by Sean » Mon May 08, 2006 9:18 am
something i got of another forum:
"Human studies report that CO2 inhalation is adversive, with a linear relationship between concentration and distress and/or pain sensation - this has raised concern as to the humaneness of the use of CO2 for animals"
The gas molecule essentially diffuses in to the blood, body and brain from the lungs. Faced with excessive levels of the gas, the inherent capacity of the blood to buffer for CO2 is overwhelmed and results in acidosis (the lowering of the pH of the blood and associated fluids). Low to moderate concentrations of CO2 cause mild respiratory acidosis leading to a compensatory increase in depth and rate of respiration in an effort to 'blow off' the excess CO2 (hyperventilation), changes in heart rate and blood pressure. Higher concentrations then lead to more profound respiratory acidosis, suppressing the respiratory centres of the brain, leading to a slow, gasping respiratory pattern. :-(
Without the buffering capacity of blood, the pH of the cerebrospinal fluid drops precipitously which is directly related to anaesthetic depth and subsequent insensibility to pain, stupor & finally unconsciousness & death.
Of welfare interest however - and THIS is the question - is the duration and effect PRIOR to insensibility and unconsciousness. Some literature show indications of a state similar to conscious drowning!
Observations that may be consistant with pain or distress have been reported with the use of CO2 and include: increased locomotion, excitation, serious agitation, increased rearing, defecation and urination, irritation of mucosal membranes, hyperventilation, gasping, heads turned upwards and backwards, etc. These signs generally increase in frequency and intensity with the increase in concentration of CO2 from 25 - 100% until aneasthesia is induced.
Other literature that I've read actually say that CO2 is the LEAST preferred inhalation agent when compared to halothane, isoflurane, argon, etc.
Recommendations that I've come across for anaesthesia are halothane for rats, and enflurane for mice, because at the appropriate concentrations they induce a rapid and effective induction with the minimum distress. but now I ask you, where does Joe Schmoe who's 10 years old, get his hands on halothane which is a very volatile liquid? Then, once unconsciousness has been induced, CO2 can be used as a killing agent as the animal is then already unconscious.
personally think the only "humane" way to kill a rodent is hitting its head against a wall with enuf force to kill it 1st time
billygoats taste of chicken