Conditions to optimise the reversal action of neostigmine upon a vecuronium-induced neuromuscular block

Background: Since neostigmine was introduced for reversal of neuromuscular block, there has been controversy about the optimum dose for antagonizing neuromuscular block. The purpose of this study was to characterise recovery of neuromuscular transmission following a vecuronium-induced block 15 min after neostigmine administration using different stimulation patterns, and to determine the effects of different doses of neostigmine given at various pre-reversal twitch heights. Methods: Adductor pollicis (AP) mechanical activity in response to low (0.1 and 2 Hz) and high (50 and 100 Hz) frequency stimulation, was recorded 15 min after 20, 40 and 80 μg/kg neostigmine, given to reverse a vecuronium-induced block at 10, 25 and 50% pre-reversal twitch height (TH). Fifty four ASA class I and II anaesthetised (methohexital, fentanyl, N₂O/O₂) young adult patients were studied and randomly allocated into 9 groups of 6 patients each. Results: In contrast to twitch height (TH) and residual force after 50 Hz, 5 s tetanic stimulation (RF50_Hz), the greater sensitivity of train-of-four (TOF) ratio and residual force after 100 Hz, 5 s tetanic stimulation (RF100_Hz) points out the best reversal conditions (prereversal TH and the optimal neostigmine dose) (P<0.001, two-way analysis of variance). The highest reversal scores (about 0.9 TOF ratio and RF100_Hz) were obtained when 40 μg/ kg of neostigmine was given at 25 and 50% TH. A 0.9 TOF ratio was also observed when 40 μg/kg of neostigmine was given at 10% TH, but, under these conditions, RF100_Hz was only 0.6 (P<0.05, Duncan test). Conclusion: To optimise the reversal action of neostigmine in order to obtain the highest neuromuscular transmission recovery (0.9 TOF ratio and RF100_Hz) during a vecuronium-induced neuromuscular block, the 40 μg/kg dose has to be given at 25 to 50% recovery of TH.     

Monitoring of neuromuscular transmission by electromyography (II)

The feasibility of the compound electromyogram (EMG) was evaluated during onset and recovery from pancuronium block in the tibialis anterior muscle of ten cats. The evoked EMG area, amplitude and duration of the total response and of the major negative deflection were evaluated and compared to the mechanomyogram during 0.1 Hz and train-of-four (TOF) stimulation. EMG areas and amplitudes were found to be linearly and similarly related to the mechanomyogram during onset and recovery. Slopes of the regression lines ranged between 1.00–1.02 and between 1.10–1.22 during onset and recovery, respectively, with high individual correlation coefficients (>0.95). The TOF ratio of the mechanomyogram was linearly related to the EMG TOF ratio during onset and to the square root of the EMG TOF ratio during recovery, with no differences between EMG areas and amplitudes, suggesting a higher initial recovery of the TOF ratio of the mechanomyogram during recovery. EMG duration increased as the level of block increased but was unsuitable for neuromuscular monitoring. Evaluation of the agreement between the two methods showed that the EMG may be from 15% below to 10% above the mechanomyogram during onset and from 40% below to 45% above the mechanomyogram during recovery, in spite of high correlation coefficients. In contrast, agreement between EMG parameters was found to be high. In conclusion, EMG is more reliable than the mechanomyogram for evaluation of neuromuscular transmission in the cat. EMG amplitudes and areas both reflect the degree of neuromuscular blockade equally well     

Single acceleromyographic train-of-four, 100-Hertz tetanus or double-burst stimulation: which test performs better to detect residual paralysis?

BACKGROUND: Acceleromyography is regularly used as an isolated test to detect residual paralysis. The performance of acceleromyography, however, has not been investigated for the setting where calibration is impossible. This study first evaluated the reliability of a single acceleromyographic train-of-four (TOF) ratio (T4/T1) to detect residual paralysis and compared it with tactile estimation of fade after double-burst stimulation and 100-Hz, 5-s tetanus. The second part of the study investigated whether uncalibrated acceleromyographic TOF ratio can predict time to complete recovery. METHODS: Anesthesia was induced and maintained with propofol and sufentanil. In the first part of the study (n = 40) neuromuscular blockade was assessed by mechanomyography. After signal stabilization 0.15 mg/kg cisatracurium was given. At the end of surgery a first physician evaluated manual fade after double-burst stimulation, then, in the same patient, a single acceleromyographic TOF ratio was recorded; thereafter a second physician, unaware of the results, assessed fade after a 100-Hz, 5-s tetanus. Sensitivity, specificity, and negative and positive predictive value of the three tests to detect a mechanomyographic TOF > or =0.9 were calculated. In the second part of the study (n = 25) neuromuscular recovery was assessed simultaneously with mechanomyography and uncalibrated acceleromyography (current set manually at 60 mA); the time intervals from acceleromyographic TOF ratios of 0.6, 0.7, 0.8, and 0.9 until complete recovery, i.e., adductor pollicis mechanomyography 0.9 TOF ratios, were determined. RESULTS: The sensitivity of double burst stimulation was 29% (95% confidence interval [CI], 13-45%), its specificity was 100%, the negative predictive value was 29% (95% CI, 13-45%), and the positive predictive value was 100%. For a single acceleromyographic TOF ratio the respective values were 70% (95% CI, 54-86%), 88% (95% CI, 67-100%), 47% (95% CI, 23-71%) and 95% (95% CI, 86-100%). The respective values for 100-Hz, 5-s tetanus were 74% (95% CI, 59-89%), 55% (95% CI, 23-88%), 38% (95% CI, 12-64%), and 85% (95% CI, 72 -99%). At an uncalibrated acceleromyographic TOF ratio was 0.6, complete recovery occurred within 16 min (95% CI, 13.5-17.8 min). At acceleromyographic TOF ratios of 0.7, 0.8, and 0.9 this time interval was 12.5 min (95% CI, 10.2-14.8 min), 8 min (95% CI, 6.1-9.9 min), and 4 min (95% CI, 2.7-5.8 min), respectively. CONCLUSIONS: Acceleromyographic TOF performed better than double-burst stimulation or 100 Hz tetanus, but it did not reliably detect low degrees of residual paralysis when used as an isolated test at the end of surgery. The uncalibrated acceleromyographic TOF ratio, however, did predict the time to complete recovery.     

Brief review: Neuromuscular monitoring: an update for the clinician

PURPOSE: To review established techniques and to provide an update on new methods for clinical monitoring of neuromuscular function relevant to anesthesia. SOURCE: A PubMed search of relevant article for the period 1985-2005 was undertaken, and bibliographies were scanned for additional sources. PRINCIPAL FINDINGS: There is no substitute for objective neuromuscular monitoring; for research purposes, mechanomyography (MMG) is the gold standard; however, the most versatile method in the clinical setting is acceleromyography since it can be applied at various muscles and has a long track record of clinical utility. Kinemyography is valid to monitor recovery of neuromuscular transmission at the adductor pollicis muscle (AP), whereas phonomyography is easy to apply to various muscles and shows promising agreement with MMG. Monitoring of the corrugator supercilii muscle (CS) may be used to determine the earliest time for tracheal intubation as it reflects laryngeal relaxation better than monitoring at the AP. Recovery of neuromuscular transmission is best monitored at the AP, since it is the last muscle to recover from neuromuscular blockade (NMB). If train-of-four (TOF) stimulation is used, a TOF-ratio > 0.9 should be the target before awakening the patient. If surgery or the type of anesthesia necessitates NMB of a certain degree, e.g., TOF-ratio = 0.25, monitoring of muscles which best reflect the degree of NMB at the surgical site is preferable. CONCLUSION: Objective methods should be used to monitor neuromuscular function in clinical anesthesia. Acceleromyography offers the best compromise with respect to ease of use, practicality, versatility, precision and applicability at various muscles. The CS is the optimal muscle to determine the earliest time for intubation, e.g., for rapid sequence induction.     

The relationship between acceleromyographic train-of-four fade and single twitch depression

BACKGROUND: During offset of nondepolarizing neuromuscular block, a train-of-four (TOF) fade ratio of 0.70 or greater is considered to reliably indicate the return of single twitch height (T1) to its control value. Studies using mechanomyography or electromyography confirm this observation. The authors' impressions when using the acceleromyograph as a neuromuscular monitor did not support these results. Therefore, the authors studied the relation between T1 and the TOF ratio (when measured by acceleromyography) during recovery from neuromuscular block. METHODS: Sixteen adult patients were studied. Anesthesia was induced with intravenous opioid plus 2.0-2.5 mg/kg propofol. Laryngeal mask placement or tracheal intubation was accomplished without the use of muscle relaxants. Anesthesia was maintained with nitrous oxide, desflurane (2.0-3.0%, end-tidal), and fentanyl. The response of the thumb to ulnar nerve stimulation was recorded with the TOF-Guard acceleromyograph (Organon Teknika BV, Boxtel, The Netherlands). TOFs were administered every 15 s. After final calibration, 0.15 mg/kg mivacurium was administered. No further relaxants were administered. T1 and the TOF ratio were then recorded until the TOF ratio had returned to its initial value (+/- 5%). RESULTS: At a TOF ratio of 0.70 (during recovery of neuromuscular function), T1 averaged only 69 +/- 8% of control. At a TOF ratio of 0.90, T1 averaged 86 +/- 5% of control. To achieve 90% recovery of T1, a TOF ratio of 0.93 +/- 0.08 was required. CONCLUSION: Assumptions regarding the relation between T1 and the TOF ratio derived from studies using mechanomyography and electromyography do not necessarily apply to observations obtained using acceleromyography.     

Residual paralysis at the time of tracheal extubation

Respiratory and pharyngeal muscle function are impaired during minimal neuromuscular blockade. Tracheal extubation in the presence of residual paresis may contribute to adverse respiratory events. In this investigation, we assessed the incidence and severity of residual neuromuscular block at the time of tracheal extubation. One-hundred-twenty patients presenting for gynecologic or general surgical procedures were enrolled. Neuromuscular blockade was maintained with rocuronium (visual train-of-four [TOF] count of 2) and all subjects were reversed with neostigmine at a TOF count of 2-4. TOF ratios were quantified using acceleromyography immediately before tracheal extubation, after clinicians had determined that complete neuromuscular recovery had occurred using standard clinical criteria (5-s head lift or hand grip, eye opening on command, acceptable negative inspiratory force or vital capacity breath values) and peripheral nerve stimulation (no evidence of fade with TOF or tetanic stimulation). TOF ratios were measured again on arrival to the postanesthesia care unit. Immediately before tracheal extubation, the mean TOF ratio was 0.67 +/- 0.2; among the 120 patients, 70 (58%) had a TOF ratio <0.7 and 105 (88%) had a TOF ratio <0.9. Significantly fewer patients had TOF ratios <0.7 (9 subjects, 8%) and <0.9 (38 subjects, 32%) in the postanesthesia care unit compared with the operating room (P < 0.001). Our results suggest that complete recovery from neuromuscular blockade is rarely present at the time of tracheal extubation.     

Monitoring of the neuromuscular transmission by electromyography (I). Stability and temperature dependence of evoked EMG response compared to mechanical twitch recordings in the cat

The stability over time and the effect of muscle temperature change were evaluated for the evoked compound EMG and for the mechanomyogram of the tibialis anterior muscle of 7 anaesthetized cats. Both EMG areas and amplitudes were recorded. During stimulation for 3 h with 0.1 Hz (one leg) and train-of-four (TOF) (the other leg), the EMG was stable while the mechanomyogram initially increased 35-50% in the first 7-8 min and then decreased 19-22% and 5-8% over the first and second 1.5-h period, respectively. During subsequent mean muscle temperature reduction to 28.8 degrees C (0.1 Hz) and 29.7 degrees C (TOF) and rewarming, an inverse linear relationship was found between temperature and both the EMG and the mechanomyogram. During temperature reduction EMG increased about 6% (areas) and 2% (amplitudes) per degrees C. During rewarming, parameters decreased about 4.5% and 2% per degrees C, respectively (P less than 0.05 comparing EMG areas during cooling and rewarming). TOF ratio of the EMG was not affected by temperature. A very large interindividual variation was observed for the effect of temperature on the mechanomyogram with changes ranging up to 15% per degrees C for some cats. TOF ratio of the mechanomyogram was reduced from 1.02 to 0.94 at lowest muscle temperature. It is concluded that the evoked EMG may be preferable to the mechanomyogram in cat experiments investigating the neuromuscular transmission.     

The Relationship between Acceleromyographic Train-of-four Fade and Single Twitch Depression

Background: During offset of nondepolarizing neuromuscular block, a train-of-four (TOF) fade ratio of 0.70 or greater is considered to reliably indicate the return of single twitch height (T1) to its control value. Studies using mechanomyography or electromyography confirm this observation. The authors' impressions when using the acceleromyograph as a neuromuscular monitor did not support these results. Therefore, the authors studied the relation between T1 and the TOF ratio (when measured by acceleromyography) during recovery from neuromuscular block.

Methods: Sixteen adult patients were studied. Anesthesia was induced with intravenous opioid plus 2.0-2.5 mg/kg propofol. Laryngeal mask placement or tracheal intubation was accomplished without the use of muscle relaxants. Anesthesia was maintained with nitrous oxide, desflurane (2.0-3.0%, end- tidal), and fentanyl. The response of the thumb to ulnar nerve stimulation was recorded with the TOF-Guard(R) acceleromyograph (Organon Teknika BV, Boxtel, The Netherlands). TOFs were administered every 15 s. After final calibration, 0.15 mg/kg mivacurium was administered. No further relaxants were administered. T1 and the TOF ratio were then recorded until the TOF ratio had returned to its initial value (+/- 5%).

Results: At a TOF ratio of 0.70 (during recovery of neuromuscular function), T1 averaged only 69 +/- 8% of control. At a TOF ratio of 0.90, T1 averaged 86 +/- 5% of control. To achieve 90% recovery of T1, a TOF ratio of 0.93 +/- 0.08 was required.     

Single Acceleromyographic Train-of-Four, 100-Hertz Tetanus or Double-Burst Stimulation: Which Test Performs Better to Detect Residual Paralysis?

Background: Acceleromyography is regularly used as an isolated test to detect residual paralysis. The performance of acceleromyography, however, has not been investigated for the setting where calibration is impossible. This study first evaluated the reliability of a single acceleromyographic train-of-four (TOF) ratio (T4/T1) to detect residual paralysis and compared it with tactile estimation of fade after double-burst stimulation and 100-Hz, 5-s tetanus. The second part of the study investigated whether uncalibrated acceleromyographic TOF ratio can predict time to complete recovery.

Methods: Anesthesia was induced and maintained with propofol and sufentanil. In the first part of the study (n = 40) neuromuscular blockade was assessed by mechanomyography. After signal stabilization 0.15 mg/kg cisatracurium was given. At the end of surgery a first physician evaluated manual fade after double-burst stimulation, then, in the same patient, a single acceleromyographic TOF ratio was recorded; thereafter a second physician, unaware of the results, assessed fade after a 100-Hz, 5-s tetanus. Sensitivity, specificity, and negative and positive predictive value of the three tests to detect a mechanomyographic TOF >=0.9 were calculated. In the second part of the study (n = 25) neuromuscular recovery was assessed simultaneously with mechanomyography and uncalibrated acceleromyography (current set manually at 60 mA); the time intervals from acceleromyographic TOF ratios of 0.6, 0.7, 0.8, and 0.9 until complete recovery, i.e., adductor pollicis mechanomyography 0.9 TOF ratios, were determined.

Results: The sensitivity of double burst stimulation was 29% (95% confidence interval [CI], 13-45%), its specificity was 100%, the negative predictive value was 29% (95% CI, 13-45%), and the positive predictive value was 100%. For a single acceleromyographic TOF ratio the respective values were 70% (95% CI, 54-86%), 88% (95% CI, 67-100%), 47% (95% CI, 23-71%) and 95% (95% CI, 86-100%). The respective values for 100-Hz, 5-s tetanus were 74% (95% CI, 59-89%), 55% (95% CI, 23-88%), 38% (95% CI, 12-64%), and 85% (95% CI, 72 -99%). At an uncalibrated acceleromyographic TOF ratio was 0.6, complete recovery occurred within 16 min (95% CI, 13.5-17.8 min). At acceleromyographic TOF ratios of 0.7, 0.8, and 0.9 this time interval was 12.5 min (95% CI, 10.2-14.8 min), 8 min (95% CI, 6.1-9.9 min), and 4 min (95% CI, 2.7-5.8 min), respectively.     

Posttetanic potentiation and fade in the response to tetanic and train-of-four stimulation during succinylcholine-induced block

We designed this study to confirm anecdotal observations that neuromuscular block after a single administration of succinylcholine is characterized by fade to train-of-four (TOF) or tetanic stimulation, as well as posttetanic potentiation. This prospective, randomized, 2-center observational study involved 100 patients. Patients were allocated to 1 of 5 groups and received 0.1, 0.3, 0.5, 0.75, or 1.0 mg/kg succinylcholine during propofol/fentanyl/nitrous oxide anesthesia. Neuromuscular function was monitored by TOF using mechanomyography. At 10%-20% spontaneous recovery of the first twitch of TOF, the mode of stimulation was changed from TOF to 1-Hz single-twitch stimulation followed by a tetanic stimulus (50 Hz) for 5 s. Three seconds later, the single twitch (1 Hz) was applied again for approximately 30 s followed by TOF stimulation until full recovery of the TOF response. Succinylcholine-induced neuromuscular block had the following characteristics: 1) twitch augmentation before twitch depression, which was seen more frequently in patients given smaller doses (0.1 and 0.3 mg/kg) than in those given larger doses (0.5-1.0 mg/kg); 2) TOF fade during onset and recovery of the block; 3) tetanic fade; and 4) and posttetanic potentiation. Posttetanic potentiation was related to the pretetanic twitch height but was not related to the dose of succinylcholine administered. Some characteristics of Phase II block were detectable during onset and recovery from doses of succinylcholine as small as 0.30 mg/kg. Posttetanic potentiation and fade in response to train-of-four and tetanic stimuli are characteristics of neuromuscular block after bolus administration of different doses of succinylcholine. IMPLICATIONS: Posttetanic potentiation and fade in response to train-of-four and tetanic stimuli are characteristics of neuromuscular block after bolus administration of different doses of succinylcholine. We also conclude that some characteristics of a Phase II block are evident from an initial dose (i.e., as small as 0.3 mg/kg) of succinylcholine.     

Halothane-induced variability in the neuromuscular transmission of patients with myasthenia gravis

The purpose of the present clinical study was to explore the skeletal muscle mechano (MMG)- and electromyographic (EMG) responses during halothane/oxygen/air anaesthesia in patients with myasthenia gravis (MG) compared with patients with normal neuromuscular transmission. The majority of MG-patients had a significant decremental response of the evoked muscle action potentials to a train-of-four (TOF) stimulation during halothane exposure (mean decrease of train-of-four ratio was 33% during the highest mean halothane concentration of 1.9 MAC). An excellent correlation was found between MMG- and EMG-measurements (r2 = 0.878, P less than 0.001). However, marked individual variations in the neuromuscular response to halothane were seen. Neither preoperative muscle fatigability nor acetylcholine receptor antibodies predicted the decremental muscle responses produced by halothane among MG-patients. The increased presence of HLA-B8 among myasthenics with halothane-suppressed muscle responses after TOF stimulation could be demonstrated (P less than 0.01).     

Comparison of the Neuromuscular Blocking Effect of Atracurium and Vecuronium on the Adductor Pollicis and the Geniohyoid Muscle in Humans

Background: Residual paralysis of suprahyoid muscles may occur when the adductor pollicis response has completely recovered after the administration of a neuromuscular blocking agent. The response of the geniohyoid muscle to intubating doses of muscle relaxants is evaluated and compared to that of adductor pollicis.

Methods: Sixteen patients undergoing elective surgery under general anesthesia were given 5-7 mg *symbol* kg sup -1 thiopental and 2 micro gram *symbol* kg sup -1 fentanyl intravenously for induction of anesthesia. Eight (half) patients then received 0.5 mg *symbol* kg sup -1 atracurium, and the other eight received 0.1 mg *symbol* kg sup -1 vecuronium. The evoked response (twitch height, TH) of the adductor pollicis was monitored by measuring the integrated electromyographic response (AP EMG) on one limb and the mechanical response, using a force transducer (AP force), on the other. The activity of geniohyoid muscle (GH EMG) was measured using submental percutaneous electrodes. The following variables were measured: maximal TH depression; onset time for neuromuscular blockade to 50%, 90%, and maximal TH depression (OT50, OT90, and OTmax); times between administration of neuromuscular blocking agent and TH recovery to 10%, 25%, 50%, 75%, and 90% of control; and time for return of train-of-four ratio to return to 0.7.

Results: The principal findings were (1) OTmax was significantly (P < 0.01) shorter for geniohyoid than for adductor pollicis after either atracurium or vecuronium (OTmax was 216, 256, and 175 s for AP force, AP EMG, and GH EMG, with atracurium and 181, 199, and 144 s with vecuronium, respectively), and (2) the evoked EMG of geniohyoid recovered at the same speed as the EMG of adductor pollicis after an intubating dose of atracurium or vecuronium (recovery of TH to 75% of control at 50, 48, 42 min with AP force, AP EMG, and GH EMG with atracurium and 46, 45, and 42 min with vecuronium, respectively).     

Comparison of double-burst and train-of-four stimulation to assess neuromuscular blockade in children

Double-burst stimulation (DBS), a new technique to evaluate neuromuscular function, consists of two 50-Hz trains of 60-ms duration and 750 ms apart. DBS was compared with train-of-four (TOF) stimulation in 21 children aged 3-10 yr, during halothane anesthesia. On one arm the ulnar nerve was stimulated supramaximally with TOF stimulation every 12 s and the force of the evoked contraction of the adductor pollicis measured with an FTO3 force transducer and recorded on paper. Atracurium (0.4-0.5 mg.kg-1) was administered. During recovery from neuromuscular blockade, TOF stimulation was interrupted periodically and DBS substituted. The same stimulation patterns were applied to the ulnar nerve of the other arm simultaneously, and the clinical anesthesiologist was asked to estimate the degree of fade with both. There was good correlation between the measured TOF ratio (ratio of fourth to first response) and DBS ratio (ratio of second to first response). The TOF and DBS ratios above which fade could no longer be appreciated manually were (mean +/- SEM) 0.44 +/- 0.03 and 0.67 +/- 0.04 (P = 0.0002). Corresponding ranges were 0.3-0.8 for TOF and 0.4-0.9 for DBS, but DBS fade was always apparent if TOF fade could be detected. Therefore, in children, DBS is more sensitive than is TOF stimulation for the clinical assessment of recovery from neuromuscular blockade.     

Neuromuscular monitoring: methods and machines

Muscle relaxing agents are clinically in use for general anaesthesia to optimize the conditions to the endotracheal intubation as well as the surgical conditions. Therefore different musclerelaxants with specific pharmacological characteristics are available. Many factors that depend on the condition of the patient and the used musclerelaxant agent influence the duration of the neuromuscular blockade. Rapid reversal of their effects, particularly in cases of profound blockades, proved to be difficult. In cases of postoperative residual paralysis hypoxic complications because of failure of the ventilation increase the morbidity and mortality of the perioperative period. To avoid these complications in cause of postoperative residual neuromuscular blockade it seems to be necessary to evaluate the status of the muscle function. For the tactile or visual assessment or the objective measurement of stimulation the train-of-four (TOF), double-burst (DBS) or tetanus-stimulation of peripheral nerves like the ulnar nerve may be used. Established methods for the objective monitoring of neuromuscular function is the mechanomyography (MMG), the acceleromyography (AMG), the electromyography (EMG), the kinemyography (KMG) and the phonomyography (PMG). A sufficient recovery of the neuromuscular transmission is reached to a TOF-ratio of 0,9 and should be aimed before the extubation at the end of surgery. No subjective evaluation of the neuromuscular recovery is able to identify residual paralysis above a TOF-ratio of 0,5. Recent studies suggest that objective methods should be used to monitor neuromuscular function to avoid postoperative residual blockades.     

Temporal Relation between Acoustic and Force Responses at the Adductor Pollicis during Nondepolarizing Neuromuscular Block

Background: Contracting muscle emits sounds. The purpose of this study was to compare the time course of muscular paralysis at the adductor pollicis muscle (AP) with use of acoustic myography and mechanomyography.

Methods: Thirteen elective surgery patients, American Society of Anesthesiologists physical status I, received rocuronium (0.6 mg/kg intravenously) as a bolus dose during general anesthesia. Force of AP was measured with use of a strain gauge, and sounds were recorded simultaneously with use of a small condenser microphone fixed on the palmar surface of the hand over the AP. Supramaximal stimulation was applied to the ulnar nerve at 0.1 Hz for 45-60 min. In seven patients, the response to train-of-four stimulation was also recorded during recovery.

Results: Force and sounds both were equally sensitive in measuring maximum block. The relation between sound and force was curvilinear, with good agreement near 0 and 100% and acoustic response exceeding mechanical response at intermediate levels of block. The acoustic signal had a slower onset and a faster recovery than the force response. The fade response of sound to train-of-four stimulation also recovered faster than that of force.     

Conditions d'intubation: importance de la fréquence de répétition du train de quatre

ObjectivesTo assess that neuromuscular relaxation onset of the adductor pollicis (AP) is related to neuromuscular stimulation rate. To assess that train-of-four (TOF) at 0.05 Hz is a more accurate indicator of optimal tracheal intubation time and conditions, than TOF at 0.08 Hz.Study designProspective, comparative, randomized doubleblind study.PatientsForty adults, physical class ASA 1 or 2, undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the sequence of stimulation of the AP: either TOF at 0.05 Hz (test group) or TOF at 0.08 Hz (control group).MethodsInduction of anaesthesia was achieved with thiopentone, fentanyl and vecuronium (0.1 mg·kg⁻¹). Neuromuscular monitoring was obtained with force displacement transducers attached to each AP. Tracheal intubation was performed once AP muscular response obtained with TOF at 0.05 Hz for test group and TOF at 0.08 Hz for control group was abolished. Results are expressed as± SEM. Fisher exact test was used for intubation conditions comparison. Curarization time between groups was compared with unpaired Student's t test (P< 0.05 accepted).ResultsTOF with 0.05 Hz stimulation significantly increased curarization time: 217 ± 7 versus 162 ± 6 s (P< 0.001). Intubation conditions were excellent in 95% and good in 5% of patients in the study group, compared to 15 and 40% in the control group, respectively (P < 0.01). In 45% of the control group patients coughing at intubation occurred.ConclusionLow stimulation rate (TOF at 0.05 Hz) of AP is a reliable technique to determine the appropriate intubation time for patients paralyzed with vecuronium.     

Temporal relation between acoustic and force responses at the adductor pollicis during nondepolarizing neuromuscular block

BACKGROUND: Contracting muscle emits sounds. The purpose of this study was to compare the time course of muscular paralysis at the adductor pollicis muscle (AP) with use of acoustic myography and mechanomyography. METHODS: Thirteen elective surgery patients, American Society of Anesthesiologists physical status I, received rocuronium (0.6 mg/kg intravenously) as a bolus dose during general anesthesia. Force of AP was measured with use of a strain gauge, and sounds were recorded simultaneously with use of a small condenser microphone fixed on the palmar surface of the hand over the AP. Supramaximal stimulation was applied to the ulnar nerve at 0.1 Hz for 45-60 min. In seven patients, the response to train-of-four stimulation was also recorded during recovery. RESULTS: Force and sounds both were equally sensitive in measuring maximum block. The relation between sound and force was curvilinear, with good agreement near 0 and 100% and acoustic response exceeding mechanical response at intermediate levels of block. The acoustic signal had a slower onset and a faster recovery than the force response. The fade response of sound to train-of-four stimulation also recovered faster than that of force. CONCLUSION: Acoustic myography is an alternative method to monitor muscular paralysis that is easy to set up and applicable to most superficial muscles. However, the time course of relaxation at AP using acoustic myography differs from the time course of force relaxation. Therefore, these two methods are not equivalent when applied to AP.     

Comparison of phonomyography with balloon pressure mechanomyography to measure contractile force at the corrugator supercilii muscle

PURPOSE: Phonomyography is based on the creation of low frequency sounds during muscle contraction, which can be recorded and used for neuromuscular monitoring. In this study, balloon pressure mechanomyography, a novel method to measure the force of contraction via pressure changes in an air-filled balloon, was compared with phonomyography to determine neuromuscular blockade at the corrugator supercilii muscle. METHOD: After approval of the Ethics Committee and informed consent, 15 patients were studied. A small condenser microphone was taped to the area just above the eyebrow for phonomyography; an air-filled balloon was taped to the area just above the opposite eyebrow. After induction of anesthesia using remifentanil and propofol, a laryngeal mask airway was inserted without the aid of neuromuscular blocking agents. The facial nerve was stimulated supramaximally with single-twitch stimulation (0.1 Hz) using superficial electrodes placed on both temporal areas for onset and train-of-four stimulation every 12 sec during offset of neuromuscular blockade produced by mivacurium 0.1 mg.kg(-1). Onset and recovery measured by the two methods were compared using the t test and agreement between phonomyography and balloon pressure mechanomyography was examined using the Bland-Altman method. RESULTS: Onset, peak effect, and time to reach 25%, 75%, and 90% of control twitch response for phonomyography vs balloon pressure method were 83 +/- 16 sec vs 81 +/- 15 sec, 80 +/- 15% vs 82 +/- 17%, 7.7 +/- 2.3 min vs 7.5 +/- 2.4 min, 9.9 +/- 4.1 min vs 10.5 +/- 4 min, and 12.6 +/- 4.3 min vs 13.1 +/- 4.5 min respectively without being significantly different. Mean bias was 1% with limits of agreement of -9 and +9% of twitch height (T1). CONCLUSION: We applied a balloon pressure method to measure the force at the corrugator supercilii. Phonomyography at the corrugator supercilii shows good agreement with this modified version of mechanomyography.     

Phonomyographic measurements of neuromuscular blockade are similar to mechanomyography for hand muscles

PURPOSE: Phonomyography consists of recording low frequency sounds created during muscle contraction. In this study, phonomyography of three regions of the hand was compared to mechanomyography of the adductor pollicis. METHODS: In 12 patients, phonomyography was recorded via small condenser microphones taped over the thenar mass, the hypothenar eminence, and the dorsal groove between the first and second metacarpal bones to record the acoustic signals of adductor pollicis and the hypothenar and first dorsal interosseus muscles, respectively. Mechanomyography of the adductor pollicis was recorded simultaneously using a force transducer. After induction of anesthesia, the ulnar nerve was stimulated supramaximally using train-of-four (TOF) stimulation every 12 sec. Onset, maximum effect, and offset of neuromuscular block after rocuronium 0.6 mg x kg(-1) were measured using phonomyography and compared to mechanomyography using ANOVA and the Bland-Altman test. RESULTS: Phonomyographic measurements of onset and maximum effect of neuromuscular blockade were not significantly different from mechanomyographic measurements. Phonomyographic measurements of offset (T25%, T75 %, TOF 0.8) of neuromuscular block at the thenar muscles and first dorsal interosseus muscles were not significantly different from mechanomyographic measurements at adductor pollicis; however, T50%, T75% and T90% phonomyographic measurements at the hypothenar muscle were significantly shorter than at any other muscle site. CONCLUSION: There was good agreement between mechanomyographic measurements at the adductor pollicis muscle and phonomyographic measurements at the thenar and the first dorsal interosseus muscles. Phonomyography of those two muscles could be used interchangeably with mechanomyography of adductor pollicis for clinical purposes.     

Clinical recovery and train-of-four ratio measured mechanically and electromyographically following atracurium

Indices of clinical recovery were compared with mechanically (adductor pollicis muscle) and electromyographically (first dorsal interosseal muscle) recorded train-of-four (TOF) ratios during antagonism of atracurium blockade in 23 healthy neurolept anesthetized patients. Clinical recovery was evaluated from the ability to lift the head, sustain headlift for 5 or 10 s, protrude the tongue, open the eyes, and the presence of ptosis of the eyelids. In all patients the mechanical TOF ratio was recorded. In 17 patients TOF ratios based on measurements of the potential area and the amplitude of the major negative deflection of the compound EMG response were recorded as well. At each TOF ratio interval of 0.05 from a TOF ratio of 0.5-0.85, the number of patients being able to perform the individual tests was recorded. Further, the mechanical TOF ratio during recovery was compared with the EMG TOF ratios. Headlift could not be sustained for 5 s in any patient at a TOF ratio of 0.5, whether recorded mechanically or by EMG, and TOF ratio had to recover to 0.8 before all patients could sustain headlift for 5 s. All patients could open the eyes and protrude the tongue at a TOF ratio of 0.65, and ptosis remained present during the entire testing period. There was no statistically significant difference between the mechanical and the EMG methods with regard to the TOF ratios at which the tests could be performed. During recovery a linear relationship was found between mechanical TOF ratios and the square root of the EMG TOF ratios.(ABSTRACT TRUNCATED AT 250 WORDS)