John S. Packer

An Adaptive Controller for Closed-Loop Management of Blood Pressure in Seriously Ill Patients

An adaptive control strategy is described which has been used for closed-loop computer control of blood pressure in patients in the Intensive Care and Cardiac Surgical Units of the Royal Melbourne Hospital. The initial development and testing of the control algorithm was done by simulation using computer facilities in the Intensive Care Unit. Adaptation to patient variability utilizes a model reference strategy. Control is based on readings of mean arterial pressure obtained from a standard patient monitor unit and implemented by controlling the infusion rate of a volumetric infusion pump. Patient data are displayed graphically on a VDU during control and stored on disk for subsequent postcontrol display and analysis by the medical staff. Clinical trials have indicated that the system is robust and can maintain effective control following sudden large variations in the patients blood pressure.

Clinical evaluation of closed-loop control of blood pressure in seriously ill patients

ObjectiveTo compare the effectiveness of a new method of closed-loop (automatic) control of BP with usual manual control. DesignWithin-subject crossover trial. SettingGeneral and open heart ICUs in a university teaching hospital. PatientsConvenience sample of 74 seriously ill patients aged 17 to 88 yr. Twenty had hypertension: postoperative (n = 7), neurologic damage (n = 6), miscellaneous (n = 7), and were prescribed nitroprusside (n = 11) or nitroglycerin (n = 9). Fifty-four had hypotension: septic (n = 33), other (n = 21), and were prescribed norepinephrine (n = 30), dopamine (n = 11), epinephrine (n = 8), or dobutamine (n = 5). An additional 21 trials were omitted from analysis because of technical (n = 7), clinical (n = 1), or drug-related problems (n = 13). InterventionClosed-loop and manual drug administrations 1-hr were studied during periods in each patient. The target and observed mean arterial pressure (MAP) and drug infusion rate were recorded electronically every 30 sec. Main Outcome MeasurementsTime taken to achieve initial control (min); fidelity of control (the integral of size and duration of error from target MAP ±10% in mm Hg-hr/hr); and average drug dose administered (ug/min as % maximum possible per drug). ResultsCompared with manual control, closed-loop achieved faster initial control (log-rank X1 = 5.04, p < .05) and greater fidelity (mean 1.37 vs. 2.36; F = 7.15, p < .01). There was no difference in average drug dose administered. There was uniformity in the efficacy advantage of closed-loop drug administration across drugs and patient classifications. ConclusionThe new closed-loop system is more effective than the usual manual control in managing acute BP disturbances in the seriously ill patient. (Crit Care Med 1991; 19:166)

Automatic control of arterial carbon dioxide tension in mechanically ventilated patients

This paper presents a method of controlling the arterial carbon dioxide tension of patients receiving mechanical ventilation. Controlling of the CO2 tension is achieved by regulating the ventilator initiated breath frequency and also volume per breath.

VAD: ventilation management in the ICU

VAD (ventilation advisor), an expert system intended to assist in the management of mechanical ventilation for critically ill patients, is discussed. The system continuously interprets patient data collected from standard intensive care unit (ICU) equipment to offer staff advice on the patients status, unexpected ventilation events, and the appropriateness of current ventilator therapy. VADs encoded medical expertise is provided by clinical and nursing specialists in intensive care. It has been implemented as a custom expert tool written in C, and run in real time on an IBM-AT-compatible computer. VAD is currently being tuned and evaluated in closely regulated clinical trials within the ICU.<<ETX>>

A closed-loop system for controlling blood oxygen and carbon dioxide levels in mechanically ventilated patients

Abstract A closed-loop system that regulates arterial O 2 and CO 2 tensions has been presented. While maintaining acceptable blood gas levels, the system attempts to direct a patient from total or partial ventilator dependency to independent breathing.

An Adaptive System for Patient Controlled Analgesia

Abstract Patient Controlled analgesia (PCA) has become accepted as an important means of self regulated relief from post surgical pain. In commonly used PCA systems, patients use a hand held push button to indicate the presence of pain and initiate a predetermined bolus of drug infusion. A disadvantage of this system is that no means is provided to accommodate variations in the intensity of pain or the sensitivity of the patient to the analgesic in use. The PCA system described in this paper uses a specially designed handset which allows the patient to indicate pain intensity and so vary the level of the drug infusion. Data derived from the handset signals provides a basis for adapting the drug dosage to patient sensitivity as well as pain intensity. In addition a capnograp h and oximeter provide direct monitoring of the patients state and allow for a larger range of adaption.

Closed-loop control of multiple drug infusions

An original approach for the development of a closed-loop system for the adjustment of drug and fluid infusions has been investigated. The approach, based on expert system techniques, resulted in a system with a high level of clinical utility and which exhibited robust control characteristics. This work represents the first known clinical application of a closed-loop system for the control of multiple drug and fluid infusions. Current attention is focused on the incorporation of a Doppler device for continuous monitoring of cardiac output into this system.<<ETX>>

Pain relief using smart technology: an overview of a new patient-controlled analgesia device

A new adaptive patient-controlled analgesia (PCA) system designed to improve PCA through the use of a variable bolus dose and a variable background infusion is outlined here. The handset allows patients to rate their pain on a scale of 1-10. Data derived from the handset signals are used by an expert algorithm to repeatedly adapt the drug dosage of the bolus and the background infusion according to both pain intensity and patient response to previous dosages. A feasibility study of the system consisted of a small number of randomized, double-blind, crossover clinical trials. The new system was alternated with a conventional system every 12 h. When the new system was active, 12 h questionnaire pain scores were significantly lower and a trend toward fewer bolus requests was found in alternating intervals. In addition, when the new system was used to commence trials, the number of bolus requests were significantly lower and there was a trend toward lower handset scores, lower questionnaire pain scores, and lower verbal pain scores over the entire trial period. The new adaptive PCA system was well accepted by both patients and clinical staff. The trials successfully established the feasibility of the new system. Further development is being carried out as a result.

A hybrid fuzzy-neural control system for management of mean arterial pressure of seriously ill patients

In this paper, a fuzzy-neural control system is applied to regulate mean arterial blood pressure in seriously ill patients using sodium nitroprusside. This hybrid system consists of an adaptive fuzzy controller and a network based predictor. Computer simulation results illustrate that the system has ability to learn control rules from off-line training process as well as to adjust the parameters during control process. Clinical trials are being carried out in Intensive Care Unit at the Royal Melbourne Hospital.

On-line estimation of patient and ventilator respiratory work

An algorithm that estimates the patient and ventilator work components of mechanically ventilated patients is presented. The algorithm requires the continuous measurement of inspiratory airflow rate and mouth pressure and it is suitable to be incorporated in ventilators for on-line estimation of the patient and ventilator contributions to the total work of breathing.