Characteristics of the synergistic actions of platelet agonists

Platelets are activated by many different agonists that act synergistically. Since there is a characteristic pattern of responses to each agonist, and since there is a clear distinction between weak and strong agonists, understanding the nature of the synergism and its physiologic significance requires characterization of the pattern of responses to the synergistic action of the various agonists. Shape change, aggregation, and secretion of ATP by human platelets in citrated plasma were analyzed after activation by ADP, epinephrine, arachidonic acid, gamma-thrombin, or collagen, either singly or in pairs. The patterns of responses were characteristic of the agonist in higher concentration relative to its threshold concentration; if neither was clearly higher, the pattern of responses was intermediate between the responses characteristic of each agonist. No combination of weak agonists had the characteristics of a strong agonist. These results help define the extent to which platelet responses can be attributed to the synergistic actions of weak agonists.     

Intermediate-term outcome following the fontan operation: a survival, functional and risk-factor analysis.

OBJECTIVE: To investigate survival and risk factors influencing intermediate outcome after the Fontan procedure. METHODS: Retrospective analysis of 122 patients operated between April 1991 and September 2002. Poor outcome was defined as late death or poor functional status (intractable supraventricular arrhythmias/NYHA 3-4) necessitating revision surgery. RESULTS: 64(52%) patients had an intermediate bi-directional cavo-pulmonary shunt (BCPS). 91 (76%) patients had a lateral tunnel total cavo-pulmonary connection, 21(17%) patients had an atrio-pulmonary connection and 10 (8%)patients had a Kawashima connection. There were 6 (5%)early deaths. Over a median follow up of 54 months (1-133), 12 (10%)patients have had surgical revision for poor functional status. There were 7 (6%) late deaths, 5 of which occurred after revision surgery. Univariate analysis identified older age at operation (>4 years) (P=0.04), higher postoperative pulmonary artery pressure at 24h (P=0.012), arrhythmia postoperatively (P=0.03) or during follow-up (P=0.01) and the requirement for anticoagulation during follow-up (P=0.03) as significant predictors of poorer outcome. Patients who had an intermediate BCPS (P=0.002) or Norwood Stage 1 (P=0.05) had a better outcome. Multivariate analysis identified an intermediate Glenn shunt and lower postoperative pulmonary artery pressure as significant predictors of better outcome. Actuarial freedom from death or revision is 93% (+/-2), 88% (+/-3), 86% (+/-4) and 69% (+/-7) at 1, 5, 7 and 9 years respectively. Actuarial freedom from death or revision for the lateral tunnel group is 92% (+/-2), 89% (+/-3), 85% (+/-5) and 66% (+/-10) respectively. CONCLUSION: Atrio-pulmonary connection results in a higher incidence of arrhythmias and failure than the lateral tunnel Fontan. Even in patients with a lateral tunnel Fontan there is a continuing hazard phase in the intermediate term. Mid-term outcome appears to be favorably influenced by an intermediate BCPS.     

Aspekte der Hämostase bei Patienten mit mechanischer Herzunterstützung

Background

Bleeding events and thromboembolism are severe complications in patients with ventricular assist devices (VAD). Possible causes are the interaction of platelets with the foreign material as well as pathological blood flow conditions due to the high pulsating tension within the VAD system. Up to now there have been only a few studies which investigated platelet function in VAD patients.

Objective

In this study platelet function was investigated with respect to bleeding and the role of foreign surfaces in the development of thromboembolism for optimization of the therapy management of VAD patients.

Material and methods

The study investigated a total of 39 VAD patients without a VAD (before implantation n = 11 and after explantation n = 8) in an early (≤ 14 days after implantation n = 28) and a late (≥ 30 days after implantation n = 30) postoperative phase. Platelet function was analyzed via light transmission aggregometry according to the method of Born. In addition postoperative bleeding events were monitored. To investigate the role of foreign surfaces in the development of thrombosis, glass surfaces were covered with hydrogels with different degrees of swelling and analyzed under whole blood perfusion and pulsation strength.

Results

Platelet dysfunction was detected in 18 out of the 19 patients without a VAD and in all patients after VAD implantation. Bleeding events occurred in 44?% of patients in the early and in 64?% in the late postoperative period. Extensive platelet adhesion was detected on uncoated and polyurethane (PU) coated glass. No platelet adhesion occurred on glass surfaces covered with hydrogels with a degree of swelling higher than 1.5.

Conclusion

The results indicated that platelet function is most often impaired in VAD patients before implantation and even after explantation of a VAD. Coagulation disorders in VAD patients are multifactorial and the management represents a tightrope walk between increased tendency to bleeding and increased risk of thrombosis.

     

Stable azole drug resistance associated with a substrain of Candida albicans from an HIV-infected patient

Oral candidiasis is one of the earliest and most frequent complications of a failing immune system in HIV-infected individuals. For several years, oral candidiasis has been treated effectively with azole drugs, the one most frequently used is fluconazole. Unfortunately, extensive use of the drug for treatment and prophylaxis has led to treatment failure in an increasing number of patients. In most of these cases, strains of C. albicans isolated from the infection are less susceptible to fluconazole. The development of azole resistance in strains of C. albicans has been studied biochemically and more recently with molecular techniques. One excellent example of the development of azole resistance in C. albicans has been documented in a series of 17 C. albicans isolates from a single patient over a 2-year period. During this time, the patient experienced 14 episodes of oral candidiasis and was treated with increasing doses of fluconazole. Molecular and biochemical analyses confirms that the isolates are the same strain of C. albicans and that the resistance in these isolates is stable over 600 generations, suggesting that the changes in this strain are genetic in nature. In addition, the development of resistance is correlated with the identification of a substrain or variant of the original strain, as identified by restriction fragment length polymorphism (RFLP) analysis with the moderately repetitive probe, Ca3. The analysis of this series of isolates demonstrates that azole drug resistance is associated with several small genetic changes, each of which contributes to the overall resistance of the strain. Clearly, continual use of azole drugs by a patient can select for genetic changes that render oral candidiasis refractory to treatment.     

Photodynamic therapy of viral contaminants with potential for blood banking applications

A photodynamic method has been evaluated as a means of eradicating viral contaminants with the potential for rendering blood safe for transfusion. Herpes simplex virus type 1 (HSV-1) was tested under flowing conditions in culture media or in blood supplemented with the virus. Hematoporphyrin derivative was used as the sensitizer and was photoactivated with visible light at 630 nm and 5 J/cm2. HSV-1 in suspension both in culture medium as well as in blood was shown to be killed. The human immunodeficiency virus was also found to be photoinactivated in flowing cell culture medium and, thus, potentially may be inactivated in blood. These findings extend our previous studies which demonstrated that enveloped viruses can be photoinactivated with hematoporphyrin derivative in a static fluid system. Analysis of blood cell number, red cell lysis, plasma proteins, and other standard hematological tests showed no significant change. The possibility that transfusion-associated acquired immunodeficiency syndrome (AIDS) may result from a blood unit infected with human immunodeficiency virus that tested negative makes it imperative that a safe and effective means of viral killing be developed. The system reported here offers promise as an effective approach to this problem.     

A novel system for providing compatible blood to patients during surgery: "self-service" electronic blood banking by nursing staff

BACKGROUND: A good blood bank must be able to provide compatible blood units promptly to operating room patients with minimal wastage. A "self- service" by nursing staff blood banking system that is safe, efficient, and well-accepted has been developed. STUDY DESIGN AND METHODS: Specific blood units are no longer assigned to surgical patients who have a negative pretransfusion antibody screen, irrespective of the type of surgery. A computer-generated list of the serial numbers of all group-identical blood units currently in the blood bank inventory is provided for each patient. The units themselves are not labeled with a patient's name. The group O list will be provided for group O patients, the group A list for group A patients, and so forth. Should the patient require transfusion during surgery, the operating room nurses go to the refrigerator, remove any group-identical unit, and check the serial number of the unit against the serial numbers on the patient's list. If the serial number is on that list, the blood bank will accept responsibility for compatibility. The system was implemented in 1995. RESULTS: Since implementation, a total of 2154 patients have undergone operations at this hospital. Thirty-two patients received more than 10 units of red cells each. There were no transfusion errors. The crossmatch-to-transfusion ratio was reduced from 1.67 to 1.12. Turnaround time for supplying additional or urgent units to patients in operating room was shortened from 33 to 2.5 minutes. There was no incidence of a blood unit's serial number not being on the list. Work by nurses and technical staff was reduced by nearly 50 percent. CONCLUSION: The "self-service" (by nursing staff) blood banking system described is safe and efficient. It saves staff time and can be easily set up.