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F J Sasse

Publications and source records attributed to F J Sasse.

5 recordsLinked to original sources
PubMed1998

Model for the administration of low-flow anaesthesia.

A general (multiple-gas) three-compartment mass-balance model of the circle-absorber breathing circuit with intermittent positive-pressure ventilation has been developed. We propose it as a tool to determine flowmeter and vapourizer settings for inhalation anaesthesia by low-flow methods (less than 1 litre min-1 total fresh gas flow). This model reproduces the results of various previously-published mass-balance models, but it appears to underestimate slightly the delivery of fresh gases to the inspired limb of the breathing circuit when tested with clinical data from surgical cases. Low-flow dosing schedules for 35% inspired oxygen and 1% inspired halothane were computed with the model and tested in vitro with a circle-absorber breathing circuit and an active gas-exchange lung at nine values of simulated patient gas exchanges. The mean inspired oxygen concentration over all trials was 32.8% (SD = 1.9%), while the mean inspired halothane concentration was 1.2% (SD = 0.3%). The flow meter and vapourizer settings calculated from the model appear to have sufficient accuracy to be useful in the clinical setting in conjunction with active oxygen and anaesthetic agent monitoring.

Adult↗
PubMed1997

The response of anesthetic agent monitors to trifluoromethane warns of the presence of carbon monoxide from anesthetic breakdown.

OBJECTIVE: Trifluoromethane and CO are produced simultaneously during the breakdown of isoflurane and desflurane by dry CO2 absorbents. Trifluoromethane interferes with anesthetic agent monitoring, and the interference can be used as a marker to indicate anesthetic breakdown with CO production. This study tests representative types of gas monitors to determine their ability to provide a clinically useful warning of CO production in circle breathing systems. METHODS: Isoflurane and desflurane were reacted with dry Baralyme at 45 degrees C. Standardized samples of breakdown products were created from mixtures of reacted and unreacted gases to simulate the partial degrees of reaction which might result during clinical episodes of anesthetic breakdown using 1% or 2% isoflurane and 6% or 12% desflurane. These mixtures were measured by the monitors tested, and the indication of the wrong agent or a mixture of agents due to the presence of trifluoromethane was recorded and related to the CO concentration in the gas mixtures. RESULTS: When presented with trifluoromethane from anesthetic breakdown, monochromatic infrared monitors displayed inappropriately large amounts of isoflurane or desflurane. Agent identifying infrared and Raman scattering monitors varied in their sensitivity to trifluoromethane. Mass spectrometers measuring enflurane at mass to charge = 69 were most sensitive to trifluoromethane. CONCLUSION: Monochromatic infrared monitors were unable to indicate anesthetic breakdown via interference by trifluoromethane, but did indicate falsely elevated anesthetic concentrations. Agent identifying infrared and Raman monitors provided warning of desflurane breakdown via the interference of trifluoromethane by displaying the wrong agent or mixed agents, but may not be sensitive enough to warn of isoflurane breakdown Some mass spectrometers provided the most sensitive warnings to anesthetic breakdown via trifluoromethane, but additional data processing by some patients monitor units reduced their overall effectiveness.

Air Pollutants, Occupational↗
PubMed1987

Automatic control of anesthesia using two feedback variables.

A new controller of an ON/OFF type was implemented for halothane anesthesia. A proportional-plus-integral controller with time-delay compensation proved not to be robust enough for the known clinical situation, as shown both in computer simulations and in animal trials. The ON/OFF controller proved to be less sensitive to parameter mismatches, and repeated animal trials showed a short response time and acceptable steady-state tracking. A method for switching the controlled effect of the drug was also developed, since anesthetic agents have multiple effects. Mean arterial blood pressure and a measure of EEG frequency were chosen as controlled variables, both being depressed by halothane. A coordinator forces the system state as near the desired values of these variables as possible, given that only one drug is used.

Algorithms↗
PubMed1979

The "D circle": closed-circuit operation of the Bain circuit.

A method of converting a Mapleson D (Bain) circuit to closed-circuit operation is presented, utilizing a laboratory air pump and a Waters carbon dioxide absorber canister to recirculate exhaled gas. The elimination of carbon dioxide from the circuit was studied and found to be adequate. The circuit would allow the use of low fresh gas flows for the maintenance of anaesthesia without the danger of carbon dioxide rebreathing. We suggest that such a circuit could provide appropriate conditions of gas humidity and temperature for endotracheal anaesthesia, while realizing the advantage of a circulator in mask anaesthesia is possible. Further design considerations for a "D circle" breathing system for clinical use are discussed.

Anesthesiology↗