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Biomedical subjects

D J Murray

Publications and source records attributed to D J Murray.

At least 19 recordsLinked to original sources

Pancreatic duct obstruction treated with percutaneous antegrade insertion of a metal stent: report of two cases.

Expanding metal stents were used to treat symptomatic pancreatic duct obstruction in two patients with chronic pancreatitis. Both patients initially underwent percutaneous external pancreatic duct drainage and then had metal stents inserted for internal drainage. Both patients remained asymptomatic, and the stents were patent during short-term follow-up periods of 6 and 9 months, respectively. Percutaneous insertion of metal stents, which can be performed to treat pancreatic duct obstruction after a trial of external drainage has been shown to relieve the patient's symptoms, should be considered as an alternative to endoscopic stent placement or surgical drainage.

Aged

Comparative hemodynamic depression of halothane versus isoflurane in neonates and infants: an echocardiographic study.

The purpose of this study was to measure and compare the relationship of cardiovascular depression and dose during equal potent levels of halothane and isoflurane anesthesia in neonates (n = 19) (16.7 +/- 6.9 days) and infants (n = 54) (6.1 +/- 3.1 mo). Seventy-three children had heart rate, arterial blood pressure, and pulsed Doppler pulmonary blood flow velocity as well as two-dimensional echocardiographic assessments of left ventricular area and length recorded just before anesthesia induction. Anesthesia was induced by inhalation of increasing inspired concentrations of halothane or isoflurane in oxygen using a pediatric circle system and mask. During controlled ventilation, halothane and isoflurane concentrations were adjusted to maintain 1.0 MAC and then 1.5 MAC (corrected for age), and echocardiographic and hemodynamic measurements were repeated. A final cardiovascular measurement was recorded after intravenous administration of 0.02 mg/kg of atropine. All measurements were completed before tracheal intubation and the start of elective surgery. In neonates, 1.0 MAC concentrations of halothane and isoflurane decreased cardiac output (74% +/- 16%), stroke volume (75% +/- 15%), and ejection fraction (76% +/- 15%) similarly from awake levels. Decreases in cardiac output, stroke volume, and ejection fraction with halothane and isoflurane were significantly larger at 1.5 MAC (approximately 35% decreases from awake values) than at 1.0 MAC. Heart rate decreased significantly during 1.5 MAC halothane anesthesia (94% +/- 4%) but remained unchanged during isoflurane anesthesia. In infants, 1.0 MAC halothane and isoflurane decreased cardiac output (83% +/- 12%), stroke volume (78% +/- 12%), and ejection fraction (74% +/- 12%) when compared with awake measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure

Application of digital signal processing to hearing aids: a critical survey.

An audiologic rationale for the application of digital signal processing techniques to hearing aids is developed. These techniques enable complex processing beyond that possible in presently available analog aids. A critical survey of algorithms for filtering, nonlinear processing, noise reduction, speech enhancement, and feedback reduction is presented. The paper concludes with a discussion of practical considerations for implementation.

Algorithms

The additive contribution of nitrous oxide to isoflurane MAC in infants and children.

The purpose of this study was to determine the contribution of nitrous oxide to isoflurane MAC in pediatric patients. MAC was determined in 47 infants and small children (mean ages 16.6 +/- 6.7 months) during isoflurane and oxygen anesthesia (n = 11) and isoflurane and nitrous oxide anesthesia (25% nitrous oxide [n = 12], 50% nitrous oxide [n = 12], and 75% nitrous oxide [n = 12]). After assigning patients to one of four groups, anesthesia was induced with increasing inspired concentrations of isoflurane in oxygen. After anesthetic induction and tracheal intubation, ventilation was controlled (carbon dioxide partial pressure = 32 +/- 5 mmHg), and nitrous oxide was added to the inspired gas mixture to achieve end-expired nitrous oxide concentrations of 0, 25, 50, or 75%. Inspired and expired gas samples were obtained from a distal sampling port in the tracheal tube. The response to skin incision in each patient was assessed at a previously selected end-tidal concentration of isoflurane. The MAC of isoflurane was determined in each group using the up-and-down method described for evaluating quantal responses. The mean duration of constant end-tidal concentrations prior to skin incision was 14 +/- 7 min (range 6-46 min). The ratio of expired to inspired nitrous oxide and isoflurane concentrations during the period of constant end-tidal concentrations was 0.96 +/- 0.01 and 0.93 +/- 0.03 respectively. The MAC of isoflurane in oxygen was 1.69 +/- 0.13 vol% (mean +/- standard deviation).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging

Additive contribution of nitrous oxide to halothane MAC in infants and children.

Fifty-one infants and small children (14.7 +/- 7.2 mo) were studied to determine the MAC of halothane in O2 (n = 11) and in the presence of three different nitrous oxide (N2O) concentrations (25% [n = 13], 50% [n = 13], and 75% [n = 14]). In the three N2O groups, after randomly assigning patients to an N2O group, anesthesia was induced with halothane and N2O using a pediatric circle system. After endotracheal intubation, halothane and N2O end-expired concentrations were adjusted to predetermined concentrations. The initial halothane concentrations in each group were based on the assumption that each percent N2O reduced halothane concentrations by 0.01 vol % (assumed halothane MAC = 1.0 vol %). Based on the response of the preceding subject in each group, halothane concentrations were increased or decreased depending on whether the response was to move or not to move, respectively, in response to the surgical incision. The mean duration of constant end-tidal concentrations before skin incision was 10 min. End-tidal gases were sampled and measured from a separate distal sampling port of an endotracheal tube during controlled ventilation (Perkin-Elmer Mass Spectrometer). The MAC value for halothane in O2 was 0.94 +/- 0.08 vol % (mean +/- SD). The MAC values of halothane in the presence of 25%, 50%, and 75% N2O were 0.78 +/- 0.12 vol %, 0.44 +/- 0.10 vol %, and 0.29 +/- 0.06 vol %, respectively. All concentrations of N2O significantly reduced the MAC of halothane. A regression analysis through all four data points yielded a linear relationship (r2 = 0.87) with a predicted MAC for N2O of 105 vol %. Unlike halothane and isoflurane, the predicted MAC of N2O in infants and children is similar to that reported by others in adults. Similar to the results of clinical studies in adults, the contribution of N2O to halothane MAC in children is additive.

Anesthesia, Inhalation

Haemodynamic effects of rectal methohexitone for induction of anaesthesia in children.

Pulsed Doppler and two-dimensional echocardiography were used to determine the haemodynamic effects of rectal methohexitone in 12 children 32.4 +/- 3.8 months old and weighing 13.3 +/- 1.1 kg (mean +/- SEM). Heart rate, blood pressure and echocardiographic measurements of cardiac output, stroke volume and left ventricular end-diastolic and end-systolic volumes were obtained prior to the induction of anaesthesia. Anaesthesia was induced with 25 mg.kg-1 two per cent rectal methohexitone. Immediately following the onset of sleep all cardiovascular measurements were repeated. Following the induction of anaesthesia with rectal methohexitone there was a significant increase in heart rate. Blood pressure, cardiac index, stroke volume and ejection fraction were unchanged. It is concluded that rectal administration of two per cent methohexitone for the induction of anaesthesia in healthy paediatric patients has minimal haemodynamic effect.

Anesthesia, Rectal

Neuromuscular and cardiovascular effects of mivacurium chloride in surgical patients receiving nitrous oxide-narcotic or nitrous oxide-isoflurane anaesthesia.

The neuromuscular and cardiovascular effects of mivacurium chloride were studied during nitrous oxide-oxygen narcotic (fentanyl) (n = 90) and nitrous oxide-oxygen isoflurane (ISO) anaesthesia (n = 45). In addition, a separate group (n = 9) received succinylcholine during fentanyl anaesthesia to compare its neuromuscular effects with mivacurium. Mivacurium was initially administered as a single bolus in doses from 0.03 mg.kg-1 to 0.25 mg.kg-1 to study the dose-response relationships, as well as the cardiovascular effects of mivacurium. Neuromuscular block (NMB) was measured by recording the twitch response of the adductor pollicis muscle following ulnar nerve stimulation (0.15 Hz, 0.2 ms supramaximal voltage). The ED95 values for mivacurium were estimated to be 0.073 mg.kg-1 and 0.053 mg.kg-1 in the fentanyl and ISO groups respectively. The duration of block (time from injection to 95 per cent recovery) for a dose of 0.05 mg.kg-1 mivacurium was 15.3 +/- 1.0 min and 21.5 +/- 1.3 min for fentanyl and ISO anaesthesia, respectively. The recovery index (25-75 per cent) between initial bolus dose (6.1 +/- 0.5 min), repeat bolus doses (7.6 +/- 0.6 min), mivacurium infusion (6.7 +/- 0.7 min) and succinylcholine infusion (6.8 +/- 1.8 min) were not significantly different. There was minimal change in mean arterial pressure (MAP) or heart rate (HR) following bolus doses of mivacurium up to 0.15 mg.kg-1. Bolus administration of 0.20 mg.kg-1 or 0.25 mg.kg-1 of mivacurium decreased MAP from 78.2 +/- 2.5 to 64.0 +/- 3.2 mmHg (range 12-59 per cent of control) (P less than 0.05). The same doses when administered slowly over 30 sec produced minimal change in MAP or HR.

Adult

Haemodynamic effects of atropine during halothane or isoflurane anaesthesia in infants and small children.

In this study, two-dimensional and pulsed Doppler echocardiography were used to measure cardiovascular changes before and after IV atropine in 31 infants and small children during halothane (n = 15) or isoflurane (n = 16) anaesthesia. Prior to induction of anaesthesia heart rate (HR), mean blood pressure (MBP), and two-dimensional echocardiographic dimensions of the left ventricle and pulmonary artery blood flow velocity were measured by pulsed Doppler echocardiography. Cardiovascular measurements were repeated while anaesthesia was maintained at 1.5 MAC halothane (n = 15) or isoflurane (n = 16). Atropine 0.02 mg.kg-1 IV was then administered and two minutes later, a third set of cardiovascular data was obtained. Heart rate decreased during halothane anaesthesia but did not change significantly during isoflurane anaesthesia. Mean blood pressure, cardiac output (CO) and stroke volume (SV) decreased similarly during 1.5 MAC halothane or isoflurane anaesthesia. Ejection fraction (EF) decreased and left ventricular end-diastolic volume (LVEDV) increased significantly in both groups, but decreases in EF (32 +/- 5 per cent vs 18 +/- 5 per cent) and increases in LVEDV (18 +/- 7 per cent vs 7 +/- 5 per cent) were significantly greater during halothane than during isoflurane anaesthesia. Following atropine, HR increased more in the patients maintained with halothane (31 +/- 6 per cent), than during isoflurane anaesthesia (18 +/- 5 per cent). Atropine increased CO in both groups of patients, but SV and EF remained unchanged. When compared with awake values, HR increased similarly and significantly (18 +/- 4 per cent) following atropine in both groups, and CO returned to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation

Evaluation of an animal model for teaching fibreoptic tracheal intubation.

Twenty-seven anaesthesia faculty, fellows and residents compared a standard intubating mannequin and an anaesthetized pig as models for teaching fibreoptic tracheal intubation. When likened to the clinical situation, the anatomic characteristics of the pig airway were rated as significantly more realistic than the airway characteristics of the mannequin with the exception of the appearance of the epiglottis. In addition, the overall score for the pig model was significantly higher than the score for the mannequin and 26 of 27 evaluators rated the anaesthetized pig as the more effective teaching model. We conclude that an anaesthetized, spontaneously breathing pig is a valid model for teaching fibreoptic endotracheal intubation.

Anesthesiology

Pharmacokinetics of two per cent rectal methohexitone in children.

Plasma methohexitone concentrations were determined in 60 children, aged one to six years, following administration of 15 mg.kg-1, 20 mg.kg-1, 25 mg.kg-1 or 30 mg.kg-1 two per cent rectal methohexitone. Time to the onset of sleep was determined by a blinded observer and venous blood samples obtained 15, 30, 45 and 120 minutes following drug administration. Fifty of 60 children were asleep within 15 minutes. Nine of the ten children that did not fall asleep were sedate and could be separated easily from their parents to undergo inhalational induction of anesthesia. Time to the onset of sleep was inversely related to the dose of rectal methohexitone administered. Sleep was achieved more reliably following the use of 25 to 30 mg.kg-1 rectal methohexitone. In addition, plasma methohexitone concentrations following 30 mg.kg-1 rectal methohexitone were significantly higher for up to 120 minutes following drug administration than the plasma concentrations achieved after 15 mg.kg-1 or 20 mg.kg-1 methohexitone. There was no difference in the incidence of complications. The authors recommend that clinical circumstances be carefully considered and the dose of rectal methohexitone administered be individualized to meet the specific anaesthetic requirements of each child.

Anesthesia, Rectal

The neuromuscular blocking and cardiovascular effects of doxacurium chloride in patients receiving nitrous oxide narcotic anesthesia.

The purpose of this study was to evaluate neuromuscular and cardiovascular effects of doxacurium chloride, a new long-acting neuromuscular blocking agent, during a stable state of nitrous oxide and narcotic anesthesia. Ninety-three ASA physical status I or II patients were studied after informed written consent had been obtained. Eighty-one patients (group A) received doxacurium. The 81 patients were divided into nine subgroups according to the dose of doxacurium administered (0.01-0.06 mg.kg-1). Patients in a control group (group B) (n = 12) received pancuronium. To assess neuromuscular responses, a force displacement transducer recorded the twitch response of the adductor pollicis muscle following ulnar nerve stimulation. The ED50 and ED95 for doxacurium were estimated to be 0.013 mg.kg-1 and 0.023 mg.kg-1, respectively. The time to maximum twitch suppression following a dose of 1.0 (ED95) and 1.7 (ED95) was 10.3 +/- 1.3 min and 7.6 +/- 0.8 min, respectively. After an ED95 dose of doxacurium the time to spontaneous recovery to 95% of control twitch height was 73.7 +/- 8.7 min. With larger doses of doxacurium, 0.04 mg.kg-1 (1.7 X ED95) and 0.05 mg.kg-1 (2.2 X ED95), the time to spontaneous recovery to 95% of control twitch height was 125.8 +/- 24.8 and 204.0 +/- 21.2 minutes, respectively. When 25% twitch height recovery or more was present the reversal of doxacurium induced neuromuscular blockade was prompt.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent

Coagulation changes during packed red cell replacement of major blood loss.

A greater proportion of blood replacement needs are being met by packed red cell concentrates rather than whole blood in situations of major blood loss. Twelve patients, who required major blood replacement during elective surgery, were studied to determine the changes in coagulation when packed red cells were used to replace major blood loss. In addition, the coagulation abnormalities present at the time an observer noted excessive bleeding were determined. Prior to blood product replacement and after the estimated loss of each 0.3 blood volume, coagulation tests were obtained including prothrombin time (PT), partial thromboplastin time (aPTT), platelet count, thrombin time (TT), fibrinogen levels, and assays of coagulation Factors V, VIII, and IX. Coagulation tests were repeated when clinical hemostasis was judged inadequate by the anesthesiologist and attending surgeon. Significant decreases in platelet count, fibrinogen levels, and Factor V, VIII, and IX levels occurred as increasing blood volumes were replaced. Increases in PT and aPTT above control occurred in nine of the 12 patients prior to replacement of 1 blood volume; none of the nine patients had increased clinical bleeding. In four of seven patients who had blood replacement of greater than 1 blood volume, increased clinical bleeding was noted by the observer. Platelet counts were less than 100,000/mm3 in each of these four patients, and a platelet concentrate obtained by pheresis of a single donor was administered. In two of the four patients platelet counts increased, but clinical bleeding did not resolve.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Coagulation

Uptake and subcellular localisation of bismuth in the gastrointestinal mucosa of rats after short term administration of colloidal bismuth subcitrate.

Despite the topical action of colloidal bismuth subcitrate in promoting the healing of peptic ulcers, slight absorption of bismuth from the gastrointestinal tract has been reported in colloidal bismuth subcitrate-treated animals and man. The uptake and subcellular distribution of bismuth by the gastrointestinal tract of rats after 24 hours of colloidal bismuth subcitrate administration was studied. Mucosal uptake of bismuth (mean +/- SEM nmol/g protein) by gastric fundus (8.85 +/- 1.0) and antrum (7.23 +/- 1.50) was similar, but was significantly less than duodenum (19.2 +/- 3.7, p less than 0.05), jejunum (26.9 +/- 2.4, p less than 0.001) or ileum (22.4 +/- 2.2, p less than 0.001). Bismuth concentrations in antral and duodenal mucosae fell progressively over 72 hours to approximately 10% of initial concentrations (p less than 0.02). Subcellular fractionation studies of colloidal bismuth subcitrate treated duodenal enterocytes showed a brush border membrane and cytosolic localisation. These data suggest that some gastrointestinal mucosal uptake of bismuth occurs in colloidal bismuth subcitrate treated rats.

Animals