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Biomedical subjects

C Prys-Roberts

Publications and source records attributed to C Prys-Roberts.

At least 37 records · Page 2Linked to original sources
PubMed1994

Propofol infusion and the suppression of consciousness: the EEG and dose requirements.

We have used Median Power Frequency (MPF) to study changes in the electroencephalogram during propofol infusions in 52 women about to undergo gynaecological surgery. Patients were allocated to receive propofol by one of nine different manually-controlled infusion schemes designed to achieve and maintain a stable blood propofol concentration between 1.0 and 6.0 micrograms ml-1, covering a range of states between conscious sedation and full anaesthesia. We recorded the changes in MPF and the response to clinical signs of loss of consciousness at these different doses and concentrations of propofol. Using probit analysis, we derived MPF values corresponding to 50% and 95% suppression of response to verbal (9.3 Hz and 6.8 Hz), eyelash (8.9 Hz and 6.7 Hz) and venepuncture (5.7 Hz and 3.0 Hz) stimuli. Likewise, we obtained dose and concentration requirements for propofol to suppress these stimuli. The mean (95% confidence intervals) ED50 (5.8 (3.5-6.8) mg kg-1 h-1) and ED95 (8.3 (7.1-16.9) mg kg-1 h-1) propofol doses for suppression of consciousness were similar to the values for suppression of the eyelash reflex (6.2 (5.3-6.8) mg kg-1 h-1 and 8.6 (7.8-10.8) mg kg-1 h-1, respectively). The EC50 for loss of consciousness was a propofol concentration of 2.3 (1.8-2.7) micrograms ml-1 and for 50% suppression of MPF was 3.1 (2.7-3.5) micrograms ml-1. The dose required for 50% suppression of MPF was 7.1 (6.2-8.0) mg kg-1 h-1. After 30 min, at blood propofol concentrations > 4.0 micrograms ml-1, consistent with stable anaesthesia, the mean MPF was 5.6 (4.5-6.3) Hz.

Adolescent↗
PubMed1994

Epidural infusions of sufentanil with and without bupivacaine: comparison with diamorphine-bupivacaine.

The requirements for supplementary 3 ml epidural injections of bupivacaine 0.5% (top-ups) were used in a randomized double-blind study to compare the effects of five types of thoracic epidural infusions given at 2.5 ml h-1 for the first 24 h after major surgery to the upper abdomen in 99 patients and the lower abdomen in 72. The infusions were: bupivacaine 0.167% alone; diamorphine 0.167 mg ml-1 (0.417 mg h-1) in bupivacaine 0.167%; sufentanil 2 micrograms ml-1 (5 micrograms h-1) in 0.167% bupivacaine; sufentanil 4 micrograms ml-1 (10 micrograms h-1) in 0.167% bupivacaine; and sufentanil 4 micrograms ml-1 (10 micrograms h-1) in normal saline. The patients who had upper abdominal surgery were on average older than those having lower abdominal surgery and a larger proportion of them were female. They received on average fewer top-ups. After both upper and lower abdominal surgery, epidural infusions of bupivacaine alone required the most frequent supplementation (inter-quartile range 6-14 top-ups in 24 h) and the two sufentanil-bupivacaine mixtures required the fewest (interquartile range 0-12 top-ups in 24 h). The infusions of sufentanil without bupivacaine were significantly less effective than the sufentanil-bupivacaine mixtures after upper (but not lower) abdominal surgery. Although the two sufentanil-bupivacaine mixtures were indistinguishable in analgesic effectiveness after either upper or lower abdominal surgery, the lower (5 micrograms h-1) dose rate of sufentanil gave a significantly higher average breathing rate and lower average PaCO2 for the first 24 h after lower (but not upper) abdominal surgery. Blood samples were taken (as an afterthought) from 11 patients receiving sufentanil 10 micrograms h-1, just before the epidural infusion was stopped. The concentrations were mostly above the range for systemic analgesia, but below the values that would have been expected if a steady state had been achieved.

Abdomen↗
PubMed1993

Comparison of automatic oscillometric arterial pressure measurement with conventional auscultatory measurement in the labour ward.

We have compared two non-invasive methods of arterial pressure (AP) measurement used in labour wards: an automatic oscillometric measurement obtained by Dinamap 1846, and a conventional auscultatory measurement obtained by midwives. A total of 369 AP measurements were recorded, involving 28 normotensive and hypertensive pregnant women during labour, with or without extradural analgesia. Compared with the midwife group, the Dinamap group had a greater systolic AP, by 2.7 mm Hg (P < 0.01) and smaller diastolic AP, by 9.8 mm Hg (P < 0.01). The correlations between the two methods were highly significant, but the limits of agreement were relatively wide for both systolic and diastolic AP measurements. We conclude that a clinically important difference exists in diastolic AP measurements. Dinamap diastolic AP must be corrected using a regression equation, or simply by adding 10 mm Hg, before being compared with the available normal and hypertensive AP values.

Adult↗
PubMed1993

The influence of diamorphine on spinal anaesthesia induced with isobaric 0.5% bupivacaine.

In a randomised, double-blind study, the effect of addition of 1 mg of diamorphine to 4 ml of 0.5% bupivacaine for spinal anaesthesia was studied in two groups each of 30 patients presenting for either transurethral genito-urinary surgery, or for lower limb arterial surgery or inguinal herniorrhaphy. Addition of 1 mg diamorphine to intrathecal 0.5% bupivacaine produced a prolonged and satisfactory analgesia in more than half the patients undergoing lower limb arterial or inguinal surgery, and the analgesic requirements of the remainder during the first postoperative 24 h were much less than those who received bupivacaine alone. In the urological surgery set there were no significant differences between the group who received bupivacaine and diamorphine, and the group who received bupivacaine alone. The mixture of diamorphine 1 mg in 4 ml 0.5% bupivacaine was slightly less hypobaric (0.9981 at 37 degrees C) than bupivacaine alone.

Aged↗
PubMed1993

Capnothorax: implications for the anaesthetist.

Ten patients underwent a laparoscopic surgical technique for thoracic and cervical dissection of the oesophagus during oesophagogastrectomy. Thoracotomy was avoided with potential benefits to the patient. To facilitate surgical access the right lung was collapsed using a double-lumen bronchial tube and carbon dioxide was insufflated into the right pleural cavity to compress the lung. Changes in haemodynamic and respiratory variables occurred. In the majority of the patients airway pressure and end-tidal CO2 increased, despite alterations in ventilation. In five patients systolic blood pressure decreased suddenly by between 15 and 35 mmHg, and in four patients SpO2 decreased to 91% or less, despite an FIO2 of 1.0. If carbon dioxide was insufflated too fast, or the lung failed to deflate adequately, the clinical picture was that of a tension pneumothorax. One patient developed surgical emphysema and a contralateral pneumothorax. Postoperatively two patients had recurrent laryngeal nerve damage. Suggestions are made to minimise the changes in haemodynamic and respiratory variables during carbon dioxide insufflation into the thorax.

Aged↗
PubMed1992

Somatic movement and oesophageal motility during isoflurane anaesthesia.

The quantal responses for somatic movement, and spontaneous and provoked lower oesophageal contractions (motility) were noted at the time of incision in 72 patients aged 40-65 yr, receiving varying concentrations of isoflurane. Probit analysis of the alveolar concentration of isoflurane required to prevent somatic movement revealed an MAC or EC50 (95% confidence limits) of 1.00 (0.82-1.17)% and EC95 of 2.16 (1.69-3.89)%. The EC50 of isoflurane to suppress spontaneous lower oesophageal contractions was 1.27 (1.12-1.43)%, and the EC95 2.13 (1.78-3.22)%. The EC50 for provoked lower oesophageal contractions was 1.31 (0.93-3.48)% and the EC95 was 6.18% (unable to compute confidence limits).

Adult↗
PubMed1992

Propofol and alfentanil in children: infusion technique and dose requirement for total i.v. anaesthesia.

We estimated the dose of propofol (initial dose followed by a stepped infusion) when given with two different infusion rates of alfentanil for total i.v. anaesthesia in 59 children aged 3-12 yr. Patients in series 1 (four groups) received an alfentanil loading dose of 85 micrograms kg-1 and an infusion of 65 micrograms kg-1 h-1. Patients in series 2 (groups 5 and 6) received an alfentanil loading dose of 65 micrograms kg-1 and infusion of 50 micrograms kg-1 h-1. Parents gave their informed consent. Premedication comprised temazepam 0.3 mg kg-1. Glycopyrronium 5 micrograms kg-1 was administered and anaesthesia induced and maintained with alfentanil (loading dose and infusion) followed by propofol (loading dose and three-stage manual infusion scheme). Suxamethonium 1 mg kg-1 was used to facilitate tracheal intubation and the lungs were ventilated artificially to normocapnia with 30% oxygen in air. Probit analysis was used to determine the dose requirement of propofol. In series 1, the ED50 was 6.0 mg kg-1 h-1 (95% confidence limits 5.5-6.2 mg kg-1 h-1) and ED95 8.6 (6.8-7.8) mg kg-1 h-1. Corresponding values for series 2 were ED50 7.5 (8.0-9.8) mg kg-1 h-1 and ED95 10.5 (9.6-13.1) mg kg-1 h-1.

Adult↗
PubMed1991

Oesophageal contractility during total i.v. anaesthesia with and without glycopyrronium.

Somatic movement and spontaneous and provoked oesophageal contractions were noted at time of incision in 51 patients receiving total i.v. anaesthesia with alfentanil and propofol. Probit analysis of the dose of propofol required to prevent spontaneous movement revealed an ED50 (95% confidence limits) of 2.5 (1.8-2.9) mg kg(-1) h(-1) and ED95 of 4.7 (4.0-7.5) mg kg(-1) h(-1). Corresponding venous blood concentrations gave an EC50 of 1.2 (0.4-1.6) micrograms ml(-1) and an EC95 of 4.0 (2.8-18.5) micrograms ml(-1). ED50 of propofol for preventing spontaneous oesophageal contraction was 3.0 (1.9-3.6) mg kg(-1) h(-1). ED95 was 6.9 (5.0-27.3) mg kg(-1) h(-1); EC50 for oesophageal contractions was 1.7 (0.7-2.3) micrograms ml(-1) and EC95 was 5.9 (3.7-70.6) micrograms ml(-1). Another group of 10 patients were given glycopyrronium 5 micrograms kg(-1) at induction; oesophageal contractility was significantly reduced in this group.

Adult↗
PubMed1991

Total i.v. anaesthesia with propofol and alfentanil for coronary artery bypass grafting.

The haemodynamic effects of total i.v. anaesthesia with a combination of propofol and alfentanil infusions were studied in eight patients with good left ventricular function undergoing coronary artery bypass surgery. Haemodynamic indices were measured before anaesthesia and at specified intervals before cardiopulmonary bypass. The technique resulted in haemodynamic changes comparable to those reported with opioid-based anaesthesia for coronary artery surgery, and has potential advantages.

Alfentanil↗
PubMed1991

Combined morphine-bupivacaine caudals for reconstructive penile surgery in children: systemic absorption of morphine and postoperative analgesia.

We wished to determine if the addition of a small dose of morphine (0.05 mg.kg-1) to a caudal solution of 0.25% bupivacaine could extend the duration of analgesia after major reconstructive penile surgery and also to measure the systemic absorption of morphine after caudal injection. Thirty children undergoing reconstructive penile surgery received a caudal injection of 0.25% bupivacaine 0.75 ml.kg-1 with or without morphine 0.05 mg.kg-1. All patients awoke pain-free, but eight of the fifteen patients receiving bupivacaine alone required supplementary injections of opioid postoperatively, whereas none of the patients receiving the bupivacaine-morphine mixture required additional opioids. The incidence of side-effects was similar for the two groups. Morphine was absorbed rapidly after caudal injection to reach a peak plasma level of 21.2 (+/- 4.8) ng.ml-1 at ten minutes and then fell to 10.1 (+/- 3.8) ng.ml-1 at one hour and 4.1 (+/- 2.6) ng.ml-1 at three hours. These levels are low compared with plasma levels associated with systemic analgesia. We conclude that the extended duration of analgesia from morphine 0.05 mg/kg given caudally is due at least in part to specific spinal analgesia.

Analgesia, Epidural↗
PubMed1991

Plasma inorganic fluoride concentrations during and after prolonged (greater than 24 h) isoflurane sedation: effect on renal function.

We studied the effect of prolonged sedation (greater than 24 h) with isoflurane on plasma inorganic fluoride concentrations and renal function in 60 critically ill patients allocated randomly to receive either isoflurane or midazolam for sedation. In the isoflurane group, plasma fluoride increased from a mean concentration of 3.1 mumol/L to 20.0 mumol/L at the end of sedation, continued to increase to a peak of 25.3 mumol/L 16 h later, and then decreased exponentially (t1/2 = 111 h) to reach normal levels by the fifth day. In the midazolam group, the plasma fluoride increased from a mean concentration of 4.2 mumol/L to a peak of 6.8 mumol/L 12 h after starting the sedation and then decreased toward normal. Serum and urinary electrolytes, urine osmolality, and creatinine clearance during and after sedation were similar in the two groups. Isoflurane sedation was associated with an increase in plasma fluoride concentration without any clinical deterioration of renal function.

Adolescent↗
PubMed1990

Plasma catecholamine concentration during sedation in ventilated patients requiring intensive therapy.

The effects of isoflurane and midazolam sedation on the catecholamine responses of ventilated patients were studied over a 24-h period. Sixty ventilated patients admitted to our intensive therapy unit were allocated randomly to receive either isoflurane or midazolam sedation. Arterial blood samples for plasma catecholamine concentrations were taken at baseline, 6 h after starting sedation and at the end of the study period. Patients sedated with isoflurane showed a progressive reduction in both adrenaline and noradrenaline concentrations during the period of sedation which reached statistical significance for adrenaline at 6 h (p less than 0.02) and at the end of the study (p less than 0.001). Patients sedated with midazolam showed no significant changes of adrenaline or noradrenaline concentrations. Overall, a more satisfactory degree of sedation was achieved with isoflurane.

Administration, Inhalation↗
PubMed1990

Self-tuning adaptive control of induced hypotension in humans: a comparison of isoflurane and sodium nitroprusside.

Induced hypotension is commonly used during surgery to decrease arterial pressure. Sodium nitroprusside and isoflurane are well-known hypotensive agents. The use of self-tuning adaptive control of induced hypotension was assessed with the use of sodium nitroprusside and isoflurane as hypotensive agents. Nineteen surgical patients were studied during closed-loop control of hypotension induced with sodium nitroprusside. This group of patients was compared with 10 similar patients in whom infusions of sodium nitroprusside were controlled manually by an anesthesiologist. Although the results of the two studies varied, no conclusion could be drawn regarding the superiority of either manual or closed-loop control. When manual versus automatic control of isoflurane-induced hypotension was assessed in a similar fashion, the two methods of induction were found to be comparable.

Algorithms↗
PubMed1990

Study of the possible interaction between fentanyl and propofol using a computer-controlled infusion of propofol.

A computer-controlled infusion of propofol designed to achieve a target blood concentration of propofol 3 microgram ml-1 was used to investigate the possibility of an interaction between propofol and fentanyl in 32 patients undergoing body surface surgery. In 16 patients who were not receiving a neuromuscular blocker during maintenance anaesthesia with 67% nitrous oxide, there were no significant differences in blood concentrations of propofol between eight patients who received fentanyl 5 micrograms kg-1 before induction of anaesthesia, and eight patients who did not. In a further 16 patients who received vecuronium during maintenance anaesthesia with 67% nitrous oxide, there were no significant differences in blood propofol concentrations between eight patients who received fentanyl 5 micrograms kg-1 before induction of anaesthesia, and eight patients who did not. Fentanyl administered i.v. immediately before a computer-controlled infusion of propofol resulted in more satisfactory anaesthetic conditions than when fentanyl was not used, but did not significantly prolong the recovery time.

Adult↗
PubMed1990

Isoflurane sedation for patients undergoing mechanical ventilation: metabolism to inorganic fluoride and renal effects.

The metabolism and renal effects of isoflurane sedation were studied for 24 h in patients undergoing mechanical ventilation. Forty-six patients admitted to our intensive therapy unit were allocated randomly to receive either 0.1-0.6% isoflurane or midazolam 0.01-0.2 mg kg-1 h-1 for sedation. In 26 patients sedated with isoflurane, plasma inorganic fluoride increased from a mean concentration of 4.03 mumol litre-1 to 13.57 mumol litre-1 12 h after stopping sedation. Plasma inorganic fluoride concentrations in 20 patients sedated with midazolam were unchanged from baseline values (mean 5.32 mumol litre-1). Serum electrolyte, urea and creatinine concentrations, and urine output rates during and after sedation in patients who received isoflurane were similar to those who received midazolam. We conclude that, following isoflurane sedation for up to 24 h, metabolism to inorganic fluoride is insufficient to cause clinical renal dysfunction.

Aged↗
PubMed1990

Postoperative analgesia after paediatric orchidopexy: evaluation of a bupivacaine-morphine mixture.

The value of combining morphine with bupivacaine for caudal analgesia was investigated. Thirty children, undergoing orchidopexy, received a caudal block of 0.125% bupivacaine with or without morphine 0.05 mg kg-1. Analgesia, side-effects, ventilatory frequency and oxygen saturation (SaO2) were recorded after operation. None of the 15 patients receiving the bupivacaine-morphine mixture required post-operative opioids, whereas eight of 15 patients receiving bupivacaine alone needed additional opioid analgesia. The incidence of side effects after surgery was similar for the two groups and there was no detectable difference in ventilatory frequency or SaO2.

Analgesia, Epidural↗