2. General Considerations
1. breed
2. temperament
3. physical/health status
4. purpose of anesthesia
5. familiarity with the drugs to be used
6. any concurrent medication
7. equipment and available assistance
3. Safe Anesthetic Practices
1. use of reversible agents whenever
possible
2. endotracheal intubation should be
mandatory to assure patent airway at all
times
3. careful monitoring of all anesthetized
patients, including the preanesthetic and
recovery periods
4. preanesthetic fasting (food 8-12 hours;
water 2-4 hours in small animals), except
in the very small, young or debilitated
4. Pre-Anesthetic
A. Be sure you are familiar with the physical
status of each patient
1. obtain complete history and review prior to
anesthesia
2. perform a thorough physical examination
3. an accurate weight is important
particularly in small animals
adjust for lean body weight
4. review laboratory data
determines need for preanesthetic stabilization
directs drug selection
directs further preoperative tests
5. Pre-Anesthetic
B. Formulate specific anesthetic plan
1. choose a protocol appropriate for the patient
2. anticipate complications that may arise based on
physical examination and laboratory data, the procedure
being performed, anesthetic drugs used (plan for failure)
3. calculate doses carefully
4. draw up drug, label syringes appropriately
5. prepare anesthetic record
6. Pre-Anesthetic
C. Place intravenous catheter
1. aseptic technique
2. place after premedication, prior to the
induction of anesthesia
3. exceptions
intractable animals that must be chemically
immobilized prior to handling
restraint for catheter placement causes
excessive stress and danger to the patient
short procedures in healthy patients
7. Pre-Anesthetic
D. Gather equipment and supplies
1. Endotracheal tube
2. Laryngoscope
3. Preparation of Anesthetic Machine
4. Assemble monitors
5. Other Equipment
8.
9. Premedication
A. Selection is based on:
1. patient condition
2. patient temperament
3. procedure
4. familiarity with drugs
10.
11. Premedication
B. Route of Administration
1. based on temperament
2. SC, IM, IV all possible routes
12.
13.
14. Premedication
Dogs
1. Possible Drugs/Combinations
Acepromazine + Hydromorphone
Medetomidine + Hydromorphone
Midazolam + Hydromorphone
Hydromorphone (or some other opioid) alone
16. INDUCTION
A. Intravenous Agents
a. never inject rapidly
b. preanesthetics alter the required dose of inhalants,
sometimes profoundly
c. most induction agents are titrated to effect
d. adjust induction dose according to the degree of
sedation following premedication
18. Induction
Specific Drugs
dose of induction drug can be reduced by administering
lidocaine (1 mg/kg) or diazepam (0.2 mg/kg)
useful in depressed patients
Lidocaine helps stabilize myocardium
19. Induction
Endotracheal Intubation
be prepared – this should be accomplished quickly (but
don’t panic!!)
choose a range of tube sizes
cats: 3.0 – 5.0 mm i.d.
dogs: 4.0 mm i.d. – 12 mm i.d.
adequate anesthesia is required prior to intubation
laryngospasm can occur (especially in cats)
20. Induction
Procedure
2 people required
animal in sternal position, lined up along its longitudinal axis
once appropriate depth of anesthesia has been reached, pull
tongue out of mouth
use laryngoscope!
cats
larynx is sensitive and prone to laryngospasm
lidocaine spray or 0.1 ml 2% lidocaine will reduce incidence of
laryngospasm
brachycephalic breeds
use a laryngoscope
elongated soft palate may need to be moved dorsally to release the
epiglottis.
21.
22.
23.
24. Checking for proper tube
placement
1. check for respiratory gas
condensation on the inside of the tube
during inspiration
2. a correctly placed tube will often
stimulate a cough reflex immediately
following placement
3. watch for movement of the
rebreathing bag (keeping in mind that
a patient may become apneic
immediately following induction)
25. Checking for proper tube
placement
4. palpate the neck for two tubes – if
you feel two tubes, you are feeling the
trachea and the endotracheal tube in
the esophagus.
5. auscultate the chest during assisted
ventilation.
6. hemoglobin saturation (Pulse
oximetry)
7. Capnography
26. Maintenance
General Considerations
once the patient is at an appropriate level
of anesthesia, turn down vaporizer and
oxygen flow rate to maintenance levels.
immediately following induction, check
pulse, respiratory rate, pulse quality,
capillary refill time.
start anesthetic record
attach monitors
start fluid administration at an appropriate
rate (5-10 ml/kg/hr)
27. Recovery
Continue oxygen administration as long as possible after
vaporizer has been turned off
Deflate cuff and remove tube only when swallowing is
observed
Watch carefully during recovery.
28. Recovery
Post-anesthetic monitoring should continue until
the animal can maintain sternal recumbency or
lift its head and until vital signs are stable
External heat source should be applied to raise
body temperature to within 1 or 2 degrees of
normal body temperature
Stimulating the animal will speed recovery but
keep in mind that once the stimulation is
stopped that the animal will likely go back to
sleep
Post-operative analgesics should be
administered as required.
29. Recovery
Sedation may be required for the animal that
is experiencing a rough recovery
a. acepromazine
b. medetomidine
Fluid therapy should be continued in the
recovery period until the animal is
completely recovered from anesthesia.
Some disease states will require continued
fluid administration.
30. MAINTENANCE OF ANESTHESIA
WITH INJECTABLE AGENTS
used for short duration procedures or when inhalant
anesthesia is unavailable or contraindicated
achieved by a single dose for short procedures or small
intermittent boluses doses of a drug or a constant rate
infusion in longer duration procedures
31. MAINTENANCE OF ANESTHESIA
WITH INJECTABLE AGENTS
Specific drugs or drug combinations:
1. propofol
2. ketamine combinations
3. Ketamine/Alpha 2 Agonist Combinations
4. Telazol
5. GXK (Triple drip) in horses/cattle
32. References
Slatter, D. Textbook of Small Animal
Surgery 3rd
Edition, Volume II, 2003,
Section 17, p. 2503-2623.
Pain Management for the Surgical Patient
Patient Monitoring
Operating Room Emergencies
Anesthesia and Analgesia for the Trauma
or Shock Patient
Anesthesia for the Pediatric and Geriatric
Animal
33.
34.
35.
36.
37.
38. Common Anesthetic Problems
Bradycardia
Tachycardia
Hypotension
Hypertension
Blood loss
Apnea
Tachypnea
Too Light
Too Deep
39. Bradycardia
Remember that a heart rate defined as
bradycardic is specific to a particular
animal/breed. Smaller breeds are
much less tolerant of lower heart rates
while larger breeds don’t have a
problem with a heart rate of 60.
The target heart rate for an animal
should be its pre-anesthetic heart
rate, keeping in mind that the pre-
anesthetic rate will often be elevated
because of stress/anxiety.
41. Bradycardia
Treatments:
remove cause (if possible – as in hypothermia)
anticholinergic
glycopyrolate 0.005 – 0.02 mg/kg IV
atropine 0.01 – 0.02 mg/kg IV
if administering dopamine or dobutamine – discontinue and
wait approximately 5 minutes before administering
anticholinergic
42. Bradycardia
Atropine – faster onset than glycopyrolate
don’t be afraid to administer > 1 dose of an
anticholinergic. If the first dose doesn’t work, try a
second or a third. After 3 doses of one anticholinergic,
I will usually administer a dose of the other to see if
that works.
43. Bradycardia
bradycardia induced by alpha 2 agonists
such as Domitor can be approached this
way:
if the heart rate is just low, blood pressure
is fine and there are no arrhythmias, then
you don’t really need to treat.
if arrhythmias do start to appear (second
degree AV block, escape complexes) then it
may be best to administer a small amount of
the reversal (atipamezole) to bring the heart
rate up rather than giving an anticholinergic
(debatable).
44. Bradycardia
bradycardia in response to hypertension is a good
thing. Leave it alone. Correct the hypertension and
the bradycardia will usually go away.
47. Tachycardia
Treatment:
remove cause
in animals with high heart rates and normal
blood pressures that are at an appropriate
depth of anesthesia, it is often the case that
they have lower than normal circulating
volume so that the heart has to work
harder/faster to maintain good cardiac output
and blood pressure. Often, the first response
to tachycardia in an animal that is assessed to
be appropriately managed in terms of its
pain, is to administer a fluid bolus (10 ml/kg
crystalloids over 15 min) to see if an increase
in volume will bring the heart rate down.
48. Tachycardia
high ETCO2 will produce sympathetic
stimulation that can cause an increase
in heart rate. Solution: ventilate
when an animal is responding to surgical
stimulation, then you should reevaluate
your approach to pain management in
this animal. Often, a supplemental
dose of an opioid (hydromorphone,
fentanyl) will provide you with the
additional analgesia that is required.
49. Hypotension
Possible Causes:
hypovolemia/blood loss
excessive anesthetic dose (usually inhalant but can occur
with injectables such as propofol)
poor myocardial contractility
bradycardia (see above)
50. Hypotension
Treatments:
generally, the first approach to dealing
with hypotension in an animal under
anesthesia is to a) reduce the dose of
inhalant anesthesia and b) administer a
bolus of either crystalloids (10 ml/kg over
15 min) or dextrans (5 ml/kg initially –
can go up to 20 ml/kg in more emergent
cases) (if non-responsive to a bolus of
crystalloids or you don’t want to give any
more crystalloids.
51. Hypotension
in cases where the inhalant concentration cannot be
lowered but you REALLY need to reduce it because of
cardiovascular depression, you can consider giving a
supplemental dose of narcotic (say hydromorphone =
0.05 – 0.1 mg/kg IV). This will allow you to reduce
the dose of inhalant required for anesthesia.
52. Hypotension
poor contractility can lead to hypotension and can be
the result of cardiovascular depression due to the
inhaled anesthetic or preexisting cardiovascular
disease (i.e. dilated cardiomyopathy). In these cases
administering either dobutamine (3 – 10 ug/kg/min
IV) or dopamine (3-10 ug/kg/min) may be helpful.
53.
54.
55. Hypertension
Possible Causes:
too light/inadequate anesthesia
excessive dobutamine or dopamine administration
alpha 2 agonist administration
excessive fluid administration
elevated ETCO2
56. Hypertension
Treatments:
increase depth of anesthesia (either by increasing inhalant
concentration or administering an additional dose of
narcotic)
reduce dobutamine or dopamine administration
ventilate if ETCO2 is elevated
diuresis if volume overload
57. Blood Loss
Most blood loss during anesthesia occurs
because of a surgical or medical procedure.
Acute blood loss can lead to hypovolemia,
hypotension and reduced oxygen delivery.
Anesthetized animals have greater difficulty
compensating for blood loss than do conscious
animals. Ongoing efforts to quantify blood
loss must be made so that adequate volume
replacement can be made. When quantifying
blood loss, keep in mind that for every 1 ml
of blood lost, you need to give 3 ml of
crystalloids back to restore the volume. This
should be provided in addition to the
calculated maintenance solutions. Animals
that lose 20% of their blood volume should
have that volume replaced with whole blood
rather than crystalloids.
58. Apnea
can occur at 2 different, distinct time points in the
anesthetic process. 1
. following induction (particularly with an injectable
anesthetic)
occurs frequently and will generally resolve on its own
proceed with intubation, denitrogenating the anesthetic circuit
and lungs (by giving 2-3 good breaths of oxygen once the animal is
connected to the anesthetic machine)
wait for the animal to redistribute the induction drug to the point
where it begins to respond to carbon dioxide again.
59. Apnea
In animals where you are particularly concerned about
induction apnea (i.e. animals that already have some
respiratory embarrassment), preoxygenating prior to
the induction of anesthesia will help to reduce the
impact of induction apnea on oxygen levels.
60. Apnea
May also occur because of being either too deep under
anesthesia (or too light)
61. Tachypnea
Possible causes:
too light for the procedure
excessive ETCO2
hyperthermia
hypoxemia
The most common cause of tachypnea during anesthesia is
an inadequate depth of anesthesia – too light (see below).
63. TOO LIGHT
Possible causes:
mismatch between the depth of anesthesia (inadequate)
and the level of surgical stimulation (excessive).
Usually occurs at the beginning of surgery.
during the transfer of an animal to inhalant anesthesia
following induction with propofol.
64. TOO LIGHT
Treatments:
if the animal is moving, then you need to
increase the depth of anesthesia - giving a
supplemental dose of the induction drug is
indicated.
if you just need to increase the depth
slowly because you have noticed that the
animal is responding a little to surgical
stimulation (i.e. mild increase in blood
pressure, heart rate or respiratory rate),
then you can produce an increase in depth
of anesthesia by a) turning up the
vaporizer and b) increasing the fresh gas
flow rate.
65.
66. TOO DEEP
Possible Causes:
mismatch between the depth of anesthesia (excessive) and
the level of surgical stimulation (inadequate.)
67. TOO DEEP
too much induction drug
vaporizer set too high.
Preventing an animal from becoming too
deep under anesthesia requires close
attention to the anesthetic needs of the
animal.
Before administering an injectable induction
drug, carefully evaluate how sedate the animal
is following the premedication. If it is very
sedate, then you will not have to give much
induction drug.
In the same vein, if an animal is very deep
after you induce anesthesia, then you will not
have to give much inhalant initially.
68. TOO DEEP
Treatment:
if the depth of anesthesia is too deep because of
injectable drugs you can either
a) reverse part or all of any reversible drugs
b) support the animal as it metabolizes any non-reversible
drugs.
69. TOO DEEP
inhaled anesthesia:
decreasing the vaporizer setting
increasing the fresh gas flow (this increases the rate at
which the gas containing the reduced concentration
replaces the gas with the “old”, higher concentration of
anesthetic.
72. 5. The components of an anesthetic machine are listed below.
Choose the order that best describes the flow oxygen through the
machine:
a) cylinder, pressure gauge, pressure regulator, precision
vaporizer, flow meter, fresh gas outlet/port, breathing circuit,
overflow (pop-off) valve.
b) pressure regulator, cylinder, pressure gauge, precision
vaporizer, flow meter, fresh gas outlet/port, overflow (pop-off)
valve, breathing circuit
c) cylinder, pressure gauge, pressure regulator, flow meter,
precision vaporizer, fresh gas outlet/port, overflow (pop-off)
valve, breathing circuit
d) cylinder, pressure gauge, pressure regulator, flow meter,
precision vaporizer, fresh gas outlet/port, breathing circuit,
overflow (pop-off) valve.
e) pressure regulator, cylinder, pressure gauge, precision
vaporizer, flow meter, overflow (pop-off) valve, fresh gas port,
breathing circuit
73. 6. All of the following statements concerning
the rebreathing bag are correct except:
a) it acts as a reservoir bag from which the
animal may breath oxygen and anesthetic gas
b) it can be used to manually support
ventilation
c) it allows visual assessment of the respiratory
rate
d) it traps carbon dioxide expired by the animal
e) it allows visual assessment of the tidal
volume
74. Physical Exam/Data:
Chest:
Rhythm:
Other:
Labs/Rads/ECG/Other:
Assessment:
ASA Status:
I II III
IV V
PLAN/RECOMMENDATIONS:
FURTHER DIAGNOSTICS:
PRE-ANESTHETIC THERAPY:
PREMEDICATION:
INDUCTION:
MAINTENANCE:
ANALGESIA:
FLUIDS: MONITORING:
PRE-ANESTHETIC EVALUATION FORM
Date: Time:
Patient Name:
Requested By:
History:
PROCEDURE/REASON FOR ANESTHESIA:
=
_________________________________
Glenn Pettifer, DVM, DVSc, DACVA
