Biomedical subjects

P Feigenwinter

Publications and source records attributed to P Feigenwinter.

9 recordsLinked to original sources

PubMed1996

Fuzzy logic control of inspired isoflurane and oxygen concentrations using minimal flow anaesthesia.

In order to evaluate the performance of feedback fuzzy logic control of inspired oxygen and isoflurane concentrations, we studied 30 patients undergoing discectomy for lumbar (n = 26) or cervical (n = 4) disc herniation. Patients were allocated random to one of two groups: a standard group (n = 15) with low flow anaesthesia (1.2-1.3 litre min-1) and manual control of gas concentrations; and a fuzzy group (n = 15) with minimal flow (0.5 litre min-1) and fuzzy logic feedback control of gas concentrations. Fuzzy logic control achieved and maintained very accurately the desired isoflurane concentration. Oxygen concentration was controlled more precisely than in the standard group. Delivery and costs of oxygen and nitrous oxide were significantly lower in the fuzzy group (P < 0.01). Accumulation of foreign gases was observed in one patient during low flow and in 11 patients during minimal flow anaesthesia. In conclusion, fuzzy logic control of inspired oxygen and isoflurane concentration during minimal flow anaesthesia was reliable and reduced anaesthetic gas delivery and costs.

Adult↗

PubMed1996

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.

Adolescent↗

PubMed1996

Five oxygen-nitrous oxide proportioning systems compared.

The majority of contemporary gas delivery modules, on anaesthetic workstations, are equipped with oxygen-nitrous oxide proportioning systems which should prevent the delivery of hypoxic gas mixtures. We investigated five modules, of two different types, using fresh gas flows ranging from 50 mL min-1 to 20 L min-1 with minimally acceptable proportions of oxygen and maximally acceptable proportions of nitrous oxide set at the flow control valves. The oxygen concentrations of the resulting gas mixtures were measured at the fresh gas outlet of the gas delivery modules. All the modules prevented the delivery of hypoxic fresh gas flows both under normal and abnormal working conditions (unequal supply of gas pressures). All systems showed increased O2 concentrations at fresh gas flows below 1 L min-1. The systems can be used with low flow anaesthesia techniques with one exception (Dameca) also with minimal flow techniques.

Anesthesiology↗

PubMed1995

The accuracy of the flowrate in flush-devices of disposable pressure transducers.

BACKGROUND: Arterial and venous pressure is commonly measured using fluid filled catheters. To avoid obstruction they are continuously spilled by a flush-device. The accuracy of the flowrate has not been investigated previously. METHODS: The accuracy of 5 different flush-devices available in Switzerland was checked for flowrate when factory new, after a single sterilization with ethylen-oxide, in a long-term test over 96 hours, after repeated handling of the integrated bypass and under application of a pulsing counter-pressure. RESULTS: Flow is linearly related to differential-pressure and is constant over time. The flow of each flush-device at 200 mmHg differential-pressure was below the indicated 3 ml per hour (1.69 - 2.49 ml/h). Sterilization in two types produced a significant but not relevant difference in flowrate. Longtime-use, bypass actuation and pulsing pressure did not alter the flowrate significantly (p <0.05). In two factory-new flush-devices and 4 re-used ones a plugged capillary induced cessation of flow. CONCLUSIONS: Flowrate in flush-devices is accurate under sterilization, longtime use, bypass-actuation and pulsing counter pressure. A plugged capillary occurred in a few new and reused flush-devices, which can be the explanation for clotted catheters in clinical use.

Blood Pressure Determination↗

PubMed1995

Arterial pressure control with isoflurane using fuzzy logic.

Arterial pressure is still one of the most important measures in estimating the required dose of inhaled anaesthetics. It is measured easily and reacts rapidly which makes it suitable as a variable for feedback control of depth of anaesthesia. Fuzzy logic, a novel approach to feedback control, was used to control arterial pressure in 10 patients during intraabdominal surgery by automatic adjustment of the concentration of isoflurane in fresh gas. During anaesthesia, fuzzy control periods of 45-min duration were alternated randomly with human control periods of equal duration. During the skin incision period (-3 to + 12 min) 48.2% of all fuzzy control pressure values were within +/- 10% of the desired mean arterial pressure compared with 40.4% of the human control values (P < 0.05). The corresponding values for the remainder of the operation were 78.3% and 83.2%, respectively. Thus fuzzy out-performed human control at skin incision, but was slightly inferior during the rest of the operation. We conclude that fuzzy logic is a promising new technique for control of isoflurane delivery during routine anaesthesia.

Adult↗

PubMed1994

Simulation of inhalational anaesthetic uptake using a lung model with charcoal.

A physical lung model for simulation of volatile anaesthetic uptake is described. Two communicating water-filled chambers simulate pulmonary mechanics allowing adjustment of functional residual capacity, resistance and compliance. The uptake of the volatile anaesthetics is reproduced by pumping gas from the lung chamber through a charcoal absorber at different rates; using a second pump for a bypass an arterial to end-tidal gradient can be generated. Changes of cardiac output are simulated by adjusting pump speed and of alveolar ventilation by adapting the ventilator setting. The results are reproducible and correspond with patient studies and computer stimulation, not necessitating empirical correction factors as in a previously described oil-based lung model. The model can serve as a teaching instrument, for the comparison and testing of anaesthetic equipment and the development of feedback systems.

Anesthetics, Inhalation↗

PubMed1992

Gas leakage in eight anaesthesia circle systems.

Eight currently used factory-new anaesthesia circle systems (Dräger Cicero, Dräger Sulla, Dräger AV1, Gambro Engström Elsa, Megamed 700A, Ohmeda Modulus II Plus, Siemens Ventilator 710 and Siemens Servo Ventilator 900 D with circle system) and a Megamed 077 which had been clinically used for 11 years were tested for gas leaks according to the Draft European Standard Anaesthetic Workstations and Their Modules. All measurements were performed using the Cicero ventilator developed by Dräger with its integrated test program for the detection of system leakage. All the factory-new systems showed leakage rates of less than 50 ml min-1 at a test pressure of 3 kPa (30 cmH2O). In the 'manual' position and with the soda-lime canister and the volumeter (or flow-sensor) included, the following leak rates were determined: Dräger Cicero, 5.0 ml min-1; Dräger Sulla, 22.8 ml min-1; Dräger AV1, 7.7 ml min-1; Gambro Engström Elsa, 33.4 ml min-1; Megamed 700A, 11.5 ml min-1; Ohmeda Modulus II Plus, less than 0.1 ml min-1; Siemens Ventilator 710, 0.3 ml min-1; Siemens Servo Ventilator 900D with circle system 985, 9.6 ml min-1; Megamed 077, 47.5 ml min-1. All anaesthesia breathing circle systems tested performed below the leakage limit of 100 ml min-1 proposed by the draft standard.

Anesthesia, Closed-Circuit↗

PubMed1991

Fresh gas utilization of eight circle systems.

The fresh gas utilization (FGU) of a semi-closed breathing system is defined as the ratio of the amount of gas reaching the patient's lungs to the total amount of fresh gas flowing into the breathing system. It indicates to what extent a breathing system conserves anaesthetic gases and provides inspired gas concentrations as close as possible to those in the fresh gas, even at low fresh gas flows (FGF). We have measured FGU in eight circle systems used conventionally in Europe: Dräger Cicero, Dräger Sulla 808V with circle system 8 ISO and ventilator Ventilog, Dräger AV1, Ohmeda Modulus II Plus, Gambro Engström Elsa, Siemens Servo Ventilator 900 D with circle system 985, Siemens Ventilator 710 and Megamed 700A with circle system 219. The Tests were performed according to the Draft European Standard "Anaesthetic Workstations and Their Modules". None of the systems tested showed the characteristics of an ideal system which would reach 100% FGU with an FGF less than minute volume. At FGF 3 litre min-1, FGU was: Gambro Engström Elsa 97.8%, Siemens Servo Ventilator 900 D with circle system 96.1%, Dräger Cicero 93.4%, Ohmeda Modulus II Plus 93.1%, Dräger 8 ISO 92.3%, Dräger AV1 87.6%, Megamed 700A 77.0% and Siemens Ventilator 710 74.1%.

Anesthesia, Closed-Circuit↗

PubMed1991

[Inspiratory and expiratory resistance of 8 semi-closed circle systems].

The resistance of a circle system is an important factor that determines the respiratory effort of the patient. The inspiratory and expiratory resistances were measured in eight semi-closed circle systems used in Europe: Dräger Cicero, Dräger 8 ISO, Dräger AV1, Ohmeda Modulus II Plus, Gambro Engström Elsa, Siemens Servo Ventilator 900 D with circle system 985, Siemens Ventilator 710, and Megamed 700A with circle system 219. The measurements were all performed in the position "spontaneous breathing" according to a new proposal of the CEN (Comité Européen de Normalisation). The following circle systems exceeded the proposed limit of 0.6 kPa at a gas flow of 60 l/min (with CO2-Absorber): Dräger AV1 in expiration and Siemens Servo Ventilator in both expiration and inspiration. The expiratory resistance was also determined by using intermittent flows. The results differed, as the expiratory gas flow can be influenced by the falling or rising ventilator bellows. The authors conclude that considerable differences exist between various breathing systems and that not all systems can be recommended for use in patients with limited breathing force, such as small children.

Airway Resistance↗