Anesthesia In Dogs And Cats
Today we’re talking anesthesia. Let’s break the word down into its component parts to understand its literal meaning. The Latin prefix, an, means “without”. The root, esthesia, means “to feel.” So, anesthesia literally means to induce a state of the patient not feeling.There are many uses for anesthesia. The most common is to perform surgery. Obviously, if a potentially painful incision is to be made on a patient, one needs the patient to be perfectly still so that the surgical procedure can proceed in a controlled fashion, and it’s important for the patient not to hurt during the procedure.
These two parameters are usually accomplished through the use of general anesthesia, meaning administration of medications to place the patient in a state of total unconsciousness. Bodily functions continue: the heart beats, the patient breathes, kidneys remove impurities from the blood and transfer them to urine, etc. When the procedure is finished, the administration of the anesthetic is terminated and the patient soon wakes up.
It’s also important to recognize that some very important steps occurred long before the general anesthesia was begun. The procedure started with a thorough preoperative physical examination, to ensure that the patient was well enough for surgery. Special attention is paid to the heart sounds and lung sounds. Perfusion, meaning the ability of the heart to put out sufficient blood to peripheral parts of the body, is tested. Laboratory testing may be indicated for certain patients or certain procedures prior to anesthesia, as discussed in an earlier column, to help ensure safety during the anesthesia. If so, this is done before anesthesia is begun.
If the physical examination is normal, the next decision to be made is choice of preanesthetic medications. These include medications to sedate or tranquilize the patient, making him calmer, possibly slowing an excited heart rate and an overeager breathing rate to a safer and more efficient range. Medication may be given to reduce salivation and other secretions. Often these drugs are given in combination so that less of any one drug has to be used. Doing so leads to faster removal of all drugs once they are no longer needed, and prevents prolonged sedation in the recovery period.
Next an intravenous (IV) catheter is placed in a vein for two reasons. First, it allows us to have emergency access to the circulation should an unusual reaction occur during the procedure. Through this catheter we can administer emergency drugs to help the heart if the beat becomes too weak or if the rhythm becomes irregular. Medication may be needed to improve the characteristics of breathing, to improve blood pressure, to treat for shock or allergic reactions.
Another important use of the IV catheter is steady administration of fluid therapy. During anesthesia, blood pressure drops, which leads to a reduction of blood flow to vital organs such as the heart, kidneys, liver and brain. Administration of fluids offsets this drop in blood pressure, allowing lifesaving blood flow to continue to all organs.
For safety purposes during anesthesia, many forms of monitoring methods now exist, and multiple monitors may be used on one patient during a procedure. Two methods used routinely for decades include the EKG or electrocardiogram, and the audible breathing monitor. The EKG tells us about the electrical activity of the heart, how fast the heart is beating, as well as being an indicator of regular and irregular heart rhythms and even certain electrolyte (chemical) imbalances.
The audible breathing monitor allows the surgeon to hear his patient’s breathing, evaluating the rate and the depth of every breath.
Modern technology has brought us the Pulse Oximeter, which allows us to know how much breathed oxygen is actually getting to the bloodstream, as well as telling us the rate of heartbeat. End Tidal CO2 machines tell us how much waste gas is breathed out of the patient. Combination machines can even give a constant readout of body temperature, as well.
Twenty years ago many medical conditions might have made us question, or even rule out the possibility of using general anesthesia in those patients. Today, thanks to preanesthesia laboratory testing, modern monitoring equipment and newer anesthetics, we routinely anesthetize those same patients with great safety.