No abstract

There is a growing interest in the potential benefits to be obtained from closed-loop control of drug infusion [1-5]. The most widely available infusion pump which is specifically designed for control by computer is the 929 volumetric infusion pump produced by Imed. The increasing availability of microcomputers suggests that they will be used more frequently to control such pumps. However, difficulties can arise when the attempt is made to establish communication between the computer and the pump [6] and a method employed for this purpose is described in this article. The aim was to provide a simple method of conducting the required communication between the computer and the pump using a high-level language. The commands specified in the high-level language are passed to a machine-code subroutine which organizes transmission to and receives data from the pump.

A system for monitoring, recording and storing arterial pressure and heart rate during continuous extradural analgesia has been developed using an Apple II microcomputer and a Dinamap 1846 non-invasive arterial pressure monitor. The administration of local anaesthetic (or vasopressor) was recorded using a light pen. The computer was programmed to recognize this, and to initiate automatically more frequent measurements of heart rate and arterial pressure. The results of a study using this equipment are reported. The commands for computer control of the Dinamap 1846 are described.

A computerized system which incorporated haemodynamic, temperature and arterial pH (pHa) monitoring was developed to record data and to improve temperature and pHa control during hypothermic cardiopulmonary bypass (CPB).The system was evaluated in the course of a study of haemodynamics and metabolism during CPB. It was planned to have three 10 minute periods of study in 24 patients, during which time arterial and nasopharyngeal temperatures would be maintained between 27° and 29°C and pHa between 7.38 and 7.42. Repeated recordings of haemodynamic variables, temperature and pHa were made during each period. Only 59 of a possible 72 periods were obtained due to shortage of time at stable hypothermia. The mean number of total readings was 73.5 (70.1, 77.0) and the mean number of acceptable readings was 71.2 (67.3, 75.1). Good nasopharyngeal temperature control was achieved, with all the 95% confidence intervals of the means falling within the prescribed limits. Control of arterial temperature was less good as there were five periods in which the 95% confidence intervals of the means fell outwith the prescribed range. Poor pHa control was achieved since there were 16 periods in which the 95% confidence intervals of the mean were outside the preset range. The system functioned well in recording data and resulted in good temperature control, but poor pHa control.

Machine code programs have been produced to allow a simple method of communication between a computer and the Braun Infusomat pump. Commands are set up as character strings using a high-level language and passed to a machine code program which transmits them to the pump. Messages from the pump are received under interrupt control for display by the high-level language. Any error in communication is stored in memory and the appropriate action taken by the main application program.