Rapid tracheal intubation with atracurium--a comparison of priming intervals

To determine the optimal interval between the administration of the priming dose and the intubating dose, atracurium was given to 44 patients either in a single dose of 0.5 mg X kg-1 or in an initial dose of 0.06 mg X kg-1 followed two, three or five minutes later with 0.44 mg X kg-1. When atracurium was given as a single bolus of 0.5 mg X kg-1 the time to 100 per cent twitch suppression (onset time) was 90.9 +/- 36 (mean +/- SD) seconds. When the priming interval was two minutes, the onset time of the intubating dose was 76.6 +/- 42.2 seconds (p = NS). But when the priming interval was three or five minutes, the onset times were 42.2 +/- 16.5 (p less than 0.01) and 52.6 +/- 28.8 (p less than 0.05) seconds respectively. Waiting for five minutes after the administration of the priming dose did not improve the intubating conditions. It is concluded that three minutes appears to be the optimal time interval for the administration of atracurium in divided doses. When a priming dose of atracurium is given three minutes before the intubating dose, it can provide an alternative to succinylcholine for rapid endotracheal intubation.     

The optimal priming dose for atracurium

To determine the optimal priming dose for administration in divided doses, atracurium was given to 77 patients either in a single dose of 0.5 mg X kg-1 or in an initial dose of 0.04, 0.05, 0.06, 0.07, 0.08 or 0.09 mg X kg-1, followed three minutes later by the remainder of the 0.5 mg X kg-1 dose. Patients were anaesthetized throughout the study. When atracurium was given as a single bolus of 0.5 mg X kg-1, the mean time to complete neuromuscular block was 141.5 seconds. Administration in divided doses accelerated the onset time (p less than 0.01), that is the time from the intubating dose to the complete suppression of train-of-four (TOF) response. The TOF ratio decreased slightly but statistically significantly following the priming doses. When the priming dose was 0.05 mg X kg-1, the mean onset time was 70.9 seconds and priming with larger doses did not add any further advantage. It is concluded that 0.05 mg X kg-1 appears to be the optimal priming dose for the administration of atracurium in divided doses. When 0.05 mg X kg-1 is given three minutes before the intubating dose, tracheal intubation can be accomplished in less than 90 seconds.     

Speed and ease of tracheal intubation: priming with mivacurium compared with succinylcholine

This study examined the efficacy of mivacurium priming (0.015 mg · kg^?1) with five minutes between the priming and intubating doses by comparing the effects of one, two and three times the ED₉₅ dose (0.075 mg · kg^?1) of mivacurium after priming (Groups 1, 2 and 3, respectively), with a saline prime and 2 × ED₉₅ mivacurium (Group 4) or 1 mg · kg^?1 dose of succinylcholine (Group 5). The time from the intubating dose injection to intubation was measured and intubating conditions were rated on a five-point scale with 4 being optimal and 0 being failure. Mean times (± SEM) in seconds between the administration of the intubating dose and tracheal intubation were: 106.4 ± 5.1, 89.6 ± 6.7, 81.9 ± 2.7, 169.9 ± 7.8 and 82.9 ± 3.5 for Groups 1–5 respectively. The times for Group 2 (2 × ED₉₅ with priming), Group 3 (3 × ED₉₅ with priming) and Group 5 (succinylcholine with saline) were shorter than the times of Groups 1 (1 × ED₉₅ with priming) and 4 (2 × ED₉₅ with saline) P < 0.05. Mean intubating condition scores (± SD) for the five groups respectively were 3.1 ± 0.6, 3.4 ± 0.6, 3.5 ± 0.5, 3.2 ± 0.6 and 3.8 ± 0.4. Scores for Groups 2, 3 and 5 were higher than those of Group 1 (P < 0.05). The data demonstrated that (1) priming with mivacurium shortens the intubation time and is accompanied by good intubating conditions with doses 2× and 3× ED₉₅, and (2) intubating times and conditions similar to those achieved with succinylcholine can be obtained using mivacurium 2× (total dose 0.150 mg · kg^?1) or3 × ED₉₅ (total dose 0.215 mg · kg^?1) with a five-minute priming interval. Priming provides an alternative technique in those clinical circumstances where succinylcholine is contraindicated.     

Onset of vecuronium-induced neuromuscular block after a long priming interval

Purpose. We examined whether a new application of the priming principle, i.e., having the priming dose of vecuronium administered before the insertion of the epidural catheter, would hasten the onset of the neuromuscular block induced by the intubating dose of vecuronium. Methods. Forty-five adult female patients scheduled for general anesthesia combined with epidural anesthesia were studied. In group A (n = 15), the priming dose of vecuronium, 0.01 mg·kg⁻¹, was administered before insertion of the epidural catheter. The intubating dose of vecuronium, 0.09 mg·kg⁻¹, was given after the insertion of the epidural catheter. In group B (n = 15), the priming dose of vecuronium, 0.01 mg·kg⁻¹, was given 4 min before the intubating dose of vecuronium, 0.09 mg·kg⁻¹. In the control group (n = 15), no priming dose was given, and only the intubating dose of vecuronium, 0.10 mg·kg⁻¹, was administered. In all three groups, general anesthesia was induced with propofol 2.5 mg·kg⁻¹, and the trachea was intubated when T1/control value (control twitch height in response to train-of-four stimuli) was less than 0.1. Results. In group A, the priming dose was given 16 ± 3 min (mean ± SD) before the administration of the intubating dose. The times to onset of neuromuscular block in groups A and B, and the control group were: 145 ± 30, 184 ± 45, and 219 ± 23 s, respectively (P < 0.05 among the three groups). In all three groups, intubating conditions (graded on a four-point scale) were excellent (P = 0.59). Before the induction of anesthesia, symptoms of paralysis were observed in 5, 4, and 0 patients in groups A and B and the control group, respectively (P < 0.05 between group A or B vs control group). Conclusions. If the priming dose of vecuronium is given after a long priming interval (16 ± 3 min), the time to onset of the neuromuscular block caused by the intubating dose of vecuronium is markedly shorter than when the conventional priming interval of 4 min is employed. Received: March 5, 2001 / Accepted: October 4, 2001     

Different priming techniques,including mivacurium,accelerate the onset of rocuronium

Different priming sequences of equipotent doses of rocuronium and mivacurium on the onset of maximum neuromuscular block and intubating conditions were compared with those obtained after succinylcholine. During thiopentone-fentanylnitrous oxide anaesthesia, 70 patients were randomly assigned into seven groups. Group I received mivacurium 0.15 mg · kg^?1 as a single bolus dose. Group II received a priming dose of mivacurium 0.015 mg · kg^?1 followed three minutes later by mivacurium 0.135 mg · kg^?1. Group III received rocuronium 0.6 mg · kg^?1 as a single bolus dose, and Group IV received an initial dose of rocuronium 0.06 mg · kg^?1 followed by rocuronium 0.54 mg · kg^?1. Group V received a priming dose of mivacurium 0.015 mg · kg^?1 followed by rocuronium 0.54 mg · kg^?1. Group VI received an initial dose of rocuronium 0.06 mg · kg^?1 followed by mivacurium 0.135 mg · kg^?1. Group VII received succinykholine 1.0 mg · kg^?1. Groups I, III, and VII received a placebo injection before the administration of the neuromuscular blocking drug. Additional thiopentone 2 mg · kg^?1 iv was given 30 sec before intubation. Onset times (mean (95% confidence interval)) after priming a rocuronium block with either rocuronium (73 (57–90) sec) or mivacurium (58 (47–69) sec) were similar to those after succinykholine (54 (40–68) sec), and were shorter (P < 0.01) than that observed in other groups. Intubating conditions were not different between the groups. The duration of neuromuscular block was shortest with succinykholine. It is concluded that priming a rocuronium block with either mivacurium or rocuronium resulted in a neuromuscular block comparable to that of succinykholine in both the onset of action and intubating conditions.     

Priming with atracurium: improving intubating conditions with additional doses of thiopental

The effects of different intubating doses of atracurium on the time of onset, and the effect of an additional dose of thiopental on intubating conditions, were studied in 72 patients divided into six groups (n = 12 in each). Stratified sampling was used to obtain an even sex distribution. Groups I, III, and V (controls) received atracurium as a single bolus dose of 0.4, 0.5 or 0.6 mg/kg respectively. Groups II, IV, and VI received an initial (priming) dose of 0.05 mg/kg followed 3 min later by 0.35, 0.45, or 0.55 mg/kg respectively. The time of onset, that is the time from the intubating dose to complete suppression of the train-of-four (TOF) response, was significantly accelerated after administration of atracurium in divided doses. Increasing the intubating dose of atracurium after an initial 0.05 mg/kg from 0.35 to 0.55 mg/kg did not result in further significant acceleration of the onset time, but resulted in prolongation of the duration of neuromuscular blockade. When divided doses of atracurium were given, administration of 2 mg/kg thiopental (in addition to the 5 mg/kg used for induction) before the injection of the intubating dose resulted in improvement of intubating conditions as reflected by statistically significant changes in intubating scores. This result was probably due to the increase by thiopental in the depth of anesthesia. Therefore, when thiopental is given as supplement, the priming technique can be made to provide better conditions for tracheal intubation in less than 90 sec.     

Intubationsbedingungen nach Gabe von Atracurium und Vecuronium Bolusmethode vs. Primingtechnik

Prompted by the ongoing discussion of the pros and cons of using succinylcholine, this study was conducted to compare the responses to bolus injections of atracurium or vecuronium with those after sequential injection of these drugs (priming principle). We evaluated the earliest possible intubation times, intubating conditions, and the onset times (i.e. times from the end of injection to the maximum blockade) under conditions approaching real use as closely as possible. Methods. The randomized and double-blind study was carried out with 80 ASA risk class 1 and 2 patients. Approval of the institutional ethics committee was obtained, and each patient gave informed consent. Patients were randomly allocated to four study groups of 20 patients each. Isotonic saline was administered to those patients assigned to the atracurium or vecuronium bolus groups, whereas the patients assigned to the other two groups received a priming injection of either atracurium (0.05 mg/kg) or vecuronium (0.01 mg/kg). We observed the patients for signs of incipient muscular weakness before the induction of anaesthesia. Anaesthesia was induced with thiopental 3.5 min after the first injection (5 mg/kg and 50–100?mg before intubation). After a further 1 min during which adequate mask ventilatin with oxygen was assured, corresponding to a priming interval of 4.5?min, 0.5 mg/kg of atracurium or 0.1 mg/kg of vecuronium was administered to the patients in the bolus groups and 0.45 mg/kg of atracurium or 0.09 mg/kg of vecuronium as intubating doses to those in the priming groups. Intubation was attempted at 90, 120, 150 and 180?s thereafter. Intubating conditions were evaluated on the basis of laryngoscopy, vocal cord movement and coughing or bucking of the patients. Neuromuscular function was monitored via accelerometry at the adductor pollicis muscle (TOF stimulation of the ulnar nerve every 15?s). Results. The priming doses did not diminish the elicited twitches of the adductor pollicis muscle, but led to heavy eyelids and double vision in 35% of the atracurium patients and 47% of the vecuronium patients; these symptoms were well tolerated by the patients. At the time of intubation the adductor pollicis muscle was relaxed to approximately the same degree in all groups (mean±SD for the TOF ratios in the bolus groups was 0.46±0.37 for atracurium, 0.45±0.4 for vecuronium; in the priming groups 0.52±0.39 for atracurium, 0.53±0.36 for vecuronium). The administration of the relaxants in divided doses significantly shortened the intubating time after atracurium (100 vs 124?s) and improved the intubating conditions of vecuronium (good vs tolerable), but had no effect on the time course of the neuromuscular blockade (onset times in the bolus groups 224±84?s for atracurium and 209±64 s for vecuronium; in the priming groups 249±112?s for atracurium and 205±52 s for vecuronium). Conclusions. The priming technique presented here is clinically superior to the bolus method and therefore should be preferred in all elective cases and in those patients in whom succinylcholine is contraindicated.     

Target controlled priming for rapid onset of intubation dose: A new approach

Purpose To determine the pattern of onset of the intubating dose when given at a monitored target priming block in either phase of the priming drug effect. Methods Sixty consenting ASA I and II patients were premedicated by intramuscular buprenorphine (5 μg·kg⁻¹) 1h before surgery. Neuromuscular junction monitoring was done by stimulating the ulnar nerve at the wrist using Myotest and recording the adductor pollicis response on Myograph-2000. After stabilization of the twitch tension at the titrated supramaximal stimulus (1 Hz), double-burst stimuli (DBS) were given to monitor the priming effect of vecuronium bromide (Vb) (0.015 mg·kg⁻¹). The DBS ratio (DBSr=D ₂/D ₁) was calculated for the DBS response, repeated at 20s. Depending on the target priming block level (DBSr 0.8, 0.6, or 0.5) and the phase of the priming block to give an intubating dose of Vb (0.8 mg·kg⁻¹) injection, all patients were randomly assigned to six study groups: group 1 (DBSr 0.8), group 3 (DBSr 0.6), and group 5 (DBSr 0.5) during the priming block progression phase (before peakD ₁ suppression), and group 2 (DBSr 0.8), group 4 (DBSr 0.6), and group 6 (DBSr 0.5) during the priming block regression phase (after peakD ₁ suppression). Anesthesia was induced by thiopental (5–7 mg·kg⁻¹) just before the intubating dose. The effect of the intubating dose on twitch stimuli (1 Hz) was monitored. Results We observed that in spite of significantly variable priming intervals for identical DBSr in two different phases, the onset time of the intubating dose to 0 response was identical in similar DBSr group patients; i.e., at 0.8 DBSr, 65.0±5.2s (group 1)vs 66.0±8.0s (group 2); at DBSr 0.6, 55.2±3.7s (group 3)vs 55.2±4.9s (group 4); and at DBSr 0.5, 43.5±4.8s (group 5)vs 43.5±4.2s (group 6). At 0 twitch response, the intubating conditions were comparable in patients of the six groups. Conclusion In conclusion, target controlled priming (DBSr) for administration of the intubating dose appears to be a useful double-vision sign to predict the onset of the effect of the intubating dose precisely.     

A randomised controlled trial comparing rocuronium priming, magnesium pre-treatment and a combination of the two methods

We investigated whether magnesium sulphate combined with rocuronium priming shortens the onset of neuromuscular blockade, compared with these methods used alone. Ninety‐two patients scheduled for general anaesthesia were randomly allocated to one of four groups: controls were given 0.6 mg.kg^?1 rocuronium; patients in the prime group were given 0.06 mg.kg^?1 rocuronium three minutes before a further dose of 0.54 mg.kg^?1 rocuronium; patients in the magnesium group were given an infusion of 50 mg.kg^?1 magnesium sulphate before rocuronium and patients in the magnesium and prime group were given both the magnesium sulphate and the priming dose of rocuronium. Tracheal intubation was attempted 40 s after the rocuronium injection. The time to onset of neuromuscular blockade was the primary outcome; duration of blockade and tracheal intubating conditions were also measured. The group allocation and study drugs were coded and concealed until statistical analyses were completed. The magnesium and prime group had the shortest mean (SD) onset time (55 (16) s; p < 0.001), and best tracheal intubating conditions (p < 0.05). No statistical difference was found for the duration of blockade. As for adverse events, a burning or heat sensation was reported in eight (35%) and six (26%) patients in the magnesium and magnesium and prime groups, respectively. The combination of magnesium sulphate and rocuronium priming accelerated the onset or neuromuscular blockade and improved rapid‐sequence intubating conditions, compared with either magnesium sulphate or priming used alone.     

Rapid tracheal intubation with atracurium: the timing principle

The “Timing Principle” utilises a single bolus of nondepolarising neuromuscular blocking drug followed by thiopentone given at the onset of clinical weakness. The purpose of this study was to compare the intubating conditions after succinylcholine and after atracurium used according to the “timing principle.” Eighty patients were randomly assigned to four groups of 20. Three study groups were given atracurium 0.5, 0.75 or 1 mg · kg^?1 (Groups I, II and III respectively) and the control group (Group IV) received succinylcholine 1.5 mg · kg^?1. The study groups received fentanyl 1 μg · kg^?1, atracurium three minutes later, followed by thiopentone 4–6 mg · kg^?1 at the onset of ptosis. The control group had a defasciculating dose of atracurium (0.025 mg · kg^?1) and fentanyl (1 μg · kg^?1) followed by thiopentone (4–6 mg · kg^?1) and succinylcholine three minutes later. The trachea was intubated one minute after thiopentone was given. The intubating conditions were then graded by a laryngoscopist who was unaware of the induction sequence. All patients were interviewed on the day after surgery. Intubation scores of patients in Group I were worse than in Groups II, III and IV (P < 0.005) but there were no differences between Groups II, III and IV. The technique was not associated with severe haemodynamic changes. All patients, except one were able to cough well after administration of atracurium, before induction of anaesthesia with thiopentone. Patients were generally satisfied with this method of induction. It is concluded that atracurium, when used according to the timing principle, can be an alternative to succinylcholine during rapid-sequence induction.     

Intubation conditions following rocuronium: influence of induction agent and priming

A small priming dose of rocuronium can shorten the onset time of neuromuscular blockade. Induction agents with less cardiovascular depression also reduce the onset time. We hypothesized that ketamine, compared to thiopentone, would reduce onset time and improve intubating conditions following priming. Sixty patients ASA I to II, randomized by computer-generated sequence to four groups were investigated in a double-blind controlled trial. In the two groups with priming, 0.04 mg/kg of rocuronium was followed by three minutes of priming interval. Induction was followed by an intubation dose of 0.4 mg/kg of rocuronium. After 30 seconds, intubation was attempted within a further 20 seconds. In the two control groups, the same sequence was repeated except sham priming (saline) was given. For induction, S-ketamine (1 mg/kg) or thiopentone (4 mg/kg) were administered. Intubating conditions were graded as excellent, good, poor, or not possible. Neuromuscular transmission was monitored by acceleromyography of the thumb. There were no measured differences in onset time of neuromuscular block or in haemodynamics between the groups. The proportion of good to excellent intubating conditions was higher when ketamine was preceded by priming compared to ketamine without priming (87% vs 20%; P<0.05). In both priming and control groups intubating conditions were improved when using ketamine compared to thiopentone (P<0.05). The mechanism of this effect was not clear from this study.     

Atracurium for short surgical procedures: a comparison with succinylcholine

A comparison was made between atracurium and succinylcholine in 40 patients undergoing short gynaecological procedures of 30 minutes or less. Good intubating conditions were produced in 76.7 +/- 39.3 seconds (mean +/- S.D.) with succinylcholine 1 mg . kg-1 and 198 +/- 84 seconds with atracurium 400 micrograms . kg-1. Muscle relaxation was maintained with the initial dose of atracurium or with repeated boluses of succinylcholine. The mean time of surgery was 17.65 +/- 5.3 minutes in the atracurium group and 15.2 +/- 4.6 minutes in the succinylcholine group. Residual neuromuscular block with atracurium was reversed with neostigmine 0.036 mg . kg-1 and atropine 0.018 mg . kg-1. Recovery of neuromuscular function following reversal, assessed by return of all responses to train-of-four stimulation occurred in 5.05 +/- 4.6 minutes in the atracurium group but half the above doses of neostigmine and atropine were repeated in three patients. We conclude that a single dose of atracurium 400 micrograms . kg-1 is suitable for intubation and maintainance of muscle relaxation for short surgical procedures. However, the onset of action is slow, compared to succinylcholine. Residual neuromuscular block can be antagonised with standard doses of neostigmine, less than 20 minutes after the initial dose of relaxant. Atracurium appears to be a suitable alternative for short procedures where succinylcholine is unsuitable or contraindicated.     

Ketamine, but not priming, improves intubating conditions during a propofol–rocuronium induction

Purpose

Both ketamine and priming may shorten the onset time of rocuronium. This study investigates the effects of ketamine and priming as components of a propofol induction on intubating conditions and onset of neuromuscular block.

Methods

This prospective randomized double-blind study was performed in 120 American Society of Anesthesiologists (ASA) I–II patients who were assigned to one of four groups of 30 patients each: control, priming, ketamine, and ketamine-priming. Ketamine 0.5 mg ? kg^?1 or saline was given before priming and induction. Rocuronium 0.06 mg ? kg^?1 or saline was injected 2 min before propofol 2.5 mg ? kg^?1. This was followed by rocuronium 0.6 mg ? kg^?1 or by rocuronium 0.54 mg ? kg^?1 if priming was given. Intubation was performed one minute later. Intubating conditions were graded as excellent, good, or poor. Heart rate, noninvasive blood pressure, and train-of-four (TOF) response were monitored.

Results

Intubating conditions were graded excellent in 20% of the control group, 30% of the priming group, 47% of the ketamine group, and 57% of the ketamine-priming group. Analysis using forward stepwise regression indicated that ketamine improved intubating conditions (P = 0.001) but priming did not (P = 0.35). Time to reach a TOF count of zero was shortened by ketamine (P = 0.001) but not by priming (P = 0.94): 216 ± 20 s in the control group, 212 ± 27 s in the priming group, 162 ± 18 s in the ketamine group, and 168 ± 22 s in the ketamine-priming group.

Conclusion

A low-dose ketamine used with a propofol–rocuronium induction improved intubating conditions and shortened onset time. Priming did not influence intubating conditions or onset time.     

Myalgia in outpatient surgery: comparison of atracurium and succinylcholine

We studied 60 outpatients randomly divided into two groups. Anesthesia was induced withfentanyl 1.5 µg.kg^-1 plus thiopentone 5-7 mg.kg^-1. Patients in Group I were intubated with the aid of succinylcholine 1.5 mg.kg^-1 after pre-treatment with d-tubocurarine 0.05 mg.kg^-1, Group II received atracurium 350 µg.kg^-1 three minutes after a priming dose of 50 µg.kg^-1. Anesthesia was maintained with isoflurane 1-2 per cent in a mixture of nitrous oxide 60 per cent and oxygen 40 per cent. No supplemental doses of fentanyl or atracurium were given. Intubation conditions were satisfactory for all patients in both groups. There was no significant difference in intubation score between the two groups. The incidence of myalgia was 76 per cent in the succinylcholine group compared to 23 per cent in the atracurium group (p < 0.0005). Fifty per cent of the patients in the succinylcholine group had myalgia necessitating bed rest or analgesics compared to 23 per cent in the atracurium group (p < 0.05). We conclude that atracurium is a suitable neuromuscular relaxant for outpatient surgery and that myalgia is a major morbidity factor in this population that can be reduced by the use of atracurium instead of succinylcholine.     

Is the priming principle both effective and safe?

This study determined the priming dose of vecuronium (V), pancuronium (P) and atracurium (A) that resulted in the most rapid onset of neuromuscular blockade (NMB) in 150 patients given either V 0.08 mg/kg, P 0.1 mg/kg or A 0.6 mg/kg. Patients were further divided (n = 10 per group) to receive no prime or 5%, 10%, 15% or 20% of the total dose as a prime followed 5-7 minutes later by the remaining (intubating) dose. A further 10 patients received 0.04 mg/kg d-tubocurarine followed by 1.5 mg/kg succinylcholine (S). Priming significantly shortened the onset of NMB. The priming doses producing the most rapid onset were 0.012 mg/kg for V, 0.015 mg/kg for P and 0.09 mg/kg for A. The S resulted in significantly greater NMB at 60 sec than any priming dose of A, V or P. There was no difference between the three nondepolarizing neuromuscular blockers in shortening the onset of NMB produced by priming. To evaluate both the effect of the "optimal" priming dose in awake patients and the effect of increasing intubating doses on NMB an additional 40 patients were given V 0.012 mg/kg followed by V 0.08, 0.1, 0.12 or 0.15 mg/kg. Increasing the intubating dose did not improve onset of NMB. The "optimal" priming dose, however, resulted in a high incidence of symptoms of muscle weakness. We conclude that priming shortens the onset of NMB similarly between V, P and A but the priming dose producing the most rapid onset of NMB also results in a high incidence of side effects and therefore the priming principle should be used with caution.     

Propofol reduces succinylcholine induced increase of masseter muscle tone

Purpose

Succinylcholine is known to increase the tone of the masseter muscles. As excessive jaw tension may complicate rapid sequence induction, we investigated three induction techniques, all including the use of succinylcholine, with respect to masseter muscle tone, neuromuscular blockade, intubation conditions, and time course of intubation.

Methods

Sixty adult patients were allocated to one of three induction groups: Group THIO received 5 mg · kg^?1 thiopentone, Group THIO/ATR received 5 mg · kg^?1 thiopentone plus 0.05 mg · kg^?1 atracurium for precurarization, and Group PROP received 2.5 mg · kg^?1 propofol. All patients received 3 μg · kg^?1 fentanyl and 1.5 mg · kg^?1 succinylcholine. Time for induction of anaesthesia was recorded, and, after inserting a Grass Force Transducer between upper and lower incisors, jaw tone and the time course of jaw tension was recorded before and after the administration of succinylcholine.

Results

No differences in the onset of sleep were observed among the three groups (Group THIO 33 ± 2 sec: THIO/ATR 30 ± 2 sec: PROP 35± 2 sec, mean ± SE). Masseter preloads following induction of anaesthesia were similar in all three groups (THIO 16.4 ± 2.1 N: THIO/ATR 15.1 ± 2.0 N: PROP 12.7 ± 1.6 N). However, after administration of succinylcholine, the increase in masseter tone was less in Groups PROP (5.0 ±1.1 N) and THIO/ATR (6.4 ± 2.1 N) than in Group THIO (12.4 ± 3.0 N;P < 0.05).

Conclusion

Jaw tension after administration of succinylcholine is influenced by the choice of induction agent. The increase of masseter muscle tone is lower following propofol or thiopentone/atracurium induction than with thiopentone alone.     

Intubating conditions after vecuronium and atracurium given in divided doses (the priming technique)

Intubating conditions have been assessed at 60 s following administration of vecuronium 0.1 mg kg-1 or atracurium 0.5 mg kg-1 given either as a single dose after induction of anaesthesia with thiopentone or in divided doses; vecuronium 0.015 mg kg-1 followed 4 or 6 min later by 0.085 mg kg-1, or atracurium 0.075 mg kg-1 followed 4 or 6 min later by 0.425 mg kg-1. In the divided dose groups the smaller initial (priming) dose was given prior to induction of anaesthesia. Onset and duration of clinical relaxation were assessed using a peripheral nerve stimulator. The intubating conditions at 60 s improved significantly, with the use of relaxants in divided doses being acceptable in 80 and 70% of patients, respectively, with vecuronium and atracurium, but the conditions are not as good as those commonly found using suxamethonium. Priming at 6 min has no advantage over priming at 4 min. The onset of complete block was accelerated with priming, but the difference was not significant. The duration of clinical relaxation of vecuronium was significantly prolonged by giving it in divided doses. Unpleasant awareness of muscle weakness was observed in 15 patients, requiring early induction of anaesthesia in five of them.     

Thiopental bolus during carotid endar-terectomy-rational drug therapy?

Ten studies were performed to examine the time course of arterial and venous thiopenlal concentrations following the administration of thiopental (4mg.kg^-1 over 3 min) for cerebral protection during carotid occlusion in nine patients undergoing elective carotid endarterectomy; in five patients the time course of EEC change was also studied. The arterial and venous thiopental concentrations were similar with no evidence of a sustained arterial-venous gradient. The average arterial concentration was 20.1 μg.ml^-1 ± 10 (SD) at 2 min after thiopental, and fell rapidly to 13.0 μg.ml^-1 ± 3.2 at 5 min, 10.7 μg.ml^-1 ± 4.4 at 10minand 6.2 μg-ml^-1 at 30 min. After thiopental the EEG record showed an increase in delta activity and in four patients a burst suppression pattern was seen. The duration of burst suppression activity was variable (130 to 367 seconds) but in all instances cortical activity had returned to the pre-lhiopental level by five to ten minutes. Thus concentrations of thiopental of 10-30 μg.ml^-1 were associated with EEG burst suppression and both were seen only within the first five minutes after drug administration. In contrast the carotid artery was occluded for considerably longer (26 ± 4) minutes. We conclude that, since there was no sustained arterial-venous gradient, either arterial or venous concentrations are adequate for the study of thiopental pharmacokinetics. However, using burst suppression as an index of cerebral protection with thiopental it appears that the administration of thiopental (4mg.kg^-1 over three minutes) before carotid occlusion is not adequate to protect for the duration of the carotid endarterectomy procedure.     

A comparison between vecuronium and atracurium in myasthenia gravis

We evaluated the effect of vecuronium bromide and atracurium besylate on the train–of–four response in the management of muscle relaxation in 20 patients with myasthenia gravis (MG) who were undergoing thymectomy. We confirmed the safe use of these two non–depolarizing muscle relaxants in MG patients. Vecuronium (0.04 mg–kg^-1) demonstrated a lesser clinical duration than did atracurium (0.2 mg–kg^-1) (38± 19 vs 50 ± 21 min, mean ± s.e.mean). The recovery time for vecuronium patients was shorter than that for atracurium patients (22 ± 18 vs 38± 18 min), but the time until onset of neuromuscular blockade was longer with vecuronium (246 ±105 vs 107 ± 103 s). During spontaneous recovery from neuromuscular relaxation, at Tl/C of 25% and 100%, the train–of–four fade with vecuronium was significantly greater than that with atracurium (0.04 ± 0.02, 0.16 ± 0.03 vs 0.17 ±0.01, 0.83 ± 0.03), suggesting that vecuronium had a greater prejunctional effect than did atracurium.     

Evaluation of the timing principle with small priming doses of vecuronium]

The intubating conditions using the timing principle combined with small priming doses of vecuronium were evaluated in forty patients who underwent elective surgery. They were randomly assigned to one of two groups: 1) timing, 2) timing with priming. In timing group, vecuronium 0.15 mg.kg-1 was administered, and at the onset of clinical muscle weakness, thiopental 4-5 mg.kg-1 was given promptly. Sixty seconds after thiopental, patients were intubated. In the timing with priming group, vecuronium 0.005 mg.kg-1 was administered as priming doses. Four minutes later vecuronium 0.15 mg.kg-1 was given. The administration of thiopental and the intubation were done in the same way as in timing group. The time to onset of clinical weakness after the administration of vecuronium 0.15 mg.kg-1 was significantly shorter in the timing with priming group than that in the timing group (46.1 +/- 4.8 vs. 57.6 +/- 7.8, P < 0.01). There were no significant differences in intubating score, T1, TR, onset time, and duration between the two groups. We conclude that the timing principle combined with small priming doses of vecuronium might be safe and useful for rapid tracheal intubation.