General Anesthesia

What is the definition of general anesthesia?

State of unconsciousness

When you are under general anesthesia, what are the main parts of it?

Lack of sensation

Lack of memory

Motor responses are gone

Depressed reflexes are present

Is controlled and reverisble*

What are the components of anesthesia?

Preanesthesia period

Induction

Maintenance

Recovery

What is the induction period mostly about?

The stage where you produce unconsciousness

What is the maintenance period of anesthesia about?

Where we maintain anesthetic depth

What is the recovery period of anesthesia?

Elimination of drugs - drug gets metabolized, redistributed, exhaled, and reversed

What does anesthesia do in terms of safety?

Affects vital centers of the brain - is basically “controlled poisoning”

What systems does anesthesia affect?

CNS

Cardiovascular system - HR can go faster or slower

Thermoregulation - always affected

How do we minimize the risk factors of anesthesia?

MDB - minimum data base results creates a customized protocol for each animal

Stabilize if not at a good risk status

Preanesthetics - use balanced anesthesia

Drug ID - 6 rights and label syringes*

Minimum dose required - titration → as little drug it takes to do the job

Each animal responses differently to anesthesia, so what are some factors that affect it?

Age

Breed

Physical condition

Preanesthetics

Metabolism - esp organ function

What are the different anesthesia stages?

Stage I

Stage II

Stage III* - Planes 1-4

Stage IV

What is the Stage I anesthesia stage?

Conscious but disoriented

All reflexes are present

What is the Stage II stage of anesthesia?

Excitement stage - like in euthanasia

*Not conscious

Reflexes are still present

What is the Stage III, Plane 1 stage of anesthesia?

Light - could wake up

Good muscle tone

Reflexes depressed - palpebral and pedal reflex are still present, eyes are central but has nystagmus

What do vitals look like for a pt in Stage III, Plane 1 stage?

Respirations - regular, 12-20 rpm

Cardiovascular - pulse strong, >90

What does Stage III, Plane 2 stage of anesthesia look like?

For surgical use* - ideal in most surgeries

Relaxed muscles

Fewer reflexes present - corneal reflex and patellar are still there

Eyes are rotated ventrally

What do vitals look like in Stage III, Plane 2 stage of anesthesia?

Respirations - regular but more shallow, 12-16 rpm

Cardiovascular - rate >90 bpm, decreased pulse strength

What does Stage III, Plane 3 stage of anesthesia look like?

Deep

Minimal to no tone

Reflexes minimal - mostly absent except for like corneal

Eyes return centrally - just like plane 1

What do vitals look like for Stage III, Plane 3 look like?

Respirations - shallow, <12 rpm (slower)

Cardiovascular - pulse weak, rate 60-90, increased CRT

Why is it easy to mistaken Stage III Plane 3 with Plane 1 and how do you differentiate between the two?

Eyes return centrally in both phases

Differentiate it by looking at vitals, reflexes, and muscle tone (jaw tone)

What does Stage III, Plane 4 stage of anesthesia look like?

Excessive - way too deep

Flaccid muscles - soft, limp, loose

No reflexes*

Eyes are central - but no nystagmus

What do vitals look like for pts in Stage III, Plane 4 look like?

Respirations - irregular, no coordination, shallow breaths

Cardiovascular - rate is <60 bpm, decreased pulse strength, increased CRT, pale MM

What does Stage IV stage of anesthesia?

Moribund/dying - near death

Flaccid muscles

No reflexes present

Eyes central

What do vitals look like for a pt in Stage IV anesthesia?

Respiration - apnea (no breaths)

Cardiovascular - collapse

Near death man

What are the ways to identify the stage of anesthesia in a pt?

Reflexes

Eyes position

Respiration

HR/pulse

Jaw tone

What is the ideal stage of anesthesia?

The stage that makes the pt have no perception of surgery

The stage that isn’t excessive - don’t kill them pls

What are the methods of induction?

IV*

IM

Inhalation

Oral

What are the benefits to doing an induction via IV?

Rapid

Can bypass stage II and straight to stage III

Agent is titrated - “to effect”

Duration variable

Repeated dosing is okay

Constant infusion is given through IV

Can rescue the pt if the wake up too early

What is constant infusion?

Using a pump to give induction agent like propofol slowly over time - maintains blood levels of propofol

What are the indications to doing an IM induction?

If IV is difficult to hit - very small dose, uncontrollable behavior

What are the characteristics of IM induction?

Needs a increased dose than IV - 2-3x more than IV

Difficult to titrate/adjusting a medications dosage b/c it’s one set dose - you can make a pt go deeper than you want

Longer time to onset (takes longer to hit)

Longer recovery (longer to get out of it)

Why is the inhalation method of induction not the best?

Agent variability - can take too long to kick in

Delivery - if a mask is put on a pt, they can fight it, if the pt is put in a chamber, we can’t monitor them

Waste gas pollution - if not careful, we can breathe excess gases

Stress increases → increased epinephrine = bad for pts with heart problems

Emesis → aspiration pneumonia = bad

Why is oral induction so rare?

Only for fractious cats* - we use ketamine, gets them straight to stage 3, plane 1

Extra-label is needed b/c anesthesia use is not listened in label use