Death may also be caused using carbon dioxide once unconsciousness has been achieved by inhaled anaesthetic.[6] Carbon dioxide is often used on its own for euthanasia of wild animals.[7] There are mixed opinions on whether it causes distress when used on its own, with human experiments lending support to the evidence that it can cause distress and equivocal results in non-humans.[8] In 2013, the American Veterinary Medical Association (AVMA) issued new guidelines for carbon dioxide induction, stating that a flow rate of 10% to 30% volume/min is optimal for the humane euthanization of small rodents.[9]