Blood pressure control during surgical operations

The benefits of using Guyton's model in a hypotensive control system

In order to improve the intraoperative applications, this paper presents the advantages of using Guyton's model in hypotensive control system development. In this system, the mean arterial pressure is decreased and maintained at a low level during anaesthesia by controlling sodium nitroprusside infusion rate. The key of the study is to develop a physiological model of cardiovascular dynamics to present the mean arterial pressure response to sodium nitroprusside, which was considered as a linear model in most of known blood pressure control systems. Being linear, the previous models cannot accurately mimic a physiological system of human circulation, especially at deep hypotensive control with strong reaction of the body. The enhanced model in this study was modified based on Guyton's model of human circulation. It is useful to design a PID controller, which allows studying and handling the wide range of the body sensitivities. This model is also helpful for studying the behaviors of patients under anaesthesia conditions, such as the perfusion of organs and the reaction of the body at hypotensive state. A fuzzy gain scheduler and a supervising algorithm were also developed for online tuning the controller to handle the behavior of the body. The control system was tested on 25 experiments on seven pigs in the animal laboratory. Simulation and experiment results proved the usefulness of Guyton's model in control system design which can present the dynamical response of blood pressure in the circulation under and after hypotensive control. The results also indicated the safety and stability of the controller.

Novel control system for blood glucose using a model predictive method

We developed a novel blood glucose control system, using a model predictive method, to achieve optimal control of the blood glucose level in severely diabetic or pancreatectomized patients. This system is designed to predict glucose level changes in advance, considering delayed response time and the administered doses of insulin. This method is also designed to calculate the most appropriate insulin infusion rate by considering differences in individual response to insulin. In this study, we compared our system with a conventional proportional and differential controller (PD controller) to determine whether the new system could regulate the glucose level efficiently in pancreatectomized dogs. The model predictive control method resulted in a significant reduction of mean insulin infusion rate compared with the conventional PD controller (0.71 mU/kg per min vs. 1.81 mU/kg per min, p = 0.0005), when the glucose level in both methods reached the planned target level (100 mg/dl). The new system also tended to have a reduced mean glucose infusion rate for compensating for overshooting of the glucose level compared with the PD controller (0.7 mg/kg per min vs. 1.1 mg/kg per min, p = 0.16). These results indicate that the new system should be a useful tool for regulating the glucose level in severely diabetic patients.

Improving regulation of mean arterial blood pressure during anesthesia through estimates of surgery effects

In this paper, a scheme for improvement of the regulation of mean arterial blood pressure (MAP) during anesthesia based on model predictive control (MPC) and estimates of the effects of disturbances (surgical events) is proposed. A linear model for the combined effects of surgical stimulations and volatile anesthetics on MAP is derived from experimental data. Based on it the potential improvement in blood pressure regulation is evaluated via a simulation study. The simulation study shows that when information about the effect of the surgical events on MAP is utilized by the controller maximum MAP deviations can be reduced by as much as 50% even when this information is inaccurate. At worst, (highly inaccurate information) no improvement is obtained.

Significance of local recurrence of rectal cancer as a local or disseminated disease

BACKGROUND

The nature of 'local recurrence' of rectal cancer remains unclear.

METHODS

Fifty-nine patients with locally recurrent rectal cancer who underwent extended repeat resections including total pelvic exenteration (39) and sacrectomy (43) were reviewed. Twelve patients had distant metastases before or at the time of repeat resection.

RESULTS

The 5-year survival rate was 25 per cent. A second recurrence occurred in 45 patients including five of the eight 5-year survivors. Thirty-six of these recurrences had locoregional manifestations and 29 had distant metastases. Of 18 prognostic factors examined, the most significant determinant was the postoperative carcinoembryonic antigen doubling time (CEADT), followed by the preoperative CEADT, carcinoembryonic antigen (CEA) level and occurrence of distant metastases, in decreasing order. Late onset of first recurrence was also a favourable indicator. Thus, the growth rate of the tumour had a more profound impact on survival than the current extent of tumour progression. After operation the CEADT was reduced in patients with second recurrence (P = 0.05).

CONCLUSION

Locally recurrent rectal cancer is a manifestation of disseminated disease spreading locoregionally and often to distant organs with a low probability of long-term cure. However, survival varies widely depending on the tumour growth rate, which is biologically predetermined and is also influenced by surgery.