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Anesthesia Preparation

Ensure that all equipment and medications deemed necessary for the procedure to be performed are readily accessible and in working order before induction of anesthesia. Regularly ensure proper maintenance and function of all anesthetic equipment. Table 2 provides a convenient maintenance checklist. Have emergency supplies and protocols available before any anesthetic procedure (e.g., tracheal suction; emergency lighting in the event of power failure). Conspicuously post a chart of emergency drug doses or preemptively calculate such doses for each patient. Familiarize yourself with the most current recommendations for cardiopulmonary cerebral resuscitation and stock appropriate drugs. Useful emergency drug dose charts are available in many texts and also from the Veterinary Emergency and Critical Care Societyg.

Prepare a written anesthetic record for each patient, beginning with preparation for the anesthetic event and continuing through the recovery period. Record preanesthetic patient status and all perianesthetic events, including drugs and dosages administered, routes of administration, patient vital signs, events, and interventions. Record resuscitation orders in the anesthetic record at the time consent is obtained. Regularly record patient parameters at 5–10 minute intervals, or more frequently if sudden changes in physiologic status occur. An anesthetic record template is available from AAHAh.

TABLE 2

Anesthetic Equipment Checklist

CO2 absorbent Change the CO2 absorbent regularly based on individual anesthesia machine manufacturer recommendations.
The useful lifespan of absorbent varies with the patient size and fresh gas flow rate.
Color change is not always an accurate indicator of remaining absorption capacity.
Oxygen Ensure supply lines are attached.
Ensure the flowmeter is functioning.
Ensure the supply tank and at least one spare tank is sufficiently full.
To calculate the estimated remaining tank volume, follow this example: An E-cylinder contains 660 L, and has a full-pressure of 2,200 psi. Pressure drop is proportional to remaining O2 volume. A tank with 500 psi has 150 L. When used at a flow rate 1 L/min, it will last approximately 2 ½ hr.22
Endotracheal tubes and masks Have access to various sizes of masks and endotracheal tubes.
Provide a light source such as a laryngoscope.
Check cuff integrity and amount of air needed to properly inflate the cuff.
Breathing system Refer to anesthesia machine’s documentation for proper leak-checking procedures.
Conduct a check before every procedure.
Select the appropriate size and type of reservoir bag and breathing circuit.23
Non-rebreathing systems are generally used in patients weighing less than 5–7 kg or when the work of breathing associated with the circle system might not be easily sustainable by an individual patient.24
Inhalant Ensure vaporizer is sufficiently full.
Waste scavenging equipment Verify a functioning scavenging system.
If using a charcoal absorbent canister, ensure there is sufficient capacity remaining for the duration of the procedure.
Observe all regulations concerning the dispersion of waste anesthesia gases.25,26
Electronic monitoring equipment Ensure devices are operational and either connected to a power source or have adequate battery reserve.
Check alarms for limits and activation.

Patient Preparation

Preparing a patient for anesthesia may include some or all of the following:
  • Inserting an IV catheter and administering IV fluids. This helps to avoid perivascular administration of induction drugs. It facilitates intravascular volume support, which may correct hypovolemia resulting from vasodilation and blood loss that can occur during surgery. It also allows for rapid admin-istration of emergency medications.
  • Connecting monitoring equipment appropriate for the disease condition present and that the patient will tolerate before induction (Table 3).
  • Stabilizing hemodynamically unstable patients, including but not limited to:
    • Administering IV fluid boluses. Hypovolemic patients may require isotonic crystalloids, colloids, and/or hypertonic saline to improve vascular filling, cardiac output, and tissue perfusion.
    • Managing cardiac arrhythmias.
    • Providing blood products. Hypoproteinemia, anemia, or coagulation disorders can aggravate the de-creased delivery of O2 to the tissues that normally occurs as a result of hypoventilation and recumbency.
    • Preoxygenation reduces the risk of hemoglobin desaturation and hypoxemia during the induction process. Preoxygenation is especially beneficial if a prolonged or difficult intubation is expected or if the patient is already dependent on supplemental oxygenation. However, preoxygenation may be contraindicated if it agitates the patient. Removing the rubber diaphragm from the face mask may increase patient tolerance of the mask.29

Once the patient is as stable as possible, proceed according to the individual patient plan.

TABLE 3

Anesthesia Monitoring Tools

  • Electrocardiogram
  • Pulse oximeter (SpO2)
  • Arterial blood pressure monitor
  • Direct intraarterial BP: Most accurate, but technically difficult to perform
  • Noninvasive BP (Doppler or oscillometric monitor): Technically easy, but can be inaccurate.27,28 Evaluate trends in conjunction with other patient parameters. Select cuff width of 40–50% of circumference of limb.
  • Thermometer: Esophageal probe or periodic rectal temperature with conventional thermometer
  • Anesthetic gas analyzer (measures inspired and expired inhalant concentration)
  • Capnometer/capnograph (measures and/or displays CO2 in expired and inspired gas, and respiratory rate)
  • Physical observations
  • Visualization (e.g., eye position, mucous membranes, chest excursion, blood loss, bag volume, and movement with ventilation, equipment function)
  • Palpation (e.g., pulse quality, jaw tone, palpebral reflex)
  • Auscultation (heart, lungs): Precordial or esophageal stethoscope
*BP, blood pressure; SpO2, saturation level of O2.

Anesthetic Induction

Anesthetic induction is best achieved using rapid-acting IV drugs, although this may not always be a reasonable option for fractious patients.30 IV induction allows for rapid airway control and allows for titration of the induction drug to effect within the given dosage range. Sick, debilitated, or depressed patients will require less drug than healthy, alert patients. A patient’s response to preanesthetic drugs can influence the amount and type of induction drug needed.

Mask or chamber inductions can cause stress, delayed airway control, and environmental contamination.31 Adequate room ventilation must be present to minimize exposure to personnel. Reserve these techniques for situations where other alternatives are not suitable.

Ensure endotracheal (ET) tubes and intubation aids (e.g., stylets, laryngoscope) are readily available. Establish and maintain a patent airway using an ET tube as soon as possible. Use the largest-diameter ET tube that will easily fit through the arytenoid cartilages without damaging them; this will minimize resistance and the work of breathing. Insert the ET tube such that the distal tip of the tube lies midway between the larynx and the thoracic inlet. Applying a light coating of sterile lubricating jelly improves the cuff’s ability to seal the airway against fluid migration.32

Inflate the cuff sufficiently to create a seal for adequate positive pressure ventilation, being aware that overinflation may cause tracheal damage.33 When changing the patient’s position after intubation, take care not to rotate the ET tube within the trachea. This might induce tracheal tears, especially if the cuff is relatively overinflated. The American Veterinary Medical Association (AVMA) Professional Liability Insurance Trust (PLIT) has indicated that tracheal tears are a significant issue in anesthetized intubated catsi.34 However, tracheal intubation, when properly performed and maintained, is an essential part of maintaining an open and protected airway.

Apply corneal lubricant postinduction to protect the eyes from corneal ulceration.

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