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Biomedical subjects

A Ewen

Publications and source records attributed to A Ewen.

10 recordsLinked to original sources
PubMed2001

The prone position is associated with a decrease in respiratory system compliance in healthy anaesthetized infants.

Ten healthy (ASA I or II) anaesthetized infants undergoing clubfoot surgery were studied. General anaesthesia included rocuronium, nitrous oxide and isoflurane. Volume controlled ventilation (12 ml.kg-1) was delivered via a coaxial Mapleson-D (Bain) system and a Datex AS/3 ventilator. Pulmonary mechanics were measured sequentially in the supine and prone positions using a Bicore CP-100 pulmonary function monitor. Subjects had a mean age of 6 (+/- 2) months and a mean weight of 8.3 (+/- 1.4) kg. Dynamic compliance (CDYN) and static compliance (CSTAT) were both significantly lower in the prone position than in the supine position (P < 0.0005). Mean CDYN decreased from 14.9 +/- 4.9 ml.cmH2O-1 (supine) to 11.6 +/- 3.5 ml.cmH2O-1 (prone). Mean CSTAT decreased from 10.2 +/- 2.8 ml.cmH2O-1 (supine) to 8.9 +/- 2.3 ml.cmH2O-1 (prone). No clinically significant differences in gas exchange were noted, however, on repositioning.

Anesthesia, General↗
PubMed1996

Thiopentone induced enhancement of somatic motor responses to noxious stimulation: influence of GABAA receptor modulation.

PURPOSE: This study was conducted to determine whether hyperalgesic effects of subanaesthetic concentrations of thiopentone could be attributed to GABAA receptor effects. METHODS: All studies were performed on 50 rats in a prospective, randomized, blinded fashion using saline-injected animals as controls. Using a modified Randall-Selitto technique, the motor behavior stimulated by noxious stimulation was quantified by determining the lowest tail pressure required to provoke a withdrawal response (somatic motor response threshold, SMRT). In the first protocol (21 rats), we studied the effects of 0.5, 1.5 and 5 mg.kg-1 i.v. of the GABAA agonist, muscimol, on SMRT. In the second protocol (20 rats), the effects of administration of saline, muscimol 0.5 mg.kg-1, or the competitive GABAA antagonist, bicuculline 0.25 mg.kg-1, upon the SMRT-reducing effects of a standardized thiopentone infusion were observed. RESULTS: No dose of muscimol produced hyperalgesia. The highest dose of muscimol used (5 mg.kg-1) produced pronounced analgesic effects, raising the SMRT above 750 g. No change in SMRT was detected with the smaller doses of muscimol. Given in combination with muscimol (0.5 mg.kg-1), thiopentone produced analgesia, as shown by an increase in SMRT (P = 0.009). In the bicuculline treated animals, SMRT decreased linearly with increasing plasma thiopentone concentrations (P < 0.001). The slope of the relationship in the bicuculine group was not significantly different from that observed in the saline-treated group, indicating that bicuculline did not block the hyperalgesic effects of thiopentone. CONCLUSION: The results of these studies suggest that hyperalgesia associated with thiopentone is not mediated primarily by GABAA receptors.

Animals↗
PubMed1995

Hyperalgesia during sedation: effects of barbiturates and propofol in the rat.

Subhypnotic doses of thiopentone are considered to possess antianalgesic or hyperalgesic properties. In this study, we have tested the hypothesis that the coincidence of sedation and hyperalgesia is a property of both barbiturate and non-barbiturate anaesthetic agents. In a randomized, prospective, blinded study, the effects of slow (20 min) iv infusions of thiopentone, pentobarbitone, methohexitone or propofol on nociceptive threshold were measured in rats by tail pressure analgesimetry and compared with saline-infused control animals. Nociceptive thresholds were correlated with measurements of plasma drug concentrations and behavioural assessments. Comparison of pre-infusion nociceptive threshold with the lowest threshold obtained during drug infusion revealed decreases in all four treatment groups. As a percentage of the pre-infusion values, the decreases were: thiopentone: 42.5% (P < 0.001), pentobarbitone: 27.8% (P = 0.014), methohexitone: 24.9% (P = 0.013), propofol: 21.6% (P = 0.006). There were no changes in nociceptive threshold in the control groups. The relationship between nociceptive threshold and plasma drug concentration was usually characterized by an initial decline followed by a rise in nociceptive threshold as the plasma concentration and degree of sedation increased. The results support the hypothesis that hyperalgesia is a property of different anaesthetic agents when administered at sub-hynotic concentrations.

Animals↗
PubMed1994

Plasma, brain, and spinal cord concentrations of thiopental associated with hyperalgesia in the rat.

BACKGROUND: Although low doses of barbiturates are widely believed to increase sensitivity to pain, studies of the electrophysiologic effects of these drugs on the neurons involved in nociception in the spinal cord have detected only depressant effects. The goal of the studies reported here was to quantify the hyperalgesia resulting from low-dose thiopental infusions and to measure the associated concentrations of thiopental in the plasma, brain, and spinal cord. METHODS: Nociception was measured using the threshold for motor response to pressure stimulation of the tail (nociceptive threshold) and tail flick latency in the rat. Thiopental was administered by intravenous infusions designed to produce plasma concentrations that either slowly increased or remained at a steady state. Plasma and tissue thiopental concentrations were measured by high-performance liquid chromatography. RESULTS: We observed a reduction in nociceptive threshold that was correlated with the plasma thiopental concentration over the range 2-20 micrograms.ml-1 (7.6-76 microM). The relationship was nonlinear. Nociceptive threshold reached a nadir (36% less than control values) at a mean plasma thiopental concentration of 13.7 micrograms.ml-1 (51.9 microM). The steady-state study showed a similar reduction in nociceptive threshold, with an equilibrium plasma thiopental concentration of 7.6 +/- 1.3 micrograms.ml-1 (28.8 +/- 4.9 microM). Concentrations of thiopental in brain and spinal cord samples were 1.7 +/- 0.03 and 3.5 +/- 1.7 micrograms.g-1, respectively. CONCLUSIONS: These studies confirm previous reports of hyperalgesia in association with small doses of thiopental. Reductions in nociceptive threshold and tail flick latency were observed in association with spinal cord concentrations of thiopental in a range reported by others to depress the electrophysiologic activity of neurons involved in nociception.

Animals↗
PubMed1992

Exposure of operating room personnel to nitrous oxide during paediatric anaesthesia.

This study was undertaken to quantify the exposure of operating room staff to nitrous oxide during routine paediatric otolaryngeal surgery and to determine the influence of the method of induction of anaesthesia on this exposure. The nitrous oxide exposure of the anaesthetist, the surgeon and the circulating nurse were measured, using body-worn passive atmospheric samplers, during twelve routine paediatric otolaryngeal surgical lists. During six of the lists an inhalational technique, with nitrous oxide, oxygen and halothane, was used for the induction of anaesthesia. During the other six lists anaesthesia was induced using intravenous thiopentone. In all cases, anaesthesia was maintained using nitrous oxide, oxygen and halothane. Regardless of the induction technique used, the mean nitrous oxide exposures of the anaesthetist, the surgeon and the nurse all exceeded the maximum level of 25 ppm.hr-1 recommended by the United States National Institute for Occupational Safety and Health (NIOSH). The use of an intravenous technique for the induction of anaesthesia reduced the nitrous oxide exposure of the anaesthetist and the circulating nurse. This suggests that, although the use of an intravenous induction may reduce exposure to nitrous oxide, the NIOSH recommendations for maximum exposure of operating room personnel to nitrous oxide are currently unattainable in practice.

Adult↗
PubMed1988

Gastric fluid volume, pH, and emptying in elective inpatients. Influences of narcotic-atropine premedication, oral fluid, and ranitidine.

One hundred and twenty healthy, elective surgical inpatients were randomly assigned to one of four groups. Between two and three hours before the scheduled time of surgery all patients ingested a marker dye, phenol red, 50 mg in 10 ml water, with placebo tablet alone (Groups 1 and 2), placebo tablet with 150 ml oral fluid (Group 3), or oral ranitidine 150 mg with oral fluid 150 ml (Group 4). Patients in Group 1 received oral diazepam or no premedication, while those in Groups 2, 3, and 4 received IM narcotic and atropine one hour preoperatively. Following induction of anaesthesia the residual gastric fluid was aspirated through a Salem sump tube and its volume, pH, and phenol red content measured. Mean volumes were Group 1: 24 ml; Group 2: 13 ml; Group 3: 17 ml; Group 4: 14 ml. Mean pH values were Group 1: 2.99; Group 2: 3.03; Group 3: 3.44; Group 4: 5.28. The amount of phenol red in the samples indicated at least 90 per cent gastric emptying had occurred in 90 per cent of patients. We conclude that, in healthy patients, 150 ml oral fluid is almost completely emptied from the stomach within two hours of ingestion, even when followed one hour later by narcotic-atropine premedication.

Adolescent↗
PubMed1986

Continuous infusion epidural analgesia in obstetrics. A comparison of 0.08% and 0.25% bupivacaine.

The effects of 0.08% (Group A) and 0.25% (Group B) solutions of bupivacaine were compared in a random manner, to assess continuous pump infusion epidural analgesia in labour. Both solutions were infused at a dose rate of 20 mg bupivacaine/hour. The results in all the mothers who had received infusions lasting more than 4 hours were studied. There were 25 in Group A and 28 in Group B. Any treatment during the infusion epidural for inadequate analgesia, hypotension, etc., was recorded as an intervention. The mean of the intervention-free intervals was significantly greater in Group A than in Group B, and significantly fewer top-up injections were required in Group A. The results show that the administration of a 0.08% solution of bupivacaine into the epidural space by continuous pump infusion is more labour saving than the infusion of a 0.25% solution. The concept that a greater volume infusion rate maintains a more extended liquid sleeve of local anaesthetic in the epidural space is supported.

Adult↗