Articles: closed-circuit-anesthesia.
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IEEE Trans Biomed Eng · Aug 2001
Modeling and closed-loop control of hypnosis by means of bispectral index (BIS) with isoflurane.
A model-based closed-loop control system is presented to regulate hypnosis with the volatile anesthetic isoflurane. Hypnosis is assessed by means of the bispectral index (BIS), a processed parameter derived from the electroencephalogram. Isoflurane is administered through a closed-circuit respiratory system. ⋯ Anti-windup measures protect against performance degradation in the event of saturation of the input signal. Fault detection schemes in the controller cope with BIS and expired concentration measurement artifacts. The results of clinical studies on humans are presented.
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Comparative Study Clinical Trial
Comparison of closed-loop controlled administration of propofol using Bispectral Index as the controlled variable versus "standard practice" controlled administration.
This report describes a new closed-loop control system for propofol that uses the Bispectral Index (BIS) as the controlled variable in a patient-individualized, adaptive, model-based control system, and compares this system with manually controlled administration of propofol using hemodynamic and somatic changes to guide anesthesia. ⋯ A closed-loop system for propofol administration using the BIS as a controlled variable together with a model-based controller is clinically acceptable during general anesthesia.
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Case Reports
Xenon anaesthesia for laparoscopic cholecystectomy in a patient with Eisenmenger's syndrome.
There are few reports on anaesthesia for patients with Eisenmenger's syndrome requiring non-cardiac surgery and none of the use of xenon. We describe the use of xenon with a closed-circuit system in a patient with Eisenmenger's syndrome having a laparoscopic cholecystectomy.
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Recent evidence has suggested that the rate of uptake of inhalational anaesthetic is constant during maintenance of anaesthesia, contrary to the predictions of multi-compartment uptake models. We measured isoflurane uptake using a totally closed anaesthetic system during up to 10 h of stable anaesthesia for maxillo-facial surgery on 12 adult patients. Liquid isoflurane was injected into the system under computer control to produce an end tidal concentration of 1.3 MAC of isoflurane. ⋯ Anaesthetic usage for a 70 kg patient was 0.44e(-0.51t)+0.044e(-0.013t)+0.058e(-0.00098t) ml min(-1) of liquid isoflurane, where t is duration of anaesthesia in minutes. There was a continuing reduction in anaesthetic requirement even at the end of the period of study that was statistically significant. These data do not support the notion that isoflurane uptake is constant during stable maintenance of anaesthesia but is compatible with the conventional multi-compartment model of anaesthetic uptake and distribution.
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Anesthesia and analgesia · May 2001
Randomized Controlled Trial Clinical TrialPreoxygenation with tidal volume and deep breathing techniques: the impact of duration of breathing and fresh gas flow.
Various techniques of "preoxygenation" before anesthetic induction have been advocated, including tidal volume breathing (TVB) for 3-5 min, four deep breaths (DB) in 0.5 min, and eight DB in 1 min. However, no study has compared the effectiveness of these techniques, assessed extending deep breathing beyond 1 min, or investigated the influence of fresh gas flow (FGF) in the same subjects using a circle absorber system. In 24 healthy adult volunteers breathing oxygen from a circle absorber system by tight-fitting mask, we compared TVB/5 min and deep breathing at a rate of 4 DB/0.5 min for 2 min at 5, 7, and 10 L/min FGF. Inspired and end-tidal respiratory gases were measured at 0.5-min intervals. During TVB, end-tidal oxygen (ETO2) increased rapidly and plateaued by 2.5 min at 86%, 88%, and 88% with 5, 7 and 10 L/min FGF, respectively. ETO2 values of > or =90% were attained between 3 and 4 min. Four DB/0.5 min increased ETO2 to 75%, 77%, and 80% at 5, 7, and 10 L/min FGF. Eight DB/min resulted in ETO2 values of 82% and 87% at 7 and 10 L/min, respectively. Extending deep breathing to 1.5 and 2 min with 10 L/min FGF increased ETO2 by > or =90%, although a decrease in ETCo(2) was noted. We concluded that TVB/3-5 min was effective in achieving maximal "preoxygenation" whereas 4 DB/0.5 min resulted in submaximal "preoxygenation," and thus should be used only when time is limited. Increasing FGF from 5 to 10 L/min does not enhance "preoxygenation" with either TVB or 4 DB/0.5 min. Deep breathing yields maximal "preoxygenation" when extended to 1.5 or 2 min, and only when high (10 L/min) FGF is used. ⋯ Using a circle absorber system, normal breathing of oxygen for 3-5 min achieves optimal oxygenation of the lungs; whereas 4 deep breaths in 30 s does not. However, extending deep breathing to 1.5-2 min and using a high flow of oxygen improves oxygenation of the lungs to the same degree as normal breathing for 3-5 min. This may have important implications for patient safety.