Comparison between a new acceleration transducer and a conventional force transducer in the evaluation of twitch responses

Neuromuscular Blockade Monitoring

Neuromuscular monitoring is essential for optimal management of neuromuscular blocking drugs. Postoperative residual neuromuscular blockade continues to occur with an unacceptably high incidence and is associated with adverse patient outcomes. Use of a peripheral nerve stimulator and subjective tactile or visual assessment is useful for intraoperative management of neuromuscular blockade, especially when the patient's hand is accessible. Quantitative monitoring is necessary for confirmation of adequate reversal and for identification of patients who have recovered spontaneously and therefore should not receive pharmacologic reversal agents. Guidelines, as well as more user-friendly monitoring equipment, have created momentum toward improving routine perioperative neuromuscular monitoring.

Comparison of the TOFscan and the TOF-Watch SX during Recovery of Neuromuscular Function

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What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Quantitative neuromuscular monitoring is required to ensure neuromuscular function has recovered completely at the time of tracheal extubation. The TOFscan (Drager Technologies, Canada) is a new three-dimensional acceleromyography device that measures movement of the thumb in multiple planes. The aim of this observational investigation was to assess the agreement between nonnormalized and normalized train-of-four values obtained with the TOF-Watch SX (Organon, Ireland) and those obtained with the TOFscan during recovery from neuromuscular blockade.

Methods

Twenty-five patients were administered rocuronium, and spontaneous recovery of neuromuscular blockade was allowed to occur. The TOFscan and TOF-Watch SX devices were applied to opposite arms. A preload was applied to the TOF-Watch SX, and calibration was performed before rocuronium administration. Both devices were activated, and train-of-four values were obtained every 15 s. Modified Bland–Altman analyses were conducted to compare train-of-four ratios measured with the TOFscan to those measured with the TOF-Watch SX (when train-of-four thresholds of 0.2 to 1.0 were achieved).

Results

Bias and 95% limits of agreement between the TOF-Watch SX and the TOFscan at nonnormalized train-of-four ratios between 0.2 and 1.0 were 0.021 and −0.100 to 0.141, respectively. When train-of-four measures with the TOF-Watch SX were normalized, bias and 95% limits of agreement between the TOF-Watch SX and the TOFscan at ratios between 0.2 and 1.0 were 0.015 and −0.097 to 0.126, respectively.

Conclusions

Good agreement between the TOF-Watch SX with calibration and preload application and the uncalibrated TOFscan was observed throughout all stages of neuromuscular recovery.

The Effect of Anesthetic Choice (Sevoflurane Versus Desflurane) and Neuromuscular Management on Speed of Airway Reflex Recovery

BACKGROUND

Nonintubated patients receiving sevoflurane have slower protective airway reflex recovery after anesthesia compared with patients receiving desflurane. We asked whether this difference would remain significant among intubated patients receiving rocuronium or whether the impact of variable neuromuscular recovery would predominate and thus minimize differences between anesthetics.

METHODS

After obtaining written informed consent, patients were randomly assigned to receive sevoflurane (n = 41) or desflurane (n = 40), with neuromuscular monitoring by quantitative train-of-four (TOF) method using accelerometry. Intubation was facilitated by administration of 1 mg/kg rocuronium. Neuromuscular block was produced, with the goal of maintaining 10% to 15% of baseline function. After surgery, neostigmine 70 µg/kg + glycopyrrolate 14 µg/kg was administered. When TOF ratio reached ≥ 0.7, anesthetic was discontinued and fresh gas flow was raised to 15 L/m. The time of first response to command was noted, after which patients were given a 20-mL water swallowing test at 2, 6, 14, 22, 30, and 60 minutes. The following average time intervals were compared between the 2 intervention groups: anesthetic discontinuation to first response to command (T1); first response to command to first successful passing of swallow test (T2); and anesthetic discontinuation to first successful passing of swallow test (T3). We also compared the rates of successful swallow tests at 2 minutes after first response to command in the 2 groups, first categorizing as failures all those who were unable to take the test at 2 minutes, and then excluding 10 patients unable to take the test at this time for reasons other than somnolence (n = 10).

RESULTS

Patients receiving desflurane passed the swallowing test at shorter time intervals after first response to command than did patients receiving sevoflurane (Wilcoxon-Mann-Whitney odds = 1.60; 95% confidence interval [CI], 1.01-2.69; P = 0.054). Two minutes after the first response to command, among all 81 patients, the chance of passing the swallowing test was higher after desflurane compared with sevoflurane anesthesia (relative risk = 1.6; 95% CI, 1.0-2.5; P = 0.04). Of the 71 patients (as above), we observed a significantly higher chance of passing at 2 minutes after first response to command (relative risk = 1.8; 95% CI, 1.2-2.7; P = 0.006) in patients receiving desflurane (25/33) compared with those receiving sevoflurane (16/38). In 18 of 81 and 16 of 71 patients, the neuromuscular monitoring and reversal protocols were not followed (neostigmine underdosed, extubation at TOF <0.7, or reliance on tactile as opposed to quantitative TOF measurement). In both the total cohort and the subset of 71, neuromuscular protocol adherence increased the chance of passing the swallow test, independent of anesthetic assignment in multivariable logistic regression (P = 0.02 and P = 0.006, respectively), demonstrating significant effect on airway reflex recovery independent of chosen anesthetic.

CONCLUSIONS

Compared with sevoflurane, desflurane allowed faster recovery of airway reflexes after anesthesia in intubated patients. Clinical management of neuromuscular block, including full reversal and the use of quantitative TOF, affects airway reflex recovery-an effect that may be at least as profound as the choice of potent inhaled anesthetic.

Recovery of neuromuscular function after cardiac surgery: pancuronium versus rocuronium

The use of pancuronium in fast-track cardiac surgical patients may be associated with delays in clinical recovery. Our objective in this study was to evaluate the incidence and severity of residual neuromuscular blockade after cardiac surgery in patients randomized to receive either pancuronium (0.08-0.1 mg/kg) or rocuronium (0.6-0.8 mg/kg). Eighty-two patients undergoing cardiopulmonary bypass were randomized to a pancuronium (n = 41) or rocuronium (n = 41) group. Intraoperative and postoperative management was standardized. In the intensive care unit, train-of-four (TOF) ratios were measured each hour until weaning off ventilatory support was initiated. Neuromuscular blockade was not reversed. After tracheal extubation, patients were examined for signs and symptoms of residual paresis. When weaning of ventilatory support was initiated, significant neuromuscular blockade was present in the pancuronium subjects (TOF ratio: median, 0.14; range, 0.00-1.11) compared with the rocuronium subjects (TOF ratio: median, 0.99; range, 0.87-1.21) (P < 0.05). Patients in the rocuronium group were more likely to be free of signs and symptoms of residual paresis than patients in the pancuronium group. Our findings suggest that the use of longer-acting muscle relaxants in cardiac surgical patients is associated not only with impaired neuromuscular recovery, but also with signs and symptoms of residual muscle weakness in the early postoperative period.

IMPLICATIONS

The use of long-acting muscle relaxants in fast-track cardiac surgical patients is associated with significant residual neuromuscular block in the intensive care unit, including signs and symptoms of residual paresis.

The effect of cerebral palsy on the action of vecuronium with or without anticonvulsants

Patients with cerebral palsy who are treated with anticonvulsant medication are resistant to vecuronium. We examined the contributions to vecuronium resistance made by cerebral palsy and anticonvulsants in a study of children with cerebral palsy and a control group. The acceleromyographic responses of the following three groups of children were studied: children with cerebral palsy not taking anticonvulsant medication (n = 11); children with cerebral palsy taking anticonvulsant medication (n = 8); and a control group of children who did not have cerebral palsy and were not taking anticonvulsant treatment (n = 10). Using a standardised technique, general anaesthesia was induced and maintained with 0.5-1. 5% isoflurane in a 60/40 nitrous oxide in oxygen mixture. After a stabilisation period which was performed with supramaximal train-of-four stimuli (2 Hz every 15 s) an intubating dose of vecuronium 0.1 mgkg-1 was administered. The first twitch of the train-of-four response (T1), the onset time, the times to 25, 50, 75 and 90% recovery of T1, recovery index, and the time to 70% recovery of train-of-four ratio were recorded. Recovery times to T1 and train-of-four responses were reduced significantly in both groups of children with cerebral palsy compared with the control group. These results suggest that children with cerebral palsy display resistance to vecuronium whether or not they are taking anticonvulsant drugs.

Good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents

Based on an international consensus conference held in Copenhagen in the autumn of 1994, a set of guidelines for Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents are presented. The guidelines are intended to be a help for people working in this research field, and it is hoped that the guidelines will assist researchers, editors, and drug companies to enhance the quality of their pharmacodynamic studies of neuromuscular blocking agents.

Measurement of neuromuscular blockade--a comparison between a new "homemade" force displacement transducer and the accelerometer

Train-of-four (TOF) ratios are compared between a new homemade force pressure transducer and a commercially available accelerometer. Twenty adult patients were studied and 600 simultaneous TOF ratio pairs were recorded during anaesthesia with varying degrees of muscle relaxation. Laboratory testing revealed that the output from the homemade device was linear up to 900 g and that there was a linear relationship between the output from the new device and the accelerometer (y = 0.802x + 5.167, R = 0.943, t = 69, P < 0.0001). Although the homemade device underestimates the accelerometer TOF ratio by 20%, it is a reliable and economic alternative to commercially available products for measuring TOF ratios.

Differential effects of vecuronium on the thumb and great toe as measured by accelography and electromyography

We evaluated possible differential effects of vecuronium on the thumb and great toe using two types of neuromuscular transmission monitor. Train-of-four stimuli were simultaneously applied to the ulnar nerve and tibial nerves using cutaneous electrodes. The responses were quantified with accelographs (thumb and left great toe) and an electromyograph (right great toe). Twenty ASA 1 or 2 patients received, by random allocation, one of two types of anaesthesia: neuroleptanaesthesia or sevoflurane-based anaesthesia. With both techniques, the shortest time to maximum block after vecuronium 0.1 mg.kg-1 occurred in the thumb as measured by accelography. The average (SD) values with neuroleptanaesthesia were: 173(23) s for thumb using accelography; 220(16) s for great toe using accelography; 205(44) s for great toe using electromyography. The average (SD) value(s) with sevoflurane-based anaesthesia were: 137(15) for thumb using accelography; 179(21) for great toe using accelography; 153(23) for great toe using electromyography. The differences between the thumb and great toe were statistically significant during both types of anaesthesia when measured with the accelograph (p < 0.01). The time from completion of maximal block to 25% recovery of twitch height in the thumb was significantly longer than that of the great toe as measured by accelography during both types of anaesthesia (p < 0.05). In contrast, there were no statistically significant differences between time to maximum block and 25% recovery of twitch height of the thumb as measured by accelography compared to the values measured for the great toe using electromyography during either anaesthetic technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of vecuronium on the thumb and the big toe muscles evaluated by acceleration measurement

To clarify the differential effects of vecuronium on the thumb and on the big toe, train-of-four (TOF) stimuli were applied to the ulnar nerve at the wrist and the tibial nerve at the ankle in anesthetized patients using two acceleration transducers. Ten adult patients, aged 21-55 years, were studied. Anesthesia was induced by an intravenous injection of thiopental, and vecuronium 0.1 mg·kg^-1 was used for paralysis. Anesthesia was maintained with nitrous oxide (66%)-oxygen-sevoflurane (1 MAC). The duration of time to the maximal twitch depression on the thumb and the big toe was 136.5±32.5 s and 183.0±40.1 s (P<0.05), respectively. The time to 25% recovery of the twitch height on the thumb and the big toe was 48.1±17.3 min and 39.1±11.6 min, respectively; the time to 50% recovery of twitch height on the thumb and the big toe was 54.1±16.1 min and 40.0±9.2 min (P<0.05), respectively. When paralysis was reversed at 25% of TOF ratio on the thumb, the value of the TOF ratio on the big toe was 58.5±18.2% (P<0.01).

A computer-controlled, closed-loop infusion system for infusing muscle relaxants: its use during motor-evoked potential monitoring

A microcomputer-controlled closed-loop infusion system (MCCLIS) has been developed that provides stable intraoperative levels of partial neuromuscular blockade. Complete neuromuscular blockade interferes with intraoperative motor-evoked potential (MEP) monitoring used for patients undergoing surgical procedures that place them at risk for spinal cord ischemia. Nine patients were studied during which the MCCLIS maintained stable levels of partial neuromuscular blockade and allowed transcranial magnetic motor-evoked potential (TcM-MEP) monitoring during thoracoabdominal aortic aneurysmectomy. The use of TcM-MEP for monitoring intraoperative spinal cord function was balanced against surgical considerations for muscle relaxation with 80% to 90% neuromuscular blockade fulfilling each requirement. Intraoperative adjustment of partial neuromuscular blockade to facilitate TcM-MEP monitoring was also possible with the MCCLIS. The MCCLIS should allow for further investigation into the sensitivity, specificity, and predictability of TcM-MEP monitoring for any patient at risk for intraoperative spinal cord ischemia including those undergoing thoracoabdominal aortic aneurysmectomy.

Simultaneous monitoring of force, acceleration and electromyogram during computer-controlled infusion of atracurium in sheep

Five sheep were anaesthetised with sodium thiopentone, nitrous oxide and oxygen, and the lungs ventilated artificially. A computer-controlled infusion of atracurium employing feedback from isometric force measurement was set to maintain 15, 50 and 85% depth of neuromuscular block. Each was held constant for 30 minutes, while isometric force and electromyogram were measured on the left forelimb and acceleration on the right. The acceleration transducer records at the three levels of block were practically identical with those from force measurements: mean differences (SD) between simultaneous measurements being 3.6 (5.4)%. EMG value was 10.1 (12.0)% different from force measurement. Correlation between simultaneous force and either acceleration or EMG was excellent (r = 0.986 and 0.938 respectively). In clinical practice all three techniques measure block comparably. In the sheep forelimb, EMG was a less reliable method of measuring block.

A unified approach to providing general anaesthesia monitoring with special reference to developing countries

Information concerning general anaesthesia, monitoring and ergonomics has been assembled to present a plan for the introduction of necessary monitors into a department of anaesthesia. This includes reference to: (i) The need for instrumental monitors; (ii) Division of tasks between anaesthetist and monitor; (iii) User education; (iv) Anaesthetist/monitor interface; (v) Hospital infrastructure. Emphasis is placed on the continued need for anaesthetists to employ their own senses for monitoring in the traditional manner and the essential role instrumental monitors should play in helping trainees to refine and calibrate their clinical skills. It is suggested that in situations where neither mechanical ventilators are available nor instrumental monitors necessary to refine the conduct of general anaesthesia a transitional stage in evolution could be the presence of two persons with clearly defined responsibilities for all the anaesthesia tasks necessary during a safely conducted case.

Comparison of thumb acceleration and thenar EMG in a pharmacodynamic study of alcuronium

We compared thumb acceleration (Acc) and thenar electromyography (EMG) techniques by evaluating the neuromuscular blocking properties of alcuronium in 14 ASA physical status I patients. The dose-response curves determined by the two techniques were parallel but the EMG-curve was shifted 25% to the right (P less than 0.001). Acc reflected 8-11% greater neuromuscular block than simultaneous EMG in every patients (P less than 0.05). Concurrently, the duration of greater than 90% neuromuscular block maintained by alcuronium 280 micrograms/kg was significantly longer when measured by the Acc transducer (30 vs. 19 min, P less than 0.001). Although the TOF ratios were in good correlation (r2 = 0.82), clinically significant differences existed between the two simultaneous techniques. The results underline the importance of the method of assessment of neuromuscular transmission when evaluating the action of neuromuscular blocking drugs.