Hmmmmm.... forget the masking down idea. I just found this article.
"Masking Down" a Safer Way to Anesthetize? Guess Again
It's no secret that most pet owners fear having their pets anesthetized for any reason, from a simple dental cleaning to life-saving surgery. And it would make perfect sense that we might think that the fewer drugs, the better in any anesthesia procedure. More drugs would mean more risk. It seems logical.
However logical it might seem, however, it's not true, and owners who refuse to use multi-drug anesthesia protocols, or veterinarians who opt not to use them, are doing a grave and potentially life-threatening disservice to those animals.
I'm referring here to the practice known as "masking down" or "gassing down" a pet, where the anesthesia gas, usually isoflurane, is given via face mask to get the cat or dog anesthetized enough to be intubated and then given a maintenance dose of the gas. This procedure was once believed to be easier on the pet, especially older or medically fragile pets, but nothing could be further from the truth.
There are a number of risks associated with "masking down" a pet, all of which are substantially reduced if a protocol of injectable induction agents is used instead.
First, you have to use a LOT higher dose to induce with gas than to maintain anesthesia, which increases the risk. We think we are using "less drug" this way, but we end up using a LOT more.
Second, the gas anesthetics are very potent vasodilators (they dilate the blood vessels), which means that they can send blood pressure plummeting, more so with the high doses needed to induce with it. This is very dangerous for any dog or cat, but much more so for pets with kidney or heart problems - the very pets some veterinarians reserve this procedure for! You also get more severe cardiovascular depression, with its obvious risks.
Furthermore, when you gas induce, you have no control over stage 2 anesthesia, which is the stage of involuntary excitement. You HAVE TO go through stage 2 to get to full surgical anesthesia (stage 3), but with gas inductions it lasts much longer. Stage 2 anesthesia is accompanied by catechol release, which is very hard on the heart; this effect is dose dependent, so again, the increased dosage substantially increases the risk. Arrythmias in particular are more likely to occur, risky for all pets but especially for senior pets or those with heart disease.
When you use gas to "mask down" the animal instead of inducing with injectable drugs, you have no way to get rapid control of the airway during the procedure. This increases risk, once more. In fact, the delay in getting control of the airway could be the difference between the animal surviving an adverse reaction, and being killed by it.
From the vet/staff's points of view, gas inductions expose THEM to waste gases and are hazardous. Improper venting and disposal of waste gases is a huge workplace safety issue for veterinary staff and not something that should be taken lightly.
Please do not use a vet who wants to mask down your pet, nor try to convince your vet to do it instead of using injectable induction. It is outdated, it's unsafe, it's bad for the pet AND the vet staff, and it's bad medicine.
Want more information and evidence?
"Induction of Anesthesia" by Peter W. Hellyer, DVM, MS, Diplomate, American Academy of Veterinary Anesthesiologists, Colorado State University
"Paradoxically, mask or box induction is frequently reserved for sick and compromised animals, the group that is least likely to tolerate the high concentrations of inhalant anesthetic required to induce anesthesia. .... Mask or box induction should be reserved for animals that cannot be approached otherwise (e.g., vicious cat), or that no acceptable injectable technique is available (e.g., birds, pocket pets, etc.). Mask or box induction is frequently stressful for the animal as demonstrated by a wide variety of excitatory reactions. Premedicating the animal prior to induction of anesthesia helps to decrease or eliminate the excitatory phase. Induction of anesthesia with just an inhalant usually requires fairly high doses, particularly if the animal needs to be deep enough for endotracheal intubation or surgery. Those high doses of inhalant anesthesia are deleterious to the cardiopulmonary systems, resulting in marked hypotension and hypoventilation. If no additional anesthetic drugs are used, depth of anesthesia may change markedly in response to changes in surgical stimulation or decreasing vaporizer setting. Mask or box induction increases the amount of waste gas pollution that employees are exposed to and may increase environmental pollution to unacceptable levels."
Veterinary Anesthesia Support Group
"Induction Protocols"
http://www.vasg.org/s_thru_u.htm
"Mask inductions are not recommended for most patient groups
Cautionary information
(a) Increased patient stress
(i) Increased arrhythmic risk
(b) Unnecessary staff exposure to anesthetic agents
(c) Time required for complete induction of anesthesia is longer than compared to IV agents.
(d) Prolonged period of unsecured airway with an increased risk of airway
compromise or obstruction
(e) High concentrations of inhalant agents are required to achieve mask induction. Higher doses produce more cardiovascular and respiratory depression than seen with comparable doses of IV induction agents.
(i) During intubation removal of the mask results in cessation of drug administration of the drug and recovery from anesthesia begins as the drug is eliminated.
(ii) Once intubated higher concentrations of inhalant are required compared to use of IV induction drugs.
(f) Contraindicated in brachycephalic patients"