimulation in the other 15 patients. Data analysis was by difference plots. Results: Both devices had acceptable coefficients of repeatability. The M‐NMT® module was biased by + 1.3% (upper limit of agreement 14.2%, lower limit −12.9%) for the recovery of the train‐of‐four ratio, and by + 1.09% (17%, −16%) for the recovery of double‐burst stimulation ratio. Conclusions: The Datex‐Ohmeda M‐NMT® gives measurements that are repeatable and gives good enough correspondence with a force transducer that it can be used clinically to assess recovery of neuromuscular blockade, but the limits of agreement rule out research applications.

Differential sensitivity of abdominal muscles and the diaphragm to mivacurium: an electromyographic study.

Background Respiratory muscles are considered to be more resistant to muscle relaxants as compared with peripheral muscles. However, the relative sensitivity of respiratory muscles participating to the pump function has not been compared. We used electromyography to compare pharmacodynamic parameters of the diaphragm and abdominal muscles after mivacurium. Methods Forty adults undergoing elective surgery were randomly allocated in five dosing groups of mivacurium (50, 100, 150, 200, and 250 &mgr;g/kg). Patients anesthetized with propofol and fentanyl underwent intubation without relaxants. Anesthesia was maintained with nitrous oxide and propofol. The right phrenic nerve, the left 10th intercostal nerve, and the ulnar nerve were stimulated. Electromyography of the diaphragm and abdominal muscles was recorded from surface electrodes. Mechanomyography was used to measure adductor pollicis evoked contraction. After a 5-min stable recording period, patients received a single intravenous bolus (20 s) dose of mivacurium. By using log dose–probit effect regression analysis, dose–response curves were constructed. Effective doses and 95% confidence intervals were derived for the diaphragm and abdominal muscles and were compared. Results The dose–response regression line of abdominal muscles differed from that of the diaphragm. Calculated ED50 and ED90 were higher for the diaphragm than for the abdominal muscles (104 [82–127] and 196 [177–213] &mgr;g/kg, and 67 [51–82] and 161 [143–181] &mgr;g/kg, respectively). The onset of block was faster and recovery of control responses were shorter at the diaphragm than at the abdominal muscles. Conclusion Diaphragm and abdominal muscles have differential sensitivity to mivacurium. The diaphragm is more resistant to mivacurium than abdominal muscles are.

Comparison of the neuromuscular blocking effect of cisatracurium and atracurium on the larynx and the adductor pollicis

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 ED95 doses of cisatracurium (100 µg/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 ED95. To understand this discrepancy better, we evaluated the potency and onset of atracurium and cisatracurium directly at the larynx adductors in humans.

Effect of metoclopramide on mivacurium-induced neuromuscular block

In order to investigate the effect of metoclopramide on the duration of action of mivacurium, 45 patients were randomized into three groups. Group M10 (n = 15) and M20 (n = 15) received 10 and 20 mg of metoclopramide i.v., respectively, and group S (n = 15) received saline 2 min before induction of anesthesia with fentanyl, thiopental and mivacurium. Plasma cholinesterase activity (pCHE) was measured before induction of anesthesia and 2 min after injection of metoclopramide and saline. Neuromuscular block was monitored by a force transducer using train of four nerve stimulation. Anesthesia was maintained with isoflurane and N2O. Time to recovery of a twitch height of 90% was significantly prolonged in group M10 and M20 (44 ± 15 and 57 ± 10 min) as compared to group S, 32 ± 9 min, P < 0.05). A slight but significant decrease in pCHE was observed in group M20. Because of the risk of prolonged duration of action of mivacurium, neuromuscular blockade should always be monitored whenever metoclopramide is given before injection of mivacurium.

Sensibilité à l’atracurium des muscles abdominaux latéraux

OBJECTIVE: To study the effect of atracurium on the electromyographic activity of the lateral abdominal muscles and adductor pollicis in anaesthetized subjects. STUDY DESIGN: Prospective, comparative, open study. PATIENTS AND METHODS: Sixteen patients, ASA physical status 1 or 2, undergoing elective orthopaedic surgery under general anaesthesia were studied. Anaesthesia was induced with propofol/fentanyl and orotracheal intubation performed after glottic local anaesthesia without using muscle relaxant. Anaesthesia was maintained with isoflurane/nitrous oxide/oxygen and fentanyl reinjections. Supramaximal percutaneous stimulations in a simple twitch mode (0.1 Hz) were applied at the 9th-10th intercostal nerve on the posterior axillary line and at the ulnar nerve at the wrist. The electromyographic responses were registered using skin surface electrodes, placed on the D9-D10 dermatome in regard of the lateral abdominal muscles and of the thenar muscles. After a single bolus dose of atracurium 0.5 mg.kg-1, the following parameters were studied: the maximum effect (Emax), the time for obtaining Emax (Delay) and the recovery time of 5, 10, 25, 50, 75 and 100% of the control neuromuscular response (T5, T10, T25, T50, T75, T100). RESULTS: The dose of 0.5 mg.kg-1 of atracurium induced 100% block in both lateral abdominal muscles and adductor pollicis. Lateral abdominal muscles blockade had faster onset (136 +/- 4 s versus 205 +/- 29 s) and shorter recovery, T5, T10, T25, T50, T75 and T100 were significantly (p < 0.05) shorter than at the adductor pollicis. CONCLUSION: Lateral abdominal muscles blockade have faster onset and recovery than adductor pollicis.

Effects of an opioid on respiratory movements and expiratory activity in humans during isoflurane anaesthesia

Opioids increase abdominal muscle activity during anaesthesia. We proposed that opioid activity during anaesthesia would change chest wall size and movement, and contribute to ventilation. Using an optical system to measure chest wall volume, we studied 10 patients during isoflurane anaesthesia, first under the influence of an opioid and then after reversal with naloxone. Measurements were made during quiet breathing and with carbon dioxide stimulation. Airway occlusion pressure was measured to assess inspiratory and expiratory muscle activity. Chest wall volume decreased with the onset of spontaneous breathing, and decreased further when breathing was stimulated by carbon dioxide. Reversal of opioid activity increased chest wall volume. Breathing movements were predominantly abdominal. Opioid action affected the timing and amplitude of breathing but the pattern of abdominal movement was not affected. Since opioids augment abdominal muscle action during expiration, the unchanged pattern of movement can be attributed to both diaphragm and abdominal activity displacing the abdominal wall reciprocally, in the inspiratory and expiratory phases of the respiratory cycle, respectively.

Does repetition of post-tetanic count every 3 min during profound relaxation affect accelerographic recovery of atracurium blockade?

Background:  Post‐tetanic count is a valuable method to assess profound neuromuscular blockade. However, subsequent responses to repetitive stimulation might be altered due to post tetanic facilitation (PTF). To avoid PTF, it has been advocated to limit the interval of stimulation from 6 to 10 min. The impact of PTF on 90% recovery of the TOF ratio has not been evaluated. Therefore, we assessed the effect of repetitive PTC stimulation on atracurium blockade with the primary outcome being the time to reach 90% TOF recovery in comparison to classical TOF stimulation.

The mechanism of pancuronium potentiation of mivacurium block: use of the isolated-arm technique.

UNLABELLED The neuromuscular blocking effects of mivacurium are greatly enhanced when mivacurium is preceded by a subparalyzing dose of pancuronium. The mechanism of this potentiation has not been elucidated. This study investigated the effects of the anticholinesterase activity of a small dose of pancuronium on the neuromuscular blocking effects of mivacurium. Forty patients were enrolled in the study. The neuromuscular effects of 7.5 and 15 microg/kg pancuronium, followed by 50 and 100 microg/kg mivacurium, were assessed in Groups PM1 and PM2 (n = 20), respectively. The neuromuscular effects of 65 and 130 microg/kg mivacurium were assessed in Groups M1 and M2 (n = 20), respectively. One arm was excluded from circulation with a tourniquet, which was inflated before the injection of pancuronium and deflated 3 min after the injection of mivacurium. The plasma cholinesterase activity was measured before induction for all patients and 3 min after the injection of pancuronium for Groups PM1 and PM2. The plasma cholinesterase activity was decreased by 16% and 33% after pancuronium administration in Groups PM1 and PM2, respectively. In the nonexcluded arm, pancuronium significantly potentiated the effects of mivacurium. In the excluded arm, no significant block was detected for Groups M1 and M2, whereas the maximal degree of neuromuscular block was 79% and 100% for Groups PM1 and PM2, respectively. Using the isolated-arm technique, we suggest that pancuronium potentiation of the neuromuscular blocking effects of mivacurium is more likely attributable to an increase in the effective plasma concentration of mivacurium than to occupancy of postsynaptic acetylcholine receptors. IMPLICATIONS Using the isolated-arm technique, we suggest that pancuronium potentiation of the neuromuscular blocking effects of mivacurium is more likely attributable to an increase in the effective plasma concentration of mivacurium than to occupancy of postsynaptic acetylcholine receptors.

Potentiation of Mivacurium blockade by low dose of pancuronium: A pharmacokinetic study

BACKGROUND Mivacurium is potentiated by pancuronium to a much greater extent than other relaxants. In a previous investigation we suggested that this potentiation could be due to the ability of pancuronium to inhibit plasma cholinesterase activity, but we did not measure plasma concentrations of mivacurium. In the current study we performed a pharmacokinetic analysis by measuring the plasma concentration of mivacurium when preceded by administration of a low dose of pancuronium. METHODS After induction of general anesthesia with propofol and fentanyl and orotracheal intubation, 10 patients (pancuronium-mivacurium group) received 15 microg/kg pancuronium followed 3 min later by 0.1 mg/kg mivacurium, whereas 10 other patients (mivacurium group) received saline followed by 0.13 mg/kg mivacurium 3 min later. Plasma cholinesterase activity was measured before and 3 and 30 min after pancuronium dosing in the pancuronium-mivacurium group and was measured before and after administration of saline in the mivacurium group. Arterial plasma concentrations of mivacurium and its metabolites were measured at 0.5, 1, 1.5, 2, 4, 10, 20, and 30 min after injection. Neuromuscular blockade was assessed by mechanomyography. RESULTS Plasma cholinesterase activity decreased by 26% in the pancuronium-mivacurium group 3 min after injection of pancuronium (P < 0.01) and returned to baseline values 30 min later; however, no significant variation was observed in the mivacurium group. The clearances of the two most active isomers (Cis-Trans and Trans-Trans) were lower in the pancuronium-mivacurium group (17.6 +/- 5.1, 14.7 +/- 5.3 ml. min-1. kg-1, respectively) than in the mivacurium group (32.4 +/- 20.2, 24.8 +/- 13.5 ml. min-1. kg-1; P < 0.05). CONCLUSIONS A subparalyzing dose of pancuronium decreased plasma cholinesterase activity and the clearance of the two most active isomers of mivacurium. Pancuronium potentiates mivacurium more than other neuromuscular blocking agents because, in addition to its occupancy of postsynaptic acetylcholine receptors, it slows down the hydrolysis of mivacurium.