COMPARING THE COSTS OF INHALED ANESTHETICS

Background. The immediate cost of an inhaled anesthetic results from a n interplay between four factors: (1) the cost per milliliter of liqui d anesthetic, (2) the volume of vapor that results from each millilite r of liquid, (3) the effective potency of the anesthetic (what concent ration must be delivered from a vaporizer to provide a clinically appr opriate level of anesthesia), and (4) the background flow of gases tha t is chosen. A background flow that supplies only the gases/vapors req uired (taken up) by the patient (a ''closed circuit'') produces the le ast cost but also the least control of anesthetic level, whereas a hig h flow prevents rebreathing (a non-rebreathing system) but produces th e greatest cost and control. We define greater ''control'' as a smalle r ratio of delivered to alveolar concentrations. A lower solubility of an anesthetic accords the same level of control at a lower background flow rate than is achieved at a higher background flow rate with a mo re soluble anesthetic. Thus, a poorly soluble anesthetic may be used w ith a lower background flow rate than a more soluble anesthetic and ma y offer greater control and/or decreased cost. Methods. This report pr esents a method of determining the cost of inhaled anesthetic use. As an example, the cost of delivering a desflurane anesthetic is compared with that of delivering an isoflurane anesthetic, assuming both provi de an alveolar concentration of 1 MAC. The comparison is based on the pharmacokinetic differences of the two anesthetics: taking into accoun t that for a given therapeutic anesthetic concentration (MAC), for des flurane a lower flow rate of background gas is needed to produce simil ar control (relationship between delivered and alveolar gases) than is needed for isoflurane. Results. The analysis demonstrates that the re lative cost of administering the newer and less soluble anesthetic, de sflurane, can be less than, greater than, or the same as the cost of a dministering isoflurane, depending on the background gas inflow rate s elected. Conclusion: The manner in which inhaled anesthetics are used and their kinetic differences are important determinants of relative c ost.