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Biomedical subjects

J Watkins

Publications and source records attributed to J Watkins.

At least 109 records · Page 6Linked to original sources
PubMed1986

Metallurgical analysis of failed Björk-Shiley cardiac valve prostheses.

An investigation into the mechanisms of failure of current Björk-Shiley cardiac valve prostheses is reported. Two failed valves, one apparently unfailed but defective valve, and one unused valve, were examined by scanning electron microscopy and metallographic section. In the first two valves (removed 12 and 23 months after implantation) fracture was associated with the welds joining the short strut to the valve ring. The fracture surfaces in all cases were heavily faceted and showed branching cracks. Extensive wear had occurred on one fracture surface in the first case, suggesting that one leg of the short strut had failed before the other, though this had been clinically undetectable. The third valve was removed owing to failure of the suturing (24 months after implantation) but one leg of the short strut was found to be completely fractured. The other leg showed extensive cracking and porosity in the weld region. A metallographic section taken through the weld region of the fourth (unused) valve illustrated several sizable defects directly attributable to the welding process. It is suggested that the valves failed by fatigue and that these problems could be overcome if the complete valve cage were machined as a single piece.

Aged↗
PubMed1986

Histaminoid response after intradermal and intravenous administration of atracurium, vecuronium and tubocurarine: a comparative study.

The object of this study was to investigate the histaminoid responses after intradermal administration of atracurium, vecuronium and tubocurarine and to compare these with the cutaneous and cardiovascular responses to intravenous administration of the above relaxants in the same patients. Positive local cutaneous responses to intradermal injection were most common after tubocurarine (92%) and least common after vecuronium (12%). Tubocurarine produced the greatest fall in systolic pressure 3 min after intravenous administration but there was no difference in this respect between atracurium and vecuronium. In any individual patient the response to intradermal injection of a relaxant was not a reliable predictor of the response to subsequent intravenous administration of the same relaxant. Twenty patients had plasma IgE levels below 12 IU ml-1. This abnormally low titre occurred more frequently in female patients and was associated with an increase in the incidence and degree of histaminoid responses to atracurium and tubocurarine. Low plasma IgE may be associated with a deficiency in surface IgE on mast cells which therefore have an increased sensitivity to drugs that cause direct pharmacological histamine liberation.

Adolescent↗
PubMed1986

Type A influenza.

Explore the source record for details and available documents.

Disease Outbreaks↗
PubMed1986

The allergic reaction to intravenous induction agents.

There is an increasing awareness of adverse drug reactions and particularly those relating to anaesthesia and surgery where a wide variety of substances may be administered intravenously. The intravenous route offers considerable therapeutic and diagnostic advantage to the clinician. With pharmacologically active drugs the route avoids drug deactivation by digestive enzymes and first-pass hepatic metabolism. With large volumes of fluids, electrolytes, blood, blood fractions and their substitutes it is the only possible way of administration.

Anaphylaxis↗
PubMed1985

The early diagnosis of impending coagulopathies following surgery and multiple trauma.

Blood coagulation problems, either disseminated intravascular coagulation (DIC) or adult respiratory distress syndrome (ARDS) are frequent complications during the recovery of the polytraumatized surgical patient or accident victims. The key to their successful control lies in prompt recognition and aggressive treatment of the disease as soon as it appears. Unfortunately their onset is not usually well defined clinically and success in handling usually depends upon clinical expertise in recognising "high risk" situations coupled with measurements in the haematological laboratory of changes in plasma coagulation factors. It is suggested in this communication that a relatively simple examination of plasma complement profiles in the high risk, intensive care patient, may not only provide early warning of the onset of a coagulopathy but also distinguish the type. Simple tests are described, based on the assessment of plasma complement C5 levels, which have a high predictive value for the onset of ARDS, a disease with few early clinical manifestations and notably lacking in early changes in haematological parameters. In prospective trials complement tests correctly identified 18 patients who later developed ARDS but were no more effective than haematological tests in the identification of 24 patients who subsequently developed DIC.

Blood Protein Electrophoresis↗
PubMed1985

Complement and clinical intervention.

The nine major components of the complement protein system are normally activated in sequence by antigen-antibody complexes, initiating the inflammatory response. The clinical manifestations arise mainly from the release of histamine, mediated by anaphylatoxin action on mast cells. In rampant infection, this classical pathway is enhanced by further activation of complement C3 through a specific enzyme loop, the alternative pathway. Unfortunately the complexity of the complement system makes it vulnerable to external interference, particularly to man's intervention both through the administration of intravenous "drugs" and by certain surgical procedures. This results in gross systemic activation of complement, particularly C3 giving rise to anaphylactoid shock. More recently, direct activation of complement C5 has been reported, particularly as a result of polytrauma. This has consequences on polymorphonuclear leucocyte behaviour and is likely to be involved in adult respiratory distress syndrome (ARDS). Similarly, excessive activation of C3 may stimulate disseminated intravascular coagulation (DIC) rather than immediate anaphylactoid response. The clinical outcome of complement activation appears to depend upon the rate of activation and its extent, as well as upon the particular component involved. In immediate reactions, complement may be involved in both immune and non-immune activations. Bias to certain pathways is revealed by certain drugs or procedures, and practical methods of evaluating reaction mechanisms are discussed. Despite the high incidence of complement involvement in immediate reactions, there are no useful screening pointers to the patient "at risk". Delayed effects have received little attention. Although C3 conversion is certainly associated with DIC, its predictive value in a clinical trial was not very great.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphylaxis↗
PubMed1985

Skin testing in the investigation of reactions to intravenous anaesthetic drugs. A prospective trial of atracurium and tubocurarine.

Intradermal skin testing is widely used to determine the causative drugs of presumed anaphylactic anaesthetic reactions. This paper sets out to evaluate the usefulness of skin tests, both intradermal and prick testing, in the prediction of anaesthetic reactions. The muscle relaxant drugs tubocurarine and atracurium were chosen for study since they are known to produce a high incidence of minor histaminoid reactions. A trial was conducted in 22 female patients about to undergo elective gynaecological surgery for non-malignant conditions. In intradermal tests, positive wheal and flare reactions to one or other relaxant (diluted 1 in 1,000) occurred in 17 patients and reactions to both drugs in 11 patients. Despite this high incidence of positive reactions, none of the patients had received either drug previously, a view confirmed by the negative results of prick testing. Likewise, when anaesthetized for surgery using atracurium or tubocurarine allocated randomly, the minor histaminoid manifestations observed showed no correlation whatsoever with the intradermal tests results. The results of the trial, combined with external reports to this centre, indicate that intradermal testing of anaesthetic drugs, particularly muscle relaxants, produces a high incidence of false positive results. This probably reflects their pharmacological activity rather than antigenicity. It is recommended, therefore, that skin testing should be reserved for situations in which there are strong indications from laboratory tests, backed by case history, of immune sensitization.

Adult↗
PubMed1985

Histaminoid responses to atracurium, vecuronium and tubocurarine.

Sixty patients scheduled for elective surgery underwent intradermal testing with 0.1 ml of the following solutions diluted in 0.9% saline: vecuronium and tubocurarine (1 in 1,000), atracurium (1 in 1,000 and 1 in 10,000), thiopentone (1 in 100) and also a 0.9% saline control. Thirty minutes later, an area of erythema of greater than 1.5 cm, or a wheal exceeding 1.0 cm in diameter, was recorded as a positive reaction. The patients then randomly received equipotent doses of atracurium, vecuronium or tubocurarine during a standardized anaesthetic induction. Any cutaneous reaction and the percentage fall in systolic pressure three minutes after administration of the relaxant were recorded. In 51 patients plasma IgE levels were measured. The incidence of positive cutaneous reactions to intradermal and intravenous relaxants was significantly different with each agent (p less than 0.01). The percentage fall in systolic pressure after tubocurarine was significantly different relative to the other two agents (p less than 0.01). This was regarded as reflecting potency in releasing histamine and placed the relaxants in the same order: tubocurarine, atracurium and vecuronium. The response to intradermal administration was no guide to the subsequent response after intravenous administration of the three relaxants. IgE levels below 15 IU X ml-1 occurred significantly more often in females and were associated with a significantly higher incidence of cutaneous reactions after intradermal atracurium (1 in 1,000 and 1 in 10,000) (p less than 0.05 and 0.001 respectively) and tubocurarine (1 in 1,000). With these two agents, generalized flushing after intravenous administration was also more common in this group, relative to the normal/high IgE group.

Adult↗
PubMed1985

Allergy, plasma IgE level and anaphylactoid response: a hypothesis.

Any simple test predictive of immediate hypersensitivity-like (anaphylactoid) response to anaesthetic agents would be clinically useful. Possession of the traits of allergy or atopy, and of raised plasma IgE levels, all easily established, have previously been reported as predisposing factors. The usefulness of such observations has been limited by the fact that many reactions are not immune and do not involve IgE antibodies. This hypothesis suggests how IgE levels may be widely predictive of other reaction mechanisms and partially explains some of the divergent views on the mechanisms of anaphylactoid response which occur in the literature.

Adult↗