Flow Requirements in the Hafnia Modifications of the Mapleson Circuits during Spontaneous Respiration

Abstract

The Mapleson A, B, C and D circuits can be changed into non-polluting circuits by employing continuous gas evacuation directly from the circuit, via an ejector flowmeter (Jørgensen 1974); Mapleson A and C circuits with this modification have been described previously as the Hafnia A and C circuits (Christensen 1976, Thomsen & Jørgensen 1976). If evacuation from a closed reservoir is employed, total removal of the expired and surplus gases from the operating theatre is obtained (Jørgensen & Thomsen 1976). There will be resistance to expiration in all the circuits with a relief valve for the discharge of surplus gas. If surplus gas is continuously removed directly from the anaesthetic circuit, the patient breathes in an air compartment at ambient pressure, as long as the removal rate equals the inflow of fresh gas. The relief valve is only included in the circuit to ensure that high pressures do not develop. As in any other circuit, the relief valve remains open except during controlled ventilation. A dumping valve may also be included as a safeguard against low pressures (Jørgensen & Thomsen 1976). The flow requirements of the Hafnia B and D circuits and the corresponding Mapleson circuits have been studied in conscious, spontaneously breathing subjects, and the results are discussed in relation to the flow requirements of other semi-closed system.

Efficacy of the Ejector Flow‐meter. A Scavenging Device for Anaesthetic Gases

“…The positive pressure relief valve is a Heidbrink valve. Fresh gas requirements for the Hafnia D system are the same as for the Mapleson D system (7,8,9). Fresh gas flows of 75-125 ml kg-' min-' were used, while a flow of 3.5 I min-I or more was used for children.…”

Paediatric anaesthetic breathing systems

“…It is not commercially available. Miller & Cooper 1983) d. The Hafria system (Christensen et al 1978;…”

Editorial I: Fifty years after—reflections on ‘The elimination of rebreathing in various semi-closed anaesthetic systems’

“…Miller's 'preferential flow' system 18 is a somewhat similar, but more sophisticated, modification of System A. To avoid pollution of the theatre atmosphere, Danish anaesthetists invented a complete set of modified Systems A-D: the 'Hafnia' systems 19 -Hafnia was the Roman name for Copenhagen. In each of these systems, the spill valve was replaced by a steady flow of suction which had to be matched to the fresh-gas flow.…”