8. Canine and Feline Anesthesia
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Transcript of 8. 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
2Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Patient Preparation
Don’t take shortcuts Don’t skip steps Incomplete patient preparation can result in
life-threatening consequences
3Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
4Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
5Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
6Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Induction with an IM Agent or Combination
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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
8Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Induction with an IV Injection of an Ultra–short-acting Agent to Effect
9Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
10Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Total Intravenous Anesthesia (TIVA) by IV Boluses of an Ultra–short-acting Agent
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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
12Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Total Intravenous Anesthesia by Constant Rate Infusion
13Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
14Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Induction and Maintenance with an Inhalant Agent
15Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
16Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
IV Induction and Maintenance with an Inhalant Agent
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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
18Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
19Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
20Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
21Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
22Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
23Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
24Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
25Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
26Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
27Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
28Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
29Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
30Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
31Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
32Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
33Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Feline Intubation
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Equipment for Endotracheal Intubation
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
35Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Intubation Equipment
36Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
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Proper Endotracheal Tube Placement
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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
39Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anatomy of the Pharynx
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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
41Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Endotracheal Intubation in Small Animals
42Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
43Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
44Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
45Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
46Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
47Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Maintenance of General Anesthesia
Inhalant agent Repeated boluses of ultrashort-acting agents Continuous rate infusion (CRI) Injectable and inhalant agents Intramuscular injections
48Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
49Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Patient Positioning, Comfort, and 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
50Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Patient Positioning, Comfort, and 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
51Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
52Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
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
53Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
The Anesthetist’s Role in Recovery (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
54Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
The Anesthetist’s Role in Recovery (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
55Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
The Anesthetist’s Role in Recovery (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
56Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
The Anesthetist’s Role in Recovery (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