Model-based neuro-fuzzy control of FiO2 for intensive care mechanical ventilation
© The Author(s) 2001
Received: 15 January 2001
Published: 2 March 2001
The knowledge-based approach to fuzzy logic control of mechanical ventilation on the ICU can be prone to bias in the experts' knowledge and errors resulting from poor communication during rule-base derivation. Therefore, a different approach was explored in the development of a fuzzy controller to control the inspired oxygen fraction (FiO2). The performance of such a controller was compared with the performance of the clinicians.
(1) The development of a neuro-fuzzy controller
This was developed by training a neural network to generate an optimal change in the FiO2 in order to achieve a target arterial oxygen tension (PaO2) on a mathematical model of the gas exchange system (SOPAVent). The neural network learnt the relationship between the blood gases, FiO2 and PEEP and other ventilator settings. This was done by exposing the neural network to the blood gas results produced by applying a range of FiO2 and PEEP values to the SOPAVent model. This first neural network was then combined with another neural network which represented a fuzzy logic rule-base. The fuzzy rule-base consists of a set of 'If ..., Then ...' statements based around combinations of FiO2, PEEP and PaO2. The fuzzy rule-base was then adjusted by changing the weights of the neuro-controller (which correspond to the 'Then ...' part of the fuzzy rules) during neural network training. The neuro-controller output is equivalent to the output from a fuzzy inference system of three inputs (the difference between the actual PaO2 and the target, the PEEP level and the FiO2).
(2) Comparing neuro-fuzzy and clinicians' control
The scenarios were based on the data from three real patients with sepsis in the ICU. Seventy-one blood gases, ventilatory settings and respiratory parameters at the sampling times were presented to nine consultant intensivists. They were asked to optimise the PaO2 of the patient scenarios in the simulator by adjusting the FiO2. Similarly, the neuro-fuzzy controller was presented with the same data and asked to adjust the FiO2. The impact of these changes on the patient's PaO2 was then calculated using the SOPAVent model. The FiO2 adjustments and corresponding new PaO2 levels were compared to see how close were the decisions of the clinicians and the neuro-fuzzy controller.
44.60 ± 11.63
14.62 ± 4.08
43.95 ± 11.03
14.12 ± 2.69
The control of PaO2 provided by the neuro-fuzzy controller was similar to the clinicians' control. Neural networks can provide an alternative means for fuzzy rule-base derivation and tuning for ventilator control.
This project was funded by EPSRC Grant no. R/M96483.