Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow.

BACKGROUND: The assessment of volatile agents' consumption can be performed by weighing vapourisers before and after use. This method is technically demanding and unavailable for retrospective analysis of anaesthesia records. Therefore, a method based on calculations from fresh gas flow and agent concentration is presented here. METHODS: The presented calculation method herein enables a precise estimation of volatile agent consumption when average fresh gas flows and volatile agent concentrations are known. A pre-condition for these calculations is the knowledge of the vapour amount deriving from 1 ml fluid volatile agent. The necessary formulas for these calculations and an example for a sevoflurane anaesthesia are presented. RESULTS: The amount of volatile agent vapour deriving from 1 ml of fluid agent are for halothane 229 ml, isoflurane 195 ml, sevoflurane 184 m, and desflurane 210 ml. The constant for sevoflurane is used in a fictitious clinical case to exemplify the calculation of its consumption in daily routine resulting in a total expenditure of 23.6 ml liquid agent. CONCLUSIONS: By application of the presented specific volatile agent constants and equations, it becomes easy to calculate volatile agent consumption if the fresh gas flows and the resulting inhaled concentration of the volatile agent are known. By this method, it is possible to extract data about volatile agent consumption both ways: (1) retrospectively from sufficiently detailed and accurate anaesthesia recordings, as well as (2) by application of this method in a prospective setting. Therefore, this method is a valuable contribution to perform pharmacoeconomical surveys.

Halothane: how should it be used in a developing country?

The anaesthetic agent halothane is still widely used in developing countries including the Islamic Republic of Iran because of its low price. Because of halothane-induced hepatitis, a rare complication, it has been replaced by other inhalation anaesthetics in Western countries; it has been suggested by some Iranian professionals that the Islamic Republic of Iran should do the same. We evaluated various dimensions of this replacement through a literature review to assess the incidence of halothane-induced hepatitis and costs of anaesthetics in the country. We also conducted a questionnaire survey of 30 anaesthesiology/gastroenterology experts about their views on the subject. The results indicate that the incidence of halothane hepatitis in the Islamic Republic of Iran is very low and could mostly be avoided by strict adherence to guidelines. Complete withdrawal of halothane in the Islamic Republic of Iran might not be appropriate at present. Comprehensive cost-effectiveness studies are needed before a decision is made on complete replacement of halothane with other anaesthetics.

Prevalence of low flow anesthesia and its cost comparison with other anesthesia techniques in an Indian tertiary care center.

BACKGROUND: The usage of high fresh gas flows with expensive volatile agents is known to cause substantial economic losses. Practicing low flow anesthesia can minimize these costs. The average costs of different anesthetic techniques, used for maintenance of general anesthesia and the frequency of use of low flows were evaluated. METHODS: We noted the consumption of anesthetic gases and volatile agents during routine surgeries in our institute for two weeks (10 consecutive full working days). According to the anesthetic agent and fresh gas flow used, all general anesthetics were divided into four groups i.e. low flow (gas flows < or = 1 L/min) and high flow anesthesia (gas flows > 1 L/min) with isoflurane, halothane anesthesia (gas flows > 1 L/min) and propofol intravenous anesthesia (gas flows > 1 L/min). We calculated the individual cost of maintenance of anesthesia on per hour basis for each group based on average flows and anesthetic concentrations used. RESULTS: Low flow anesthesia is sparingly used in our institution (4.1%). Halothane with fresh gas flow > 1 L/min is the most commonly used anesthetic technique (45.9%). Propofol anesthesia was nearly equal to low flow isoflurane anesthesia in terms of costs. Using higher fresh gas flows with isoflurane increases this cost by three times. CONCLUSIONS: Low flow anesthesia is still sparingly used. Low flow isoflurane anesthesia is equivalent in terms of costs to propofol anesthesia though more expensive than conventional anesthesia with halothane.