Post-tetanic count at adductor pollicis is a better indicator of early diaphragmatic recovery than train-of-four count at corrugator supercilii

Background: Because the intensity of neuromuscular block at the diaphragm(DIA) is indirectly assessed, the electromyographic measurementsof the DIA (DIA_EMG) from surface electrodes were related toinformation provided by visual estimation of neuromuscular transmissionat the adductor pollicis (AP) and the corrugator supercilii(CSC) during recovery from vecuronium block. Methods: Twelve adult patients were studied during balanced anaesthesia.After induction of anaesthesia and tracheal intubation withoutneuromuscular blocking agent, supramaximal stimulations wereapplied to phrenic, ulnar and facial nerves. During recoveryfrom vecuronium 0.1 mg kg^–1 an independent observer blindedto DIA_EMG counted visually detectable train-of-four (TOF) atCSC (TOF_CSC) and post-tetanic AP (PTC_AP) responses. Times torecovery of PTC_AP = 1, 5, <10 and >10, and TOF_CSC = 1–4responses were related to DIA_EMG. Values are means (SD). Results: Reappearance of the first response to PTC_AP occurred significantly(P < 0.05) earlier and for a lower recovery of DIA_EMG thanthat of TOF_CSC [24 (8) min vs 33 (9) min, and 10 (10)% vs 25(8)%, respectively]. With PTC_AP 5 response, DIA_EMG recoverywas 21 (11)%. Recovery of TOF_CSC = 1 and 2 coincided with DIA_EMGrecovery of 25 (8)% and 47 (9)%, respectively. Conclusions: PTC_AP may better reflect early recovery of vecuronium-inducedDIA paralysis than TOF_CSC. The findings suggested that PTC_AP 5 warranted deep neuromuscular block of the DIA.     

Acceleromyography of the orbicularis oculi muscle II: comparing the orbicularis oculi and adductor pollicis muscles

BACKGROUND: The orbicularis oculi (OO) muscle has been recommended for neuromuscular monitoring when the adductor pollicis (AP) muscle is not available. We investigated whether neuromuscular block could be measured reliably from the orbital part of the OO muscle by the use of acceleromyography. METHODS: During propofol, fentanyl, and alfentanil anaesthesia two TOF-Guards (Organon Teknika NV, Boxtel, the Netherlands) with acceleration transducers placed on the distal phalanx of the thumb and over the middle of the eyebrow, respectively, were used to measure neuromuscular block simultaneously in 23 patients during vecuronium-induced and neostigmine-antagonized neuromuscular block. For both muscles, the simultaneously recorded first response (T1) in the train-of-four (TOF) and TOF-ratio were measured both during onset and recovery of the block. Furthermore, both the AP muscle T1 and TOF-ratio responses were plotted against 10% intervals of the OO muscle responses during onset and recovery, respectively. RESULTS: The orbicularis oculi muscle had a shorter latency and a faster recovery to TOF-ratio 0.80 compared with the AP muscle. During onset and recovery, pronounced variations of the AP muscle T1 and TOF-ratio responses were observed when compared with the OO muscle. CONCLUSION: A significant clinical disagreement exists between the degree of paralysis measured at the OO and the AP muscles. It is impossible to obtain a reasonable estimate of the degree of block at the AP muscle when the block is measured from the OO muscle with acceleromyography. If used, there is substantial risk of overlooking a residual block, and adequate recovery of the block should be confirmed by a final AP muscle measurement.     

TRAIN-OF-FOUR FADE DURING ONSET AND RECOVERY OF NEUROMUSCULAR BLOCK: A STUDY IN NON-ANAESTHETIZED SUBJECTS

The actions of alcuronium, vecuronium and tubocurarine havebeen studied in the isolated forearms of six healthy, non-anaesthetizedvolunteers. The responses of adductor pollicis were measuredduring onset and recovery of neuro-muscular block for each agent.There was a drug-related disparity between mechanomyo-gram (MMG)and electromyogram (EMG) measurement of the first response ofthe train-of-four (T1) and of the ratio of the fourth (T4) tothe first response (TOF ratio). There were significantly higherT1 values for the EMG than for MMG during alcuronium blockade(P = 0.03). For tubocurarine, however, the relationship wasreversed. The relationship between T1 and TOF ratio during onsetand recovery of neuromuscular block was a hysteresis. The TOFratio at 50% T1 was significantly higher during onset than duringrecovery for all three drugs, measured by MMG or EMG (P <0.005). Analysis of variance of the differential fade loopsfailed to show a drug-related effect. We conclude that careshould be taken in assuming interchangeability between MMG andEMG measurement of T1. Relationships between T1 and TOF ratioderived during recovery do not necessarily apply during onsetand may lead to error in estimating the degree of muscle relaxation.     

Monitoring of neuromuscular block after administration of vecuronium in patients with diabetes mellitus

Background. We studied the supramaximal current for ulnar nervestimulation during electromyographic monitoring of onset andrecovery of neuromuscular block using a neuromuscular transmissionmodule (M-NMT Module, Datex-Ohmeda) in patients with Type 2diabetes undergoing anaesthesia with nitrous oxide, oxygen,isoflurane and fentanyl. Methods. Thirty-six diabetic patients were randomly assignedto a post-tetanic count (PTC) group (n=17) or train-of-four(TOF) group (n=19). In addition, 30 non-diabetic patients weredivided into control PTC (n=15) and TOF groups (n=15). Results. In the diabetic patients (diabetes PTC and diabetesTOF groups), the mean supramaximal stimulating current was significantlyhigher than in the non-diabetic patients (control PTC and TOFgroups) (50.5 (SD 14.1) vs 33.4 (6.1) mA, P<0.01). Onsetof neuromuscular block (time to disappearance of T1) after vecuronium0.1 mg kg^–1 in the diabetic patients did not differ significantlyfrom that in the non-diabetic patients (276 (77) vs 244 (44)s, P=0.055). Time to return of PTC1 did not differ significantlybetween the diabetes and control PTC groups (21.0 (12.1) vs15.7 (5.0) min, P=0.126). Times to return of T1 and T4 in thediabetes TOF group were significantly longer than in the controlTOF group (T1: 37.5 (15.2) vs 25.7 (7.6) min, P=0.01; T4: 61.4(23.7) vs 43.5 (11.4) min, P=0.01). During recovery, PTC andT4/T1 in the diabetes PTC and TOF groups were similar to thosein the control PTC and TOF groups, respectively. T1/T0 in thediabetes TOF group was significantly less than in the controlTOF group, 80–120 min after vecuronium (P<0.05). Conclusions. In diabetic patients, supramaximal current is higherthan in non-diabetic patients. After vecuronium, onset of neuromuscularblock and recovery of PTC or T4/T1 are not altered, but timeto return of T1 or T4, and recovery of T1/T0 are delayed indiabetic patients. Br J Anaesth 2003; 90: 480–6     

Effect of tetanic stimulation on subsequent train-of-four responses at various levels of vecuronium-induced neuromuscular block

Tetanic stimulation influences subsequent neuromuscular responses.In addition, the tetanus- induced changes in neuromuscular responsesdiffer according to the level of neuromuscular block at whichtetanic stimulation is delivered. We studied the tetanus-inducedeffect on subsequent train-of-four (TOF) responses at variouslevels of vecuronium-induced neuromuscular block in 45 anaesthetizedpatients. Tetanic stimulation was applied when a twitch heightof T1 returned to 25%, 50% and 75% of its control twitch height(T0) (groups 1, 2 and 3, respectively) after administrationof vecuronium 0.1 mg kg^–1. Maximum post-tetanic percentageincreases in TOF responses in groups 1, 2 and 3 were 257 (SD119)%, 107 (75)% and 68 (54)% for T1/T0 (P < 0.001 for group1 vs 2; P < 0.001 for group 1 vs 3) and 535 (259)%, 421 (213)%and 292 (171)% for T4/T1 (P < 0.01 for group 1 vs 3), respectively.Durations of post-tetanic increases in TOF responses in groups1, 2, and 3 were 52 (19)s, 37 (14)s, and 32 (13) s for T1/T0(P / 0.05 for group 1 vs 2; P < 0.01 for group 1 vs 3) and53 (17)s, 46 (15)s and 35 (12)s for T4/T1 (P < 0.05 for group1 vs 3), respectively. These data suggest that the tetanus-inducedeffect on subsequent TOF is more apparent and lasts longer atgreater degrees than at lesser degrees of neuromuscular block.     

The effects of sevoflurane are similar to those of isoflurane on the neuromuscular block produced by vecuronium

We have examined the interactions of 1 MAC of isoflurane andsevoflurane (and 66% nitrous oxide in oxygen) with vecuronium,using the EMG response of the abductor digiti minimi to train-of-four(TOF) stimulation of the ulnar nerve. We constructed dose-responsecurves for vecuronium in 54 patients. The curves for both isofluraneand sevoflurane had a significant leftward shift compared withthat for fentanyl-nitrous oxide anaesthesia (P < 0.01). Whenthe amplitudes of the first response (T1) had recovered to 50%of control in another 32 patients, subsequently we comparedthe spontaneous recovery rate of the ratio of the fourth tothe first TOF response (T4:T1) at 3-min intervals during the15-min period, in the presence of two volatile anaestheticsor after discontinuation of administration of anaesthetic. Therate of recovery of T4:T1 was significantly greater when bothanaesthetics were discontinued. However, this rate was similarfor both anaesthetics, suggesting that the mechanism of actionof the two anaesthetics is similar. (Br. J. Anaesth. 1994; 72:465–467)     

Impaired neuromuscular transmission after recovery of the train-of-four ratio

BACKGROUND: Residual neuromuscular blockade may increase the risk of development of post-operative pulmonary complications, but is difficult to detect clinically. It was speculated that patients may have impaired neuromuscular transmission after surgery of long duration, despite the recovery of the train-of-four (TOF) ratio. METHODS: The muscle force (mechanomyography), motor compound muscle action potential amplitude and fatigue of the adductor pollicis (AP) muscle were assessed after recovery of the TOF ratio to 0.9. Thirteen patients receiving repetitive administration of neuromuscular blocking agents (NMBAs) during surgery (median, 5.3 h; interquartile range, 3.4-6 h) were studied post-operatively in the intensive care unit. At the time of the measurements, patients were scheduled for extubation and the AP TOF ratio amounted to a mean (standard deviation, SD) of 0.94 (0.05). Six healthy volunteers of similar age, weight and gender were studied for comparison. Force-frequency curves were generated by stimulation (10-80 Hz) of the ulnar nerve, and the AP electromyogram (EMG) amplitude was measured, in parallel, before and after evoked muscle fatigue. RESULTS: The maximum AP force at a stimulation frequency of 20-80 Hz was significantly lower in patients than in controls [40 N (16 N) vs. 65 N (18 N) at 80 Hz]. In patients, but not in controls, the EMG amplitude decreased with increasing nerve stimulation frequency, and a tetanic fade of both force and EMG, amounting to 0.41 (0.33) (EMG) and 0.61 (0.35) (mechanomyography) at 80 Hz, was observed. Force after fatiguing contractions did not differ between the groups. CONCLUSION: After repetitive administration of NMBAs during surgery, even with recovery of the TOF ratio to 0.9 or more, muscle weakness from impaired neuromuscular transmission can occur. The clinician should consider that post-operative recovery of the TOF ratio to 0.9 does not exclude an impairment of neuromuscular transmission.     

The agreement between adductor pollicis mechanomyogram and first dorsal interosseous electromyogram

The agreement between evoked adductor pollicis mechanomyogram and first dorsal interosseous evoked electromyogram (EMG) was evaluated during a pharmacodynamic study of rocuronium and vecuronium. In the first place the effective doses of rocuronium producing 50% and 90% block (ED₅₀ and ED₉₀, respectively) were established in 32 neurolept anaesthetized patients from the adductor pollicis mechanomyogram and the first dorsal interosseous EMG area and amplitude. Secondly, limits of agreement between the two methods were evaluated from the mean difference between methods 2 s.d. in 20 patients during onset of block following 2 × ED₉₀ of rocuronium and vecuronium, and during recovery from the last supplementary dose of 1/2 × ED₉₀. Limits of agreement show how much the EMG may be above or below the mechanomyogram. No differences were found between mechanomyographical and EMG based ED₅₀ (0.20 mg kg^-1) and ED₉₀ (0.30–0.32 mg kg^-1), respectively. The first EMG train–of–four (TOF) response overestimated block at 25% recovery and underestimated block at 75% and 90% recovery by only 3–7%. Limits of agreement suggested that the EMG may be 7–8% above or below the mechanomyogram during onset compared to 12–17% during recovery. The EMG TOF ratio lagged behind that of the mechanomyogram by 0.05 at TOF ratios below 0.50. No difference was found between methods at a TOF ratio of 0.75. Limits of agreement indicated that the EMG TOF ratio may be 0.12–0.15 above or below that of the mechanomyogram. Agreement between the amplitude and the area of the EMG were better than between the mechanomyogram and the EMG. Evaluation of the time courses of action showed that rocuronium had a faster onset of action than vecuronium (1.8 min compared to 2.8 min) while duration of action and reversal were similar. In conclusion, the first dorsal interosseous EMG amplitude and area can be used to assess rocuronium and vecuronium block.     

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).     

Recovery of post-tetanic and train-of-four responses at the first dorsal interosseous and adductor pollicis muscles in patients receiving vecuronium

Purpose

To compare recovery of accelographical responses to post-tetanic twitch (PTT) and train-of-four (TOF) stimuli obtained at the first dorsal interosseous muscle (DI) with those at the adductor pollicis muscle (AP) after administration of vecuronium 70 μg · kg^?1.

Methods

Sixty adult patients were randomly assigned to one of four groups: PTT-DI (n = 15), PTT-AP (n = 15), TOF-DI (n = 15), or TOF-AP (n = 15) group. In PTT-DI and PTT-AP groups, responses to PTT were measured accelographically at the DI and at the AP, respectively. In TOF-DI and TOF-AP groups, responses to TOF were measured at the DI and at the AP, respectively.

Results

The T₁/T₀ (T₀ = control) was greater in the TOF-DI than in TOF-AP group throughout recovery (P < 0.05), and the T₄/T₁ was greater in the TOF-DI than in TOF-AP group during the 30–40 min after vecuronium injection (P < 0.05). Time to the return of the first response to PTT (post-tetanic count₁, PTC₁) was less in the PTT-DI than in the PTT-AP group (17.7 ± 4.2 vs 21.7 ± 5.6 min, mean ± SD, P = 0.0341). The post-tetanic count PTC (number of single twitch stimuli in response to PTT) was greater in the PTT-DI than in the PTT-AP group during the 10–30 min after vecuronium (P < 0.05). Time to the return of T₁ was less in the TOF-DI than in the TOF-AP group (23.1 ± 6.0 vs 27.6 ± 4.9 min, P = 0.0334).

Conclusion

Recovery of responses to PTT and TOF stimuli occurred earlier at the DI than at the AP.     

Epidurally administered mepivacaine delays recovery of train-of-four ratio from vecuronium-induced neuromuscular block

BACKGROUND: The aim of this study was to examine the efficacy of epidurally administered mepivacaine on recovery from vecuronium-induced neuromuscular block. METHODS: Eighty patients were randomly assigned to one of two study groups. They were either given epidurally a bolus of 0.15 ml kg(-1) of mepivacaine 2%, followed by repetitive injections of 0.1 ml kg(-1) h(-1) throughout the study, or were not given epidurally. General anaesthesia was induced and maintained with fentanyl, propofol and nitrous oxide. Neuromuscular block was induced with vecuronium 0.1 mg kg(-1) and monitored using acceleromyographic train-of-four (TOF) at the adductor pollicis. Patients in each treatment group were randomized to receive neostigmine 0.04 mg kg(-1) at 25% recovery of the first twitch of TOF or to recover spontaneously to a TOF ratio of 0.9. The effect of epidural mepivacaine on speed of spontaneous and facilitated recovery of neuromuscular function was evaluated. RESULTS: The time from administration of vecuronium to spontaneous recovery to a TOF ratio of 0.9 was significantly longer in the epidural mepivacaine group [105.4 (14.2) min] as compared with the control group [78.5 (9.1) min, P < 0.01]. Neostigmine administered at 25% of control in T1 shortened recovery from neuromuscular block, however the time required for facilitated recovery to a TOF ratio of 0.9 in the epidural group was significantly longer than that in the control group [7.6 (1.6) min vs 5.8 (2.1) min, P < 0.01]. CONCLUSIONS: In clinical anaesthesia, it should be recognized that epidurally administered mepivacaine delays considerably the TOF recovery from neuromuscular block.     

Infusion of amino acid enriched solution hastens recovery from neuromuscular block caused by vecuronium

We investigated the effect of an amino acid infusion on neuromuscularblock produced by vecuronium, and on rectal temperature andsurface temperature over the adductor pollicis muscle. Sixtyadult patients undergoing general anaesthesia were randomlydivided into four groups of 15 patients each: amino acid (AA)-post-tetaniccount (PTC); AA-train-of-four (TOF); control (C)-PTC; or C-TOFgroup. In the AA-PTC and AA-TOF groups, after a bolus of vecuronium0.1 mg kg^–1, a continuous infusion of an 18 amino acidenriched solution (AMIPAREN^®) was started at a rate of 166kJ h^–1. In the C-PTC and C-TOF groups, normal saline wasadministered. Time from vecuronium to the return of the PTCin the AA-PTC group was significantly shorter than in the C-PTCgroup (mean (SD), 13.3 (4.5) versus 18.0 (5.6) min, P<0.05).Times to return of T1, T2, T3, and T4 (first, second, third,and fourth twitch of TOF) in the AA-TOF group were significantlyshorter than in the C-TOF group (21.1 (4.5) versus 28.0 (8.2)min for T1, P<0.05). PTC in the AA-PTC group was significantlygreater than in the C-PTC group; 25–35 min after administrationof vecuronium (P<0.05). T1/T0 and T4/T1 in the AA-TOF groupwere significantly higher than in the C-TOF group, 40–120and 50–120 min after vecuronium respectively (P<0.05).Rectal temperature and surface temperature over the adductorpollicis muscle in the AA-PTC and AA-TOF groups were significantlyhigher than in the control groups 50–120 and 100–120min after vecuronium respectively (P<0.05). Infusion of aminoacid enriched solution hastens recovery from neuromuscular block. Br J Anaesth 2001; 86: 814–21     

Rate of injection through whitacre needles affects distribution of spinal anaesthesia

A prospective, randomized, double-blind study was performedto investigate whether altering the rate of injection of localanaesthetic through a Whitacre needle had any effect on thespinal block achieved. Twenty patients scheduled for electiveurological surgery under spinal anaesthesia received an injectionof 3 ml of 0.5% plain bupivacaine either by hand (fast)over 10 s (18 ml min^–1) or by infusionpump (slow) over 3 min (1 ml min^–1). Allpatients were in the sitting position both during insertionof the spinal needle and for 3 min after the start of spinalinjection, and they then changed to the supine position. Theslow injection group achieved peak sensory block earlier, aftera median interval of 20 (95% confidence interval 12.5–30) minvs 30 (22.5–45) min (P<0.05) for the fast group. Thelevel of peak sensory block was similar: T3.5 (T2–T4.5)vs T4 (T1.5–T6.5). The time to lowest mean arterial pressureoccurred earlier in the slow group, at 10 (8 to 18) vs 20 (15–31) min(P<0.05). Duration of the motor block was shorter in theslow group: 180 (152–242) vs 270 (225–300). We concludethat a slow spinal injection of plain bupivacaine results ina block of more rapid onset and recovery. Br J Anaesth 2001; 86: 245–8     

USE OF VECURONIUM AND DOXAPRAM IN PATIENTS SUSCEPTIBLE TO MALIGNANT HYPERTHERMIA

Neuromuscular blockade was obtained with vecuronium 108 µgkg^–1 in 44 patients under-going diagnostic muscle biopsyas part of an investigation of malignant hyperthermia (MH) susceptibility.At the termination of anaesthesia doxapram 1.43 mg kg^–1was given in an attempt to antagonize postoperative respiratorydepression. Rectal, muscle and skin temperatures, blood lactateconcentration and venous PCO₂ were measured before, during andafter anaesthesia. Susceptibility to MH was established by invitro contracture tests according to the protocol of the EuropeanMH Group. Twenty patients were susceptible to MH (MHS), 19 wereMH nonsusceptible (MHN) and five MH equivocal (MHE). No adverseeffects of the drugs were observed. There were no differencesbetween the three groups in rectal or muscle temperature, bloodlactate concentration or venous PCO₂ at any time. Doxapram didnot prevent an increase in postoperative PCO₂. It is concludedthat vecuronium and doxapram may be safely administered to patientssusceptible to MH.     

Sevoflurane and propofol decrease intraocular pressure equally during non-ophthalmic surgery and recovery

Background. To provide good control of intraocular pressure(IOP) during anaesthesia and surgery, we conducted a study comparingthe effects on IOP during maintenance and recovery of sevofluranevs propofol anaesthesia in 33 patients (ASA I–II) undergoingelective non- ophthalmic surgery. Methods. Anaesthesia was induced with propofol 2 mg kg^–1,fentanyl 2 µg kg^–1 and vecuronium 0.1 mg kg^–1.Patients were allocated randomly to receive either propofol4–8 mg kg^–1 h^–1 (group P; n=16)or 1.5–2.5 vol% sevoflurane (group S; n=17) for maintenanceof anaesthesia. Fentanyl 2–4 µg kg^–1was added if necessary. The lungs were ventilated with 50% airin oxygen. Blood pressure, heart rate, oxygen saturation andend-tidal carbon dioxide were measured before and throughoutanaesthesia and in the recovery room. IOP was determined withapplanation tonometry (Perkins) by one ophthalmologist blindedto the anaesthetic technique. Results. There was a significant decrease in IOP after inductionand during maintenance of anaesthesia in both groups. No significantdifferences in IOP between the two groups was found. Conclusion. Sevoflurane maintains the IOP at an equally reducedlevel compared with propofol. Br J Anaesth 2002; 89: 764–6     

Residual curarization in the recovery room after vecuronium

We have investigated residual block after anaesthesia which included the use of the neuromuscular blocking agent vecuronium but no anticholinesterase, in 568 consecutive patients on admission to the recovery room. The ulnar nerve was stimulated submaximally using TOF stimulation (30 mA). Postoperative residual curarization was defined as a TOF ratio < 0.7. Of the 568 patients, 239 (42%) had a TOF < 0.7 in the recovery room. These patients had received a larger cumulative dose of vecuronium than patients who had full recovery (mean 7.7 (SD 3.6) mg vs 6.2 (2.7) mg; P < 0.05) and a shorter time had elapsed since the last vecuronium dose (117 (70) min vs 131 (80) min; P < 0.05). Of 435 patients whose trachea was extubated, 145 (33%) exhibited inadequate recovery from neuromuscular block. Six of these had one or no response to TOF stimulation and were reintubated. In the remaining 139 patients, neuromuscular block was successfully antagonized. Only 20 patients (3.5%) remembered TOF stimulation when questioned 2 h later in the recovery room, and discomfort associated with it was assessed using a visual analogue scale before discharge. We conclude that it is necessary to antagonize residual block produced by vecuronium.      

Assessment of neuromuscular block: comparison of three clinical methods and evoked electromyography

Three clinical methods, visual, tactile and 'spring', for the assessment of neuromuscular blockade were compared to the EMG recording evoked during enflurane anaesthesia and relaxation with vecuronium in 33 patients. During maintenance of the block, the tactile method, based on the recognition of the strength of movement of the patient's thumb against the observer's fingers, was more accurate than the two other methods. The correlation coefficient compared to the TI of the EMG was 0.77. The tactile method led to over-estimation of muscle strength in only 9-10% of the assessments made by the anaesthetists, while this happened in about one-third of the cases when the visual method was applied. The observers under-estimated the muscle power in about 30% of the assessments made with each of the clinical methods. During the recovery, the mean train-of-four (TOF) ratio of the EMG was less than 40% when the anaesthetists announced that they could detect no fade with the visual or tactile methods. The corresponding value obtained with the spring method (standardized preload with a rubber spring) was significantly higher, 66%. Using the spring, a clinically significant residual fade (TOF less than 0.50) could be detected in nine of the 11 cases. As residual relaxation cannot be ruled out using the clinical methods, quantitative recording of neuromuscular function is recommended in cases where complete recovery from muscle relaxation is of special importance. The spring method is the most reliable clinical method during recovery, while the tactile method is the most accurate during the maintenance of neuromuscular block.     

Magnesium sulphate enhances residual neuromuscular block induced by vecuronium

Magnesium sulphate (MgSO4) is currently used for haemodynamic control during anaesthesia and the early postoperative period. We have investigated the effect of this treatment on residual neuromuscular block after administration of vecuronium. Twenty adult patients were allocated randomly to one of two groups to receive MgSO4 60 mg kg-1 either at recovery from vecuronium block to a train-of-four (TOF) ratio of 0.7, or 1 h after recovery to a TOF ratio of 0.7. Neuromuscular transmission was monitored using electromyography and TOF stimulation. MgSO4 caused rapid and profound recurarization in all 20 patients. MgSO4 decreased the amount of acetylcholine released at the motor nerve terminal and thus may lead to recurarization in patients previously exposed to neuromuscular blocking agents.      

Oral clonidine premedication attenuates the hypertensive response to ketamine

Clonidine diminishes sympathetic nervous system activity viaa central action. To test if the haemodynamic responses to ketamine,a centrally acting sympathomimetic drug, are attenuated by clonidine,we studied arterial pressure (AP) and heart rate (HR) changesafter ketamine 1 mg kg^–1 in 40 normotensive patients undergoinggeneral anaesthesia. They were allocated randomly to receiveclonidine 5 µg kg^–1 and famotidine 20 mg (n = 20)or to a control group (n = 20) which received only famotidine20 mg orally 90 mm before induction of anaesthesia. After administrationof ketamine 1 mg kg^–1 and vecuronium 0.2 mg kg^–1ventilation of the lungs was controlled with 67% nitrous oxidein oxygen to maintain end-tidal carbondioxide at 4–4.7kPa. AP and HR were measured non-invasively at 1-min intervalsfor 10 min after ketamine. After induction of anaesthesia, APwas increased significantly from resting values in the controlgroup, but remained unchanged in the clonidine group (P <0.05). Maximum changes in mean AP were also significantly greaterin the control group compared with the clonidine group (29.2(12.8) vs 19.5 (13.1) mm Hg, P = 0.02). However, no change inHR was noted throughout the 10-min study.     

Evaluation of twitch responses obtained from abductor hallucis muscle as a monitor of neuromuscular blockade: Comparison with the results from adductor pollicis muscle

The twitch responses evoked from the abductor hallucis muscle (AHM) and the adductor pollicis muscle (APM) were examined simultaneously in 20 anesthetized patients following a single bolus intravenous administration of 0.04 mg·kg⁻¹ of vecuronium bromide. The mean onset time of vecuronium-induced depression of AHM twitch responses was significantly slower than that of APM twitch responses (4.9±1.5 minvs 3.7±1.2 min, mean±SD,P<0.001), and when the clinical duration times of vecuronium were compared, AHM twitch responses recovered more quickly than APM twitch responses (15.3±4.1 minvs 19.6±6.7 min,P<0.01), although there was no statistically significant difference in the spontaneous recovery time between AHM and APM (9.8±2.9 minvs 10.0±3.6 min). It is concluded that the twitch responses of AHM may be a useful monitor of neuromuscular blockade in anesthetized patients in whom setting the blockade monitor on the patient's arms is difficult, although monitoring of twitch response of AHM is less sensitive than that of APM in case of vecuronium administration.