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Biomedical subjects

G Meakin

Publications and source records attributed to G Meakin.

At least 19 recordsLinked to original sources
PubMed1999

Effective time to satisfactory intubation conditions after administration of rocuronium in adults. Comparison of propofol and thiopentone for rapid sequence induction of anaesthesia.

We determined the effective time to satisfactory intubation conditions after the administration of rocuronium 0.6 mg.kg-1 to 120 unpremedicated adult patients anaesthetised with propofol 2.5 mg.kg-1 or thiopentone 5 mg.kg-1. Intubation conditions were assessed in 10 subgroups of 12 patients at 30, 40, 50, 60 and 70 s. The effective times to satisfactory intubation conditions in 50 and 90% of patients were obtained by the method of maximum likelihood after log time-probit response transformations. Intubation conditions after induction of anaesthesia with propofol were satisfactory in 5/12 patients at 30 s, 7/12 at 40 s, 10/12 at 50 s, 11/12 at 60 s and 11/12 at 70 s compared with 1/12 patients at 30 s, 2/12 at 40 s, 5/12 at 50 s, 7/12 at 60 s and 8/12 at 70 s after induction with thiopentone. The effective times to satisfactory intubation conditions in 50% and 90% (95% confidence intervals) of patients after rocuronium 0.6 mg.kg-1 were 34 (26-40) s and 61 (50-81) s in patients given propofol compared with 57 (48-69) s and 101 (79-167) s in patients given thiopentone. We conclude that rocuronium 0.6 mg.kg-1 may be a suitable alternative to suxamethonium during rapid sequence induction of anaesthesia with propofol in situations where suxamethonium is contraindicated.

Adolescent↗
PubMed1997

Oral midazolam compared with diazepam-droperidol and trimeprazine as premedicants in children.

Ninety children were assigned randomly to one of three groups for premedication with oral midazolam 0.5 mg.kg-1, diazepam 0.25 mg.kg-1 with droperidol 0.25 mg.kg-1, or trimeprazine 2 mg.kg-1. On arrival at the anaesthetic room, anxiolysis was satisfactory in 26 out of 29 (90%) children who received midazolam compared with 23 out of 29 (79%) who received diazepam-droperidol and 18 out of 29 (62%) who received trimeprazine (P < 0.05); at induction of anaesthesia these proportions were 24 out of 29 (83%), 16 out of 29 (55%) and 11 out of 29 (40%) respectively (P < 0.001). When individual groups were compared, anxiolysis was significantly greater in the midazolam group compared with the trimeprazine group on arrival in the anaesthetic room (P < 0.05) and significantly greater in the midazolam group than in either the diazepam-droperidol or the trimeprazine groups at induction of anaesthesia (P < 0.05 and P < 0.001 respectively). There were no significant differences in times to early recovery between the groups (25.4, 24.4 and 28.5 min). Analysis of behavioural questionnaires completed two weeks after hospitalization showed a trend towards fewer postoperative behavioural disturbances in children who received midazolam or diazepam-droperidol compared with trimeprazine (47 and 44% vs 75%); when the results for the benzodiazepine-containing premedicants were combined, the difference between these groups and trimeprazine was statistically significant (P < 0.05).

Adjuvants, Anesthesia↗
PubMed1997

A comparison of acceleromyography and mechanomyography for determination of the dose-response curve of rocuronium in children.

In order to compare an acceleromyograph (TOF-Guard) with a mechanomyograph (Grass FT03), the dose-response relationship of rocuronium was simultaneously determined in both arms of 15 children aged 3-11 years during anaesthesia with thiopentone, alfentanil and nitrous oxide. Three subgroups of five children received rocuronium 120, 180 or 240 micrograms.kg-1 randomly. The effective doses to produce 50% and 95% depression of the first twitch of the train-of-four determined by acceleromyography were 206 and 337 micrograms.kg-1, respectively, while these values determined by mechanomyography were 151 and 331 micrograms.kg-1, respectively. The dose-response curve obtained by acceleromyography was steeper and shifted to the right compared with that obtained by mechanomyography (p < 0.0001). The difference between the effective dose producing 50% twitch depression determined by the two devices was highly significant (p < 0.0001). In 13 out of 15 children, the acceleromyograph control train-of-four ratio was significantly greater than unity. Although there was a good correlation (r = 0.85) between simultaneous pairs of measurements of neuromuscular block, the acceleromyograph exhibited a bias of -25% relative to the mechanomyograph with wide limits of agreement (-62 to +12%). We conclude that acceleromyographic and mechanomyographic measurements should not be used interchangeably when determining the potency of muscle relaxants.

Androstanols↗
PubMed1997

Dose-response relationship and effective time to satisfactory intubation conditions after rocuronium in children.

We assessed the neuromuscular blocking effects of, and intubation conditions following, rocuronium in 81 children aged 2-12 years. The study was conducted in three parts. Parts 1 and 2 were undertaken during anaesthesia with thiopentone, alfentanil and nitrous oxide. Neuromuscular blockade was evaluated by recording the force of contraction of the adductor pollicis in response to train-of-four stimulation at 2 Hz repeated every 10s. In Part 1 the potency of rocuronium was determined in 15 children using a single dose-response technique; in Part 2 onset and recovery times were determined in six children following rocuronium 0.6 mg.kg-1. In Part 3 of the study, intubation conditions were assessed in five groups of 12 children whose tracheas were intubated 30, 40, 50, 60 and 70s after rocuronium 0.6 mg.kg-1 during anaesthesia with thiopentone. The times to satisfactory intubation conditions in 50% and 90% of children were determined by probit analysis. The effective doses of rocuronium to produce 50% and 95% twitch depression were 151 micrograms.kg-1 (95% confidence intervals: 129-173 micrograms.kg-1) and 331 micrograms.kg-1 (95% confidence intervals: 249-543 micrograms.kg-1), respectively. The mean times (SD) to 90% and 100% depression of control twitch following rocuronium 0.6 mg.kg-1 were 42 (11.8) s and 60.3 (19.3) s, respectively. The times to 5%, 25%, 75% and 90% recovery were 20.5 (3.1) min, 26.1 (4.1) min, 35.1 (5.4) min, and 39.5 (6.4) min, respectively. Intubation conditions were satisfactory in 4/12 children at 30 s, 6/12 at 40 s, 8/12 at 50 s, 11/12 at 60 s and 12/12 at 70 s. The times to satisfactory intubation conditions in 50% and 90% of children after rocuronium 0.6 mg.kg-1 were 38 s (95% confidence intervals: 30-44 s) and 61 s (95% confidence intervals: 55-70 s), respectively.

Androstanols↗
PubMed1996

Dose of propofol for laryngeal mask airway insertion in children: effect of premedication with midazolam.

We determined the dose-response curves and effective doses of propofol for insertion of the laryngeal mask airway (LMA) in 50 unpremedicated children and in 60 children premedicated with midazolam, aged 3-12 yr. One of several doses of propofol was administered i.v. over 15 s to groups of 10 children, and conditions for LMA insertion were assessed at 60 s. The dose-response curves were parallel (P = 0.94), but the curve for premedicated children was shifted significantly to the left of that for unpremedicated children and propofol requirements were reduced by one-third (P < 0.0001). The doses required for satisfactory LMA insertion in 50% and 90% of unpremedicated patients (ED50, ED90) (95% confidence interval) were 3.8 (3.4-4.2) mg kg-1 and 5.4 (4.7-6.8) mg kg-1, respectively; those for premedicated patients were 2.6 (2.2-2.8) mg kg-1 and 3.6 (3.2-4.3) mg kg-1, respectively.

Anesthetics, Intravenous↗
PubMed1996

Dose-response and minimum time to satisfactory intubation conditions after mivacurium in children.

We assessed neuromuscular blocking effects and tracheal intubation conditions following mivacurium in 121 anaesthetised children aged 1-10 years. The study was conducted in three parts. Parts 1 and 2 were undertaken during thiopentone-alfentanil-nitrous oxide anaesthesia; neuromuscular blockade was evaluated by recording the force of contraction of the adductor pollicis in response to train-of-four stimulation at 0.1 Hz. In part 1 the potency of mivacurium was determined in 15 children using a single dose-response technique; in part 2 onset and recovery times were determined in six children following a dose of mivacurium 0.2 mg.kg-1. In part 3 of the study, clinical intubation conditions were assessed in two groups of 50 children whose tracheas were intubated 60 or 90 s after injection of mivacurium 0.2 mg.kg-1 during thiopentone-nitrous oxide anaesthesia. The ED50 and ED95 of mivacurium were 54 and 105 micrograms.kg-1 respectively. The times to 90% and 100% depression of control twitch were 1.3 (0.3) and 1.9 (0.5) min; times to 5%, 25%, 75% and 90% recovery were 6.4 (1.0), 8.4 (1.1), 12.5 (1.1) and 14.4 (1.9) min, respectively. Intubation conditions were rated satisfactory in 33/50 children (0.66, 95% confidence interval 0.51-0.79) at 60 s and in 49/50 children (0.98, 95% confidence interval 0.89-1.0) at 90 s (p = 0.0001). Intubation conditions 90 s after mivacurium 0.2 mg.kg-1 were significantly better than those obtained in 10 patients given anaesthetic drugs alone (p = 0.002).

Alfentanil↗
PubMed1996

Economics of low-flow anaesthesia in children.

We have measured the consumption of isoflurane and fresh gas flows in 77 infants and children during 20 all-day operating sessions using either the enclosed Mapleson A or the circle absorber mode of the Carden 'Ventmasta' ventilator. The average consumption (SD) of isoflurane in 37 patients anaesthetised using the A mode of the Carden system with a mean fresh gas flow of 2.61 min-1 was 11.1 (4.2) g.h-1, while that in 40 patients anaesthetised using the circle absorber mode with a mean fresh gas flow of 1.21 min-1 was 4.7 (1.0) g.h-1. These figures represent an overall saving of 58% in the use of isoflurane (p < 0.0001) and a mean reduction in fresh gas flow of 54% (p < 0.0001) as a result of using low-flow anaesthesia. With the addition of small bore breathing hoses the adult circle absorber system was practical to use in both infants and children. These findings should stimulate interest in the use of low-flow techniques in children.

Adolescent↗
PubMed1994

Efficiency of the Carden "Ventmasta" in A and D modes during controlled ventilation in children.

We have determined the efficiencies of the enclosed Mapleson A and Mapleson D modes of the Carden "Ventmasta" ventilator during controlled ventilation in 19 anaesthetized children. In addition, we determined the suitability for the A mode of the fresh gas formula, VF = 0.6 x weight0.5. Efficiency was assessed in terms of the fraction of fresh gas delivered to the alveoli. When the minute volume to fresh gas flow ratio exceeded 1.5, fractional delivery of fresh gas was 23% greater in the A mode than in the D mode (0.74 vs 0.60) (P < 0.0001). Under the same conditions, mean end-tidal carbon dioxide concentration in 27 children undergoing ventilation in the A mode with VF = 0.6 x weight0.5 was 4.6% (range 3.5-5.4%). We conclude that the Carden system is up to 23% more efficient in the A mode than in the D mode, and that under the conditions of this study, normocapnia or mild hypocapnia was produced accurately using the formula VF = 0.6 x weight0.5.

Adolescent↗
PubMed1993

Fresh gas requirements of an enclosed afferent reservoir breathing system in anaesthetized, spontaneously breathing adults.

Using two methods of determining the onset of rebreathing, we have determined the minimum fresh gas flow rate (VF) of the Ohmeda enclosed afferent reservoir breathing system (EAR) in anaesthetized, spontaneously breathing adults. Rebreathing as defined by the Kain and Nunn criteria did not occur when the VF/VE ratio was greater than 0.70. A mathematical model was used to calculate the degree of rebreathing at each VF. From this model, rebreathing did not occur when VF was 0.86 VE or more and this value of VF/VE is considered appropriate to eliminate rebreathing in clinical practice.

Aged↗
PubMed1992

Fresh gas requirements of an enclosed afferent reservoir breathing system during controlled ventilation in children.

An enclosed afferent reservoir breathing system (EAR) designed by Ohmeda was evaluated during anaesthesia with controlled ventilation in 104 healthy children. Carbon dioxide production and arterial carbon dioxide tension were measured in 12 children in order to determine the proportion of fresh gas (VF) involved in gas exchange. When the ratio of minute volume ventilation to fresh gas flow (VE:VF) exceeded 1.5, fractional utilization of fresh gas with the EAR was 0.92. This value and values of carbon dioxide production obtained from 43 children were used to derive a simple formula relating fresh gas flow requirements to body weight. The formula, VF = 0.6 x weight 0.5, was assessed in 49 children weighing 10-70 kg. The mean end-tidal partial pressure of carbon dioxide in these patients was 4.5 kPa (range 3.8-5.2 kPa). We conclude that the EAR has an efficiency of 92% in the use of fresh gas during controlled ventilation in healthy children, provided the VE:VF ratio is greater than 1.5. Under these conditions, normocapnia to mild hypocapnia was produced accurately using the formula VF = 0.6 x weight 0.5.

Adolescent↗
PubMed1992

Age-dependent variation in response to tubocurarine in the isolated rat diaphragm.

The EC50 of tubocurarine was determined in phrenic nerve-hemidiaphragm preparations obtained from 35 Sprague-Dawley rats aged 0-46 days. We measured also the ratio of the fourth to the first twitch in the train-of-four (T4:T1) when the first twitch of the train was depressed to 50% of control. The preparation was not unduly sensitive to tubocurarine at 0 days and there was little evidence of T4:T1 fade. However, by age 11 days the preparation exhibited fade and a three-fold sensitivity to tubocurarine similar to that in the human neonate. We conclude that the phrenic nerve-hemidiaphragm preparation from 11-day-old rats should be a suitable model in which to investigate the biochemical and electrophysiological basis of the sensitivity seen in humans.

Age Factors↗
PubMed1992

Fresh gas requirements of an enclosed afferent reservoir breathing system in anaesthetized, spontaneously ventilating children.

We have determined the minimum fresh gas flow rate (VF) for use with the Ohmeda enclosed afferent reservoir breathing system (EAR) in 10 anaesthetized children breathing spontaneously. First, we determined the VF required to prevent rebreathing as detected by increased total ventilation (VE) and end-tidal carbon dioxide partial pressure. Second, we used a mathematical model to calculate the degree of rebreathing occurring at each VF. A VF equal to the predicted alveolar ventilation was sufficient to prevent clinically detectable rebreathing in all patients. From the model, no rebreathing occurred when VF/VE was 0.78 or more. We have shown previously that the EAR functions efficiently during controlled ventilation with a VF = 0.6 x weight 0.5. As this VF is slightly greater than the predicted alveolar ventilation, we suggest that the EAR may be used with a VF = 0.6 x weight 0.5 regardless of the mode of ventilation.

Adolescent↗