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Biomedical subjects

W A Tweed

Publications and source records attributed to W A Tweed.

At least 37 records · Page 2Linked to original sources
PubMed1991

Tussive effect of a fentanyl bolus.

The aim of this study was to investigate the incidence of pre-induction coughing, after an iv bolus of fentanyl. The study sample was 250 ASA physical status I-II patients, scheduled for various elective surgical procedures. The first 100 were randomly allocated to receive 1.5 micrograms.kg-1 fentanyl via a peripheral venous cannula (Group 1), or an equivalent volume of saline (Group 2). Twenty-eight per cent of patients who received fentanyl, but none given saline, coughed within one minute (P less than 0.0001). The second 150 patients were then randomly assigned to three equal pretreatment groups. Group 3 received 0.01 mg.kg-1 atropine iv one minute before fentanyl. Groups 4 and 5 received 0.2 mg.kg-1 morphine im, and 7.5 mg midazolam po, respectively, one hour before fentanyl. Thirty per cent of patients in Group 3, 6% in Group 4, and 40% in Group 5, had a cough response to fentanyl. Fentanyl, when given through a peripheral cannula, provoked cough in a considerable proportion of patients. This was not altered by premedication with atropine or midazolam, but was reduced after morphine (P less than 0.01). Coughing upon induction of anaesthesia is undesirable in some patients, and stimulation of cough by fentanyl in unpremedicated patients may be of clinical importance.

Adult↗
PubMed1991

Large tidal volume ventilation improves pulmonary gas exchange during lower abdominal surgery in Trendelenburg's position.

Impaired pulmonary gas exchange is a common complication of general anaesthesia. Periodic hyperinflation of the lungs and large tidal volume ventilation were the first preventive measures to be widely embraced, but their effectiveness in clinical practice has never been clearly established by controlled clinical studies. To assess their effects in high-risk patients we studied 24 adults having lower abdominal gynaecological surgery in the Trendelenburg (head down) position. Pulmonary oxygen exchange was determined during four steady-states: awake control (AC), after 30 min of conventional tidal volume (CVT, 7.5 ml.kg-1) or high tidal volume (HVT, 12.7 ml.kg-1) ventilation, introduced in random order, and five minutes after manual hyperinflations (HI) of the lungs. The patients' lungs were ventilated with air/O2 by an Ohmeda volume-controlled ventilator via a circle system. The FIO2 was controlled at 0.5, and FETCO2 was controlled by adding dead space during HVT. Arterial blood gas analysis was used to calculate the oxygen tension-based indices of gas exchange. There was significant deterioration of (A-a)DO2 at 30 min in Group A, whose lungs were first ventilated with CVT (81.6 +/- 7.2 to 166.8 +/- 13.7 mmHg, P less than 0.001); but not in Group B, whose lungs were first ventilated with HVT (77.0 +/- 9.9 to 104.4 +/- 16.8 mmHg). When Group A and B data were pooled there was no difference between randomized CVT and HVT, but improvement occurred after HI. In this model of compromised O2 exchange large inflation volumes (HVT and HI) were of considerable clinical benefit, HVT prevented and HI reversed the gas exchange disorder.

Abdomen↗
PubMed1990

Re-evaluation of the Farman entrainer in a low-pressure system for field anaesthesia.

The aim of this project was to develop a portable anaesthesia system that was compatible with modern anaesthesia practice under field conditions, when compressed gas supplies are limited. We assembled and evaluated a low-pressure plenum system, based upon the Farman entrainer, which was adaptable to spontaneous, assisted or intermittent positive pressure ventilation (IPPV). The entrainer was tested using a low flow of compressed gas, O2 at 1-3 L.min-1. We measured the fresh gas flow (FGF) and O2 concentrations (F1O2) delivered at various source gas flow rates (O2 flow), and with various breathing circuits. Entrainment ratio, FGF, and F1O2 were highly dependent upon resistance to flow in the different breathing circuits. With a wide bore T-piece the air/O2 entrainment ratio was 6:1, and the F1O2 was 0.3. When circuit resistance was higher, e.g., with the Bain circuit, air entrainment and FGF were reduced, but F1O2 was higher. Because it offered the lowest resistance, the T-piece circuit was selected for a clinical trial.

Anesthesia, Inhalation↗
PubMed1990

A low-pressure portable anaesthesia system for field use: clinical trials.

This is a report of our experience with a portable anaesthesia system that was developed for use under field conditions, when compressed gas supplies are limited. We first assembled and bench-tested a low-pressure plenum system, based upon the Farman entrainer. The entrainer required a low flow of compressed gas, O2 at 1-2 L.min-1, and generated a low-pressure mixture of O2 and air which was directed through an Oxford miniature vaporizer, a non-return valve, and a widebore T-piece circuit. With this system we anaesthetized 24 patients with intermittent positive pressure ventilation (IPPV) and nine patients breathing spontaneously. During IPPV, the circuit resembled a T-piece and provided effective gas exchange with a FGF of 1.2 times minute ventilation. Inspiratory and expiratory valves were arranged so that the spontaneous mode was non-rebreathing, and FGF was adjusted to equal minute ventilation. The system was very economical, using 1-2 L.min-1 O2 and 20-25 ml.hr-1 liquid halothane to produce a FGF of 6-10 L.min-1, an FIO2 of 0.33, and FIhal of 1-1.5 per cent. We have demonstrated that this is a versatile, safe, and economical system, compatible with the practice of modern inhalational anaesthesia under field conditions. It can be readily assembled from commercially available components.

Adult↗
PubMed1989

Endogenous opioids may protect the perinatal brain in hypoxia.

Endogenous opioids are released in great amounts in perinatal asphyxia. The role of this release has been unclear. In a study of cerebral blood flow and oxygen metabolism in 5 hypoxic newborn lambs, naloxone blocking of opioid receptors resulted in a proportional increase in telencephalic cerebral blood flow and oxygen metabolism. It is suggested that endogenous opioid release protects the neonatal brain in hypoxia by diminishing the cerebral metabolic rate of oxygen.

Animals↗
PubMed1987

Effects of isoproterenol-induced tachycardia on myocardial blood flow and glycogen in the fetal lamb.

In utero tachycardia is a cause of fetal congestive heart failure and fetal hydrops. We investigated the effects of isoproterenol-induced tachycardia (IIT) on cardiac output and its distribution, on myocardial blood flow and intramyocardial blood flow distribution as well as on regional myocardial glycogen in 8 chronically prepared, near-term fetal lambs and 3 control twins (for myocardial glycogen only). Blood flows were measured by the radioactive microsphere method, myocardial glycogen by an enzymatic method. In animals with IIT (heart rate 200-280), cardiac output (excluding lung flow) increased from 0.399 to 0.544 ml/g/tissue/min (+36%), blood flow to the carcass increased from 0.19 to 0.32 ml/g/tissue/min (+68%) and myocardium increased from 2.31 to 7.72 ml/g/tissue/min (+234%), while kidney blood flow decreased from 1.34 to 0.72 ml/g/tissue/min (-46%). The normal intramyocardial blood flow distribution and predominance of flow to the endocardium of both ventricles was preserved during IIT. In the three sets of twins, glycogen was lower in the right (RV) and left (LV) ventricular walls of each animal stressed by IIT (mean RV = 0.19, mean LV = 0.44) than of its unstressed twin (mean RV = 0.75, mean LV = 0.70). Furthermore, a metabolic acidemia (mean pH 7.21, mean BE -8.4) developed in the stressed animals. Although we were unable to demonstrate regional myocardial ischemia at the maximal fetal heart rates achieved by isoproterenol infusion, our data suggest that metabolic acidemia and myocardial glycogen depletion are consequences of severe inotropic and chronotropic stress in the fetal lamb.

Animals↗
PubMed1987

Cerebral autoregulation and flow/metabolism coupling during cardiopulmonary bypass: the influence of PaCO2.

Measurement of 133Xe clearance and effluent cerebral venous blood sampling were used in 38 patients to determine the effects of cardiopulmonary bypass, and of maintaining temperature corrected or noncorrected PaCO2 at 40 mm Hg on regulation of cerebral blood flow (CBF) and flow/metabolism coupling. After induction of anesthesia with diazepam and fentanyl, mean CBF was 25 ml X 100 g-1 X min-1 and cerebral oxygen consumption, 1.67 ml X 100 g-1 X min-1. Cerebral oxygen consumption during nonpulsatile cardiopulmonary bypass at 26 degrees C was reduced to 0.42 ml X 100 g-1 X min-1 in both groups. CBF was reduced to 14-15 ml X 100 g-1 X min-1 in the non-temperature-corrected group (n = 21), was independent of cerebral perfusion pressure over the range of 20-100 mm Hg, but correlated with cerebral oxygen consumption. In the temperature-corrected group (n = 17), CBF varied from 22 to 32 ml X 100 g-1 X min-1, and flow/metabolism coupling was not maintained (i.e., CBF and cerebral oxygen consumption varied independently). However, variation in CBF correlated significantly with cerebral perfusion pressure over the pressure range of 15-95 mm Hg. This study demonstrates a profound reduction in cerebral oxygen consumption during hypothermic nonpulsatile cardiopulmonary bypass. When a non-temperature-corrected PaCO2 of approximately 40 mm Hg was maintained, CBF was lower, and analysis of pooled data suggested that CBF regulation was better preserved, i.e., CBF was independent of pressure changes and dependent upon cerebral oxygen consumption.

Acid-Base Equilibrium↗
PubMed1987

Pharmacologic EEG suppression during cardiopulmonary bypass: cerebral hemodynamic and metabolic effects of thiopental or isoflurane during hypothermia and normothermia.

We have determined the effects of thiopental or isoflurane upon cerebral blood flow (CBF) and the cerebral metabolic rate for oxygen (CMRO2) when these agents are used in sufficient dose to attain a deep burst suppression pattern on the electroencephalogram (EEG) during hypothermic and normothermic cardiopulmonary bypass (CPB). Thirty-one patients undergoing coronary artery bypass graft surgery were anesthetized with fentanyl 0.1 mg X kg-1, and were randomly allocated to one of three groups: control (no further anesthetics during bypass and continuous EEG activity), thiopental treatment (EEG suppression), or isoflurane treatment (EEG suppression). Hypothermia (25-29 degrees C) was routinely induced at onset of nonpulsatile cardiopulmonary bypass. In the treatment groups, thiopental or isoflurane were used during bypass to achieve a deep burst suppression pattern. Cerebral blood flow and cerebral metabolic rate for oxygen were determined during hypothermia and upon rewarming to normothermia (37 degrees C). Pharmacologic EEG suppression with either isoflurane or thiopental was associated with lower cerebral metabolic rate than control values during both hypothermic and normothermic bypass. However, only thiopental-induced EEG suppression was associated with lower cerebral blood flow than control. Cerebral blood flow during isoflurane-induced EEG suppression was similar to control values in spite of the reduced cerebral metabolic rate.

Blood Gas Analysis↗
PubMed1986

Hydroxylation and glucuronidation of various xenobiotics by hepatic microsomes from the fetal lamb, pregnant ewe and human fetus.

The ability of microsomes isolated from liver of pregnant ewes and their fetuses at near term to catalyze the biotransformation of benzo[a]pyrene, hexobarbital, meperidine, methadone and morphine was investigated. Cytochromes P-450 and b5, NADPH and NADH cytochrome c reductase, methadone and meperidine N-demethylase and morphine glucuronyltransferase activities were detected in microsomes from both maternal and fetal livers. Fetal hepatic microsomes however, lacked the ability to catalyze the hydroxylation of hexobarbital and benzo[a]pyrene.

Animals↗
PubMed1985

Preferential blood flow increase to the brain stem in moderate neonatal hypoxia: reversal by naloxone.

Previous studies have shown that severe neonatal asphyxia and hypoxia lead to a redistribution of cerebral blood flow (CBF) with a preferential perfusion of the brain stem. The present study shows that this mechanism is operative also in moderately hypoxic newborn lambs (oxygen saturation 32.7-65.2) with a threshold of about 25% reduction in oxygen saturation. In hypoxia, the mean increase in total CBF, brain stem and telencephalic blood flow was 44%, 68% and 43%, respectively (five lambs). We found that naloxone reverses this redistribution, and that the effects of naloxone on telencephalic perfusion and cerebral metabolic rate of oxygen (CMRO2) were proportional. In hypoxia + naloxone (1 mg/kg), a further increase in total CBF, brain stem, and telencephalic blood flow of 30%, 7% and 31% was noted. We therefore suggest that the redistribution of CBF is an important opioid-mediated homeostatic mechanism, which diminishes the metabolic requirements of the newer part of the brain in hypoxia and allows a preferential perfusion of the vital structures of the brain stem.

Animals↗
PubMed1984

Foetal responses to acute haemorrhage under halothane anaesthesia.

The effect of halothane anaesthesia on the foetal responses to acute haemorrhage was studied in chronically prepared ewes. An average of 27.9 ml X kg-1 of foetal blood was withdrawn resulting in an acute 20 per cent decrease in mean arterial pressure which returned toward the control value after 186 seconds. After the blood loss, cardiac output was reduced by 26.1 per cent and heart rate decreased by 26 per cent. Blood flows to the kidneys, placenta and musculoskeletal structures were reduced by 24.7, 38.2 and 35.3 per cent respectively but flow to the brain increased by 30 per cent. Reinfusion of lost blood, corrected flow reductions and the supply to the gastrointestinal organs increased above control values. This study showed that foetal lambs were able to tolerate an acute blood loss under halothane anaesthesia. An adequate perfusion pressure and blood flow to critical organs, such as the brain was maintained by increasing systemic vascular resistance. The compensation, however, was incomplete. Placental blood flow, maternal-foetal gas exchanges, and redistribution of cardiac output away from gastrointestinal tract and skin were impaired.

Anesthesia, Obstetrical↗
PubMed1984

The regional distribution and determinants of myocardial blood flow during asphyxia in the fetal lamb.

The syndrome of hypoxemia-related myocardial dysfunction in the newborn is generally associated with severe intrapartum asphyxia. We investigated the changes in total and regional distribution of myocardial blood flow (MBF) that occur during asphyxia and the factors that regulate MBF, in the chronically prepared, near term, fetal lamb. Studies were done in the awake, physiologically stable state 36-72 h after surgical preparation. In utero asphyxia was produced by partial cord occlusion and blood flow to fetal organs was measured by the radioactive microsphere technique. A complete set of control measurements was made, and then an occlusion loop was inflated to partially occlude the umbilical vessels. After 30-60 min of partial occlusion, all measurements were repeated. The third set of measurements was made after release of the occlusion loop. Six animals were studied and 17 sets of measurements obtained. Partial umbilical cord constriction produced a progressive asphyxia and acidosis. Cardiac output was severely depressed, although the increase in percentage of cardiac output directed to the myocardium (%F) was very significant. Release resulted in improved cardiac output and O2 and CO2 exchange, although the metabolic acidosis was worse. No change occurred in the intramyocardial distribution of MBF during asphyxia or recovery. Total MBF was not significantly increased during asphyxia. Multiple linear regression analysis indicated that arterial oxygen saturation (SaO2) and heart rate were statistically significant predictor variables for absolute MBF, accounting for about 45% of the variation in MBF.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Pharmacists' role in smoking cessation.

"Time to quit", a program piloted in Winnipeg in 1983, is an example of the importance of the pharmacist in the smoking cessation issue. Through the Manitoba Pharmaceutical Association, pharmacies were utilized as distribution centres for a self-help smoking cessation booklet. In the city of Winnipeg, 82% of city pharmacies received a total of 40,500 books; 93.5% of these booklets were picked up by the public. Pharmacists also had the option to become more involved in the anti-smoking campaign if they so desired. Pharmacists not only have the knowledge to discuss the area of smoking cessation, they arein a strategic position for dissemination of that knowledge.

Canada↗