Anesthesia Final Info

What are the 4 stages of anesthesia?

Stage 1: administer induction drug to loss of consciousness

Stage 2: excitement stage (hope to avoid)

stage 3: surgical anesthesia (we focus here)

stage 4: extreme CNS depression (try to avoid this)

What are the 5 standards that we monitor the most?

• CNS

• oxygenation

• ventilation

• circulation

• temperature

What is the objective of monitoring CNS depression?

adequate depth to prevent patient awareness and movement while minimizing adverse effects of anesthetic agents.

What do you see when in light, medium and deep plane in the context of eye position, muscle tone, anal tone, palpebral reflex, cornea lacrimation, movement in response to stimuli, and cardiopulmonary variations in response to stimulus?

There was no palpebral reflex, absent muscle tone, central positioned eye, not moving in response to stimulation (steady HR).

What stage and level of anesthesia?

• stage 3, deep

What is an advanced monitoring technique for CNS depression?

inspired and expired inhalant concentrations

What is the objective of monitoring oxygenation? What are the two minimum recommendations?

• ensure adequate oxygenation of the blood and to enable rapid recognition of hypoxemia.

• MM colour and pulse oximetry

What does pulse oximetry measure?

• percent saturation of hemoglobin with oxygen (SpO2)

How does pulse oximetry work?

Clip has a transmitter and a receiver side. Clip over non pigmented tissue (usually tongue). Transmitter transmits two wave forms, a visible red and an infrared light. Red light is absorbed by hemoglobin. How much light passes through? It will tell us a percentage.

Also senses pulsatile flow—> pulse rate

What does the heights of the waves in a pulse oximetry graph tell us?

• tells us about the volume of the pulses.

• Tall wave=pulses are strong with high volume.

• Narrow or flat graph=vasoconstriction or poor perfusion. 

If breathing 100%, SpO2 should always be above __%.

95

What are three advanced methods of monitoring oxygenation?

• arterial blood gas analysis

• inspired oxygen concentrations

• co-oximetry

What is the objective of monitoring ventilation? What are the minimum requirements?

to ensure adequate ventilation and to enable rapid recognition of hypocarbia and hypercarbia

• resp rate, estimated tidal volume, pulmonary auscultation,

• capnography

How does mainstream capnography work? How does side stream work?

• Mainstream: sensor is built in—> shows end tidal CO2 reading (want between 35 and 45**). 

• Mainstream has sensor built into adapter while side stream draws a sample out and analyzes it. 

  • Must scavenge gases from side stream was the sample has some waste inhalant 

In capnography, what does the trough show?

trough is inspire (peak is expire)

What is normal end tidal CO2?

35-45mmHg

What does a CO2 >45mmHg tell us? What about <35mmHg?

• hypoventilation

• hyperventilation (not common)

What is the normal fraction of inspired CO2?

0 mmHg because the anesthetic machine should prevent all rebreathing of CO2

What are two advanced recommendations for monitoring ventilation?

• arterial blood gas analysis

• spirometry

What are the minimum requirements for monitoring circulation?

• peripheral pulses, heart sounds, MM colour, cap refill time

• ECG

• noninvasive blood pressure

What are you feeling when you feel a pulse?

• we feel the difference between systolic and diastolic pressure but not numbers—> (150/90 feels the same as 120/60). Look if the rhythm is in sync, regular or irregular, etc. 

What does a cap refill >2 seconds indicate?

• hypoperfusion

What does an ECG tell us?

Does NOT tell us if the heart is actually beating just tells us if the electrical portion of the heart is normal. 

What is the normal HR ranges for dog? Cats? Horses? Cattle?

• 60-140

• 120-220

• 30-40

• 60-80

How does oscillometric non invasive bloop pressure work?

Oscillometric method: like what they do at shoppers. Cuff inflates, feel it slowly deflate and can feel pulse.

• put cuff around limb or tail, inflates until blood flow is occluded. Slowly deflate. When pulses return, the pulses push against cuff and sense the oscillations in the cuff. Run them and generate a systolic and diastolic pressure and mean arterial blood pressure and pulse rate

• width of this cuff is about 40% of the circumference of the limb

• limitations: moving animals can impact readings, works only for regular rhythms not arrhythmias  

How does the doppler non invasive BP work?

Doppler: choose cuff the same way as oscillometric (40% of circumference). Shave a spot over peripheral a. Attach doppler probe. The speaker allows you to hear pulse. Inflate until you dont hear pulse anymore then deflate. Watch the pressure and if you hear the pulse again then that is the systolic pressure. 

• limitations: takes a bit more skill, done manually (can’t set and forget)

• good thing is you can hear the pulse rate which is helpful to pick up arrhythmias 

What does the doppler measure? When is it considered hypotensive?

• systolic BP

• <90mmHg

What is normal systolic BP? What is normal mean arterial BP? When is it considered hypotension?

• 100-140; <90 is hypotensive

• 70-120mmHg; <60 is SA and <70. in LA

What is gold standard for measuring BP?

Invasive BP via arterial BP through the auricular vein

What is normal temp range in general?

37-39*C

How do you recognize excessive anesthetic depth?

physical signs

How do you treat excessive depth?

decrease depth by reducing vaporizer and decreasing dose of injectables

oxygen supplementation, ventilation, etc

How do you recognize inadequate depth?

physical signs

How do you treat inadequate depth of anesthesia?

increase depth by increasing vaporizer (slower) and administer dose of injectables (way faster)

What is the definition of bradycardia in dogs? cats? horses?

<60

<90

<20

2 reasons why we worry about bradycardia?

• reduce CO

• reduced oxygen delivery to tissues

What are the two components of cardiac output?

heart rate and stroke volume

What are 5 causes of bradycardia?

• increase in vagal tone (things that stretch GIT)

• hypertension (reflex decrease in HR, seen with alpha 2s and dex)

• hypoxemia

• hypothermia

• electrolyte abnormalities (high potassium and calcium)

3 ways to treat bradycardia?

• consider an anticholinergic if due to increased vagal tone (atropine or glycopyrrolate)

• address electrolyte abnormalities

• address hypothermia

Why do we worry about tachycardia? (3)

• reduction in ventricular filling

• reduction in CO

• reduced oxygen delivery to tissues

What is the definition of tachycardia in dogs? cats? horses?

• >190

• >220

• >60

8 causes of tachycardia?

• pain/insufficient depth

• hypotension

• hypoxemia

• hypercapnia

• drugs

• hyperthermia

• hypokalemia

• concurrent diseases

NOTE: many different causes so treat the underlying cause

Why do we worry about hypotension (2)?

• reduction in tissue perfusion

• reduced oxygen delivery to tissues

What is the definition of hypotension in SA? LA? Systolic?

<60mmHg

<70mmHg

<90mmHg

What are the two main determinants of mean arteriole pressure?

• cardiac output and systemic vascular resistance

Where there is a reduction in systemic vascular resistance, think vasodilation so we treat with vasoconstriction

What are 6 ways to treat hypotension?

• assess depth

• assess HR

• assess volume (may need fluids)

• increase cardiac contractility (positive ionotropes like dopamine and dobutamine)

• increase systemic vascular resistance (epi or Nor which cause vasoconstriction)

5 reasons why we worry about hypoventilation?

acidemia

hypoxemia

increase in cerebral blood flow

CNS depression

death

What is the definition of hypoventilation?

ETCO2 or PaCO2 >45mmHg

NOTE: mild hypoventilation is tolerated in healthy patients

2 ways to diagnose hypoventilation?

• capnography

• arterial blood gas analysis (PaCO2)

What is the formula for minute ventilation?

resp rate x tidal volume

6 causes of hypoventilation?

• anesthetic drugs (inhalants are dose dependent)

• CNS disease

• abdominal distension

• positioning

• thoracic injury

• equipment malfunction

Two ways to treat hypoventilation?

reduce vaporizer

start positive pressure

work on underlying issue too

What is the definition of hypoxemia when breathing room air? 100% oxygen?

• <90%, <60mmHg

• <95%, <200mmHg

3 reasons why we worry about hypoxemia?

• lactic acidosis

• organ damage

• death

Two ways to diagnose hypoxemia?

• pulse oximetry

• arterial blood gas analysis

5 causes of hypoxemia? Which one is most common?

• ventilation/perfusion mismatch

• hypoventilation

• low fraction inspired oxygen

• diffusion impairment (ex: thickened alveoli bc fibrosis)

• right to left shunt

How do you treat hypoxemia if caused by low fraction inspired oxygen (FIO2) or hypoventilation? (3)

• intubate

• provide 100% oxygen

• institute positive pressure ventilation

What are the two types of ventilation/perfusion mismatch?

• alveoli is not ventilated but blood is perfused

• ventilated alveoli but not perfused (ex: thromboembolism)

Define hypothermia? How do you diagnose?

temp <36*C

• rectal or esophageal thermometer

6 reasons why we care if the patient is hypothermic?

• wound infection

• impaired blood clotting

• arrhythmias

• decreased metabolic rate

• metabolic acidosis

• death

4 causes of hypothermia?

• convection (losing heat from cold air surrounding the patient)

• conduction (loss of heat to surfaces)

• radiation (loss of heat to other things in the room that they aren’t in contact with)

• evaporation (ex: open abdomen)

How do you treat hypothermia? (4)

• minimize surgery and anesthesia time

• minimize prep

• passive warming

• active warming

What is the definition of a prolonged recovery in SA? LA?

• >30 min

• >60 min to stand in equines

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

Does she need to be sedated? If so what would you use?

yes— alpha 2 agonist like dexmedetomidine

NOTE: acepromazine is for mild sedation and is irreversible. Benzodiazepines provide minimal and variable sedation and potential for paradoxical excitement. Neither have any analgesic effect.

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

Does she need an opioid and what would you use?

• yes, and a full mu agonist like hydromorphone

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

Does she need to be anesthetized? What could you use?

yes

propofol; ketamine and diazepam; and alfaxolone would all be appropriate

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

How would you maintain anesthesia?

A) not needed. Induction dose of alfaxalone will be sufficient

B)constant rate infusion of propofol

C)isoflurane using a rebreathing system

D)sevoflurane using a non-rebreathing system

D

Note size of animal for non-rebreathing system

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

What supportive care will Peggy need?

A) none. Peggy’s a healthy cat

B) subQ fluids at 5ml/kg/h

C)Thermoregulatory support with forced warm air

D)intravenous fluids and thermoregulatory suppory with a circuating warm water blanket

D

Peggy: 8 month old, intact female DSH, 3.5kg, presented for an OHE and extraction of fractured canine tooth.

What is your peri-operative analgesic plan?

A) one more dose of opioid analgesic

B)one dose of NSAID

C)opioid and NSAID that continues based on pain scoring

D) local blocks of the abdominal incision and infraoribital nerve. Opioid and NSAID that continues based on pain scoring.

D

During a canine tooth extraction you auscultate a heart rate of 80bpm and there was a systolic blood pressure of 85mmHg. What problems does this dog have? How would you treat these issues?

bradycardia and hypotension

administer an anticholinergic

Spike is a 3 yo Yorkie weighing 3.2kg presented for evaluation of goose honk cough. He needs a tracheoscopy, bronchoscopy, and bronchoalveolar lavage (BAL) as you suspect a collapsing trachea. Does Spike need to be sedated? What would you use?

yes, use acepromazine and an alpha 2 agonist (dexmedetomidine)

Spike is a 3 yo Yorkie weighing 3.2kg presented for evaluation of goose honk cough. He needs a tracheoscopy, bronchoscopy, and bronchoalveolar lavage (BAL) as you suspect a collapsing trachea.

Does he need analgesia? If so, what would you use?

• yes, and I would use a mixed agonist/antagonist (butorphanol)

Spike is a 3 yo Yorkie weighing 3.2kg presented for evaluation of goose honk cough. He needs a tracheoscopy, bronchoscopy, and bronchoalveolar lavage (BAL) as you suspect a collapsing trachea.

Does he need to be anesthetized? How would you induce anesthesia?

• yes, propofol

Spike is a 3 yo Yorkie weighing 3.2kg presented for evaluation of goose honk cough. He needs a tracheoscopy, bronchoscopy, and bronchoalveolar lavage (BAL) as you suspect a collapsing trachea.

How will you maintain anesthesia?

A) not needed

B)constant rate infusion of propofol

C)constant rate infusion of ketamine and diazepam

D) sevoflurane using a re-breathing system

B

Spike is a 3 yo Yorkie weighing 3.2kg presented for evaluation of goose honk cough. He needs a tracheoscopy, bronchoscopy, and bronchoalveolar lavage (BAL) as you suspect a collapsing trachea.

When monitoring, you notice that he has a pulse ox reading of 88%, heart rate of 130bpm, and MAP of 87mmHg. What problems does he have? How would you treat?

hypoxemia

intubate and administer 100% oxygen through a NRB system

What is the resting heart rate of equines? What is a common cardiovascular finding in them?

• 28-44beats/min

• intermittent 2nd degree AV blocks

True or false:

Equines are obligate nasal breathers

true

Why are there higher mortality rates in equines compared to SA? (5)

• recumbency

• CV function is depressed leading to hypotension and then post-anesthetic myopathy and poor recovery

• impaired ventilation with muscle relaxation causing profound atelectasis

• positioning can cause myopathy and neuropathy

• nature of horses (prey animals)

Should horses be fasted before anesthesia?

no, and keep easy access to water is important

Before elective equine procedures, what bloodwork should be done?

• PCV and TP

What are the 5 general risks for anesthesia?

4H1B

hypotension

hypoxemia

hypoventilation

hypothermia

bradycardia

What are 6 species specific risks of anesthesia in horses?

• myopathy/neuropathy

• poor recovery

• safety of personnel

• upper resp obstruction

• ventilation/perfusion mismatch

• post op ileus/colic

What is the most commonly used sedation in equines?

alpha 2 agonist like xylazine

could also use acepromazine if anxious/nervous (avoid in sick horses)

What is one side effect of acepromazine unique in horses?

persistent priapism which is a concern in breeding stallions

What is a good analgesic to use after sedation in horses? One potential side effect?

• butorphanol

• decreased GI motility—> predispose to colic

What is a good induction drug for equines?

fast bolus injection of ketamine and benzodiazepine (benzo for muscle relaxation)

Two ways to do total intravenous anesthesia in equines?

• top ups but there is more swings in depth

• triple drip (mixture on guaifenesin, ketamine and xylazine) which has less swings in patient depth

When performing equine anesthesia, ALWAYS have a ________ bolus drawn up and close by.

ketamine

True or false: In equines, heart rate is an indicator of arousal.

true

Is sedation required for recovery in equines?

• xylazine can be used with inhalant anesthesia while injectable anesthesia often does not need sedation.

What is an important thing to watch for when extubating equine patients?

They are obligate nasal breathers and nasal edema can occur and result in upper airway obstruction.

2 things to keep in mind when anesthetizing draft horses?

• they have small surface area for their size so they need a decreased sedative drug dose

• higher risk for spinal cord degeneration

Does salivation production remain high in ruminants even under general anesthesia?

yes—> only difference is that they can’t swallow

Why are ruminants harder to assess pain on?

they are prey species and can mask behavioural signs of pain

What are two advantages of fasting and water deprivation in ruminants? 4 disadvantages?

• decreases incidence of hypoxemia and less likely to bloat during recumbency and anesthesia

• ruminal hypomotility, bradycardia (increased parasympathetic tone), regurgitation risk more likely, dehydration

What is one respiratory related thing we should watch for in small ruminants when doing a pre-op evaluation?

• subclinical pulmonary disease

What are 5 species specific risks for euthanasia in ruminants?

• restraint and handling risks

• neuropathy, myopathy

• regurgitation and excessive salivation

• aspiration pneumonia

• ruminal tympany (bloat)

Is atropine recommended to prevent salivary secretions in ruminants?

• no, only reduces aqueous components of salivation which makes it way more thick and harder to clear.

Ruminants are very sensitive to ________ sedation.

xylazine

Two potential side effects of xylazine in ruminants? What about sheep?

• ruminal hypomotility, uterine contractions

• hypoxemia and pulmonary edema in sheep