Review article: closed-loop systems in anesthesia: is there a potential for closed-loop fluid management and hemodynamic optimization?

Closed-loop (automated) controllers are encountered in all aspects of modern life in applications ranging from air-conditioning to spaceflight. Although these systems are virtually ubiquitous, they are infrequently used in anesthesiology because of the complexity of physiologic systems and the difficulty in obtaining reliable and valid feedback data from the patient. Despite these challenges, closed-loop systems are being increasingly studied and improved for medical use. Two recent developments have made fluid administration a candidate for closed-loop control. First, the further description and development of dynamic predictors of fluid responsiveness provides a strong parameter for use as a control variable to guide fluid administration. Second, rapid advances in noninvasive monitoring of cardiac output and other hemodynamic variables make goal-directed therapy applicable for a wide range of patients in a variety of clinical care settings. In this article, we review the history of closed-loop controllers in clinical care, discuss the current understanding and limitations of the dynamic predictors of fluid responsiveness, and examine how these variables might be incorporated into a closed-loop fluid administration system.

Closed-loop glucose control in critically ill patients using continuous glucose monitoring system (CGMS) in real time

A study was conducted to determine if continuous subcutaneous glucose monitoring (from MiniMed CGMS) could be used in real-time to control blood sugar level (BSL) in patients with critical illness. A closed-loop control system was constructed to use CGMS in a real-time manner, coupled with a proportional integral (PI) control algorithm based on a sliding scale approach, for automatic intravenous infusion of insulin to patients. A total of five subjects with high BSL (> 10 mmol/L) participated in formal studies of the closed-loop control system. Subjects were recruited from critically ill patients in the intensive care unit (ICU) after informed consent was obtained. Error grid analysis showed that 64.6% of the BSL readings as determined in real time using CGMS sensor, when compared to conventional BSL measurements on blood drawn from an arterial line, was clinically accurate (i.e., < 20% deviation from glucometer value). In the five patients who underwent closed-loop control, the controller managed to control only one patient's glycaemia without any manual intervention. Manual intervention was required due to the real-time sensor reading deviating more than 20% from the glucometer value, and also as a safety mechanism. Test on equality of mean and variance for BSL attained prior to, during, and post trial showed that the controller's performance was comparable to manual control. We conclude that the automatic sliding scale approach of closed-loop BSL control is feasible in patients in intensive care. More work is needed in the refinement of the algorithm and the improvement of real-time sensor accuracy.

The effect of physical exercise on the dynamics of glucose and insulin

Regular physical activity is indicated either to prevent and delay the onset of non-insulin-dependent diabetes or to assure a good control of diabetes by increasing insulin sensitivity and ameliorating the metabolism of glucose disappearance. Many studies and experiments have dealt with this subject. In this paper, we introduce the effect of physical activity via parameters of a mathematical model which allows us to compare the behaviour of blood glucose in normal, non-insulin-dependent diabetes and insulin-dependent diabetes people, with and without physical effort. Extreme cases of physical activity leading to hypoglycaemia or aggravating hyperglycaemia are also underlined.

Application of computers in diabetes care--a review. I. Computers for data collection and interpretation

The paper reviews the contribution of information technology (IT) to diabetes care. An appraisal of this topic with respect to insulin-dependent (type 1) diabetic patients is carried out in view of the landmark findings of the Diabetes Control and Complications Trial (DCCT) which has demonstrated that maintaining tight blood glucose control can delay the onset and slow the progression of the later life complications of diabetes. The review starts with the clinical background and the main features of the control schema in which diabetic patients receive insulin therapy. An overview is then provided of recent IT initiatives in diabetes care, and the application of IT techniques to assist in the diagnosis and characterization of patients with diabetes mellitus is considered. The role of IT approaches for short-term glycaemic control is discussed and the utilization of computers for collecting, viewing and interpreting home monitoring blood glucose data is reviewed; both quantitative and qualitative techniques being considered. In the second paper the role of decision support tools for planning insulin therapy using clinical algorithms, hand-held devices, knowledge-based approaches, telemedicine techniques and interactive simulations is reviewed, and the validation and clinical evaluation of these tools is discussed. The likely impact of the routine clinical application of implantable/non-invasive blood glucose monitoring devices is also considered. Finally, the application of computers as teaching tools is reviewed and the ways in which such educational approaches might be applied for disseminating the benefits of the DCCT trial more widely are discussed.

Recent advances in amperometric glucose biosensors for in vivo monitoring

Electrochemical biosensors for glucose, based on the specific glucose oxidizing enzyme glucose oxidase, have generated considerable interest. Several commercial devices based on this principle have been developed and are widely used for in vitro monitoring of glucose e.g. in hospitals, doctors surgeries and for home monitoring by patients themselves. A significant advance in the application of biosensor technology would be the development of portable, implantable sensors which could continuously indicate the blood glucose concentration, enabling swift corrective action to be taken by the patient. This review highlights recent developments in amperometric glucose biosensors for in vivo monitoring and also considers the remaining barrier which need to be overcome to enable successful introduction of an implantable sensor.

A semiclosed-loop algorithm for the control of blood glucose levels in diabetics

In this paper, a theoretical analysis of the control of plasma glucose levels in diabetic individuals is undertaken using a simple mathematical model of the dynamics of glucose and insulin interaction in the blood system. Mathematical optimization techniques are applied to the mathematical model to derive insulin infusion programs for the control of blood levels in diabetic individuals. Based on the results of the mathematical optimization, a semiclosed-loop algorithm is proposed for continuous insulin delivery to diabetic patients. The algorithm is based on three hourly plasma glucose samples. A theoretical evaluation of the effectiveness of this algorithm shows that it is superior to two existing algorithms in controlling hyperglycemia. A glucose infusion term representing the effect of glucose intake resulting from a meal is then introduced into the model equations. Various insulin infusion programs for the control of plasma glucose levels following a meal are then assessed. The theoretical results suggest that the most effective short-term control is achieved by an insulin infusion program which incorporates an injection to coincide with the meal.