It’s a gas

Where I work we anesthetize nearly 20 cases a week. Most of these are young and healthy patients but some of these are elderly or extremely ill patients. Of those 20 or so patients I may explain the anesthesia process to 1 or 2 clients. It’s not that I don’t enjoy explaining things, I do, it’s just that the majority of people don’t ask and I often manage my time poorly and don’t have enough of it to take the time every time to explain really important things. It’s disappointing.

So here is my explanation of anesthesia in pets. Keep in mind that we are constantly improving our anesthesia so while the information I am about to lay out may be true for today but will most likely not be true for 6 months from now and will definitely not be true for a year from now.

So what we will do is walk through the basic anesthesia process and I will do my best to explain what happens and why along the way.

Patients that are undergoing scheduled anesthesia events are fasted overnight. This helps to prevent vomiting during anesthesia. Animals and people who are under anesthesia will not cough if they accidentally inhale a small amount of vomit. This vomit can then end up in the lungs where it can cause a life threatening pneumonia.

We have most patients dropped off to us at or before 8 am they are not typically picked up before 5 pm. This gives time to prepare them for anesthesia in the morning and gives the patients the entire afternoon to recover from anesthesia.

Every patient is examined that morning to help us develop the best possible anesthesia protocol for them on that specific day. Each patient is given a numerical rating based on how critical the patient is and how dangerous anesthesia will be for them. This is one of the reasons we often request that patients also have some blood work run. Patients will need red blood cells to transport oxygen during the procedure and to wake up well. They will also respond to anesthesia differently if they have an ongoing infection or a compromised immune system.  The drugs we use are going to be bound to proteins in the plasma during anesthesia. They will also be metabolized by the liver and excreted by the kidneys. Some routine blood work can give us the information we need to make changes to our patients anesthesia protocols and avoid a bad anesthesia experience.

Every anesthesia protocol is made up of 4 basic components. There is a premedication, induction, maintenance (also called peri operative) and post operative component to each anesthesia protocol used at any hospital.

As soon as we have our blood work available and the physical exam is complete we premedicate our patients. Our premedication drugs are almost always a combination of a sedative and a pain medication. The premedication calms the patient, dulls the body’s ability to register pain and makes the remainder of the process easier on the animal. It also allows for smoother induction of and recovery from anesthesia. Using good premedication allows us to use less of the drugs we use to induce anesthesia; these drugs typically have more profound effects on the cardiovascular system so using less is always preferred.

After the premedication has sufficiently taken its affect we are able to move to the next phase of anesthesia. With the exception of very quick procedures we place intravenous catheters in every patient undergoing anesthesia. This allows us to administer the induction drugs IV. Having IV access allows us to give fluids during the procedure and in the event that anything goes wrong we have access to the circulatory system and can respond immediately.

Once the IV catheter is in place we do a quick systems check to be sure we are all completely ready to do our job. As soon as we are all prepared and ready we induce our patients with an injectable anesthetic or a combination of several different anesthetics. We always induce intravenously as it is more rapid, smoother and controllable. Every patient, again with the exception of very quick procedures, is intubated for anesthesia. This means that we place a small plastic tube with an inflatable cuff directly in their trachea. This allows us to administer oxygen during the procedure. We also routinely use inhalant anesthesia as our maintenance anesthetic. If something were to go wrong in anesthesia having control of the airway is one of the most important parts of a good outcome.

As soon as a patient is induced and intubated our goal is to get them ready for the procedure and in the surgery suite as soon as possible. Once in the surgery suite they are immediately connected to oxygen and inhalant anesthesia. If the patient is a critical case (heart failure for example) or the procedure is going to be painful we often augment the inhalant anesthesia with controlled rate infusions (CRI) of injectable anesthetics as well as pain medications. This allows us to use less inhalant and we are able to manage pain better during the procedure. We also immediately connect patients to fluids given at a surgical rate. All anesthetic drugs will alter the cardiovascular system but by giving them fluids we are able to offset those effects and maintain good blood flow to organs that may have been compromised without fluid therapy. It also offsets the amount of fluid that is lost during surgery by having a body cavity opened and exposed to the outside as well as fluid lost to breathing with the anesthesia machine.This set up moves us to the third phase of anesthesia, maintenance or peri operative anesthesia.

As soon as the patient has entered the third phase of anesthesia we attach our monitoring equipment. The reason this happens here is because between phase 1 and 2 we are monitoring from a distance, allowing the drugs to do their job. It’s typically not until the patient has been induced that they start to undergo serious cardiovascular changes. For a reference, the total time between induction and being completely set up for surgery, including monitoring equipment, at our hospital is less than five minutes. In our hospital the monitoring of anesthesia is taken very seriously. A single veterinary technician is assigned to the job.  Each patient is attached to an ECG to monitor the electrical activity of the heart. This allows us to see and hear that the nerves that control the heart are conducting. If we want to hear the physical pulse during surgery we will also connect an ultrasound device called Doppler to actually hear the pulses. We often use Doppler with critical cases or patients with severe heart murmurs.  We also monitor the patient’s temperature, blood pressure and respiratory rate during anesthesia. A system called pulse oximetry gives us a measurement of the amount of oxygen being carried by the patient’s blood. In addition to that the technician assigned to monitoring anesthesia takes note of several of the indicators we use to assess the patients level of anesthesia at specific intervals throughout the procedure. As a general rule, the person monitoring anesthesia is expected to place hands on the patient every 5 minutes or so but in reality there are often anesthetic episodes where the technician has hands on the patient almost the entire time.

As soon as the procedure is finished the inhalant anesthesia or the CRI is turned off. Every patient receives at least an additional 5 minutes of 100% oxygen and is then moved out of the surgery suite and we enter the post operative phase of anesthesia. Here we may supply external heat if the patient’s body temperature has become low during the procedure. We also formulate the medications we will want to continue to keep this patient on while they are healing from the procedure. A different veterinary technician then takes over the post operative monitoring and brings any issues to the attention of the doctor. Monitoring of anesthesia ends when the patient is able to hold itself up unassisted, the temperature is above 99.5 degrees and they respond to having their name called or to being stimulated in another way.

The majority of our anesthesia patients go home the same day. This is mainly due to us using highly specified protocols for each patient and adjusting them to fit each patient’s needs.  We are always looking to improve and add in new protocols and increase our monitoring capability so next time your pet is going under anesthesia ask if we have anything new. We’d love to explain it to you.

Thanks for reading!



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