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Biomedical subjects

G Meakin

Publications and source records attributed to G Meakin.

At least 37 records · Page 2Linked to original sources
PubMed1992

Physical characteristics of an enclosed afferent reservoir breathing system.

We have assessed the characteristics of the Ohmeda Enclosed Afferent Reservoir Breathing System (EAR) using simulated spontaneous ventilation and controlled ventilation. The additional work of breathing through the system was measured and shown to be comparable to that of a modified Mapleson D breathing system (Bain) for fresh gas flows producing similar end-tidal carbon dioxide concentrations. It was shown under conditions of simulated controlled ventilation that end-tidal gas concentration was relatively insensitive to variations in inspired to expired ratio (I: E), tidal volume (VT) and deadspace (VD). Measurement of the volume of carbon dioxide rebreathed using simulated spontaneous ventilation led to the prediction that rebreathing of carbon dioxide would begin to occur in the EAR when fresh gas flow to total ventilation ratio (VF: VE) was approximately 0.87. However, comparison of the results of model lung tests and clinical data suggests that great caution should be taken in extrapolating such results into clinical advice.

Anesthesia, Closed-Circuit↗
PubMed1992

Fractional delivery of fresh gas: a new index of the efficiency of semi-closed breathing systems.

In earlier clinical studies, we have found a significant difference in the fractional utilization of fresh gas (FU) when using an enclosed afferent reservoir breathing system (EAR) for adult patients compared with children. This difference was explained by a large arterial to end-tidal carbon dioxide difference in the adults, reflecting a larger alveolar deadspace. In the present study, a new index of breathing system efficiency, fractional delivery of fresh gas (Fd) is proposed, which is independent of alveolar deadspace. In order to demonstrate this, values of Fd were calculated for the EAR during controlled ventilation of adults, children and a lung model. There were no significant differences between the groups. A maximum efficiency of 0.94 for the EAR was close to the theoretical limit of 1.0 predicted by the results at minute volume ventilation to fresh gas flow ratio (VE:VF) values greater than 2.0. For adult patients, the values of Fd were shown to be significantly greater than the values of FU at the same VE:VF ratio (Fd = 0.91, FU = 0.72 at VE:VF = 2.0 (P < 0.05)).

Adolescent↗
PubMed1991

Efficiency of an enclosed afferent reservoir breathing system during controlled ventilation.

We describe an enclosed afferent reservoir (EAR) breathing system developed by Ohmeda and designed to operate efficiently in spontaneous and controlled ventilation. The efficiency of the system was evaluated by calculating the fractional utilization of fresh gas in 10 ASA I-III patients during anaesthesia with controlled ventilation. Maximum efficiency occurred when the minute ventilation to fresh gas flow ratio was greater than 1.5. Under these conditions, fractional utilization was relatively constant with a value of 0.73 (95% confidence interval 0.69-0.78). The minimum fresh gas flow for use during controlled ventilation was determined in another eight ASA I-III patients when the minute volume to fresh gas ratio was greater than 1.5. In view of an increased arterial to end-tidal carbon dioxide partial pressure difference in patients in the first part of the study (1.03 kPa), normocapnia was defined as an end-tidal carbon dioxide partial pressure of 4.3 kPa. Normocapnia was achieved with a mean fresh gas flow of 66 ml kg(-1) min(-1), while 70 ml kg(-1) min(-1) produced mild hypocapnia.

Aged↗
PubMed1991

Antagonism of intense atracurium-induced neuromuscular block in children.

Antagonism of intense neuromuscular block induced by atracurium 0.5 mg kg-1 was attempted in four groups of six children using one of two doses of neostigmine (0.05 mg kg-1 and 0.1 mg kg-1) or of edrophonium (0.5 mg kg-1 and 1.0 mg kg-1) when the first twitch of the post-tetanic count (PTC1) was 10% of control. For comparison with normal practice, a fifth group received neostigmine 0.05 mg kg-1 when the first twitch of the train-of-four was 10% of control. Total recovery time from PTC1 10% to a train-of-four ratio of 0.8 was not reduced by early administration of the anticholinesterases, compared with conventional administration of neostigmine at T1 10%. However, recovery from intense block was faster after neostigmine than edrophonium (P less than 0.01). Doubling the doses of the anticholinesterases did not reduce the recovery time and had the effect of increasing variability. We conclude that there is no clinical advantage in attempting to antagonize intense neuromuscular block in children using normal or increased doses of neostigmine or edrophonium.

Atracurium↗
PubMed1991

Dose requirements of atracurium in paediatric intensive care patients.

The dose requirements of atracurium were determined in 12 children who required an infusion of atracurium to facilitate mechanical ventilation in the intensive care unit. The mean duration of infusion was 98 h (range 36-284 h) during which an increasing dose requirement was observed in all patients. The mean infusion rate was 1.60 (SEM 0.08) mg kg-1 h-1, and in seven patients a mean infusion rate of 1.72 (0.15) mg kg-1 h-1 was observed at 72 h. These rates are greater than those reported previously in adults. Cessation of neuromuscular block occurred promptly upon discontinuing the infusion. No side effects were observed which could be attributed to the infusion of atracurium.

Adolescent↗
PubMed1990

Myotonic and neuromuscular blocking effects of increased doses of suxamethonium in infants and children.

The myotonic effects and duration of action of several doses of suxamethonium were determined in 24 infants and 16 children during thiopentone-fentanyl-nitrous oxide anaesthesia. Infants received suxamethonium 2, 3 or 4 mg kg-1; children received 1 or 2 mg kg-1. The increase in muscle tone during onset of neuromuscular block was independent of dose. Onset of block was faster in children who received suxamethonium 2 mg kg-1 compared with those who received 1 mg kg-1, and in infants given 2 mg kg-1 than in children given the same dose. Compared with adults given suxamethonium 1 mg kg-1, infants required 3-4 mg kg-1 and children at least 2 mg kg-1 to produce 6-8 min of neuromuscular block. These results provide a clear indication for increasing the intubating doses of suxamethonium in infants and children, and a explanation for the unduly high rate of "masseter spasm" in some paediatric centres.

Anesthesia, General↗
PubMed1989

Dose-response curves for suxamethonium in neonates, infants and children.

Single dose-response curves were determined for suxamethonium in neonates, infants and children during thiopentone-fentanyl-nitrous oxide anaesthesia. During onset of neuromuscular block, suxamethonium produced an increase in muscle tone which was greatest in neonates and infants. The dose-response curves for the three groups were parallel. The effective doses producing 90% depression of twitch height were significantly greater in neonates and infants compared with children (517 and 608 v. 352 micrograms kg-1). These values were greater than those obtained in a comparable study in adults. In view of their higher ED values compared with adults and a marked individual variability in response to small doses of suxamethonium, we recommend an intubating dose of 3 mg kg-1 for neonates and infants and 2 mg kg-1 for children. These doses are 50-100% greater than those previously recommended for paediatric patients.

Anesthesia↗
PubMed1988

Comparison of atracurium-induced neuromuscular blockade in neonates, infants and children.

The potency of atracurium was determined in neonates, infants and children during thiopentone-fentanyl-nitrous oxide in oxygen anaesthesia using single dose-response curves. The effective doses producing 50% depression of the first twitch of the train-of-four were significantly lower in neonates and infants than in children (82 and 112 v. 135 micrograms kg-1). Following a standard dose of atracurium 0.5 mg kg-1, 95% depression of the first twitch occurred more rapidly in neonates than in children (0.9 v. 1.4 min), while recovery to 10% of the control twitch height occurred more rapidly in neonates than in the other two groups (22.7 v. 29.7 and 28.6 min). It is concluded that neonates and infants require less atracurium to produce a given degree of neuromuscular blockade compared with older children. However, prompt recovery can be expected in all healthy paediatric patients following a standard intubating dose of atracurium 0.5 mg kg-1.

Anesthesia, General↗
PubMed1988

Use of the post-tetanic count to monitor recovery from intense neuromuscular blockade in children.

The post-tetanic count was investigated as a method of monitoring intense neuromuscular blockade in children. One of five myoneural blockers (atracurium, vecuronium, pancuronium, tubocurarine or alcuronium) was given to groups of six children during nitrous oxide-oxygen-halothane anaesthesia. During recovery, the first post-tetanic response always preceded the first train-of-four response. The interval between the appearance of the first post-tetanic response and the first train-of-four response was typically 5-10 min for the intermediate-acting agents vecuronium and atracurium, and 20-30 min for the long-acting agents pancuronium, alcuronium and tubocurarine. A post-tetanic count of 6 with alcuronium and tubocurarine, or 7 with vecuronium, atracurium and pancuronium indicated that recovery of the first train-of-four response was imminent.

Anesthesia, Inhalation↗
PubMed1987

Effects of fasting and oral premedication on the pH and volume of gastric aspirate in children.

The pH and volume of gastric aspirate were measured immediately after the induction of anaesthesia in 224 healthy children to determine the effects of decreasing the period of fasting and of giving oral premedicants before anaesthesia. Fasting for less than 4 h was found to increase the volume of gastric aspirate and the risk of developing pulmonary aspiration syndrome. Trimeprazine syrup was found to increase the pH of the gastric contents, and decrease the likelihood of the pulmonary aspiration syndrome. There was a significant increase in gastric volume in patients premedicated with temazepam elixir which did not occur in patients given temazepam capsules. These results support the custom of fasting patients for at least 4 h before anaesthesia and indicate that oral premedicants and their vehicles can have significant effects on the stomach.

Administration, Oral↗
PubMed1986

Blood glucose in anaesthetised children. Comparison of blood glucose concentrations in children fasted for morning and afternoon surgery.

Blood glucose levels were measured immediately after induction of anaesthesia and again intraoperatively in 26 children fasted overnight for operations in the morning and 28 children fasted from 8.00 a.m. for afternoon surgery. The mean post-induction glucose concentration of the afternoon surgery group was significantly lower than that of the morning group. However, no child in either group was hypoglycaemic. Anesthesia and surgery caused significant increases in blood glucose levels. It is concluded that pre-operative fasting is well tolerated in healthy pre-school children, regardless of the timing of surgery.

Anesthesia, General↗