Biomedical subjects

A M Zbinden

Publications and source records attributed to A M Zbinden.

67 records · Page 4Linked to original sources

PubMed1988

Influence of ventilatory and circulatory changes on the pharmacokinetics of halothane and isoflurane.

In two groups of dogs, uptake and elimination of halothane and isoflurane were studied using a closed-loop anesthesia system which automatically controlled end-tidal halothane or isoflurane partial pressure at minimal alveolar concentration (MAC) equivalent levels. Hemodynamic and respiratory variables were recorded and the anesthetic partial pressure was measured in the inspired and expired air, as well as in the arterial, cerebrovenous and mixed venous blood. Data were recorded during wash-in, hyperventilation, hypercirculation, hypotension and wash-out. For halothane, the controller delivered a higher inspired partial pressure than for isoflurane to compensate for the higher blood/gas partition coefficient. This was especially pronounced during the wash-in and the hypercirculation periods. Smaller differences between halothane and isoflurane partial pressures occurred during hyperventilation, hypotension and the wash-out period and could be explained by the lower solubility of isoflurane. These results show that even under unstable ventilatory and hemodynamic conditions, the inspired concentration of isoflurane has to be adjusted less often and to a smaller degree than that of halothane if end-tidal concentrations are to be maintained constant.

Animals↗

PubMed1988

Anaesthetic uptake and elimination: is there a difference between halothane and isoflurane in the dog?

In two groups of dogs, the uptake and elimination of halothane and isoflurane were studied using a closed-loop anaesthetic system which automatically controlled end-tidal halothane and isoflurane partial pressures at equi-MAC concentrations. Haemodynamic and respiratory variables were recorded and the anaesthetic partial pressures were measured in the inspired and expired air, as well as in the arterial, cerebrovenous and mixed venous blood. The controller delivered a higher inspired partial pressure of halothane than of isoflurane to compensate for the higher blood/gas partition coefficient. The partial pressures of halothane in the arterial, cerebrovenous and mixed venous blood increased at rates similar to those of isoflurane. During 160 min of uptake, the cerebral venous partial pressures remained significantly lower than the arterial partial pressures for both agents. On discontinuation of the anaesthetic, the partial pressures of halothane and isoflurane decreased at equal rates in arterial, cerebrovenous and mixed venous blood, and in end-tidal gas. It was concluded that the rate of uptake of isoflurane is more rapid than that of halothane from the alveolar space to the blood, but not from the blood to brain tissue. The rates of elimination from brain tissue and from blood were found to be similar for both agents.

Anesthesia, Inhalation↗

PubMed1988

Midazolam in plasma from hospitalized patients as measured by gas-liquid chromatography with electron-capture detection.

The present assay was developed for quantifying midazolam in plasma of patients hospitalized in intensive-care units or undergoing anesthesia and receiving many other drugs as well. Plasma samples are alkalinized with NaOH and midazolam is extracted into n-hexane. The organic phase is evaporated and reconstituted in n-butyl acetate, and the midazolam is quantified by gas-liquid chromatography with electron-capture detection. The calibration graph for midazolam was linear in the ranges 5-200 and 200-800 micrograms/L. The CVs for precision and reproducibility of the assay were less than 8%. The method was very specific for midazolam; most of the drugs commonly used in anesthesia and in the intensive-care unit did not interfere with the assay. The lowest detectable concentration was 1 microgram/L. The method is adaptable for use with an automated chromatographic system.

Aged↗

PubMed1987

[Development of an information system for operations].

The report describes a computer system that provides statistical information on the anesthetic and surgical procedures performed by anesthetists and surgeons, reports on the operative activity of the anesthesia and surgical departments, and assists in daily scheduling of the program. Additional programs can be used for billing, displaying the use of (operating room OR) facilities by the various surgical divisions, and showing the actual stage of on-line operations with monitors. The software system MUMPS has been found to be a low-priced yet efficient and versatile multiuser system. The main features of the program are ease of use, prospective data entry (i.e. during the entire stay of the patient), and the possibility of modifying and expanding the system easily. Missing or inaccurate data are automatically brought to the attention of those who have performed the operation or the anesthesia by a program that is run periodically. The system has been found to be a useful tool for the daily scheduling of the OR program. It provides data for better scheduling of personnel and records can also be kept regarding the professional experience of physicians. The major deficiency of the program at this stage is its lack of a hierarchical structure. For example, it is unable to record multiple operations and/or anesthetic procedures for the same patient. This deficiency will be corrected in a newer version of the program.

Anesthesia↗

PubMed1986

A laboratory investigation of two new portable gas analysers.

Two new portable infrared gas analysers, the Irina (Drägerwerke, Lübeck, Germany) and the Normac (Datex Instrumentarium Corporation, Helsinki, Finland), were tested and the results compared to those from such established methods as gaschromatography and the Beckman LB-2 (Beckman, USA) infrared gas analyser using exactly defined gas mixtures from a vaporizer developed in our laboratory. The analysers were evaluated for their accuracy and precision, noise, zero stability, gain stability and the impact of flow, over-pressure, carrier gas and humidity. All three analysers showed good accuracy and precision. The noise level was acceptable except in the older version of the Normac, but this error has now been corrected by the manufacturer. Zero and gain stability are very good; gas flow and over-pressure do not affect the measurement. The influence of carrier gases and humidity is negligible except for the strong N2O effect on the Beckman. We conclude that this new generation of highly sophisticated and reliable but handy analysers will meet the clinical demands.

Anesthesia, Inhalation↗

PubMed1986

Control of end-tidal halothane concentration. Part A: Anaesthesia breathing system and feedback control of gas delivery.

Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient, a circulating pump and feedback controllers for system volume and anaesthetic concentration. Feedback control was implemented to adjust and control automatically the end-tidal anaesthetic concentration and the volume of the system with oxygen supplied through a mass flow controller and with halothane supplied by a titrating syringe. Controller gains, as a function of body weight, were found using a nine-compartment tissue uptake model. Stability was maintained with +/- 50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal halothane concentration and system volume to provide a rapid and optimized induction of anaesthesia.

Anesthesia, Inhalation↗

PubMed1986

Control of end-tidal halothane concentration. Part B: Verification in dogs.

Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). Then followed 60 min of halothane wash-out and a further 120-min period of halothane at 1.74 vol% (2 MAC). Halothane concentrations were measured in the inspired and expired air, and in the arterial, cerebral venous and mixed venous blood. Haemodynamic and respiratory variables were measured. The system reached 95% of the target end-tidal concentration within 6 min without over-shooting. After 2 h of wash-in, significant gradients still persisted between end-tidal, arterial and cerebral venous blood concentrations. Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limits.

Anesthesia, Inhalation↗

PubMed1985

The effect of surgery and anesthetic agents on granulocyte-chemiluminescence in whole blood.

The effect of anesthesia and major abdominal surgery on zymosan-induced chemiluminescence (CL) of neutrophil granulocytes was evaluated. CL was measured in diluted whole blood taken at distinct intervals within the perioperative period. In addition, blood samples from healthy volunteers were supplemented with ether and halothane to investigate the in vitro effect of these agents. The phagocytosis-induced CL was not found to be depressed by anesthesia and surgery. Only at supranarcotic concentrations was CL reduced. Surgery and anesthesia, therefore, do not appear to impair this defense system significantly under the conditions of this investigation.

Abdomen↗

PubMed1985

Determination of the partial pressure of halothane (or isoflurane) in blood.

A gas chromatographic method is described for the direct quantitative determination of the partial pressure of halothane (or isoflurane) in blood as well as the blood-gas partition coefficient. A head space technique and a flame ionization detector were used. Standard blood was obtained by equilibrating patients' blood with known gas concentrations in a tonometer. Using an infra-red analyser to measure the halothane gas concentration in the tonometer and within the anaesthetic system allowed for the direct comparison of the partial pressure in blood to the partial pressure in the inspired gas. Technical problems associated with this procedure, and with comparable methods, are discussed.

Chromatography, Gas↗

PubMed1983