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Biomedical subjects

D R Wheeldon

Publications and source records attributed to D R Wheeldon.

15 recordsLinked to original sources
PubMed1996

An approach to the retrieval of thoracic organs for transplantation.

A critical, worldwide shortage of thoracic organs exists. The donor management program at Papworth Hospital, National Health Service Trust, Cambridge, United Kingdom, allows satisfactory transplantation of thoracic organs that initially appear unsuitable. The perioperative organ retrieval team members assess the cardiovascular status of all potential donors and manage suboptimal hemodynamics with hormonal replacement therapy consisting of triiodothyronine, antidiuretic hormone, epinephrine, and insulin. These donors' cardiovascular and pulmonary functions must be within acceptable limits at the time of organ excision. Our standardized approach facilitates objective decision making regarding the appropriate use of donor organs and has increased the number of available donor organs at Papworth Hospital by 30%. Morbidity and mortality rates in thoracic organ recipients have not increased since the authors developed the standardized approach, and more patients have benefited from thoracic organ transplantation.

Decision Making, Organizational↗
PubMed1994

Using "unsuitable" hearts for transplantation.

Donor availability is the single most limiting factor in heart transplantation. From a consecutive series of 100 heart donors, there were 21 which fell well outside our minimum criteria on initial inspection: mean arterial pressure (MAP) more than 60 mm Hg, central venous pressure (CVP) less than 12 mm Hg, pulmonary capillary wedge pressure (PCWP) less than 12 mm Hg, left ventricular stroke work index (LVSWI) more than 15 g.m. on inotropes less than 5 mcg/kg per min. Of these 13 out of 21 had a MAP less than 55 mm Hg, 6 out of 21 a CVP more than 15 mm Hg and 2 out of 21 were on inotropes at more than 20 mcg/kg per min. Following full invasive monitoring another 14 donors fell outside our criteria; 5 had a mean LVSWI of 12.4 g.m. and 9 had a mean PCWP of 19.6 mm Hg. Following the institution of our hormone-based pharmacological resuscitation regime 30 of these donors yielded 19 transplantable hearts and 11 transplantable heart-lung blocks. The other five were not used due to left ventricular hypertrophy (2), inotrope dependency (2) and persistent poor function (1). Twenty-five of the 30 recipients of these organs (83.3%) are alive and well, 4-25 months post transplant. Four early deaths occurred; one arrhythmia (heart), one acute respiratory distress syndrome (heart), one cerebrovascular accident (heart lung) and one infection (heart, lung and liver). One death occurred at 90 days from tamponade (heart). Aggressive and focussed donor management has helped us to maintain our levels of transplant activity, without compromising the outcome--a 30-day mortality of 16.2% in 1989, 11.8% in 1990 and 6.8% in 1991.

Blood Pressure↗
PubMed1994

Measurements of human coronary vascular impedance.

The aim of this study was to develop a method of measuring human coronary circulation impedance in a clinical setting. The authors measured coronary flow reserve (CFR) in 27 patients with chest pain and normal coronary arteries. A Judkins-style, 8F Doppler-tipped angiographic catheter was positioned in the left coronary ostium. Resting coronary flow velocity (RFV) and response to a hyperemic 12 mg intracoronary dose of papaverine (PFV) were measured. The signals were recorded by a recorder connected to a microprocessor with analogue-to-digital converter and a maths coprocessor. Using this the authors could obtain values for impedance at RFV (IR) and at PFV (IP). The CFR was defined as the ratio: PFV/RFV. An impedance index (II) was obtained as the ratio of coronary vascular impedance at peak hyperemia to the impedance at rest. The CFR was 3.2 +/- 1.2 and the II was 0.33 +/- 0.11. There was a strong inverse correlation between the CFR and the II (r = -0.9). The authors conclude that this new approach may allow a further insight into the coronary pathophysiology and may become useful in clinical cardiology, eg, in the assessment of heart transplant and Syndrome X patients.

Adult↗
PubMed1990

Vortex pumping for routine cardiac surgery: a comparative study.

Vortex pumping has become popular for mechanical assist applications, but has only recently received serious consideration for use as the arterial pump of choice for routine open-heart surgery. We report on a prospective randomized study designed to evaluate this pump in routine use. Sixteen patients undergoing routine coronary artery surgery were randomized into two groups in which the only difference in equipment and technique was the use of a Stockert roller pump in group S and a Biomedicus vortex pump in group B. The groups were compared with respect to haematology, perioperative fluid balance, transfusion requirements, complement activation, haemolysis and microbubble transmission. The groups were reasonably well matched, with slightly longer mean bypass and ischaemic times in group S (94.8 vs 105.5 minutes and 75.7 and 83.8 minutes respectively). Group B patients showed significant improvements over group S patients with respect to preservation of platelet numbers, decreased complement activation and reduced microbubble transmission. The afterload sensitivity of the vortex pump did not present the perfusionist with any practical problems although a different technique is required for initiating and terminating bypass. We conclude that vortex pumping would seem to offer better blood handling for routine use. More extensive testing is required to establish whether or not this would be reflected in clinically measurable improved patient outcome.

Adult↗
PubMed1990

Risk containment during cardiopulmonary bypass.

It is evident that positive attitudes towards patient care are the cornerstone of risk containment during CPB. Positive attitudes are shaped by education and training, including continuing education. Mutual respect among team members can foster positive attitudes that are manifested in an orderly, quiet operating room, with those present always mindful of the patient's welfare. Vigilance is the key in preventing complacency during CPB procedures that have now become routine. Collins writes that the best airplane pilots develop a curious and suspicious attitude in the cockpit and, again, the applicability of the aviation and perfusion analogy is apparent. Monitors, standards, protocols, and safety devices can never fully replace vigilance in overcoming human frailty or error. Vigilance has been defined as "a state of clinical awareness whereby dangerous conditions are anticipated or recognized and promptly treated." Stoelting further writes that levels of vigilance may be reduced by extraneous distractions, fatigue, and stress. Gaba et al have studied anesthetic mishaps in the context of accident investigations in unrelated fields and have suggested two responsibilities in breaking the chain of accident evolution. The first is to scrutinize our own abilities and limitations ... and implement the procedures and training that can be shown to optimize patient safety, and second ... to reexamine the entire structure of our industry, attempting to steer the interacting sources of incentive and constraint towards a system that promotes patient safety. Guides to acceptability of risk include the twin tenets of reasonableness and custom of usage, prevailing professional practice, the best available practice, and the degree of necessity or benefit.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiopulmonary Bypass↗
PubMed1976

A simple cooling circuit for topical cardiac hypothermia.

Rapid uniform cooling of the heart is the most important requirement of any method using local hypothermia for protection of the myocardium during open intracardiac surgery. We report the construction and operation of a recirculation cooling circuit comprising a reservoir, pump, and heat-exchanger for this purpose. It is operated by the perfusionist and can deliver up to 1 litre of fluid per minute at 4 degrees C into the pericardium or interior of the heart. Advantages of the system include rapid cooling of the myocardium, simplicity of operation, and applicability to all routine cardiac surgical procedures.

Aortic Valve↗
PubMed1975

Performance of heat exchangers used in whole body perfusion circuits.

The performance of some commonly used heat exchangers has been investigated with particular reference to the effect of varying the water flow. The results demonstrate that there is considerable variation in the performance of most units when the water flow is changed. It is suggested that more information should be provided by the manufacturers of heat exchangers and that there should be a supply of water in cardiothoracic theatres at a sufficient pressure to allow the full performance of the heat exchangers to be realized.

Blood Flow Velocity↗
PubMedDate not supplied

Storage and transport of heart and heart-lung donor organs with inflatable cushions and eutectoid cooling.

A system that uses a chemical method of cooling has been developed for the storage and transport of heart and heart-lung donor organs. This provides a precisely controlled environmental temperature without the use of ice, with its attendant problems of availability and potential contamination with pathogens. Storage and preservation solutions are transported to the donor hospital within the temperature-controlled polyurethane container, and the organs are returned in the same container, within an inflatable cushion. We have used this method for the distant procurement of over 260 hearts and for the most recent 30 heart-lung organ blocks. The mean ischemic time for hearts is 2.5 hours (1.5 to 4.2 hours) and for heart-lung blocks 2.2 hours (1.2 to 4.1 hours). Most donors give multiple organs such as kidney, liver, and pancreas. One patient received heart and kidney grafts from the same donor, and another received combined heart-lung and liver grafts. In relation to primary donor organ failure, there have been four deaths of patients who have had heart transplantations and no deaths of patients who received heart-lung organ blocks. We believe that the method offers advantages over the more conventional methods of organ storage with regard to convenience, temperature control, and sterility.

Cardioplegic Solutions↗
PubMedDate not supplied

Transforming the "unacceptable" donor: outcomes from the adoption of a standardized donor management technique.

BACKGROUND: Donor management remains one of the most neglected areas of transplantation. A comprehensive donor management regimen has been developed. The results of the application of this strategy form the basis of this report. METHODS: Full hemodynamic data were collected from 150 multiorgan donors between October 1990 and August 1993. The data were collected at the time of donor team arrival, after insertion of a pulmonary artery floatation catheter and immediately before cardiac excision. RESULTS: Fifty-two donors (35%) fell well outside our minimum acceptance criteria on arrival. Twenty-one of fifty-two had a mean arterial pressure less than 55 mm Hg (mean 47 mm Hg) despite inotropic support in most cases; 10 of 52 had a central venous pressure greater than 15 mm Hg (mean 18.0 mm Hg); 2 of 52 had a high inotrope requirement greater than 20 micrograms/kg/min (mean 25 micrograms/kg/min). After the insertion of a pulmonary artery floatation catheter, an additional 13 of 52 donors were found to have a pulmonary capillary wedge pressure greater than 15 mm Hg (mean 19.8 mm Hg), and the final 6 of 52 had a low left ventricular stroke work index, less than 15 gm (mean 12.8 gm). After optimal management, including hormone replacement 44 of 52 donors yielded transplantable organs (29 hearts, 15 heart and lung blocks). Thirty-seven of forty-four patients (84%) were alive and well from 13 to 48 months after transplantation. There were five early deaths (11%) caused by infection (heart), adult respiratory distress syndrome (heart), arrhythmia (heart), cerebrovascular event (heart and lung), and infection (heart, lung, and liver). Two late deaths (5%) occurred as a result of tamponade (3 months, heart) and infection (14 months, heart and lung). Eight of fifty-two organs were still unsuitable for transplantation after optimum management during the splanchnic dissection as a result of inotrope dependency (n = 4), left ventricular hypertrophy (n = 2), and coronary artery disease (n = 2). CONCLUSIONS: The data indicate that, of the organs which initially fall outside our transplant acceptance criteria, 92% are capable of functional resuscitation. Conversely, superficial assessment may not show compromised function. Optimizing cardiovascular performance also has important implications for the viability of all transplantable organs. This aggressive approach to donor management has resulted in the transplantation of 44 donor hearts that may otherwise have been turned down or inappropriately managed.

Adult↗
PubMedDate not supplied

Functional assessment and management of heart donors: a rationale for characterization and a guide to therapy.

BACKGROUND: Traditional methods for the functional evaluation of a donor heart have relied on superficial hemodynamic data and visual inspection of the action of the heart at sternotomy. The International Registry has continued to report significant mortality for heart transplant recipients from primary graft dysfunction that may be due to donor management, donor organ selection, organ preservation, or recipient factors. The literature reports the loss of at least 25% of potential donors because of the provision of inadequate physiologic support. METHODS AND RESULTS: We have now spent several years in establishing and refining a strategy for optimizing donor management, which has resulted in the safe expansion of our donor pool by approximately 30%. Central to this management regimen has been the use of comprehensive perioperative invasive monitoring used by a cardiac anesthetist who takes responsibility for donor management during the retrieval operation. CONCLUSION: This article outlines the technique which has evolved for the functional evaluation of a donor heart, which is now used in our institution as a guide to management and as a basis for decision making regarding organ suitability.

Adolescent↗
PubMedDate not supplied

Cardiovascular dysfunction. A rationale for characterization and a guide to therapy.

Traditional clinical assessment of cardiac function has relied on the indirect measurement of systemic blood pressure, heart rate and rhythm, and central venous pressure. However, because the circulation comprises complex interactions between flow and impedance in two hydraulic systems coupled in series, the usual assumptions drawn from the measurement of only a representative sample of this system can lead to serious errors in interpretation. This is particularly significant in conditions leading to physiologic distortions. Patients undergoing major surgery, or with suspected cardiac dysfunction, can only be adequately managed with a knowledge of both right and left heart pressures, together with the measurement of cardiac output. This report presents a rationale for the use of a simple method for interpreting these data and a guide to optimizing management. For those patients with heart failure who are unable to be sustained with conventional pharmacology, criteria are suggested that may help the clinician decide when more aggressive intervention, such as mechanical assist, is required.

Biometry↗