A technique to depress desflurane vapor pressure.
OBJECTIVE
To determine whether the vapor pressure of desflurane could be decreased by using a solvent to reduce the anesthetic molar fraction in a solution (Raoult's Law). We hypothesized that such an anesthetic mixture could produce anesthesia using a nonprecision vaporizer instead of an agent-specific, electronically controlled, temperature and pressure compensated vaporizer currently required for desflurane administration.


METHODS
One healthy adult female dog.


RESULTS
Propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in-circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved an 11.5% +/- 1.0% circuit desflurane concentration with a 5.2 +/- 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L minute(-1). Anesthesia was maintained for over 2 hours at a mean vaporizer setting of 6.2 +/- 0.4, yielding mean inspired and end-tidal desflurane concentrations of 8.7% +/- 0.5% and 7.9% +/- 0.7%, respectively.


CONCLUSIONS
Rather than alter physical properties of vaporizers to suit a particular anesthetic agent, this study demonstrates that it is also possible to alter physical properties of anesthetic agents to suit a particular vaporizer. However, propylene glycol may not prove an ideal solvent for desflurane because of its instability in solution and substantial-positive deviation from Raoult's Law.
Brosnan
Robert J
RJ
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. rjbrosnan@ucdavis.edu
Pypendop
Bruno H
BH
D000769:Anesthesia, Inhalation / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000737:chemistry*; D000818:Animals; D000077335:Desflurane; D004285:Dogs; D005260:Female; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D009330:Nebulizers and Vaporizers / Q000662:veterinary*; D019946:Propylene Glycol / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D044366:Transition Temperature; D014835:Volatilization
D018685:Anesthetics, Inhalation; D012997:Solvents; D019946:Propylene Glycol; D000077335:Desflurane; D007530:Isoflurane