Lecture 1 Introduction Flashcards
What is anesthesia?
loss of sensation to all or part of the body.
Define analgesia
without pain
- Define general anesthesia vs
- Analgesia or local anesthesia
- General Anesthesia: Animal is unconscious and unaware of its surroundings
- Analgesia or local anesthesia: Animal shows diminished or no perception of pain
What are the 4 general requirements for general anesthesia?
- temporary/reversible state of drug intoxication of the central nervous system where the patient neither perceives nor recalls the painful stimulus
- Physiology, pharmacology and pathology are the building blocks for the science behind anesthesia
- Adequate standard of monitoring
- Additional requirements:
- Species differences in anatomy, pharmacologic effects and metabolism of drugs
- Humane treatment – prevention of pain, relief from anxiety & stress, sympathetic handling
- Prevention of injury to animal & personnel
During general anesthesia there is a temporary/reversible state of drug intoxication of the central nervous system where the patient neither perceives nor recalls the painful stimulus which consists of 5 requirements without harming the patient
- unconsciousness (hypnosis, narcosis)
- muscle relaxation
- lack of pain (analgesia)
- loss of memory (amnesia)
- suppression of reflexes (motor, autonomic)
What are the general principles of anesthesia
- Critical evaluation of history, physical examination & laboratory data => Know your patient!
- Stabilize & correct identified abnormalities, if possible, prior to anesthesia
- Be organized and efficient to minimize anesthesia time
- Select anesthetic protocol based on patient, existing abnormalities and to minimize adverse effects
- Identify & prepare for potential complications
- Establish intravenous access whenever possible
- Secure & maintain patent airway
- Use supplemental oxygen when indicated* and provide ventilatory support
- Monitor vital body systems (cardiovascular, respiratory & CNS)
- Identify & correct abnormalities that arise
- Continue monitoring & support thru recover period
- Use appropriate analgesia & sedation to minimize pain & distress
Why is pre-anesthetic patient evaluation important?
- Identifies individual risk factors
- Underlying physiologic abnormalities
- Contributes information for development of an individualized anesthetic plan
- What are the pre-anesthetic fasting requirements for adult dogs and cats?
- Less than 4 months of age?
- Water requirements?
- 6 to 12 hours fast
- 6 hours may be sufficient
- overnight fasting is recommended at this time (no food after 10pm)
- Fast ~4 hours up to 4 months of age
- Free access to water up until procedure
What are the consequences for inadequate fasting.
regurgitation and aspiration
Why are fasting recommendations different for pediatric patients?
risk of hypoglycemia
- What type of drug is Maropitant?
- Explain its use as a peri-operative medication.
- Maropitant (Cerenia) – Neurokinin-1 antagonist
- Prevents vomiting & signs of nausea associated with opioid drugs
- Provides adjunct analgesia by blocking substance P
- Faster return to feeding PO
Pre-anesthetic Fasting - Equine
- 6 to 12 hour fast
- Access to water
Because equines don’t vomit, why fast?
Weight of GI contents ↑pressure on diaphragm & limits lung expansion => ↓ ventilation results in ↓ arterial oxygen & ↑ arterial carbon dioxide levels => ventilation–perfusion mismatch
- Fasting Recommendations for cattle
- Sheep and goats
- Ruminants less than 4 weeks of age
- Cattle – 24- 48 hours food,
- 12 – 24 water
- Sheep/goats – 12 – 24 hours food,
- +/- water
- < 4 weeks fast only 2 – 4 hours, nursing, monogastric, less prone to regurgitation
Why fast ruminants?
Bloat => ↑pressure on diaphragm, limits lung expansion => ↓ ventilation results in ↓ arterial oxygen & ↑ arterial carbon dioxide levels => ventilation–perfusion mismatch
What are the 6 steps of anesthesia?
- Pre-anesthetic evaluation
- Premedication period
- Induction of anesthesia
- Maintenance
- Recovery
- Post-anesthetic period
What are the components of the pre-anesthetic minimum data base.
- Signalment
- History
- Physical Exam
- Laboratory & Diagnostic tests
What is in a signalment?
- Species
- Breed
- Age
- Sex/neuter status
- temperament
- Weight & body condition score
Think about species differences in temperment, handling, anatomy and physiology etc. that may affect the anesthetic management of the major species.
Give some examples of breed-specific anesthesia issues in dogs
- Brachycephalic breeds more prone to upper airway obstruction
- Greyhounds & drug metabolism
- Cavalier- Breed disposition to cardiac disease (Cavalier
- Give some examples of breed-specific anesthesia issues in cats
- Pigs
- Breed disposition to cardiac disease (Maine coon)
- Poland China, Landrace, Duroc pigs & malignant hyperthermia
Give some examples of breed-specific anesthesia issues in horses
- Quarterhorse and hyperkalemic periodic paralysis (HYPP)
- Draft horses and laryngeal hemiplegia – 35%
. Why might geriatric and pediatric patients have an increase in anesthetic risk?
- Geriatric patients may have ↑ anesthetic risk due to
- less organ reserve, especially cardiovascular, liver, kidney
- Pediatric patients may have ↑ risk from
- hypoglycemia,
- hypothermia,
- ↓ drug metabolism
Why is sex/ neuter status important in anesthesia
- Related to temperament
- Sex related drug metabolism differences?
How does temperment affect anesthetic management of a patient?
- aggressive/fractious temperament
- poses a danger to staff
- limits pre-anesthetic examination
- Need for more potent drugs, higher doses or combinations for aggressive or overly fearful animals
What should be included in a thorough pre-anesthetic history?
- Diet, exercise, environment
- Past medical problems
- Current medications:
- Identify all prescribed & over-the-counter medications (including aspirin) and supplements to avoid adverse drug interactions
- Past anesthesia => any complications?
Explain the pre-emptive pain score.
- Assigns level of pain to procedure/underlying disease
- None, mild, moderate, severe
- Allows for pre-emptive & intra-op analgesic plan
How does the knowledge of the specific procedure assist with anesthetic planning?
- Evaluate the procedure’s level of invasiveness & duration
- Anticipated level of pain
- Risk of hemorrhage or other complications
AFTER a complete physical exam, on which body systems should the pre-anesthetic evaluation focus?
- cardiovascular
- respiratory
- CNS
What laboratory data will be needed on a Normal Healthy or with localized disease (<5 years old)
Big 4
- packed cell volume (PCV),
- total protein (TP),
- azostrip (kidney function)
- blood glucose (BG)
what laboratory data will be needed on a > 5-7years
CBC, CHEM, urinalysis even if status I or II
Why take radiographs?
- Neoplasia – ‘met check’ – thoracic radiographs/CT
- Heart disease/murmur–thoracic radiographs, echocardiogram
- Trauma (HBC) – thoracic & abdomen radiographs
- Pulmonary contusions, pneumothorax, diaphragmatic hernia
- Urinary bladder rupture, hemoabdomen
Know the Anesthesia Physical Status Classification (I-V) and be able to give an example of each
- I Healthy, no disease
- spay,neuter
- II Healthy, localized or mild systemic disease
- patellar lux., CCR
- III Moderate systemic disease
- murmur, anemia
- IV Severe systemic disease, life threatening
- heart, liver failure
- V Moribund, not expected to live >24hrs
- multi-organ failure,
- Anesthesia Physical Status is directly related to what?
- Is there a linear increase in risk in dogs and cats when their ASA status increases?
- Directly related to risk of peri-anesthetic death
- Not linear!
- Class I – II = 0.12%, 4.8%
- Class III – V (↑40x)
Why is patient stabilization important prior to general anesthesia?
Anesthetic drugs alter normal physiology & ability to maintain homeostasis
What abnormalities should be corrected prior to anesthesia?
- rehydration, correction of acid/base & electrolyte abnormalities, anemia, hypoproteinemia
- Correct co-morbidities - pneumothorax
- will help patient better compensate during anesthesia and surgery
When is it appropriate to proceed directly to surgery despite an unstable patient?
- Elective outpatient procedure – excellent prognosis & PS I-II
- Continued blood loss – splenic tumor rupture, guttural pouch mycosis
- Acute abdomen – colon torsion colic or gastric dilatation/volvulus
A complete anesthetic plan addresses what 6 components?
- pre- & post-anesthetic sedation/tranquilization
- perioperative analgesia – preemptive, intra-op & post-op
- induction & maintenance drugs
- ongoing physiologic support
- monitoring plan
- anticipation & response plan to adverse events or complications
Note: The plan is flexible to allow for patient responses during anesthesia
What are the advantages (and disadvantages) of anesthetic premedication?
Advantages:
- ↓ patient & staff stress
- ease of handling
- ↓ induction & inhalant anesthetic doses => ↓ dose dependent CV/resp depression
- Pre-emptive analgesia
Disadvantages:
- Bradycardia – alpha-2 agonists, opioids
- Hypotension – acepromazine
- Excitement/dysphoria – benzodiazepines
Name the 3 sedative/tranquilizers used in canine pre-anesthetics and their drug class
- Acepromazine
- Dexmedetomidine
- Midazolam/Diazepam
Which drugs are commonly used in combination for feline premedication or total injectable anesthesia?
- Dexmedetomidine
- An opoid
- Butorphanol
- Buprenorphine
- Methadone
- Hydromorphone
- +/- Ketamine or Telazol:
- ↑ restraint (aggressive patients)
- analgesia
- total injectable anesthesia
Name the drugs commonly used for equine premedication.
- Alpha-2 agonist
- Xylazine, detomidine, romifidine
- Butorphanol
- Non-steroidal anti-inflammatory drugs (NSAIDs)
- Phenylbutazone, flunixin
Premedication for cattle
may or may not need
- Xylazine – 1/10 equine dose
- Butorphanol – behavior changes such as restlessness & bellowing
Premedication for goats and sheep
- Butorphanol +/- Benzodiazepine
- +/- xylazine – only healthy patients, can cause hypoxemia in sheep
- What drugs can you use for anesthetic induction for dogs?
- Cats?
- Dogs
- Propofol
- ketamine/benzodiazepine
- alfaxalone
- Cats – above or total injectable anesthesia
What drugs are used for induction in horses
- Ketamine/benzodiazepine,
- +/- guafenasin (GG)
What drugs are used for induction of cattle
Whats the common name?
Triple drip:
- guafenasin
- xylazine
- Ketamine
What drugs are used for induction of sheep and goats
ketamine/benzodiazepine
What are the considerations for anesthesia recovery?
- Sedation
- Analgesia
- Airway protection
- Hypoxemia
Name the 6 most common anesthetic related complications
- Hypotension
- Cardiac arrhythmia
- Cardiac arrest
- Respiratory insufficiency => hypoventilation & hypoxemia
- ↑ arterial carbon dioxide & ↓ arterial oxygen
- Hypothermia or hyperthermia
- Myopathy/neuropathy – equine, cattle
What is/are ways to prevent/prepare for anesthetic complications?
PREVENTION
- Anticipate possible complications & PREPARE ahead of time
- Monitoring warns of changes in patient status
- Allows early intervention before significant morbidity or mortality
- Pre-operative patient preparation plays a significant role
- correct fluid, acid/base and electrolyte abnormalities, anemia and hypoalbuminemia
- IV catheter - fluid administration & emergency use
- Intubation - patent airway, positive pressure ventilation, prevents aspiration
