Anesthesia

Anesthesia

I am frequently asked about the risks of anesthesia, especially for older pets. The conversation usually begins with, “Well, he’s too old for anesthesia, isn’t he?” Most often, the answer is no. We’ve come a long, long way from saying successful anesthesia means the patient woke up at all. With the current drugs and monitoring equipment available to us, we’re able to safely anesthetize patients. Age and medical problems do play a part on how we go about anesthesia, but it’s rare that either one totally prevents us from anesthetizing a patient.

This week, I’d like to walk you through the process of anesthetizing a patient.

Preoperative Consult

We usually discuss anesthesia as part of an appointment. If a procedure like a dental cleaning, tumor removal, spay or neuter is recommended, then anesthesia will be discussed with the client. We go over why anesthesia is necessary, then talk about what has to be done to prepare a patient to undergo the procedure.

Preoperative Diagnostics

The two things that we recommend for all patients undergoing anesthesia are bloodwork and an EKG. Bloodwork makes sure that organ function is good. The liver and kidneys are responsible for processing or getting rid of the anesthetic drugs, so we want to make sure they’re in working order. An EKG helps us screen for heart problems that might make anesthesia unsafe for a pet. The bloodwork is usually done about a week ahead of time. The EKG is done the day of the procedure.
EKG02
Jugularbloodrestraint

IV Catheter and Fluids

A
n IV catheter allows us to hook up IV fluids. Fluids help keep the blood pressure where it should be. Fluids also prevent dehydration and help flush anesthetic drugs out of a patient’s system. Keeping blood pressure normal is important to prevent damage to organs. Dehydration makes patients feel pretty terrible, so preventing that helps them feel better when they wake up. We place the IV catheter about an hour or two before the procedure.
IVCathPlacement 14

Premedication

One of the basic steps for practicing good anesthesia is to keep patients as low-stress and pain-free as possible. We begin the actual process of anesthesia by giving an injection of a mild tranquilizer and a fairly strong pain medication. These “premeds” keep patients calmer and stop pain before it starts. This allows us to use less of the actual anesthetic drugs, so the whole process is safer. Premeds are given intravenously or in a muscle.
Cephalicbloodrestraint

Induction & Intubation

Induction is the phase of anesthesia where we “knock the patient out” and place the endotracheal tube. The knockout drugs include propofol, dexmedetomidine, ketamine, and valium. Patients drift off to unconsciousness. We then open their mouth and slide a breathing tube (endotracheal tube) through the mouth, into the windpipe (trachea). The tube has a special inflatable balloon around it that makes sure the trachea is sealed off. This prevents anything from getting down into the lungs and makes sure that anesthetic gasses don’t come out into the surgery room. The tube is tied in place by a gauze strip that’s tied around the muzzle or the back of the patient’s head.
Induction008
Induction012

Maintenance

Once the patient is induced and intubated, we hook the patient up to the gas anesthesia machine. This machine is hooked up to a pure oxygen supply. The oxygen flows through a special chamber that mixes in the anesthetic gas. This is breathed in by the patient through the endotracheal tube. The anesthetic agent goes into the bloodstream, then into the brain. It keeps the brain asleep. We have to adjust the amount of anesthetic gas depending on what the surgeon is doing. The goal of maintenance is to keep the patient asleep without making them too deep under the anesthetic.
Anestheticmachine03

It takes a lot of training and experience to do this properly. Our licensed technicians are trained to perform these tasks safely. During maintenance, we have the patient hooked up to a monitor that shows us an EKG, blood pressure, temperature, oxygen levels, and breathing rate. The techs have their hands on the patient continuously. We record data for each of those measurements every 5 minutes. Between data recording points, the technicians are listening to the patient’s heartbeat and breath sounds with a stethoscope as well as checking pulses. They adjust the anesthetic depth based on how asleep the patient is.
Sxmonitor vetspecs 2

Recovery

Recovery from anesthesia is simply reversing these steps. When the surgeon is finished, the anesthetic gas is shut off. Patients then breathe pure oxygen for several minutes. When we are comfortable with them breathing on their own, we disconnect them from the pure oxygen and let them breathe normal room air. Patients slowly wake up. When they are conscious enough to be able to swallow, we remove the endotracheal tube. Patients are placed in a cage for close monitoring as they finish waking up. Most pets are awake and on their feet within an hour.

Summary & Questions

Following these steps carefully and with attention to individual patient needs lowers the risk of anesthesia even for very old or sick animals. I’m happy to answer questions that anyone has regarding the process of anesthesia. Don’t be shy! Thanks for reading!

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2 Comments

Filed under anesthesia, surgery

2 responses to “Anesthesia

  1. David Hughes

    As our Mischa is more than due for a tooth cleaning, this post is reassuring and informative. As ever, thank you.

    I’ve heard it said that the risk of anaesthesia isn’t closely related to the depth or duration of the sleep, but that there’s kinda a “fixed risk” each time the patient goes under. So shallow anaesthesia, like I guess you’d use for a tooth cleaning, has roughly the same risks as putting the patient deeply under for serious surgery (not counting the risks of the surgery itself, of course). Is there truth in that?

  2. There is indeed fixed risk in anesthesia. No matter what, patients will be induced. Patients will have to be recovered. Those are the two most dangerous times during anesthesia. The maintenance in the middle is variable. If a patient is on inhaled gas (isoflurane or sevoflurane), the deeper the anesthesia the higher the risk of low blood pressure, breathing stopping, heart stopping, etc. We do our best to use the smallest amount of gas needed to maintain the proper depth so the patient isn’t awake but paralyzed, for example. Horrifying, but it happens in humans, so we have to assume the same for animals. Use of other agents, such as opiates and dissociatives help us use less gas, which increases safety. The death rate for otherwise healthy, reasonably young (under 7 years) animals is about 1%, statistically speaking. I think we do better than that, personally, but averages are averages. Having pre-operative bloodwork and EKG done are the two best ways (after the physical examination) to assure that the patient can handle what’s coming his/her way. After that, it’s all about how the staff handles the process. I’d be happy to provide more specifics about the process if you’re interested.

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