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Biomedical subjects

C Prys-Roberts

Publications and source records attributed to C Prys-Roberts.

At least 55 records · Page 3Linked to original sources
PubMed1990

Total i.v. anaesthesia with propofol and alfentanil: dose requirements for propofol and the effect of premedication with clonidine.

We determined in 51 healthy patients undergoing body surface surgery the dose requirements for propofol, as part of a total i.v. anaesthesia technique with an alfentanil infusion. After premedication with temazepam, patients received alfentanil 50 micrograms kg-1 followed by an infusion of 50 micrograms kg-1 h-1. Patients were anaesthetized with a loading dose of propofol followed by a three-stage infusion designed to reach one of five preselected blood concentrations of propofol. The motor response to the initial surgical incision was noted and probit analysis was used to derive the ED50 (2.94 mg kg-1 h-1; 95% confidence limits: 2.35-3.37 mg kg-1 h-1) and ED95 (4.98 mg kg-1 h-1; 95% limits: 4.13-8.8 mg kg-1 h-1) for the final propotol infusion rate under these conditions. Whole blood concentration!of propofol at the time of the incision was related linearly to the inf!sion rate and the EC50 and EC95 (probit analysis) were derived as !.44 (95% confidence limits 0.62-1.87) and 4.05 (95% confidence lim!ts 2.78-30.5) micrograms ml-1, respectively. Post-operative recovery was!rapid, uncomplicated and uneventful. In a subgroup of eight patients,!the addition of clonidine 0.6 mg to the premedication significantly decreased the requirement for propofol (P less than 0.05) during surgery, but resulted in prolonged recovery times.

Administration, Oral↗
PubMed1989

Isoflurane compared with midazolam for sedation in the intensive care unit.

OBJECTIVE: To compare isoflurane with midazolam for sedation of ventilated patients. DESIGN: Randomised control study. Setting--Intensive care unit in university teaching hospital. PATIENTS: Sixty patients aged 18-76 who required mechanical ventilation. INTERVENTIONS: Sedation with either 0.1-0.6% isoflurane in an air-oxygen mixture (30 patients) or a continuous intravenous infusion of midazolam 0.01-0.20 mg/kg/h (30 patients). Sedation was assessed initially and hourly thereafter on a six point scale. Incremental intravenous doses of morphine 0.05 mg/kg were given for analgesia as required. The trial sedative was stopped when the patient was judged ready for weaning from ventilatory support or at 24 hours (whichever was earlier). END POINT: Achievement of a predetermined level of sedation for as much of the time as possible. MAIN RESULTS: Isoflurane produced satisfactory sedation for a greater proportion of time (86%) than midazolam (64%), and patients sedated with isoflurane recovered more rapidly from sedation. CONCLUSION: Isoflurane is a promising alternative technique for sedation of ventilated patients in the intensive care unit.

Adolescent↗
PubMed1989

The pharmacology of propofol.

A review of the pharmacology of propofol, a new IV anesthetic agent, is presented. Solubilized in a soybean emulsion, propofol is one of a series of sterically hindered phenols that exhibit anesthetic activity. Induction of anesthesia with propofol may be associated with pain on injection, apnea, and a reduction in arterial blood pressure (BP) and cardiac output. Caution should be ascribed to its use in patients with coronary artery disease, where these effects may have the potential for producing myocardial ischemia. The hemodynamic responses to laryngoscopy and intubation are attenuated. The pharmacokinetic profile suggests suitability as an infusion for either maintenance of anesthesia or sedation. Use of propofol as an infusion during surgery may result in a further reduction in cardiac output, particularly with the concomitant administration of adjuvant increments of fentanyl. The ventilatory response to CO2 is depressed during such an infusion. The high clearance of propofol suggests that even after a prolonged infusion, recovery should be rapid. This finding has been confirmed in a series of studies establishing propofol as an ideal agent for use in a total IV anesthetic technique. Both the quality and speed of recovery, together with the absence of emetic sequelae, support the use of propofol in an outpatient setting. Propofol appears to have no long-term effect on adrenocortical function and appears safe for use in patients with acute intermittent porphyria and susceptibility to malignant hyperpyrexia.

Adult↗
PubMed1989

Computer controlled infusion of propofol.

A computer controlled infusion pump was used to deliver propofol to two groups of eight patients undergoing body surface surgery. The patients were premedicated with morphine sulphate i.m. and anaesthesia was supplemented with 66% nitrous oxide in oxygen. Patients in group 1 breathed spontaneously, whereas patients in group 2 underwent artificial ventilation to a normal PaCO2. The computer program was designed to achieve and maintain a blood concentration of propofol 3 micrograms ml-1 as rapidly as possible, basing calculations on a three-compartment pharmacokinetic model. Mean blood propofol concentrations were found to be close to the predicted target from 10 to 120 min in group 1, but were 5-20% higher from 20 min in group 2.

Adult↗
PubMed1989

Automatic arterial pressure regulation using isoflurane: comparison with manual control.

A self-tuning, closed-loop controller, based on the algorithm of Clarke and Gawthrop, was used to regulate the inspired concentration of isoflurane to reduce arterial pressure electively in 33 patients undergoing ENT surgery. The patients were allocated randomly to one of four groups and received differing doses of fentanyl and labetalol to vary the range of sensitivities to the hypotensive action of isoflurane. The performance of the controller was evaluated at two target arterial pressures (AP), by its response to simulated changes in AP and by a comparison with a further group of eight patients with manual control of AP. The controller's undershoot of AP (range 2.8 +/- 0.5-4.5 +/- 1.3 mm Hg) and % time spent within +/- 5 mm Hg of the target AP (range 83 +/- 3.4-89 +/- 2.2%) were acceptable and equalled the manual performance figures (range 3.3 +/- 0.8 mm Hg; 90 +/- 5%). The regulation of induced hypotension in all four groups was rapid, accurate, stable and reproducible.

Adolescent↗
PubMed1989

Preinduction atropine or glycopyrrolate and hemodynamic changes associated with induction and maintenance of anesthesia with propofol and alfentanil.

Total intravenous anesthesia by infusions of propofol and alfentanil may be associated with decreases in heart rate and blood pressure. The effects of two vagolytic agents on these hemodynamic changes were studied in 24 ASA physical status 1 patients undergoing body surface surgery. Patients were randomly allocated to receive atropine 10 micrograms/kg, glycopyrrolate, 5 micrograms/kg, or 0.9% sodium chloride, intravenously, 5 min before induction of anesthesia with loading doses of alfentanil, 50 micrograms/kg and propofol 1 mg/kg. Anesthesia was maintained with infusions of alfentanil 50 micrograms.kg-1.hr-1, and propofol 10 mg.kg-1.hr-1 for the first 10 min, 8 mg.kg-1.hr-1 for the next 10 min, and 6 mg.kg-1.hr-1 thereafter. Patients given glycopyrrolate before anesthesia had significantly higher arterial pressures than did patients receiving either atropine or saline, even though heart rates increased equally after glycopyrrolate and atropine.

Adult↗
PubMed1988

Clonidine premedication for isoflurane-induced hypotension. Sympathoadrenal responses and a computer-controlled assessment of the vapour requirement.

The effect of single-dose clonidine premedication on the vapour requirement for isoflurane-induced hypotension in patients undergoing middle ear or nasal surgery was evaluated in an open, controlled, randomized study. Inspired isoflurane concentration was regulated by a microcomputer-based, self-tuning control program when hypotension was required. Patients given clonidine 0.6 mg by mouth 2 h before operation required a mean inspired isoflurane concentration of 2.0% to induce hypotension (mean intra-arterial pressure 50 mm Hg) compared with 3.01% in the control group (P less than 0.05). Five out of 10 patients in the control group required a supplementary dose of labetalol 5 mg i.v. to achieve satisfactory hypotension, compared with one of 10 patients given clonidine premedication (Fisher's exact probability, 0.07). A mean concentration of 1.4% isoflurane was required to maintain hypotension in the clonidine group, compared with 2.3% in the control group (P less than 0.01). Plasma adrenaline and noradrenaline concentrations did not increase during induced hypotension in each group.

Adolescent↗
PubMed1988

Induction and maintenance of propofol anaesthesia. A manual infusion scheme.

A simple, manually controlled infusion scheme for continuous administration of propofol was derived by simulation of a computer algorithm designed to achieve a predetermined blood concentration of propofol within 2 minutes and to maintain a constant blood level for the duration of surgery. The manual infusion scheme for a target blood propofol concentration of 3 micrograms/ml, consisted of a loading dose of 1 mg/kg followed immediately by an infusion of 10 mg/kg/hour for 10 minutes, 8 mg/kg/hour for the next 10 minutes and 6 mg/kg/hour thereafter. An overall mean blood propofol concentration of 3.67 micrograms/ml was achieved within 2 minutes and maintained stable for the subsequent 80-90 minutes of surgery. The decrease of systolic and diastolic arterial pressures at induction was much less than that previously described after larger induction doses of propofol and there was a negligible haemodynamic response to laryngoscopy and intubation or to the subsequent surgery. The quality of induction and maintenance of anaesthesia was satisfactory in every patient.

Adult↗
PubMed1988

Antihypertensive mechanism of ketanserin in postoperative hypertension after cardiopulmonary bypass.

The effect of ketanserin (0.15 mg/kg followed by an infusion at 6 mg/hr) was studied in 13 patients who developed hypertension (blood pressure greater than 150/90 mm Hg) after cardiopulmonary bypass (CPB) for coronary artery bypass grafting. Eleven patients responded to ketanserin with a decrease of arterial pressure from 159 +/- 15/83 +/- 10 mm Hg to 131 +/- 9/70 +/- 12 mm Hg (P less than 0.01), which was sustained during the subsequent infusion of ketanserin. Mean plasma ketanserin concentrations were maintained at 187 micrograms/L (range 118-525). No significant changes in plasma levels of 5-hydroxyindoles or in platelet 5-hydroxytryptamine content were observed during or after CPB, or after administration of ketanserin. Plasma epinephrine (398 +/- 124 pg/ml) and norepinephrine (1161 +/- 673 pg/ml) concentrations were markedly increased during the hypertensive period after CPB. Plasma epinephrine concentrations decreased (P less than 0.01) during ketanserin infusion to 213 +/- 101 pg/ml, whereas plasma norepinephrine concentrations did not change. The pressor response to three graded doses of phenylephrine was decreased during CPB (P less than 0.01), and a further decrease (P less than 0.05) occurred during infusion of ketanserin. The hypotensive effect of ketanserin after CPB may be attributable to alpha 1-adrenoceptor blockade rather than to its antiserotoninergic effect. Serotonin does not appear to be involved in the short-term disturbances of arterial pressure during or after CPB.

Aged↗
PubMed1987

On using a self-tuning controller for blood pressure regulation during surgery in man.

The generalized minimum-variance self-tuning controller of Clarke and Gawthrop has been used to adjust the flow rate of a modified Vickers Treonic IP4 syringe pump delivering phenylephrine to 20 patients undergoing lower abdominal surgery during epidural analgesia. This proved to be a very effective method of restoring and maintaining normal arterial pressure. The method has also been used to produce controlled hypotension in 18 patients undergoing plastic or neurosurgical procedures via sodium nitroprusside infusions. Valuable insight into patient responses to surgical stimuli, blood loss, fluid loads, opioids, relaxants and other agents was provided.

Anesthesia, Epidural↗
PubMed1987

Dose requirements of propofol by infusion during nitrous oxide anaesthesia in man. II: Patients premedicated with lorazepam.

The infusion rate of propofol required to supplement 67% nitrous oxide in oxygen to maintain surgical anaesthesia was determined in 72 patients premedicated with lorazepam. Following an induction dose of propofol 2 mg kg-1, groups of eight patients received an infusion of propofol varying from 60 to 200 micrograms kg-1 min-1. Probit analysis was used to determine the ED50 (130 micrograms kg-1 min-1; 95% confidence limits: 106-167 micrograms kg-1 min-1) and ED95 (348 micrograms kg-1 min-1; 95% confidence limits: 233-1296 micrograms kg-1 min-1) for propofol infusion. Whole blood propofol concentrations at the time of surgical incision correlated strongly with the infusion rate, giving an EC50 value of 2.5 micrograms ml-1, and an EC95 value of 5.92 micrograms ml-1. There was no significant correlation between the rate of infusion of propofol, or the total propofol dose, and the times to response to command, or to recall of birthdate.

Adolescent↗
PubMed1987

Haemodynamic effects of a prolonged infusion of propofol as a supplement to nitrous oxide anaesthesia. Studies in association with peripheral arterial surgery.

The haemodynamic effects of propofol at two infusion rates (54-65 and 108-130 micrograms kg-1 min-1) have been studied during peripheral arterial surgery in eight elderly patients premedicated with morphine sulphate 0.15 mg kg-1. The haemodynamic response to laryngoscopy and intubation was partially suppressed: neither arterial pressure nor heart rate exceeded awake values. During stable anaesthesia at the lower infusion rate before surgery, systolic (SAP) and diastolic (DAP) arterial pressures were significantly decreased from awake values (SAP: -47%; DAP: -46%) as a result of decreases in cardiac output (-32%) and systemic vascular resistance (SVR) (-9%). During surgery, with either spontaneous (SV) or intermittent positive pressure (IPPV) ventilation, both infusion rates were associated with decreases in arterial pressures when compared with the awake state. Cardiac output was decreased (SV: -35%, IPPV: -36%) and SVR increased (SV: +22%, IPPV: +45%) at the lower infusion rate; similar changes were observed during the faster infusion rate.

Aged↗