After successfully pressure checking the anesthesia machine, check the vaporizer to make sure it has enough liquid inhalant. Next check to make sure the CO2 absorbent is fresh. The absorbent granules should be soft and crumble easily if they are fresh. Exhausted absorbent is hard and will not crumble. Absorbent granules are designed to change to a violet color as they are exhausted. A canister should be completely changed when two-thirds of the canister turns violet during use. The absorbent will change back to white when not in use, so it is necessary to make note of the color change during a procedure. Active absorbent will produce heat as it is being used. The violet-colored exhausted absorbent will not produce heat because no chemical reaction is taking place within it. When filling the canister the contents should be shaken gently to settle them so that channeling of gases does not occur and the gas flows evenly throughout the canister. The machine should be pressure-checked after the canister is replaced to make sure it has sealed. Absorbent that is too old and exhausted will not absorb CO2 and could result in elevated inspired CO2. If oxygen tanks are being used, check to make sure that the tanks are not depleted. The last step in preparing the anesthesia machine is to connect the appropriate size of Y-piece and rebreathing bag or nonrebreathing system.
Monitoring equipment should be set up prior to induction and should be checked to make sure that it is working properly. EKG, pulse oximetry, blood pressure (oscillimetric or Doppler instrument), and end-tidal carbon dioxide (ETCO2) are some of the common parameters to monitor. Not every clinic has the same monitoring equipment, but whatever equipment is present should be checked prior to starting a procedure. Turn on the monitor(s), and confirm that the battery is charged or that it is plugged into an outlet. If it is a multifunction monitor, make sure the screen turns on and has every needed function turned on. A Doppler monitor can be checked by placing the probe on a staff member and confirming that it will produce sound with the pulse without static.
Once all of the equipment is checked out, the next step is to prepare for induction. A good method is to dedicate a tray, table, or countertop space on which to lay out all needed supplies for induction (Fig. 5.3).
This space should include all preop medications, induction agents, IV catheters, tape, syringes of heparinized saline, endotracheal tubes, laryngoscope, endotracheal tube tie, lubrication for the endotracheal tube, ophthalmic lubrication, gauze squares, and fluids with appropriate drip sets.
The premedication and induction agents should be drawn up and labeled. Labeling syringes prevents any confusion if the syringes are accidentally moved. Guessing the drug based on the size and volume of the syringe is not good practice because many drugs look alike. If a patient has a reaction after receiving an injection, it is important to know positively what was given so appropriate treatment can be initiated.
The proper endotracheal tube should be chosen for each patient. It is prudent to choose more than one size, usually a size smaller and one larger than the one that is anticipated, in case the first choice does not fit. If the patient has a potential laryngeal mass, has a congenital anatomic abnormality or is a brachycephalic breed, it is best to have many different sizes of endotracheal tubes available as well as a stylet and/or guide tube. Brachycephalic breeds will generally have a much smaller trachea than other breeds of the same size. Always check that the cuffs of the endotracheal tubes do not leak prior to using them. To check the cuffs, use a 5–10 mL syringe and measure the amount of air it takes to inflate the cuff. After 5–10 minutes, deflate the cuff. There should be the same amount of air taken out of the cuff that was put in. If there is not the same amount of air, the cuff has a leak and should not be used. A leaky cuff prevents a good seal between the tube and the trachea. Failing to adequately protect the airway can potentially increase the risk for aspiration and possibly pneumonia. As with any leak, a leaky cuff will make it difficult to maintain a consistent level of anesthesia and will increase waste gas exposure. A sterile water-soluble lubrication jelly should be used to lubricate the endotracheal tube to minimize trauma when passing the endotracheal tube past the arytenoids and into the trachea. Roll gauze or recycled IV tubing may be used to secure the endotracheal tube to the patient and prevent accidental extubation.
Also on the tray are supplies for IV catheterization. First, decide how many IV catheters the patient will require. Patients likely to require transfusions or multiple infusions will need at least two catheters in case of emergency, and potentially an arterial catheter. Include injection caps or t-sets for the catheters. Catheters should be secured with tape or suture.
Arterial catheters should be clearly identified to avoid accidental intra-arterial injections. Bright-colored labels are commercially available for this purpose. Catheters should be flushed with heparinized saline after placement, and several flush syringes should be available on the tray. Some gauze squares are helpful to clean up any blood and also to hold the tongue during intubation. A laryngoscope is very helpful for intubation (especially with cats) but a pen-light will also work. A small syringe with 0.1 mL of 2% lidocaine is very useful to squirt on the cat’s larynx to reduce or eliminate laryngeal spasm.
Anesthetized animals cannot protect their eyes, and certain induction agents can prevent them from closing their eyes, so a mild ophthalmic ointment should be used to lubricate and protect them once the patient is induced.
Prepare the appropriate IV fluids (crystalloid/colloid) and have them ready to connect to the patient. This step will save some time if the patient has a poor response to induction anesthesia and needs immediate resuscitation.
Another important aspect of anesthetic preparation is to prepare for potential emergencies. For example, calculate emergency drug doses for the patient ahead of time. Time is very important during emergency events, and spending even 60 seconds calculating a drug dose can make a difference. Excel worksheets can be designed and stored on the computer so that simply entering the patient’s weight results in a complete printable table of all possible emergency drugs needed in an emergency. Drug doses that should be calculated ahead of time include epinephrine, atropine, calcium gluconate, and lidocaine. These calculations should be written down and kept with the patient or anesthetist. Many practices will have a printed list of emergency drugs and their doses posted in operating rooms and any rooms where anesthesia is performed.
Every practice should also have at least one “crash kit” or “crash cart” (Fig. 5.4). A crash cart can be a toolbox or a larger cart with several drawers on wheels, and it should be equipped with everything needed for cardiopulmonary arrest or other emergencies. The crash cart should include many syringes of different sizes, needles of multiple sizes, crystalloids and colloids, IV catheters, heparin flushes, and emergency drugs. These emergency drugs should always include epinephrine, atropine, and lidocaine. Other drugs that could be in a crash cart are calcium, sodium bicarbonate, vasopressors such as dopamine or norepinephrine, dopram, naloxone (narcotic reversal agent), flumazenil, neostigmine, dextrose, heparin, dexemethasone, and vasopresson. A chart with a list of all the emergency drugs and their doses should also be included. It helps if the crash cart is portable, but there should be at least one crash cart available anywhere there is an anesthesia machine.