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Old September 24th, 2009, 11:03 PM
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Dr Lee Dr Lee is offline
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This is a great question - how safe is multiple anesthetic procedures within a short period of time?

My answer is this - it comes down to the anesthetist.

I would rather undergo ten episodes of anesthesia with a great anesthetist than one with a bad one. Heck, lets make it twenty!

Many of the anesthetic compounds are gone and out of the system in a very short period of time despite the fact that the recovery takes longer. Human studies have shown that 30 minutes after extubation (breathing tube taken out) about 90% of isoflurane has been breathed out. Propofol's "elimination half-life is about 1.4 hours and [its] clearance is about 50 ml/kg/min." (Plumb's Veterinary Drug Handbook Fifth Edition) That is also pretty quick. So it not that anesthetics build up in the body.

So what is the negative long lasting or 'summative' effects of anesthesia?

1) There is always a potential for a catastrophic idiosyncratic reaction to the anesthesia involving cardiac arrest. These are extremely rare though.

2) There is a potential that the pet is sensitive to a type of anesthesia - this has been ruled out if the pet has been anesthetized before with the same medications.

3) The patient's blood pressure drops and is not adequately addressed. This is probably the one I worry about most in our field. All anesthetics can drop blood pressure. It can frequently drop low enough to cause very small minute damage to the kidneys and other organs or even not so small damage. There was an anesthetic lecture that talked about a dog study with dogs being under for 45min at an anesthetic depth equivalent to a spay that lead to some animals having as much as 5% kidney loss. These blood pressure drops can occur without any obvious change in the patient's vitals other than blood pressure. I believe that blood pressure monitoring and having an intravenous catheter with fluids is important.

4) Stress. Yes going to the vet and having an anesthetic procedure is stressful. Some animals handle it well and others do not. (I am a wimp and handle any minor visit to the dentist with a great deal of stress - others are braver than I). Does this lower the immune system? Possibly, to some degree. Less stress is always better but anesthesia is not done without a good reason - one that should out weight the stress (and this can be different for each patient).

5) Other problems associated with lack of attention and care: pressure sores, heating pads/bottle burns, IV drugs leaking into the subcutaneous space, too great an anesthetic level, clogged airway, ET tube too far in or not far enough in, too much or too little fluids, mild or moderate asphyxia, tracheal pressure from incorrect tube size, etc....

6) Other underlying diseases such as heart disease may be affected by the stress of the anesthesia.

So if problems (1) and (2) don't occur that day - then there is no long term effect here, period. Problems (3) and (4) are harder to quantify. Until over 50% of the kidney's have been damaged, you cannot see it on the blood work (the study unfortunately had each of the beagles euthanized and their kidneys microscopically evaluated - that was the only way to get the numbers accurately). So problem for problem (3) we really must rely on a good veterinarian, with a good blood pressure monitor and an IV catheter with fluids going. Problem (4) relies on a friendly staff as well as the personality of the patient (no matter how nice the dentist is, I always cringe). while problem (5) may show up immediately or may show up later - with a careful anesthetist and supportive team, these should not occur. Problem (6) should be handled with careful pre-anesthetic evaluation of the patient. Sometimes it is impossible to know until after the procedure - this is one problem that multiple session of anesthesia likely have a summative damage versus a single anesthesia.



So bottom line, if you pet medically needs to be sedated/anesthetized repeatedly in a short period of time, then as long as you have a good veterinarian with a good support staff (this is as important as a good veterinarian) your pet should be fine. Can there always be a horrible unexpected and unpredicable crisis? Yes, but less likely with a pet that we know can handle anesthesia and less likely with a good vet who has a good team.

Why do I mix sedation and anesthesia terms? Because they are basically the same. In fact injectable sedation is often more risky than anesthesia. With anesthesia we have an ET tube in place that we can breathe for the pet and give oxygen, we have several monitor systems in place, we have intravenous fluids in place, etc.... Furthermore with gas anesthesia, if we have a problem we can turn off the amount of anesthetic going into the patient. With an injectable sedative, the amount of anesthetic has already been given in a single dose.

Good luck and I hope this helps.
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Christopher A. Lee, DVM, MPH, Diplomate ACVPM
Preventive Medicine Specialist With a Focus on Immunology and Infectious Disease
myvetzone.com
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