Practicing Safer Anesthesia

Kristin Spring, CVT, VTS(ECC, Anes.), CVPP, explains how you can better your anesthesia knowledge and improve your patient’s anesthesia experience, even without expensive monitoring equipment.

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As technicians, some of us practice anesthesia as the core part of our job; for some of us it is just a small part of the many things we do. No matter how often we monitor anesthetized patients we should always strive to do the best we can. No matter who you are, you can always do anesthesia better (read: don’t worry, there is always another challenge around the corner!), and you don’t need a bunch of fancy toys to practice safe anesthesia.

Turn down the gas

One really good way to keep your patient safe is by practicing balanced anesthesia. This means using several different types of drugs in combination to get the sedative, anesthetic, and analgesic effects that you want. When using drugs in combination, a much smaller dose of each drug is needed to get the desired outcome. Using smaller doses also decreases the undesired effects of each drug individually. For example:

  • Pre-medicate your patient with a sedative and an analgesic appropriate to the procedure you are performing. This benefits both the patient and anesthetist in several ways:
    • It allows the patient to have a chance to calm down before induction thereby lowering the risks associated with the catecholamine release that stressed animals have.
    • Anesthesia will likely be achieved with a much lower dose of the induction drug.
    • By giving analgesia prior to a pain stimulus the patient will likely have a more smooth anesthetic experience and hopefully not experience wind up.
  • Once anesthesia induction has occurred, you may consider putting your patient on a continuous rate infusion (CRI) of an opioid and/or ketamine in addition to your inhaled gas to sustain an anesthetic plane. This will allow you to maintain your patient on a much lower percentage of gas which will help preserve their blood pressure. In addition, you can give small boluses and titrate these CRIs if your patient becomes light or painful during the procedure rather than turning the anesthetic gas up and down. This is particularly important when managing a hypotensive patient. Slowly weaning the patient off of their CRI after the procedure will provide an easier recovery for the patient.
  • After the procedure is complete, consider multimodal pain management such as a local block or lidocaine patch near the incision site in addition to the appropriate NSAIDs and opioids. We are very lucky to have so many options. Most importantly, know the drugs you are using and tailor them specifically to your patient’s needs.

Hypothermia is common but not trivial

Patients get cold under anesthesia. It happens to everyone and should be expected, right?  Right. Should it be tolerated? No. Hypothermia is very common but also very dangerous to our patients. A hypothermic state induces stress and an inability to compensate.

How is heat lost? Remember, in thermoregulation everything wants to come to equilibrium. Heat is lost by conduction (laying on a cold preparation surface), convection (lavaging with room temperature fluids), radiation (opening up a body cavity to room temperature air), and evaporation (dry forced gases, open body cavity, increased surface area exposed).

Why is it that our anesthetized patients get so cold? When you anesthetize your patient, vasodilation causes a precipitous decline in body temperature.
Then we shave off insulating hair and scrub the patient with evaporating scrub and alcohol. Now we can start to see why our patients become so cold during the initial prep period. Next there is a progressive linear decline in the body’s temperature. Anesthesia abolishes many of the body’s compensatory mechanisms. The vasoconstrictive response in which the body tries to keep itself warm by shunting most of its circulation to the core to keep vital organs warm is diminished or absent. Anesthetic gasses reset the thermoregulation center in the brain so that a wider range of temperatures are tolerated without a corrective response from the body. By the time the body does respond, a normal response (shivering, shunting blood to the core) is not enough to compensate for the dramatic change in body temperature.

So what’s so bad about having a cold little patient? Just warm them up after the procedure and everything is a–okay, right? Not quite. Hypothermia has many deleterious effects on a postoperative patient:

  • Clotting times are affected by hypothermia with impaired platelet function, decreased activity of coagulation pathways, and increased fibrinolysis.
  • Wound healing is affected by hypothermia with decreased macrophage function leading to an increased risk of infection.
  • The patient is affected by a catabolic stress response which is the break down of muscle protein and a negative nitrogen balance. As little as a 4°F drop in temperature results in a doubling of urea nitrogen excretion compared to a normothermic patient. In addition, shivering that occurs post operatively leads to increased metabolic oxygen needs; so much so that flow–by oxygen is recommended for a shivering patient.
  • Hypothermia also changes the patient’s anesthetic needs. A 2°F loss in temperature results in a 5% decrease in the minimum alveolar concentration (MAC) of inhalational anesthetics. Hypothermia also decreases the clearance of drugs from the body and results in a prolonged recovery.

How cold is cold? A patient’s catecholamine release increases by 2–7 times at 95 °F resulting in vasoconstriction, tachycardia, and possible hypertension. Morbidity usually occurs during recovery. At 86°F the patient is at an increased risk for atrial fibrillation. At 75°–82°F the patient is at risk for refractory ventricular fibrillation and death.

There are many things you can do for your patient to prevent hypothermia. Prevention is a lot easier than trying to fix a problem later.

  • Use bubble wrap to insulate the extremities.
  • Turn down the oxygen flow. The metabolic needs for oxygen are 15-50ml/kg/min.  For ease, I use 30ml/kg/min. Use this formula to calculate the oxygen flow rate and you may be surprised at how little you need to use (remember the rate should be higher for a non-rebreather circuit). You can also place water bottles around the patient's anesthetic circuit to warm the air it is breathing.
  • Use a Bair Hugger®, Hot Dog® warmer, circulating warm water blanket or other appropriate warming device.
  • Use warmed fluid for lavage.
  • Insulate the patient with bubble wrap and blankets.
  • Don’t forget to warm the hind end. You can place insulated warm water bottles on the femoral arteries instead of having the hind legs splayed open to room temperature air.
  • Heat up your IV fluids with a special fluid warmer or wrap the IV line around a hot water bottle taking into consideration how close the hot water bottle is to your patient and the rate the fluids are being delivered.

Other tricks

Try using an esophageal stethoscope. I am a huge fan of this simple instrument. When placed during the preparation period, it is easy to grab an esophageal stethoscope and listen when monitors fail and easier than trying to get under a sterile drape to listen to your patient with a regular stethoscope.

Use a pulse oximeter and understand the limitations as well as the interpretation. If you have the ability to monitor end tidal CO2, learn about your machine, the normal parameters, and how to affect them. Capnograph monitoring is the gold standard for monitoring ventilation.

Be prepared. Anticipate problems your patient might face under anesthesia due to the specific surgery being performed. Know when checking an intraoperative glucose is appropriate. Have colloids and vasopressors ready and on standby if needed. Have IV access easily accessible. Know your patient’s resuscitation code status, and have an emergency drug sheet and emergency drugs handy.

My final and best piece of advice is to learn all you can about your craft. It will enhance your experience as well as your patient’s safety.

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Comments

Dana May's picture

great article! excited to utilize many of these techniques on my next surgical patient.

Becky Ellis's picture

Awesome article! A lot of great and very helpful tips! :-)

Nicole Dockrey's picture

Really great, though I would suggest doing a local block (incisional, nerve, bier, etc.) BEFORE cutting rather than after (the old "closing the barn door after the horses are already out" thing,) though lidocaine patches, soaker/diffusion wound catheters, and cold compresses are all great postoperative options, too.

Kristin Spring's picture

Dr. D. I do absolutely agree that getting a local blocks done before the pain stimulus is present is important and allows for us to block the stimulus before it perceived. This is how my patients are treated.

My reasoning for listing this as a post procedure tool is that some doctors prefer local blocks, especially line blocks to be done after their procedure due to the inflammation that it may cause in the procedure area. Does that make sense?

Tracie Vestal's picture

This is a great article! This will be the first article in my Anesthesia binder at work! And I'm glad you brought up line blocks...our DVM's are still divided over their efficacy and do, in fact, have issue with the tissue inflammation they can cause (although I suspect that this would be relieved by administering the block soon enough to allow it to work).

Christen Price's picture

I'm eager to start implementing some of these techniques for reducing hypothermia in my surgery patients.

Kaitlin Lindsey's picture

Can you give an example of the oxygen flow rate equation? Say, for a 10# dog and a 50# dog?

Megan Brashear's picture

Kaitlin, for oxygen flow rate I will use 30-50ml/kg/min on a rebreathing system (minimum 0.5L/min), and 300-500ml/kg/min on a non-rebreathing system (minimum 2L/min). Most patients on a rebreathing system will fall between 0.5L/min and 1L/min, meaning on many of our patients we are just wasting oxygen! Another good rule for inhaled anesthesia is to increase the oxygen flow rate to 2-3L/min for the first 5-10 minutes of anesthesia to more quickly saturate the anesthetic circuit with the oxygen/anesthetic gas mixture which can make for a more smooth transition from injectable anesthesia to inhaled. Just remember to turn that flow rate back down after the first 10 minutes.

Caroline Tanner's picture

So doing that calculation out, for instance if you have a 20 lb animal on a rebreathing system that would be 273 Mls per minute at minimum. Does that mean you set the 02 flow at 2.5 or 3? That seems really high.

Megan Brashear's picture

Caroline, that's correct - non-rebreathing systems require much higher oxygen flow rates compared to regular anesthetic curcuits. It is one of the reasons why we only use non-rebreathing systems for the very small and/or debilitated patients - they require higher flow rates to provide fresh oxygen with each breath.

Reanna Pearson's picture

Thank you for this article! I am fresh out of school and I'm trying to learn more about anesthesia.