I'm Afraid of Anesthesia for My Pet, Part III

I Am Afraid of Anesthesia for My Pet - PART III

Sandra L Waugh VMD, MS

When we ended article two in the last issue of 4 Legs & a Tail, our patient was under general anesthesia, wrapped in a “pet burrito” for warmth, connected to the anesthesia machine by the endotracheal tube and to the intravenous (IV) fluid pump and the IV pain medicine pump via the IV catheter. He was also connected to the various monitors by wires and sensors. Now the task of monitoring the depth of anesthesia begins. While anesthesia holds our patient still so we can do the procedure, it depresses the heart rate, blood pressure, temperature and respiration. Our job is to keep the patient still enough to allow surgery to be performed while keeping the depth of anesthesia as minimal as it can be. The goal is for the animal to wake up quickly “as if nothing had happened”, be able to walk out the door and act basically normal by the next day.

Let’s start with the cardiovascular system (heart and circulatory system, which is composed of blood vessels, including arteries, capillaries and veins) and the respiratory system, composed of the lungs and trachea. The heart is actually two pumps. The left side of the heart pumps blood throughout the body, except for the lungs, providing oxygen, electrolytes (salts), and glucose (food) to the cells of all of the organs. Oxygen, electrolytes and glucose leave the blood to provide the cells with what they need to produce energy. CO2 and lactate go out of the cells and into the blood which is then pumped back to the right side of the heart and then through the lungs. The lungs allow CO2 to leave the bloodstream and exit the body through the exhaled gas and more oxygen to load onto the red blood cells. The blood is then returned to the left side of the heart and the whole process repeats. (Lactate and electrolytes are taken care of by the liver and kidneys which we will not describe!)

Heart function is monitored in several ways: Pulse Rate, ECG, Blood Pressure, Lactate concentration in the blood, CO2 concentration in the expired gas, and Oxygen saturation in the blood. The last two measurements also monitor the respiratory system.

ECG dots must make good contact with the skin in order to work correctly. The hair must be clipped off. Then a small amount of gel is used between the pad and the skin. Wires lead from the dots to the monitor.

Appearance of an ECG with artifacts (red arrow) introduced by movement of the wires. Sometimes we need to adjust things and the wires get bumped. Since we know when we were moving things we know what is an artifact and what is real.

Blood Pressure: we attach a blood pressure cuff to a leg or the tail so we can see the high, mean and low pressure of the blood flowing through an artery under the cuff.

The green arrow points to the pulse rate on both the ECG and the blood pressure monitor. Our blood pressure monitor is made specifically for animals from the very small to the very large.

Blood Lactate: We also measure peripheral blood perfusion by a lactate measurement . Lactate builds up if the blood flow and oxygenation to the tissue is poor. To measure the lactate level in the blood we clip a toe nail slightly short, so that a drop of blood can be captured on a lactate test strip connected to a lactate meter. 5 seconds later and the result is displayed on the meter.

Blood Oxygen: A Pulse Oximeter (SpO2) is attached to the tongue, ear flap or skin webbing in between the toes. (If you go to your doctor a clip is attached to your finger for this purpose.) We also get a tracing of the movement of the level as blood pulses by the sensor. The number represents the percent of saturation of the blood i.e. 97 = 97% saturation. Pulse rate is also measured by the pulse oximeter. SpO2 is affected both by the function of the lungs and of the heart.

CO2 concentration in the expired gas, referred to as End-Tidal CO2: Again our monitor gives us numbers but also give a tracing of the measurement over each cycle of breathing. This information is quite useful. The respiratory rate is also shown on this monitor. Again, the heart and the lungs both are involved.

When we first start anesthesia we closely monitor the respiratory rate. If the rate is too low we can press the rebreathing bag to mechanically cause a breath. Sometimes at the very beginning our patients are slow to breath but quickly start to breath well on their own. No intervention is then required. Some patients just don’t want to breath well on their own. In this case we use a mechanical ventilator which breaths for the patient. The machine is set at the beginning according to the weight of the patient and then adjusted for that specific patient’s needs. The ventilator can be used on large dogs (left) or cats and small dogs (right).

Miley hopes you are still awake after all that technical information!

In the next issue we will wrap up this series on anesthesia by talking about the most important component for excellence in anesthesia...

Dr. Waugh is a graduate of the

University of Pennsylvania School of

Medicine. She also holds a Masters

Degree from Washington State University of Veterinary Medicine and is owner of Windsor Pet Dental, PLC. Spring 2021