Propofol, but not thiopentone or etomidate, enhances isoflurane-induced coronary vasodilatation in dogs

Purpose

To test the hypothesis that thiopentone, propofol, and etomidate alter the coronary vascular effects of abruptly administered isoflurane.

Methods

Dogs (n = 6) received inspired isoflurane 5% in the presence of thiopentone (20 mg·kg^?1 induction dose and 20 mg·kg^?1·hr^t-1 infusion), propofol (5 mg·kg^?1 induction dose and 40 mg·kg^?1·hr^?1 infusion), etomidate (2 mg·kg^?1 induction dose and 5 mg·kg^?1·hr^?1 infusion), or isoflurane (1.0 MAC) anaesthesia in a random fashion. Haemodynamics were assessed in the conscious state, during baseline anaesthesia, and at 30 sec intervals for five minutes after beginning isoflurane 5%.

Results

Rapidly administered isoflurane caused greater (P < 0.05) reductions in coronary vascular resistance in thiopentoneor propofol-than in isoflurane-anaesthetized dogs. Isoflurane produced greater (P < 0.05) increases in the ratio of coronary blood flow velocity to pressure-work index (an index of myocardial oxygen consumption; +109 ± 19 % during isoflurane alonevs + 182 ± 27 % change from baseline during propofol and isoflurane) consistent with relatively greater direct coronary vasodilatation during baseline propofol than during baseline isoflurane anaesthesia. Isoflurane caused larger increases in coronary blood flow velocity in dogs anaesthetized with etomidate concomitant with higher coronary perfusion pressure and pressure-work index than in those anaesthetized with isoflurane alone.

Conclusions

The results suggest that thiopentone, propofol, and etomidate each uniquely modify the coronary vascular responses to abrupt administration of high inspired concentrations of isoflurane in chronically instrumented dogs.     

Recovery of neuromuscular function after atracurium and pancuronium maintenance of pancuronium block

The study was undertaken to determine whether a neuromuscular blockade induced with pancuronium but maintained with atracurium was associated with a shorter time to complete recovery after administration of neostigmine than if the blockade was maintained with pancuronium alone. Anaesthesia consisted of thiopentone, N₂O/O₂/enflurane and fentanyl, and the neuromuscular blockade, induced by pancuronium 0.1 mg · kg^?1 was monitored by the force of contraction of adductor pollicis during major abdominal surgery lasting 2–5 hr. In 24 patients — Group 1 — atracurium 0.07 mg · kg^?1 was repeated when the first twitch of the train-of-four (TOF) returned to 25% of control (T₁/ TC 25). In 28 patients — Group 2 — pancuronium 0.015 mg · kg^?1 was given at similar recovery of T₁/ TC. At the end of surgery, neostigmine 0.07 mg · kg^?1 and glycopyrrolate 0.015 mg · kg^?1 were given to reverse the residual neuromuscular blockade which was indicated by a T₁/TC of less than 25% in all patients. The time from injection of the reversal drugs to a TOF ratio of 70% was similar in both groups (Group 1, 11.6 ± 7.6 min; Group 2, 10.1 ± 6 min; P = NS), but the recovery index was smaller in Group 2 (Group 1, 4 ± 2.6 min; Group 2, 2.61 ± 1.2 min; P < 0.05). Furthermore, there was no difference between groups in the duration of action of each redose. The study showed that when compared with pancuronium, equipotent doses of atracurium were not associated with (a) a shorter time to complete recovery from a neuromuscular blockade induced with pancuronium or (b) a shorter duration of action.     

Atropine-induced heart rate changes: a comparison between midazolam-fentanyl-propofol-N2O and midazolam-fentanyl-thiopentone-enflurane-N2O anaesthesia

Atropine-induced heart rate (HR) changes were studied in 19 patients (ASA physical status I) during anaesthesia maintained predominantly with propofol-N₂O or thiopentone-enflurane-N₂O. Ten patients (Group A) received midazolam (0.07 mg · kg^?1), fentanyl (1 μg · kg^?1), propofol (2 mg · kg^?1) and succinylcholine (1 mg · kg^?1). Following tracheal intubation, anaesthesia was maintained with propofol (6 mg · kg^?1 · hr^?1), N₂O (67 per cent) and O₂ (33 per cent). In nine patients (Group B) thiopentone (4 mg · kg^?1) was substituted for propofol and anaesthesia maintained with N₂O (67 per cent) O₂ (33 per cent), and enflurane (0.5 per cent inspired concentration). The study was non-randomised because Group B patients were only included if HR before administration of atropine < 90 beats · min^?1. IPPV was performed in all patients using a Manley ventilator (minute vol. 85 ml · kg^?1; tidal vol. 7 ml · kg^?1). Ten minutes after tracheal intubation, incremental doses of atropine (equivalent cumulative doses: 1.8, 3.6, 7.2, 14.4, 28.8 μg · kg^?1) were administered at two-minute intervals and HR responses calculated during the last 45 sec of each intervening period. No differences were observed between the groups following 1.8 and 3.6 μg · kg^?1 atropine, but propofol-N₂O anaesthesia was associated with reduced responses (P < 0.01) following 7.2, 14.4 and 28.8 μg · kg^?1 atropine. These results suggest that there is a predominance of parasympathetic influences during propofol-N₂O anaesthesia compared with thiopentone-enflurane-N₂O anaesthesia.     

Continuous caudal anaesthesia with chloroprocaine as an adjunct to general anaesthesia in neonates

Purpose

The authors prospectively evaluated the use of a continuous caudal epidural infusion of chloroprocaine as an adjunct to genera! anaesthesia during intra-abdominal surgery in neonates.

Clinical features

The technique was used in 25 neonates ranging in age from 1 to 28 days and in weight from 2.2 to 4.9 kg. Following anaesthetic induction and tracheal intubation, an initial bolus dose of chloroprocaine 3% (1 or 1.5 ml · kg^?1) was followed by a continuous infusion of 1 or 1.5 ml · kg^?1 · hr^?1 administered through a caudal epidural catheter. No parenteral opioids were administered. The duration of the surgical procedures varied from one hour five minutes to three hours 15 min. The first three neonates received a bolus dose of 1.0 ml kg^?1 followed by an infusion of 1.0 ml · kg^?1 · hr^?1 chloroprocaine 3%. These three neonates required an additional bolus dose followed by an increase in the infusion to 1.5 ml · kg^?1 · hr^?1 to provide surgical anaesthesia. Adequate intraoperative anaesthesia was achieved in all 25 neonates with an infusion of 1.5 ml · kg^?1· hr^?1 of chloroprocaine 3%. This was evidenced by a lack of haemodynamic response to surgical manipulation. No neonate required more than 0.2% isoflurane or 70% nitrous oxide in oxygen. No episodes of haemodynamic instability (decreased blood pressure/bradycardia) related to the caudal epidural anaesthesia were noted. Twenty-three of 25 of the neonates’ tracheas were extubated immediately (within 10 minutes) following the surgical procedure.

Conclusions

Caudal anaesthesia with a continuous infusion of chloroprocaine can be used as an adjunct to general anaesthesia during abdominal surgery in neonates. Our initial experience suggests that the combined technique may eliminate the need for parenteral opioids and limit the intraoperative requirements for inhalational anaesthetic agents.     

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.     

Modification of intravenous lidocaine-induced convulsions by epinephrine in rats

We studied intravenous lidocaine-induced convulsions in rats to determine whether added epinephrine influences the provocation of lidocaine toxicity. Wistar rats (200–250 g) were divided into three groups of ten, depending on the concentration of epinephrine added to lidocaine. Group 1: plain 1.5% lidocaine; Group 2: 1.5% lidocaine with 1∶200,000 epinephrine; Group 3: 1.5% lidocaine with 1∶100,000 epinephrine. After surgical preparation and recovery from anaesthesia, all rats received a continuous iv infusion of lidocaine (15 mg·ml^?1) at a rate of 4.0 mg·kg^?1·min^?1 until generalized convulsions occurred. The epinephrine-treated animals developed acute hypertension after one minute of lidocaine infusion (105±2 to 141±2 mmHg in Group 2 and 103±2 to 151±2 mmHg in Group 3). The PaO₂ values in the epinephrine groups at the onset of convulsions were decreased significantly (88.3±1.0 to 84.0 ±1.5 mmHg in Group 2 P < 0.05 and 86.9±1.2 to 78.1±2.4 mmHg in Group 3 P<0.01). However, these values were still within physiological ranges. Serum potassium concentrations in all groups were decreased P<0.05, (4.24±0.09 to 3.52±0.12 mEq·L^?1 in Group 1, 4.02±0.09 to 3.63±0.17 mEq·L^?1 in Group 2, and 4.15±0.10 to 3.69 ±0.17 mEq·L^?1 in Group 3). Blood sugar concentrations in all groups were increased at the onset of convulsions, and the levels in the epinephrine groups were higher than in Group 1 P<0.01 (119±4 to 149±7 mg·dl^?1 in Group 1: 120±4 to 195±10 mg·dl^?1 in Group 2, and 127±3 to 190±6 mg·dl^?1 in Group 3). There were differences in the cumulative convulsant doses of lidocaine among the groups, as follows: Group 1=41.9±1.3 > Group 2=30.0±0.7 > Group 3=24.2±0.9 mg·kg^?1; P<0.01. At the onset of convulsions, not only the plasma lidocaine concentrations (Group 1=10.7±0.3 > Group 2=8.3±0.2 (P<0.01) > Group 3=7.5±0.2 μg·ml^?1 (P<0.01 vs Group 1, P < 0.05 vs Group 2), but also the brain lidocaine concentrations which were extracted from the whole brain homogenates: Group 1=48.7±1.9 > Group 2=38.2±1.1 (P<0.01) > Group 3=33.0±1.3 μg·g^?1 (P <0.01 vs Group 1, P<0.05 vs Group 2) showed differences. The brain/plasma lidocaine concentration ratios were, however, similar in the three groups (Group 1=4.5±0.1; Group 2=4.6±0.1; Group 3=4.4±0.2). Our data show that added epinephrine decreases the threshold of lidocaine-induced convulsions dose-dependently; however, the added ephinephrine does not cause a greater proportion of the infused lidocaine to enter the CNS.     

Haemodynamic instability and myocardial ischaemia during carotid endarterectomy: A comparison of propofol and isoflurane

The purpose of this study was to compare two anaesthetic protocols for haemodynamic instability (heart rate (HR) or mean arterial pressure (MAP) <80 or > 120% of ward baseline values) measured at one-minute intervals during carotid endarterectomy (CEA). One group received propofol/alfentanil (Group Prop; n = 14) and the other isoflurane I alfentanil (Group Iso; n = 13). Periods of haemodynamic instability were correlated to episodes of myocardial ischaemia as assessed by Holler monitoring (begun the evening before surgery and ceasing the morning of the first postoperative day). In Group Prop, anaesthesia was induced with alfentanil 30 μg · kg^?1 rv, propofol up to 1.5 mg · kg^?1 and vecuronium 0.15 mg · kg^?1, and maintained with infusions of propofol at 3–12 mg · kg^?1· hr^?1 and alfentanil at 30 μg · kg^?1 · hr^?1. In Group Iso, anaesthesia was induced with alfentanil and vecuronium as above, thiopentone up to 4 mg · kg^?1 and maintained with isoflurane and alfentanil infusion. Phenylephrine was infused to support MAP at 110 ± 10% of ward values during cross-clamp of the internal carotid artery (ICA) in both groups. Emergence hypertension and/or tachycardia was treated with labetalol, diazoxide or propranolol. Myocardial ischaemia was defined as ST-segment depression of >-1 mm (60 msec past the J-point) persisting for >-one minute. For the entire anaesthetic course (induction to post-emergence), there was no difference between groups for either duration or magnitude outside the <80 or >120% range for HR or MAP. However, when the period of emergence from anaesthesia (reversal of neuromuscular blockade to post-extubation) was assessed, more patients were hypertensive (P = 0.004) and required vasodilator therapy in Group Iso (10/ 13 vs 5/14; P = 0.038 Fisher’s Exact Test). The mean dose of labetalol was greater in Group Iso (P = 0.035). No patient demonstrated myocardial ischaemia during ICA cross-clamp. On emergence, 6/13 patients in Group Iso demonstrated myocardial ischaemia compared with 1/14 in Group Prop (P = 0.029). Therefore, supporting the blood pressure with phenylephrine, during the period of ICA cross-clamping, appears to be safe as we did not observe any myocardial ischaemia at this time. During emergence from anaesthesia, haemodynamic instability was associated with myocardial ischaemia. Under these specific experimental conditions, with emergence, hypertension and myocardial ischaemia were more prevalent with more frequent pharmacological interventions in patients receiving isoflurane.     

Isoflurane compared with nitrous oxide anaesthesia for intraoperative monitoring of somatosensory-evoked potentials

Intraoperative monitoring of somatosensoryevoked potentials is a routine procedure. To determine the depressant effect of nitrous oxide relative to isoflurane, the authors recorded the scalp, cervical and brachial plexusevoked responses to stimulation of the median nerve under different anaesthetic conditions. Eight subjects, age 35 ± 6 (SD) yr, weight 68 ± 12 kg, were studied. Following recording of awake control responses, anaesthesia was induced with thiopentone 5 mg· kg^{? 1} and fentanyl 3 μg· kg^{? 1} and was followed by succinylcholine 1 mg· kg^{? 1}. During normocapnia and normothermia, and with a maintenance infusion of fentanyl 3 μg · kg^{? 1}· hr^{? 1}, evoked potential recording was repeated under three different anaesthetic conditions; 0.6 MAC nitrous oxide, 0.6 MAC nitrous oxide ± 0.6 MAC isoflurane, and 0.6 MAC isoflurane. Among the anaesthetic conditions, the combination of nitrous oxide-isoflurane had the most depressant effect on the cortical amplitude (67 ± 4% reduction, P < 0.05). Nitrous oxide decreased the cortical amplitude more than an equipotent dose of isoflurane (60 ± 4% vs 48 ± 7%, P < 0.05). The latency was unchanged by nitrous oxide, but increased slightly by isoflurane and isofluranenitrous oxide anaesthesia (1.0 and 0.9 msec respectively, P < 0.05). We conclude that somatosensory-evoked potential monitoring is feasible both during nitrous oxide anaesthesia and isoflurane anaesthesia, but the cortical amplitude is better preserved during 0.6 MAC of isoflurane alone relative to 0.6 MAC of nitrous oxide alone. The depressant effect is maximal during nitrous oxideisoflurane anaesthesia but less than the predicted additive effect.     

Thoracic epidural block attenuates cardiovascular response to apnea in rabbits

Purpose

Apnea is one of the potential complications during anaesthesia. If sympathetic nerve activity is blocked by epidural anaesthesia, circulatory responses to apnea might change. Our objective was to assess the potential modifying effects of epidural anaesthesia on the cardiovascular responses to apnea in the animals.

Methods

Twenty rabbits anaesthetised with pentobarbital (25 mg·kg^?1 iv, 8 mg·kg^?1·hr^?1) and pacuronium bromide (0.2 mg·kg^?1·hr^?1 iv) were randomly assigned to one of two groups: control (n = 10) and epidural (n = 10). In the control group, 0.6 ml saline, and in the epidural group, 0.6 ml lidocaine 1% was injected into the epidural space respectively. After mechanical ventilation with FIO₂ 0.4, apnea was induced by disconnecting the anaesthetic circuit from the endotracheal tube, and mean arterial pressure (MAP), heart rate (HR), and time to cardiac arrest were measured.

Results

Before apnea MAP was lower in the epidural than in the control group (73 ± 10vs 91 ± 10 mmHg,P < 0.05). Heart rate was not different between groups (264 ± 36vs 266 ± 24 bpm). Mean arterial pressure increased in the control group after apnea, but not in the epidural group. The time to cardiac arrest was less in the epidural group than in the control group (420 ± 67vs 520 ± 61 sec,P < 0.05). Heart rate decreased markedly after apnea in the control group whereas it decreased gradually in the epidural group.

Conclusion

Thoracic epidural anaesthesia attenuated cardiovascular response to apnea and reduced the time to cardiac arrest.     

Antagonism of atracurium-induced block in obese patients

Purpose

To investigate the relationship between total body weight (TBW) or body mass index (BMI) and atracurium reversal time.

Methods

The study population comprised 25 patients with TBW < 80 kg and 25 patients with TBW ≥80 kg anaesthetised with midazolam, thiopentone, fentanyl, nitrous oxide and halothane. Neuromuscular block was induced with 0.5 mg· kg^?1 atracurium and maintained with doses of 0.15 mg· kg^?1. Neuromuscular transmission was recorded using train-of-four (TOF) nerve stimulation and mechanomyography. Neostigmine, 0.07 mg· kg^?1, was administered when the first twitch in TOF had recovered to 10% of control. Reversal time was defined as: time from administration of neostigmine until TOF ratio recovered to 0.70.

Results

There was no difference in reversal time between patients with TBW < 80 kg (7.2 ± 2.6 min, mean ± SD), and patients with TBW ≥80 kg (6.9 ± 3.6 min). When patients were grouped according to BMI there was no difference in reversal time between groups with low BMI (6.9 ± 2.6 min) or high BMI (7.1 ± 3.6 min). There was, furthermore, no difference in reversal time between the 15 patients in the study population with the smallest TBW or BMI and the 15 patients with the greatest TBW or BMI. There was no correlation between TBW or BMI and reversal time.

Conclusion

When atracurium-induced neuromuscular block is antagonised with 0.07 mg· kg^?1 neostigmine, TBW or BMI have no influence on reversal time.     

Edrophonium requirements for reversal of deep neuromuscular block following infusion of mivacurium

Mivacurium is a new non-depolarizing muscle relaxant consisting of three stereoisomers. The two active isomers (cis-trans andtrans-trans) undergo rapid metabolism by plasma cholinesterase (t_1/2 β<2 min). Due to its rapid elimination, the need for reversal of mivacurium-induced neuromuscular block is controversial, and to date there have been no studies evaluating reversal of deep blocks. The object of the current investigation was to establish the lowest effective dose of edrophonium required to reverse deep mivacurium-induced neuromuscular block. One hundred ASA Class I and II patients undergoing outpatient surgery in two teaching institutions were studied in this randomized, placebo-controlled double-blind trial. Under balanced propofol/nitrous oxide/alfentanil anaesthesia, a continuous infusion of mivacurium was adjusted to maintain between 5– 10% of control T₁ amplitude. Upon completion of surgery, neuromuscular block was reversed by injecting normal saline (Group PLAC), edrophonium 0.125 mg · kg^{? 1} (Group EDR- 1), 0.25 mg · kg^{? 1} (Group EDR- 2), or 0.50 mg · kg^{? 1} (Group EDR- 3), in addition to a corresponding dose of atropine. 4Spontaneous recovery, from a T₁ response of<10% to a TOF ratio ≥0.7, required 13.5 ± 2.6 min (PLAC Group). In comparison, patients in the EDR- 1 group required 9.2 ± 2.6 min (P < 0.01). Higher doses of edrophonium conferred no advantage. Four patients (4%) had not achieved a TOF ratio of ≥ 70%, 20 min after reversal, and required additional edrophonium. Two patients (PLAC group), had dibucaine numbers and cholinesterase levels consistent with an E^UE^A genotype, whereas the two patients with delayed recovery in the EDR- 1 group had characteristics of a normal genotype. We conclude that a very low dose of edrophonium (0.125 mg · kg^{? 1}) hastens reversal of deep mivacurium-induced neuromuscular block by approximately four minutes, and that edrophonium doses exceeding 0.125 mg · kg^{? 1} provide no additional benefit. Heterozygous patients with atypical plasma cholinesterase levels, as well as certain individuals with normal dibucaine numbers and plasma cholinesterase activity, are at risk for prolonged neuromuscular block, but the block is easily reversed with edrophonium.     

Reduced-dose rocuronium for day-case tonsillectomy in children where volatile anaesthetics are not used: operating room time saving

Objectives: Mivacurium, rocuronium, and vecuronium are neuromuscular blocking agents (NMB) commonly used in pediatric day‐case anesthesia. Mivacurium is the most appropriate NMB for short surgical procedures where NMB drugs were required but is not available in all countries. Aim: We evaluated the operating room time minimization after reduced‐dose rocuronium (0.45 mg·kg^?1) during elective day‐case tonsillectomy in children. Methods/Materials: One hundred and five children (6–9 years, ASA I/II status) scheduled for day‐case tonsillectomy were included in prospective, double blind clinical study. Children were randomly divided in three equal groups. All children were premedicated (midazolam 0.25 mg·kg^?1 orally, EMLA). Anesthesia was induced (2.5 mg·kg^?1) and maintained (0.1 mg·kg^?1·min^?2) by propofol and alfentanil (0.0015 mg·kg^?1·min^?1) and supplemented by inhalation mixture of 50% of O2/Air. Neuromuscular block was achieved by vecuronium (0.1 mg·kg^?1) (V) or rocuronium in standard (0.6 mg·kg^?1) (R) or reduced dose (0.45 mg·kg^?1) (LD). Neuromuscular transmission was monitored by acceleromyography. Time analysis of NMB drugs action was performed. Results: Time difference from the end of tonsillectomy to T90 neuromuscular block recovery was significantly shorter in LD Group (7.3 ± 0.41 min), (V = 15.9 ± 1.06, R = 16.0 ± 1.7 min) (P = 0.0011). The onset time of neuromuscular block was prolonged in LD Group (LD=3.1 ± 0.4, R = 1.3 ± 0.4, V = 2.2 ± 0.2 min) (P = 0.0039) without changing the intubating conditions. The maximum operation room time saving per each tonsillectomy was 37% in LD Group (Group V 21%, Group R 17%) (P = 0.0001). Low incidence of postoperative nausea and vomiting (PONV) 3–6% (0.4577) and good visual analog scale (VAS) score (≤2) (0.5969) were found in all study groups 12 h after surgery. Conclusions: Reduced‐dose rocuronium in addition with propofol and alfentanil in children where volatile anesthetics are not used effectively saves the operating room time during short elective surgical procedures, avoids delays in patient recovery, allows high level of acceptable intubating conditions, and improves the optimal surgical work. Low incidences of PONV as VAS score may achieved successfully.     

Potency of atracurium on masseter and adductor pollicis muscles in children

The sensitivity of the masseter to atracurium was measured in ten children aged 3–10 yr undergoing elective surgery, and compared with that of the adductor pollicis. During nitrous oxide-halothane anaesthesia and mechanical ventilation, supramaximal nerve stimulation was applied to the ulnar nerve at the elbow and to the nerve to the masseter, at a point inferior to the zygomatic arch, anterior to the mandibular condyle. Jaw closure was measured by a force displacement transducer system attached to an oral airway and connected to a metal frame fixed to the operating table 10 cm caudad to the chin. Cumulative dose—response curves for atracurium were obtained by the injection of doses followed by an infusion to compensate for elimination. The mean ED_5Os and ED₉₅s were similar at the masseter and the adductor pollicis. At the masseter, these were 0.150 ±0.013, mean ±SEM, mg · kg^?1 and 0.254 ±0.021 mg · kg^?1, respectively. At the adductor pollicis, corresponding values were 0.145 ±0.009 mg · kg^?1, and 0.259 ±0.016 mg · kg^?1. However, this relationship was not constant in every patient, and in some patients the masseter was much more sensitive than the adductor pollicis. The time from injection of the first dose of atracurium to maximum blockade was 2.5 ±0.2 min at the masseter and 3.2 ±0.2 min at the adductor pollicis (P < 0.05). It is concluded that when atracurium is administered to paediatric patients, neuromuscular blockade is usually of the same intensity at each muscle but occurs sooner at the masseter than at the adductor pollicis. However, because of the large interpatient variability, return of adductor pollicis function may not imply complete masseter muscle recovery.     

Contribution of muscle relaxant to the haemodynamic course of high-dose fentanyl anaesthesia: a comparison of pan-curonium,vecuronium and atracurium

To define the role of muscle relaxants in haemodynamic responses to high-dose (75 µg·kg^-1) fentanyl anaesthesia and to noxius stimuli associated with intubation and sternal spread during coronary artery bypass surgery, we compared haemodynamics between three groups of patients given either pancuronium (0.1 mg·kg^-1, n = 11), vecuronium (0.086 mg·kg^-1, n = 11) or atracurium (0.43 mg·kg^-1, n = 12). Additional doses of the relaxants were given to maintain a 90 per cent neuromuscular block. Patients given pancuronium showed no increases in mean values of heart rate, arterial pressure or cardiac output during the induction of anaesthesia or after intubation, whereas a decrease in these variables was observed in the vecuronium group. The haemodynamics in the atracurium group were intermediate compared with the other two study groups. In spite of a decrease in coronary perfusion pressure, no patient given vecuronium developed myo cordial ischaemia. An advantage of vecuronium over pancuronium and atracurium was an attenuation of the blood pressure response to sternotomy. Patients given atracurium had a small increase in pulmonary vascular resistance during sternotomy. Our patients continued their beta-adrenergic antagonist medication until the morning of the day of operation and they were pretreated with a small intravenous dose ofdiazepam (0.1 mg·kg¹) before induction of anaesthesia. These drugs may have prevented the deleterious haemodynamic effects observed by some investigators after the administration of pancuronium during high-dose fentanyl anaesthesia.     

Comparison of neuromuscular effects, efficacy and safety of rocuronium and atracurium in ambulatory anaesthesia

Purpose

To compare the neuromuscular effects, efficacy, and safety of equi-effective doses of rocuronium and atracurium in ambulatory female patients undergoing surgery.

Methods

Forty-one patients undergoing laparoscopic gynaecological surgery were randomized to receive 2 × ED₉₀ rocuronium (0.6 mg·kg^?1; n = 20) or atracurium (0.5 mg·kg^?1; n = 21) during intravenous propofol/alfentanil anaesthesia with N₂O/O₂ ventilation. Neuromuscular block was measured with a mechanomyogram eliciting a train-of-four (TOF) response at the wrist. Intubation conditions 60 sec after administration of muscle relaxant and immediate cardiovascular disturbances or adverse events during the hospital stay were noted by blinded observers.

Results

Compared with atracurium, rocuronium was associated with a shorter onset time (59.0 ± 22.2vs 98.6 ± 41.4 sec;P < 0.001) and clinical duration of action (33.3 ± 7.1vs 44.7 ± 7.2 min;P < 0.001), but longer spontaneous recovery index (9.6 ± 2.41vs 6.9 ± 1.89 min;P = 0.023) and a similar time to spontaneous recovery to TOF 70%; 53 ± 6.31vs 59.2 ± 7.59 min;P =0.139). Tracheal intubation was accomplished in < 90 sec in all patients receiving rocuronium but in only 14 of 21 patients receiving atracurium. The incidence of adverse events and the cardiovascular profiles for the two drugs were similar, although one patient receiving atracurium experienced transient flushing of the head and neck.

Conclusion

Rocuronium has minimal side effects, provides conditions more suitable for rapid tracheal intubation, and is associated with a shorter clinical duration than atracurium. Once begun, the spontaneous recovery profile of rocuronium is slightly slower than that of atracurium.     

Smoking increases the requirement for rocuronium

Purpose

To compare the potency of rocuronium in non-smokers and smokers during general anaesthesia.

Methods

In a randomized, open clinical study, 40 patients, 17–62 yr of age, were anaesthetized with propofol, alfentanil and nitrous oxide in oxygen. After obtaining individual dose-response curves for rocuronium, bolus doses of rocuronium were given to maintain neuromuscular block at 90–99% for 60 min. Evoked adductor pollicis electromyography (EMG) was used to monitor neuromuscular block.

Results

The ED₉₅ values (± SEM) for rocuronium were 460.5 ± 28.9 and 471.5 ± 22.1 μg·kg^?1 for nonsmokers and smokers, respectively (P:NS). However, doses of rocuronium to maintain 90–99% neuromuscular block (± SEM) were 620.1 ± 46.7 and 747.4 ± 56.0 μg·kg^?1·hr^?1 for non-smokers and smokers, respectively (P = 0.0504).

Conclusion

The results may indicate increased metabolism of rocuronium in smokers rather than increased requirement of rocuronium at the receptor site.     

Surgeon-controlled mivacurium administration during elective Caesarean section

We have compared the dose requirements and recovery characteristics of a continuous mivacurium infusion given by the anaesthetist to maintain 95–100% block at the hand muscles with that of a surgeon-controlled, on-demand dosing technique based on the direct assessment of abdominal muscle tone during elective Caesarean section. Twenty-four full term pregnant patients were included. A rapid-sequence induction using thiopentone 3–5 mg· kg^?1 and succinylcholine 1 mg· kg^?1 was used. Anaesthesia was maintained with fentanyl, N₂O and iso-flurane 0.5%. The mechanomyographic response of the adductor pollicis muscle to supramaximal train-of-four (TOF) ulnar nerve stimulation was recorded. Muscle relaxation was achieved initially with mivacurium 0.1 mg· kg^?1 followed either by a continuous infusion of mivacurium to maintain 95–100% block at the adductor pollicis muscle (n = 12) or by surgeon-controlled relaxation (SCR) technique using a syringe pump for patient-controlled analgesia to administer on-demand doses of mivacurium 0.05 mg · kg^?1 (n = 12). The lockout interval was three minutes and the maximum hourly dose of mivacurium allowed was 0.6 mg · kg^?1. The total doses of mivacurium (mean ±SD) were 23.2 ± 10.4 and 12.4 ± 3.5 mg in the infusion and SCR groups, P < 0.01. On-demand, surgeon-controlled doses of mivacurium were injected at a mean of T₁ 42.3 ± 36%. At the end of surgery, T₁ and TOF ratio were respectively 16.7 ± 13%, 5 ± 10% and 48 ± 37%, 30 ± 24% in the infusion and SCR groups. Five patients in the SCR group and one patient in the infusion group did not receive antagonist at the end of surgery. The time to adequate recovery, TOF 75%, after skin closure was 8.2 ± 2.3 and 5.3 ± 4 min in the infusion and SCR groups, P = 0.05. It is concluded that, compared with a continuous mivacurium infusion, the SCR technique is associated with reduced mivacurium requirements, a substantial degree of neuromuscular recovery at the end of surgery and a reduced need for neostigmine reversal in full term pregnant patients undergoing elective Caesarean section.     

Neostigmine requirements for reversal of neuromuscular blockade following an infusion of mivacurium

Purpose

To study the efficacy of neostigmine compared with placebo for the antagonism of neuromuscular blockade at the end of a mivacunum infusion, and to determine its optimal dose.

Methods

One hundred adult patients undergoing an elective surgical procedure received a standardized anaesthetic with 20–30 mg·kg^?1 alfentanil, a propofol infusion and nitrous oxide. Muscle relaxation was maintained at 90–95% T1 depression with 0.2 mg·kg^?1 mivacunum followed by an infusion. Neuromuscular blockade was measured with an integrated evoked electromyogram in response to train-of-four (TOF) stimuli at the ulnar nerve every 20 sec. Patients were randomized into four groups. At the end of surgery, the mivacunum infusion was stopped and patients received. immediately, in a double-blind manner, neostigmine (10, 20. or 40 mg·kg^?1) or placebo according to a random number table. The Tl and TOF ratio were recorded until adequate recovery of neuromuscular function (TOF ratio > 0.70). During the reversal penod, non-invasive blood pressure and heart rate were recorded every minute. The incidence of postoperative nausea and vomiting (PONV) was recorded in the recovery room.

Results

Data from 94 patients who completed the protocol were analysed. Compared with placebo, neostigmine 10 gmg·kg did not reduce the time to TOF > 0.70 (17.0 ± 5.1 vs 14.6 ± 4.2 mm respectively). However the time was decreased with neostigmine 20μg·kg and 40 μ·?^?1 (P < 0.001), but with no difference between these last two groups (11.4 ± 3.0 and 11.4 ± 3.5 min respectively). Changes in systolic blood pressure and heart rate were not different between the four groups. Very few PONV events were observed in all groups (global incidence 7.4%).

Conclusion

Recovery of neuromuscular blockade following a mivacunum infusion is accelerated by neostigmine. A dose of neostigmine 20μ·kg^?1 appears optimal with no further reduction in recovery time obtained from a larger dose.     

Supraventricular tachycardia associated with continuous furosemide infusion

Three cases of supraventricular tachycardia (SVT) associated with the use of furosemide infusion (F1) in children following cardiac surgery are reported. The SVT occurred three to seven hours after starting an infusion at 1.0 mg · kg^?1 · hr^?1. All three patients had a diuresis of 8–10 ml · kg^?1 · hr^?1 compared with a mean average of 2.5 ml · kg^?1 · hr^?1 in 22 other patients who had received a similar infusion. A rapid fluid shift was the most likely mechanism of the tachycardia. Sotalol was effective in controlling the tachycardia in the two patients in whom it was tried. We now recommend a starting dose of 0.3 mg · kg^?1 · hr^?1 in using furosemide as a continuous infusion, with hourly increments of 0.1 mg · kg^?1 · hr^?1 until the desired diuresis is obtained.     

Comparison of the cardiovascular effects of cisatracurium and vecuronium in patients with coronary artery disease

Purpose

Cisatracurium besylate (Nimbex® Injection, Glaxo Wellcome Inc., Research Triangle Park, NC) is an intermediate-acting bis-benzylisoquinolinium neuromuscular blocking drug that is one of the stereoisomers of atracurium. At doses ≤. 8 × ED95, it caused no clinically important cardiovascular side effects or histamine release in healthy patients. The purpose of the present study was to investigate the haemodynamic effects of high doses of cisatracurium in patients with coronary artery disease.

Methods

One hundred patients undergoing myocardial revascularization participated in a pilot study (seven patients) and a double-blinded, randomized, controlled trial comparing the haemodynamic effects of cisatracurium with vecuronium at three centres. The patients were anaesthetized using oxygen 100%, with etomidate, fentanyl and a benzodiazepine, and tracheal intubation was facilitated using succinylcholine. After baseline haemodynamic measurements, the study drug was administered over 5–10 sec according to group assignment: Group A (pilot) cisatracurium, 0.20 mg·kg^?1 (4 × ED₉₅), (n = 7); Group B-cisatracurium, 0.30 mg·kg^?1 (6 × ED₉₅), (n = 31); Group C-vecuronium, 0.30 mg·kg^?1 (6 × ED₉₅), (n = 31); Group D cisatracurium, 0.40 mg·kg^?1 (8 × ED₉₅), (n = 21); Group E-vecuronium, 0.30 mg·kg^?1 (6 × ED₉₅), (n = 10). The haemodynamic measurements were repeated at 2, 5, and 10 min after cisatracurium or vecuronium.

Results

Two patients in Group D had > 20% decreases in MAR but only one required therapy for hypotension. The haemodynamic changes from pre-to post-injection in the cisatracurium patients were minimal and similar to patients receiving vecuronium.

Conclusions

In patients with coronary artery disease, rapid cisatracurium (4-8×ED₉₅) boluses and vecuronium (6×ED₉₅) result in minor, clinically insignificant haemodynamic side effects.