Why is my patient waking up while still under anesthesia?

In addition to going through the basic steps, be sure to keep breathing and stay calm to help evaluate your patient rationally

Small patients, especially cats, are at risk for obstruction of the ETT by a mucus plug. Photo courtesy Phil Zeltzman
Small patients, especially cats, are at risk for obstruction of the ETT by a mucus plug.
Photo courtesy Phil Zeltzman

The art and science of anesthesia is keeping the patient under an appropriate anesthetic depth. Not too light, not too deep. Just right. Although sometimes it feels like an impossible Goldilocks-like compromise, administering anesthesia requires taking a step back and going through the basics to answer the most stressful question: “Why is my patient waking up?”

1) Vaporizer

Is your anesthesia machine functioning properly? Remember, vaporizers lose calibration over time. While you may have your gas set at two percent, it may only be delivering 1.5 percent. Your anesthesia machine, valves, and vaporizer should be checked and calibrated every year by a professional. So if it’s been 10 years since you last had your equipment serviced, it’s definitely time.

2) Leaks

Is there a leak in the anesthesia hose or bag? The question is not whether if it will happen, but when. The busier you are, the more frequently a leak will happen. The goal is to find out before anesthesia, not in the middle of surgery.

This is the reason why pressure-checking your machine, tubing, and bag should be done at the beginning of every surgery day (and ideally before each anesthesia). This quick precaution keeps your patients safe and prevents you from anesthetizing yourself.

3) Scavenger

Is your scavenger system working properly? If you have an active scavenging system that doesn’t function correctly, the vacuum pressure may be too high. This may deflate the bag and remove the gas anesthesia before it gets to the patient. Again, the solution is to have your system evaluated regularly by a professional.

4) Soda

Are you replacing your soda lime adequately? Observing color change is not an accurate way to tell when your CO2 absorbent has been exhausted. In addition, color pattern is not consistent among manufacturers, so it’s important to know what to expect.

Many times, color change takes place in the middle of the canister, before it is visible in the outer layers. Rather than relying erroneously on color change, follow the time recommendation from your supplier. Keep a time log so you know how many hours your soda lime has been used, and change it accordingly.

5) Tube

Have you checked your endotracheal tube (ETT)? Is it in the right location? Is it the proper size? Is it not far enough into the trachea or too far? Is it properly inflated?

Dead space in the tube decreases the effectiveness of the anesthetic exchange. Just because the cuff appeared to be intact at the beginning of surgery does not mean a failure didn’t occur intra-op.

Could there be a mucus plug in the ETT? This happens more frequently in cats, but may also occur in small dogs. Have a second tube at the ready in case the first one requires replacement for any reason. You can also use it to measure the inserted ETT “externally” to make sure it is positioned correctly.

6) Premed

Have you premedicated your patient properly? The use of proper premedication—chosen safely for each patient, rather than blindly following a recipe—helps in the administration of smooth anesthesia. It also decreases significantly the percentage of gas anesthesia needed, keeping the patient safer. I perform tibial plateau leveling osteotomies (TPLOs) regularly on 0.5 percent when my patient is properly premedicated and placed on a constant rate infusion (CRI).

7) Analgesia

Speaking of pain management, are you providing adequate pain control? If not, the patient may very well be overstimulated and become light during surgery. Using mild analgesics (e.g. butorphanol)—or none—and keeping your patient at a high gas percentage (four or five percent isoflurane, seven or eight percent sevoflurane) is not considered appropriate in the 21th century. The idea is exactly the opposite: Use multimodal analgesia to decrease the gas percentage. That is a much more humane and much safer approach for your patient.

8) Sizes

Is the anesthesia administration setup correct for the patient? Make sure the size of the hose and bag is adequate for the patient. Consider using a non-rebreathing system for patients under 20 lbs., so they don’t have to fight against the pressure of a larger system at every breath. Everything should be tailored to the patient’s weight. And speaking of weight…

9) Overweight

Is your patient overweight or obese? If so, there is a good chance panting is related to your patient physically being unable to properly ventilate (Pickwickian syndrome). This means manual ventilation is required (or mechanical ventilation if you have a ventilator).

Capnography is the best way to judge the efficacy of your patient’s breathing efforts—and your nurse’s. Pulse oximetry is a terrible way to do the same. Please don’t ask your nurse to close and open an old-style pop-off valve every 10 seconds to give a breath. Instead, acquire a pop-off valve restrictor (around $70), so breaths can be administered at the push of a button. In addition, this valve eliminates the risk of forgetting to reopen the pop-off valve and destroying your patient’s lungs.

10) Monitoring

Is your anesthesia nurse only relying on monitoring equipment? Although standard of care should include anesthetic monitoring with all parameters, you cannot depend solely on the numbers on the screen. Anesthetic depth, respiratory rate, heart rate, gum color, capillary refill time, and quality of pulse should also be regularly monitored.

By the same token, it is important to track your readings and findings in an anesthesia log. If you did, maybe you could have predicted your patient was about to wake up because his heart rate and the blood pressure kept rising. Keeping a log is a great way to look at trends, while someone’s memory is the worst way to do it.

Another important value to track regularly is the patient’s temperature. Although it’s more common to deal with hypothermia, hyperthermia is a possibility, especially in small patients with heat support. Hyperthermia can cause panting even under anesthesia.

Administration of anesthesia should never be passive. Sometimes, smooth anesthesia requires constant changes in the gas percentage, oxygen volume, and CRI rate.

As you can see, none of the above is rocket science. In addition to going through the basics, don’t forget to breathe yourself! If you are so stressed that you are breathing poorly, it will be harder for you to evaluate your patient rationally. Even simple corrections won’t be obvious if you are in panic mode.

Figure out what helps you stay calm. Use checklists, practice breathing exercises, or ask a coworker to be on standby for moral support. Prepare the night before so you don’t feel rushed the day of surgery.

Whatever makes you feel more comfortable allows you to take better care of your patients. In addition to breathing, eating, drinking, it won’t hurt to take bathroom breaks either.

Phil Zeltzman, DVM, DACVS, CVJ, Fear Free Certified, is a board-certified veterinary surgeon and author whose traveling surgery practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at DrPhilZeltzman.com. He also is cofounder of Veterinary Financial Summit, an online community and conference dedicated to personal and practice finance (vetfinancialsummit.com). AJ Debiasse, a technician in Blairstown, N.J., contributed to this article.

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