Combined heart-liver transplantation with extended cardiopulmonary bypass.

We report a case of combined heart and liver transplantation for familial amyloid polyneuropathy. This is the first such combined transplant performed in Asia, and differs from previously described cases, in that cardiopulmonary bypass was continued at partial flow during liver transplantation in our case. This was done in order to provide haemodynamic support to the cardiac graft and to protect it from the impending reperfusion insult that frequently accompanies liver transplantation. The utility of this management course is discussed, along with its actual and potential complications. We also describe the impact of a lung-protective ventilation strategy employed during cardiac transplantation.

Total intravenous anaesthesia using 3-in-1 mixture of propofol, alfentanil and mivacurium.

INTRODUCTION: To avoid errors and confusion associated with 3 separate infusions, we conducted a feasibility study of total intravenous anaesthesia (TIVA) using 1 electrically-powered syringe pump to deliver a 3-in-1 mixture containing fixed proportions of propofol, alfentanil and mivacurium. MATERIALS AND METHODS: The 3-in-1 mixture was obtained by mixing 200 mg propofol, 1 mg alfentanil, 20 mg mivacurium, and making up to 40 mL with 5% dextrose solution. Electrical zone sensing sizer and light microscopy were used to compare emulsion instability of the 3-in-1 with control mixtures. In 50 ASA 1 patients, bolus infusions of 0.4 mL of the 3-in-1 mixture per kg body weight were given for induction of anaesthesia. All patients were subsequently intubated and ventilated with air-oxygen mixtures. Anaesthesia was maintained using a continuous infusion of the 3-in-1 mixture with the infusion rate titrated to satisfactory clinical response. Intravenous morphine 0.1 mg/kg was given for intra- and postoperative analgesia. Residual neuromuscular blockade was reversed using glycopyrronium and neostigmine at the end of surgery. RESULTS: The 3-in-1 mixtures remained stable for up to 5 hours after preparation. Induction and maintenance of anaesthesia were smooth, intubation conditions satisfactory, and intraoperative haemodynamic changes acceptable. Recovery from anaesthesia and neuromuscular blockade was rapid. There were no major intra- or immediate postoperative complications. CONCLUSIONS: The 3-in-1 mixtures remained stable for up to 5 hours after preparation. It may be feasible to provide TIVA using the 3-in-1 mixture for induction and maintenance of anaesthesia in ASA 1 patients.

Outpatient general anaesthesia for oral surgery.

Outpatient general anaesthesia (GA) is administered for extraction of carious teeth in children and straightforward dento-alveolar surgery such as removal of impacted teeth, cyst enucleation and dental implantology in adults. Although oral surgery is often performed under local anaesthesia, GA is indicated in conditions when local anaesthesia is ineffective and in uncooperative patients because of age, fear or anxiety, mental impairment or physical disability. Outpatient GA for oral surgery yields a high satisfaction score from the patients. The incidence of major morbidity is acceptably low because of proper patient and procedure selection, improved perioperative patient monitoring, and the use of newer, faster recovery anaesthetic agents with fewer side-effects. Effective pain management is important for optimal postoperative analgesia and patient satisfaction. The principles, conduct, and management of common problems of outpatient GA for oral surgery are discussed.

Bone marrow harvesting using EMLA (eutectic mixture of local anaesthetics) cream, local anaesthesia and patient-controlled analgesia with alfentanil.

Bone marrow harvesting (BMH) was performed on 40 consecutive allogeneic or autologous donors using EMLA (eutectic mixture of local anaesthetics), local anaesthesia (LA) and patient-controlled analgesia with alfentanil (PCA-A). The effect of alkalinizing the LA solution on reducing pain during LA infiltration in the presence of EMLA was also investigated. EMLA 10 g with occlusive dressing was applied to the harvest sites at least 60 min before BMH. The PCA device was programmed to deliver an intravenous loading dose of 15 microg/kg alfentanil, followed by a background alfentanil infusion of 0.05 microg/kg/min. Demand dose was 4 microg/kg and lockout time was 3 min. Donors were randomized to receive either alkalinized (n = 19) or non-alkalinized (n=21) LA solution (lignocaine 1% with 1:100000 adrenaline). While post-operative nausea and vomiting were the only side-effects, all donors in both groups reported satisfactory pain scores during LA infiltration and satisfactory overall intra-operative comfort scores. They completed BMH using either regimen successfully, found this technique acceptable and would recommend this form of anaesthesia to others. Alkalinizing the LA solution did not significantly improve the pain scores during LA infiltration in the presence of EMLA. In conclusion, BMH can be performed safely using EMLA, LA and PCA-A without major complications.

Simulations of the erythrocyte cytoskeleton at large deformation. I. Microscopic models.

Three variations of a polymer chain model for the human erythrocyte cytoskeleton are used in large deformation simulations of microscopic membrane patches. Each model satisfies an experimental observation that the contour length of the spectrin tetramers making up the erythrocyte cytoskeleton is roughly square root of 7 times the end-to-end distance of the tetramer in vivo. Up to modest stress, each brushy cytoskeletal network behaves, consistently, like a low-temperature, planar network of Hookean springs, with a model-dependent effective spring constant, keff, in the range of 20-40 kBT/s(o)2, where T is the temperature and s(o) is the force-free spring length. However, several features observed at large deformation distinguish these models from spring networks: 1) Network dimensions do not expand without bound in approaching a critical isotropic tension (square root of 3 keff) that is a characteristic limit of Hookean spring nets. 2) In surface compression, steric interactions among the chain elements prevent a network collapse that is otherwise observed in compression of planar triangulated networks of springs. 3) Under uniaxial surface tension, isotropy of the network disappears only as the network is stretched by more than 50% of its equilibrium dimensions. Also found are definitively non-Hookean regimes in the stress dependence of the elastic moduli. Lastly, determinations of elastic moduli from both fluctuations and stress/strain relations prove to be consistent, implying that consistency should be expected among experimental determinations of these quantities.

Simulations of the erythrocyte cytoskeleton at large deformation. II. Micropipette aspiration.

Coarse-grained molecular models of the erythrocyte membrane's spectrin cytoskeleton are presented in Monte Carlo simulations of whole cells in micropipette aspiration. The nonlinear chain elasticity and sterics revealed in more microscopic cytoskeleton models (developed in a companion paper; Boey et al., 1998. Biophys. J. 75:1573-1583) are faithfully represented here by two- and three-body effective potentials. The number of degrees of freedom of the system are thereby reduced to a range that is computationally tractable. Three effective models for the triangulated cytoskeleton are developed: two models in which the cytoskeleton is stress-free and does or does not have internal attractive interactions, and a third model in which the cytoskeleton is prestressed in situ. These are employed in direct, finite-temperature simulations of erythrocyte deformation in a micropipette. All three models show reasonable agreement with aspiration measurements made on flaccid human erythrocytes, but the prestressed model alone yields optimal agreement with fluorescence imaging experiments. Ensemble-averaging of nonaxisymmetrical, deformed structures exhibiting anisotropic strain are thus shown to provide an answer to the basic question of how a triangulated mesh such as that of the red cell cytoskeleton deforms in experiment.

Preoperative prediction of intra and postoperative red blood cell transfusion in surgical patients.

Anaesthetists were asked to predict the need for intra and postoperative red blood cell transfusion in 1706 patients before surgery. Each prediction was made using only the individual patient's medical history and physical examination, the results of routine preoperative laboratory investigations, and knowledge of the proposed surgical procedure. Only 159 patients (9.3%) received red blood cell transfusion. The sensitivity and specificity of this preoperative prediction were 85.5% and 96.6% respectively, whereas the positive and negative predictive values were 72.3% and 98.5% respectively. Using a stepwise logistic regression model, preoperative haemoglobin concentration, Surgical Table of the procedure, and age of patients were found to significantly determine the need for intra and postoperative red blood cell transfusion. It is recommended that type and screen should replace group and crossmatch procedures in surgical patients where no intra and postoperative red blood cell transfusion is predicted as necessary.

A two-year experience of an acute pain service in Singapore.

The first anaesthesia-based acute pain service in Singapore is described. The benefits, risks and resource implications of such a service during its first two years are reviewed. One thousand two hundred and sixty-eight (1,268) post-operative patients were treated with either patient-controlled analgesia (310 patients) or epidural opioid analgesia (958 patients). Retrospective analysis of the data revealed good patient satisfaction with a low incidence of potentially life threatening side-effects: more than 79% of patients reported satisfaction with pain control while only 0.2% of patients receiving epidural opioid analgesia experienced clinically significant respiratory depression. There were no reports of respiratory depression in the patient-controlled analgesia group. The authors conclude that the provision of an acute pain service in the local context was safe and resulted in excellent post-operative patient satisfaction.

Bone marrow harvesting using local anaesthesia and PCA-alfentanil: a feasible alternative to general or regional anaesthesia.

We examined the feasibility of combined use of local anaesthesia (LA) and patient-controlled analgesia with alfentanil (PCA-alfentanil) for bone marrow harvesting (BMH) in 16 consecutive in-patient donors (nine allogeneic and seven autologous). A loading dose of alfentanil 15 micrograms/kg was delivered at the time of skin preparation followed by a background infusion of alfentanil 0.05 microgram/kg/min. On -demand bolus doses of alfentanil were 4 micrograms/kg with lockout intervals of 3 min. Local anaesthesia was achieved using 1% lignocaine (up to 7 mg/kg) with 1:200,000 adrenaline. All donors were mildly sedated during BMH, tolerated the procedure well, and experienced no cardiovascular or respiratory complications. Post-operative nausea and vomiting were the only side-effects. All donors indicated that the combined use of LA with PCA-alfentanil was acceptable for BMH. Our preliminary results suggest that although optimal PCA settings have yet to be determined, this technique may be a feasible and effective alternative for BMH in situations where general or regional anaesthesia is undesirable.

Barrier-free paths of directed protein motion in the erythrocyte plasma membrane.

A model is presented for the steric interaction between a plasma membrane protein and the membrane cytoskeleton in the human erythrocyte. The cytoskeleton is treated as a network of polymer chains attached to a flat bilayer, and the membrane protein is a hemisphere of effective radius R(e) with center on the bilayer edge. The simulation is used to investigate the barrier-free path L for linear guided motion of a protein in the bilayer plane. It is shown that the barrier-free paths of small proteins can be used to extract the effective in-plane diameter of cytoskeletal components. For example, the in-plane diameter of an ankyrin attachment site is found to be approximately 12 nm in the simulation, or twice the computational spectrin diameter. The barrier-free paths of large proteins (R(e) > 23 nm) vanish when the proteins are corralled by the cytoskeleton. For intermediate size proteins, L decreases approximately as L is directly proportional to S-1.4 where S is proportional to the sum of the protein and cytoskeleton chain radii.

Withdrawal forces during removal of lumbar extradural catheters.

After performing successful continuous lumbar extradural conduction block, we investigated the effects of the extradural insertion technique (midline (M) or paramedian (P)) and patient position during extradural catheter removal (flexed lateral (L) or sitting (S)) on the force required to remove extradural catheters. One hundred parturients were allocated randomly to four groups: ML, MS, PL, PS. The results indicated that neither the midline nor paramedian approach affected withdrawal forces. However, more than 2.5 times as much force was required to remove the catheters when patients were in the flexed sitting compared with the lateral position (P < 0.005). For ease of removal of catheters from the lumbar extradural space we therefore strongly recommend the flexed lateral position.

Preoperative plateletpheresis does not reduce blood loss during cardiac surgery.

Acute preoperative plateletpheresis has been reported to be effective in reducing blood loss and blood component transfusion while improving haematological profiles in patients undergoing open-heart surgery. However, in these studies, the concomitant use of cell saver techniques may have been responsible for the beneficial effects because they remove free haemoglobin and activated procoagulants and, therefore, could mask the deleterious effects of combined plateletpheresis and cardiopulmonary bypass (CPB). In the present study, 40 patients undergoing primary myocardial revascularization were randomly divided into two groups: a control group without plateletpheresis performed, and a second group in which preoperative platelet-rich plasma 10 ml.kg-1 (PRP group) was collected and later reinfused after reversal of heparin. Standardized surgery, anaesthesia and CPB without concomitant cell saver techniques were employed. In the PRP group, blood transfusion was reduced (1.5 +/- 1.3 vs 2.4 +/- 1.3 units, P < 0.05) but this was accompanied by lower postoperative haemoglobin concentrations. There were no differences in blood loss (992.6 +/- 327.4 vs 889.6 +/- 343.7 ml), fresh frozen plasma (2/19 vs 3/20 patients) or platelet requirements (1/19 vs 1/20 patients). Reinfusion of autologous PRP did not improve platelet count and function, nor tests of coagulation. Fibrinogen concentrations were lower in the PRP group on the operative day (P < 0.05), suggesting increased fibrinogen consumption; and more patients in the PRP group had low haptoglobin levels during CPB (8/19 vs 0/20 patients, P < 0.005), which indicated greater haemolysis in this group. We conclude that acute preoperative plateletpheresis offers no advantage in haemostasis during elective primary myocardial revascularization surgery.