Comparative study of the efficacy and tolerance of propofol and thiopental in induction and in continuous perfusion with neuroleptanesthesia

We have studied 40 ASA I/II patients aged from 18 to 65 years undergoing otorhinolaryngologic surgery of 40-100 minutes of duration. Patients were randomly assigned to two groups. Anesthesia in group I was induced with thiopental, 4 mg/kg and maintained with N2O at 66% and a variable perfusion of fentanyl. In group II, anesthesia was induced with propofol, 2.5 mg/kg and maintained with a perfusion of 6-12 mg/kg/hour and an initial perfusion of fentanyl, 4 micrograms/kg/hour. Loss of consciousness occurred in 37.49 +/- 9.78 seconds in group I and in 46.25 +/- 12.62 seconds in group II, with no significant differences. Two minutes after induction, propofol group presented a significant decrease in systolic blood pressure of - 12 mm Hg and both groups presented comparable increases in systolic blood pressure and heart rate during intubation. Five minutes later, systolic blood pressure regained normal values. Maintenance in group II was achieved in a proper fashion with a mean propofol consumption of 9.5 +/- 2.6 mg/kg/hour and fentanyl consumption of 4.94 +/- 2.22 micrograms/kg/hour whereas in group II, with N2O at 66%, the amount of fentanyl required was 6.85 +/- 2.95 micrograms/kg/hour, which was significantly higher. Eye opening from the time of interruption of anesthetics was achieved at 6.6 +/- 3.2 minutes in group I and 12.44 +/- 6.34 in group II. Consciousness was regained at 11.25 +/- 3.96 and 16.87 +/- 6.95 minutes, respectively. Pain on injection occurred in 15% with propofol and in 10% with thiopental. No patient presented major complications nor phlebitis after administration of the anesthetic.     

Morphine and fentanyl interactions with thiopental in relation to movement response to noxious stimulation

The effects of morphine-thiopental and fentanyl-thiopental combinations on the movement response caused by tail clamping were studied in rats. Doses that prevented movement response when the agents were given singly and when the agents were given in combination were determined by a probit procedure and compared with isobolographic analysis. With doses of the above agents sufficient to block the movement response to tail clamping (ED50 values: 4.7 (3.3-6.6) mg/kg intravenously for morphine; 8.3 (5.8-11.3) micrograms/kg intravenously for fentanyl; and 18.8 (17.9-19.7) mg/kg intravenously for thiopental) both fentanyl and, to a lesser extent, morphine have a less than additive or an antagonistic interaction with thiopental. This antagonism is a relative one that does not increase the requirement for one agent upon the addition of another agent.     

Reduction of the MAC of desflurane with fentanyl.

Opioids are known to affect the MAC of inhalational anesthetics. We have determined the interaction between fentanyl and desflurane, following a bolus injection of fentanyl at induction in 134 adult patients. Five groups of patients were studied. Four groups received desflurane or isoflurane in oxygen with either fentanyl 3 or 6 micrograms/kg and thiopental 2-5 mg/kg given as a bolus injection at the time of induction. An additional group received desflurane in oxygen alone. Groups were stratified by age. MAC determination, in response to the stimulus of skin incision, was made using the "up-down" method and logistic regression. The MAC desflurane in oxygen was 6.3% (5.3-7.6%, 95% confidence interval [CI]). Fentanyl 3 micrograms/kg produced a fentanyl plasma concentration of 0.78 +/- 0.53 ng/ml at skin incision and resulted in a MAC for desflurane of 2.6% (2.0-3.2%, 95% CI) %. Fentanyl 6 micrograms/kg produced a fentanyl plasma concentration of 1.72 +/- 0.76 ng/ml at skin incision and resulted in a MAC for desflurane of 2.1% (1.5-2.6%, 95% CI). To compare recovery times to eye-opening and response to commands, patients were grouped according to the plasma fentanyl concentrations at the time of awaking. Recovery was faster in patients who received desflurane than in those who received isoflurane. The authors conclude that the MAC of desflurane is significantly reduced 25 min following a single dose of 3 micrograms/kg of fentanyl and that increasing the fentanyl dose to 6 micrograms/kg produces little further decrease in MAC. Desflurane is also associated with faster recovery from anesthesia than is isoflurane.     

The neuromuscular effects of ORG9426 in patients receiving balanced anesthesia

In searching for a nondepolarizing muscle relaxant with intermediate duration but more rapid onset of action than the presently available compounds, the neuromuscular and circulatory effects of ORG9426 were investigated in two studies in humans receiving fentanyl, droperidol, thiopental, and nitrous oxide-oxygen anesthesia. Eighty patients, randomly assigned to one of four groups of 20 each, received 0.12, 0.16, 0.20, or 0.24 mg/kg ORG9426. In the first study, the doses (in milligrams per kilogram) of ORG9426 that caused 50% (ED50), 90% (ED90), or 95% (ED95) neuromuscular block were determined by the individual dose-response method; they were 0.170, 0.268, and 0.305 mg/kg, respectively. In the second study, after induction of anesthesia, patients received 0.6 mg/kg (about 2 x ED95) of ORG9426, either in a single bolus (group 1) or in two unequal (0.1 and 0.5 mg/kg) increments 4 min apart (group 2). After the administration of 0.6 mg/kg ORG9426, maximal neuromuscular block developed in 1.5 +/- 0.12 min in group 1 and in 1.2 +/- 0.14 min in group 2. Patients tracheas were intubated after development of the maximal neuromuscular effect of the intubating dose and after the recording of heart rate and systolic and diastolic blood pressure. There was no difference in the clinical duration of the intubating doses, which were 40.0 +/- 3.2 (15-73) min in group 1 and 39.3 +/- 2.4 (19-57) min in group 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of fentanyl in neonates

The pharmacokinetics of fentanyl were studied in fourteen neonates undergoing major surgical procedures. Five patients were less than 1 day of age, seven were 1-4 days old, and two were 7-14 days old. Fentanyl was given intravenously, 10 micrograms/kg (n = 1), 25 micrograms/kg (n = 4), or 50 micrograms/kg (n = 9), and plasma concentrations measured at intervals of up to 18 hr. Average weight was 2.9 kg. The injection of 25 or 50 micrograms/kg of fentanyl over 1-3 min was hemodynamically well-tolerated by all patients. Four newborns without respiratory impairment secondary to surgery or disease needed ventilatory support for an average of 24 hr (range 11-40 hr). Plasma concentrations of fentanyl were most appropriately described by a two-compartment model. The mean +/- SEM values of selected model parameters were volume of the central compartment, 1.45 +/- 0.34 L/kg; volume of distribution at steady state, 5.1 +/- 1 L/kg; clearance, 17.94 +/- 4.38 ml X kg-1 X min-1; and terminal elimination half-life (t 1/2 beta), 317 +/- 70 min. In seven patients transient rebound in plasma fentanyl concentrations of 0.5 ng/ml or greater occurred. In three patients with markedly increased intraabdominal pressure, the t 1/2 beta was 1.5-3 times the population mean. Thus fentanyl disposition in neonates is highly variable, but the t 1/2 beta is predictably prolonged in the presence of increased abdominal pressure.     

Comparison of psychomotor skills and amnesia after induction of anesthesia with midazolam or thiopental

In two groups of 31 healthy patients undergoing minor elective surgery, anesthesia was induced intravenously with either midazolam maleate, 0.2 mg/kg, or thiopental, 3.5 mg/kg. All subjects received 2 micrograms/kg fentanyl 5 min before the induction agents. Induction time with midazolam was significantly longer than with thiopental (97.1 +/- 10.9 sec vs 59.4 +/- 5.0 sec) and time to orientation postoperatively was significantly longer after midazolam (31.7 +/- 4.2 min vs 11.0 +/- 1.1 min). Continued recovery after orientation, measured by a series of psychomotor tests, was also significantly longer with midazolam than with thiopental. Anterograde amnesia was evident in 84.8% of the midazolam treated patients and in only 31.4% of the thiopental group. This degree of absence of recall was acknowledged positively by the affected patients. The protracted recovery period may limit the use of midazolam in short surgical procedures.     

Comparison of the effects of 15 and 60 micrograms/kg fentanyl used for induction of anesthesia in patients with coronary artery disease

We compared the effects of 15 and 60 micrograms/kg fentanyl used for induction in 40 patients, 50-72 yr old, with coronary artery disease and mildly impaired ventricular contractility. Morphine (0.1 mg/kg) and scopolamine (0.4 mg) were used for premedication. Crystalloid (500 ml) was administered before induction, and nitroglycerin (0.3 micrograms X kg-1 X min-1) was infused during the study. Fentanyl, 15 or 60 micrograms/kg, was administered at a rate of 1.2 micrograms X kg-1 X sec-1. Pancuronium (0.04 mg/kg) and metocurine (0.16 mg/kg) were used for muscle relaxation. Data were collected 2 min before induction (baseline), before intubation (3 min), at 6 min, and at 13 min. Responses to 15 and 60 micrograms/kg were similar. At 3 min the heart rate (HR) in patients given 15 micrograms/kg increased by 6; whereas the HR in those given 60 micrograms/kg increased by 14 (P less than 0.01). Subsequent differences in HR were not significant. There were no dose-related differences in mean arterial pressure, cardiac index, central venous pressure, or pulmonary capillary wedge pressure. The EEG showed high-voltage low-frequency activity within 2 min in all patients. Arterial plasma fentanyl concentrations at 3 min averaged 25.9 +/- 3.8 ng/ml with 15 micrograms/kg and 89.9 +/- 15.2 ng/ml with 60 micrograms/kg. At 4 hr, plasma concentrations averaged 0.4 +/- 0.2 ng/ml and 3.6 +/- 0.7 ng/ml, respectively. We conclude that anesthesia for induction and intubation is achieved by the rapid administration of 15 micrograms/kg fentanyl and that 60 micrograms/kg has no substantially different effect on cardiovascular responses.     

Fentanyl does not alter the "sleep" plasma concentration of thiopental.

Thiopental and fentanyl are commonly combined for induction of anesthesia. The effect of an analgesic concentration of fentanyl on the plasma concentration of thiopental to induce sleep was studied in 46 unpremedicated patients. As a measure of drug effect, sleep (the lack of response to open eyes to a verbal command) was used. Forty-six patients were randomized to receive thiopental infused to one of several predetermined plasma concentrations. Twenty-two of these patients also received a fentanyl infusion to a desired analgesic concentration of 1 ng/mL. Thiopental and fentanyl were infused by means of a pharmacokinetic model-driven infusion device (computer-assisted continuous infusion, CACI). Venous blood samples were taken from the contralateral antecubital fossa at 5 and 10 min after the start of the infusion. At 10 min, the patients' names were firmly spoken, and they were instructed to open their eyes. If they did not respond to this command, they were considered to be asleep. Only patients in whom the 5- and 10-min measured plasma concentrations of thiopental and fentanyl, respectively, were within +/- 30% of each other were used for the determination of the Cp50(asleep), the plasma concentration at which 50% of the patients were asleep. The Cp50(asleep) with and without fentanyl was calculated by logistic regression. The Cp50(asleep) for patients in whom concentrations were maintained within +/- 30% for thiopental alone (n = 17) was 7.32 micrograms/mL (95% confidence interval, 5.53-10.95); for thiopental in the presence of fentanyl (n = 18 with a measured fentanyl concentration of 1.27 +/- 0.5 ng/mL), this was 7.22 micrograms/mL (95% confidence interval, 4.83-10.15).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the effects of fentanyl on respiratory mechanics under propofol or thiopental anaesthesia

Twenty patients were randomly anaesthetized with either thiopental 5 mg/kg followed by a 15 mg/kg/h continuous infusion, or propofol 2.5 mg/kg followed by a 9 mg/kg/h continuous infusion, paralysed with vecuronium 0.1 mg/kg, intubated and ventilated with nitrous oxide 50% in oxygen. Fifteen minutes after induction, fentanyl 5 micrograms/kg was injected. Inspiratory tracheal pressure (PT), gas flow (V) and volume (V) were continuously measured while the lungs were inflated with a constant inspiratory flow ventilator. Respiratory compliance (Crs) and resistance (Rrs) were calculated from the regression of PT on V. In both groups Crs decreased following anaesthesia. Fentanyl injection elicited an increase in Rrs (from 1.04 +/- 0.70 to 1.63 +/- 0.92 kPa x l-1 x s) and a further decrease in Crs (from 0.55 +/- 0.30 to 0.42 +/- 0.10 l x kPa-1) in the thiopental group but not in the propofol group (Rrs: 1.26 +/- 0.69 to 1.08 +/- 0.44 kPa x l-1 x s, Crs: 0.49 +/- 0.11 to 0.48 +/- 0.13 l x kPa-1). These results suggest that the dose of propofol administered in this study may prevent fentanyl-induced bronchoconstriction.     

Lack of interaction between propofol and vecuronium.

We estimated the potency of vecuronium and measured the onset and duration of its action during total intravenous anesthesia with propofol to examine the possibility of any interaction between these two drugs. Propofol infusion was administered according to a three-step dosage scheme, and neuromuscular block was monitored by measuring the force of contraction of the adductor pollicis muscle after single-twitch stimulation of the ulnar nerve at 0.1 Hz. A control group of patients were similarly studied during anesthesia with thiopental, nitrous oxide, oxygen, and fentanyl. The ED50 and ED95 (dose required to produce a 50% and 95% depression of twitch tension, respectively) of vecuronium in patients given total intravenous anesthesia (n = 24) were 24 (22-27, 95% confidence limits) and 41 (37-48, 95% confidence limits) micrograms/kg, respectively, and in the control group (n = 24), 20 (17-24) and 39 (34-37) micrograms/kg, respectively. The onset of action of an 80-micrograms/kg dose (2 x ED95) of vecuronium was 3.6 +/- 1.2 and 4.1 +/- 1.7 min (mean +/- SD), in the propofol (n = 10) and control (n = 10) groups, respectively. The respective times to recovery of the twitch height to 25% of control and the recovery indices (25%-75% recovery of twitch height) in the propofol versus control groups were 28.3 +/- 6.6 and 28.0 +/- 1.7 min and 13.3 +/- 6.8 and 15.4 +/- 11.9 min, respectively. There were no significant differences in any of the measured variables between the propofol and control groups, indicating the lack of any interaction between propofol and vecuronium.     

Clinical pharmacology of pipecuronium bromide

The neuromuscular blocking and cardiovascular effects of pipecuronium, in doses ranging 2-3 times its ED95, were evaluated in 46 patients during thiopental, fentanyl, N2O/O2 anesthesia. The neuromuscular blocking effect of pipecuronium was evaluated by recording of the mechanical twitch of the adductor pollicis muscle in response to stimulation of the ulnar nerve at the wrist. Heart rate, systolic and diastolic blood pressures, and cardiac output were non-invasively measured during the onset of the neuromuscular blockade and compared to a saline control group to separate the effect of anesthesia from those of pipecuronium. The mean +/- SD time from administration of pipecuronium to 90% suppression of the first twitch (T1) of the train-of-four was 2.6 +/- 0.8, 2.0 +/- 0.6, and 2.1 +/- 0.6 min following the 70 micrograms/kg, 85 micrograms/kg, and 100 micrograms/kg dose, respectively. There was no significant difference between the different doses of pipecuronium in the time to 90% suppression of T1. In general, all three doses of pipecuronium provided good to excellent intubating conditions within 3 minutes after its administration. The time from the administration of pipecuronium to 5% recovery of T1 was 52.3 +/- 18.2 min in the group given 70 micrograms/kg. This was significantly longer in patients given 85 micrograms/kg (71.9 +/- 15.7 min) or 100 micrograms/kg (71.8 +/- 22.1 min). Times to the start of recovery of T1 and to 25% recovery of T1 showed a similar significant pattern.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of intravenous clonidine on the dose of thiopental required to induce anesthesia.

A randomized, double-blind, controlled trial was conducted to investigate the influence of intravenous clonidine on thiopental dose requirements when used for induction of anesthesia and associated hemodynamic effects. Sixty ASA physical status I or II patients were randomly allocated to one of three treatment groups: normal saline solution (control, n = 20); clonidine (2.5 micrograms/kg, n = 20); or clonidine (5 micrograms/kg, n = 20). The test drug was administered 15 min before induction of anesthesia with intravenous thiopental. The dose of thiopental to produce loss of lash reflex was recorded as well as mean arterial blood pressure and heart rate at 3-min intervals up to induction of anesthesia and then at 1-min intervals for 5 min. Significant decreases in thiopental dose were observed in both groups receiving clonidine compared with the control group, but there was no significant difference between clonidine groups. With dosage calculated according to total body mass, the control group required 5.50 +/- 1.15 mg/kg (mean +/- SD) of thiopental, whereas those who received 2.5 micrograms/kg of clonidine required 4.15 +/- 1.46 mg/kg of thiopental (a reduction of 25%), and those who received 5.0 micrograms/kg of clonidine required 3.48 +/- 1.06 mg/kg of thiopental (a reduction of 37%). When thiopental dose was adjusted for lean body mass, similar reductions were obtained. Clonidine, in both doses, produced more sedation than control, and the 2.5-mg/kg dose produced less sedation than the larger dose. Mean arterial blood pressure was lower in the groups receiving clonidine. There were no significant differences in heart rate among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Priming with vecuronium and atracurium--a comparison

Vecuronium (V) and atracurium (A) were compared in a randomised study in premedicated patients undergoing laparoscopy for gynecological pathology. Both groups contained ten patients. Anesthesia was induced with fentanyl (0.1 mg) and thiopentone (1 mg/kg initially and subsequently 4 mg/kg). A priming dose of vecuronium (20 micrograms/kg) or atracurium (100 micrograms/kg) was given one minute before the intubating dose (60 micrograms/kg for vecuronium and 300 micrograms/kg for atracurium). Ninety seconds thereafter intubation was performed. Maintenance of anesthesia consisted of isoflurane at an inspiratory concentration of 1% in a mixture of O2/N2O (50%/50%) with small supplements of fentanyl. Neuromuscular block was monitored with the Datex Relaxograph. Results show that neither drug offers major clinical advantages over the other: there is no difference in speed of onset (V:T190sec 14.6 +/- 4.3%; A:T190sec 23.5 +/- 6.5%; Mean +/- SEM) and duration of neuromuscular block (V:T150sec 34.2 +/- 3.5 min; A:T150sec 41.3 +/- 2.8 min; Mean +/- SEM) and intubation conditions are almost identical.     

Thiopental requirements for induction of anesthesia in neonates and in infants one to six months of age

The authors determined the thiopental dose needed for satisfactory induction in ten neonates, 0-14 days of age, and 20 infants, 1-6 months of age. A single iv bolus of thiopental was given. Thirty seconds after injection the anesthesia mask was applied and the response was observed during the following 30 s while the patient breathed oxygen. Induction was considered satisfactory if there were no gross movements or coughing. The dose required for satisfactory induction in 50% of patients, ED50 (+/- SE), was 3.4 +/- 0.2 mg/kg in neonates and 6.3 +/- 0.7 mg/kg in infants (P less than 0.001). It is concluded that the thiopental dose needed for satisfactory induction is less in neonates than in infants.     

Dose-response relations of doxacurium and its reversal with neostigmine in young adults and healthy elderly patients.

Dose-response relationships for doxacurium and neostigmine were established in 24 young (18-40 yr) and 24 elderly (70-85 yr) patients, ASA physical status I or II, anesthetized with thiopental, fentanyl, nitrous oxide, and isoflurane. Mechanomyographic response of the adductor pollicis muscle to the train-of-four stimulation of the ulnar nerve was recorded. Doxacurium (5, 10, 15, or 20 micrograms/kg IV) was administered by random allocation. After maximal blockade, and additional dose, for a total of 30 micrograms/kg, was administered. When first twitch height recovered to 25%, incremental doses of 5 micrograms/kg were administered for maintenance of relaxation. Neostigmine (5, 10, 20, or 40 micrograms/kg) was injected at 25% first twitch recovery, and neuromuscular monitoring was continued for 10 min. The doses of doxacurium (+/- SEM) required to produce a 50%, 90%, and 95% depression of twitch tension in the young patients were, respectively, 13.3 +/- 1.6, 23.6 +/- 2.8, and 28.6 +/- 3.4 micrograms/kg, not statistically different from corresponding values in the elderly, 11.8 +/- 1.3, 21.2 +/- 2.3, and 25.9 +/- 2.9 micrograms/kg, respectively. Time to 25% recovery after 30 micrograms/kg was 80.2 +/- 12.2 min in the young versus 133.0 +/- 17.1 min in the elderly (P less than 0.05). Neostigmine-assisted recovery was not significantly different in both groups. The estimated doses of neostigmine to obtain 70% train-of-four recovery after 10 min were 53.6 +/- 7.5 micrograms/kg in the young and 41.6 +/- 5.8 micrograms/kg in the elderly (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory effects of epidural and subcutaneous morphine, meperidine, fentanyl and sufentanil in the rat

This study compared the respiratory effects of subcutaneous and epidural morphine, meperidine, fentanyl, and sufentanil in rats breathing air or 8% CO2 in air. A whole body plethysmographic technique was used to measure minute volumes of breathing. The ED50s of subcutaneously injected morphine, meperidine, fentanyl, and sufentanil in depressing the minute volume response to 8% CO2 in air were 2300 micrograms/kg, 8800 micrograms/kg, 20 micrograms/kg, and 2.3 micrograms/kg, respectively. These doses were nearly the same as the subcutaneous ED50s of these compounds in producing analgesia, found in an earlier study. Roughly equianalgesic doses of the four opiates after epidural injection, however, failed to cause any detectable respiratory effect. Fourfold greater doses increased significantly the incidence of low minute volumes with fentanyl and sufentanil, but soon after epidural injection, i.e., at the time that analgesia was produced. None of the epidurally injected opiates had a significant delayed effect on respiration. However, one of the seven rats treated epidurally with the higher dose of morphine developed depression of the minute volume response to 8% CO2 in air as late as 7 hours after the injection. We conclude that epidural injection, in contrast to subcutaneous injection, of analgesic doses of morphine, meperidine, fentanyl, and sufentanil produces no significant respiratory effects.     

Methohexital dissolved in lipid emulsion for intravenous induction of anesthesia in infants and children.

The induction dose of thiopental and propofol has been shown previously to vary during childhood. The methohexital dose needed for satisfactory induction of anesthesia in 50% of patients (ED50) was determined in 75 infants and children, 1 month to 16 yr of age. An intravenous bolus of methohexital, dissolved in a lipid emulsion to decrease pain on injection, was given over 10 s. After 30 s the anesthesia mask was applied. The patient was considered to be asleep if there were no gross movements when the head was placed in the sniffing position and the anesthesia mask applied, and no response to verbal command (tested in children more than 4 yr of age) during the next 30 s while the patient breathed O2. ED50 (+/- SE) was 2.6 +/- 0.2 mg/kg in infants 1-6 months of age, 1.9 +/- 0.1 mg/kg in infants 7-11 months of age, 1.4 +/- 0.1 mg/kg in children 1-3 yr of age, 1.1 +/- 0.1 mg/kg in children 4-7 yr of age, and 1.3 +/- 0.1 mg/kg in children 8-16 yr of age. ED50 in each of the two groups of infants was significantly greater than ED50 in each of the three other groups (P less than 0.05). Pain or discomfort on injection was observed in 1 infant and 3 children (5%). Eight patients (11%) had apnea longer than 15 s, and excitatory phenomena occurred in 9 (12%). It is concluded that the dose of methohexital needed for induction of anesthesia varies with age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of volatile anesthetics on vecuronium-induced neuromuscular blockade in children

We studied 60 children undergoing elective surgery to evaluate the effect of interactions between vecuronium and isoflurane or halothane on the potency and duration of neuromuscular blockade, as measured by electromyography. Vecuronium was first administered by a logarithm-based cumulative method (14, 22, 35, 56, 89 micrograms/kg) in 10 children anesthetized with thiopental (5 mg/kg), alfentanil (15 micrograms/kg first dose, then 10 micrograms/kg), and N2O/O2 (60:40) until a 95% +/- 2% twitch depression (ED95) was obtained. Thirty children given the same balanced anesthesia were then randomly assigned to three groups (n = 10 in each) to receive a single ED20 (21 micrograms/kg), ED50 (33 micrograms/kg), or ED80 (47 micrograms/kg) intravenous bolus of vecuronium calculated from the mean regression line of twitch responses of the first 10 children. In the second part of the study, 20 children were anesthetized with isoflurane (1.2%) or halothane (0.7%) and compared with the previous 10 children anesthetized with alfentanil-N2O. Potency of vecuronium determined by single-bolus or logarithm-based cumulative techniques was not significantly different. Isoflurane and halothane significantly decreased ED50 (22.3 +/- 1.6 and 25.4 +/- 1.4 micrograms/kg, respectively; mean +/- SE) and ED95 (41.5 +/- 3.3 and 46.7 +/- 3.2 micrograms/kg, respectively) compared with alfentanil-N2O (ED50: 32.8 +/- 0.8 micrograms/kg, ED95: 70.5 +/- 2.6 micrograms/kg). Recovery rate from vecuronium-induced neuromuscular blockade was significantly longer with isoflurane than with alfentanil-N2O or halothane. We conclude that in children single-bolus and logarithm-based cumulative techniques give similar potency estimates for vecuronium. Isoflurane and halothane increase by similar amounts the neuromuscular potency of vecuronium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical effects of intrathecally administered fentanyl in patients undergoing cesarean section.

The clinical effects of spinally (subarachnoid) administered, preservative-free fentanyl were assessed in 120 healthy women who underwent cesarean section with spinal anesthesia using 0.5% hyperbaric bupivacaine. Subjects were divided at random into four groups (n = 30) the first of which received 2 mL of saline containing no fentanyl (group 0); the second, 0.25 micrograms/kg (group 25); the third, 0.5 micrograms/kg (group 50); and the fourth, 0.75 micrograms/kg (group 75) of fentanyl in a blinded manner. Surgical anesthesia was excellent in 100% of treated patients and in 87% of group 0. Respiratory rate decreased significantly in groups 50 and 75 and was recorded as early as 4 min after the administration of the drug. Nevertheless, respiratory depression did not develop in any patient, and 40 min later all groups had a similar respiratory rate. Regression of anesthesia to the T-12 dermatome took a longer time as the dose of fentanyl increased, but all patients had recovered by 240 min after the injection. Effective postoperative analgesia lasted longer and significantly increased with the dose of fentanyl administered: group 0, 197 +/- 77 min; group 25, 305 +/- 89 min; group 50, 640 +/- 142 min; and group 75, 787 +/- 161 min (data expressed as mean +/- SD; P less than 0.001 between groups). Neonatal status was the same in all groups. Sedation and pruritus were the main side effects. The combination of bupivacaine and a low dose of fentanyl (0.25 micrograms/kg) provides excellent surgical anesthesia with short-lasting postoperative analgesia and very few negative side effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Effect of Isoflurane, Halothane, Sevoflurane, and Thiopental/Nitrous Oxide on Respiratory System Resistance after Tracheal Intubation

Background: After tracheal intubation, lung resistance and therefore respiratory system resistance (Rrs) routinely increase, sometimes to the point of clinical bronchospasm. Volatile anesthetics generally have been considered to be effective bronchodilators, although there are few human data comparing the efficacy of available agents. This study compared the bronchodilating efficacy of four anesthetic maintenance regimens: 1.1 minimum alveolar concentration (MAC) end-tidal sevoflurane, isoflurane or halothane, and thiopental/nitrous oxide.

Methods: Sixty-six patients underwent tracheal intubation after administration of 2 micro gram/kg fentanyl, 5 mg/kg thiopental, and 1 mg/kg succinylcholine. Vecuronium or pancuronium (0.1 mg/kg) was then given to ensure paralysis during the rest of the study. Postintubation R sub rs was measured using the isovolume technique. Maintenance anesthesia was then randomized to thiopental 0.25 mg [center dot] kg sup -1 [center dot] min sup -1 plus 50% nitrous oxide, or 1.1 MAC end-tidal isoflurane, halothane, or sevoflurane. The Rrs was measured after 5 and 10 min of maintenance anesthesia. Data were expressed as means +/- SD.

Results: Maintenance with thiopental/nitrous oxide failed to decrease Rrs, whereas all three volatile anesthetics significantly decreased Rrs at 5 min with little further improvement at 10 min. Sevoflurane decreased Rrs more than either halothane or isoflurane (P < 0.05; 58 +/- 14% of the postintubation Rrs vs. 69 +/- 20% and 75 +/- 13%, respectively).