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Biomedical subjects

D A Pybus

Publications and source records attributed to D A Pybus.

At least 19 recordsLinked to original sources
PubMed1996

The use of a load cell for continuous cardiotomy reservoir level measurement during cardiopulmonary bypass.

We have examined the use of a 6 kg strain-gauge load cell for the purpose of continuous measurement of cardiotomy reservoir volume during cardiopulmonary bypass. It performed reliably and reproducibly and was found to be simple to interface to an anaesthesia monitor. The resolution of the cell was +/- 15 ml and the bias and limits of agreement for a series of 221 measurements were +15 ml and 175 ml, respectively. A continuously available digital level signal can present significant advantages to the perfusionist. The signal can be presented remotely in the form of a bar graph or a digital display, or can be interfaced to an intelligent alarm system which can be triggered on the basis of "time to expected reservoir exhaustion' rather than absolute reservoir level. The alarm state can also be conveyed in spoken form using speech synthesis. Finally, when recorded by an automatic record keeping system, the reservoir level constitutes an important addition to the perfusion record.

Cardiac Volume↗
PubMed1994

Alterations in endotracheal tube position during general anaesthesia.

The effect of head and neck movement and Trendelenburg tilt on endotracheal tube position, relative to the carina, was studied in fifty adult patients requiring intubation for elective surgery. On average, inward movement, that is shortening of the distance between the endotracheal tube tip and the carina, resulted from neck flexion (mean = -5.5 mm), whereas outward movement occurred with neck extension (mean = 6.3 mm). Neck rotation, to right and left, and Trendelenburg tilt did not show any trend towards inward nor outward movement (mean = 0.3 mm/1.7 mm/-0.6 mm, respectively). Whilst these mean positional changes for flexion and extension confirm the findings of earlier investigations, our range of maximum inward and outward displacement for flexion (23 mm in/19 mm out), extension (21 mm in/33 mm out), rotation to right (19 mm in/17 mm out), to left (22 mm in/19 mm out) and Trendelenburg tilt (22 mm in/16 mm out) indicate that for any given postural change in any one patient, the direction and magnitude of endotracheal tube displacement is not readily predictable.

Adult↗
PubMed1991

Measuring the efficiency of an artificial lung: 1. Carbon dioxide transfer.

The performance of a hollow fibre artificial lung ('Capiox E') was analysed by measurement of the 'parallel deadspace' of the device under varying conditions in 21 patients. The efficiency with which carbon dioxide was exchanged was determined by the time available for equilibration between the blood and gas phases. When this equilibration coefficient was less than 12 seconds per litre of blood flow per litre of gas flow, there was a marked reduction in the efficiency of gas exchange. Under certain conditions, the 'counter-current' design of the device apparently permitted the clearance of carbon dioxide at a partial pressure greater than that which was found in the mixed venous blood. This anomalous behaviour may represent in vivo confirmation of the Haldane effect.

Adult↗
PubMed1986

Relationship of train-of-four ratio to twitch depression during pancuronium-induced neuromuscular blockade.

The relationship of train-of-four (TOF) ratio to the depression of the first twitch (TD) was investigated in 16 patients given pancuronium in doses insufficient to eliminate the fourth response in the train. In ten patients the block was allowed to spontaneously recover (Group 1) and in six it was reversed with neostigmine (Group 2) once maximum depression of TOF ratio had occurred. Maximum depression of the first response occurred in 6.5 +/- 4.3 min (mean +/- SD). Maximum depression of the TOF ratio was not present until 28.0 +/- 11.0 min. TOF ratio was usually still decreasing when recovery of TD had begun. However, once the TOF ratio began to recover, the recovery rates for TD and TOF ratio were similar in both the spontaneously recovering and the reversed groups. TOF ratio at complete TD recovery was 74.9 +/- 15.7 and 86.2 +/- 15.4% for the two groups. A kinetic analysis yielded significantly different elimination rate constants for the two effects from the "effect compartment." These findings suggest that these two effects of pancuronium are exerted at different sites.

Dose-Response Relationship, Drug↗
PubMed1985

Relationships between inspired oxygen concentration and venous admixture during nitrous oxide-oxygen-halothane anaesthesia.

The inspired oxygen concentration (F/O2) was changed on 43 occasions at about 30-min intervals in 13 patients during artificial ventilation with mixtures of nitrous oxide (N2O), oxygen and halothane. Ventilator settings remained unchanged for each patient and at the end of each period, samples of arterial and central venous blood (and, in six patients, pulmonary arterial blood) and inspired and expired gases were collected. Oxygen tension was measured with a dedicated electrode shown to be unaffected by N2O. Venous admixture (Qva/Qt) was calculated at each F/O2. There was a highly significant correlation between the direction of change of F/O2 and that of Qva/Qt, irrespective of whether F/O2 increased or decreased. In 10 patients, there was a progressive increase in Qva/Qt as F/O2 increased above 40%, and in all patients Qva/Qt on nearly 100% oxygen was greater than that measured at the next lowest concentration (60-80%). These results are at variance with the pattern of behaviour predicted from the "critical Va/Q" theory and support the concept of an oxygen-dependent redistribution of perfusion.

Adult↗
PubMed1985

A double blind comparison of alfentanil and fentanyl.

Alfentanil and fentanyl were compared as supplements to thiopentone, nitrous oxide, relaxant anaesthesia in a randomised, double blind trial carried out on 55 adult patients undergoing elective surgery. The fentanyl-treated patients resumed spontaneous ventilation more rapidly at the end of anaesthesia (3 minutes) than the alfentanil-treated group (5.1 minutes, p less than 0.02). In other respects the drugs appeared indistinguishable. A computer model is used to explain why, despite the shorter elimination half-life, the alfentanil-treated patients did not awaken more rapidly than those in the fentanyl group.

Adjuvants, Anesthesia↗
PubMed1984

Extradural administration of morphine and bupivacaine. A controlled comparison.

Analgesia, following operation, was provided by the extradural administration of morphine or bupivacaine in 24 patients, in a double-blind, randomized, cross-over study. Observations were made of vital signs, peak expiratory flow rate (PEFR), quality and duration of pain relief and the occurrence of adverse effects. Vital signs were little affected by morphine, but hypotension requiring active treatment occurred in three patients following the administration of bupivacaine. The PEFR was improved about equally by each drug, and the improvement was significant compared with control values (P less than 0.001). Pain relief as judged by the linear analogue scale was significantly better following bupivacaine than after morphine (P less than 0.001), but the pain score system, while showing effective pain relief in most patients with both drugs, did not demonstrate a significant difference between them. The duration of effect of morphine was significantly longer (P less than 0.05) than that of bupivacaine. Adverse effects, other than bupivacaine-induced hypotension, were not serious.

Adolescent↗
PubMed1983

Postoperative analgesia for haemorrhoid surgery.

Seventy patients undergoing haemorrhoidectomy under general anaesthesia were randomly allocated to one of five treatment groups in order to compare the effectiveness of various caudal agents in the control of postoperative pain. Four groups were given a caudal injection of either 2% lignocaine, 0.5% bupivacaine, 2% lignocaine + morphine sulphate 4 mg or normal saline + morphine sulphate 4 mg, while the fifth (control) group did not receive an injection. The number of patients requiring postoperative opiates was significantly higher in the lignocaine group than in the morphine (p less than 0.05) and morphine-lignocaine (p less than 0.05) groups. No agent significantly reduced the number requiring opiates. In those who received opiates, the mean analgesic period was 228 minutes in the control group, and was significantly longer following bupivacaine (577 min, p less than 0.01), morphine-lignocaine (637 min, p less than 0.05) and morphine (665 min, p less than 0.0). The mean analgesic period following lignocaine (349 min) was not significantly different from control. The incidence of catheterisation was lowest in those patients who did not receive caudal analgesia.

Analgesia↗
PubMed1982

Dose-effect relationships of extradural morphine.

The effectiveness of three different doses of extradural morphine (4, 6 and 8 mg) in relieving post-operative pain was compared in 24 patients. Although there was no significant difference in the efficacy of the three doses, increasing dosage increased the average duration of analgesia provided by the drug (4 mg--593 min; 6 mg--772 min; 8 mg--885 min). All three doses increased the average peak expiratory flow rate, the greatest increases being seen at the higher dosages. Increasing dosage was not accompanied by an increase in the occurrence of adverse effects.

Adolescent↗
PubMed1982

Comparison of four narcotic analgesics for extradural analgesia.

The effectiveness of extradural injections of morphine sulphate 6 mg, methadone 6 mg, pethidine 60 mg and fentanyl 60 micrograms in relieving pain after operation were compared in 24 patients. The average duration of pain relief following morphine was 12.3 h; methadone 8.7 h, pethidine 6.6 h and fentanyl 5.7 h. There was no significant difference in the efficacy of the four drugs. There were no effects of clinical importance on heart rate, respiratory frequency or arterial pressure, but arterial systolic pressure decreased after morphine and pethidine. Pethidine also caused a statistically significant reduction in diastolic pressure.

Adult↗
PubMed1982

Subclavian venous catheterisation in small children using the Seldinger technique.

Subclavian venous catheterisation, using a Seldinger technique, was attempted in 25 children weighing less than 10 kg (mean 6.4 kg). Catheterisation was successful in 24 cases. Initial catheter position was satisfactory in 19 of the 24 cases (79%) and with repositioning it was possible to obtain satisfactory flow and pressure-wave recordings in all 24 patients. The technique is simple and provides reliable access to the central circulation in small infants. There was no serious morbidity attributable to the technique.

Body Weight↗
PubMed1982

Clinical audit of an intensive care unit.

A computer-based data storage and analysis system has been used to examine data obtained from 1257 patients admitted to an intensive care unit. The system readily provides administrative and clinical information which can be used to assess the workload, therapeutic efficiency and cost-effectiveness of such a unit. As the data-based expands, we expect that we will be able to identify sensitive predictors fo both complications and mortality and thereby permit the more efficient use of intensive therapy.

Aging↗
PubMed1981

Saphenous vein grafting for angina.

An analysis of 200 consecutive patients treated by saphenous-vein bypass grafting has been carried out. One patient died in hospital, and one died nine months after surgery. Some of the factors which predispose to postoperative complications can be defined preoperatively. These are unstable angina, multiple vessels disease, and impaired left ventricular function. The complications of postoperative infarction, low cardiac output, and arrhythmia were higher in the presence of these factors. The use of cardioplegic myocardial protection lessened the incidence of complications in patients with impaired left ventricular function. Early follow-up revealed 96% of patients truly or virtually angina-free. Three patients suffered infarction within nine months of operation.

Angina Pectoris↗
PubMed1981

Clinical experience with epidural morphine.

Epidural analgesia with morphine sulphate was administered to 130 patients. Of 96 patients with postoperative pain, 74 experienced good analgesia, 14 obtained a fair degree of pain relief, and in eight the method was unsatisfactory. Of the 34 non-operated patients 30 had good pain relief and the method failed in one. The most common cause of failure of analgesia was an incorrectly placed epidural catheter. Urinary difficulties and pruritus were encountered as the principal side-effects. One patient suffered depression of the level of consciousness following epidural drug administration and in one, epidural opiate appears to have contributed to hypotension.

Adolescent↗
PubMed1980

Experimental comparison of extradural and i.m. morphine.

Morphine sulphate 3 or 4 mg was administered to the extradural space in five volunteers. Morphine 10 or 15 mg i.m. was given as control. Extradural administration resulted in an increase of pain threshold in the legs but not in the forehead. There was no significant depression of carbon dioxide response or deterioration of co-ordination or short-term memory. I.m. morphine caused an increase in forehead pain threshold, depression of the carbon dioxide response and some deterioration of cerebral function. Extradural morphine caused urinary retention in four and inability to ejaculate in three of the subjects. The principal site of action of extradural morphine appears to be regional, at spinal cord level, but it appears that autonomic function as well as pain perception can be affected.

Adult↗