PubMed · 11695295
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G Mion, J C Tortosa, F Petitjeans. 2001. [Ketamine and respiratory function].. https://doi.org/10.1016/s0750-7658(01)00454-3
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BACKGROUND: Based on previous pharmacokinetic and pharmacodynamic studies, we have developed an EEG-controlled closed-loop system for the i.v. hypnotic agent propofol in rats. METHODS: Seven adult male Sprague-Dawley rats (weight 423-584 g) were included in the study. EEG was recorded with occipito-occipital needle electrodes and the EEG power spectrum was estimated. The median frequency (MEF) was extracted from the power spectrum and was modified MEF (mMEF) to account for the occurrence of spikes and burst suppression patterns in the EEG. Propofol infusion was controlled by a model-based adaptive control algorithm to maintain a set point of mMEF=3.0 (sd 0.5) Hz. The performance of the feedback system was characterized by the median performance error MDPE=median[(mMEF-set point)/set point] and the median absolute performance error (MDAPE). The effective therapeutic infusion (ETI) to maintain the set point was determined from the resulting infusion rates. RESULTS: In all rats a feedback period of 90 min could be performed. Mean MDPE was 1.2 (se 0.4)% and MDAPE was 13.9 (0.3)%. The ETI was 0.73 (sd 0.20) mg kg(-1) min(-1). Mean arterial pressure before propofol infusion was 148 (14) mm Hg, with the lowest value during closed-loop infusion being 110 (20) mm Hg. CONCLUSIONS: The feedback system presented here may be a useful tool not only for automatic drug control to maintain a defined hypnotic effect but may also be a powerful device in pharmacological studies such as the determination of dose requirements or the assessment of drug-drug interactions.
Propofol is an intravenous anaesthetic agent, which presents interesting features for its use in neuro-anaesthesia: it is a powerful hypnotic that does not increase the intracranial pressure. The delay of recovery is short even after several hours of continuous infusion. This is essential for a fast neurologic examination. Continuous infusion should be preferred to bolus in order to prevent hypotension and decrease of the cerebral perfusion pressure. Target-controlled infusion models based on effect site concentrations are now available through several softwares. This technique appears especially useful for awake craniotomy and functional neurosurgery. The level of consciousness is easily fixed between deep anaesthesia and light sedation permitting to ask the patient to move following orders. A sedation controlled by the patient himself is even possible.
The fabrication and testing of a minimally intrusive (2 mm high, 10 mm diameter) biomedical interface pressure sensor are described. Such sensors are needed for the implementation of improved safety features in the next generation of automated intravenous regional anaesthesia (IVRA) systems. The sensor utilizes a structured elastomer as a deflection element sandwiched between the plates of a parallel plate capacitor device. Simple mechanical modifications allow sensitivity and zero offset adjustment. The sensor is housed in a package machined from an engineering polymer. The device is easily calibrated using either a bench-top or an on-body calibration procedure. The device is particularly sensitive to cuff artefacts arising from variations in cuff-wrap tightness and folding of the cuff. As such, it offers some promise for detecting potential hazard conditions which can occur during conventional IVRA procedures. For the purpose of unit conversion, 1 Pa = 1 N/m2, 1 MPA = 1 N/mm2 and 40 kPa approximately equal to 300 mmHg.