The Cost of Anesthetic (Anaesthetic) Gases

In South Africa, controversy has arisen over the cost of anesthetic gases charged by private hospitals.

According to the Board of Healthcare Funders (BHF), which represents medical schemes (insurers), hospitals are overcharging for anesthetic gases because they charge by the minute rather than for each milliliter of anesthetic agent consumed.

For those unfamiliar with the intricacies of anesthetic pharmacology I will attempt to explain the problem, without delving into the political aspects of this issue.

Volatile anesthetic agents (isoflurane, halothane, sevoflurane) are liquids at room temperature which get turned into gases by vaporizer devices. The quantity of volatile agent utilised during an anesthetic depends on the vaporizer setting and on the fresh gas flow passing through the vaporizer. The fresh gas flow, also called the “carrier gas” is made up of oxygen mixed with either air, or nitrous oxide.

The cost associated with the use of volatile anesthetic agents therefore is:

cost of volatile agent + cost of carrier gas

The cost (in Rands) of the volatile anesthetic agent is given by this rather complicated formula:

[anesthetic vaporizer concentration (%) x fresh gas flow (liters per minute) x duration of anesthesia (minutes) x molecular weight of anesthetic (g) x cost (R per mL)] / 2,412 x density (g per mL)

An anesthesiologist can deliver essentially the same anesthetic ignoring cost (high fresh gas flow) or conserving it (low fresh gas flow). (There are some caveats. For example, fresh gas flows generally need to be increased at the beginning and end phases of an anesthetic, and reliable oxygen monitoring systems must be in place).

Fresh gas flow can be safely reduced to 1-2 liters per minute, or even less, or can be set higher; 3-6 liters per minute would not be unusual.
The cost varies in a linear fashion with the gas flow.

Sevoflurane, commonly used in private hospitals in South Africa, is rather expensive, but I don’t know the actual cost paid by hospitals. In my hospital in Cleveland, Ohio, the cost about a year ago was roughly US$170 for a 250 ml bottle. Isoflurane is very much less expensive.

Charging per minute therefore does not reflect the actual consumption of anesthetic agent unless one takes into account the fresh gas flow averaged out over the duration of the case, as well as the average setting on the vaporizer. This information is not easy to obtain accurately without the aid of automated anesthesia record-keeping systems which are not commonly in use today.

Note to S African readers: anesthesiologist=anaesthetist; anesthetic=anaesthetic; vaporizer=vaporiser


4 Responses to The Cost of Anesthetic (Anaesthetic) Gases

  1. Mike Sparks says:

    I am a South African reader of your mail re the use of Anaethetics and the charge made to the patient. Anaethetics are clasified as sheduled medicines in RSA and the prices of scheduled medicines are strictly controlled. It would seem that due to their properties volatile agents are difficult to quantify and apply the strict formulae that apply to tablets, capsules and liquids etc, in price calculations, so there is room for exploitation, and overcharging. How many patients on average would one 250ml bottle of Sevoflurane service? Or put another way, how many minutes on average would it last? I do realise that these are difficult questions to answer, but approximations would help.

  2. surgiprep says:

    A spreadsheet that calculates volatile anesthetic costs is available at It uses the formula of Dion which was published some years ago in the Canadian Journal of Anaesthesia.
    Based on this spreadsheet, assuming the underlying formulas to be correct, a 60 minute anesthetic, using an average fresh gas flow rate of 2 liters per minute, at a dialed concentration of 2%, with a sevoflurane cost of $172 for 250 ml, would consume $9.01 of sevoflurane. That’s about 13 ml of liquid sevoflurane.

    If the flow rate is doubled (4l/minute), the cost would be doubled.

    If you have access to the South African pricing of this anesthetic agent would you please follow-up with the corresponding local costs?

  3. surgiprep says:

    Assuming a cost of R1800 for 250 ml of sevoflurane, which apparently is a local benchmark, the anesthetic referred to above, at a 2 l/min average fresh gas flow, would cost roughly R94.00, at R7.20 per ml of liquid sevoflurane.

  4. Belinda says:

    Nice work. Wish more would read it. We see lots of responses to the debate which is based on not understanding teh real issue.

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