MAINTAINING ANESTHESIA - Dr. Roberta Dev Anand

Report
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Involves both vital signs and reflexes
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Can be done with or without machines
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Tell us how well a patient is maintaining
homeostasis through respiration & circulation
◦ Often grouped according to whether they reflect
circulation, oxygenation, or ventilation
◦ For example, values that reflect circulation are: HR,
heart rhythm, pulse strength, CRT, mucous membrane
color, and blood pressure
◦ Values that reflect oxygenation are: mucous
membrane color, hemoglobin saturation,
measurement of arterial blood oxygen
◦ Values that reflect ventilation are: RR, respiratory
depth, breath sounds, expired CO2 levels,
measurement of arterial CO2
THE MOST IMPORTANT MONITORING TOOLS ARE YOUR
HANDS, EYES, & EARS!
MACHINES WILL FAIL!
ONLY RELY ON MACHINES FOR VALUES THAT YOU CANNOT
GET ON YOUR OWN(blood pressure, ECG, SPO2)
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Anesthetic agents are expected to lower the heart
rates of patients
While under anesthesia, the following heart rates
are appropriate for dog:
◦ Large dogs: 60 - 140 beats per minute
◦ Small dogs: 70-160 beats per minute
◦ Notify the vet if heart rates are outside these ranges
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While under anesthesia, the following heart rates
are appropriate for cats:
◦ 100-180 beats per minute
AUSCULTATION
PALPATION
ESOPHAGEAL STETHOSCOPE
An esophageal stethoscope is a thin, flexible tube that is attached
to a regular stethoscope. Lubrication is applied to the end of the
tube which is placed in the oral cavity and down the esophagus
until a heartbeat is heard.
This allows a person to listen to the heart on an animal that is
draped in for a surgical procedure
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The rate of the return to color for mucous
membranes after the application of digital pressure
compresses capillaries and blocks blood flow
temporarily
Provides information about tissue perfusion
A normal CRT does not guarantee that the patient
is normal, however a prolonged CRT (longer than 2
seconds) means that tissue perfusion is not
adequate
◦ Possibly due to vasoconstriction, hypotension,
hypothermia, heart failure, shock, or increased anesthetic
depth
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IDEALLY, COLOR SHOULD BE PINK!
◦ If gums are pigmented, look at the conjunctiva, or
the inner prepuce or vulva
◦ If pale, there may be blood loss, anemia, or poor
perfusion
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CYANOSIS = purple or blue discoloration=
EMERGENCY!
ICTERUS=yellow discoloration, may indicate
severe liver disease or hemolysis
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Can be done at the lingual, femoral,
metacarpal/metatarsal, and dorsal pedal
arteries
Should be strong and match the heart beat
Weak pulses may indicate hypotension
Causes: excessive anesthetic depth,
cardiac insufficiency, excessive blood loss
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Excessive blood loss can
cause complications
such as shock
One soaked3x3 gauze =
~5-6 mL of blood
One soaked 4x4 gauze=
~10mL blood
The actual amount lost
may be more due to clotting
or pooling of blood
Healthy animal can tolerate
~ 13mL/kg blood loss
during surgery
Intra-abdominal blood clot
Intra-abdominal blood pooling
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Anesthetic agents are expected to reduce the
tidal volume, which is the amount of air inhaled
with each breath.
Can be evaluated by watching
the patient’s chest or the reservoir
bag on the anesthetic machine
Normal values while under
anesthesia for dogs & cats: 8-20 bpm
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Bagging the patient refers to the process of
manual ventilation.
Gentle squeezing of the reservoir bag causes
oxygen/anesthetic gas to be forced into the
patient’s lungs
◦ Can be used to increase anesthetic
depth. If an animal is waking up, manually
forcing anesthetic gas into the lungs will cause it
to fall asleep more rapidly
◦ Can be to increase respiratory rate. If the
respiratory rate is low, we can provide manual
breaths ~q20 seconds to increase the rate
◦ To reverse atelectasis. Atelectasis refers to the
collapse of alveoli
RESPIRATORY RATE & DEPTH
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Hyperventilation=Increase in respiratory
depth
Tachypnea = increase in respiratory rate
Causes of hyperventilation and tachypnea:
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Increased CO2 in the blood
Underlying pulmonary disease
Surgical stimulation
Decrease in anesthetic depth (animal is too light)
RESPIRATORY RATE AND DEPTH
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Normal breaths are smooth and regular, not
gasping or labored
DO NOT FORGET TO USE YOUR STETHOSCOPE
TO EVALUATE BREATH SOUNDS!
◦ Should not hear crackles or wheezes
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Hypothermia is the most common anesthetic
problem
◦ Begin prevention from the moment the animal is
induced.
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The greatest decrease in body temperature is
within the first 20 minutes of anesthesia.
The following can decrease body temperature:
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Shave and scrub of the surgical area
Inability of the animal to shiver to create body
heat
Decreased metabolic rate
Exposure of the internal organs to the air
Anesthetic agents that cause vasodilation, and
increase the rate of heat loss
Pediatric and geriatric animals
Room temperature
Check the patient’s temperature at least every
30 minutes if there is not an esophageal probe
available. In between temp checks, feel the
animal’s extremities
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Several methods to avoid hypothermia:
◦ Circulating warm water heating pad. Electric heating
pads may cause more burns. For all heating pads,
put a towel between the heating pad and the
patient
◦ IV fluid line warmer
◦ Hot water bags/rice socks
◦ Saran wrap/bubble wrap
◦ Bair hugger
◦ Warm towels
◦ Heated surgery table
◦ Baby booties on the paws
Circulating warm water
heating pad
Self-warming surgery table
Fluid line warmer
Bair
Huggers
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Excessive efforts to warm a patient could
cause thermal injuries.
◦ Always place towels between the patient and the
heat source!
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Some patients, usually cats, will become
hyperthermic post-operatively. This is due
to the effects of some drugs such as
ketamine and opioids.
◦ If the temp reaches 103.5˚ or higher, we should
begin cooling methods.
 Taking all blankets/towels out of the cage
 Putting a fan in front of the cage
 Wiping the patient down with a wet washcloth
 Applying alcohol to the footpads.
•Reflexes are involuntary reactions to a
stimulus
•It is also important to monitor reflexes,
which will help you determine the stages
and planes of anesthesia.
Palpebral Reflex
Touch the corner of the eyelids and the animal
blinks.
The palpebral reflex is stimulated by tapping
the skin at the medial canthus of the eye or
by running the finger along the eyelashes.
This disappears in light to medium plane of
surgical anesthesia in small animals.
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Simulation of the larynx will cause the animal
to swallow. This is a mechanism to prevent
accidental aspiration of fluids into the lungs.
◦ passing an endotracheal tube
◦ presence of secretions at the larynx.
Withdrawal Reflex
Pull a limb gently, pinch the toe and the
animal will pull back the limb.
The reflex is obtained by firm pressure of
the interdigital skin in the dog and cat,
squeezing the claws together in cattle and
swine and firm pressure on the pastern of
horses. The reflex disappears late in phase
III and indicates deep anesthesia. When
checking the reflex, the legs should be held
in extension. Probably more useful in
monitoring laboratory animal patients and
birds.
Pupillary Reflex
Shine a light in the eye and the pupil constricts.
The pupillary responses under anesthesia are heavily
influenced by pre-medication. Species variations
exist. There is also variability in response to
different anesthetics. In general, in unpremedicated patients, the pupil is dilated in the
early excitement phase and then becomes
progressively constricted as surgical anesthesia
occurs. With very deep surgical anesthesia the
pupil begins to dilate again and with entry into
phase IV, with respiratory and cardiac arrest, the
pupil is maximally dilated.
Corneal Reflex
Touch the cornea and the animal blinks. Be
careful not to damage the cornea if this
reflex is tested.
The corneal reflex is obtained by gentle
palpation of the lateral aspect of the
cornea. This causes reflex closure of the
eyelids. The reflex disappears in the deeper
levels of phase III, plane II. This reflex is not
always reliable in the dog, particularly if the
eyeball is markedly rotated.
EAR FLICK REFLEX
Pinnal reflex used in cats. Gently touch the hair
on the inner surface of the ear and watch the
pinna twitch.
Don’t test too frequently or the reflex will be
inaccurately lost.

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