Anesthesia Flashcards
ASA Scale
American Society of Anesthesiologists
* assessment for anesthetic risk
* scale I-V; also E
ASA Scale
I
Minimal risk
* normal / healthy patient
* routine: spays and neuters
ASA Scale
II
Slight risk
* mild systemic issues
* cruciate repairs / neonates and geriatrics
ASA Scale
III
Moderate risk
* moderate systemic issues / disease with mild C/S
* murmurs, anemia, ect
ASA Scale
IV
High risk
* severe systemic issues that are life threatening
* shock or gastric torsion
ASA Scale
V
Extreme risk
* surgery to save life - will die otherwise
* shock / organ failure / trauma
ASA Scale
E
Emergency
* any previous risk class presenting for immediate surgery
Preanesthetic Drugs
Classes
- Anticholinergics
- Tranquilizers / Sedatives
- Opioids
- Neuroleptanalgesics
Anticholinergics
Block actions of Parasympathetic NS via acetylcholine
* Atropine and Glycopyrrolate
* prevent bradycardia
* may cause tachycardia - do not give if preexisting heart condition
* not for use in rabbits
Atropine
- Anticholinergic
- Faster and more potent than Glycopyrrolate
- Crosses blood-brain and placental barriers
Glycopyrrolate
- Anticholinergic
- Slower and less potent than Atropine, but works longer
- Does not cross blood-brain or placental barriers
Tranquilizers / Sedatives
- Tranquilizer: calms anxiety without necessarily sedating
- Sedation: reduces mental activity
- Phenothiazines
- Benzodiazepines
- Alpha 2 Agonists
Phenothiazines
- Tranquilizers / Sedatives
- Block dopamine receptors in brain
- No analgesia
- Depression effects
- Can cause penile paralysis in horses
- Example: acepromazine
Benzodiazepines
- Tranquilizers / Sedatives
- Bind to GABA receptors in brain - reduces brain activity
- Metabolized in liver - do not use if has condition
- Examples: Diazepam / Midazolam
- Reversed with Flumazenil
Diazepam
- Benzodiazepine
- Not water soluble - do not mix with others
- Not taken well IM
- Can increase appetite in cats and ruminants
- Combine with Ketmaine for induction
Midazolam
- Benzodiazepine
- Water soluble - can be mixed with others
- Can be given IM
Alpha 2 Agonists
- Tranquilizers / Sedatives
- Reduce norepinephrine release
- Causes depression
- Profound sedation with moderate analgesia
- Can be added with opioids to enhance effects
- Examples: Xylazine and Dexmedetomidine
Xylazine
- Alpha 2 Agonist
- Trade Name: Rompun
- Common for large animal use
- Reversal: Yohimbine
Dexmedetomidine
- Alpha 2 Agonist
- Trade Name: Dexdomitor
- Reversal: Atipamezole (Antisedan)
Neuroleptanalgesics
Any combination of an opioid analgesic and a tranquilizer
* enhances CNS depression effects
* mix drugs or give separately
Barbiturates
- Cause sedation / muscle relaxation
- Nonreversible - give to effect
- Examples: Pentobarbital and Thiopental
Pentobarbital
- Barbiturate
- Previously used for anesthesia - now common for seizure control
Nonbarbiturate Anesthetic Drugs
- Propofol
- Alfaxalone
- Fentanyl
- Guaifenesin
Propofol
- Nonbarbiturate Anesthetic Drug
- Binds to GABA - depresses CNS
- Poor analgesia
- Crosses placental barrier
Alfaxalone
- Nonbarbiturate Anesthetic Drug
- Binds to GABA - depresses CNS
- No analgesia
- Use in dogs and cats only
- Safe to combine with any preanesthetic but do not give IV with others
Fentanyl
- Nonbarbiturate Anesthetic Drug
- Primarily used for analgesia - used as neuroleptanalgesic
- Safe for high risk - does not depress RR or HR
Guaifenesin
- Nonbarbiturate Anesthetic Drug
- Blocks transmission of spinal cord and brain
- Common in large animals for muscle relaxation
- Minimal HR and RR effects
- Crosses placental barrier - minimal effects
Dissociative Anesthetics
Induces unconscious and conscious brain functions - dissociate from one’s environment
* CNS excitement
* some analgesia
* examples: Ketamine and Tiletamine
MAC
Minimum Alveolar Concentration
* potency of inhalant anesthetic agents
* lower MAC = more potent = lower concentration needed
Inhalation Anesthetic Drugs
Produce general anesthesia in all species
* minimal depression on RR and HR
* some analgesia
* Examples: Isoflurane / Sevoflurane / Desflurane
Isoflurane
- Purple label on bottle
- Least expensive
- Lowest MAC
Sevoflurane
- Yellow label on bottle
- Faster induction / recovery than Isoflurane
- More expensive than Isoflurane
- Ideal for avian species
Desflurane
- Blue label on bottle
- Fastest acting inhalation agent
- Highest MAC - less potent
- Expensive
Measuring ET Tube
Measured from tip of nose to thoracic inlet
Breathing Circuits
- Circle System
- Bain System
Circle System
Breathing Circuit
Standard re-breathing circuit
* Y-tube
* excessive weight and dead space - not ideal for smaller patients
Universal F-circuit
Breathing Circuit
Modified circle system
* inspiration hose inside expiration hose
Bain System
Breathing Circuit
One tube inside another tube
* non-rebreathing system
* ideal for smaller patients
Monitor CNS
Eye Position
Eyes rotate ventromedially during Stage 3 Plane 2 of anesthesia
* central position = too light or too deep
Monitor CNS
Palpebral Reflex
Observation for blink
Monitor CNS
Corneal Reflex
Done via light touching or sterile drops to cornea
* should be present under anesthesia
* absence = anesthesia overdose
* done as a last resort to monitor patient status
Monitor CNS
Pupil Size
- Light, non-surgical plane = dilated
- Light, surgical plane = constricted
- Deep plane = dilated
- Be aware, some drugs cause pupil dilation (Atropine)
Monitor CNS
Pedal Reflex
Pain response
* done by pinching skin between toes
Blood Pressure
Monitoring
- Noninvasive System: indirect readings; taken every few minutes
- Invasive System: direct readings via arterial line; continuous
- BP cuff should fit 40-60% around the limb
Paradoxical Breathing
Breathing appears “opposite” how you should see it
* abdomen rises, chest falls during inspiration
* observed when too deep of anesthesia
Hypoventilation
Respiratory acidosis
* increased CO2
Hyperventilation
Respiratory alkalosis
* decreased CO2
Stages of Anesthesia
- Range from Stage 1 - Stage 4
- Ideally should have smooth induction from Stage 1 to Stage 3, quickly passing Stage 2
Stages of Anesthesia
Stage 1
Induction Stage
* loss of pain
* sensations dulled
* voluntary movement
Stages of Anesthesia
Stage 2
Excitement Stage
* involuntary muscle movement
* reflexes present - may be exaggerated
* panting or breath holding
Stages of Anesthesia
Stage 3
Surgical Stage
* regular respiration
* palpebral reflex gone
* subdivided into 4 planes: plane 2 ideal for surgery
Stages of Anesthesia
Stage 4
Medullary Paralysis Stage
* apnea
* cardiac arrest
Rebreather
Bag Size
- 0.5 L = <6 kg
- 1 L = 6 - 16 kg
- 2 L = 16 - 35 kg
- 3 L = >35 kg
