Anesthesia - Keeping The Big Sleep Safe

Few things make owners as nervous as anesthesia. Heck, when I was first unleashed upon the world as "Dr. Rowland" anesthesia wracked my nerves way more than surgery. I distinctly remember the first time I knocked a patient out - I calculated the dose, double-checked it, then looked it up and checked it again, then read the drug monogram for the Nth time and checked the dose several more times. I've gotten over that, of course. Wouldn't see many patients at that rate!

Here's the thing - with the right drugs, good monitoring, and a relatively healthy patient anesthesia is quite safe. But anesthesia is never without risk, and should never be taken lightly. Today's article is geared toward relieving the anxiety most of us feel when our pets need to be anesthetized - by giving you knowledge about what the risks really are, and what we (vets and owners) can do to minimize them.

Monitoring
Guess what the best way to miss a problem is? Not looking for it.

A fully-functional veterinary monitor.

Anesthetic drugs don't just cause loss of consciousness - they may affect heart rate, blood pressure, respiration and more. In case you don't know, these things are kind of important. The body has needs - nutrients, oxygen, and removal of waste products produced by using those things. Respiration and circulation are how the body gets it done. So it only makes sense to closely monitor how all that's working, right? And since a living body is a pretty complicated bugger, there are many things that can go wrong and many things we can watch to recognize problems and address them before they get out of hand. Here's what I consider minimum monitoring for most procedures:

• Heart rate and blood pressure - These are the main determinants of blood flow, but they can also clue us in on "depth" of anesthesia and even other problems like blood loss.
• Electrocardiogram (ECG) - That's the green wave with the reassuring beep on the TV hospital shows. The heart is a complicated pump running on electricity; an ECG looks at that electricity to identify problems with rate, rhythm, or coordination of the heart.
• Respiratory rate and blood oxygenation - Blood flow to your pet's tissues does little good if it doesn't have oxygen. And, even if you are breathing, lung or circulation problems can keep the body from getting the oxygen it needs.

Except for pulse and respiration, all those require special equipment to monitor. But this belies an important question - who monitors the monitors? Indeed, the most important monitor of all is the human being keeping track of, interpreting, and responding to all this information. Since the veterinarian is usually kind of busy -cutting this, stitching up that, and keeping sterile all the while - the best monitor is a living, breathing, highly-trained veterinary technician. They keep an eye on all that data for problems, address the minor stuff, and let me know when I need to stop playing with this or that organ and focus on what the rest of the patient is doing. Plus they monitor important stuff no machine can, like reflexes and gum color, and administer whatever treatment the vet deems necessary if problems do arise. 

How Do I Know You're Healthy?

A 2008 British study showed that anesthetic risk increased almost 7 times for patients with significant systemic disease. That's not exactly surprising, but I'd go farther and say the most common reason for anesthetic problems in patients we think are healthy is that they aren't healthy. Pets with early or mild disease often compensate well and show no outward problems - until we knock them out with a bunch of drugs that reduce their ability to compensate. Here's what I recommend before any anesthetic procedure, to feel reasonably comfortable your pet is healthy:

Occasionally, bloodwork is really surprising.
This pet appears to be possessed by demons.
(okay, not really...)

• A Good History & Physical Exam - The importance of these can't be overstated. Changes in appetite, activity level, urination or other behaviors are major clues to systemic problems. Likewise, many problems with the heart and lungs can be heard with a stethoscope. Some diseases leave early signs that can be seen with a good look at the eyes, skin, or mouth. And more than once I've felt something that shouldn't be there in the abdomen of an outwardly normal patient.
• Basic Bloodwork - Simple blood tests can identify problems with the liver or kidneys that may not cause clinical problems in your pet - until we challenge them with a bunch of anesthetic drugs. A blood count can also catch problems like anemia or inflammation, which in turn may be clues to undiagnosed infections or immune diseases.

Realistically, even if we ran thousands of dollars worth of MRI's and fancy bloodwork we couldn't be 100% sure your pet didn't have some strange, subtle disease. But those simple things will rule out the majority of problems without breaking the bank - a simple blood panel runs about $40-$60 most places. 

Anesthetic Drugs

The drugs used for anesthesia are really your vet's prerogative, and far beyond the scope of this article. However, it's worth briefly mentioning two things about drug choices. First off, when we do find a health issue with a pet that requires anesthesia we use that knowledge to select the safest anesthetic drugs for the condition. Each drug has it's own profile of side-effects that may impact the heart, liver, kidneys, etc; none are without side effects, but we can choose those least likely to aggravate the patient's individual problems.

Secondly, pain and stress also impact many of the things we worry about during anesthesia - heart rate, blood pressure, and even the heart's electrical rhythm. While I haven't came across any studies establishing that good pain control leads to safer anesthesia, it stands to reason that a less stressed, pain-free patient should handle anesthesia better. Most of us nowadays provide sedation prior to inducing anesthesia and various kinds of pain relief (analgesia) during procedures for just this reason.

What Should You Do With This Knowledge?

Here's the point - understanding all this means you can make informed choices when your pet needs anesthesia. Here are some questions you should now be able to ask when choosing a vet for a procedure:

• What kind of things do you monitor when Muffy's asleep?
• Is there a person watching Muffy while he's out? What kind of training do they have?
• What kind of bloodwork do you recommend? 
• Based on your exam, do you think Muffy's okay for anesthesia? Is there anything else we should check?
• If the procedure may be painful, what kind of pain control do you provide?
• Do you have any other questions about Muffy, Doc? (That is a smart owner question.)

So, why tell you all this? Thing is, many great, smart veterinarians don't do all the things they'd like to or feel they should because of financial reasons - that is, you won't pay for it. Not every clinic provides all these services, and many clinics that do offer everything mentioned above make them "optional" for an additional fee. Those monitors I talked about run $3,000-$10,000, with a life expectancy of a few years. The technician monitoring the monitors is $13-25 per hour. If you won't pay for it, we can't pay for it - or we have to cut costs somewhere else, which isn't good for your pet either. Honestly, I don't put the blame for that on pet owners, but squarely on we vets - we can't expect you to pay more if you don't understand why the extra money is worthwhile. Hopefully now you do, and can make informed decisions about who treats your pet and how. The most expensive place in town may not necessarily be the best, but I can pretty much guarantee if you price-shop around for the cheapest place your pet is missing out on some or all of these safety measures. 

Likewise, some vets make good arguments that some of the things discussed here aren't necessary. And maybe they aren't strictly necessary - the vast majority of outwardly health animals are indeed healthy, and would probably be fine if knocked out with a 20-year old drug protocol and ignored. Bear that in mind if you truly can't afford the extra money for all the "best" care. But most of us can handle an extra $100-150 for good monitoring, pain control, and some basic bloodwork; the peace of mind it buys is worth a lot more, if you ask me. 

Heartworm 102 - Prevention & Testing

Click here for Part I.

In the last article, we talked about what heartworms are and how they affect pets. You might check that one out first if you missed it, as a basic understanding of the life cycle is helpful in understanding today's topics - prevention and testing.

Prevention Strategies

Yeah, Joe was skeptical too.

I'm forever the skeptic, so I'll admit if someone told me I needed to buy pills for my pets every month for life I'd be the first to scan their eyes for dollar signs - veterinarian or otherwise. I certainly understand when the occasional client looks at me incredulously, or asks about just giving during the summer. But we aren't making this stuff up - with a little understanding of preventatives and the biology of disease, you should agree.

First off, it's worth noting that we're generally talking about preventing disease, not infection. The major problem with heartworms are adults (cats are a bit different, but we'll address that in the last article), and it takes about six months for them to mature after infection. The microscopic larvae that cause initial infection are susceptible to low doses of certain anti-parasite drugs, so the idea is that by giving pets a dose at regular intervals we can stop the disease (adult worms) from developing, even if we haven't stopped infection per say. That's good, because as anyone who's been to Louisiana in July will tell you, it's bloody near impossible to keep from getting a bitten by mosquitoes no matter what you do. And it only takes one.

So, why monthly instead of every six months? That's how long it takes to get adults, right? Well, the trouble is that as they age, larvae develop resistance to those relatively safe anti-parasite drugs. Effectiveness gets unpredictable 4-5 weeks after infection, and eventually they become pretty impervious to those drugs. We have to resort to drastic measures to kill adults - in fact, the standard treatment for adult infection is in the arsenic family. So monthly dosing is the safest bet (and a lot easier to remember). On the flip side, it's worth noting that if you miss a dose by a week or two you'll probably be okay. No guarantees, but it makes for easier sleeping when life (or memory) inevitably mucks with your schedule.

And why every month? Mosquitoes don't wear snowshoes, right? I could tell you that "heat islands," warm areas near houses and the like, may create microenvironments where mosquitoes can hatch even in the winter. I could tell you it only takes one infected mosquito to threaten the life of your pet. I could tell you many preventatives have important benefits other than just heartworm protection, and I'll discuss those below. All are true, but I'll level with you. Even if I could guarantee your pet wouldn't see a mosquito until April 1st or after October 31st (I can't), I know most of us - myself included - would forget to start until sometime in May or miss that last dose in the fall. And say you snowbird it somewhere warm for Christmas - what then? It's just easier to be consistent if you're on a consistent schedule. And where heartworm is concerned, consistency can save pets' lives.


Types of Preventatives
The currently available preventatives fall into three broad categories - monthly oral or topical products, and one injectable product that's given every six months. All of these are valid, effective choices for heartworm prevention; the main difference between products is what they cover in addition to heartworm.

Most oral and topical products have additional anti-parasite drugs that worm your pets monthly for GI parasites they're likely to get into, such as roundworms and hookworms. This is actually another big argument for monthly preventatives, as those are parasites people can get - specifically, those small people who rarely wash their hands and like to suck on their fingers after playing with the dog. Roundworms would likely survive a nuclear fallout, so they can certainly infect your pet in the middle of winter, and that monthly "heartworm pill" is a good way to keep them from infecting your three-year-old in turn.

Certain products will cover additional parasites such as tapeworms, whipworms, and even fleas. To my knowledge no single product currently covers everything, so it's worth talking to your veterinarian about what product or combination of products best covers the risks specific to your area and your pets lifestyle. I should also point out that's the big drawback to the "heartworm shot" - it doesn't provide monthly protection against all that other disgusting stuff pets tend to get into, just heartworm. It will kill off hookworms, but only every six months at the time the shot is given. For most dogs I recommend an oral heartworm product in addition to a topical flea-and-tick; for cats I usually recommend a topical product since getting an oral product in them can be a feat in itself.

Heartworm Testing
Yes, your dog should be tested for heartworm yearly even if you give monthly preventatives. Nothing is 100% effective, and disease caught early and treated early does far less harm. There are many scenarios that might lead to treatment failure, such as:

• You miss a dose for whatever reason. This is by far the most common situation - heck, I've  missed doses.
• Your pet has some indigestion and throws up the pill, unbeknownst to you.
• Your pet goes swimming shortly after a dose, or another pet grooms it off them.
• The medication has been mishandled and has lost its effectiveness. Heat can destroy most drugs - say, you forgot and left it in the car for a few summer days, or you bought it from somewhere other than your veterinarian and it was inappropriately handled (that's a whole other can of worms, and the subject of a future article). 

There has also been some concern over possible resistance developing to the drugs we use; at this point reports of "treatment failures" are few, and I'm fairly sure most could really be traced back to one of the above reasons. However, realistically we have to expect that some degree of resistance will develop eventually. 

It's worth noting the standard heartworm test looks for the presence of adult female worms. Think back to the first article where we discussed the parasite's life cycle and you will realize this means the test won't be positive until at least six months post infection. Likewise, if there are only a few worms and all are male, the test would be negative as well - I don't generally recommend regular testing for cats partially due to this, but we'll come back to that in the last article. It's complicated.

So, to summarize - all pets should get monthly preventatives (or the six-month shot for dogs), and dogs should be tested annually. Hopefully it's clear now why that's in their best interest. Please comment with any lingering questions and I'll gladly address them. In the final article, we'll talk specifically about heartworms and cats. They have some unique concerns and complications - as a professor liked to remind us back in school, "they aren't just small dogs."