What is a safe waiting time for coronary artery bypass surgery?

To determine the factors that influenced doctors' prioritization and decisions on safe waiting time for coronary artery bypass surgery, 50 'paper patients', based on a random sample of cases who actually had surgery, were assessed by 33 clinicians. We used linear regression models to reflect the impact of clinical and non-clinical 'cues' on safe waiting time and priority decisions. The benefits of surgery tended to be over-estimated. For example, the average perceived gain in life expectancy for patients with left main-stem disease was 6.74 years. However, models incorporating only the perceptions of benefit as independent variables (i.e. the anticipated symptom reduction, MI risk reduction and life expectancy extension), had only modest explanatory power (mean R2 was 0.55 for safe waiting time, and 0.56 for priority decisions). Models which incorporated perceptions of benefit and the cases' clinical and non-clinical characteristics had generally much higher explanatory power (mean R2, 0.83 and 0.86, respectively). Lifestyle and demographic variables had much less impact on the doctors' judgements than the major clinical cues of angina severity and left main-stem stenosis. Demographic and lifestyle cues had different impacts on safe waiting time and priority for about 25% of doctors.      

Thrombosis in inflammatory bowel disease: clinical setting, procoagulant profile and factor V Leiden

Patients with inflammatory bowel disease have an increased frequency of thromboembolism, and microvascular thrombosis has been proposed as a contributory pathogenic factor. The mechanism of enhanced procoagulant activity is not understood. We examined the clinical setting of thromboembolic events in 52 patients with Crohn's disease or ulcerative colitis, and assessed the procoagulant laboratory profile, including Factor V Leiden, in a subset of 20 patients to identify procoagulant risk factors. Patients who developed thrombosis tended to be young; 60% of thrombotic events occurred in patients under 50 years. Multiple thromboembolic episodes occurred in 13% and unusual sites of thrombosis (e.g. intracardiac, cerebral, inominate veins) in 11%. No risk factor was identifiable in 52% of cases and two-thirds of thromboses occurred in an out-patient setting. The mortality rate was 8%. Evidence for inflammatory disease activity was found in only 45% of patients with ulcerative colitis at the time of the thromboembolic event, in contrast to 89% of those with Crohn's disease. Assays for specific coagulation defects were negative in all cases tested (protein S, C were normal in 17/17; anti-thrombin III, anti-phospholipid antibodies and activated protein C resistance were negative in 20/20, and only 1/20 patients was found to be heterozygous for Factor V leiden. Thrombosis in inflammatory bowel disease is important because it occurs in a young population, often in unusual sites, and has a high mortality. The development of thrombosis is related to active inflammatory disease in most patients with Crohn's disease but apparently not in those with ulcerative colitis. Since approximately half of the patients had no other identifiable risk factor, there remains a substantial group of patients with IBD who develop thrombosis for unknown reasons.      

Effect of freezing on the in vivo recovery of irradiated red cells

BACKGROUND: Transfusion-associated graft-versus-host disease can be prevented by gamma radiation of blood components. The increased use of blood components donated for patients by their family members has resulted in an increased demand for the storage and handling of irradiated units, and the ability to freeze the cells would allow storage beyond their current expiration date. STUDY DESIGN AND METHODS: To assess the effect of freezing and deglycerolization on irradiated red cells, studies of autologous radiolabeled red cell recovery were performed using normal volunteers. Each unit of CPDA-1 red cells was immediately divided into two equal volumes. Further handling of each half was identical except that one was irradiated (3500 cGy). The units were grouped under three protocols: I, irradiated on Day 0 and frozen on Day 5 (n = 4); II, irradiated on Day 7, rejuvenated, and frozen on Day 14 (n = 5); and III, irradiated on Day 14, rejuvenated, and frozen on Day 18 (n = 3). All cells were frozen for 3 to 10 months at -80 degrees C. RESULTS: Irradiated and control units showed no significant differences in supernatant potassium or hemoglobin. Autologous 24-hour posttransfusion recoveries (mean +/− SD) for the three groups were: I, 89.7 +/− 5.6 percent (control, 90.6 +/− 3.2%); II, 85.3 +/− 5.7 percent (control, 83.7 +/− 3.0%); and III, 79.5 +/− 1.4 percent (control, 82.6 +/− 5.2%). CONCLUSION: Irradiated red cells can be frozen after being stored under various conditions and can still meet established guidelines requiring 75-percent recovery 24 hours after transfusion.     

The stated and tacit impact of demographic and lifestyle factors on prioritization decisions for cardiac surgery

In a clinical judgement analysis, we used linear regression models to reflect the impact of clinical and non-clinical cues on priority decisions, by comparing the stated prioritization policies of 30 clinicians with their actual policies as revealed by an appraisal of 50 'paper patients'. Correspondence was modest for some cues, e.g. 25 doctors said they accounted for age, but age only had a significant bearing in the derived decision models of two doctors. Correspondence between the derived and expressed weights was greatest for clinical angina grade and the presence of left main stem stenosis. Correlation between the rank order of importance between the two models was poor for most of the cues, and statistically significant only for smoking. However, stated policies made it appear that lifestyle factors such as smoking habit would influence prioritization decisions for most clinicians but policies derived from actual prioritization decisions seldom related to lifestyle or demographic variables. There were significant differences in the degree of correlation between the two models according to the experience of the clinician. However, correspondence was not significantly better for doctors with cardiological training than those without. The overall contribution of demographic and lifestyle factors to decision making appears to be small, suggesting that they should be omitted from prioritization guidelines.      

Quantifying the roles of tidal volume and PEEP in the pathogenesis of ventilator-induced lung injury

Management of patients with acute lung injury (ALI) rests on achieving a balance between the gas exchanging benefits of mechanical ventilation and the exacerbation of tissue damage in the form of ventilator-induced lung injury (VILI). Optimizing this balance requires an injury cost function relating injury progression to the measurable pressures, flows, and volumes delivered during mechanical ventilation. With this in mind, we mechanically ventilated naive, anesthetized, paralyzed mice for 4 h using either a low or high tidal volume (Vt) with either moderate or zero positive end-expiratory pressure (PEEP). The derecruitability of the lung was assessed every 15 min in terms of the degree of increase in lung elastance occurring over 3 min following a recruitment maneuver. Mice could be safely ventilated for 4 h with either a high Vt or zero PEEP, but when both conditions were applied simultaneously the lung became increasingly unstable, demonstrating worsening injury. We were able to mimic these data using a computational model of dynamic recruitment and derecruitment that simulates the effects of progressively increasing surface tension at the air–liquid interface, suggesting that the VILI in our animal model progressed via a vicious cycle of alveolar leak, degradation of surfactant function, and increasing tissue stress. We thus propose that the task of ventilating the injured lung is usefully understood in terms of the Vt–PEEP plane. Within this plane, non-injurious combinations of Vt and PEEP lie within a “safe region”, the boundaries of which shrink as VILI develops.     

Rising incidence of type 1 diabetes in Scottish children, 1984-93. The Scottish Study Group for the Care of Young Diabetics

OBJECTIVES: To calculate the incidence of type 1 diabetes in Scottish children aged less than 15 years between 1984 and 1993; to examine changes in incidence; and to calculate the prevalence of diabetes at the end of this period. DESIGN: Three data sources were used to construct the Scottish Study Group for the Care of Young Diabetics register: active reporting of all new cases; reports from the Scottish Morbidity Register 1; and local registers. SUBJECTS: All children resident in Scotland diagnosed with primary insulin dependent diabetes mellitus when less than 15 years of age between 1984 and 1993. MAIN OUTCOME MEASURES: Annual incidence and prevalence rate for Scotland; time trend in incidence over the 10 years; differences in incidence between the three different age groups; and completeness of the register. RESULTS: The average annual incidence for Scotland was 23.9/100,000 children. The prevalence rate was 1.5/1000 in 1993. A total of 2326 cases was identified from the three sources. Capture-recapture analysis suggests a case ascertainment of 98.6%. The annual incidence rates increased at a rate of 2% each year (rate ratio = 1.02, 95% confidence interval (CI) 1.01 to 1.03). The incidence was higher in boys than girls (rate ratio = 1.08, 95% CI 1.00 to 1.18), and the incidence rates increased with age: 15.3/100,000/year for age 0-4 years, 24.4/ 100,000/year for age 5-9 years, and 31.9/ 100,000/year for age 10-14 years. CONCLUSIONS: The incidence of type 1 diabetes in Scotland is increasing and the prevalence is relatively high. These findings have important implications for health service resource allocation. The Scottish Study Group for the Care of Young Diabetics' register provides a base for monitoring and research.