Mitral valve replacement with the Carpentier-Edwards standard bioprosthesis: performance into the second decade.

From March 1978, 196 Carpentier-Edwards standard bioprostheses (stCE) were implanted in 194 patients. There were 154 isolated mitral valve replacements (MVR) and 42 aortic plus mitral valve replacements (AVR/MVR) with a mean follow-up of 7.05 (range 0-15.2) years and 7.15 (range 0-13.8) years, respectively. Freedom from structural valve failure at 10 years was 70.8% +/- 4.9% (MVR) and 59.6% +/- 11.1% (AVR/MVR). The incidence of structural valve failure increased sharply after 7 years. Freedom from thromboembolism was 83.0% +/- 3.8% (MVR) and 89.0 +/- 6.0% (AVR/MVR). Thromboembolic events were related to the presence of atrial fibrillation in patients not receiving anticoagulation. Anticoagulant-related haemorrhage was rare. Freedom from mitral valve prosthetic endocarditis at 10 years was 90.9% +/- 3.1% (MVR) and 86.1% +/- 8.4% (AVR/MVR). Prosthetic valve endocarditis was associated with more than 60% mortality. The probability of event-free survival at 10 years follow-up was 43.6% +/- 4.6% (MVR) and 33.3% +/- 8.6% (AVR/MVR). The performance of the stCE in the mitral position shows a low rate of thromboembolic events and anticoagulant-related haemorrhage, but the long-term performance of the prosthesis is unsatisfactory due to a high rate of structural valve failure. This confirms earlier reports.

Using the proportional hazards model to study heart valve replacement data.

The proportional hazards model is used to study the effect of various concomitant variables on the time to valve failure, mortality, or other complications, for patients who have had artificial heart valves inserted. The data are from a database, which is still being assembled as more information is acquired, at Killingbeck Hospital. A suite of computer programs, not specifically developed with this application in mind, has been used to carry out the exploratory data analysis, the estimation of parameters and the validation of the model. These three elements of the analysis are all illustrated. The present report is seen as a preliminary study to assess the usefulness of the proportional hazards model in this area. Follow-up work as more data are accumulated is intended.

Problems in the development of a computerized ward monitoring system for a paediatric intensive care unit.

A computerised ward monitoring system based on Archimedes PC's at each bedside is under development for the PICU at Killingbeck Hospital in Leeds. This work was initiated with a view to reducing the amount of paperwork in the unit. The present paper charts have been broken down into sections for the purpose of entry into the computer. The completed charts may be viewed in tabular form. There are several alternative displays. The default display mode illustrates the patients principal cardiovascular variables over the previous six hours. Alternative graphical displays include 12 hour trend curves for the cardiovascular variables, a screen with one hour trend graphs and panels illustrating the latest values of other patient variables, and graphical 12 hour reviews for clear fluid balance, blood volume balance and respiratory variables. The program also serves as a vehicle for testing an alarm generating system and a cardiovascular status index in the paediatric environment. A separate program has been developed which allows the retrospective construction of data bases by using some or all of the data from one or more of the charts for a series of patients. Finally the difficulties encountered in preliminary trials of the system are discussed. At the present time the program is being run at a central station while attempts are being made to surmount these difficulties.

Preliminary clinical trials of a computer-based cardiac arrest alarm.

The use of a high reliability cardiac arrest alarm utilising the continuously monitored values of patient heart rate and mean arterial blood pressure is described, based on a sample of 167 patients monitored for a total of 5116 h. The analogue heart rate and mean blood pressure signals are sampled at 1 s intervals, and a smoothing algorithm is applied to each of the resulting series which rejects artefacts, and identifies slope and step changes in each. Certain combinations of events in the 2 series, occurring within a preset time window, determine whether a cardiac arrest alarm or warning signal should be activated by the system. A total of 30 acute events occurring in 14 patients during the course of the study were each identified within 10 s. No cardiac arrest event was misdiagnosed by the algorithm during the period of the study. The algorithm also generates warnings which may have predictive value, and which will be the subject of further research. A final false alarm rate of about 1/200 h of monitoring was observed in adults (1/50 h in children), with evidence that these rates could be substantially improved.

An introduction to programming in BBC BASIC.

The rudiments of programming in BASIC for the BBC microcomputer are outlined. The topics covered are input to and output from the computer, variable names, loops, arithmetic operations, data statements, arrays, branching, string variables and an introduction to structured programming. The topics are illustrated by simple programming exercises based on the calculation of stroke volume indices. In conclusion a brief review is given of some of the additional facilities which are available on the computer together with references for further reading.

A sampling study of bedside nursing activity in a cardiac surgical intensive care unit. Part 1: Analysis of the elements of activity in the nursing workload, and its variation with patient age group and pathology.

For a selected group of 17 patients following cardiac surgery, 33 discrete elements of nursing workload have been defined. It was possible to identify 3 broad types of activity undertaken by the bedside nurse; technical nursing care (Type 1), intermittent nursing care (Type 2), and learning activities (Type 3). The latter is the balance of the nurses time which is largely concerned with observation and liaison with other staff. The 17 patients comprised 4 groups of pathologies, 2 each representative of the adult and paediatric workload. The primary bedside nurse performs virtually all of the Type 1 activities, recruiting the assistance of a secondary nurse principally to change the patients' posture (a Type 2 activity). The only practically significant period of time spent by the secondary nurse is in clinical discussion with the bedside nurse, largely at change of shift. Statistically significant differences in bedside nursing activities between age groups can be explained by the relative physical size of the patients and equipment. However the nurse maintains a higher level of awareness with shorter periods of inattention when nursing children. A greater number of significant differences between pathologies were found within the paediatric group of patients; this may indicate that a broader spectrum of such differences is to be found in this age group. An estimate was made of the impact of computer technology on the nurse's bedside workload.

A microcomputer implementation of status and alarm algorithms in a cardiac surgical intensive care unit.

Algorithms have been developed for monitoring the cardiovascular status of patients on their return to an intensive care unit after cardiac surgery and also for giving an immediate alarm of a critical deterioration in this status. The two systems for implementing these algorithms were initially developed on Z80 based microprocessor systems and preliminary clinical trials based on the resulting instruments proved encouraging. For further clinical trials of the algorithms the systems have been integrated and implemented on a BBC microcomputer with a 6502 second processor. The development and structure of the programs for implementing the algorithms are described, together with the program input and output facilities and diagnostic techniques used to analyse the information output from the program.

A sampling study of bedside nursing activity in a cardiac surgical intensive care unit. Part 2. The effect of time and shift on the nursing workload.

For a selected group of 17 patients following cardiac surgery, 33 discrete elements of nursing workload have been defined, and the nurse's bedside activities logged at 1 min intervals throughout the 24 h immediately following the patient's return from the operating theatre. It is possible to identify three broad types of activity undertaken by the bedside nurse; technical nursing care (Type 1), intermittent nursing care (Type 2), and the balance of the nurse's time, largely concerned with observation and liaison with other staff--learning activities (Type 3). The time devoted to technical nursing care reduces significantly over the patient's first 24 h in the ward. On the other hand the time devoted to intermittent nursing care and learning activities is shown to be shift dependent. The effect of the efficient utilisation of computer technology is estimated, and it is demonstrated that the implementation of such technology would result in the expansion of the time available for the nurse to observe the patient. The potential benefits and drawbacks of this are discussed.

Preliminary studies in the identification of cardiac status in a cardiac surgical intensive therapy unit.

Sets of the most commonly monitored cardiovascular data have been collected retrospectively in four categories of patients following cardiac surgery: survivors and non-survivors with and without inotropic support. A data set was recorded in the surviving categories when the patient had achieved an optimum cardiovascular state, and in the nonsurviving categories 2 h before death. Three statistical methods of discriminating between the categories are compared. The best discriminants of cardiovascular status are peripheral skin temperature, mean arterial blood pressure, and urine output; there is little to be gained by using more than three variables. A method is suggested of reducing the relevant information in cardiovascular data to a single variable which can be used to predict future status.