Week 6 - SA Protocols, Equine Anesthesia

True or false: It is generally considered safe to anesthetize an azotemic patient.

- False

What is the minimum database required for any patient to be anesthetized at the VTH?

- PCV

- TP

- Glucose

- BUN

Elective anesthesia (i.e., dental procedures) should not be performed on patients with what ASA status?

- Patients with an ASA status of 3 or above

True or false: Much of case "management" occurs before a patient is anesthetized.

- True

What is the recommended preanesthetic fasting for small animals? What about for neonates?

- Food: 6-12 hours

- Water: 1-2 hours

- Neonates not routinely fasted (BG will drop)

What are some commonly used sedatives/pre-medications in small animal anesthesia?

- Acepromazine

- Alpha-2 agonists (Dexmedetomidine, Medetomidine)

What are some commonly used opioids in small animal anesthesia?

- Hydromorphone

- Methadone

- Butorphanol

What are some commonly used benzodiazepines in small animal anesthesia?

- Midazolam

- Diazepam

What are some commonly used anticholinergics in small animal anesthesia?

- Atropine

- Glycopyrrolate

Describe whether anticholinergics result in the following effects:

A. Analgesia

B. Decreased anxiety and stress

C. Sedation/chemical restraint

D. Autonomic reflex

E. Decreased anesthetic requirements

A. No

B. No

C. No

D. Yes

E. No

Describe whether phenothiazines result in the following effects:

A. Analgesia

B. Decreased anxiety and stress

C. Sedation/chemical restraint

D. Autonomic reflex

E. Decreased anesthetic requirements

A. No

B. Yes

C. +/-

D. No

E. Yes

Describe whether benzodiazepines result in the following effects:

A. Analgesia

B. Decreased anxiety and stress

C. Sedation/chemical restraint

D. Autonomic reflex

E. Decreased anesthetic requirements.

A. No

B. +/-

C. +/-

D. No

E. Yes

Describe whether alpha-2 adrenergic agonists result in the following effects:

A. Analgesia

B. Decreased anxiety and stress

C. Sedation/chemical restraint

D. Autonomic reflex

E. Decreased anesthetic requirements

A. Yes

B. Yes

C. Yes

D. No

E. Yes

Describe whether opioids result in the following effects:

A. Analgesia

B. Decreased anxiety and stress

C. Sedation/chemical restraint

D. Autonomic reflex

E. Decreased anesthetic requirements

A. Yes

B. Yes

C. +/-

D. No

E. Yes

Is intravenous catheterization recommended for all anesthetic procedures?

- Yes!

What is the purpose of intravenous catheterization?

- Administration of anesthetic agents

- Fluid administration

- Emergency drugs

Is predication necessary for IV catheter placement?

- No!

What are some factors to consider when selecting a drug/anesthetic protocol method?

- Side effects

- Administration options

- Required equipment

- Cost

- Recovery characteristics

- Personal preference/familiarity with drug or procedure

What is the preferred method of drug administration in almost all cases?

- Intravenous

What are some benefits of IV drug administration?

- Rapid loss of consciousness

- Less patient stress

- Less risk of injury to patient or staff (less likely to see stage II anesthetic event)

- Rapid control of airway

What are some limitations of IV drug administration?

- Metabolism of drug required for recovery

What are some limitations of inhalant drug administration for induction?

- Slow loss of consciousness

- More patient stress

- Slow control of the airway

- More risk to patient or staff

- More exposure of staff to anesthetic vapors

What are some benefits of inhalant drug administration for induction?

- No metabolism required for recovery

What are the most common options for IV drug administration and induction?

- Propofol

- Alphaxalone

- Ketamine/Diazepam

- Ketamine/Midazolam

- Ketamine/propofol

- Etomidate

What are some less common options for IV drug administration and induction?

- Telazol® (tiletamine/zolazepam)

- Etomidate

- Neuroleptanalgesic (opioid + tranquilizer)

- (Thiopental)

What is a "Midazolam sandwich"?

- Induction protocol in which an induction drug (commonly Alphaxalone or Propofol) is given, followed by some Midazolam, followed by more induction agent (titrate to effect)

What are the benefits of a "Midazolam sandwich"?

- Decreased required dose of induction drug

- Provides good muscle relaxation (Midazolam is not a great sedative when used alone)

What is the slowest, least controlled, least safe induction method?

- Tank induction

Tank inductions are associated with an increased frequency of what events? There is also considerable ______________________ contamination.

- Stage II anesthetic event (excitement and stress)

Environmental

What is the proper technique for tank inductions?

- Use appropriate tank (good seals, smallest volume possible)

- Attach to anesthetic machine common gas outlet

- Highest O2 flow & vaporizer setting possible

- Remove patient with loss of consciousness/chemical restraint

- Finish induction via mask

Unless you are choosing inhalant induction for a short, simple procedures with the goal of rapid recovery & discharge, it is preferable that animals have heavy ____________ prior to starting.

- Sedation

Describe the appropriate technique for mask induction of a patient.

1) Use smallest size mask (less dead space) w/ tight seal

2) Use high flows (200-300 mls/kg)

3) Two options:

- Start low and turn up the vaporizer slowly

- "Pedal to the medal" (Start high and adjust down as indicated)

What are some limitations of mask inductions?

- Associated with high degree of struggle, high/dangerous levels of sympathetic output, stage II anesthesia

- Environmental contamination

Mask induction is most commonly used for what kinds of patients?

- Very young patients

Intravenous maintenance of anesthesia (TIVA or PIVA) may be a better option for what kinds of procedures?

- Short procedures

What factors must still be considered during maintenance of anesthesia in a small animal protocol, even if the maintenance is intravenous only (as opposed to inhalant)

- Airway protection

- O2 supplementation

- Ventilatory support

- Adequate monitoring & vigilance

What are some options for intravenous maintenance of anesthesia?

- Propofol

- Alphaxalone

- Ketamine/benzodiazepine

- Ketoflo (Ketamine and Propofol)

What are some factors to consider in selecting an inhalant?

- Cost

- Vaporizers available

- Case and case load

- Knowledge and level of comfort

Non-rebreather circuits are best for what patients?

- < 5-7 kgs

What fresh gas flow rates are appropriate for use with a non-rebreather circuit?

- 200 to 300 mLs/kg/min

What are some types of non-rebreather circuits?

- Bain

- Ayers

- T-piece

What are some types of rebreather circuits?

- Circle

- "Y"

- Universal F

For what patients is a rebreathing circuit most ideal?

- Patients >5 - 7 kg

What flow rates are appropriate for use with a rebreathing circuit?

- Induction flow rate: 100 - 150 mls/kg/min*

- Maintenance flow rate: 30 - 50 mls/kg/min*

What does it mean to use a closed rebreathing circuit system?

- Flow rate = metabolic O2 consumption (3 - 5 mls/kg/min)

Why is it ideal to use a non-rebreathing circuit in patients under 5 kg?

- Higher O2 flow rates increased cost

- Less resistance to breathing (No valves, No CO2 absorbent)

- Less deadspace (?)

True or false: It is a hard and fast rule that pediatric patients or any patients under 5 kg should NOT be put on a rebreather system.

- False; patients as small as 2.5 kg may do fine on a circle and pediatric circle systems are available with small breathing tubes and lower volumes

What is the appropriate volume for a reservoir bag?

- 5-6 × tidal volume

What is tidal volume equal to?

- Tidal volume = 10 - 20 mls/kg

What is the appropriate size of reservoir bag for patients of the following weight:

A. < 5 kgs

B. 5-10 kgs

C. 10-25 kgs

D. 25-40 kgs

E. > 40 kgs

A. 500 mLs

B. 1 L

C. 2L

D. 3L

E. 5L

If in doubt, one should heir on the side of a smaller or larger reservoir bag?

- Larger

For ET intubation, one should use the _____________ diameter tube that comfortably fits in the patient.

- Largest

What is the largest source of airflow resistance in an anesthetic circuit?

- ETT (resistance is proportional to diameter)

How can the appropriate length of an ETT for a patient be estimated?

- Nose to point ot shoulder

Why are excessively long ETTs problematic?

- Avoid endobronchial intubation

- Excessive dead space

Prior to ET intubation, cats should receive what?

- Lidocaine spray/drop to reduce laryngospasm

What is the maximum volume which should be put into an ETT for a cat? What about for a dog?

- 2-3 mLs (If it doesn't seal -> Need a bigger cuff)

- 8-10 mLs

An ETT cuff should be inflated by titrating to what point?

- To where a leak is prevented at 20 cm H20 airway pressure

What are some common airway anomalies of brachycephalic breeds?

- Stenotic nares

- Elongated soft palate

- Everted laryngeal saccules

- Hypoplastic trachea

What are some particular considerations for anesthesia of brachycephalic breeds?

- Prone to regurgitation

- Consider pre-oxygenation

- Induce/intubate rapidly

- Maintain ETT as long as possible in recovery

What is the appropriate routine maintenance fluid rate for a dog and cat under anesthesia?

- Dogs: 5 mls/kg/hour

- Cats: 3 mls/kg/hour

What are some options for keeping patients warm during anesthesia?

- Circulating warm water blankets

- Heat lamps

- Electric blankets

- Hot water bottles

- Rice socks

- Force air blankets (Bair Hugger)

What sympathomimetic support drugs are available (inotropes)?

- Dopamine

- Dobutamine

- Norepinephrine

During intermittent positive pressure ventilation, what is the target RR, tidal volume, and airway pressure?

- RR: 10-15 bpm

- Tidal Volume: 10-15 mLs/kg

- Pressure: 10-15 cmH20

What are some ways to monitor the nervous system under anesthesia?

- Reflexes (palpebral, corneal)

- Eye position (globe rotated ventromedial deal

- Jaw tone

True or false: Recovery is as important as any other stage of anesthesia.

- True (In fact, it is the number one time in veterinary medical anesthesia when bad things happen)

What are some potential adverse events which can occur during anesthetic recovery?

- Hypoxemia/hypercapnia

- Airway obstruction

- Regurgitation/aspiration

What is the goal of anesthetic recovery?

- Smooth transition from unconsciousness to consciousness

What steps should be taken with regards to anesthetic machinery when it is time to recovery the patient?

- Turn the inhalant off and remove the patient from the ventilator (Support ventilation at slow rate (2 - 4 bpm) if apneic)

- Increase O2 flow if using a circle system ("Wash out" residual inhalant)

- Leave the patient attached to the circle system for several minutes to scavenge residual inhalant and maintain oxygen support

- Extubate smoothly and gently

How does one know when to extubate a dog and cat?

- Dogs: 1st or 2nd swallow; head lift

- Cats: ear flick, tongue movement (laryngospasm)

If a patient has a rough recovery, it may be one of what two things?

1) Pain (If in doubt, treat for pain)

2) Emergence delirium (dysphoria)

How is emergence delirium (dysphoria) after anesthesia managed?

- Time

- Tranquilizers/sedations (Acepromazine, alpha-2 adrenergic agonists, propofol)

What is the mortality rate of equine anesthesia? How does it relate to other species?

- 1%

- More than humans (100-1000x greater), dogs (20x greater), cats (10x greater)

- Similar to rabbits (0.78%)

Horses are at a higher risk for mortality under anesthesia if the duration is over _________________.

- 1 hour

Anesthesia is safest in horses of what age?

- 2-7 years old

What breeds of horses are most likely to succumb to morbidity and mortality under anesthesia?

- Arabians

- Warmbloods

Describe some physiologic/anatomic particularlities of horses which may relate to anesthetic complications and management.

- "Flight" species (Want to get up and run around)

- Obligate nasal breathers (elongated soft palate)

- Vomiting/regurgitation uncommon

- Susceptible to recumbency related complications due to size (myopathy, neuropathy)

Never anesthetize an _______________ horse.

- Excited

What is the most important component of equine anesthesia?

- Planning and preparation

What pre-operative laboratory work should be done in horses?

- PCV and TP

- CK and AST

- CBC

What fasting should be performed in horses pre-operatively?

- Fast 8 - 12 hours

- Water ad lib

How are horses catheterized for intravenous access?

- Jugular catheter

- 12 - 16 ga X 13 cm

Why should one wash out a horse's mouth prior to anesthesia?

- They like to hold food and other things in there

Describe the Xylazine/Ketamine IV protocol for horses.

- Xylazine IV followed by Ketamine IV

- Must have good sedation from xylazine before administering ketamine ("five-point stance")

- If needed, administer additional xylazine

Describe the duration of the Xylazine/Ketamine IV protocol for horses.

- Gives you about 15 minutes of anesthesia

- May redose with ½ doses of both xylazine and ketamine as needed to extend the anesthetic time

- Do not exceed about an hour total (poor recovery)

What effect on the cardiopulmonary and respiratory systems does the Xylazine/Ketamine IV protocol for horses have?

- Usually results in good cardiopulmonary stability and good quality recoveries

What are some alternatives to xylazine for horses (often in combination with ketamine)? What implications do they have as compared to xylazine?

- Detomidine (similar induction, longer duration)

- Romifidine (less sedation may result in poor quality of anesthesia - need additional sedation/muscle relaxation with a benzodiazepine or guaifenesin); Can't really get this anymore

What is the effect of administering a benzodiazepine with ketamine in equine intravenous anesthesia?

- Increases the duration by 5 - 10 minutes, muscle relaxation, and minimal impact on cardiopulmonary performance or anesthetic recovery

What are some additional drugs to consider in horses to improve the quality and duration and IV anesthesia?

- Propofol

- Opioids (Butorphanol provides additional analgesia and facilitates smooth recoveries)

What are some alternatives to ketamine for equine IV anesthesia?

- Telazol® (following sedation with xylazine)

What duration of anesthesia does a Xylazine/Telazol protocol provide in horses?

- 30 - 40 minutes of anesthesia (Note: If you need to prolong anesthesia, do not administer more Telazol - use ketamine/xylazine instead)

What is Guifenesin?

- A centrally acting muscle relaxant that facilitates induction in large animals

What are some limitations to Guifenesin?

- Not commercially available

- At greater than 10% concentration may cause significant hemolysis, very irritating to tissues if injected peri-vascularly

What is "triple drip" or GKX?

- Guaifenesin - Ketamine - Xylazine

- An option for equine TIVA in the field

When using triple drip for TIVA, do not exceed _________________ duration of anesthesia.

- 60 minutes (Should be on inhalant anesthetic on a padded surgery table at that point)

- However, if duration is kept under 60 mins, recovery is usually very smooth

What is another option for TIVA in horses (alternative to GKX not commonly used anymore)?

- Midazolam - Ketamine - Xylazine TIVA

True or false: Propofol is a great induction agent when used alone in horses.

- False; Has a very short duration and may lead to abrupt collapse or flipping backwards

What is a limitation of using Midazolam in horses?

- "Midazolam drunks" in horses recovering from Midazolam anesthesia

In what ways is Propofol used in horses?

- In combination with Ketamine (Ketoflo)

- For induction in foals following sedation with midazolam or xylazine and burophanol - less than 4-6 weeks old)

What are options for oxygen supplementation in horses?

- "Flow by" (15 L/min - pass oxygen line into ventral nasal meatus)

- Hudson demand valve (Requires intubation, allows PPV)