StandardsEconomical
The Humphrey ADE-circle system - a remarkable achievement in cost-effectiveness.
What is required for anaesthesia is enough; any more than that is wasted and expensive. This section looks at the economies to be gained by using the Humphrey ADE-circle system since in every mode of use the system uses the anaesthetic gas with maximum efficiency. Some research results were originally controversial but all observations have now been independently verified by well-known academic institutions such as the Royal Postgraduate Medical School, Hammersmith London and the Hospital for Sick Children, Great Ormond Street, London.
The Humphrey ADE system reduces running costs of inhalational anaesthesia
The most expensive part of the anaesthetic is the vapour, with nitrous oxide next, followed by oxygen. Costs can vary greatly in different environments since in developing countries everything including oxygen can be expensive.
Three main factors determine actual costs;
- patient age and weight
- the anaesthetic breathing system used
- the mode of ventilation
When gases are not recycled, the general principle is that the heavier the patient the more fresh gas is required. Younger patients require a greater flow per kilogram body weight than older patients. Once flows exceed 3-4 l/min the only fresh gas saving principle is to re-cycle gases through a soda lime canister, in which case a FGF of 1 litre/min is safe and economical provided adequate monitoring is available and the mixture contains 50% oxygen. The Humphrey ADE offers both techniques and always functions with the lowest flow necessary. (For more details see the section The ADE as a semi-closed system and The ADE as a circle system).
In summary the Humphrey ADE system without the circle requires an average fresh gas flow (FGF) of only 3-4litres/min for adults, 2-3 litres/min for children; with the absorber flows can be reduced to as low as the anaesthetist feels comfortable but 1 litre/min is generally a safe flow. No other system offers these combined benefits.
Cost savings with other systems compared.
The HUMPHREY ADE as a semi-closed system: Without re-cycling, the general efficiency of other anaesthetic systems varies from about 70% to as little as 25%; in other words some function on three times less fresh gas than others and yet achieve the same effect. In all modes of use the Humphrey ADE system uses the lowest fresh gas flow. The Humphrey ADE system has already proved itself worldwide where it has been used in an estimated 10 million anaesthetics by 1999. In this mode of use, the Humphrey ADE is simple to use and is safe because it provides a gas mixture with known inspired gas and vapour tensions which are as set on the anaesthetic machine. This reduces the need for monitors or user expertize as are required for the re-cycling technique. (For more detail see ADE as a semi-closed system).
Low fresh gas flows are required at all times such that, for the first half hour of anaesthesia, there is little to gain financially from re-cycling except with the very insoluble vapours such as sevoflurane and desflurane (see Figs 4a, 4b). Because of the efficiency within the system itself, the average fresh gas flow with the HUMPHREY ADE system is only 3-4 l/min for adults and 2-3 l/min for children, significantly lower than 6-8 l/min used for other systems such as the Bain, Magill and T-piece. Based on costs in the UK in pounds sterling, up to £16/hour can be saved with sevoflurane, saving many thousands of pounds per year. For longer operations significant savings can be made with other vapours. Fig 4a and 4b
Local cost savings in other countries can be calculated as a ratio of the costs shown in the bottom right corner in Figs 4a and 4b.
The HUMPHREY ADE-CIRCLE as a circle system: In this mode the soda lime canister is attached such that it is possible to re-cycle anaesthetic gases. For longer operations further significant savings can be achieved compared with the semi-closed mode, especially with flows reduced to 1 l/min (Fig 4a, 4b). At these low flows, the cost expensive vapours such as sevoflurane, desflurane and isoflurane are reduced to levels that are even more easily afforded. (For more detail see ADE as a circle system).
Because the ADE canister has innovative design features and has a small volume, it offers significant economic advantages over larger "jumbo" canisters.
- Lower fresh gas flow for induction and nitrogen wash-out can be used; 4 l/min (compared to 6-8 l/min for jumbo canisters) is recommended.
- Maximum efficient use of soda lime, waste gases being eliminated on the expiratory side. The anaesthetist thus has a choice of technique as a semi-closed system without the soda lime canister or as a circle system with the canister.
The Anaesthetist's Choice
Humphrey ADE system (without absorption)
- halothane
- enflurane
- isoflurane - short cases
- paediatrics (sevoflurane)
- FGF 2-3 l/min adults
- monitors useful
Humphrey ADE-circle system
- sevoflurane
- desflurane
- isoflurane - larger cases
- FGF 500ml - 2 l/min (after high induction flow of 4 l/min)
- accurate low flow equipment
- monitors essential