[French survey on anesthesia systems and peroperative respiratory monitoring equipment]

[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.

[Pros or cons of accessory anesthetic circuits. I. Arguments for their use]

In addition to the circle breathing system, which represents the main circuit of the anaesthetic machine, the use of an accessory breathing system (ABS), either a partial rebreathing system according to Mapleson's classification, or a system including a non-rebreathing valve, is appropriate for the anaesthetic management of many patients, depending on their physical status, age, indication and duration of surgery. The same safety rules, namely full checking procedure before use of the system and monitoring of inhaled gases and end-tidal CO2 must be applied as for the main circle system. Potential complications resulting from non compliance with these rules cannot be considered valuable reasons for denying the use of breathing systems that have safely been used for decades in millions of patients.

[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.

[Hypoxia secondary to the failure of an oxygen-air-nitrous oxide mixer]

A case is reported of hypoxia occurring during anaesthesia in a spontaneously breathing ASA I patient. The patient became cyanotic twice when breathing a gas mixture delivered by a safety mixer. Changing the machine solved the immediate problem. The diagnosis was difficult to make because the rotameters all showed normal delivery of oxygen and nitrous oxide. Oximetry elucidated the cause, which was found to be a defective rapid oxygen control. Because these machines do not appear to be absolutely reliable, the use of gas analysers should become more systematic.