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Delayed induction time

In Induction of anaesthesia with halothane and isoflurane in the rabbit: a comparison of the use of a face-mask or an anesthetic chamber the authors look at the effects of anesthetic induction of rabbits using a face-mask and an induction chamber.  They recognized using a face-mask often results in struggling and observed using a face-mask seems stressful.  To avoid using short-acting injectables prior to inducing with a face-mask, they became interested in using an induction chamber, inducing anesthesia with a volatile agent alone.  They were unable to find detailed evaluations of this method and therefore designed a study to investigate the short-term effects of induction of anesthesia with halothane and isoflurane; comparing induction using either a face-mask or an anesthetic chamber.

They looked at anesthetic chamber characteristics and measured anesthetic gas concentrations at 3 different levels of the chamber.  They found the highest levels of anesthesia at the lowest level of the chamber (5cm) reached 3% anesthetic gas within 2 minutes.  The middle of the chamber (15cm) reached 3% within 4 minutes.  The highest part of the chamber (25cm) didn't reach 3% for up to 6 minutes when filling with isoflurane and up to 8 minutes with halothane.  

Noted in the discussion; the stratification of vapor often resulted in rabbits inhaling very high concentrations of anesthetic gas, rather than being exposed to a gradually rising concentration of the agent.  

The Induction Chamber Evacuation System addresses this problem by adding a baffle to the lid of our induction chamber.  The baffle directs the flow of incoming gas to all four sides of the chamber at same time.  Anesthetic gas fills the chamber uniformly and efficiently  This results in a faster and less stressful induction period.