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newSchoolWorks.com › VoTechWorks › Health & Personal Services › Veterinary Technology / Vet Assistant › Veterinary Anesthesia: Patient Preparation, Monitoring, and Recovery › Lesson 6
HLT-VET42-05 · Lesson 6 · 24 clock hours · demo

Induction Agents and Intubation Assistance

Objective. Students will describe the action of common injectable induction agents, select an appropriately sized endotracheal tube for a given patient, and assist a veterinarian or credentialed technician during endotracheal intubation on a model or cadaver.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Induction Agents and Intubation Assistance

Anesthetic induction is the transition from a conscious, sedated state to unconsciousness deep enough to allow endotracheal intubation. As a veterinary assistant, you will not administer induction agents — that is within the scope of a licensed veterinarian or a credentialed veterinary technician working under veterinary supervision. However, you must understand how these drugs work, recognize their risks, and be ready to assist efficiently the moment induction begins.

Common Injectable Induction Agents

Propofol is a short-acting, lipid-emulsion hypnotic widely used in dogs and cats. It works quickly (onset within about 30–60 seconds after IV injection) and recovery is smooth because it is rapidly metabolized. Disadvantages include apnea (temporary cessation of breathing) if given too fast, cardiovascular depression, and pain on injection in some patients. Because propofol does not provide analgesia, it is almost always preceded by premedication with opioids or other pain-control agents. Monitor heart rate, respiratory rate, and mucous membrane color immediately after induction.

Alfaxalone is a neuroactive steroid that also produces rapid, smooth induction and recovery in dogs and cats. It has a somewhat wider margin of cardiovascular safety than propofol in many patients and causes less pain on injection. Like propofol, it provides no analgesia and can cause apnea if administered too rapidly. Alfaxalone is also used in exotic and zoo species.

Ketamine combinations (ketamine is almost always combined with a benzodiazepine such as diazepam or midazolam) produce a dissociative anesthetic state. The patient may keep its eyes open and maintain some muscle tone — this is normal and not a sign of inadequate depth. Ketamine raises heart rate and blood pressure, making it useful in hemodynamically compromised patients. It is not appropriate as a sole agent because it increases muscle tone and can cause seizure-like activity without a benzodiazepine. Recovery can be longer than with propofol or alfaxalone.

Telazol (tiletamine–zolazepam) is a pre-mixed dissociative/benzodiazepine combination available as a powder reconstituted with sterile water. It is often used for patients that are difficult to handle or for field situations because it can be given intramuscularly. Recovery is prolonged compared to propofol or alfaxalone, and it is not reversible. Use is common in wildlife and exotic medicine.

Why Intubation Matters

Endotracheal intubation places a tube into the trachea so that:

Failure to confirm correct tube placement is a life-threatening error. A tube placed in the esophagus delivers no oxygen and no anesthetic — the patient will wake up or suffocate. Confirm placement every time by watching bilateral chest rise, feeling warm exhaled air, and using a colorimetric capnograph indicator or capnograph waveform showing exhaled CO₂.

Selecting the Correct Endotracheal Tube

Endotracheal tubes (ET tubes) are sized by their internal diameter in millimeters. A general guideline is that the correct tube should pass easily into the trachea with little resistance, and after cuff inflation no air should leak around the tube at normal ventilation pressures.

For most dogs, tube sizes range roughly from 6 mm (toy breeds) to 14 mm (large breeds). For most cats, sizes in the 3–5 mm range are common. Always have one size smaller and one size larger available on your tray. Using a tube that is too large risks tracheal injury; using one that is too small allows anesthetic gas to leak and does not adequately protect the airway.

Cuff inflation: Inflate the cuff slowly using the cuff inflator with manometer. Standard practice is to inflate just until the air leak disappears when the reservoir bag is gently squeezed — do not over-inflate. Excessive cuff pressure damages tracheal mucosa. A manometer helps maintain cuff pressure within a safe range (follow the veterinarian's or technician's direction and your facility's protocol).

Your Role During Intubation

When a veterinarian or credentialed technician is intubating, the assistant's job is to work as a smooth, silent partner:

1. Position the patient in sternal or dorsal recumbency as directed.

2. Extend the neck gently to straighten the airway — hold the muzzle and extend the head back, but do not hyperextend.

3. Open the mouth by placing your thumb on the lower jaw and pulling gently downward.

4. Provide the laryngoscope with blade in place and light confirmed on before handing it over.

5. Pass the ET tube handle-first when asked, keeping the tube clean.

6. Inflate the cuff promptly after the tube is placed and the technician signals.

7. Secure the tube with umbilical tape tied around the tube and then behind the patient's head or around the muzzle, following your facility's method.

8. Confirm placement by watching for chest rise and observing the capnograph.

9. Connect to the breathing circuit only after placement is confirmed.

10. Document the tube size used in the anesthesia record.

Safety Points

Key terms10

Induction agentAn injectable drug used to rapidly bring a patient from a sedated or conscious state to unconsciousness suitable for endotracheal intubation and maintenance of anesthesia.
PropofolA short-acting lipid-emulsion induction agent that provides rapid onset and smooth recovery but can cause apnea, cardiovascular depression, and provides no analgesia.
AlfaxaloneA neuroactive steroid induction agent used in dogs, cats, and exotic species; offers smooth induction and recovery with relatively good cardiovascular stability but no analgesia.
Dissociative anesthesiaA state produced by agents such as ketamine or tiletamine in which the patient is unconscious but may retain muscle tone and open eyes; a benzodiazepine is required to prevent unwanted muscle activity.
Endotracheal tube (ET tube)A flexible tube inserted into the trachea to maintain a patent airway, deliver oxygen and inhalant anesthetic, protect against aspiration, and allow mechanical ventilation.
Cuff inflationThe process of gently filling the balloon on a cuffed ET tube with air until an airtight seal is formed around the trachea, preventing gas leaks and aspiration; over-inflation can injure the tracheal mucosa.
CapnographyMonitoring of exhaled carbon dioxide concentration; confirms correct endotracheal tube placement in the trachea (not the esophagus) and reflects the patient's ventilation and circulatory status.
ApneaTemporary cessation of breathing; a recognized risk immediately following administration of induction agents, requiring prompt recognition and, if prolonged, ventilatory support.
LaryngoscopeAn instrument with a handle and lighted blade used to visualize the larynx and vocal cords during intubation, allowing accurate placement of the endotracheal tube.
Scope of practiceThe legally and professionally defined boundaries of tasks a person with a given credential may perform; veterinary assistants must not administer controlled or prescription drugs or perform procedures reserved for licensed veterinarians or credentialed technicians.

Worked examples4

1. You have a mixed-breed dog whose trachea on the model measures approximately 14 mm in external diameter. The ET tube trays have sizes 7.0, 8.0, 9.0, and 10.0 mm internal diameter. Which size should you select first, and which backup sizes should you place on the tray?
  1. Recognize that ET tube size refers to internal diameter (ID), not tracheal external diameter. The tube must fit inside the trachea with room for the cuff to seal without over-distending the airway.
  2. A common clinical rule of thumb for dogs is to estimate tube ID as roughly 20–25% smaller than the measured tracheal external diameter: 14 mm × 0.75 = 10.5 mm, which rounds to a 10.0 mm tube as the first-choice starting size.
  3. Place one size smaller (9.0 mm) and one size larger (if available) on the tray as backups in case resistance is met or a leak cannot be sealed.
Answer: Select the 10.0 mm ID tube as the primary choice; have 9.0 mm ready as a smaller backup. Always defer to the supervising technician's or veterinarian's final size decision based on patient anatomy.
2. A cat is being induced and the technician asks you to prepare a tube. The feline mannequin trachea measures approximately 6 mm external diameter. Available tubes are 2.5, 3.0, 3.5, 4.0, and 4.5 mm ID. Which tube do you hand first?
  1. Apply the same estimate: 6 mm × 0.75 = 4.5 mm. This is the largest tube on the tray.
  2. However, cats are prone to laryngospasm and tracheal trauma. A 4.5 mm may be too snug for some cats with a 6 mm external tracheal diameter. Clinical practice commonly uses 3.0–4.5 mm for average adult cats.
  3. Present the 4.0 mm tube as the primary option and keep 3.5 mm and 4.5 mm within easy reach; confirm with the supervising technician before passing the tube.
Answer: Hand the 4.0 mm ID tube first with 3.5 mm and 4.5 mm ready as backups; follow the supervising technician's direction.
3. After placing a cuffed ET tube, you inflate the cuff. The supervising technician gently squeezes the reservoir bag to about 20 cm H₂O and you still hear a hiss of air escaping around the tube. What should you do?
  1. A leak at normal ventilation pressure means the cuff is under-inflated or the tube is too small.
  2. Add a small amount of air to the cuff using the cuff inflator, then re-test by having the technician squeeze the bag again while you listen near the patient's mouth and throat.
  3. If the leak stops, the cuff is now sealed. If the leak persists after adding reasonable air volume, alert the technician — the tube may be too small and a larger size should be tried.
  4. Do not over-inflate trying to seal a consistently leaking cuff; notify the supervising clinician.
Answer: Add a small increment of air to the cuff, re-test for the leak, and if leaking continues after reasonable inflation, notify the supervising technician that a larger tube may be needed.
4. You connect the ET tube to the breathing circuit and watch the patient. The capnograph shows a flat line (no CO₂ detected) and the chest is not rising when the reservoir bag is squeezed. What is the most likely problem and what do you do?
  1. A flat capnograph line with no chest rise strongly suggests esophageal intubation — the tube is in the esophagus, not the trachea.
  2. Immediately alert the supervising veterinarian or credentialed technician. Do not continue ventilating through an esophageally placed tube.
  3. Disconnect from the circuit. The clinician will remove and reposition the tube into the trachea.
  4. Once the tube is repositioned, confirm placement again: watch for bilateral chest rise, feel for warm exhaled air at the tube connector, and look for a normal CO₂ waveform on the capnograph before reconnecting.
Answer: Suspect esophageal intubation; immediately notify the supervising clinician so the tube can be repositioned. Never ignore a flat capnograph line — this is a patient safety emergency.

The math in this lesson1

Learners estimate ET tube size as 75% of a 14 mm tracheal diameter, about 10.5 mm, rounded to 10.0 mm.
7.RP.3
Brush up in the math halls at newSchoolWorks.com:
In class: Lecture and video review covering injectable induction agents (propofol, alfaxalone, telazol combination, and ketamine combinations) including advantages, disadvantages, and monitoring priorities for each. · Hands-on sizing exercise: students measure the tracheas of canine and feline mannequins/models, select ET tube sizes from a tray, inflate cuffs, confirm seal by listening for air leak, and document size chosen. · Intubation assistance simulation: instructor or credentialed technician intubates a canine model; students take turns positioning the patient, extending the neck, providing laryngoscope light, passing the tube on request, inflating the cuff, and confirming tube placement by watching chest rise and using a capnograph trainer.
Materials: Canine and feline intubation training models or preserved cadavers; endotracheal tubes (multiple sizes, cuffed and uncuffed); laryngoscopes with multiple blade sizes; cuff inflator with manometer; capnograph trainer or indicator; 12-mL syringe; umbilical tape for tube ties; printed induction agent comparison chart
Check: Skills checklist (10 steps) evaluated by instructor on intubation assistance simulation; correct tube size selection and cuff inflation technique required; pass mark 80%, with zero tolerance for failure to confirm tube placement.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Anesthesia and Pharmacology
1. Which of the following best describes a key advantage of propofol as an induction agent?
Anesthesia and Pharmacology
2. A patient induced with ketamine–diazepam keeps its eyes open and retains some muscle tone during induction. The supervising technician is unconcerned. Why is this expected?
Professional and Legal Responsibilities
3. Which action is outside the scope of practice for a veterinary assistant during the induction phase of anesthesia?
Anesthesia Monitoring and Patient Safety
4. After intubation, the capnograph shows a flat line and no chest rise is observed when the reservoir bag is squeezed. What is the most likely explanation?
Anesthesia and Patient Safety
5. When selecting an endotracheal tube, a student is choosing between sizes 7.0 mm and 9.0 mm for a medium-sized dog. She selects the 9.0 mm tube, but it meets resistance and will not pass easily. What is the safest next step?
Anesthesia and Pharmacology
6. Telazol is most commonly chosen over propofol in which of the following clinical scenarios?
Anesthesia Monitoring and Patient Safety
7. Which step should be completed immediately before connecting the endotracheal tube to the anesthetic breathing circuit?
Anesthesia and Patient Safety
8. Over-inflation of an endotracheal tube cuff is most likely to cause which complication?
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