[Practical information on materiovigilance in anesthesia-resuscitation].
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Anesthesia↗
Biomedical subjects
L Beydon
Publications and source records attributed to L Beydon.
[Practical information about material vigilance in anesthesia and recovery. 3].
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Anesthesia Recovery Period↗
[Accessory anesthetic circuit and principal circuit].
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Anesthesia, Closed-Circuit↗
[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↗
[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↗
[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↗
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↗
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↗
[Easy to handle fibroscope].
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Fiber Optic Technology↗
Sleep apnea-like syndrome induced by nitrous oxide inhalation in normal men.
To study the relationship between sedation and respiration under N2O, we performed polysomnographic recordings in 15 healthy men with documented normal breathing patterns during sleep. In a first study in five subjects, we found that 50% N2O in O2 compared to 50% O2 increased sleep latency to stage 2 (59 +/- 12 vs. 17 +/- 3 min), total sleep duration (59 +/- 12 vs. 26 +/- 11 min), depth of sleep and respiratory events during sleep (18 +/- 5 vs. 1 +/- 1/h of sleep). In a second study, ten subjects were exposed to N2O (30 and 50%) in O2 during two consecutive experimental periods. Eight subjects had EEG features of physiological sleep, but nevertheless exhibited a total of 181 respiratory events. Respiratory disturbance index (RDI) during sleep was similar under 30 and 50% N2O (25 +/- 7 and 25 +/- 5/h of sleep, respectively). Obstructive events predominated, except in three subjects during N2O 30% and one during N2O 50% exposure. We conclude that N2O can induce central and obstructive sleep apneas.
Administration, Inhalation↗
[Interviews with families of organ donors: analysis of motivation for acceptance or refusal of donation].
OBJECTIVE: The reasons for organ donation acceptance or refusal are still unclear. This study analysed the influence of the circumstances of the conversations with the relatives of brain dead patients on their consent for organ donation. STUDY DESIGN: Prospective study. MATERIAL: The analysis included 41 questionnaires collected over nine months in one organ harvesting centre and focusing on the circumstances of death, the conditions of the conversations and the reasons for acceptance or refusal. METHODS: Questionnaire filled in by the physicians after the interviews of the relatives of brain dead patients. RESULTS: The refusal rate was higher (54 vs 21%) when only one physician participated in the conversation, when more than two relatives had to decide (42 vs 24%), when conversations took place during night or when the request for organ donation followed immediately the announcement of death (43 vs 20%). Most often the relatives gave their decision within minutes following the request. CONCLUSION: The circumstances of conversation with families play an essential role in their decision-making. A written guideline implementation for these conversations would probably be beneficial for the decisions of families in favour of organ donation.
Adolescent↗
[Anesthesia ventilators].
OBJECTIVE: To review anaesthesia ventilators in current use in France by categories of ventilators. DATA SOURCES: References were obtained from computerized bibliographic search. (Medline), recent review articles, the library of the service and personal files. DATA SYNTHESIS: Anaesthesia ventilators can be allocated into three groups, depending on whether they readminister expired gases or not or allow both modalities. Contemporary ventilators provide either constant volume ventilation, or constant pressure ventilation, with or without a pressure plateau. Ventilators readministering expired gases after CO2 absorption, or closed circuit ventilators, are either of a double- or a single-circuit design. Double-circuit ventilators, or pneumatical bag or bellows squeezers, or bag-in-bottle or bellows-in-bottle (or box) ventilators, consist of a primary, or driving circuit (bottle or box) and a secondary or patient circuit (including a bag or a bellows or membrane chambers). Bellows-in-bottle ventilators have either standing bellows ascending at expiration, or hanging bellows, descending at expiration. Ascending bellows require a positive pressure of about 2 cmH2O throughout exhalation to allow the bellows to refill. The expired gas volume is a valuable indicator for leak and disconnection. Descending bellows generate a slight negative pressure during exhalation. In case of leak or disconnection they aspirate ambient air and cannot act therefore as an indicator for integrity of the circuit and the patient connection. Closed circuit ventilators with a single-circuit (patient circuit) include a insufflating device consisting either in a bellows or a cylinder with a piston, operated by a electric or pneumatic motor. As the hanging bellows of the double circuit ventilators, they generate a slight negative pressure during exhalation and aspirate ambient air in case of leak or disconnection. Ventilators not designed for the readministration of expired gases, or open circuit ventilators, are generally stand-alone mechanical ventilators modified to allow the administration of inhalational anaesthetic agents.
Anesthesia, Closed-Circuit↗
Changes in cerebral hemodynamics after a single dose of clonidine in severely head-injured patients.
alpha 2-Adrenergic agonists induce cerebral vasoconstriction, reduce intracranial pressure (ICP) in experimental animals and may be useful in the hemodynamic management of head-injured patients. We studied the effects of the alpha 2 agonist clonidine on the cerebral circulation in 12 head-injured patients (Glasgow Coma Scale score < 8). Middle cerebral artery flow velocity (MCAV), ICP, mean arterial pressure (MAP), and cerebral perfusion pressure (CPP), were continuously recorded before (T0), at the end (T1), and 30 min after (T2) a 10-min intravenous (i.v.) infusion of 2.5 micrograms/kg clonidine. The cerebral arteriovenous oxygen content difference (AVDO2) and Paco2 were sequentially obtained. ICP, Paco2, AVDO2, and MCAV did not change after clonidine administration. In contrast, MAP and CPP decreased (P < 0.05 and P < 0.05, respectively, at T1 and T2). Three subjects displayed a transient increase in ICP (> 10 mm Hg) at T1; this increase was concomitant with the decrease in MAP. Clonidine administered as an i.v. infusion may induce a critical but transient increase in ICP in some severely head-injured patients. This effect may result from cerebral autoregulatory vasodilation and increased cerebral blood volume as a response to the hypotensive effects of clonidine.
Adrenergic alpha-Agonists↗
Pressure-volume curves in acute respiratory failure: automated low flow inflation versus occlusion.
Pressure-volume (P-V) curves of the respiratory system allow determination of compliance and lower and upper inflection points (LIP and UIP, respectively). To minimize lung trauma in mechanical ventilation the tidal volume should be limited to the P-V range between LIP and UIP. An automated low flow inflation (ALFI) technique, using a computer-controlled Servo Ventilator 900C, was compared with a more conventional technique using a series of about 20 different inflated volumes (Pst-V curve). The pressure in the distal lung (Pdist) was calculated by subtraction of resistive pressure drop in connecting tubes and airways. Compliance (Cdist), Pdist(LIP), and Pdist(UIP) were derived from the Pdist-V curve and compared with Cst, Pst(LIP), and Pst(UIP) derived from the Pst-V curve. Nineteen sedated, paralyzed patients (10 with ARDS and 9 with ARF) were studied. We found: Cdist = 2.3 + 0.98 x Cst ml/cm H2O (r = 0.98); Pdist(LIP) = 0.013 + 1.09 x Pst(LIP) cm H2O (r = 0.96). In patients with ARDS: Pdist(UIP) = 4.71 + 0.84 x Pst(UIP) cm H2O (r = 0.94). In ARF, we found differences in UIP between the methods, but discrepancies occurred above tidal volumes and had little practical importance. They may reflect that Pdist comprises dynamic phenomena contributing to pressure in the distal lung at large volumes. Compliance, but not LIP and UIP, could be accurately determined without subtraction of resistive pressure from the pressure measured in the ventilator. We conclude that ALFI, which is fully automated and needing no ventilator disconnection, gives useful clinical information.
Acute Disease↗
Correlation between simple clinical parameters and the in vitro humidification characteristics of filter heat and moisture exchangers. Groupe de Travail sur les Respirateurs.
STUDY OBJECTIVE: This study on ventilated patients in ICUs examined a large sample of heat and moisture exchanger filters (HMEFs) to determine whether simple clinical parameters are correlated with exchanger humidity output. DESIGN: A total of 594 HMEFs (18 types of HMEF) were tested in nine university hospital ICUs. PATIENTS: Each HMEF was tested on one different unselected and consecutive patient for 24 h. INTERVENTIONS: The following parameters were rated at each tracheal aspiration on a scale of 0 to 3: secretion abundance, viscosity (Visc), suction catheter adherence (Adh) to the endotracheal tube, and the amount of water condensed in the flex tube (Cond). Individual values for each type of HMEF and each variable were averaged and correlated with the humidity output (HO) of the HMEFs, values which were supplied by the manufacturers. RESULTS: There were significant correlations between HO and Cond (r=0.82, p<10(-3)), Visc (r=-0.67, p=0.002), and Adh (r=-0.56, p=0.01). A second study recorded the same variables, for three consecutive 24-h periods, using first a high-humidifying HMEF (DAR Hygrobac), followed by a low-humidifying one (Pall BB22-15), and again DAR Hygrobac. Visc and Adh were higher (p<0.05) and Cond was lower (p<0.05) with the Pall than with the DAR. CONCLUSIONS: Simple clinical parameters correlate well with the efficiency of HMEFs. The apparent water condensed in the flex tubing seems to be the best indicator of the humidifying efficiency of HMEFs.
Adhesiveness↗
[A survey of operating and recovery room ventilators and monitoring equipment as well as their maintenance].
OBJECTIVE: To survey the monitoring and anaesthetic devices available in a sample of French hospitals and the modalities of their maintenance. STUDY DESIGN AND METHOD: Survey carried out in 21 private and public hospitals (including eight university hospitals), affilated to the French Association for Research in Anaesthesia and Intensive Care (ARAR). RESULTS: More than 84% of all operating theaters were equipped with at least an ECG, a SpO2, and a non invasive blood pressure monitor. The non equipped anaesthesia sites were mainly delivery rooms, plaster cast rooms and X-ray rooms. The figure of recovery room beds was, generally speaking in accordance with the French recommendations. Maintenance policy was not systematic and not budgeted in 72% of the surveyed centres. CONCLUSION: The equipment in most anesthetic sites has significantly increased, however maintenance policy remains still heterogenous.
Anesthesia Recovery Period↗
[A study of pneumatic performances of 2 new anesthesia ventilators: a trial].
OBJECTIVE: To assess the pneumatic performance of two new anaesthesia ventilators. STUDY DESIGN: Test bench study. MATERIAL: ADU (Datex), Excel 7900 (Ohmeda) ventilators both included in "bellows-in-box" class, with rising bellows at expiration. METHODS: The accuracy of spirometry and pressure measurements was tested in various conditions of downstream charge and ventilation. The bench comprized a passive lung model with adjustable compliance and resistances, and flow and pressure gauges. RESULTS: Pneumatic performance and accuracy were good in normal as well as in severe ventilatory conditions. This is made possible by the compensation algorithm included in these machines, which automatically corrected the delivered volume for errors related to tubing and gas compressibility. CONCLUSION: These two new machines with pneumatic compensation overcome the main drawback seen with conventional "bellows-in-box" ventilators.
Anesthesia, General↗
Respiratory resistance by end-inspiratory occlusion and forced oscillations in intubated patients.
Measurement of respiratory impedance by the forced oscillation technique (FOT) in intubated patients requires corrections for the flow-dependent resistance, inertance, and air compression inside the endotracheal tube (ETT). Recently, we published a method to correct respiratory impedance for the mechanical contribution of the ETT. To validate this correction, we compared the respiratory resistance obtained with this method (Rfo) to the intrinsic (Rmin) and total resistances (RT) measured by the airway-occlusion technique (OCT) in 16 intubated sedated paralyzed ventilated patients. The FOT was applied at functional residual capacity in the 4- to 32-Hz frequency range, whereas the OCT was performed at the end of a normal constant-flow inspiration. Rmin corrected with Rfo measured at 16 and 32 Hz [Rfo(16) = 1.10 x Rmin + 0.10 cmH2O.s.l-1, r = 0.96, P < 0.001; Rfo(32) = 0.93 x Rmin + 0.72 cmH2O.s.l-1, r = 0.97, P < 0.001]. RT corrected with Rfo at 4 Hz [Rfo(4) = 1.11 x RT - 1.48 cmH2O.s.l-1; = 0.92; P < 0.001]. We conclude that the FOT improved by correction for the behavior of the ETT is in good agreement with the OCT in intubated patients.
Adult↗