R D Slight

Royal Society of Edinburgh, Edinburgh, Scotland, United Kingdom

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Publications (15)38.02 Total impact

  • BJA British Journal of Anaesthesia 04/2009; 102(3):294-6. · 4.24 Impact Factor
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    ABSTRACT: Blood transfusion remains one of the commonest interventions carried out upon individuals undergoing cardiac surgery. Despite this, the scientific rationale on which to base this decision is limited. Currently, hemoglobin concentration is often used as the sole guide as to when a transfusion may be required. A fall in hemoglobin concentration is often assumed to be associated with a similar drop in red cell volume. A review was undertaken of all the relevant peer-reviewed literature to determine what factors we should consider when deciding to transfuse elective cardiac surgery patients. The large fluid load associated with cardiac surgery, primarily from the cardiopulmonary bypass circuit, may have a significant dilutional effect. In such a scenario, several interlinked protective mechanisms may ensure that tissue oxygenation is maintained, including a reduction in blood viscosity, a decrease in systemic afterload, and an increase in cardiac output. Furthermore, oxygen requirements during the initial perioperative phase are reduced because of the effect of general anesthesia and hypothermia during cardiopulmonary bypass. When deciding to transfuse, consideration should be given to red cell volume, circulatory status, and oxygen requirement. It is possible that such an all-encompassing approach would reduce the incidence of unnecessary, and potentially counterproductive, red cell transfusion in cardiac surgery.
    Transfusion medicine reviews 02/2009; 23(1):42-54. · 3.61 Impact Factor
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    ABSTRACT: For many years it has been assumed that patients undergoing cardiac surgery utilizing cardiopulmonary bypass accumulate an "oxygen debt" that requires a higher postoperative hemoglobin concentration for its reversal. Much of this evidence has now been discredited due to mathematical error with recent research suggesting critical levels of oxygen delivery are lower than previously thought. This article aims to explore the relationship between observed and critical oxygen delivery with an estimation of the minimal hemoglobin required. This was a single-center observational study. Nineteen adult elective cardiac surgery patients were recruited to participate with four subsequently excluded. Observed measurements of oxygen delivery were recorded and compared with calculated "critical" values adjusted for temperature. The hemoglobin value that represented critical oxygen delivery was compared with the observed value to identify any "hemoglobin reserve." At no perioperative time point did observed oxygen delivery or critical hemoglobin concentration significantly approach its corresponding critical value. Current transfusion practice in noncritically ill cardiac surgery patients may be considered excessive if systemic oxygen requirement is the sole parameter considered.
    Artificial Organs 01/2009; 32(12):949-55. · 1.96 Impact Factor
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    ABSTRACT: Cardiac surgery is currently considered one of the heaviest users of red blood cells. An explanation may be found, in part, in considering the effect of the heavy clear fluid load associated with cardiopulmonary bypass. This may result in the artificial depression of haemoglobin concentration, overestimating the requirement for red cell transfusion if this is the sole parameter considered. To address this issue, we examined the impact of a red cell volume-based transfusion guideline on transfusion requirement. This was a single-centre, randomized controlled trial. The cohort of 86 patients was allocated to receive red cells as per the red cell volume guideline (group RCV) or standard haemoglobin concentration-based departmental policy (group C). Outcome measures were red cell transfusion and clinical outcome. All preoperative data were comparable between the two groups. A significantly fewer percentage of patients in group RCV were transfused red cells (RCV = 32.6% vs. C = 53.5%, P = 0.05). No significant difference was found between any of the outcome measures with the exception of median hospital stay (RCV = 5.9 days vs. C = 6.8 days, P = 0.02). In elective cardiac surgery patients, considering haemoglobin concentration alone may overestimate the requirement for red cell transfusion. More research is required to determine the impact of restrictive transfusion policies on clinical outcome following cardiac surgery.
    Vox Sanguinis 11/2008; 95(3):205-10. · 2.85 Impact Factor
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    ABSTRACT: Sodium fluorescein flow cytometry for the calculation of red cell volume is an exciting proposition in that the repeatability of the technique in a short time frame should allow for applications such as the measurement of surgical red cell volume loss. Our results found that the rapid decay in fluorescence negated the usefulness of this technique as currently described. However, further investigation into the behaviour of the sodium fluorescein labelled red blood cells may allow for the mathematical correction of the fluorescent red cell population prior to red cell volume calculation.
    International journal of laboratory hematology 03/2008; 31(2):233-5. · 1.30 Impact Factor
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    ABSTRACT: The inadequacy of heparinization during cardiopulmonary bypass (CPB) can lead to hemostatic activation with increases in postoperative blood loss and blood product requirements after cardiac surgery. Because activated coagulation time (ACT) measurements may not be accurate during CPB, the use of a heparin management system (HMS) has been advocated. This study compared the efficacy of a modified ACT-based system versus an HMS (Hepcon; Medtronic Inc, Minneapolis, MN) for CPB anticoagulation. Randomized controlled trial. Regional cardiac surgery center. Adult elective cardiac surgical patients. Patients allocated to the HMS group (HC) received individualized heparin doses as indicated by the Hepcon system. Patients in the modified ACT group (C) received a standard weight-based heparin bolus with further doses as dictated by the ACT (Max-ACT, Helena Labs, Sunderland, UK). In addition, group C received supplemental heparin, independent of the ACT, as dictated by the volume of crystalloid added to the extracorporeal circuit. Outcome measures examined were hemostatic activation, postoperative chest tube loss, and blood product requirements. This study showed no significant difference in efficacy between the modified ACT and HMS heparinization strategies. Although the HC group received significantly greater amounts of heparin, this did not reduce hemostatic activation, postoperative blood loss, or transfusion requirements. ACT-based heparinization was found to be as efficacious as the Hepcon HMS system.
    Journal of cardiothoracic and vascular anesthesia 03/2008; 22(1):47-52. · 1.06 Impact Factor
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    ABSTRACT: Cardiac surgery, utilizing extracorporeal circulation, is associated with a heavy fluid load that may significantly depress haemoglobin concentration. Thus, considering haemoglobin alone may be an inaccurate method of replacing red cell volume loss. This study was designed to examine the impact on red cell transfusion of a red cell volume-based guideline. Patients were randomized to receive red cells as dictated by the red cell volume-based guideline or a haemoglobin-based protocol. End-points considered were red cell transfusion and clinical outcome. Patients transfused as per the red cell volume-based guideline received significantly less red cells with no associated difference in clinical outcome. Considering haemoglobin concentration alone may significantly overestimate the requirement for red cell transfusion in elective cardiac surgery patients.
    Vox Sanguinis 03/2007; 92(2):154-6. · 2.85 Impact Factor
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    ABSTRACT: Haemodilution contributes to a low post-operative haemoglobin concentration in cardiac surgery patients. An assessment of the degree of haemodilution could contribute to the avoidance of red cell transfusion when such an act is based simply on a haemoglobin "transfusion trigger". We have recorded post-operative change in total body water along with body weight to assess the impact of haemodilution on haemoglobin concentration. Total body water, measured by bio-electrical impedance analysis, haemoglobin and body weight were measured pre-operatively and on the 1st, 3rd, 5th and 10th post-operative days. The percentage peri-operative change in all three variables was used to examine the paired associations. Total body water and body weight underwent a fall from day 1, with both variables significantly associated up until day 10. Haemoglobin rose steadily from day 1 to 10. This rise was associated with falling total body water and body weight until day 5, but not from day 5 to 10. Following cardiac surgery, an individual's fluid state should be considered in determining a patient's need for red cell transfusion. Monitoring body weight provides a simple estimate. Such an approach may reduce the incidence of unnecessary, and potentially counterproductive, transfusion in cardiac surgery patients.
    Heart Lung &amp Circulation 09/2006; 15(4):256-60. · 1.25 Impact Factor
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    ABSTRACT: Haemoglobin may be a poor indicator of changes in red cell volume (RCV) because of factors such as haemodilution. This study has been designed to analyse what peri-operative variables may be associated with loss or gain in RCV due to bleeding or transfusion. Prospective observational study. Single centre study based in a regional cardiac surgery centre. Twenty-nine elective adult cardiac surgery patients. Loss and gain of RCV were measured in theatre and for the first 24 h post-operatively. Patient and operative factors analysed were age, sex, height, weight, body surface area (BSA), induction haematocrit (Hct), estimated pre-operative RCV and antiplatelet therapy taken less than 7 days before operation, cardiopulmonary bypass (CPB) time, aortic occlusion time, minimum and maximum CPB temperatures and fluid administered. Age, sex, height, weight, BSA and induction Hct were found to predict red cell transfusion but not RCV loss. The total number of red cells transfused was significantly associated with RCV lost when expressed as a percentage reduction in the estimated pre-operative RCV but not the absolute RCV lost. Pre-operative RCV, as predicted by the variables outlined above, is more important than RCV lost in triggering red cell transfusion.
    Transfusion Medicine 07/2006; 16(3):169-75. · 1.26 Impact Factor
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    ABSTRACT: Current blood prescription in cardiac surgery is based largely on hemoglobin (Hb) concentration. Hb may not provide a reliable guide to the patient's red cell (RBC) volume (RCV) during cardiac surgery as a consequence of the high fluid loads infused. This study provides estimates of the perioperative changes in RCV, plasma volume (PV), and blood volume (BV) with a view to developing a more accurate way of assessing a patient's need for transfusion. Thirty adult elective cardiac surgery patients were recruited to the study. The preoperative RCV was calculated by use of a standard nomogram. Losses and gains in RCV at several time points were added or subtracted from the baseline value. Estimates of PV and BV were derived from patient hematocrit level and RCV for each time point. The greatest perioperative loss of RCV occurred during cardiopulmonary bypass (CPB); however, half of this loss was returned to the patient at the end of CPB. A net gain of RCV occurred during the period of intensive care management. PV and BV showed two distinct peaks, immediately after CPB and at 16 hours after intensive therapy unit return. PV and BV expansion are significant factors that may lead to a Hb value that is misleadingly low in that it overestimates the decrease in RCV. This effect could lead to unnecessary transfusion if the RBC transfusion threshold is based only on Hb concentration.
    Transfusion 04/2006; 46(3):392-7. · 3.53 Impact Factor
  • O Nzewi, R D Slight, V Zamvar
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    ABSTRACT: Blunt traumatic aortic transection (TAT) is an uncommon injury in clinical practice that is associated with a high morbidity and mortality. The approach to patients with such an injury is controversial with specific regard to the most effective diagnostic tools, timing of surgical intervention and mechanisms of spinal cord protection. Chest X-ray with widening of the mediastinum is unreliable as a diagnostic tool. Contrast enhanced helical CT Scan has replaced the traditional angiography as the screening diagnostic tool of choice Emergency thoracotomy and repair should be reserved for the few patients with isolated TAT without any major concomitant injuries. Delayed management approach with aggressive blood pressure control and serial radiological monitoring is a safe and recommended option for those with severe concomitant injuries or other medical co-morbidity that puts surgery at high risk. Active augmentation of the distal perfusion pressure during cross clamp offers the best protection against development of paraplegia during open surgical repair. Endovascular stenting offers a minimally invasive method of treatment but the long-term durability of the endovascular stent is still unknown. We feel that the greater feasibility of the endovascular repair in the acute phase of the thoracic injury is an advantage over the open surgery and should be the treatment of choice in patients with severe concomitant injuries.
    European Journal of Vascular and Endovascular Surgery 02/2006; 31(1):18-27. · 2.82 Impact Factor
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    ABSTRACT: Cor-triatriatum sinister is a rare congenital heart defect resulting from the division of the left atrium by a fibro-muscular membrane. It is usual for patients to present in infancy and early childhood, although some cases remain undetected until adult life. As a consequence of trans-membrane flow obstruction, the clinical features often mimic mitral stenosis. At present, the reasons for late presentation are poorly understood. A complete review of all cases of cor-triatriatum sinister published in the English literature from 1966 to date as mitral stenosis was performed. Statistical analysis was carried out to determine associations between measurements reflecting the communicating membrane fenestration area, the presence of several clinical variables and patient age at initial presentation. Both pulmonary capillary wedge pressure and mean pressure gradient were significantly higher in younger adults. In addition, the incidence of atrial fibrillation and mitral regurgitation was found to rise with advancing age. Cor-triatriatum sinister remains an uncommon form of congenital heart disease although it is being diagnosed with increasing frequency in adults due to improvements in diagnostic imaging. This diagnosis should be considered in all patients presenting with signs or symptoms of mitral stenosis.
    Heart Lung &amp Circulation 04/2005; 14(1):8-12. · 1.25 Impact Factor
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    R D Slight, O C Nzewi, P S Mankad
    Heart (British Cardiac Society) 02/2004; 90(1):63. · 5.01 Impact Factor
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    ABSTRACT: Cor triatriatum sinister is a rare congenital defect in which the left atrium is divided by a fibromuscular membrane into two distinct chambers. Classically, patients present in infancy although in some cases they remain asymptomatic until adulthood. The clinical features on presentation can mimic those of mitral stenosis due to the obstructive properties of the membrane. Cor triatriatum sinister presented in this case in an adult as mitral stenosis. Factors that may be relevant in determining late presentation are also discussed.
    Heart (British Cardiac Society) 11/2003; 89(10):e26. · 5.01 Impact Factor
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    ABSTRACT: 35 to 40 years.2 We report two cases of SCAD that presented at our institution. In both instances no cardiac risk factors were identified and angiography did not demonstrate any evidence of coronary artery disease. An important observation was the menstrual status of both patients. We propose a potential pathogenesis for SCAD in pre-menopausal women. Case reports Case 1 A 49-year-old female GP was admitted with a one-hour history of central, crushing chest pain. There was no history of cardiovascular disease or identifiable coronary risk factors. The patient was noted to be at the beginning of her menstrual cycle. ECG on admission revealed antero-lateral ischaemic changes and the patient subsequently underwent thrombolysis with streptokinase. Due to the persistence of chest pain and the ECG changes, urgent angiography was performed, which demonstrated dissection of the proximal two thirds of the left anterior descending (LAD) artery (Figure 1). No additional coronary disease was identified. Surgical intervention was felt to be the most appropriate course of action in order to preserve a large first diagonal branch. The patient was haemodynamically stable prior to surgery. The presence of intra-mural haematoma, compressing the lumen of the LAD, was confirmed at operation. Two saphenous-vein coronary artery bypass grafts (CABG) were performed to the LAD and the first diagonal branch with the aid of standard cardiopulmonary bypass (CPB). Elective intra-aortic balloon pump (IABP) support was used to discontinue CPB. Re-exploration was performed on the first post- operative day for continuing blood loss and a vein side branch was ligated. Echocardiography on the fourth post-operative day demonstrated antero-apical akinesis with normal valvular function consistent with a trans-mural myocardial infarction. Further recovery was uneventful and the patient was well enough to be discharged home on the eighth post-operative day.
    The New Zealand medical journal 10/2003; 116(1181):U585.