Fuzzy logic control of mechanical ventilation during anaesthesia.

We have examined a new approach, using fuzzy logic, to the closed-loop feedback control of mechanical ventilation during general anaesthesia. This control system automatically adjusts ventilatory frequency (f) and tidal volume (VT) in order to achieve and maintain the end-tidal carbon dioxide fraction (FE'CO2) at a desired level (set-point). The controller attempts to minimize the deviation of both f and VT per kg body weight from 10 bpm and 10 ml kg-1, respectively, and to maintain the plateau airway pressure within suitable limits. In 30 patients, undergoing various surgical procedures, the fuzzy control mode was compared with human ventilation control. For a set-point of FE'CO2 = 4.5 vol% and during measurement periods of 20 min, accuracy, stability and breathing pattern did not differ significantly between fuzzy logic and manual ventilation control. After step-changes in the set-point of FE'CO2 from 4.5 to 5.5 vol% and vice versa, overshoot and rise time did not differ significantly between the two control modes. We conclude that to achieve and maintain a desired FE'CO2 during routine anaesthesia, fuzzy logic feedback control of mechanical ventilation is a reliable and safe mode of control.

Micro-determination of plasma diphenylhydantoin by gas-liquid chromatography.

A selective, sensitive and precise gas-liquid chromatographic method for the determination of diphenylhydantoin in micro samples of blood plasma is described. After a double extraction with chloroform containing an analogue of diphenylhydantoin as an internal standard, the drug and standard are N,N-dimethylated in alkaline aqueous solution with methyl iodide followed by extraction into acetone. The methylated derivatives are separated gas chromatographically and measured using a flame-ionization detector. The lowest concentration of diphenylhydantoin in plasma which can be measured in a 100 mul sample is 1 mug/ml, which is well below the normal therapeutic concentration of 10-20 mug/ml in plasma. The methylated derivatives of diphenylhydantoin and the internal standard have been identified by their proton magnetic resonance spectra and mass spectra.

The determination of phanquone in biological material by gas-liquid chromatography.

A gas-liquid chromatographic method for the quantitative determination of phanquone is described, based on the formation of a dimethoxine prior to its extraction from biological material. The sensitivity of the procedure is about 15 ng/ml in biological fluid.