Spontaneous recovery from nondepolarizing neuromuscular blockade: correlation between clinical and evoked responses

Optimal effect-site concentration of propofol for tracheal suctioning during emergence from ophthalmic surgery

In ophthalmic surgery, coughing during emergence from general anesthesia may have a detrimental effect on intraocular pressure. Tracheal suction during emergence may elicit this reflex. The optimal effect-site concentration (EC) of propofol to prevent triggering of the cough reflex during tracheal suctioning is unknown. The aim of this study is to assess the optimal EC of propofol for tracheal suctioning during emergence in patients undergoing ophthalmic surgery.Twenty-one patients were enrolled, all of them American Society of Anesthesiologists (ASA) physical status I or II non-smokers undergoing ophthalmic surgery. Anesthesia was induced and maintained under total intravenous anesthesia using target-controlled infusion. During emergence from general anesthesia, tracheal suction was performed at different propofol concentrations as required for Dixon's up-and-down method with a step size of 0.2 μg/ml. A propofol concentration at which the cough reflex was not triggered during tracheal suctioning was considered successful.The EC50 of propofol for tracheal suction without cough was 1.4 μg/ml and the EC95 was 1.6 μg/ml.Tracheal suction may be accomplished without triggering the cough reflex when the propofol effect-site concentration is higher than 1.6 μg/ml.

Audit of peripheral neuromuscular stimulators at the hospitals staffed by the Department of Anaesthesia and Perioperative Medicine at the University of Cape Town

Background: Inadequate monitoring of neuromuscular blockade (NMB) may result in worse patient outcomes, including airway compromise and postoperative pulmonary complications. Therefore, NMB monitor availability is a minimum requirement for perioperative care according to the South African Society of Anaesthesiologists’ (SASA) 2018 guidelines. The authors performed an audit of peripheral nerve stimulators (PNS) functionality and availability at their institution. Methods: The PNSs were attached to an electrical circuit with a skin equivalent resistance. The resultant current impulses generated using Train-of-Four (TOF) mode and Double Burst Stimulation (DBS) mode were recorded with a voltage scope meter. PNS availability was assessed in theatre and recovery areas. Results: Of the 65 PNS units assessed, 39 units were dysfunctional and 26 units fully functional. The most frequent fault found (30 units) related to faulty or absent PNS electrode cables. Eight functional PNS units with TOF ratio display capability were found. The working PNSs showed good inter-device peak voltage measurement correlation. Of the 59 areas identified where PNSs should be easily available, only 37 areas met the PNS availability criteria suggested in the SASA guidelines. Conclusion: This audit highlighted the need for more new generation PNSs with TOF-ratio-display-ability to align the institution with recommendations from SASA standards and the anaesthetic literature. It also highlighted the accuracy and consistency of delivered current bursts by the working PNS devices.

The RECITE Study: A Canadian Prospective, Multicenter Study of the Incidence and Severity of Residual Neuromuscular Blockade

BACKGROUND

Postoperative residual neuromuscular blockade (NMB), defined as a train-of-four (TOF) ratio of <0.9, is an established risk factor for critical postoperative respiratory events and increased morbidity. At present, little is known about the occurrence of residual NMB in Canada. The RECITE (Residual Curarization and its Incidence at Tracheal Extubation) study was a prospective observational study at 8 hospitals in Canada investigating the incidence and severity of residual NMB.

METHODS

Adult patients undergoing open or laparoscopic abdominal surgery expected to last <4 hours, ASA physical status I-III, and scheduled for general anesthesia with at least 1 dose of a nondepolarizing neuromuscular blocking agent for endotracheal intubation or maintenance of neuromuscular relaxation were enrolled in the study. Neuromuscular function was assessed using acceleromyography with the TOF-Watch SX. All reported TOF ratios were normalized to the baseline values. The attending anesthesiologist and all other observers were blinded to the TOF ratio (T4/T1) results. The primary and secondary objectives were to determine the incidence and severity of residual NMB (TOF ratio <0.9) just before tracheal extubation and at arrival at the postanesthesia care unit (PACU).

RESULTS

Three hundred and two participants were enrolled. Data were available for 241 patients at tracheal extubation and for 207 patients at PACU arrival. Rocuronium was the NMB agent used in 99% of cases. Neostigmine was used for reversal of NMB in 73.9% and 72.0% of patients with TE and PACU data, respectively. The incidence of residual NMB was 63.5% (95% confidence interval, 57.4%-69.6%) at tracheal extubation and 56.5% (95% confidence interval, 49.8%-63.3%) at arrival at the PACU. In an exploratory analysis, no statistically significant differences were observed in the incidence of residual NMB according to gender, age, body mass index, ASA physical status, type of surgery, or comorbidities (all P > 0.13).

CONCLUSIONS

Residual paralysis is common at tracheal extubation and PACU arrival, despite qualitative neuromuscular monitoring and the use of neostigmine. More effective detection and management of NMB is needed to reduce the risks associated with residual NMB.

Recovery of train-of-four ratio to 0.70 and 0.90 is delayed in type 2 diabetes with vecuronium-induced neuromuscular block

CONTEXT

The recovery profile of train-of-four ratio to more than 0.70 in patients with diabetes mellitus has not been well investigated.

OBJECTIVE

Our primary objective was to evaluate the spontaneous recovery profile of neuromuscular block by vecuronium until train-of-four ratio more than 0.90 in patients with type 2 diabetes mellitus compared with controls, using first dorsal interosseous electromyography.

DESIGN

Single-centre prospective case-control study.

SETTING

The operating theatres of Fukuoka University Hospital.

PATIENTS

Fourteen adults with type 2 diabetes mellitus (diabetes mellitus group) and 14 control patients (control group) were included in this study.

INTERVENTION

Evoked responses to train-of-four stimuli were measured by electromyography at the first dorsal interosseous muscle. General anaesthesia was induced with propofol, fentanyl and remifentanil. Vecuronium (0.1  mg kg) was administered to all patients. Anaesthesia was maintained with propofol, fentanyl and remifentanil. The neuromuscular block was assessed until spontaneous recovery to train-of-four ratio more than 0.90.

MAIN OUTCOME MEASURES

Recovery times to train-of-four ratio 0.70 and 0.90.

RESULTS

Recovery times to train-of-four ratio 0.70 and 0.90 were significantly longer in the diabetes mellitus group than the control group (P = 0.041 and P = 0.027, respectively). The time from train-of-four ratio 0.25 to 0.90 was also significantly longer in the diabetes mellitus group than the control group (P = 0.029). In five of 14 patients in the diabetes mellitus group, the time from train-of-four ratio 0.25 to 0.90 was longer than 60  min, which is longer than the duration of action of neostigmine. The time from train-of-four ratio 0.25 to 0.90 was longer than 60  min in only one of 14 in the control group.

CONCLUSION

Recovery times to train-of-four ratio 0.70 and 0.90 were delayed in patients with type 2 diabetes mellitus. Neuromuscular block by vecuronium should be carefully monitored in patients with type 2 diabetes mellitus until recovery of train-of-four ratio to a safe level is confirmed.

Failure to reverse prolonged vecuronium-induced neuromuscular blockade with edrophonium in an anesthetized dog

A case of prolonged muscle relaxation after vecuronium in an anesthetized dog is presented. After using peripheral nerve stimulation to confirm partial recovery of neuromuscular transmission, administration of 0.5 mg/kg IV of intravenous edrophonium failed to complete the reversal process. Subsequent administration of neostigmine resulted in complete recovery from blockade. Without monitoring neuromuscular function with a peripheral nerve stimulator until reversal was complete, it was very likely this patient would have been extubated with incomplete neuromuscular transmission. Several factors affecting the duration of neuromuscular blockade and its reversal are addressed.

Residual neuromuscular block: lessons unlearned. Part I: definitions, incidence, and adverse physiologic effects of residual neuromuscular block

In this review, we summarize the clinical implications of residual neuromuscular block. Data suggest that residual neuromuscular block is a common complication in the postanesthesia care unit, with approximately 40% of patients exhibiting a train-of-four ratio <0.9. Volunteer studies have demonstrated that small degrees of residual paralysis (train-of-four ratios 0.7-0.9) are associated with impaired pharyngeal function and increased risk of aspiration, weakness of upper airway muscles and airway obstruction, attenuation of the hypoxic ventilatory response (approximately 30%), and unpleasant symptoms of muscle weakness. Clinical studies have also identified adverse postoperative events associated with intraoperative neuromuscular management. Large databased investigations have identified intraoperative use of muscle relaxants and residual neuromuscular block as important risk factors in anesthetic-related morbidity and mortality. Furthermore, observational and randomized clinical trials have demonstrated that incomplete neuromuscular recovery during the early postoperative period may result in acute respiratory events (hypoxemia and airway obstruction), unpleasant symptoms of muscle weakness, longer postanesthesia care unit stays, delays in tracheal extubation, and an increased risk of postoperative pulmonary complications. These recent data suggest that residual neuromuscular block is an important patient safety issue and that neuromuscular management affects postoperative outcomes.

The undesirable effects of neuromuscular blocking drugs

Neuromuscular blocking drugs are designed to bind to the nicotinic receptor at the neuromuscular junction. However, they also interact with other acetylcholine receptors in the body. Binding to these receptors causes adverse effects that vary with the specificity for the cholinergic receptor in question. Moreover, all neuromuscular blocking drugs may cause hypersensitivity reactions. Often the symptoms are mild and self-limiting but massive histamine release can cause systematic reactions with circulatory and respiratory symptoms and signs. At the end of anaesthesia, no residual effect of a neuromuscular blocking drug should be present. However, the huge variability in response to neuromuscular blocking drugs makes it impossible to predict which patient will suffer postoperative residual curarization. This article discusses the undesirable effects of the currently available neuromuscular blocking drugs including the definitions, diagnosis and causes of hypersensitivity reactions and postoperative residual curarisation.

Clinical limitations of acetylcholinesterase antagonists

Administration of a nondepolarizing neuromuscular blocking drug (muscle relaxant) is a standard practice in many anesthetic scenarios. These muscle relaxants work by competitive antagonism of the neurotransmitter acetylcholine at nicotinic cholinergic receptors within the neuromuscular junction of skeletal muscle (Martyn et al; Neuromuscular physiology and pharmacology, anesthesia. Edited by RD Miller, Philadelphia, Churchill Livingstone, 2000). At the conclusion of the procedure for which the muscle relaxant was administrated, there will be a greater or lesser degree of residual muscle weakness. It is usually necessary to pharmacologically reverse this residual weakness to restore full function to the patient's muscles. Indeed, failure to reverse neuromuscular block is associated with increased perioperative morbidity and mortality (Arbous et al; Impact of anesthesia management characteristics on severe morbidity and mortality. Anesthesiology 2005;102:257-268; quiz 491-2). Pharmacologic reversal currently relies on the administration of an anticholinesterase drug, which decreases the metabolism of acetylcholine at the neuromuscular junction and allows its concentration to increase and hopefully overcome the effect of the muscle relaxant. This approach to reversal has significant limitations; the mechanism of reversal is indirect, the efficacy is limited and unpredictable, and undesirable autonomic responses occur. This review will address these limitations.

Curarisation résiduelle

Despite the availability of modern neuromuscular blocking agents with short or intermediate duration of action, incidence of residual neuromuscular blockade remains very high. Evidences have been recently provided that residual curarization must be defined as a train-of-four ratio below 0.9 at the thumb adductor during the recovery period after anaesthesia. Residual curarization may be associated with serious adverse events related to respiratory depression, pharyngeal dysfunction, hypoxemia and prolongation of the length of stay in the recovery room. Appropriate choice of drugs, perioperative monitoring of neuromuscular function and large indications of pharmacological reversal may reduce the incidence of residual curarization and improve the patient's safety in the postoperative setting.

Tactile Assessment for the Reversibility of Rocuronium-Induced Neuromuscular Blockade During Propofol or Sevoflurane Anesthesia

We sought to determine whether tactile train-of-four (TOF) count can predict the efficacy of neostigmine administration for rocuronium-induced blockade during propofol or sevoflurane anesthesia, and to follow subsequent recovery until the TOF ratio reached 0.9. One-hundred-sixty patients, divided into eight equal groups, were randomly allocated to maintenance of anesthesia with propofol or sevoflurane. The tactile response of the adductor pollicis to TOF stimulation was evaluated on one arm, and the mechanomyographic response was recorded on the other. Neuromuscular block was induced with rocuronium 0.6 mg/kg and maintained with rocuronium to 15% of the control first twitch in TOF. Neostigmine 0.07 mg/kg was administered on reappearance of the first (Group I), second (Group II), third (Group III), or fourth (Group IV) tactile TOF response in each anesthesia. At this time, sevoflurane or the propofol dosage was reduced in each group (n = 20 in each group). The times from administration of neostigmine until the TOF ratio recovered to 0.7, 0.8, and 0.9 were recorded. The times [median (range)] to TOF ratio = 0.9 were 8.6 (4.7-18.9), 7.5 (3.4-9.8), 5.4 (1.6-8.6), and 4.7 (1.3-7.2) min in Groups I-IV during propofol anesthesia, respectively, and 28.6 (8.8-75.8), 22.6 (8.3-57.4), 15.6 (7.3-43.9), and 9.7 (5.1-26.4) min in corresponding groups during sevoflurane anesthesia, respectively (P < 0.0001). We recommend more than 2 TOF responses with propofol anesthesia and 4 TOF responses with sevoflurane anesthesia for adequate reversal within 10 and 15 min, respectively. The more tactile TOF responses present at the time of reversal achieved greater adequate recovery; however, tactile TOF responses are not a completely reliable predictor within a reasonable time period.

Neuromuscular blocking agents

In summary, with proper vigilance, neuromuscular blocking agents can be used safely in anesthetized equine patients to optimize conditions for certain surgical procedures. By appropriate use of neuromuscular monitoring techniques and reversal agents, residual blockade and muscle weakness should be avoided, allowing the horse to recover to standing without difficulty. Research is ongoing to develop the ideal muscle relaxant, one that has a rapid onset, predictable duration and recovery times, and negligible hemodynamic effects. As newer agents become available, they should be evaluated for their suitability for use in equine patients.

Monitoring neuromuscular transmission

Persistent neuromuscular blockade is not uncommon in the recovery room and contributes to postoperative morbidity and possibly mortality. The use of neuromuscular monitoring and intermediate rather than long-acting neuromuscular blocking drugs have been shown to reduce its incidence. Clinically available methods of detecting and quantitating neuromuscular blockade are reviewed. The writer concludes that such monitoring should be routine when neuromuscular blocking drugs are used.

Unmasked residual neuromuscular block after administration of vecuronium for days

IMPLICATIONS

Significant neuromuscular block may be present in patients who have received vecuronium for days.

A comparison of antagonism of rocuronium-induced neuromuscular blockade during sevoflurane and isoflurane anaesthesia

Volatile anaesthetic agents potentiate neuromuscular blocking agents and retard their rate of reversal. We hypothesised that there was a difference in the rate of reversal of rocuronium-induced neuromuscular blockade based on the selection of inhalation agent. Thirty-eight patients undergoing elective surgical procedures received either sevoflurane or isoflurane, by random allocation. Neuromuscular blockade was induced using rocuronium 0.6 mg.kg-1 followed by continuous intravenous infusion to maintain 90% suppression of the single twitch response. Upon completion of surgery, the rocuronium infusion was discontinued, neostigmine 50 microg.kg-1 and glycopyrrolate 10 microg.kg-1 were administered. Times from reversal to T1 = 25, 50 and 60% and train-of-four ratio = 0.6 were recorded. The mean (SD) times to train-of-four ratio = 0.6 in the isoflurane and sevoflurane groups were 327 (132) and 351 (127) s, respectively. The mean (SD) times to single twitch response T1 = 25, 50 and 60% in the isoflurane group were 81 (33), 161 (59) and 245 (84) s, respectively, and in the sevoflurane group were 95 (35), 203 (88) and 252 (127) s, respectively. It is concluded that reversal of rocuronium-induced neuromuscular blockade is similar during isoflurane and sevoflurane anaesthesia.

Sevoflurane as a sole anaesthetic for thymectomy in myasthenia gravis

Myasthenia gravis is a challenging situation for anaesthesiologists due to its neuromuscular involvement. The main concerns are respiratory muscle weakness and side effects due to a heavy dose of anticholinesterases. This limits the use of sedatives, hypnotics and muscle relaxants. Inhalational anaesthetics are best suited. We describe our experience with sevoflurane as a sole anaesthetic in a child having juvenile-type myasthenia gravis with thymoma, who underwent thymectomy by midsternal incision. Very smooth and short duration of induction (35 s) and easy intubation within 60 s without use of muscle relaxant were the remarkable features. Sevoflurane in oxygen and nitrous oxide (MAC=0.5-0.7) was used for maintenance of anaesthesia. Recovery was smooth and fast with no residual respiratory insufficiency. Hence we found sevoflurane to be a highly suitable agent for thymectomy in mysthenia gravis.

Newer neuromuscular blockers. Is the practitioner ready for muscle relaxants?

Current research on the development of new neuromuscular blocking agents is directed towards producing agents that have a rapid onset of action and predictable duration of action and recovery times, with minimal hemodynamic effects. For the veterinary practitioner, these newer agents should be considered when muscle relaxation is required for certain surgical procedures. Care must be taken to monitor paralyzed patients appropriately to ensure adequate ventilation and anesthetic depth. Vigilant monitoring should exist during the recovery period for the development of muscle weakness from residual blockade and the ability to reverse the effects of neuromuscular blockade. The use of neuromuscular blocking agents in veterinary patients should continue to increase as newer drugs and better monitoring techniques are developed.

Common peroneal nerve stimulation for neuromuscular monitoring: evaluation in awake volunteers and anesthetized patients

The study was conducted in two parts. First, evoked responses to common peroneal nerve stimulation at four electrode positions were tested in 25 awake volunteers. The initial threshold stimulus current (ITS) (minimal current producing dorsiflexion or eversion of the ankle joint and great toe) and the supramaximal stimulus current (SMS) (the point at which further increases in current did not produce increases in twitch tension) were defined. SMS was not reliably achieved using electrodes at each side of the fibular head. However, an exploratory electrode accurately located the nerve and enabled SMS in all volunteers (SMS/ITS = 3.4). Second, 16 anesthetized, paralyzed patients were studied. The common peroneal and ulnar nerves were stimulated simultaneously. Evoked tension was recorded at the adductor pollicis using a force transducer and at the great toe by a blinded observer. Reversal was given when the train-of-four count at the great toe reached four. Onset times were longer, and median posttetanic counts were greater, at the great toe compared with the adductor pollicis. Time from reversal to train-of-four ratio = 0.7 at the adductor pollicis was 207+/-160 s. We conclude that neuromuscular monitoring at the common peroneal nerve was not equivalent to monitoring at the ulnar nerve.

IMPLICATIONS

Accurate neuromuscular monitoring is important for patient safety. We studied the accuracy of monitoring at the common peroneal nerve in volunteers and patients. An exploratory electrode accurately located the common peroneal nerve. Monitoring at the common peroneal nerve was not equivalent to monitoring at the ulnar nerve in patients.

The clinical neuromuscular pharmacology of cisatracurium versus vecuronium during outpatient anesthesia

Neither comparisons of the clinical neuromuscular effects of cisatracurium and vecuronium nor comparative studies of their antagonism by neostigmine have been reported. In addition, the efficacy of administering cisatracurium in divided doses has not been investigated. Accordingly, we applied supramaximal electrical stimuli to the ulnar nerve of 165 ASA physical status I and II patients receiving nitrous oxide/alfentanil/propofol anesthesia. Forty-five patients received cisatracurium 5, 10, or 15 microg/kg, and the evoked response at the adductor pollicis was recorded for 15 min. One hundred-twenty patients received cisatracurium 5, 10, or 15 microg/kg or normal saline placebo followed 5 min later by either cisatracurium 100 microg/kg or vecuronium 100 microg/kg (always after placebo). Time to clinical onset (maximal ablation of single twitch response) was measured. When the evoked response spontaneously recovered to 10% of control height, neostigmine 5, 10, 30, or 50 microg/kg or placebo was administered, and recovery of neuromuscular function was recorded for the next 15 min. The clinical onset of vecuronium without priming (2.8 +/- 0.8 min) (mean +/- SD) was significantly (P < 0.05) faster than the onset of cisatracurium without priming (4.6 +/- 1.4 min). Cisatracurium 5, 10, or 15 microg/kg administered before cisatracurium 100 microg/kg significantly (P < 0.05) accelerated the time to complete ablation of the evoked response (3.9 +/- 0.9, 2.9 +/- 0.8, or 3.0 +/- 0.9 min, respectively) compared with cisatracurium 100 microg/kg without priming. The dose of neostigmine required to achieve 50% assisted recovery of the train-of-four ratio at 5 min was significantly (P < 0.05) smaller in patients who received vecuronium (29.1 [17.9-55.3] microg/kg) (mean [95% confidence interval]) compared with those who received cisatracurium (53.7 [31.6-131.5] microg/kg). Given its faster clinical onset and greater sensitivity to antagonism by neostigmine, we conclude that vecuronium may be more suitable than cisatracurium for use in outpatient anesthesia.

IMPLICATIONS

We investigated the onset of muscle relaxation using intravenous vecuronium and cisatracurium and assessed the ability of neostigmine to antagonize (reverse) this effect. Our results suggest that vecuronium works faster than cisatracurium and is more sensitive to neostigmine. Vecuronium therefore may be more useful than cisatracurium in outpatient anesthesia.

Plasma cholinesterase deficiency

Plasma cholinesterase (PCE) is an enzyme necessary for the metabolism of certain anesthetic-related medications. Individuals with abnormal cholinesterase activity (e.g., insufficient quantity of functional PCE or atypical PCE genotypes) may exhibit a prolonged paralytic response to the muscle relaxants succinylcholine and mivacurium. A review of perianesthesia nursing considerations and treatment modalities relating to patients presenting with this interesting clinical picture will be offered.

Optimum time for neostigmine reversal of atracurium-induced neuromuscular blockade

PURPOSE

The aim of the study was to determine the optimum time for administration of neostigmine during recovery from atracurium-induced neuromuscular blockade.

METHODS

The study comprised 103 patients anaesthetised with midazolam, fentanyl, thiopentone, halothane, and nitrous oxide. Relaxation was induced with atracurium 0.5 mg. kg-1 and maintained with supplements of 0.15 mg. kg-1. The ulnar nerve was stimulated with train-of-four (TOF) and double burst stimulation (DBS). Evoked MMG responses were recorded. Patients were randomized to spontaneous recovery (n = 20) or to assisted recovery by neostigmine (0.07 mg.kg-1) at varying intervals (6-50 min) from the last atracurium dose (n = 83).

RESULTS

The reversal time (time from administration of neostigmine to TOF ratio 0.7) was always < 13 min, when T1 (first twitch in TOF) was detectable or when D1 (first twitch in DBS) was > 5%. Total assisted recovery time (time from last supplemental atracurium dose to TOF ratio 0.7) increased with increasing T1 and D1 twitch heights (P < 0.05). The curve fitted to the scattergram with total assisted recovery time vs time from last atracurium supplement to neostigmine administration decreased to reach a minimum after which it increased to approach the line of identity. The minimum of the curve (total assisted recovery time 30.7 min) was reached when neostigmine was given 18.6 min after last atracurium supplement. At this time the T1 and D1 twitch height averaged 4 and 8% respectively. If prolongation of the minimum total recovery time of 2.5% is accepted, neostigmine can be given at T1 and D1 twitch height values of 0 to 8% and 4 to 15%, respectively.

CONCLUSION

The optimum time for neostigmine administration, taking both the reversal time and total recovery time into consideration, is when 0 < T1 < 8% or when 5 < D1 < 15%. Giving neostigmine at more profound degrees of blockade prolongs reversal time, while giving neostigmine later in the recovery phase prolongs total recovery time.

Perioperative train-of-four monitoring and residual curarization

It has been suggested that perioperative train-of-four (TOF) monitoring does not reduce the incidence of postoperative residual curarization (PORC). The purpose of this study was to examine whether the use of tactile assessment of the response of the adductor pollicis to supramaximal TOF stimulation of the ulnar nerve at the wrist during anaesthesia affected the incidence of PORC. Thirty-nine ASA I or II surgical patients were studied during thiopentone/fentanyl N2O/enflurane anaesthesia. Pancuronium (70-100 micrograms.kg-1) was used to facilitate tracheal intubation and additional pancuronium increments used to maintain surgical relaxation. The requirement for incremental doses of pancuronium and adequacy of recovery following reversal were assessed according to random allocation, either with (Group A; n = 20) or without (Group B; n = 19) access to TOF monitoring. Patients in the two groups received neostigmine in similar doses (Group A: 53 micrograms.kg-1 (5.9); Group B: 55 micrograms.kg-1 (5.4)). On arrival of the patient to the recovery area, neuromuscular function was assessed electromyographically (using the Datex NMT 221 to measure TOF ratio) and clinically. The incidence of PORC (TOF ratio < 70%) was greater in Group B (47%) than in Group A (15%) (P = 0.029). We conclude that the use of perioperative TOF monitoring decreases the incidence of pancuronium-induced PORC.

Reversal of residual neuromuscular block with neostigmine at one to four hours after a single intubating dose of vecuronium

The purpose of this study was to measure the degree of residual neuromuscular block at different times after a single dose of vecuronium, and to evaluate the effectiveness of two different doses of neostigmine in antagonizing this residual block. Train-of-four (TOF) ratios were examined for up to 4 h after a single dose of vecuronium, 0.1 mg/kg, in 60 patients during nitrous oxide/isoflurane/fentanyl anesthesia. The effect of neostigmine, 40 micrograms/kg, was studied at 1,2,3, or 4 h. The effect of neostigmine, 20 micrograms/kg, was studied at 2 or 4 h after the vecuronium. Before neostigmine administration, the TOF ratio was less than 0.75 in 17 patients (including one patient at 4 h). Neostigmine produced an increase in TOF ratio in 52 patients and a decrease in 8. The TOF ratio decreased after neostigmine only, at 2,3, or 4 h after vecuronium, when the TOF ratio was > or = 0.9 and when neostigmine 40 micrograms/kg was administered. One patient, at 1 h, had a TOF ratio of 0.00 and this did not reach 0.75 until 57 min after neostigmine, 40 micrograms/kg. There was a high incidence (50%) of adverse cardiovascular effects after both doses of neostigmine. In making the decision as to whether neostigmine should be administered, the risk to the patient of residual neuromuscular block must be balanced against the adverse cardiovascular effects of the neostigmine.

Train-of-four recovery after pharmacologic antagonism of pancuronium-, pipecuronium-, and doxacurium-induced neuromuscular block in anaesthetized humans

Previous studies have suggested that the increased duration of action of long-acting neuromuscular relaxants may make their pharmacologic antagonism more difficult and, thus, increase the likelihood of residual block. This hypothesis was tested in healthy, adult humans who received a background of isoflurane/N2O/fentanyl anaesthesia. Study subjects were paralyzed with either pancuronium (N = 8), pipecuronium (N = 8), or the longer-acting relaxant, doxacurium (N = 8). Neuromuscular function was monitored, and, using a blinded, randomized study design, the relaxants were titrated to identify the ED95 dose in each patient. Thereafter, spontaneous recovery was observed until there was 25% of baseline response to the first supramaximal twitch (T1) in a train-of-four (TOF). At this time, the block was antagonized with neostigmine 0.07 mg/kg and glycopyrrolate 0.014 mg/kg i.v., and recovery of TOF was recorded. Spontaneous recovery to 25% of the baseline T1 response occurred at 52 +/- 14 min (mean +/- SD) following administration of either pancuronium and pipecuronium, and 85 +/- 33 min following doxacurium (P < 0.05 for doxacurium versus pancuronium and pipecuronium). In doxacurium-treated patients, reversal of block with neostigmine was less predictable and less complete than with the other two relaxants. For example, the ratio of the fourth to first twitch (T4/T1) of the TOF at 10 and 15 min after reversal was significantly less with doxacurium (59 +/- 14% and 61 +/- 16%, respectively) than with either pancuronium (75 +/- 6% and 75 +/- 10%) or pipecuronium (76 +/- 9% for both).(ABSTRACT TRUNCATED AT 250 WORDS)

Surgeon-controlled mivacurium administration during elective caesarean section

We have compared the dose requirements and recovery characteristics of a continuous mivacurium infusion given by the anaesthetist to maintain 95-100% block at the hand muscles with that of a surgeon-controlled, on-demand dosing technique based on the direct assessment of abdominal muscle tone during elective Caesarean section. Twenty-four full term pregnant patients were included. A rapid-sequence induction using thiopentone 3-5 mg.kg-1 and succinylcholine 1 mg.kg-1 was used. Anaesthesia was maintained with fentanyl, N2O and isoflurane 0.5%. The mechanomyographic response of the adductor pollicis muscle to supramaximal train-of-four (TOF) ulnar nerve stimulation was recorded. Muscle relaxation was achieved initially with mivacurium 0.1 mg.kg-1 followed either by a continuous infusion of mivacurium to maintain 95-100% block at the adductor pollicis muscle (n = 12) or by surgeon-controlled relaxation (SCR) technique using a syringe pump for patient-controlled analgesia to administer on-demand doses of mivacurium 0.05 mg.kg-1 (n = 12). The lockout interval was three minutes and the maximum hourly dose of mivacurium allowed was 0.6 mg.kg-1. The total doses of mivacurium (mean +/- SD) were 23.2 +/- 10.4 and 12.4 +/- 3.5 mg in the infusion and SCR groups, P < 0.01. On-demand, surgeon-controlled doses of mivacurium were injected at a mean of T1 42.3 +/- 36%. At the end of surgery, T1 and TOF ratio were respectively 16.7 +/- 13%, 5 +/- 10% and 48 +/- 37%, 30 +/- 24% in the infusion and SCR groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacology of rocuronium (Org 9426): study of the time course of action, dose requirement, reversibility, and pharmacokinetics

STUDY OBJECTIVE

To evaluate the time course of action, dose requirement, reversibility, and pharmacokinetics of rocuronium (Org 9426) under 3 anesthetic techniques (nitrous oxide-fentanyl supplemented with propofol, halothane, or isoflurane).

DESIGN

Prospective, randomized study.

SETTING

Operating suite at a university hospital.

PATIENTS

36 ASA physical status I-III patients aged 18 to 65 years who were scheduled for elective surgery.

INTERVENTIONS

The time course of action of an intubation dose of rocuronium 600 micrograms/kg was investigated in 36 patients. In 18 of these patients, the maintenance dose requirement of rocuronium and reversibility by neostigmine were evaluated. In the remaining 18 patients, the pharmacokinetics of rocuronium after the intubating dose were studied. Neuromuscular transmission was monitored by mechanomyography. Venous blood samples and urine were analyzed by high-performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

With the exception of a longer clinical duration of rocuronium-induced neuromuscular block in the isoflurane group compared with the propofol group (p = 0.03), time course of action variables were similar in the 3 groups. In patients receiving maintenance doses of rocuronium, the dose requirement until reversal was 636 +/- 191 micrograms/kg/hr, 496 +/- 107 micrograms/kg/hr, and 384 +/- 127 micrograms/kg/hr for the propofol, halothane, and isoflurane groups, respectively (p = 0.02 for the isoflurane group vs. the propofol group). With respect to the reversal of a rocuronium-induced neuromuscular block, there were no differences in the percentage recovery or rate of recovery among the 3 groups. Pharmacokinetic analysis showed no significant differences for rocuronium during the 3 anesthetic techniques.

CONCLUSION

Isoflurane potentiates the rocuronium-induced neuromuscular block, resulting in a longer clinical duration and lower maintenance dose requirement. This difference is not explained by differences in pharmacokinetics but is probably due to increased sensitivity of the neuromuscular junction to rocuronium during isoflurane anesthesia.

The use of muscle relaxants in the intensive care unit

Neuromuscular blocking agents are frequently used in the Intensive Care Unit to facilitate tracheal intubation and the application of continuous paralysis. This review will focus on various conditions of the critically ill patient such as multi-organ dysfunction, acid-base and electrolyte imbalance, prolonged immobility, multiple drug interactions and specific disease/injury processes that may affect the pharmacokinetic and pharmacodynamic behaviour of muscle relaxants. As such, due to the complex nature of the critically ill patients, the effects of neuromuscular blocking agents are unpredictable. Therefore, guidelines regarding their administration and the methodology and requirement for continuous bedside monitoring of neuromuscular function will be presented.

The effect of bambuterol on plasma cholinesterase activity and suxamethonium-induced neuromuscular blockade in subjects heterozygous for abnormal plasma cholinesterase

Bambuterol is a new bronchodilator which is also a reversible inhibitor of plasma cholinesterase. In patients with normal plasma cholinesterase genotype, bambuterol prolongs suxamethonium-induced neuromuscular blockade. In the present study, we investigated the interaction of bambuterol and suxamethonium in nine patients heterozygous for abnormal plasma cholinesterase during anaesthesia with fentanyl, thiopentone, halothane and nitrous oxide in oxygen. The patients (seven E1uE1a and two E1uE1s) were given 20 mg of bambuterol orally 2 h before anaesthesia. Suxamethonium 1 mg.kg-1 was given for tracheal intubation. The neuromuscular function was monitored using train-of-four (TOF) stimulation of the ulnar nerve and a force displacement transducer. Plasma cholinesterase activity decreased in all patients following bambuterol (P less than 0.001). In patients with genotype E1uE1a, median time to 90% recovery of twitch height and TOF ratio greater than or equal to 0.7 (37.5 min) was prolonged compared to 28 E1uE1a patients not treated with bambuterol (14.0 min) (P less than 0.001). Four of these patients developed a phase II block apparently not correlated to plasma cholinesterase activity. In the E1uE1s; patients, full recovery was seen after 22.0 and 31.4 min, respectively. It is concluded that in patients heterozygous for abnormal plasma cholinesterase, bambuterol 20 mg taken 2 h before anaesthesia causes a 2-3 times prolongation of the neuromuscular blockade following suxamethonium 1 mg.kg-1 and in some patients a phase II block.

The effect of bambuterol (carbamylated terbutaline) on plasma cholinesterase activity and suxamethonium-induced neuromuscular blockade in genotypically normal patients

Bambuterol (the bisdimethylcarbamate prodrug of terbutaline) is a new bronchodilator with a prolonged duration of action due to its inhibition of plasma cholinesterase during metabolism. The effect of bambuterol on suxamethonium-induced neuromuscular blockade was studied in 10 patients undergoing elective laparotomy. Thirty mg of bambuterol was given 2 h before anaesthesia, which was performed with thiopentone, fentanyl, halothane and nitrous oxide in oxygen. Neuromuscular function was monitored using supramaximal train-of-four stimulation of the ulnar nerve and a force displacement transducer. Suxamethonium 1 mg.kg-1 was given i.v. for endotracheal intubation. Plasma cholinesterase activity was measured before and after intake of bambuterol and during anaesthesia. The results from the 10 patients were compared with those of 41 patients not given bambuterol but otherwise studied during the same conditions. Following bambuterol, all patients had a significant decrease of plasma cholinesterase activity (P less than 0.001) and the suxamethonium-induced blockade was 3-4 times prolonged compared to patients not given bambuterol (P less than 0.001). Five patients with very low plasma cholinesterase activity developed a long-lasting phase II block.