[Maintenance and obsolescence of medical devices]. / Maintenance et obsolescence des dispositifs médicaux.

Maintenance of medical devices is either curative, in case of a failure of the device, or preventive. Preventive maintenance (PM) is undertaken either at constant time intervals or when a given parameter crosses a specified limit. The aim of PM is to amend wear from intensive use as well as from ageing. Normally, the modalities of PM are defined by the manufacturer who must anticipate the possible deficiencies of the device. Some manufacturers tend to recommend exaggerated maintenance procedures. Obsolescence of a medical device is defined by one of the following criteria: a) loss of its initial performances; b) development of medical techniques requiring a wider spectrum of performances; c) presence of new devices with improved securities.

[Anesthetic equipment: fresh gas delivery systems. II. Electronic systems]. / Appareil d'anesthésie: systèmes d'alimentation en gaz frais. II. Systèmes électroniques.

OBJECTIVES: To analyse the design, functioning, benefits and drawbacks of electronic fresh gas delivery units (FGDUs) included in anaesthetic machines marketed in France in 1999. DATA SOURCES: Articles were obtained from a Medline review (1980-1999; search terms: anaesthetic machine, flowmeter, vaporizer), textbooks and personal files; specific data were also provided by manufacturers. STUDY SELECTION AND DATA EXTRACTION: The articles were analysed in considering the differences between mechanical and electronic FGDUs. DATA SYNTHESIS: Four anaesthetic machines out of 11 are equipped with electronic FGDUs. In comparison to mechanical units, they include the following benefits: wide range of accurate gas flow, especially in the low flow range, with analog and digital display; intermittent delivery of each gas, which is essential for automated gas delivery and quantitative anaesthesia or target controlled (FET vapor) inhalational anaesthesia; facilitated oxygen ratio control; possibility to print the gas and vapor flows on the automated anaesthetic record; interruption of gas flow when the main switch of the machine is set to off; and absence of risk for retropollution. Three FGDUs out of four are adapted for gas delivery to an accessory (ancillary) anaesthetic circuit. However, only one of them delivers a gas flow up to 30 L.min-1. The specificity of the ADU AS/3 (Datex-Ohmeda) is the bypass vaporizer included in the FGDU with an exchangeable vaporizing chamber (cassette). The specificity of the Julian (Dräger) is the delivery of fresh gas limited to the expiratory phase during mechanical ventilation. The specificity of the the FGDU from Kion (Siemens) is the possibility to act as an open circuit ventilator, similar to a Servoventilator. The specificity of the PhysioFlex is an FGDU included in the circle circuit, each gas and liquid anaesthetic being directly injected into the circuit. Data from the French medical device surveillance commission indicate that the main failures occur in the power supply device and the microprocessor.

[Anesthesia equipment: fresh gas delivery systems. I. Mecanical systems with rotameters and calibrated vaporizers]. / Appareil d'anesthésie: systèmes d'alimentation en gaz frais. I. Systèmes mécaniques avec rotamètres et vaporisateurs calibrés.

OBJECTIVES: To analyse the design, performance, failures, the checking before use of mechanical fresh gas delivery units (FGDUs) equipped with bobbin or ball-flowmeters delivering a continuous gas flow and calibrated vaporizers, marketed in France in 1999. DATA SOURCES: Articles were obtained from a Medline review (1960-1999; search terms: anaesthetic machine, flowmeter, vaporizer), textbooks and personal files; specific data were provided by manufacturers. STUDY SELECTION AND DATA EXTRACTION: The articles were considered for performance data, benefits and drawbacks, and characteristics, as well as the risks carried by mechanical FGDUs. DATA SYNTHESIS: Seven anaesthetic machines out of 11 are equipped with mechanical FGDUs, including rotameters delivering a gas mixture up to 30 L.min-1, calibrated vaporizers and an O2-flush valve delivering at least 500 mL O2 per second (30 L.min-1). These units allow closed circuit anaesthesia. They carry a risk for barotrauma as three out of them can deliver at the gas outlet of the FGDUs a gas mixture at a pressure reaching 3.5 bars and four others at a pressure of 150-200 mmHg. They also carry a risk for hypoxia, either from a preferential leak of oxygen at the corresponding rotameter or the O2-flush valve, or from a leak of fresh gas mixture either in a vaporizer or the selectatec manifold. The vaporizers carry a risk for vapor delivery at a concentration differing notably from the value set on the concentration dial. Therefore their accuracy must be checked periodically and the FGDUs checked for a leak after the addition to or the removal of a vaporizer from the selectatec manifold. The optimal technique for leak detection is the negative pressure test.

[Defective gas mixers, a cause of retro-pollution of medical gas distribution pipelines]. / Mélangeurs de gaz défectueux, cause de rétropollution du circuit de distribution des gaz médicaux.

A defective Air/O2 mixer of a ventilator located downstream of the gas outlets of two pipelines is a potential cause of retropollution. Retropollution of O2 with Air or vice versa carries a risk of either a) a hypoxic gas mixture delivery during anaesthesia, including O2-N2O administration, when the O2 pipeline supplies Air instead of O2, or b) a hyperoxic gas mixture delivery in the intensive therapy unit for neonates during administration of a O2-Air mixture, when the Air pipeline supplies O2 instead of Air. A defective O2/N2O flowmeter-mixer of an anaesthesia machine, with N2O flow control by O2 through a differential pressure manometer, can cause retropollution of O2 supply pipeline with N2O or vice versa. The prerequisite for retropollution is the association of three events: build-up of a pressure difference between the two gas lines; defective or absent back-flow check value in the circuit of the gas at a lower pressure; one of the following defects: a) the pressure equilibrating valves of the mixer cannot amend the pressure difference and allow a gas reflow at the gas mixture outlet; b) leak in the diaphragm of a pressure equilibrating valve; c) defective bypass supply valve. The optimal means for the recognition of a pipeline contamination by another gas is the O2 analyzer, especially in anaesthetic areas where the presence of N2O and Air carries the risk of a hypoxic gas mixture delivery. The mixer or flowmeter-mixer responsible for retropollution can be recognized in plunging successively the various quick couplers underwater into a glass, while the others remain connected to their outlets and the mixer set at a O2 concentration of 50 vol% or the flowmeters set at a similar flow. In case of retropollution, the gas reflow produces bubbles. It is recommended: a) in anaesthetic areas to set the O2 pressure at about 0.2 bar above that of Air and the latter at a pressure of about 0.2 bar above that of N2O; b) in intensive therapy units for neonates, to set the Air pressure at about 0.2 bar above that of O2; c) in all areas to disconnect from the gas outlets the devices equipped with a mixer or a flowmeter-mixer when not in use.

[Wrong connection of a flexible medical air hose to a nitrous oxide outlet caused by a defective safety device]. / Erreur de branchement d'un flexible d'air médical sur une prise de protoxyde d'azote par défaillance du système détrompeur.

When plugging the O2, N2O and air hoses into the corresponding wall sockets, the air hose was wrongly inserted into the N2O wall outlet. This was made possible because of faulty retaining clasps of the male coupler of the air probe. French "fail-safe" connections consist of a two-clasp male coupler for air, three clasps for O2 and four clasps for N2O hoses. Additionally the clasps of the air probe are broader then those of the N2O probe. However, the latter difference was lost due to wear. The incident was recognized without delay as the N2O hose could not be inserted into the air outlet. However, it could have remained unnoticed had there been two N2O wall outlets and could have resulted in severe adverse effects.

[Ventilators for anesthesia. Models available in France. Criteria for choice]. / Appareils d'anesthésie. Modèles disponibles en France. Critères de choix.

This update article discusses the criteria for the choice of an anaesthetic machine and provides a short analysis of the main components of the models commercialized in France in 1994. The following items are considered: the design of the machine, the fresh gas delivery system, the anaesthesia breathing system(s), the ventilator and the waste gas scavenging system, the monitors associated with the machine and other criteria such as facility of learning to run the machine and of its daily use, ease of "in-house" maintenance and quality of after-sales service, cost of the machine and of its use (driving gas, disposable equipment).

[Arguments for the addition of an oxygen reserve container to the anesthetic equipment]. / Arguments en faveur de l'équipement de l'appareil d'anesthésie d'une bouteille d'oxygène de secours.

In France, the presence of an emergency oxygen cylinder as part of every the anaesthetic machine is not made compulsory by an official regulation. This article provides arguments in favour of such a presence, as recommended by the French Society of Anaesthesia and Intensive care (SFAR).

[Pollution and retro-pollution by the distribution system of medical gases]. / Pollution et rétropollution du réseau de distribution d'un gaz médical.

The anaesthetic machine, the recovery room or the ICU ventilator as well as any other simple oxygenation device can be accidentally supplied with a "wrong" gas, or a mixture of "wrong" and "true" gases, or a gas containing chemical impurities, as a result of one of the following causes: a) the source of the medical gas pipeline supply contains a "wrong" gas or impurities; b) the gas pipeline is polluted by a "wrong" gas or solvents, introduced during the installation or maintenance of the pipeline; c) the pipeline is polluted by a wrong gas at a point of inter-connection or cross-connection of two pipelines; d) supply of a "wrong" gas through wrong quick couplers connected to the pipeline; e) back flow of a gas in another pipeline supply through a defective gas mixer, which is today the most common cause of pipeline contamination or retropollution. It occurs with some types of mixers in case of absence or malfunction of non-return valves, associated with a pressure difference between the two gas lines. The means of prevention, recognition and emergency treatment of these events include: a) systematic removal of mixers and flowmeter-mixers from supplies when not in use; b) periodical checking of these devices for an accidental communication between the gases to be mixed; c) systematic use of an oxygen analyser for a continuous measurement of FIO2, especially when the machine is connected to the N2O pipeline supply; d) the presence of a reserve cylinder of oxygen connected to every anaesthetic machine.