Tuesday, October 15, 2013

Go to sleep, little kitty!

I'm on anesthesia rotation right now. Ax scares the crap out of me. The drugs we use to induce and maintain anesthesia have some profound systemic effects. They slow the heart, drop blood pressure, make them stop breathing... It's scary. When you think about the fact that the Illinois teaching hospital is a referral hospital, and we don't get average, every day, healthy pets for the most part, but difficult, involved cases, often with multiple combined illnesses, it's terrifying.

Usually, an Ax protocol goes like this:

Premedication: This is to make the animal sedate and relieve anxiety before placing an IV catheter and and inducing anesthesia. Usually a combination of an alpha-2 agonist or benzodiazepine with an opioid.

Induction: After you've placed an IV catheter, you induce anesthesia with propofol, thiopental, alfaxalone, etc. These agents usually induce apnea (no breathing). You've got about a minute from the time you induce until you need to have an endotracheal tube in that animal so you can hook them up to oxygen and ventilate them if necessary. It can be very scary. Cats in particular are difficult to intubate, because their largyngeal muscles spasm with stimulation and can cause a dry choke where their airway closes and then you cannot get a tube in. We often use a lidocaine splash block on the arytenoids to desensitize them and then use a thin wire stylet to guide the ET tube to avoid that.

Maintenance: You can use a TIVA (total intravenous anesthesia) of a combination of drugs to maintain sedation, but more often we use inhalants. Inhalants like isofluorane are extremely cardiovascular depressive. They cause hypotension and bradycardia.

That's all pretty intense, in and of itself. If you also have a bunch of complications that make you have to be very selective in your choice of drugs, and have to add CRIs (constant rate infusions) intra-op to correct the things that the anesthetic causes (dopamine to improve blood pressure, diuretics to improve blood flow to the kidneys in renal failure patients, dextrose for hypoglycemic patients)... Shit gets complicated and intimidating.

Two of my anesthesias wound up being cancelled because it wasn't safe to anesthetize them. Both were very involved, with bad systemic illnesses, and I was scared. I'm glad they were cancelled, not just because it was very unsafe for them and likely could've killed them, but also because it was a relief that I didn't have to go through with it. I am very happy, though, that I spent a long time researching for each case, carefully putting together what I thought was the safest anesthetic protocol uniquely crafted to that patient, and each time the faculty or resident anesthesiologist barely altered it at all. And my protocols were REALLY involved. Each of them involved 2-4 premeds, a co-induction with propofol and fentanyl, and at least two intra-op CRIs. Both had hypotension concerns, so I needed to keep my inhalant down as low as possible while still keeping them under.

It's nice when a board-certified specialist looks at your work and says, "I'm happy with this. Tweak this a bit, lower the dose of that, and we're good to go." And those changes were based on experience with those drugs in the specific conditions my patients had that I don't possess yet. So I'm pretty pleased with my performance so far.

1 comment:

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