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Biomedical subjects

L Beydon

Publications and source records attributed to L Beydon.

At least 19 recordsLinked to original sources
PubMed2001

[Electroencephalographic effects of sevoflurane in pediatric anesthesia: a prospective study of 20 cases].

OBJECTIVE: To study electroencephalographic (EEG) changes in children during induction of anaesthesia with 8% sevoflurane. PATIENTS: Twenty patients were consecutively included (ASA I-II; aged: 13-101 months). MATERIAL AND METHOD: Prospective study; approved by the Ethics Committee; written informed consent obtained from parents; anaesthesia induced with 8% sevoflurane in oxygen; no premedication was given; to collect the EEG data, non-invasive electodes were installed before induction; EEG was recorded continuously and stored on a computer for later analyses (descriptive analysis). RESULTS: Myoclonics movements were observed during induction of anaesthesia in two boys. Myoclonics movements stopped spontaneously without therapy. Epileptiform EEG activity (spikes and poly-spikes, burst suppression) was observed. In the 18 others cases, during sevoflurane induction, EEG changed rapidly with an increase in the range of beta activity (> 13 Hz) (n = 15) and in slow (< 8 Hz) and delta activity (< 4 Hz). In 14 patients, at time of laryngoscopy, the EEGs showed monophasic slow data activity (sharp high-voltage slow waves). Periods of EEG isoelectrical (burst suppression) were seen without spikes in four cases. CONCLUSION: At 2 MAC, epileptiform EEG activity has been observed during sevoflurane anaesthesia. In a short group of patients, this raises the question of avoiding sevoflurane in patients who have a history of epilepsy.

Anesthetics, Inhalation↗
PubMed2000

[Performance studies of 6 new anesthesia ventilators: bench tests].

OBJECTIVE: To assess the pneumatic performances of six new anaesthesia ventilators. STUDY DESIGN: Bench test study. MATERIAL: The study included one ventilator operated by an electric motor: ABT 5300 (Kontron); four ventilators of "bellows-in-bottle" category: ADU version 97 (Datex-Ohmeda); Aestiva 3000 (Datex-Ohmeda), Kion (Siemens), the two versions of Julian (Dräger); and an original ventilator devised for quantitative, or self-regulating target controlled inhalation anaesthesia, with a totally closed circuit, made of four ventilating chambers: PhysioFlex (Dräger). METHODS: The bench test included a passive lung model with adjustable compliance and resistances, and flow and pressure gauges. The accuracy of volume and pressure measurements was tested in various conditions of resistance and compliance. RESULTS: Pneumatic performance and accuracy were satisfactory, even in severe ventilatory conditions. All the ventilators, except ABT 5300 and Julian 1, have a compliance compensation system permitting to deliver and to maintain a constant tidal volume under various conditions of downstream load, particularly under maximal load condition. Variations of tidal volume with the increase of the fresh gas flow are negligible. CONCLUSION: Recent technological progress has improved pneumatic performance of anaesthesia ventilators and the marketed models are more homogeneous at present. Ergonomics and training for the use of the machine are becoming major criteria for the global assessment and the choice of a ventilator.

Airway Resistance↗
PubMed2000

[Equipment surveillance of implantable catheter ports (1996-1998). Members of Sub-Commissions 4a and 4b for Equipment Surveillance].

We analyse all incident reports to the French Health Ministry over the 1996-1998 period, concerning implantable catheter ports. They represent 7% of all reports in the field of anaesthesia and intensive care. Two hundred eleven reports have been analysed. There were 93 catheter ruptures with 77 intravascular migrations. In more than 50% of cases, a pinch-off syndrome mechanism was responsible of these ruptures and a displacement of the O'ring was involved in 25%. Additional minor complications were reported and discussed in regard to literature. We conclude that implantable catheter ports may lead to serious incidents which are preventable in most cases.

Catheters, Indwelling↗
PubMed2000

[Perfusion instruments: analysis of product surveillance in 1998 and its on-the-job training. Subcommittee 4b for Product Surveillance].

OBJECTIVES: To analyze retrospectively the data base of the French national vigilance reporting system concerning infusion devices during the year 1998. METHODS: Each report has been reviewed and classified, except implantable catheter ports. RESULTS: The study included 309 reports. Among them, 28% concerned infusion pumps and 72% single use devices, i.e. catheters, infusion lines, taps, connectors, etc. We observed six deaths and 23 severe incidents. Only 25% of devices could be formally investigated by manufacturers. The origins of incidents were very different between infusion pumps and single use devices. The first showed simple failures, software errors, maintenance omissions or errors, and problems related to obsolescence of the device. The second revealed manufacturer quality insurance failures, design and utilization errors, and problems related to the technique itself rather than device. DISCUSSION: Our findings are similar to the few data available in international literature. They address the need to obtain an adequacy between the performances of devices which vary with generations of devices and the clinical risks: newest and safest devices should be preferred for the infusion of the most critical drugs.

Catheterization↗
PubMed2000

Cerebral hemodynamics during arterial and CO(2) pressure changes: in vivo prediction by a mathematical model.

The aim of this work was to analyze changes in cerebral hemodynamics and intracranial pressure (ICP) evoked by mean systemic arterial pressure (SAP) and arterial CO(2) pressure (Pa(CO(2))) challenges in patients with acute brain damage. The study was performed by means of a new simple mathematical model of intracranial hemodynamics, particularly aimed at routine clinical investigation. The model was validated by comparing its results with data from transcranial Doppler velocity in the middle cerebral artery (V(MCA)) and ICP measured in 44 tracings on 13 different patients during mean SAP and Pa(CO(2)) challenges. The validation consisted of individual identification of 6 parameters in all 44 tracings by means of a best fitting algorithm. The parameters chosen for the identification summarize the main aspects of intracranial dynamics, i.e., cerebrospinal fluid circulation, intracranial elastance, and cerebrovascular control. The results suggest that the model is able to reproduce the measured time patterns of V(MCA) and ICP in all 44 tracings by using values for the parameters that lie within the ranges reported in the pathophysiological literature. The meaning of parameter estimates is discussed, and comments on the main virtues and limitations of the present approach are offered.

Adolescent↗
PubMed1999

Correlation between cerebral oxygen saturation measured by near-infrared spectroscopy and jugular oxygen saturation in patients with severe closed head injury.

UNLABELLED: Near-infrared spectroscopy has been used to monitor cerebral oxygen saturation during cerebral circulatory arrest and carotid clamping. However, its utility has not been demonstrated in more complex situations, such as in patients with head injuries. The authors tested this method during conditions that may alter the arteriovenous partition of cerebral blood in different ways. METHODS: The authors compared changes in measured cerebral oxygen saturation and other hemodynamic parameters, including jugular venous oxygen saturation, in nine patients with severe closed head injury during manipulation of arterial carbon dioxide partial pressure and after mean arterial pressure was altered by vasopressors. RESULTS: The Bland and Altman representation of cerebral oxygen saturation versus jugular oxygen saturation showed a uniform scatter. Values for changing arterial carbon dioxide partial pressure were: bias = 1.1%, 2 SD = +/-21%, absolute value; and those for alterations in mean arterial pressure: bias = 3.7%, 2 SD = +/-24%, absolute value. However, a Bland and Altman plot of changes in cerebral oxygen saturation versus changes in jugular oxygen saturation had a negative slope (alteration in arterial carbon dioxide partial pressure: bias = 2.4%, 2 SD = +/-17%, absolute value; alteration in mean arterial pressure: bias = -4.9%, 2 SD = +/-31%, absolute value). Regression analysis showed that changes in cerebral oxygen saturation were positively correlated with changes in jugular venous oxygen saturation during the carbon dioxide challenge, whereas correlation was negative during the arterial pressure challenge. CONCLUSIONS: Cerebral oxygen saturation assessed by near-infrared spectroscopy does not adequately reflect changes in jugular venous oxygen saturation in patients with severe head injury. Changes in arteriovenous partitioning, infrared-spectroscopy contamination by extracerebral signal, algorithm errors, and dissimilar tissue sampling may explain these findings.

Administration, Inhalation↗
PubMed1999

[Accessory anesthetic breathing systems: verification before use].

Accessory or ancillary anaesthesia breathing systems can be defined as all those connected to the fresh gas outlet of the anaesthetic apparatus and used instead of the circle system associated with the ventilator, which is the main circuit. They include: the Mapleson systems, the systems with a nonrebreathing valve and the disposable systems with a carbon dioxide absorber. They can be a cause of major accidents when not checked before and monitored during use. This technical note describes techniques of preanaesthetic checking and monitoring during anaesthesia.

Anesthesia, Closed-Circuit↗
PubMed1998

[Admission modalities of brain dead patients at Ile de France hospitals which do not harvest organs. Cooperative Group for Transplantation of Ile de France (GCIF)].

In order to identify possible causes for the shortage in organ procurement today in France, a regional survey including 74 hospitals in the Paris area which are likely to receive brain dead patients (BDP) and in which there were neither harvesting nor transplantation activities was conducted. Of the 66 hospitals (89%) answering this survey, half of them were district general hospitals. In the 2 years before the survey, they received on average three BDP. Such a figure represents at least 10% of BDP seen in this area. For one half of the centres, care of these patients was difficult or impossible due to the available facilities. Organisational concerns were among the major problems raised by the transfer of these patients to harvesting centres. A preestablished geographical network would be of help for simplifying the transfer of these patients. Interestingly, about 50% of centres already had such links with a transplantation centre. This study provides information concerning logistics and possible points which could be improved in order to increase the number of BDP liable to be transferred to transplantation centres.

Brain Death↗
PubMed1998

[Pros and cons of adding an accessory breathing system to the main circle circuit. II. Arguments against their use].

When compared to the circle system alternative breathing systems (ABS) are of no benefit. When the only indication of an ABS is emergency oxygen administration it should be connected to the O2 pipeline upstream from the flowmeter bank and the vaporiser. The use of an ABS for anaesthesia maintenance is no longer justified because of the difficulties in monitoring pressure, flow and concentrations of the gas mixture, the cost of gas and vapour administered at a high flow and the resulting pollution. The use of an ABS for very short anaesthetics is only acceptable if the administered gas mixture is monitored.

Anesthesia, Closed-Circuit↗
PubMed1998

[Heat and moisture exchanging filters for conditioning of inspired gases in adult anesthesia and resuscitation].

OBJECTIVES: Heat and moisture-exchanging filters (HMEFs) are increasingly used in clinical practice. At the same time, new scientific data are available which clarify the benefits of these devices. DATA SOURCES: We searched in the Medline database for all papers written in English or French, without limiting date of publication, using the following key-words separately or in combination: humidity, temperature, mechanical ventilation, equipment. STUDY SELECTION: From the 200 articles provided by Medline, we selected those directly concerning HMEFs. Some older studies and those on HMEFs no longer available were excluded. DATA EXTRACTION: Principle data available from the literature were analysed. DATA SYNTHESIS: Humidification and warming of the inspired gas mixture is mandatory during mechanical ventilation. There is a direct link between HMEF performance and the characteristics of tracheal secretions. This justified the recommendation for the use of HMEFs with a humidity output above 30 mg of water per litre of gas mixture. In this case, HMEFs are as efficient as conventional heated humidifiers. HMEFs seem to decrease the rate of nosocomial pneumonia in comparison with heated humidifiers. HMEFs induce a slight increase of dead space which should be taken into consideration during weaning from mechanical ventilation. There are demonstrable data in the literature suggesting the possibility of cross viral infection via the anaesthetic machine when an HMEF is not used. There are no data which suggest a specific type of HMEF regarding viral filtration. CONCLUSION: According to the literature data, using an HMEF is essential in anaesthesia and is highly recommended in intensive care.

Adult↗
PubMed1998

Modeling cerebral autoregulation and CO2 reactivity in patients with severe head injury.

The mathematical model presented in a previous work is used to simulate the time pattern of intracranial pressure (ICP) and of blood velocity in the middle cerebral artery (VMCA) in response to maneuvers simultaneously affecting mean systemic arterial pressure (SAP) and end-tidal CO2 pressure. In the first stage of this study, a sensitivity analysis was performed to clarify the role of some important model parameters [cerebrospinal fluid (CSF) outflow resistance, intracranial elastance coefficient, autoregulation gain, and the position of the regulation curve] during CO2 alteration maneuvers performed at different SAP levels. The results suggest that the dynamic "ICP-VMCA" relationship obtained during changes in CO2 pressure may contain important information on the main factors affecting intracranial dynamics. In the second stage, the model was applied to the reproduction of real ICP and velocity tracings in neurosurgical patients. Ten distinct tracings, taken from six patients during CO2 changes at different mean SAP levels, were reproduced. Best fitting between model and clinical curves was achieved by minimizing a least-squares criterion function and adjusting certain parameters that characterize CSF circulation, intracranial compliance, and the strength of the regulation mechanisms. A satisfactory reproduction was achieved in all cases, with parameter numerical values in the ranges reported in clinical literature. It is concluded that the model may be used to give reliable estimations of the main factors affecting intracranial dynamics in individual patients, starting from routine measurements performed in neurosurgical intensive care units.

Blood Flow Velocity↗
PubMed1998

Changes in cerebral blood flow during PaCO2 variations in patients with severe closed head injury: comparison between the Fick and transcranial Doppler methods.

OBJECT: The aim of this study was to reassess whether middle cerebral artery blood flow velocity (MCAv) variations measured by transcranial Doppler ultrasonography during acute PaCO2 manipulation adequately reflect cerebral blood flow (CBF) changes in patients with severe closed head injury. METHODS: The study was performed by comparing MCAv variations to changes in CBF as assessed by measurements of the difference in the arteriovenous content in oxygen (AVDO2). The authors initiated 35 CO2 challenges in 12 patients with severe closed head injury during the acute stage. By simultaneous recording of systemic and cerebral hemodynamic parameters, 105 AVDO2 measurements were obtained. Patients were stratified into two groups, "high" and "low," with respect to whether their resting values of MCAv were greater than 100 cm/second during moderate hyperventilation. Four patients displayed an elevated MCAv, which was related to vasospasm in three cases and to hyperemia in one case. The PaCO2 and intracranial pressure levels were not different between the two groups. The slope of the regression line between 1 divided by the change in (delta)AVDO2 and deltaMCAv was not different from identity in the low group (1/deltaAVDO2 = 1.08 x deltaMCAv - 0.07, r = 0.93, p < 0.001) and significantly differed (p < 0.05) from the slope of the high group (1/deltaAVDO2 = 1.46 x deltaMCAv - 0.4, r = 0.83, p < 0.001). CONCLUSIONS: In patients with severe closed head injury, MCAv variations adequately reflect CBF changes as assessed by AVDO2 measurements in the absence of a baseline increase in MCAv. These observations indicate that both moderate variations in PaCO2 and variations in cerebral perfusion pressure do not act noticeably on the diameter of the MCA. The divergence from the expected relationship in the high group seems to be due to the heterogeneity of CO2-induced changes in cerebrovascular resistance between differing arterial territories.

Adolescent↗