Anesthesia Free guide

Anesthetic Monitoring: Depth, Vital Parameters and the Anesthetic Record

Anesthesia (D7 F; K42) 14 min read, 3,164 words Last verified

How the veterinary technician judges anesthetic depth from eye position, reflexes and jaw tone, which vital parameter values need action, and how often to check and record, with sourced AAHA, ACVA and AAFP targets.

Introduction

Anesthetic monitoring is the job of watching an unconscious patient closely enough to catch a problem before it hurts the animal. The ACVA guidelines ask for a veterinarian, technician or other responsible person to stay with the patient, and in many practices that person is the credentialed veterinary technician.2 As the anesthetist you check depth, measure vital signs, read the monitors, write the anesthetic record and tell the veterinarian when something changes. The 2020 AAHA guidelines state that monitoring decreases the odds of anesthetic death, and that both electronic monitors and hands-on assessment by the anesthetist should be used.1

This guide covers the stages and planes of anesthesia, the reflexes and eye signs used to judge depth, the target ranges for each vital parameter, how often to check and record, and what the record must contain. Capnogram shapes and complication management have their own guides.

Key facts

  • AAHA defines a surgical plane as an absent palpebral reflex, mild jaw tone and no purposeful movement.1
  • In dogs and cats the eye rotates ventromedially (down and toward the nose) at a light to medium surgical plane, then returns to center as anesthesia deepens.36 In horses a central eye is normal under anesthesia.8
  • The corneal reflex should always be present. Losing it means the patient is too deep.35
  • AAHA hypotension: systolic below 80 to 90 mm Hg, mean below 60 to 70 mm Hg, or diastolic below 40 mm Hg.1
  • AAHA hypoxemia: SpO2 below 95%; severe below 90%. Start positive pressure ventilation if EtCO2 is above 60 mm Hg.1
  • AAHA hypothermia: core temperature below 98 °F (36.7 °C).1
  • ACVA: record monitored variables at least every 5 to 10 minutes. If no one can stay with the patient, check it at least every 5 minutes.2
  • AAHA reports that 47% of anesthetic-related deaths in dogs and 60% in cats happen in the postoperative period, most within the first 3 hours, so monitoring continues through recovery.1

How the VTNE tests this

  • Judge depth from a list of signs (eye position, palpebral and corneal reflexes, jaw tone, movement) and pick the stage or plane. Domain 7 Task F, "Monitor and respond to patient status during all stages of anesthesia"; K42 includes "stages of anesthesia and troubleshooting".10
  • Interpret a number: is this heart rate, blood pressure, SpO2, EtCO2 or temperature acceptable for an anesthetized dog, cat or horse?
  • Choose the response: turn the vaporizer down, tell the veterinarian, ventilate, warm, or recheck the equipment.
  • Record keeping: what goes on the anesthetic record and how often.
  • Calculate: mean arterial pressure from systolic and diastolic values, or blood pressure cuff width from limb size.

Core concepts

Stages and planes

The classic scheme comes from Guedel's 1937 description of ether anesthesia in cats. It has four stages, and stage III is split into planes.3 Modern drug combinations blur the classic signs, so many anesthetists now simply talk of "awake" and "unconscious" and read many signs together.3 The VTNE still uses the stages, so learn them.

Table 1. Stages and planes of general anesthesia
Stage or planeWhat you seeTechnician focus
Stage I: voluntary movementFrom the first drug to loss of consciousness. The patient may struggle. Heart rate may rise and pupils may dilate. Some species urinate, defecate or salivate.Quiet handling. Have the airway and induction drug ready.
Stage II: involuntary movement (excitement)Unconscious but reacts strongly to stimuli. Paddling, vocalizing, breath holding or fast shallow breaths, fast or irregular heart rhythm, very dilated pupils. Palpebral reflex present. Vomiting may occur.Move through it quickly. Protect the patient and staff from injury.
Stage III, plane 1: lightLasts until eye movement stops. Withdrawal reflexes may still be present.Too light for surgery. Expect movement if stimulated.
Stage III, plane 2: medium (surgical)Regular breathing and pulse. Slow or absent palpebral reflex, strong corneal reflex, no laryngeal reflex, good muscle relaxation.The target for most surgery. Keep recording and watch trends.
Stage III, planes 3 and 4: deepFalling tidal volume and breathing rate, low blood pressure, marked muscle relaxation, weak corneal reflex, dilated pupils.Too deep. Tell the veterinarian and lighten the plane.
Stage IV: overdoseBreathing stops, the heart beats only briefly, very low blood pressure, very slow capillary refill, widely dilated pupils, no reflexes or muscle tone.Emergency. Turn the anesthetic off, ventilate with oxygen, start CPR as directed.

Source: University of Wisconsin RARC, Stages of Inhalant Anesthesia5; Lee, Anesthetic Monitoring (Guedel's signs).3

Depth signs and how far to trust them

Lee ranks the signs. The most reliable are purposeful movement, reflex movement to stimulation, and a sudden rise in heart rate, blood pressure or breathing when the patient is stimulated (including clipping, prepping and draping). Reliable signs include the vaporizer setting history, jaw tone, the pupillary light reflex, the palpebral and corneal reflexes, a moist cornea and eye position. Heart rate and respiratory rate alone are less reliable, because each can rise or fall as anesthesia deepens.3

  • Palpebral reflex: touch the medial canthus and watch for a blink.11 It varies between species. A dog may have no palpebral reflex at adequate surgical depth.3
  • Corneal reflex: does not disappear until anesthesia is deep and should always be present.3
  • Jaw tone: moderate to loose jaw tone is the desirable finding.3 A jaw that is hard to open means the patient is awake or light.9
  • Eye position: medioventral (ventromedial) eye position is the desirable position in most species, with horses the exception.3 In dogs given propofol, Ribeiro and colleagues saw the eye centered at the lightest plane, rotated while the palpebral reflex faded, and centered again at the deeper planes, with the corneal reflex lost last.6 A central eye therefore means either light or deep. Check the other signs to tell which.
  • Nystagmus and tears: usually mean a light plane. Ketamine is the exception: it causes nystagmus at moderate depth.3
Eye position in a dog or cat by depth of anesthesia: central when light, rotated down and toward the nose at a surgical plane, central with a dilated pupil when deep Left eye of a dog seen from the side (nose to the left) Light Stage II to Stage III plane 1 Eye central Brisk palpebral Jaw tone firm Nystagmus or tears possible Surgical Stage III plane 2 Eye rotated down and toward the nose Palpebral slow or absent Corneal present Jaw tone mild Too deep Stage III planes 3 and 4, Stage IV Eye central again Pupil dilated No palpebral Corneal weak or absent Jaw flaccid A central eye means light or deep: check the palpebral reflex, jaw tone and pupil size to decide.
Figure 2. Eye position by depth of anesthesia in a dog or cat. The eye is central when the patient is light, rotates down and toward the nose at a surgical plane, and returns to center with a dilated pupil when the patient is too deep. Horses are different: a central eye is normal at a surgical plane. Drawn from the planes described by Ribeiro and colleagues, the UW RARC stages and Lee's monitoring notes.

The vital parameters

The ACVA guidelines group monitoring into circulation, oxygenation, ventilation and temperature.2 AAHA lists respiratory rate, SpO2 (the percentage of hemoglobin saturated with oxygen) and EtCO2 (end-tidal carbon dioxide) for breathing, and blood pressure, heart rate and rhythm (ECG), capillary refill time, mucous membrane color and pulse oximetry for circulation.1

Table 2. Anesthetized dog and cat: targets and action thresholds
ParameterAcceptable under anesthesiaTell the veterinarian when
Heart rate, dogNo single range in AAHA. Watch the trend from baseline.Below 60 beats/min (Lee). Above 150 beats/min in large dogs or 190 beats/min in small dogs (AAHA).
Heart rate, cat100 to 180 beats/min (AAFP)Below 100 beats/min, which may lower cardiac output even with normal blood pressure; above 180 beats/min.
Blood pressureSystolic 90 to 120 mm Hg and diastolic 55 to 90 mm Hg (Lee)Systolic below 80 to 90, MAP below 60 to 70 or diastolic below 40 mm Hg. Hypertension: MAP above 120 to 140 or systolic above 160 to 180 mm Hg.
SpO295% or higher on 100% oxygenBelow 95% (hypoxemia); below 90% is severe.
EtCO2About 40 to 50 mm Hg (up to 55) at a surgical plane; 35 to 45 mm Hg awakeRising trend; above 60 mm Hg needs positive pressure ventilation.
Temperature98 °F (36.7 °C) or higherBelow 98 °F (36.7 °C), or a falling trend. Warm early.
Respiratory rateRead with EtCO2. Rate alone does not show how well air moves.Apnea, a falling trend, or a sudden rise when stimulated.
CRT and mucous membranesPink; a prolonged CRT suggests poor perfusion.Pale, grey or blue membranes or slow CRT. Cyanosis appears late, at an SpO2 of about 70 to 80%.

Sources: AAHA 2020 Anesthesia and Monitoring Guidelines1; AAFP Feline Anesthesia Guidelines4; Lee, Anesthetic Monitoring3 and Anesthesia Emergencies and Accidents.7 The veterinarian may set different limits on the anesthetic plan for a sick patient.

Notes on each parameter

  • Heart rate. A fast rate is not proof of a light plane. AAHA asks the anesthetist to rule out a noxious stimulus, hypoxemia, hypercarbia (high carbon dioxide) and hypovolemia, and to remember that alfaxalone, ketamine, atropine and dopamine can raise heart rate.1 Slow rates can come from deep anesthesia, increased vagal tone (brachycephalic breeds, opioids) or vagal stimulation such as a distended bladder, handling of the viscera or the oculocardiac reflex.7
  • Pulse. Compare the pulse with the heart rate. A pulse that does not match the heart rate on Doppler or the SpO2 waveform points to an arrhythmia.1
  • Blood pressure. Below a mean arterial pressure (MAP) of 60 mm Hg, organ and tissue perfusion is inadequate.3 A Doppler flow detector measures systolic pressure and works in patients of all sizes. Oscillometric monitors are automated but less accurate in small patients. Direct arterial pressure is the gold standard and gives beat-to-beat readings.34 Cuff width should be about 40% of limb or tail circumference.4
  • SpO2. An SpO2 of 90% matches an arterial oxygen pressure of about 60 mm Hg, the usual definition of hypoxemia.3 Readings are disturbed by motion (shivering), ambient light, poor blood flow from hypotension or vasoconstriction, and electrocautery.3 Before you blame the probe, confirm the patient is intubated, connected and receiving oxygen.1
  • EtCO2. End-tidal CO2 estimates arterial CO2 and shows ventilation breath by breath.3 If it climbs, first make sure the patient is not too deep by checking the vaporizer setting and the depth signs.1
  • Temperature. Hypothermia slows drug metabolism and prolongs recovery. Circulating warm-water blankets and warm air systems work best. Never use heat sources not designed for anesthetized patients, because they can cause severe burns.1

Procedure: monitoring from induction to recovery

  1. Before induction. Record the preanesthetic physical exam findings, including heart rate, respiratory rate and temperature, and compare them with earlier visits.4 Start the anesthetic record. AAHA lists an anesthesia record and patient-specific emergency drug calculations as preparation steps.1
  2. Induction and intubation. Give induction drugs to effect.9 Confirm tube placement by seeing the tube between the arytenoids, condensation in the tube, bag movement or an EtCO2 waveform. Apply eye lubricant after induction and every 2 to 4 hours.1
  3. Attach the monitors. Pulse oximeter probe on the tongue, ear, lip folds, toe pads, axillary or inguinal skin fold, prepuce or vulva; ECG leads; blood pressure cuff; capnograph adapter; temperature probe.3
  4. Check the patient first. When an alarm sounds, look at the patient before the machine. Is it breathing? Is the heart beating? Is there a pulse?9
  5. Assess depth with several signs. Eye position, palpebral reflex, jaw tone and the response to stimulation, never one sign alone.3
  6. Record at regular intervals. At least every 5 to 10 minutes (ACVA).2 AAFP recommends at least every 15 minutes for cats and notes that every 5 minutes shows change better.4 Recording is not the whole job: stay aware between entries.9
  7. Watch trends. A heart rate still inside the normal range but falling steadily for 15 minutes can mean too much anesthetic.9
  8. Report and act within your role. Tell the veterinarian about any value outside the plan's limits. Follow standing orders for the vaporizer, fluids and ventilation.
  9. Recovery. Keep monitoring heart rate, respiratory rate, SpO2, blood pressure and temperature. Extubate when breathing and SpO2 are normal and the patient swallows strongly. Stay with the patient until it is alert, normothermic and ambulatory (unless it was not ambulatory before).1

The anesthetic record

The record is a legal document and a monitoring tool. It shows trends early and shows how the patient responded to each intervention.2 To be admissible it must be contemporaneous, meaning written at the time the anesthetic was given.3

  • Every drug given in the peri-anesthetic period and early recovery, with dose, time and route, and any adverse reaction.2
  • Heart rate and respiratory rate at a minimum, plus oxygenation and blood pressure if monitored.2
  • IV catheter size and site, endotracheal tube size, fluid rate and total volume, and the quality of sedation, induction and recovery.4
  • Heart rate, respiratory rate and temperature in early recovery, and any unusual event, both for legal reasons and for the patient's next anesthetic.2
Example anesthetic record grid with values recorded every 5 minutes, showing heart rate and blood pressure rising at the skin incision Patient: Max, canine, 24 kg, ASA II OHE; ET tube 9.0 mm cuffed; IV 20 G right cephalic Premed 08:40 and induction 09:00: drug, dose (mg and mL), route Time 09:05 09:10 09:15 09:20 09:25 09:30 HR /min 9288124969086 RR /min 121018121010 SpO2 % 999998999999 EtCO2 424440444646 MAP mm Hg 787496807674 Temp °F 100.4100.199.999.799.599.4 Iso % 2.01.752.02.01.751.75 Depth VM, P-VM, P-VM, P+VM, P-VM, P-VM, P- Events 09:12 Incision: HR, RR, MAP rise. Vet told; iso to 2.0%, analgesic bolus as ordered. Values settle by 09:20. Key: VM = eye ventromedial; P- = no palpebral; P+ = palpebral present
Figure 3. An example anesthetic record grid with entries every 5 minutes. The dashed box shows a sudden rise in heart rate, breathing and blood pressure at the skin incision, one of the most reliable signs that the plane is too light for the stimulus. The slow fall in temperature is a trend to act on before it crosses the 98 °F hypothermia line. Original diagram with invented values; it is not the AAHA record form.

Flowchart: too light or too deep?

Decision tree: is the anesthetized patient too light or too deep, and what the technician does next Alarm, value change or movement Look at the patient before the machine Breathing, heartbeat and pulse all present? Check chest or bag, Doppler, pulse No Yes Emergency Call the veterinarian, vaporizer off, ventilate with oxygen, CPR per plan Signs of a light plane? Brisk palpebral, firm jaw, tears, swallowing, movement, nystagmus, or HR, RR and BP jump with stimulation No Yes Too light Tell the veterinarian. Deepen or give analgesic as ordered. Rule out pain, low SpO2, high EtCO2, hypovolemia. Reassess. Signs of a deep plane? Central eye with dilated pupil, flaccid jaw, weak corneal, falling HR, BP or breathing No Yes Too deep Turn the vaporizer down. Tell the veterinarian. Support breathing and BP as ordered. Reassess. Surgical plane Eye ventromedial, slow or absent palpebral, corneal present, mild jaw tone Values within plan limits? Yes Continue Record every 5 to 10 min. Watch trends. If a value is out of range, tell the vet.
Figure 1. Is the patient too light or too deep? Always confirm breathing, heartbeat and pulse first. Then read several depth signs together, because no single sign is reliable on its own. Every branch ends in an action and a reassessment, and the veterinarian is told whenever the plane or a value is outside the anesthetic plan. Built from Lee's depth signs, the UW RARC stages, the AAHA surgical plane definition and the VASG basics.

Species differences

  • Dog. The palpebral reflex may be absent at adequate surgical depth, so it cannot be used alone.3 Lee treats a heart rate below 60 beats/min as bradycardia.7
  • Cat. Normal anesthetized heart rate is 100 to 180 beats/min. Cats are sensitive to the cardiovascular and breathing depression of inhalants, and hypotension is common even in healthy cats on short procedures, so AAFP recommends recording blood pressure trends for every cat under general anesthesia. An esophageal stethoscope is the most reliable way to follow heart rate in cats; the ECG is the least reliable because the signal is often poor in small patients.4
  • Small patients. Oscillometric blood pressure is less reliable in patients under about 5 kg. A Doppler works on any size, from a rat to a horse.3
  • Horse. At a surgical plane the eye is central, the palpebral reflex is sluggish and the corneal reflex is strong. Complete loss of the palpebral reflex means moderately deep anesthesia.38 Nystagmus usually means a light plane, but in horses severe hypoxia or hypercapnia can also cause it, so do not deepen the anesthetic without checking oxygenation.3 Lee lists a heart rate below 24 beats/min, MAP below 60 mm Hg and respiratory rate below 4 breaths/min as potentially life-threatening, and aims to keep MAP above 60 mm Hg, or 70 mm Hg in heavily muscled breeds.8
  • Staffing. ACVA recommends a person dedicated only to the anesthetized patient for all ASA III, IV and V patients, and for horses on inhalants or anesthetized for longer than 45 minutes.2

Calculation

1. Mean arterial pressure. An oscillometric monitor shows 96/45 mm Hg but no mean. MAP = diastolic + (systolic minus diastolic) / 3.3

MAP = 45 mm Hg + (96 mm Hg minus 45 mm Hg) / 3 = 45 mm Hg + 51 mm Hg / 3 = 45 mm Hg + 17 mm Hg = 62 mm Hg. That is inside the AAHA hypotension band (MAP below 60 to 70 mm Hg), so tell the veterinarian and check depth.1

2. Blood pressure cuff width. A cat's forelimb measures 7.5 cm around at the cuff site. The cuff width should be about 40% of the circumference.4

7.5 cm × 0.40 = 3.0 cm cuff width. Choose the cuff closest to 3 cm.

  • Never leave the patient unwatched. ACVA's ideal is a veterinarian, technician or other responsible person dedicated to that patient only. If that is not possible, someone knowledgeable checks at least every 5 minutes, with audible heart and breathing monitors.2
  • The record is legal evidence. Write it as you go, with times. Record any untoward event.23
  • Heavy sedation needs monitoring too. A sedated patient that loses control of its protective airway reflexes should be monitored as under general anesthesia, with oxygen, an endotracheal tube and IV catheter materials ready. Brachycephalic breeds are at particular risk of airway obstruction.2
  • Burns. Use only warming devices made for anesthetized patients.1
  • Know your limit. If you do not know what to do, ask the veterinarian.9 Treatment decisions use both the monitors and your hands-on assessment.1
  • Client education. AAHA sets the goal that owners feel confident the team has the compassion, skills and technology to provide the safest possible anesthesia. Explain that the patient is monitored through recovery, and send home written anesthetic discharge instructions.1

Common mistakes and exam traps

  • "Central eye means awake." A central eye with a dilated pupil, no palpebral reflex and a flaccid jaw means too deep. Read the other signs.569
  • Treating the number, not the patient. Check the patient before the monitor, and confirm a strange reading with a second method, such as Doppler for an odd oscillometric value.19
  • Turning up the vaporizer for tachycardia or hypertension. Rule out pain, hypoxemia, hypercarbia and hypovolemia first. AAHA advises against raising the vaporizer to lower blood pressure.1
  • Trusting pink gums. Mucous membrane color is not a sensitive sign of hypoxemia; cyanosis appears late.14
  • A slipped cuff. A blood pressure cuff that has slid down toward the carpus gives a false reading. Check cuff position before reporting hypertension.1
  • Stopping at extubation. About half of anesthetic-related deaths in dogs (47%) and more than half in cats (60%) happen after the procedure, most within the first 3 hours.1

Quick review

  1. Stage I is voluntary movement; Stage II is involuntary excitement; Stage III is surgical anesthesia; Stage IV is overdose.
  2. Stage III plane 2 (medium) is the target for most surgery.
  3. Surgical plane in dogs and cats: eye ventromedial, slow or absent palpebral, corneal present, mild jaw tone, no movement.
  4. A central eye means light or deep; a dilated pupil and absent reflexes mean deep.
  5. Loss of the corneal reflex means too deep.
  6. The most reliable depth sign is the response to stimulation: movement or a jump in HR, BP or breathing.
  7. AAHA hypotension: MAP below 60 to 70 mm Hg or systolic below 80 to 90 mm Hg.
  8. SpO2 below 95% is hypoxemia; below 90% is severe.
  9. EtCO2 at a surgical plane is about 40 to 50 mm Hg; above 60 mm Hg, ventilate.
  10. Hypothermia is below 98 °F (36.7 °C).
  11. Record at least every 5 to 10 minutes; drugs with dose, time and route.
  12. Horses keep a central eye at a surgical plane.

Test yourself

5 questions written for this guide. Pick an answer, then check it.

Question 1A 28 kg dog is on isoflurane for cruciate surgery. The eyes are rotated ventromedially, the palpebral reflex is slow, the corneal reflex is present and jaw tone is mild. Heart rate and blood pressure did not change at the skin incision. What is the best action?

Show answer

Answer: C. Keep the current setting and continue recording and watching trends

C is right: ventromedial eyes, a slow palpebral reflex, a present corneal reflex, mild jaw tone and no response to incision describe a surgical plane, so the job is to keep monitoring and recording. A is wrong: a slow or even absent palpebral reflex is expected at surgical depth, and there was no response to stimulation. B is wrong: ventromedial rotation is the desirable eye position in dogs, not a sign of overdose. D is wrong: eye rotation is a depth sign, not a vagal sign, and the heart rate is stable.

Source 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats, Step 4d Anesthetic Maintenance, AAHA

Question 2An oscillometric monitor on an anesthetized dog displays 84/42 mm Hg but no mean value. Using MAP = diastolic + (systolic minus diastolic) / 3, what is the MAP and how should it be handled?

Show answer

Answer: B. 56 mm Hg, which is hypotension to report to the veterinarian

B is right: 42 + (84 minus 42) / 3 = 42 + 14 = 56 mm Hg. AAHA defines hypotension as a MAP below 60 to 70 mm Hg, and perfusion is inadequate below 60 mm Hg, so tell the veterinarian and check depth. A is wrong: 63 comes from averaging the two numbers, which overweights systole. C is wrong: 42 is the diastolic value, not the mean, and a reading means there is blood flow. D is wrong: 70 mm Hg is not the result of the formula.

Source Anesthetic Monitoring, Arterial blood pressure, Lee L, Western University of Health Sciences

Question 3According to the ACVA monitoring guidelines, which anesthetic record entry for a drug given during anesthesia is complete?

Show answer

Answer: D. The drug name, dose, time and route of administration

D is right: the ACVA guidelines say to record every drug given in the peri-anesthetic period and early recovery with the dose, time and route, plus any adverse reaction. A is wrong: it leaves out dose and route. B is wrong: a volume without the dose and route does not meet the recommendation. C is wrong: the weight belongs on the record, but the entry still lacks dose and time.

Source ACVA Monitoring Guidelines Update 2009, Record Keeping, American College of Veterinary Anesthesiologists

Question 4An intubated cat breathing 100% oxygen has pink mucous membranes, but the pulse oximeter reads 89% with a steady waveform. What should the technician do first?

Show answer

Answer: A. Check breathing, tube placement and oxygen supply, then tell the veterinarian

A is right: an SpO2 below 90% is severe hypoxemia by the AAHA definition, and AAHA says to verify intubation, connection and oxygen supply before troubleshooting the probe. B is wrong: cyanosis is not visible until SpO2 falls to about 70 to 80%, so pink gums do not rule out hypoxemia. C is wrong: a steady waveform suggests a good signal, and waiting 15 minutes delays treatment. D is wrong: low SpO2 is not a depth sign, and deepening a hypoxemic cat can make it worse.

Source 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats, Respiratory System Complications, AAHA

Question 5A technician who usually works with dogs is helping with equine anesthesia. Which eye findings fit an appropriate surgical plane in a horse?

Show answer

Answer: C. Eye central, palpebral sluggish, corneal reflex strong

C is right: Lee's equine monitoring notes list a central eye, a sluggish palpebral reflex and a strong corneal reflex, and the horse is the exception to the ventromedial eye seen in most species. A is wrong: complete loss of the palpebral reflex in a horse indicates moderately deep anesthesia. B is wrong: nystagmus usually means a light plane, and in horses it can also come from severe hypoxia or hypercapnia. D is wrong: a fixed dilated pupil with no corneal reflex means dangerously deep anesthesia in any species.

Source Equine Anesthesia, Monitoring, Lee L, Western University of Health Sciences

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Figure credits

  • Figure 1 Original diagram, VTNE Exam Prep
  • Figure 2 Original diagram, VTNE Exam Prep
  • Figure 3 Original diagram, VTNE Exam Prep

References

  1. Grubb T, Sager J, Gaynor JS, Montgomery E, Parker JA, Shafford H, Tearney C. 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2020;56(2):59-82. doi:10.5326/JAAHA-MS-7055 aaha.org/wp-content/uploads/globalassets/02-guidelines/2020-anesthesia/anesthesia_and_monitoring_guidelines_final.pdf
  2. American College of Veterinary Anesthesiologists. ACVA Monitoring Guidelines Update, 2009: Recommendations for monitoring anesthetized veterinary patients. acvaa.org (accessed 2026-10-30) acvaa.org/wp-content/uploads/2019/05/Small-Animal-Monitoring-Guidlines.pdf
  3. Lee L. Anesthetic Monitoring. Veterinary Anesthesia and Analgesia lecture notes, Western University of Health Sciences College of Veterinary Medicine. westernu.edu (accessed 2026-10-30) westernu.edu/mediafiles/veterinary/vet-anesthesia-analgesia/anesthetic-monitoring.pdf
  4. Robertson SA, Gogolski SM, Pascoe P, Shafford HL, Sager J, Griffenhagen GM. AAFP Feline Anesthesia Guidelines. J Feline Med Surg. 2018;20(7):602-634. doi:10.1177/1098612X18781391 pmc.ncbi.nlm.nih.gov/articles/PMC10816483/
  5. University of Wisconsin-Madison Research Animal Resources and Compliance. Species Guidelines on Anesthesia and Analgesia: Stages of Inhalant Anesthesia. rarc.wisc.edu (accessed 2026-10-30) rarc.wisc.edu/anesthesia_and_analgesia/species_guidelines.html
  6. Ribeiro LM, Ferreira DA, Bras S, Castro A, Nunes CA, Amorim P, Antunes LM. Correlation between clinical signs of depth of anaesthesia and cerebral state index responses in dogs during induction of anaesthesia with propofol. Res Vet Sci. 2009;87(2):287-91. doi:10.1016/j.rvsc.2009.02.010 pubmed.ncbi.nlm.nih.gov/19339028/
  7. Lee L. Anesthesia Emergencies and Accidents. Veterinary Anesthesia and Analgesia lecture notes, Western University of Health Sciences College of Veterinary Medicine. westernu.edu (accessed 2026-10-30) westernu.edu/mediafiles/veterinary/vet-anesthesia-analgesia/anesthesia-emergencies-accidents.pdf
  8. Lee L. Equine Anesthesia. Veterinary Anesthesia and Analgesia lecture notes, Western University of Health Sciences College of Veterinary Medicine. westernu.edu (accessed 2026-10-30) westernu.edu/mediafiles/veterinary/vet-anesthesia-analgesia/equine-anesthesia.pdf
  9. Dyer-Corso A. Don't Forget The Basics. Veterinary Anesthesia and Analgesia Support Group. vasg.org (accessed 2026-10-30) vasg.org/don't_forget_the_basics.htm
  10. American Association of Veterinary State Boards. Veterinary Technician National Examination (VTNE) Content Outline, approved March 2023. aavsb.org (accessed 2026-10-30) aavsb.org/wp-content/uploads/2025/04/AAVSB-2023-Veterinary-Technician-National-Examination-Content-Outline-2.pdf
  11. University of Guelph, Ontario Veterinary College. Assessment of Cranial Nerves. Clinical Medicine 1: Small Animal Clinical Skills Textbook (open textbook). books.lib.uoguelph.ca (accessed 2026-10-30) books.lib.uoguelph.ca/vetm3430/chapter/assessment-of-cranial-nerves/

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