Canine and feline anesthesia

1Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Canine and Feline Anesthesia
General Anesthesia Sedation
Neuroleptanalgesia Local and Regional
Anesthesia
Chapter 8

Patient Preparation
 Don’t take shortcuts
 Don’t skip steps
 Incomplete patient preparation can result in
life-threatening consequences

Selecting an Anesthetic Protocol
 The list of anesthetics and adjuncts
prescribed for a particular patient
 Includes calculated dosages, routes, and order of
administration
 Selected by the veterinarian-in-charge
 Calculate, check, and recheck drug doses, oxygen
flow rates, and fluid administration rates
 Takes into account minimum patient database,
patient physical status, and procedure
 Modified protocol for ill, pediatric, or otherwise
compromised animals

Minimize Adverse Effects
of Anesthesia
 Correct physiologic abnormalities prior to anesthesia
 Base the protocol on the results of the patient’s
minimum database
 Use a balanced protocol consisting of multiple agents
 Double-check all injectable drug doses prior to
administration
 Label all syringes with the patient name, drug name,
and drug concentration
 Administer no more than the minimum dose needed
to achieve the desired level of anesthesia
 Administer all IV agents “to effect” unless told
otherwise

General Anesthesia: IM Induction
 Anesthetic agents are administered by
intramuscular (IM) injection
 Anesthetic depth gradually increases, peaks,
and gradually decreases
 After injection the anesthetist has little control
over the anesthesia
 May administer more anesthetic if adequate depth
is not reached
 If a reversal drug is available for the anesthetic
agent, it can be administered if patient is too deep

Induction with an IM Agent
or Combination

General Anesthesia:
IV Injection and Ultra–short-acting Agent
 Technique used for short procedures
 <10 minutes of anesthesia
 Drugs:
 Propofol, methohexital, thiopental sodium, or
etomidate
 Drug is given to effect
 Anesthetic depth increases rapidly then
decreases gradually
 Anesthetist controls peak effect and can
increase depth by administering more
anesthetic agent

Induction with an IV Injection
of an Ultra–short-acting Agent to Effect

General Anesthesia:
TIVA and Ultra–short-acting Agent
 TIVA: Total intravenous anesthesia
 Patient is induced to effect; additional boluses
are administered every 3-5 minutes as
needed to maintain surgical anesthesia
 Short-to-moderate length noninvasive procedures
 Propofol is the most commonly used agent
 Anesthetist can increase depth but can’t decrease
depth if excessive

Total Intravenous Anesthesia (TIVA) by
IV Boluses of an Ultra–short-acting Agent

General Anesthesia: TIVA by CRI
 Total intravenous anesthesia by constant rate
infusion (CRI)
 Patient is induced to effect
 Anesthesia is maintained by constantly
infusing small amounts of anesthesia via a
syringe pump
 Slows down and moderates changes in depth as
seen with bolus administration

Total Intravenous Anesthesia
by Constant Rate Infusion

General Anesthesia: Inhalant Agent
 Not an injection technique
 Induction is faster than IM induction, but slower
than IV induction
 Anesthetist has control over depth of the
anesthesia; can make changes rapidly
 Delay between time dial setting is changed and
patient depth occurs
 Factors that affect delay time
 Patient respiratory drive
 Agent used and carrier gas flow rate
 Type and volume of breathing circuit

Induction and Maintenance
with an Inhalant Agent

General Anesthesia:
IV Induction and Inhalant Maintenance
 Most commonly used method of inducing and
maintaining anesthesia in small animals
 Dynamic elements of both IV and inhalant
administration
 Rapid induction
 Good control over both increases and decreases
in anesthetic depth
 Rapid recovery

IV Induction and Maintenance
with an Inhalant Agent

Equipment Preparation
 Locate, check, and prepare all equipment
needed for entire anesthetic period prior to
induction
 Intubation equipment
 Syringes, needles, drugs, fluids required
 Equipment designed to prevent hypothermia
 Small animal anesthetic machine
• Semiclosed rebreathing system (≥2.5 to 3 kg patient
weight)
• Non-rebreathing system (<2.5 to 3 kg patient weight)
 Crash cart with emergency drugs and equipment

Premedication or Sedation
 Calms the patient and prepares the patient
for anesthetic induction
 Desired effects
 Sedation, cholinergic blockade, analgesia, muscle
relaxation
 Drugs
 Tranquilizers, alpha2-agonists, opioids,
dissociatives, anticholinergics

Premedication or Sedation (Cont’d)
 After IM injection place the animal in a quiet
yet accessible place
 Close observation until agent takes effect
 Stimulation or excitement may diminish the
beneficial effects
 Induction should follow immediately after
desired effects are reached

Anesthetic Induction
 Patient loses consciousness and enters
surgical anesthesia
 Take the patient from consciousness to stage III
anesthesia smoothly and rapidly
 Intubate when possible while animal is still light
 IV induction is most common and takes animals
through the excitement stage most rapidly
 Attempt to avoid the excitement/struggling stage,
which is seen more often with mask induction
 IM induction results in smooth, gradual CNS
depression with little apparent time spent in the
excitement stage

IV Induction
 Drugs used
 Mixture of equal volumes of ketamine and
diazepam or midazolam
 Propofol
 Neuroleptanalgesics
 Thiopental sodium
 Etomidate
 Various other combinations containing
dissociatives, tranquilizers, and opioids

IV Induction (Cont’d)
 Administer IV to effect (unconsciousness)
 Don’t administer the entire calculated dose all at
once
 Allow for individual patient response to anesthetic

IV Induction (Cont’d)
 Premedication drugs can affect the dose of
general anesthetic required
 Titration
 IV drugs given as a series of bolus injections and
discontinued when desired effect is reached
 IV induction produces up to 10-20 minutes of
anesthesia
 If more time is needed, anesthesia is maintained
with inhalation anesthetics or administration of
propofol, methohexital, or etomidate by repeat
boluses or CRI

Inhalation Induction
 Anesthetic induction using a facemask or
induction chamber
 Drugs used: isoflurane and sevoflurane
 Low blood-gas solubility coefficient
 Results in rapid passage through stage II
anesthesia

Inhalation Induction (Cont’d)
 Mask induction
 Use of a facemask to induce anesthesia
 Requires skillful restraint to prevent patient or
operator injury
 Don’t restrict chest excursions or the airway
 Fit the mask prior to induction
 Mask obscures muzzle and eyes normally used
for monitoring
 Need higher oxygen flow rates than with
endotracheal tube

Inhalation Induction: Facemask
 Cautions
 Exposes personnel to waste anesthetic gas
• Need adequate room ventilation
 Patient struggling can lead to epinephrine release
• Use only on calm or sedated patients
 Longer induction period
• Avoid in patients with poor respiratory function
 Intubate immediately when possible
• To gain control of airway and ventilation
 Always keep airway open
• Don’t occlude nostrils or compress airway or chest

Inhalation Induction: Chamber
 Placing patient in a closed chamber infused
with anesthetic gas
 Patient is usually <5-7 kg body weight
 Used for small, aggressive patients
 Examine chamber prior to use
 Tight-fitting lid with two gas ports

Inhalation Induction: Chamber
(Cont’d)
 Complications
 Stress, trauma, vomiting, airway blockage
 Hard to monitor patient
 Exposes personnel to waste anesthetic gas
• Attach scavenger
 Epinephrine release
• Predisposes patient to cardiac arrhythmias and
hypotension

IM Induction
 Neuroleptanalgesic combinations and a
variety of combinations of tranquilizers,
dissociatives, and opioids used to induce
general anesthesia
 Benefits
 Use in animals in which IV injections are difficult
• Young animals, aggressive animals, wild animals,
captive animals in zoos
 May need restraint equipment, blowpipe, or
tranquilizing gun

IM Induction vs. IV Induction
 The dose of a drug needed for IM induction is
generally about twice the corresponding IV dose
 IM induction takes longer to achieve high enough
brain concentration to induce anesthesia
 After peak effect of the IM drug is reached and the
patient is still too light, an additional drug or
inhalant agent must be administered to get the
patient deep enough to intubate
 IM induction results in a longer recovery period
because of a longer metabolism time

Endotracheal Intubation
 Endotracheal tube is placed in the patient’s
airway after general anesthesia induction
 Conducts air or anesthetic gases directly from oral
cavity to trachea
 Bypasses the nasal passages and pharynx
 Can be connected to an anesthetic machine to
maintain anesthesia

Endotracheal Intubation (Cont’d)
 Benefits
 Helps maintain an open airway
• Leave in place until the swallowing reflex returns
 More efficient delivery of anesthetic gas than
facemask
• Decreased exposure of personnel to waste gas
 With inflated cuff helps prevent aspiration of vomitus,
blood, saliva
 Reduces anatomic dead space
• Improved efficiency of gas exchange
 Ventilation can be supported manually or
mechanically
• Especially useful for patients in cardiac or respiratory arrest

Feline Intubation

Equipment for
 Three endotracheal tubes of slightly different
diameters
 Two-foot length of IV tubing or rolled gauze to secure
tube
 Gauze sponge to grasp tongue
 12-mL syringe to inflate cuff
 Good light source
 Stylette for narrow diameter tubes
 Lidocaine injectable solution or gel to control
laryngospasm (cats)
 Laryngoscope with appropriate blade

Intubation Equipment

Selecting an Endotracheal Tube
 Diameter
 Small enough to not cause trachea injury
 Large enough to provide a seal with inflated cuff
 Length: minimize mechanical dead space
 Must reach the thoracic inlet
 Must not extend beyond the end of the muzzle
 Patient
 Species, conformation, and breed
 Preparation

Proper Endotracheal
Tube Placement

Intubation Procedure
 Know the anatomy of the throat
 Pharynx and larynx
 Know the proper restraint and positioning
techniques
 Don’t attempt intubation unless you can visualize
the larynx
 Have proper lighting
 Induce patient with IV anesthetic
 Unconsciousness, no voluntary movement, no
pedal reflex, sufficient muscle relaxation, no
swallowing when tongue is pulled

Anatomy of the Pharynx

Intubation Procedure
 Insert tube rapidly and correctly
 Place patient in lateral recumbency
 Secure the tube and inflate the cuff
 Turn on the oxygen
 Attach the breathing circuit
 Turn on the anesthetic vaporizer
 Begin patient monitoring

in Small Animals

Checking for Proper
Tube Placement
 Revisualize larynx and confirm the tube is in the
correct location
 Watch reservoir bag as animal breathes
 Feel for air movement from the tube connector as
patient exhales
 Fogging of the tube during exhalation
 Unidirectional valve motion
 Palpate the neck
 Ability of patient to vocalize indicates misplaced tube
 Patient coughs during intubation
 Capnometer connection

Laryngospasm
 Reflex closure of the glottis in response to
contact with an object or substance
 Common in cats, swine, and small ruminants in
light plane of anesthesia
 Makes intubation very difficult; larynx is easily
damaged
 May lead to cyanosis or hypoxemia

Laryngospasm (Cont’d)
 Prevention
 2% injectable lidocaine or lidocaine gel
 Adequate depth of anesthesia
 Wait for glottis to open before intubating
 Don’t force the tube

Securing the Tube and Cuff Inflation
 Tie the ET tube securely without compressing
the tube
 Cuff the tube
 Extend the patient’s head
 Have an assistant close the pop-off valve and
compress the reservoir bag
 Listen for gas leaks
 Inflate the cuff until the leaking just ceases at a
pressure of 20 cm H2O

Complications of Intubation
 Vagus nerve stimulation
 Brachycephalic dogs or other breed deformities
 Overzealous intubation efforts
 Overinflation of cuff
 Obstructed endotracheal tube
 Waiting too long to remove the tube
 Improper cleaning and sanitizing between uses
 Tracheal and/or laryngeal irritation leading to
postsurgical cough

Maintenance of General Anesthesia
 Inhalant agent
 Repeated boluses of ultrashort-acting agents
 Continuous rate infusion (CRI)
 Injectable and inhalant agents
 Intramuscular injections

Patient Positioning, Comfort, and
Safety
 Support the patient as it loses consciousness
(especially the head)
 Remove IV needle and syringe immediately
after successful intubation
 Lay patient in lateral recumbency immediately
after intubation; then secure the tube and
inflate the cuff
 Ensure the endotracheal tube is inserted
properly without bends or kinks

Safety (Cont’d)
 Temporarily disconnect tube when turning the
patient
 Support anesthetic machine hoses so no
drag is put on the endotracheal tube
 Check position of hoses and tube during
transfer and repositioning
 Make sure reservoir bag is visible at all times
 Put animals in as normal a position as
possible on the surgery table

Safety (Cont’d)
 Don’t use heavy drapes or instruments that
will lie on the chest of small animals
 Don’t overtighten leg restraints
 Place patient on a heat-retaining surface
 Place normal lung up if one lung is diseased
 Be cautious of tilting the surgery table
 Use artificial tears or other corneal lubricant

Anesthetic Recovery
 The period between the time the anesthetic is
discontinued and the time the patient is able
to stand and walk without assistance
 Influencing factors
 Length of anesthetic period
 Condition of patient
 Type of anesthetic administered and route of
administration
 Patient body temperature
 Patient breed

The Anesthetist’s Role in Recovery
 Discontinue administration of anesthetic
agents
 Continually to monitor patient through the
stages of recovery
 Administer oxygen as necessary, especially
to shivering patients
 Oxygen source placed close to the nostrils
 Elizabethan collar and cellophane cover
 Nasal catheter
 Oxygen cage
 Administer reversal agents if available

(Cont’d)
 Maintain patent airway and extubate when
appropriate
 Prepare by deflating cuff and untying gauze
 Remove when the swallowing reflex returns (dogs,
cats) or when signs of impending arousal are
present (voluntary limb, tail, or head movements)
 Remove the tube in one slow, steady motion

(Cont’d)
 Provide general nursing care
 Quiet handling, calm reassurance, attention to
patient comfort level
 Prior to consciousness remove all restraint ties
and make sure all accessory procedures are
complete
 Prior to consciousness remove all monitoring
equipment, probes, cuffs, and electrodes
 Be gentle when moving the patient
 Leave IV catheter in place until recovery is
complete

(Cont’d)
 Provide general nursing care (Cont’d)
 Hasten recovery with gentle stimulation
(talking, rubbing, gently move ET tube)
 Turn every 10-15 minutes to prevent hypostatic
congestion
 Never leave patient unattended
 Gradually rewarm hypothermic patients

(Cont’d)
 Provide adequate analgesia and other
prescribed medications
 Analgesics should be administered before the
onset of pain
 Adequate analgesia
• Patient sleeps comfortably with minimal signs of
discomfort
 Dose adjustment or switching to a different
analgesic may be necessary to control pain
 Prepare patient for ongoing hospital care or
prepare patient for release

Canine and feline anesthesia

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