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PubMed1985

Cardiovascular responses to tracheal intubation in small children. Effects of the induction of anaesthesia with halothane.

Cardiovascular changes in 27 children (mean age 1.5 yr) were studied during the induction of anaesthesia with 2.5% halothane and 70% nitrous oxide in oxygen. The eyelash reflex disappeared in a mean of 62 +/- 3.6 (SEM)s and tracheal intubation could be performed 4.9 +/- 0.2 min after the start of halothane anaesthesia. Intubating conditions were satisfactory in 85% of the children. Systolic arterial pressure increased by 10.8 +/- 1.9 mm Hg and diastolic pressures by 6.0 +/- 1.4 (SEM) mm Hg after intubation of the trachea. Heart rate decreased significantly after induction. No cardiac arrhythmias were noted. There were no significant changes in Q-T interval after induction, after intubation or during the later course of the anaesthetic.

Anesthesia, Inhalation↗
PubMed1985

Effect of speed of injection on induction of anaesthesia using propofol.

Sixty unpremedicated patients (30 male) were randomly allocated to three groups. They received an induction dose of propofol 2 mg kg-1 over 5, 20 or 60 s to a forearm vein. Anaesthesia was maintained with conventional inhalation anaesthetic agents. Anaesthesia was induced satisfactorily in all 20 of the patients in the 5-s group, in 19 of the patients in the 20-s group and in 18 of the patients in the 60-s group. The rate of injection had a significant influence on induction time. Mean induction time increased from 21.5 to 34.7 and 50.5 s, when injection time was increased from 5 to 20 to 60 s, respectively. Similar induction times were found in male and female patients. There was no significant difference between the groups, in depth of anaesthesia obtained--as assessed by the eyelash reflex. Mean arterial pressure decreased to the same extent in all three groups. Two minutes after induction, mean systolic arterial pressure was reduced by 15.1, 13.5 and 19.3 mm Hg in the 5-, 20- and 60-s groups, respectively, and mean diastolic arterial pressure by 10.3, 13.2 and 13.7 mm Hg. Heart rate changes were insignificant. Apnoea of more than 10 s duration was seen frequently in all three groups, but the results suggest that the incidence was not influenced by the rate of injection. Three patients experienced mild pain at the time of injection. No major adverse reactions occurred during or after anaesthesia.

Adolescent↗
PubMed1989

Closed-loop feedback control of propofol anaesthesia by quantitative EEG analysis in humans.

Propofol was administered for 2 h to 11 volunteers by an adaptive feedback control algorithm based on quantitative EEG analysis. Median EEG frequency served as the control variable. The range 2-3 Hz was chosen as the target range of control. During the feedback period, volunteers did not respond to commands and eyelash reflex was abolished. An average median frequency of 2.5 (SD 0.3) Hz was obtained by administering propofol 1452 (262) mg within 2 h. Time to recovery was 17.9 (8.0) min. Compared with a study with methohexitone using the same approach, the relative potency of propofol was 0.72. The mean recovery time was less than half that observed after methohexitone.

Adult↗
PubMed1990

Levels of consciousness in volunteers breathing sub-MAC concentrations of isoflurane.

Eight volunteers inhaled isoflurane in concentrations of 0.1, 0.2 and 0.4 MAC, and 100% oxygen as control in separate sessions more than 1 week apart. When the end-expiratory isoflurane concentration was stable, response to verbal commands was tested, and the subjects were read 30 words in two lists. Response to the commands was impaired at 0.1 MAC in three subjects and lost at 0.2 MAC in two subjects. No subject responded at 0.4 MAC. When the subjects were questioned 1 h after exposure, memory of response to commands was lost also at these concentrations. Frequently, those who responded to the command "open your eyes" failed to remember having done so; non-responders remembered nothing. At the time of that test, at 0.4 MAC, five of eight subjects had no eyelash reflex. Both recall and recognition of neutral words was lost at 0.2 MAC and greater, but the effect of attention was demonstrated by the memory of a "shock" word by four of eight subjects at 0.2 MAC.

Adult↗
PubMed1992

Changes in cardiac index and estimated systemic vascular resistance during induction of anaesthesia with thiopentone, methohexitone, propofol and etomidate.

Changes in cardiac index (CI) and estimated systemic vascular resistance (ESVR) were assessed non-invasively using pulsed Doppler ultrasound during induction of anaesthesia. Ninety-six ASA I patients were allocated randomly to one of four groups to receive alfentanil 8 micrograms kg-1 followed by a dose of thiopentone, methohexitone, propofol or etomidate sufficient to obtund the eyelash reflex. CI increased significantly by 8% 1 min after administration of both methohexitone (P < 0.05) and propofol (P < 0.05), returning to pre-induction values thereafter. CI increased after thiopentone but the increase was not statistically significant. There was a significant decrease in CI of 16% after induction with etomidate (P < 0.001). ESVR decreased significantly from pre-induction values by 18% after methohexitone (P < 0.001) and 23% after propofol (P < 0.001). ESVR in the thiopentone group decreased, but this was not statistically significant. ESVR increased significantly by 12% 1 min after induction of anaesthesia with etomidate (P < 0.05) and then decreased towards pre-induction values. The results suggest that the cardiostability of etomidate may not be as complete in all groups of patients as previous studies have suggested.

Blood Flow Velocity↗
PubMed1992

Synergistic interaction between midazolam and propofol.

We gave either midazolam or propofol for induction of anaesthesia to 140 ASA I or II female patients (18-60 yr). ED50 values were obtained by probit analysis for three clinical end-points: loss of response to command; loss of eyelash reflex; failure to respond to application of an anaesthetic face mask delivering 1% isoflurane. Propofol ED50 values (95% confidence intervals) were 1.25 (0.99-1.48) mg kg-1, 1.61 (1.29-1.94) mg kg-1 and 1.51 (1.20-1.82) mg kg-1, respectively. ED50 values for midazolam were 0.26 (0.20-0.37) mg kg-1, 0.29 (0.23-0.47) mg kg-1 and 0.25 (0.20-0.32) mg kg-1, respectively. An additional 92 similar patients received one of nine dose combinations of midazolam and propofol for induction of anaesthesia, propofol being administered 2 min after midazolam. Success of induction was based on the clinical end-point of loss of response to command. Administration of 25% of the ED50 of midazolam followed by 50% of the ED50 of propofol resulted in loss of response to command in 50% of patients, while 50% of the ED50 of midazolam, followed by 25% of the ED50 of propofol had the same effect. A probit regression model specifying a synergistic interaction between midazolam and propofol fitted the data significantly better than a model specifying no interaction.

Adolescent↗
PubMed1993

Haemodynamic and catecholamine responses to induction of anaesthesia and tracheal intubation: comparison between propofol and thiopentone.

We have studied the haemodynamic changes, QT intervals and catecholamine responses to induction of anaesthesia and tracheal intubation in 24 ASA I patients allocated randomly to receive either propofol 2.5 mg kg-1 or thiopentone 5 mg kg-1 over 60 s. After disappearance of the eyelash reflex, the lungs were ventilated with 100% oxygen for 3 min. The trachea was intubated after administration of vecuronium. With thiopentone, heart rate (HR) was greater than with propofol before intubation (P < 0.05). During induction, systolic (SAP) and diastolic arterial pressure (DAP) decreased more with propofol than with thiopentone. The QT interval was prolonged only during induction with thiopentone. In both groups, HR, SAP, DAP and the QT were increased in response to intubation (P < 0.001). The SAP and QT interval responses to intubation were significantly greater with thiopentone than with propofol (P < 0.05). One patient in the thiopentone group with a significantly prolonged QT interval had episodes of bigeminy and ventricular tachycardia. In both groups, concentrations of noradrenaline in mixed venous plasma increased after intubation (P < 0.001). Concentrations of adrenaline increased after intubation only in the thiopentone group (P < 0.001).

Adolescent↗
PubMed1994

Propofol infusion and the suppression of consciousness: dose requirements to induce loss of consciousness and to suppress response to noxious and non-noxious stimuli.

We have defined the infusion dose requirements of propofol to suppress consciousness and response to a variety of graded non-noxious and noxious stimuli in 52 unpremedicated patients aged 16-40 yr and 32 patients aged 41-65 yr. They were allocated to receive one of five loading dose-infusion schemes designed to establish stable conditions covering the range from wakefulness, through sedation, to loss of consciousness and anaesthesia. At 10 and 20 min after the loading dose, each patient's response to a graded series of stimuli was recorded. Probit analysis was used to derive mean values (95% confidence interval) for the ED50 and ED95 (as final infusion rate) for loss of response to verbal command at 4.9 (4.7-5.1) mg kg-1 h-1 and 7.9 (7.3-8.8) mg kg-1 h-1, respectively, in the young group and 4.2 (4.0-4.4) mg kg-1 h-1 and 5.8 (5.4-6.4) mg kg-1 h-1, respectively, in the older group. In both groups the dose-response curves for suppression of proprioception, finger counting and perception of light touch in conscious patients were shifted to the left of the curves for loss of consciousness and eyelash reflex. Dose-response curves for noxious stimuli were shifted to the right of those for loss of consciousness.

Adolescent↗
PubMed1994

Haemodynamic and catecholamine changes after induction of anaesthesia with either thiopentone or propofol with suxamethonium.

We have compared the haemodynamic and catecholamine responses to laryngoscopy and tracheal intubation in 43 patients after induction of anaesthesia with either thiopentone 5.1 (SD 0.9) mg kg-1 or propofol 2.2 (0.1) mg kg-1, each with suxamethonium and without opioid pretreatment. Heart rate increased significantly above baseline after induction and intubation in both groups, but there were no differences between groups. Arterial pressure increased significantly at 1 min after intubation in both groups and at 2 min in the thiopentone group only. Plasma concentrations of adrenaline increased significantly compared with concentrations before induction, 1 min after intubation in both groups and at 2 min in the thiopentone group only. Plasma concentrations of adrenaline were significantly greater in the thiopentone group than in the propofol group at both 1 and 2 min after intubation. Plasma concentrations of noradrenaline showed no significant time-based within-group changes, but were significantly greater in the thiopentone group at 1 and 2 min after intubation. We conclude that doses of either thiopentone or propofol sufficient to obtund the eyelash reflex with suxamethonium 1 mg kg-1 alone do not adequately block the catecholamine and hypertensive responses to laryngoscopy and intubation in normal patients and although propofol suppressed increases in catecholamines to a greater extent than thiopentone, there were no clinical advantages.

Adolescent↗
PubMed1997

Comparison of induction and recovery between sevoflurane and halothane supplementation of anaesthesia in children undergoing outpatient dental extractions.

We have compared sevoflurane and halothane in a double-blind controlled study for supplementation of nitrous oxide and oxygen anaesthesia in 80 children undergoing dental extraction as outpatients. Induction of anaesthesia was more rapid in those who received sevoflurane compared with those who received halothane (89 s compared with 127 s for loss of eyelash reflex). In both groups, mean duration of administration of anaesthesia was less than 4 min. Those who received sevoflurane were slower to awaken (167 s compared with 102 s), although discharge times from hospital were similar. The incidence of complications during induction and maintenance was low in both groups and return to normal appetite and activity occurred in the majority of children on the same day. More children who received halothane suffered nausea after leaving hospital. We conclude that sevoflurane is a suitable alternative to halothane, with more rapid induction of anaesthesia, but in these short procedures, awakening time was slower than after halothane.

Ambulatory Surgical Procedures↗
PubMed1997

Comparison of sevoflurane and halothane for outpatient dental anaesthesia in children.

In a prospective, randomized, double-blind clinical study, we have studied 100 children, aged 2-12 yr, to compare halothane and sevoflurane in outpatient dental anaesthesia. All patients were unpremedicated and received inhalation induction using nitrous oxide in oxygen supplemented with either halothane (maximum inspired concentration 5%) or sevoflurane (maximum inspired concentration 8%). Time to loss of the eyelash reflex was more rapid using sevoflurane although time to adequate anaesthesia (to allow insertion of a mouth prop) was slower in the sevoflurane group. The incidence of cardiac arrhythmia was higher during halothane (62%) than during sevoflurane anaesthesia (28%) (P < 0.005) and the arrhythmias were more often ventricular in origin. The two agents were comparable in terms of ease of use and quality of anaesthesia, and times to eye opening and satisfying discharge criteria were similar. We conclude that sevoflurane has qualities that have made halothane the most used inhalation agent for children, and that it is superior to halothane in dental outpatients where cardiac arrhythmias are a particular problem.

Ambulatory Surgical Procedures↗
PubMed1998

Induction and emergence in infants less than 60 weeks post-conceptual age: comparison of thiopental, halothane, sevoflurane and desflurane.

We have studied 40 infants with a post-conceptual age of less than 60 weeks undergoing general anaesthesia for herniotomy. Patients were anaesthetized with 1 MAC equivalent values for age and agent and allocated randomly to receive halothane, savoflurane or thiopental for induction, and halothane, sevoflurane or desflurane for maintenance of anaesthesia. At induction, both time to acceptance of a face mask and loss of eyelash reflex were recorded. Emergence times were noted by a blinded observer. Induction and emergence times were similar between the halothane and sevoflurane groups but were consistently shorter in the desflurane group compared with the halothane or sevoflurane groups. There were no problems at extubation or significant apnoea in any group. Induction of anaesthesia in this population was no quicker with sevoflurane than with halothane and the method used for induction did not influence recovery time. Maintenance of anaesthesia with desflurane resulted in a shorter recovery time in infants in whom anaesthesia was induced with halothane or thiopental. Desflurane maintenance may be particularly beneficial in the neonate.

Anesthesia Recovery Period↗
PubMed1999

Prediction of movement at laryngeal mask airway insertion: comparison of auditory evoked potential index, bispectral index, spectral edge frequency and median frequency.

We have studied 46 patients to compare the efficacy of the auditory evoked potential (AEP) index, bispectral index (BIS), 95% spectral edge frequency (SEF) and median frequency (MF) in predicting movement in response to insertion of the laryngeal mask airway (LMA). Anaesthesia was induced with target-controlled infusions of propofol and alfentanil. After loss of eyelash reflex and adequate jaw relaxation, the LMA was inserted without the assistance of a laryngoscope or neuromuscular blocker. Patients who showed any visible spontaneous muscle movement within 1 min of LMA insertion were defined as movers. Values in movers and non-movers at 30 s before LMA insertion were analysed. Only AEP index discriminated between movers and non-movers with a prediction probability of 0.872. BIS, SEF and MF could not predict movement at LMA insertion. AEP index was the most reliable predictor of movement in response to LMA insertion.

Adolescent↗
PubMed2000

Safety of patient-maintained propofol sedation using a target-controlled system in healthy volunteers.

We investigated the safety of a patient-maintained system that allows individuals to operate a target-controlled infusion of propofol to achieve sedation. Ten healthy volunteers were recruited and instructed to try to anaesthetize themselves with the system. A target-controlled infusion of propofol was set to deliver a target propofol concentration of 1 microgram ml-1, and the subjects allowed to increase the target in increments of 0.2 microgram ml-1 by pressing a control button twice in 1 s. There was a lockout time of 2 min and a maximum permitted target concentration of 3 micrograms ml-1. Heart rate and pulse oximetry oxygen saturation (SpO2) were monitored continuously, and non-invasive arterial pressure, ventilatory frequencies and sedation scores were measured every 5 min. Sedation was continued until the subject stopped pressing the button. A keyword was then read for the individual to remember and sedation discontinued. There were no instances of significant decrease of SpO2 or loss of airway control. Maximum target blood concentration of propofol recorded ranged from 1.4 to 3 micrograms ml-1. Two subjects became oversedated, one of whom was unrousable with loss of eyelash reflex. No subject could recall the keyword, although one recognized it from a list of 10 words. We conclude that the patient-maintained sedation system described could not be guaranteed to produce only conscious sedation in all patients, and that close clinical supervision by an anaesthetist would still be required for safe operation.

Adolescent↗
PubMed2002

Optimal rocuronium dose for intubation during inhalation induction with sevoflurane in children.

BACKGROUND: We studied 120 children aged 2-7 yr in a prospective, randomized, assessor-blinded fashion to define the optimal rocuronium dose which provides a 95% probability of acceptable intubation conditions (ED95TI) during inhalation induction with sevoflurane. METHODS: After inhalation induction with 8% sevoflurane in 60% nitrous oxide and 40% oxygen, and loss of the eyelash reflex, we administered rocuronium (0.1, 0.15, 0.22, 0.3, or 0.6 mg kg-1) or placebo. We quantified neuromuscular function by stimulation of the ulnar nerve at 0.1 Hz to produce contraction of the adductor pollicis muscle using accelerometry. Intubation conditions were assessed 2 min after test drug injection. The optimal rocuronium dose was defined as the lowest dose, which allowed acceptable intubation conditions in 95% of children (ED95TI). RESULTS: Two minutes after injection of placebo or rocuronium, intubation conditions were acceptable in 35, 45, 80, 90, 95, and 100% of children, respectively. Rocuronium 0.07 [CI 0.02-0.11], 0.24 [0.19-0.31], and 0.29 [0.23-0.38] mg kg-1 provided 50, 90, and 95% probability of acceptable intubating conditions. When thumb acceleration was depressed by 50% or more, intubating conditions were considered acceptable in 97% of children. Recovery of the train-of-four ratio to 0.8 averaged 12 (7), 16 (7), 24 (7), 24 (8), and 50 (22) min after the respective dose of rocuronium. CONCLUSIONS: During inhalation induction with 8% sevoflurane in 60% nitrous oxide, rocuronium 0.29 mg kg-1 (ED95) optimizes intubation conditions for surgery of short duration.

Androstanols↗
PubMed2002

Auditory evoked response during propofol anaesthesia after pre-induction with midazolam.

BACKGROUND: In clinical use, midazolam reduces the dose requirement for propofol. We studied the effect of midazolam given before anaesthesia on the amount of propofol needed and the time taken, to achieve loss of consciousness (LOC) in 20 patients. METHODS: We compared the auditory evoked responses (AER) in these patients with those in a group of 20 patients who were not given midazolam. RESULTS: LOC, as defined by a loss of response to verbal command and eyelash reflex, occurred after 113 (95% CI, 99-131) s in the control group and 75 (56-101) s in the midazolam group (P < 0.05). In the control group 2.3 (2.0-2.6) mg kg-1 propofol caused LOC compared with 1.3 (1.1-1.5) mg kg-1 in the group pretreated with midazolam (P < 0.001). Pa amplitude decreased by 60% in the control group and by 54% in the midazolam group while Nb latency increased by 24% in the control group and by 32% in the midazolam group following LOC. These differences were not significant. CONCLUSIONS: We confirmed that coinduction of anaesthesia with midazolam and propofol reduces the requirement of propofol. We also demonstrated that the AER reflects anaesthetic depth rather than plasma concentrations of anaesthetic drugs.

Adult↗
PubMed2004

Mid-latency auditory evoked response during propofol and alfentanil anaesthesia.

BACKGROUND: Propofol has been shown to affect the mid-latency auditory evoked response (MLAER) in a dose-dependant manner. Few studies have investigated the addition of alfentanil. Myogenic responses, such as the post-auricular responses (PAR), can confound the MLAER but there has been little investigation as to which electrode site reduces this interference. METHODS: We studied the MLAER in 27 women. They received an infusion of alfentanil 15 micro g kg(-1) h(-1), followed by either a high or low infusion regimen of propofol (final infusion rates 6 and 3 mg kg(-1) h(-1)). We compared the results with those of our study using propofol alone. We collected the data from two electrode sites: vertex-inion and vertex-mastoid. We evaluated the occurrence of the PAR and the shape of the MLAER at each electrode site. RESULTS: The infusion rate of propofol associated with loss of the eyelash response in 50% of subjects was 3.3 mg kg(-1) h(-1). This was significantly lower than using propofol alone (5.8 mg kg(-1) h(-1)). Nb latency was the best MLAER discriminator of unconsciousness (sensitivity 94%, specificity 88%), with a threshold of 46 ms (propofol alone was 53 ms). The addition of alfentanil did not alter the relationship between propofol infusion rate and MLAER. The vertex-inion electrode site gave the best protection against PAR in awake subjects (P=0.0003), and after 30 min of propofol infusion (P=0.06). The magnitude of the MLAER obtained from the vertex-mastoid electrodes was larger than from the other site, although the increase was not consistent throughout the waveform (brain stem 100%, Nb 14%). CONCLUSIONS: Addition of alfentanil lowers the propofol infusion rate required to produce unconsciousness and the Nb latency that predicts it. The better of the two sites to reduce the incidence of PAR is the vertex-inion electrode site.

Alfentanil↗
PubMed2004

Agitation and changes of Bispectral Index and electroencephalographic-derived variables during sevoflurane induction in children: clonidine premedication reduces agitation compared with midazolam.

BACKGROUND: This double-blind randomized study was undertaken to assess agitation, Bispectral Index (BIS) and EEG changes during induction of anaesthesia with sevoflurane in children premedicated with midazolam or clonidine. METHODS: Children were allocated randomly to receive rectal midazolam 0.4 mg kg(-1) (n=20) or oral clonidine 4 microg kg(-1) (n=20) as premedication. Rapid induction of anaesthesia was achieved with inhalation of sevoflurane 8% in nitrous oxide 50%-oxygen 50%. After tracheal intubation, the children's lungs were mechanically ventilated and the inspired sevoflurane concentration was adjusted to achieve an end-tidal fraction of 2.5%. The EEG and BIS were recorded during induction until 10 min after tracheal intubation. The EEG was analysed using spectral analysis at five points: baseline, loss of eyelash reflex, 15 s before the nadir of the BIS (BIS(nadir)), when both pupils returned to the central position (immediately before intubation), and 10 min after intubation. RESULTS: Agitation was observed in 12 midazolam-treated and five clonidine-treated patients (P=0.05). At baseline, EEG rhythms were slower in the clonidine group. Induction of anaesthesia was associated with similar EEG changes in the two groups, with an increase in total spectral power and a shift towards low frequencies; these changes were maximal around the end of the second minute of induction (BIS(nadir)). When the pupils had returned to the central position, fast EEG rhythms increased and BIS was higher than BIS(nadir) (P<0.05). In both groups, agitation was associated with an increase in slow EEG rhythms at BIS(nadir). CONCLUSIONS: Compared with midazolam, clonidine premedication reduced agitation during sevoflurane induction. During induction with sevoflurane 8% (oxygen 50%-nitrous oxide 50%), the nadir of the BIS occurred at the end of the second minute of inhalation. Agitation was associated with a more pronounced slowing of the EEG rhythms at BIS(nadir) compared with inductions in which no agitation was observed. The BIS may not follow the depth of anaesthesia during sevoflurane induction in children.

Adjuvants, Anesthesia↗