I received a very interesting email from Mother Stephanie about the above topic. If any members follow the Vettalk Yahoo group, you might be familiar with her.
I found this information fascinating and thought others from the group might as well.
From: Mother Stephania <srstephanie@...
To: Jordan <thegapgal@...
Sent: Tue, Aug 21, 2012 10:40 pm
Subject: Re: Question about Metacam
Sorry for the delay. I wanted to listen to a talk on "Anesthetic Management of Patients with Cardiovascular Disease" given this past April at the CVC (Central Veterinary Conference) in Washington DC by Dr Tammy Grubb of Washington State Univ (board certified Anesthesiologist). Dr Grubb has become a friend of mine and we have corresponded a bit and I met her last April when she was in Montreal. I'm really impressed with her expertise ... and she is a wonderful person and excellent teacher. She is also very supportive and encouraging of my desire to learn.
Dr Grubb believes VERY strongly that analgesia (pain medication) should be used for all patients, including those with heart disease. She commented that using analgesia (especially an opioid) can reduce the amount of inhalant anesthesia (e.g. isoflurane or sevoflurane) by 50% OR MORE. I think she made a reference to a study but I didn't get the details. I have the audio of her talk but not the slides that she used with it. I don't think that the analgesia makes the anesthesia more "potent". Rather, the presence of pain requires more anesthesia to keep the cat under. By reducing or preventing pain, it means that less anesthesia is needed to keep the cat unconscious. Dr Grubb also makes the point that pain, itself, has negative effects on the heart, e.g. causing a faster heart rate, which can increase the risk of heart failure. So, preventing or reducing pain is also beneficial as a means of reducing the stress on the heart.
Here are a couple quotes from the Proceedings for Dr Grubb's talk. First, remember that "anesthesia" is an "event" and has FOUR stages:
1) Preanesthesia - often with a sedative and analgesia to reduce stress (stress also causes higher doses of anesthesia to be needed),
2) Induction - process of inducing unconsciousness ... which needs to be done quickly with little stress (so never just "mask" a cat down with isoflurane or sevoflurane),
3) Maintenance - what most think of as "anesthesia" ... keeping them unconscious during the surgery, and
4) Recovery - actually the most critical time ... Dr Grubb said that in cats about 60% of surgery related deaths occur during the recovery time after surgery.
Here are a couple quotes from the Proceedings:
>From the section on Premedication (preanesthesia)
As previously stated, pain is a stressor that will cause an increase in heart rate with a subsequent increase in myocardial oxygen consumption. Thus, opioid-induced analgesia is an extremely valuable means of alleviating or eliminating pain-induced cardiac complications. Opioids should also be used during the maintenance phase to decrease the dosage of concurrently used maintenance drugs. Thus, ALL patients with cardiovascular disease should receive an opioid as a premedicant, even if the procedure for which the patient is being anesthetized isn‟t painful.
From the section on Maintenance
However, all inhalant anesthetic agents cause DOSE DEPENDENT myocardial depression. Regardless of which inhalant anesthetic is used, the concentration of the anesthetic must be maintained as low as possible in order to limit myocardial depression. The use of premedicants, including analgesic drugs, will greatly decrease the amount of inhalant anesthetic necessary for maintenance. In addition, the concurrent administration of a constant-rate infusion of an opioid (eg, morphine, hydromorphone or fentanyl) will allow the concentration of inhalant anesthetic to remain at a minimum.
She makes the point that the risk of anesthesia complications increases with higher dosages of anesthesia. Thus, by giving pain medication which reduces the amount of anesthesia needed ... it reduces the risk of complications.
I will attach the full written Proceedings from her talk on anesthesia for cardiovascular disease (it includes both dogs and cats ... but since HCM is common in cats and not common in dogs, references to HCM generally apply to cats). If you would like to listen to her talk, let me know. It is an mp3 audio file (about 11 Mb) and I can upload it to YouSendIt where you can download it. It is a bit technical since it is being given to vets and she tends to talk rather quickly. But I find it easier to learn from talks because the Speakers are more in "teaching" mode than in the "publication" mode that the written proceedings or studies are in.
However, having said all that ... your cat's cardiologist is much more familiar with the specifics of your cat. Also, I don't know what added complications the asthma causes. So, I wouldn't suggest you telling your vet to do anything differently than the protocol given by the cardiologist. But you might want to ask the cardiologist about the use of analgesics (especially opiods) if he hasn't included them in the anesthesia protocol.
I was thinking about writing to Dr Grubb, just to continue our short chat that we had tonight. If I do write to her, I will ask her about specific studies on the effects of analgesia on the amount of anesthesia needed. I recall she mentioned one in her talk but I don't have the reference for it.
Hope that helps. I'm glad Sheba (who is beautiful!) is doing well and the corneal ulcer healed without the need of surgery. Dr Mark Kittleson (the foremost expert on feline HCM) agrees that prior to the onset of congestive heart failure, there is no medication that has been proven to help or slow the progression of HCM. Lots of cardiologists give a beta blocker (e.g. Atenolol) or ACE inhibitor, etc ... but for mild to moderate HCM there is no evidence that they actually help ... unless there is SAM (Systolic Anterior Motion of the Mitral Valve ... which is the cause of audible heart murmurs). Dr Kittleson has actually gotten to the point that he says he does not diagnose "mild" HCM. Even as the leading expert on HCM, he can't tell in early stages if a cat actually has HCM or if the mild thickening is just normal for that cat. So, rather than calling it "mild" HCM ... he calls it "equivocal" HCM ... meaning ... the cat MAY have HCM, or the cat MAY NOT have HCM ... and he can't tell which is true. I think he would agree with your cardiologist's plan to do additional ultrasounds to watch for any progression, which would then suggest HCM. But many cats have stable HCM for many years, so I hope that is true also of Sheba.
Take care and let me know if you want the audio of Dr Grubb's talk.
Stephanie in Montreal
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