1 – Introduction Flashcards
General anesthesia:
- State of unconsciousness produced by CONTROLLED, REVERSIBLE intoxication of CNS
- Patient does not perceive or recall noxious (or other) stimuli
Triad of anesthesia:
- Unconsciousness
- Analgesia
- Muscle relaxation
*one drug CANNOT do all three components unless high doses
Mechanism of action of anesthetics:
- Largely unknown
- *LIPOPHILIC to have action within CNS due to BBB
- Interacts with GABA in BRAIN
- Interacts with Glycine in SC
Multimodal (Balanced) Anesthesia:
- Number of different drugs used to fulfil the triad of anesthesia
- Ex. unconsciousness: isoflurane
- Ex. analgesia: opioids, NSAIDs
- Ex. muscles relaxation: benzodiazepines
o *use peripheral neuromuscular blocking agents if require NO muscle tone
Overall effect on the ANS:
- CNS depression
- CVS depression
- Respiratory depression
- CNS depression
a. Loss of consciousness
b. Damping of reflexes
i. Cardiovascular=hypotension
ii. Respiratory=hypoventilation
iii. Thermoregulatory=hypothermia
iv. Postural=reduced muscle tone
c. Central modulation of nociception
- CVS depression
a. Baroreflex suppression
b. Changes in autonomic balance
c. Changes in vasomotor tone
d. Myocardial depression
i. Direct (drugs)
ii. Indirect (hypoxemia, hypercapnia)
e. HYPOTENSION
- Respiratory depression
a. Reflex suppression
b. Reduced muscle activity
c. Aleolar collapse
d. Reduced functional residual capacity
e. Ventilation/perfusion mismatch
f. HYPOVENTILATION (hypercapnia/hypoxemia)
Risks of anesthesia:
- High does leader to deeper brain depression, overdose can cause DEATH
o Suppression of reflexes with ANS and SNS
>Autonomic: BAD (hemodynamics, respiratory)
>Somatic: GOOD (proprioceptive reflexes and muscle relaxation) - Risk is linked with physical status
Ways to minimize risks:
- Vigilance (never assume!)
- Build intervention points (use SOPs)
Stages of anesthesia:
- Stage 1: voluntary excitement
- Stage 2: involuntary excitement
- Stage 3:
a. Plane 1: light
b. Plane 2: surgical depth=where most procedures are performed)
c. Plane 3: deep - Stage 4: cardiopulmonary arrest imminent
Phases of anesthesia:
- Pre-operative assessment
- Premedication
- Induction
- Maintenance: continuation
- Recovery
- Pre-operative assessment
o Stabilization and provision of analgesia
o Dogs, cats, horses: 6-8hrs fasted (horses can have hay)
o Ruminants: 24-48hrs fasted to prevent bloat
- Premedication
o Sedation and initiation of analgesia if not already provided
o Choice depends on:
Species
Facilities
Clinician preference
Health status of animal
o Ex. acepromazine, benzodiazepines, opioids
- Induction
o Rapid with IV, slower with inhalation techniques
o Stressful for body (ensure animal can tolerate changes)
- Maintenance: continuation
o If can pass an endotracheal tube=anesthesia (NOT sedation)
- Recovery
o Aftercare and continuation
Monitoring tools:
-respiratory
-cardiovascular
-CNS
Monitoring Tools: respiratory
-6-12 br/min
o Too much muscle tone can compromise lung ventilation
o ‘light’: fast, deep, breath holding
o ‘surgical’: rhythmic, intercostal/abdominal
Monitoring Tools: cardiovascular
o Minimum BP: 60
o Aim for: 120/80 (90)
o *HR not predictable of anesthetic depth
Monitoring Tools: CNS
o Reflexes
>Pedal withdrawal reflex (ex. exotics)
>Corneal reflex (not advised=corneal damage)
>Anal tone
o Muscle tone
o Breath patterns (more abdominal and less intercostal with depth)
Reflexes (CNS monitoring): Basic eye reflexes: dog/cat
*‘light’ plane
-Eye central
-Palpebral reflex present
-Shiny cornea
*‘surgical’ plane
-Eye rotated ventral
-No (or slight) palpebral reflex
-Move UPPER eyelid to check
-Dry cornea-lube
Reflexes (CNS monitoring): Basic eye reflexes: horses
*‘light’
o Tearing
o Nystagmus
o Spontaneous blinking
*‘surgical’
o Inhalation=central eye, sluggish palpebral
o Injectable=central eye, rapid palpebral
What is required for supportive care?
- Warmth
- Hydration
- BP support: IV fluids, drugs
- Delivery of oxygen and lung ventilation
- Protect musculoskeletal and NS
Why is provision of analgesia important during a surgical/anesthetic event?
- Make patient comfortable
Pre-emptive analgesia:
- Anticipate a painful event – administer analgesics beforehand
Importance of pre-emptive analgesia:
- Stop the pain pathway from firing
- Minimize the potential for wind up/sensitization
Concept of multi-modal analgesia:
- Different drugs combat pain in different ways
