Are changes in the evoked electromyogram during anaesthesia without neuromuscular blocking agents caused by failure of supramaximal nerve stimulation? (1/235)

The evoked electromyogram often decreases during anaesthesia in the absence of neuromuscular block. We have measured the electromyogram of the first dorsal interosseous muscle evoked by train-of-four stimulation of the ulnar nerve in 63 patients undergoing anaesthesia for minor surgery. We used Medicotest P-00-S electrodes, a Datex Relaxograph and a current sink in the stimulating leads in parallel with the current path through the patient. The current sink was used to shunt some of the maximum available output current from the Relaxograph while maintaining the supramaximal stimulus current passing through the patient. After 30 min of anaesthesia, when the muscle response to train-of-four was stable, the ulnar nerve stimulus current was increased by reducing the proportion shunted through the current sink. The electromyographic response did not change during the study in 13 patients. In the remaining 50 patients, the response decreased to 78.4% (SD 27.1%, range 7.5-95.0%) of baseline values over the first 20 min of anaesthesia. In 22 of these patients, the electromyographic response increased from 71.4 (SD 22.6)% to 92.3 (9.5)% of baseline responses when the stimulus current was increased by 12.3 (2.4) mA, while in the remaining 28 patients the response decreased to 83.7 (10.6)% and did not increase with increasing stimulus current. These results suggest that loss of supramaximal stimulation is partly responsible for the observed changes in the evoked electromyogram during anaesthesia.  (+info)

Antagonism of vecuronium-induced neuromuscular block in patients pretreated with magnesium sulphate: dose-effect relationship of neostigmine. (2/235)

We have investigated the dose-effect relationship of neostigmine in antagonizing vecuronium-induced neuromuscular block with and without magnesium sulphate (MgSO4) pretreatment. Neuromuscular block was assessed by electromyography with train-of-four (TOF) stimulation. First, we determined neostigmine-induced recovery in patients pretreated with MgSO4 (group A) or saline (group B) (n = 12 each). The height of T1, 5 min after neostigmine, was 43 (7)% in group A and 65 (6)% in group B (P < 0.01). Respective values after 10 min were 59 (7)% and 83 (5)% (P < 0.01). TOF ratio, 5 min after neostigmine, was 29 (6)% in group A and 29 (5)% in group B. Respective values after 10 min were 38 (11)% and 51 (7)% (P < 0.01). To gain insight into the mechanisms leading to delayed recovery after MgSO4, we calculated assisted recovery, defined as neostigmine-induced recovery minus mean spontaneous recovery. Spontaneous recovery was assessed in another 24 patients. Patients in group C received MgSO4/vecuronium and patients in group D vecuronium only (n = 12 each). Five minutes after neostigmine, assisted recovery was 22 (7)% in the MgSO4 pretreated patients and 28 (6)% in controls (P < 0.05). Ten minutes after neostigmine, values were 24 (7)% and 22 (6)%. Maximum assisted recovery was not influenced by MgSO4 pretreatment (27 (6)% in group A and 32 (6)% in group B) and time to maximum effect was comparable between groups: 6 (4-10) min and 7 (5-8) min, respectively. We conclude that neostigmine-induced recovery was attenuated in patients treated with MgSO4. This was mainly a result of slower spontaneous recovery and not decreased response to neostigmine.  (+info)

SI neuron response variability is stimulus tuned and NMDA receptor dependent. (3/235)

Skin brushing stimuli were used to evoke spike discharge activity in single skin mechanoreceptive afferents (sMRAs) and anterior parietal cortical (SI) neurons of anesthetized monkeys (Macaca fascicularis). In the initial experiments 10-50 presentations of each of 8 different stimulus velocities were delivered to the linear skin path from which maximal spike discharge activity could be evoked. Mean rate of spike firing evoked by each velocity (MFR) was computed for the time period during which spike discharge activity exceeded background, and an across-presentations estimate of mean firing rate (MFR) was generated for each velocity. The magnitude of the trial-by-trial variation in the response (estimated as CV; where CV = standard deviation in MFR/MFR) was determined for each unit at each velocity. MFR for both sMRAs and SI neurons (MFRsMRA and MFRSI, respectively) increased monotonically with velocity over the range 1-100 cm/s. At all velocities the average estimate of intertrial response variation for SI neurons (CVSI) was substantially larger than the corresponding average for sMRAs (CVsMRA). Whereas CVsMRA increased monotonically over the range 1-100 cm/s, CVSI decreased progressively with velocity over the range 1-10 cm/s, and then increased with velocity over the range 10-100 cm/s. The position of the skin brushing stimulus in the receptive field (RF) was varied in the second series of experiments. It was found that the magnitude of CVSI varied systematically with stimulus position in the RF: that is, CVSI was lowest for a particular velocity and direction of stimulus motion when the skin brushing stimulus traversed the RF center, and CVSI increased progressively as the distance between the stimulus path and the RF center increased. In the third series of experiments, either phencylidine (PCP; 100-500 microg/kg) or ketamine (KET; 0.5-7.5 mg/kg) was administered intravenously (iv) to assess the effect of block of N-methyl-D-aspartate (NMDA) receptors on SI neuron intertrial response variation. The effects of PCP on both CVSI and MFRSI were transient, typically with full recovery occurring in 1-2 h after drug injection. The effects of KET on CVSI and MFRSI were similar to those of PCP, but were shorter in duration (15-30 min). PCP and KET administration consistently was accompanied by a reduction of CVSI. The magnitude of the reduction of CVSI by PCP or KET was associated with the magnitude of CVSI before drug administration: that is, the larger the predrug CVSI, the larger the reduction in CVSI caused by PCP or KET. PCP and KET exerted variable effects on SI neuron mean firing rate that could differ greatly from one neuron to the next. The results are interpreted to indicate that SI neuron intertrial response variation is 1) stimulus tuned (intertrial response variation is lowest when the skin stimulus moves at 10 cm/s and traverses the neuron's RF center) and 2) NMDA receptor dependent (intertrial response variation is least when NMDA receptor activity contributes minimally to the response, and increases as the contribution of NMDA receptors to the response increases).  (+info)

Electromyographic assessment of neuromuscular block at the gastrocnemius muscle. (4/235)

We have assessed neuromuscular block electromyographically at the gastrocnemius muscle and compared it with that at the abductor digiti minimi muscle in 60 adult patients undergoing cervical spine surgery under general anaesthesia. All patients were in the prone position. After vecuronium 0.2 mg kg-1, times to onset of neuromuscular block at the gastrocnemius and abductor digiti minimi muscles were mean 147 (SD 24) and 145 (14) s, respectively (ns). Times to return of the first response of the post-tetanic count (PTC1) at the gastrocnemius and abductor digiti minimi muscles were 27.7 (5.6) and 37.0 (5.9) min, respectively (P = 0.0001). Times to return of the first response of the train-of-four (TOF) at the gastrocnemius and abductor digiti minimi muscles were 41.0 (9.1) and 49.9 (8.7) min, respectively (P = 0.01). Recovery of PTC, T1/T0 and TOF ratio at the gastrocnemius muscle were significantly faster than at the abductor digiti minimi muscle.  (+info)

Comparison of intubating conditions after rapacuronium (Org 9487) and succinylcholine following rapid sequence induction in adult patients. (5/235)

We have assessed intubating conditions provided by rapacuronium (Org 9487) and succinylcholine after rapid sequence induction of anaesthesia in adult patients undergoing elective surgery. We studied 335 patients, ASA I and II, in five centres. Two hundred and thirty-four subjects with normal body weight and 101 obese subjects were allocated randomly to one of four treatment groups differing in the neuromuscular blocking drug administered (rapacuronium 1.5 mg kg-1 or succinylcholine 1 mg kg-1) and in the technique used for induction of anaesthesia (fentanyl 2-3 micrograms kg-1 with thiopental 3-6 mg kg-1 or alfentanil 20 micrograms kg-1 with propofol 1.5-2 mg kg-1). Intubation was started at 50 s by an anaesthetist blinded to the drugs used. Intubating conditions were clinically acceptable (excellent or good) in 89.4% of patients after rapacuronium and in 97.4% after succinylcholine (P = 0.004), the estimated difference being 8.1% (95% confidence interval (CI) 2.0-14.1%). Neither anaesthetic technique nor subject group had an influence on intubating conditions. After intubation, the maximum increase in heart rate averaged 23.1 (SD 25.4%) and 9.4 (26.1%) after rapacuronium and succinylcholine, respectively (P < 0.001). Pulmonary side effects (bronchospasm and increased airway pressure) were observed in 10.7% (95% CI 5.8-17%) and 4.1% (95% CI 1.3-8.8%) of patients given rapacuronium and succinylcholine, respectively (P = 0.021). We conclude that after rapid sequence induction of anaesthesia in adults, clinically acceptable intubating conditions were achieved less frequently after rapacuronium 1.5 mg kg-1 than after succinylcholine.  (+info)

Rapid and reversible effects of activity on acetylcholine receptor density at the neuromuscular junction in vivo. (6/235)

Quantitative fluorescence imaging was used to study the regulation of acetylcholine receptor (AChR) number and density at neuromuscular junctions in living adult mice. At fully functional synapses, AChRs have a half-life of about 14 days. However, 2 hours after neurotransmission was blocked, the half-life of the AChRs was now less than a day; the rate was 25 times faster than before. Most of the lost receptors were not quickly replaced. Direct muscle stimulation or restoration of synaptic transmission inhibited this process. AChRs that were removed from nonfunctional synapses resided for hours in the perijunctional membrane before being locally internalized. Dispersed AChRs could also reaggregate at the junction once neurotransmission was restored. The rapid and reversible alterations in AChR density at the neuromuscular junction in vivo parallel changes thought to occur in the central nervous system at synapses undergoing potentiation and depression.  (+info)

Spontaneous or neostigmine-induced recovery after maintenance of neuromuscular block with Org 9487 (rapacuronium) or rocuronium following an initial dose of Org 9487. (7/235)

We have examined spontaneous and neostigmine-induced recovery after an initial dose of Org 9487 1.5 mg kg-1 followed by three repeat doses of Org 9487, a 30-min infusion of Org 9487 or two incremental doses of rocuronium. Mean clinical duration after incremental doses of Org 9487 0.5 mg kg-1 increased from 12.3 (SD 3.4) min to 14.0 (4.0) and 15.9 (5.9) min (P < 0.01), and after rocuronium from 14.4 (5.2) min to 19.2 (5.9) min (P < 0.01). Times for spontaneous recovery from a T1 of 25% to a TOF ratio of 0.8 after the last bolus dose of Org 9487 and after a 30-min infusion were 72.4 (16.5) and 66.1 (26.9) min compared with 36.7 (15.8) min in the group receiving reocuronium. These times were significantly reduced to 9.9 (4.5), 8.6 (6.1) and 5.7 (2.5) min, respectively, after neostigmine administration at a T1 of 25% (P < 0.05). We conclude that administration of Org 9487 by repeat bolus doses or infusion was associated with slow spontaneous recovery but neostigmine administration resulted in adequate recovery in less than 10 min.  (+info)

Anaesthesia for strabismus surgery: a regional survey. (8/235)

An increase in the demand by local surgeons for neuromuscular block during strabismus surgery, and the forced duction test in particular, led us to review the literature and conduct a regional survey of anaesthetic techniques used. A questionnaire was distributed to 379 anaesthetists in the region and 264 responses were received. The results demonstrated that 55% of paediatric patients and 66% of adult patients may have been operated on under suboptimal conditions; residual tone may have been present in the extraocular muscles during forced duction testing and strabismus correction.  (+info)

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