Twitch Response Of Muscle Research Articles

Cervical epidural analgesia via a thoracic approach using nerve‐stimulation guidance in adult patients undergoing total shoulder replacement surgery

Continuous cervical epidural anesthesia can provide excellent peri- and post-operative analgesia, although several factors prevent its widespread use. Advancing catheters from thoracic levels to the cervical region may circumvent these barriers, provided they are accurately positioned. We hypothesize that guiding catheters from thoracic to cervical regions using low-current epidural stimulation will have a high success rate and enable excellent analgesia in adults undergoing total shoulder arthroplasty. After Institutional Review Board approval, adult patients were studied consecutively. A 17-G Tuohy needle was inserted into the thoracic epidural space using a right paramedian approach with loss of resistance. A 20-G styletted epidural catheter, with an attached nerve stimulator, was primed with saline and a 1-10 mA current was applied as it advanced in a cephalad direction towards the cervical spine. Muscle twitch responses were observed and post-operative X-ray confirmed final placement. After a test dose, an infusion (2-8 ml/h) of ropivacaine 2 mg/ml and morphine 0.05 mg/ml (or equivalent) was initiated. Verbal analog pain scale scores were collected over 72 h. Cervical epidural anesthesia was performed on 10 patients. Average current required to elicit a motor response was 4.8 +/- 2.0mA. Post-operative X-ray of catheter positions confirmed all catheter tips reached the desired region (C4-7). The technical success rate for catheter placement was 100% and excellent pain control was achieved. Catheters were positioned two to the left, four to the right and four to the midline. This epidural technique provided highly effective post-operative analgesia in a patient group that traditionally experiences severe post-operative pain and can benefit from early mobilization.

Preliminary studies with a neurotoxin obtained from Bungarus caeruleus venom

The neurotoxin purified from the venom of Bungarus caeruleus causes a neuromuscular blockade on acetylcholine-induced muscle twitch response in isolated frog rectus abdominis muscle preparation. Neuromuscular blockade produced by d-tubocurarine on acetylcholine-induced muscle twitch response in an isolated frog rectus abdominis muscle preparation was reversed to normal muscle twitch response in presence of neostigmine. Whereas the purified neurotoxin produced an irreversible neuromuscular blockade in presence of the same strength of neostigmine. As it is already known, botulinum toxin, which also brings about neuromuscular blockade, is effectively used as a drug in the treatment of painful movement disorders. Since the purified toxin also causes paralysis of the muscle, we propose its possible efficacy in the treatment of neuromuscular disorders.

Comparison of Pharmacodynamics and Intubation Conditions of Muscle Relaxants Using a Continuous Infusion during Induction

Background: The doses of muscle relaxants used to facilitate tracheal intubation are 2 . However, the potency needs to be measured on a molar basis rather than by the mass of the drug. The aim of this study was to compare the pharmacodynamics and intubation conditions of the muscle relaxants using a continuous infusion during induction. Methods: The time courses of the drug response and tracheal intubating conditions of the muscle relaxants by a continuous infusion were examined in 44 patients undergoing elective surgery. The neuromuscular effects of the relaxants were quantified by recording the twitch response of the adductor pollicis muscle after stimulating the ulnar nerve (0.1 Hz, 0.2 ms, supramaximal stimuli). The onset time and duration of each group were measured and the dose-response curves were determined by logistic regression analysis. Results: The doses (mol/kg) for intubation were 1.08 0.31 of rocuronium, 0.58 0.10 of atracurium, 0.28 0.06 of vecuronium and 1.36 0.65 of succinylcholine. The relative potency of rocuronium, atracurium, vecuronium and succinylcholine was 1.00：1.86：3.86：0.79. There were no significant differences between any of the groups with regard to the onset time of the relaxants. The duration of the relaxants was succinylcholine (4 min 12 s), rocuronium (25 min 36 s), atracurium (34 min 28 s), and vecuronium (42 min 24 s). The intubation conditions of the succinylcholine group were inferior to those of the vecuronium group. Conclusions: This method can be used to determine the potency and pharmacodynamics between the neuromuscular blockers. Further study will be needed to confirm these results and to evaluate the effect of the infusion rate on this model.

Inhibition of Sarcoplasmic Ca2+Adenosine Triphosphatase in Porcine Skeletal Muscle Samples with Cyclopiazonic Acid Enables In Vitro Malignant Hyperthermia Discrimination

Inhibition of Sarcoplasmic Ca2+Adenosine Triphosphatase in Porcine Skeletal Muscle Samples with Cyclopiazonic Acid Enables In Vitro Malignant Hyperthermia Discrimination

Speed, accuracy, and stability of laryngeal movement in singing

Motor performance is often quantified in terms of speed, strength, accuracy, and stability of a target gesture, or maintaining a given posture. In the vocal system, this involves primarily the intrinsic laryngeal muscles and the respiratory muscles. Agonist–antagonist pairs of muscles are used to position the vocal folds for phonation (vocal onset), for pitch change, and for registration (as in yodeling). Maximum speed and accuracy are discussed for vocal embellishments such as trills, trillo, scales, arpeggios, yodel, and glissando. This speed and accuracy are interpreted in terms of muscle twitch and tetanic responses obtained in vitro on animal muscles, from electromyographic recordings on humans, and from muscles not easily tested on humans. The laryngeal reflex system is also described, particularly with regard to its ability to stabilize (or destabilize) neurologic tremor originating from the central nervous system.

The Neuromuscular Effects of Glucocorticoid Administration on the Skeletal Muscle of Rats

Background: The administration of high doses of glucocorticoids can produce significant side effects including skeletal muscle atrophy, weakness and aberrant pharmacology. However, available reports have yielded conflicting results ranging from facilitatory to no change to inhibitory action of glucocoticoids on neuromuscular transmission. Also, the mechanisms for such changes are not known. Therefore, this study investigated the changes in muscle contractility and pharmacology after prednisolone administration in vivo. Methods: With institutional approval, Sprague-Dawley rats were randomly allocated to 3 treatment groups, namely prednisolone (10 mg/kg daily for 7 days), saline control (equal volume of saline daily for 7 days) and an age-matched food-restriction group which grew at the same rate as the prednisolone group. On day 8 the rats were anesthetized, mechanically ventilated and the twitch response of the tibialis muscle to supramaximal stimulation of the sciatic nerve at 2 Hz for 2 sec every 12 sec, or at 50 or 100 Hz tetanus for 5 sec were monitored. The peak twitch and tetanic tensions were measured and tetanic fade was calculated. The cumulative dose-response curves of d-tubocurarine (d-TC) in the tibialis muscles were determined. The tibialis muscle weight relative to body weight was measured (muscle index), and the tension per unit muscle mass (i.e., specific tension) was calculated. The control and treatment groups were compared by a one way ANOVA test and P ＞ 0.05 was regarded as significant. Results: Prednisolone caused a decline in growth rate and the ED50 of dTC relative to saline. Food-restriction caused a decline in growth rate and an increase in muscle index relative to saline, and a decline in tension relative to prednisolone. Conclusions: These results indicate that prednisolone can alter the sensitivity of skeletal muscles to dTC even without or before changes in neuromuscular contractility become apparent. Therefore, titration of doses of nondepolarizing neuromuscular blocking agents may be indicated in patients receiving glucocorticoid therapy.

Sarcomere length-dependence of activity-dependent twitch potentiation in mouse skeletal muscle

BackgroundIt has been reported that potentiation of a skeletal muscle twitch response is proportional to muscle length with a negative slope during staircase, and a positive slope during posttetanic potentiation. This study was done to directly compare staircase and posttetanic responses with measurement of sarcomere length to compare their length-dependence.MethodsMouse extensor digitorum longus (EDL) muscles were dissected to small bundles of fibers, which permit measurement of sarcomere length (SL), by laser diffraction. In vitro fixed-end contractions of EDL fiber bundles were elicited at 22°C and 35°C at sarcomere lengths ranging from 2.35 μm to 3.85 μm. Twitch contractions were assessed before and after 1.5 s of 75 Hz stimulation at 22°C or during 10 s of 10 Hz stimulation at 22°C or 35°C.ResultsStaircase potentiation was greater at 35°C than 22°C, and the relative magnitude of the twitch contraction (Pt*/Pt) was proportional to sarcomere length with a negative slope, over the range 2.3 μm – 3.7 μm. Linear regression yielded the following: Pt*/Pt = -0.59·SL+3.27 (r2 = 0.74); Pt*/Pt = -0.39·SL+2.34 (r2 = 0.48); and Pt*/Pt = -0.50·SL+2.45 (r2 = 0.80) for staircase at 35°C, and 22°C and posttetanic response respectively. Posttetanic depression rather than potentiation was present at long SL. This indicates that there may be two processes operating in these muscles to modulate the force: one that enhances and a second that depresses the force. Either or both of these processes may have a length-dependence of its mechanism.ConclusionThere is no evidence that posttetanic potentiation is fundamentally different from staircase in these muscles.

The Role of Zinc Binding in the Biological Activity of Botulinum Toxin

Botulinum toxin is a zinc-dependent endoprotease that acts on vulnerable cells to cleave polypeptides that are essential for exocytosis. To exert this poisoning effect, the toxin must proceed through a complex sequence of events that involves binding, productive internalization, and intracellular expression of catalytic activity. Results presented in this study show that soluble chelators rapidly strip Zn(2+) from its binding site in botulinum toxin, and this stripping of cation results in the loss of catalytic activity in cell-free or broken cell preparations. Stripped toxin is still active against intact neuromuscular junctions, presumably because internalized toxin binds cytosolic Zn(2+). In contrast to soluble chelators, immobilized chelators have no effect on bound Zn(2+), nor do they alter toxin activity. The latter finding is because of the fact that the spontaneous loss of Zn(2+) from its coordination site in botulinum toxin is relatively slow. When exogenous Zn(2+) is added to toxin that has been stripped by soluble chelators, the molecule rebinds cation and regains catalytic and neuromuscular blocking activity. Exogenous Zn(2+) can restore toxin activity either when the toxin is free in solution on the cell exterior or when it has been internalized and is in the cytosol. The fact that stripped toxin can reach the cytosol means that the loss of bound Zn(2+) does not produce conformational changes that block internalization. Similarly, the fact that stripped toxin in the cytosol can be reactivated by ambient Zn(2+) or exogenous Zn(2+) means that productive internalization does not produce conformational changes that block rebinding of cation.

Epidural electric stimulation of posterior structures of the human lumbar spinal cord: 1. muscle twitches - a functional method to define the site of stimulation.

To describe an electrophysiological method for determining the relation between lumbar cord dorsal roots and cathode of epidural electrode for spinal cord stimulation (SCS). Data has been collected from 13 subjects who have been under evaluation of effectiveness of SCS for control of spasticity. Induced muscle twitches from both quadriceps (Q), adductors (A), hamstrings (H), tibial anterior muscles (TA) and triceps surae muscles (TS) were simultaneously recorded with surface-electrode polyelectromyography (pEMG) and analyzed for amplitudes, latency times and recruitment order. Stimulation of dorsal lumbar cord structures evoked characteristic EMG events during muscle twitch responses. Their amplitudes varied with stimulus strength. Latency times were rather invariable regardless of stimulus strength. Two distinct recruitment orders were demonstrated depending on whether the stimulating cathode was placed over the upper (=response from quadriceps and/or adductor muscles) or the lower (=response from tibialis anterior and triceps surae) lumbar cord segments. The chances to stimulate upper lumbar cord segments are best around the 12th thoracic vertebra. pEMG recording of muscle twitches enables us to accurately differentiate between upper and lower lumbar cord segments. Furthermore, our findings regarding amplitude, latency and recruitment order strongly suggest that we stimulate posterior roots not posterior columns of the lumbar spinal cord.

Comparison of sensitivity of sodium currents to tetrodotoxin in equine muscle specimens with that in murine and human muscle specimens

To determine sensitivity of equine skeletal muscle to tetrodotoxin and compare that with sensitivity of murine and human skeletal muscles. Semimembranosus, vastus lateralis, triceps brachii, and masseter muscle specimens from 22 euthanatized horses, vastus lateralis muscle biopsy specimens from 25 clinically normal humans, and diaphragmatic muscle specimens from 6 mice. Electrically elicited twitch responses were measured in muscle specimens incubated in medium alone and with tetrodotoxin (100 nM, 400 nM, 1.6 microM for equine specimens and 100 nM, 200 nM, 400 nM, 800 nM, 1.6 microM for murine and human specimens). Percentages of tetrodotoxin-sensitive and -resistant sodium channels were determined and compared among muscles and species. 2 sodium channels with different sensitivities to tetrodotoxin were identified in equine muscle. One was blocked with 100 nM tetrodotoxin and the other was unaffected by tetrodotoxin at concentrations up to 1.6 microM. The only difference detected among the 4 equine muscles was that masseter muscle specimens had a higher percentage of tetrodotoxin-sensitive channels than triceps brachii muscle specimens. Tetrodotoxin-resistant sodium channels constituted 31 to 66% of the equine muscle twitch response, which was greater than that determined for normal human and murine muscle (< 5%). Equine skeletal muscle contains a high percentage of tetrodotoxin-resistant sodium channels. The 4 equine muscles evaluated were more similar to each other than to murine and human muscles. Shifts in expression of sodium channel subtypes may play a role in the manifestation of certain myopathies.

Concentration-dependent stimulation of cholinergic motor nerves or smooth muscle by [Nle 13]motilin in the isolated rabbit gastric antrum

In man, rabbit and cat, the effects of motilin and motilides are neurally mediated in vivo, whereas in vitro binding and contractility studies suggest the presence of a smooth muscular receptor. The aim of this study was to investigate in vitro interactions of motilin with the enteric excitatory neurotransmission in the gastric antrum of the rabbit. Circular muscle strips from the pre-pyloric antrum were subjected to electrical field stimulation (1 ms, 1–32 Hz, 10 s train) and muscle twitch responses were recorded isometrically. Induced twitch responses were frequency dependent (1–32 Hz) and entirely neurogenic (tetrodotoxin sensitive). [Nle 13]motilin dose-dependently (10 −9–10 −8 M) enhanced the amplitude of, atropine sensitive, evoked contractions. At 4 Hz the response, expressed as a % of the response to 32 Hz, increased from 15.5±4.1% (control) to 28.1±5.8% (motilin 10 −9 M), and to 45.8±3.6% (motilin 10 −8.5 M) ( P<0.05). This effect was not inhibited by hexamethonium (10 −3.3 M) but was abolished by the motilin receptor antagonist GM-109 (10 −5 M). In unstimulated strips, motilin induced phasic-tonic contractions with a threshold concentration of 10 −8 M and an pEC 50 of 7.48, which were also inhibited by GM-109 (10 −5 M) but not by tetrodotoxin (10 −5.5 M). The maximal tension, frequency and dose-dependency of carbachol-induced contractions were not influenced by motilin (pEC 50, carbachol: 6.48±0.06 (control), 6.49±0.07 (motilin)). In conclusion, motilin enhances contractions induced by electrical field stimulation in the rabbit antrum by a post-ganglionic interaction with the cholinergic neurotransmission in vitro at low doses and interacts directly with antral smooth muscle at high doses. This model is an accurate reflection of the in vivo effects of motilin and provides a tool to study neurogenic and myogenic actions of motilin and motilides in vitro.

Extended Duration of Action of Rocuronium in Postpartum Patients

We studied the time course of action of a single bolus of 600 micro g/kg rocuronium given during anesthesia with propofol, fentanyl, and nitrous oxide was studied in 12 nonpregnant and 12 postpartum patients.Neuromuscular effects were quantified by recording the indirectly evoked twitch response of the adductor pollicis muscle after ulnar nerve stimulation. In all patients, the trachea was intubated 60 s after administration of rocuronium. Onset time was similar in both groups (nonpregnant: 91 +/- 28 s vs. postpartum: 95 +/- 30 s), with the time to 25% twitch recovery being significantly longer (P < 0.001) in the postpartum patients (31.1 +/- 3.6 min) compared with the nonpregnant group (24.9 +/- 4.0 min). The time required for recovery from 25% to 75% of the control twitch response after reversal with neostigmine and atropine was significantly longer (P = 0.003) in postpartum (4.8 +/- 0.9 min) than in nonpregnant patients (3.2 +/- 0.6 min). These data suggest that pregnancy-induced changes result in prolonged effects of rocuronium in postpartum patients. (Anesth Analg 1997;84:352-4)

Extended duration of action of rocuronium in postpartum patients.

We studied the time course of action of a single bolus of 600 micrograms/kg rocuronium given during anesthesia with propofol, fentanyl, and nitrous oxide was studied in 12 nonpregnant and 12 postpartum patients. Neuromuscular effects were quantified by recording the indirectly evoked twitch response of the adductor pollicis muscle after ulnar nerve stimulation. In all patients, the trachea was intubated 60 s after administration of rocuronium. Onset time was similar in both groups (nonpregnant: 91 +/- 28 s vs. postpartum: 95 +/- 30 s), with the time to 25% twitch recovery being significantly longer (P < 0.001) in the postpartum patients (31.1 +/- 3.6 min) compared with the nonpregnant group (24.9 +/- 4.0 min). The time required for recovery from 25% to 75% of the control twitch response after reversal with neostigmine and atropine was significantly longer (P = 0.003) in postpartum (4.8 +/- 0.9 min) than in nonpregnant patients (3.2 +/- 0.6 min). These data suggest that pregnancy-induced changes result in prolonged effects of rocuronium in postpartum patients.

Twitch response of striated muscle in patients with progressive external ophthalmoplegia, mitochondrial myopathy and focal cytochrome c-oxidase deficiency.

Some aspects of the contractile properties of skeletal muscle in patients with progressive external ophthalmoplegia (PEO), mitochondrial myopathy and focal cytochrome c-oxidase deficiency were investigated by studying the twitch response (TR) of the tibialis anterior muscle both at rest and after maximum isometric contraction. The results of needle electromyography were normal in four of the six examined patients, and myopathic in the remaining two. A slowing in muscle relaxation was the most frequently observed abnormality; significantly prolonged muscle contraction times and reduced twitch torque potentiation values after isometric contraction were also detected. TR abnormalities in PEO patients may be due either to a dysfunction of the contractile machinery depending upon impaired muscle energy supply or to altered muscle fiber characterized by the predominance of type I slow fiber. In addition to conventional electromyographic investigations, TR study may be a useful diagnostic tool in PEO patients.

Potentiation of diaphragmatic twitch after voluntary contraction in normal subjects.

Skeletal muscle twitch responses may be transiently increased by previous contractions, a phenomenon termed twitch potentiation. The aim of this study was to examine the extent and time course of diaphragmatic twitch potentiation and its relationship to both the magnitude and duration of the preceding voluntary diaphragmatic contraction. Twitch transdiaphragmatic pressure (PDI) was measured in six normal subjects, before and after voluntary diaphragm contractions of 100%, 75%, 50%, and 25% of maximum PDI (PDImax) sustained for five and 10 seconds. Twitch PDI was significantly increased after 100%, 75%, and 50% contractions. Following maximal contractions sustained for 10 seconds the mean increase in twitch PDI was 52%. Following 50% contractions sustained for five seconds the mean increase in twitch height was 28%. In all runs twitch PDI returned to rested levels within 20 minutes. Twitch potentiation can be substantial, even following submaximal contractions, and must be taken into account when twitch pressure is used to assess diaphragm contractility.

Omeprazole Potentiates Atracurium and Succinylcholine Paralysis In Vivo in Rats

We examined the effect of proton pump inhibitor omeprazole on neuromuscular paralysis induced with either nondepolarizing or depolarizing neuromuscular blocking drugs in anesthetized and mechanically ventilated rats. Neuromuscular paralysis, as judged by tibialis anterior muscle twitch tension in response to sciatic nerve stimulation, was maintained at about 50% with intravenous (i.v.) bolus and infusion regimens of either atracurium or succinylcholine. Omeprazole, 0.5, 1, and 10 mg/kg i.v., was then administered at 10-min intervals while the infusion of the neuromuscular blocker was continued. Omeprazole at all three doses increased the steady-state neuromuscular paralysis produced with either atracurium (pre-omeprazole versus final post-omeprazole paralysis; mean +/- SE, n = 6, 53.0% +/- 2.3% vs 80.0% +/- 5.3%) or succinylcholine (50.8% +/- 1.5% vs 86.4% +/- 5.1%). Omeprazole, 0.5, 1.0, and 10 mg/kg i.v., given directly and without any neuromuscular blocker, produced approximately 5% depression of the muscle twitch response. Omeprazole, i.v. at human therapeutic doses, alters neuromuscular function and enhances the action of both atracurium and succinylcholine in vivo in rats.

Isolation of a toxin from jellyfish Acromitus rabanchatu and its effect on skeletal muscle

A toxin (T-Ar) from the crude extract of jellyfish Acromitus rabanchatu was purified by (NH 4) 2SO 4 fractionation followed by ion-exchange chromatography on DEAE-cellulose column. The mol. wt of T-Ar was found to be about 182,000. T-Ar reversibly blocked the twitch response of rat diaphragm muscle stimulated either indirectly or directly. It also reversibly blocked the twitch responses of chick biventer-cervicis muscle preparations. T-Ar failed to alter the contractures of the denervated rat diaphragm muscle preparation induced by acetylcholine, potassium chloride and caffeine. Similarly, acetylcholine and carbachol-induced contractures on chick biventer-cervicis muscle preparation were not influenced by T-Ar. The T-Ar-induced blockade of twitch responses of rat phrenic nerve-diaphragm was enhanced in high Na + or low Ca 2+ medium, and reduced in low Na + or high Ca 2+-containing medium. The results suggest that the toxin (T-Ar) possesses a direct paralysing effect on the muscle membrane.

Evaluation of the Endotracheal Intubating Conditions of Rocuronium (ORG 9426) and Succinylcholine in Outpatient Surgery

The time-course of action and tracheal intubating conditions of rocuronium and succinylcholine under intravenous anesthesia with propofol, alfentanil, and nitrous oxide were studied in 30 patients undergoing outpatient surgery. The neuromuscular effects of both drugs were quantified by recording the indirectly evoked twitch response of the adductor pollicis muscle after ulnar nerve stimulation (0.1 Hz, 0.2 ms supramaximal stimuli). Patients were given either 0.6 mg/kg rocuronium (n = 20) or 1 mg/kg succinylcholine (n = 10) intravenously. Sixty seconds after the administration of the muscle relaxant, the trachea was intubated and the intubating conditions were scored by a "blinded" assessor. Intubating conditions were not different (P = 0.34) between the rocuronium and succinylcholine groups. The onset and duration of neuromuscular blockade were shorter with succinylcholine than with rocuronium. The depression of the twitch response to 5% of control value occurred in 0.8 +/- 0.1 min with 1 mg/kg succinylcholine and 1.2 +/- 0.5 min with 0.6 mg/kg rocuronium (P less than 0.01). The recovery of the twitch response to 25%, 75%, and 90% of its control value was shorter after succinylcholine (P less than 0.001) and occurred at 8.1 +/- 2.6, 10.3 +/- 3.9, 11.3 +/- 4.6 and 25.3 +/- 5.0, 33.1 +/- 5.9, 36.1 +/- 6.3 min after succinylcholine and rocuronium, respectively. Also the time required for spontaneous recovery from 25% to 75% of the control twitch response was significantly shorter (P less than 0.001) after succinylcholine (2.2 +/- 1.4 min) than after rocuronium (7.8 +/- 2.1 min). It is concluded that in spite of the pharmacodynamic differences between succinylcholine and rocuronium, the intubating conditions after administration of both compounds are similar and develop at the same rate.

The Accuracy of Train-of four Monitoring at Varying Stimulating Currents

Train-of-four (TOF) monitoring of neuromuscular block at submaximal current stimulation has been recommended because it is less painful than monitoring at supramaximal stimulation. The measurement error, however, when using submaximal stimulation has not as yet been fully elucidated. The authors therefore quantified the measurement error of TOF monitoring at low currents near the initial threshold for stimulation (ITS) by assessing precision (the difference between duplicated TOF ratios measured at the same current) and accuracy (the difference between TOF ratios at lesser currents and the TOF ratio at 58 mA, which served as the reference standard method). A stable neuromuscular block at a TOF ratio of 0.40 and subsequently 0.70 was established in 20 patients using a continuous infusion of atracurium. The ulnar nerve was stimulated at the wrist using TOF stimulation, and the evoked twitch response of the adductor pollicis muscle was measured with a force-displacement transducer. The stimulating current was varied in 5-mA steps between ITS and 55 mA. Whereas there were no statistical significant differences between the mean TOF ratios at the different currents, the standard deviation increased with decreasing currents (P less than 0.01 at currents less than 40 mA). The precision was acceptable except at ITS, where the limits of precision (mean intracurrent difference in TOF ratio +/- two standard deviations) exceeded 0.05, which was the chosen acceptable difference. The standard deviation of the accuracy was significantly increased at currents less than or equal to ITS + 25 mA (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of peripheral hypothermia on a vecuronium‐induced neuromuscular block

Seven healthy patients were investigated during midazolam-fentanyl nitrous oxide-oxygen anaesthesia. The mechanical twitch response of the adductor pollicis muscle was recorded simultaneously during bilateral supramaximal train-of-four (TOF) stimulation of the ulnar nerves at the wrist. Intense neuromuscular block was evaluated using the post-tetanic count (PTC) method. Core temperature and the peripheral skin temperature of one arm were kept normal and stable. Following cooling of the other arm to a peripheral hand skin temperature of 27 degrees C, vecuronium was administered in a bolus dose of 0.05 mg.kg-1 followed by maintenance doses of 0.02 mg.kg-1. In the hypothermic and the normothermic arm the onset time following the bolus dose was 180 +/- 40 (mean +/- s.d.) seconds and 140 +/- 30 s, respectively, the duration of action was 26.4 +/- 4.5 and 16.5 +/- 4.0 min and the recovery time was 265 +/- 90 and 130 +/- 60 s (P less than 0.01). The time course of action following maintenance doses showed a similar marked difference between the hypothermic and the normothermic arm. In the normothermic arm a close correlation was found between the number of post-tetanic twitches and the time to first response to TOF stimulation. In contrast, in the hypothermic arm the number of post-tetanic twitches showed great variation with a poor correlation to the duration of intense neuromuscular block. It is concluded that the time course of action of a vecuronium-induced neuromuscular block is markedly prolonged during peripheral hypothermia and intense neuromuscular block cannot reliably be assessed using the PTC method at low peripheral temperature.(ABSTRACT TRUNCATED AT 250 WORDS)