title: Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow.
abstract: 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.
authors: Institute of Anaesthesiology, University Hospital Zurich, Zurich, Switzerland.
authors: P
authors: P
authors: Biro
mesh_terms: D000465:Algorithms; D000769:Anesthesia, Inhalation / Q000191:economics; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000737:chemistry / Q000191:economics; D000077335:Desflurane; D016527:Drug Costs; D004363:Drug Utilization / Q000191:economics; D006221:Halothane / Q000008:administration & dosage / Q000737:chemistry / Q000191:economics; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000737:chemistry / Q000191:economics; D008499:Medical Records; D008738:Methyl Ethers / Q000008:administration & dosage / Q000737:chemistry / Q000191:economics; D009330:Nebulizers and Vaporizers; D009994:Osmolar Concentration; D012189:Retrospective Studies; D012212:Rheology; D000077149:Sevoflurane; D013696:Temperature; D014835:Volatilization; D014894:Weights and Measures
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane; D006221:Halothane