Anaesthetic machine: fresh gas delivery units. I. Mechanical units with rotameter block and calibrated vaporizers

Objectives: To analyse the design, performance, failures, the checking befo re use of mechanical fresh gas delivery units (FGDUs) equipped with bobbin or ball-flowmeters delivering a continuous gas flow and calibrated vaporize rs, marketed in France in 1999. Data sources: Articles were obtained from a Medline(R) review (1960-1999; s earch terms: anaesthetic machine, flowmeter, vaporizer), textbooks and pers onal files; specific data were provided by manufacturers. Study selection and data extraction: The articles were considered for perfo rmance data, benefits and drawbacks, and characteristics, as well as the ri sks carried by mechanical FGDUs. Data synthesis: Seven anaesthetic machines out of 11 are equipped with mech anical FGDUs, including rotameters delivering a gas mixture up to 30 L.min( -1), calibrated vaporizers and an O-2-flush valve delivering at least 500 m L O-2 per second (30 L.min(-1)). These units allow closed circuit anaesthes is. They carry a risk for barotrauma as three out of them can deliver at th e 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 hypo xia, either from a preferential leak of oxygen at the corresponding rotamet er or the O-2-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 co ncentration dial. Therefore their accurracy must be checked periodically an d the FGDUs checked for a leak after the addition to or the removal of a va porizer from the selectatec manifold. The optimal technique for leak detect ion is the negative pressure test. (C) 1999 Editions scientifiques et medic ales Elsevier SAS.