2. Anesthesia and Monitoring
Goals:
Provide a stage of reversible unconsciousness
with adequate analgesia and muscle relaxation
for surgical procedures that dose not jeopardize
the animals health.
Identify problems early institute treatment
promptly and avoid irreversible adverse outcomes
3. Why we monitor?
Anesthetic emergencies/complications:
Difficult to predict
Happen quickly
Become life threatening quickly
It is better to be proactive than reactive
Prevention is key!
4. Monitoring
Remember:
No monitoring device can
take the place of constant
human observation
The equipment we use only
enhances our ability to
monitor a patient
5. Monitoring
Starts when animal is dropped off
Pre-anesthetic evaluation
includes History, Physical Exam
Ends after recovery period
even day after
6. Pre-anesthetic Evaluation
History: what you want to know
Individual risk factors/underling problems
Age – certain risks for pediatric and geriatric patients
Breed – brachiocephalic (long recovery)
Temperament – aggressive/fractious (pre-med early)
Physical Exam – TPR, heart murmurs, lung sounds
Procedure – invasiveness, pain level
8. Stages
1. Pre-medication:
IV or IM injection – sedation/pain relief
Tranquilizer: no pain relief
ex: midazolam, acepromazine, diazepam
Add opioid for pain relief:
ex: hydromorphone, fentanyl, buprenex, morphine
+/- anticholinergic: help maintain HR
ex. atropine, glycopyrrolate
9. Stages
Pre-medication:
Decreases need for increased induction agents
and inhalant anesthetics
Aids for smoother induction and recovery
Place IV catheter during this stage
May start fluids or pain management CRI at this
time
10. Stage 1: Pre-medication
What we monitor:
Heart rate
Respiratory rate
Perfusion – MM color/CRT
Pulses
Drooling/vomiting
Level of sedation
Reactions to medications
11. Stages
2. Induction:
Use Injectable anesthetics to yield an
unconscious state
Ex: Ketamine, Propofol
Can be masked down with inhalant anesthetic
Not recommended
Induction agents are given to facilitate intubation prior to
being placed on an inhalant agent for maintenance
12. Stage 2: Induction
What we monitor:
HR/RR
Perfusion - MM color/CRT
Pulses
CNS reflex's – depth
13. Stages
3. Maintenance:
Unconscious + pain free
Inhalant anesthetic used to maintain unconsciousness
Ex. Isoflurane, sevoflurane
Procedure is performed
+/- IV fluids
+/- Pain management CRI (fentanyl, MKL)
Procedure dependant
14. Stage 3: Maintenance
What we monitor:
HR/RR
Perfusion - MM color/CRT
Pulses
CO2/O2 concentrations
Blood Pressure
CNS reflex's – depth
Temperature
15. Stages
4. Recovery:
Good = uneventful
Inhalant turned off Extubated
Vitals monitored until awake/ambulatory
every 5 – 10 min
Ideally warm quiet area
One of the most important stages of anesthesia
morbidity is higher in this stage than any others
16. Stage 4: Recovery
What we monitor:
HR/RR
Perfusion – MM color/CRT
Pulses
Temperature
CNS signs – consciousness
+/- Blood pressure
17. Planes of Anesthesia
Planes are used to describe depth of anesthesia during
the maintenance stage
Plane 1: light
Plane 2: medium
Plane 3: deep
Plane 4: too deep
19. Planes of Anesthesia
Plane 2 (medium):
Suitable for procedures
HR + RR reactive to stimulus unconscious
3rd eyelid may rotate up
Skeletal muscle relaxes
Absence limb movements
CNS signs decrease
Jaw tone decreases
Normal blood pressure
20. Planes of Anesthesia
Plane 3 (Deep):
Decrease HR + RR even with stimulus
May need ventilation
Pulses weaken
Blood pressure drops
CRT prolonged
No jaw tone or CNS signs
21. Planes of anesthesia
Plane 4 (too deep):
Significant decrease HR
Erratic jerky rest rate or apnea
No CNS signs
Pale gums – prolonged CRT
BP too low to read
Can be permanently damaging
22. What is an ideal depth?
Procedure dependent
Patient dependent
Good analgesia without depressing HR or RR
Low as possible vapor setting
IV analgesics safer (less detrimental effects) than
increasing vapor setting but more difficult to adjust
the depth
23. Monitoring
Parameters we monitor during anesthesia:
1. Central nervous system
2. Cardiovascular system
3. Respiratory system
4. Temperature
24. Monitoring CNS
Varies spp to spp and patient to patient
Good indication of DEPTH of anesthesia
CNS signs are called reflexes
Monitor multiple reflexes
Increase in anesthetic depth = a decrease of reflexes
25. Common CNS reflexes
Eye position:
Pupils begin in central position Then move
rostroventral in an adequate plane Then
move BACK central as the patient moves into a
deeper plane
More Effective in dogs
Ineffective if animal has received a dissociative
drug
Ex. Ketamine - eyes are fixed centrally
27. Common CNS reflexes
Palpebral reflex:
Touch medial or lateral canthus of the eye or
eyelashes
Looking for a blink response
Weak/absent = adequate plane
May become desensitized if over tested
28. CNS common reflexes
Pupil constriction/dilation:
• Induction – slt dilated or normal
• Maintenance:
Plane 1+2 can constrict
Planes 3+4 = more and more dilated
• Cats: unreliable if received atropine Dilated pupils
29. Common CNS reflexes
Nystagmus:
Involuntary rapid movement of eyeball
Move side/side, up/down, rotary
Can happen in an excitement phase– common in
animals that are masked down or given certain
drugs
Important reflex in recovery period:
Can be seen in dysphoric patients – common if given an opioid
Patients become light and sound sensitive
30. Common CNS reflexes
Swallowing:
• Spontaneous when awake
• Lost plane 1
• Regains after consciousness
• Important in recovery stage
• Must be present before extubation to prevent
aspiration
31. CNS common reflexes
Laryngeal reflex:
Monitored during intubation
Arytenoids close to protect trachea
Elicited by tube stimulation
Induction decreases this reflex
Lost plane 1
Cats may need deeper plane to avoid laryngospasms
33. Common CNS reflexes
Cough reflex:
Monitored during intubation
Normal response in awake animals
Intact until plane 2
Common reflex in cats during recovery stage
When extubation is warranted
34. CNS common reflexes
Pedal reflex:
• Pinching digit or pad looking for withdrawal
• Lost by plane 2
• Movement = inadequate depth for surgery
• Shouldn’t be present with inhalant anesthesia
35. CNS common reflexes
Ear/whisker reflex:
• Touch inner surface of pinna or whiskers
• Looking for twitch response
• Present = inadequate depth for surgery
• Lost by plane 2
• May become desensitized → tested too often
36. CNS common reflexes
Muscle tone:
Present in light to medium planes
Jaw Tone:
Opening jaw – estimate amount of resistance
Want some resistance
Flaccid jaw often indicative of excessive depth
Less reliable in pediatric patients
Anal Tone:
less reliable
If present = too light for surgical stimulus
37. CNS common reflexes
Response to surgical stimulus:
Movement
Lost by plane 2
Dramatic increase in HR and RR
Late indicator of inadequate depth
39. How we monitor Circulation
Heart rate
Blood pressure
Tissue perfusion
40. Monitoring HR
Heart rate:
Base rate (resting rate)
Breed, weight, age, fitness level play factor to base rate
because of this it is difficult to define universal ranges for all
patients
Normal:
• Dogs: 70 – 180 bpm
• Cats: 140 – 200 bpm
• Pediatric patients: dog 150-180bpm, cat 150-210bpm
• They need a higher rate to maintain cardiac output
41. Monitoring HR
Bradycardia: Low HR
< 60 dogs
< 120 cats
Common causes:
Drugs/inhalants (have depressant effect)
If patient is too deep
43. Monitoring HR
How we monitor heart rate:
1. Palpation
2. Auscultation
3. Pulse Oximeter
4. Electrocardiogram (ECG)
44. Monitoring HR
Palpation of chest for heart rate:
Difficult to feel
Less reliable
Palpation of peripheral artery:
Femoral, metacarpal, dorsal pedal, cranial tibial,
lingual most common
Count a rate
Note the quality – normal, bounding, weak
47. Monitoring HR
Esophageal stethoscope:
Tube passed down esophagus connected to
earpieces – creates an audible sound
Tip should be level with heart
Do not to pass into the stomach reflux/regurg
Note Rate and Rhythm
Can also hear respiratory rate and note character
49. Monitoring HR
Pulse Oximeter:
Gives pulse rate
As well as SpO2 concentration
Machine detects pulsation from
external probe and formats into
a numerical value
Has become a standard of care in veterinary medicine
50. Monitoring HR
Electrocardiography (ECG):
Shows electrical activity (cardiac cells)
Important for detecting arrhythmias
Also gives heart rate
DOES NOT give information about mechanical function of heart
(shouldn't be sole method for heart monitoring)
A deceased animal may still have electrical activity of the heart but no
actual beat
51. Monitoring HR
Electrocardiography (ECG)
Has 4 leads (most have 3): placed on armpit and flank
: Right front
Black: Left front
Red: Left hind
Green: Right hind*
* this lead is commonly left out
52. Monitoring HR
ECG Leads:
Need Good contact for proper function
Ultrasound gel VS. Alcohol as a conductor
Studies say ultrasound gel is better because:
Alcohol evaporates quickly and you need to reapply for
longer procedures
It also cools as is evaporates cause hypothermia
54. Monitoring HR
Electrocardiograph: waveform
Provides regional information about the heart
P wave
QRS complex
T wave
Each letter represents a location and function of heart
Abnormal waveform called arrhythmia
55. Monitoring HR
Common causes of arrhythmias:
Heart dz #1
Pain
Drugs - (atropine and glycopyrrolate)
Electrolyte imbalances
Poor oxygenation
57. Abnormal ECG Rhythms
Atrioventricular Block (AV block)
Absence of QRS complex and T wave (dropped beat)
58. Abnormal ECG Rhythms
Ventricular Premature Contractions (VPC’s)
Extra beat originating from from ventricles
59. Monitoring Blood Pressure
Blood Pressure:
Force of the flow of blood on vessel walls
measured in mmHg
Goal:
Maintain adequate blood flow and O2 delivery to
tissues and vital organs
64. Monitoring Blood Pressure
Dependent on:
Volume blood entering heart (before contraction)
Ability of heart to contract (muscle function)
Heart rate
Resistance to forward blood flow (vessel size)
Viscosity of blood
65. Monitoring Blood Pressure
How we monitor BP:
1. Oscillometric technique
2. Doppler technique
3. Arterial technique*
4. Central Venous Pressure technique*
* More common in critical patients not commonly used
66. Monitoring Blood Pressure
Oscillometric technique:
Indirect method – non-invasive
Cuff placed around major artery
automatically inflated
Transducer within cuff detects pressure changes within
artery
Records pulsations
Transmits # to screen
67. Monitoring Blood Pressure
Oscillometric technique:
Gives Mean, systolic, and diastolic parameters
SurgiVet monitor: labeled as NIBP
Data states systolic pressure is less accurate in this
device
HOWEVER the mean value tends to be more accurate
(mean is the more important value)
70. Monitoring Blood Pressure
Pressure Cuff: both techniques
Need uniform compression of artery
Size cuff relative to limb being compressed
Width cuff should be 40% of the circumference limb
Cats can be 30-40%
Too small cuff = higher values
Too big cuff = low values
71. Monitoring Blood Pressure
Arterial monitoring: (gold standard)
Yields most accurate results
Direct method – Invasive method
IVC placed in dorsal pedal or metacarpal ARTERIES
Need a highly skilled technician
Risks of infection and hemorrhage are high
Because of these reasons it is not common technique
72. Monitoring Blood Pressure
Arterial monitoring:
Catheter connected to electronic pressure transducer
via extension tubing and transmits signal to monitor
Displays: SAP, DAP, MAP and constant waveform
75. Monitoring Blood Pressure
Central Venous Pressure
Reflects volume capacity of the right side of heart
and amount of blood returning to the heart
Helpful in assessing fluid status (hydration)
Need: jugular catheter
Normal range:
0-5 cmH2O (trends more important than individual
numbers)
76. Monitoring Tissue Perfusion
How we monitor tissue perfusion:
1. Palpation Artery
2. Mucus membrane color
3. Capillary refill time
77. Monitoring Tissue perfusion
Palpation of peripheral artery:
Femoral, metacarpal, dorsal pedal, cranial tibial,
lingual commonly used
Note the quality – normal, bounding, weak
Weak pulses = circulatory insufficiency
Monitored in conjunction with HR
pulse should be synchronous with heart rate
Every beat should have a pulse (pulse deficit)
78. Monitoring Tissue perfusion
Mucus membrane color:
Should be pink and moist
Abnormal:
Pale = vasoconstriction, blood loss or anemia
Purple or blue = cyanosis
Dry/sticky = dehydrated (dugs)
Red/injected = heat stroke, sepsis, carbon
monoxide poisoning
Yellow (icteric) = liver disease
80. Monitoring Tissue Perfusion
Capillary refill time:
Touch gums note time it takes for color to return
should be < 2 sec
Prolonged = poor perfusion
81. Respiration
Goal:
Move O2 into the lungs and expel CO2 out
Ensure adequate O2 and CO2 concentrations
in blood
82. Physiology of Respiration
O2 in arterial blood is carried to tissues normal
metabolism occurs CO2 byproduct or metabolism
the CO2 is diverted into venous blood taken to
heart travels to lungs capillaries in lungs
CO2 transferred into alveolar sacs in lungs and
expelled out O2 transferred from alveolar sacs
into arterial capillaries travels back to the heart
pumped into systemic circulation tissues
Then repeat!
83. Anatomy of Respiration
Alveolar sac:
Blue –
venous
blood from
body high
levels of
CO2
Red –
arterial blood
high in O2
going back
to the body
85. Anatomy of Respiration
Alveoli expand and contract with respirations
Deep breath into lungs expands more of sacs
Which increases surface area for exchange:
CO2 from capillary veins into alveolar sacs
O2 and anesthetic gas into arterial blood
86. Monitoring Respiration
Inhalants are #1 respiratory depressant!
Increase anesthetic depth = decrease in volume of
air taken into the lungs (tidal volume)
Decreases by 25%
Why?
Drugs limit expansion of intercostal muscles
muscles we use to inspire
87. Monitoring Respiration
As tidal volume decreases the alveoli collapse
can decrease the function of lungs
Treat this by giving breath (bagging) – every 5 min
Watch the pressure monometer
Avoid over inflation of lungs
Never go over 20cmH2O
15cmH20 smaller patients
88. Monitoring Respiration
Varies between patients
Normal resting rates:
Dogs 10 – 20
Cats 15 – 25
Under anesthesia:
8-20 both spp.
89. Monitoring Respiration
Causes of decrease in respiration:
Drugs we give
Too deep
Heavy drapes or instruments on small patients
Dr. hand over patients chest
Low CO2 concentration
93. Monitoring CO2
Respiratory Rate:
Can correlate to amount of CO2 in blood
Normal Value: 35-45 mmHG
To high (>50) can stimulate respiration (receptors in
brain signal lungs to breath to eliminate the excess
Co2)
dependent on anesthetic depth, drugs, etc.
To low (<30) apnea or shallow breathing
95. Monitoring CO2
Blood Gas: “GOLD STANDARD”
Most accurate determinant of CO2 levels in blood
Direct – invasive method
Need:
Arterial blood sample
Blood gas analyzer
Skilled technician
Patient dependent – size, age
**Not common method**
96. Monitoring CO2
However…
Measuring end tidal CO2 (EtCO2) using
capnography is useful alternative to estimate levels
in blood (PaCO2) without invasive techniques
97. Monitoring CO2
Capnography:
Indirect – non-invasive method
Become most common method
Numerical +/- graphical display
Estimation of CO2 in arterial blood by the
concentration of CO2 that is exhaled
98. Monitoring Oxygenation
CapnoGRAPH tells us:
Graphical display CO2 that is exhaled
EtCO2 concentration
Resp rate
CapnoMETER tells us:
EtCO2 concentration
Resp rate
105. Monitoring CO2
CO2 exchange is linked to:
1. Perfusion (blood flow) to capillaries in tissue and lungs
2. Ventilation (exchange alveoli sacs)
3. Metabolism (production of CO2)
** Keep in mind all of these factors when looking at
the values on the monitors**
106. Monitoring O2
SpO2:
Measures level of arterial O2 in saturated hemoglobin
hemoglobin in RBC is the O2 carrying component in blood
Gives us an estimation of oxygenation
Helps us to determine need for O2 supplementation
SpO2 should be > than 95%
98-100% under anesthesia
107. Monitoring O2
O2 exchange is linked to:
1. Perfusion (blood flow) in tissues and lungs
Any factor that inhibits blood flow can affect
these results
2. Ventilation (exchange alveoli sacs)
109. Monitoring O2
Blood Gas: “GOLD STANDARD”
Most accurate determinant of O2 levels in blood
Direct – invasive method
Need:
Arterial blood sample
Need blood gas analyzer
Skilled technician
Patient dependant – size, age
*Not commonly used*
110. Monitoring SpO2
Pulse Oximitry:
Non-invasive – indirect method
Two red light wavelengths pass through body tissue
O2 rich blood blocks less red light than oxygen depleted
blood
Separates parameters and gives a numerical % of O2
saturation
Also gives us a Heart rate
113. Monitoring SpO2
Probes:
Tongue – most common in anesthetized patients
Can be placed on lip, ear, inguinal skin fold, toe web, tail, skin
along achilles tendon, prepuce or vulva
If placed on ear/lip red light should be inside facing out
Light should face down
to avoid risk of ambient light can lead to falsely increased values
115. Pulse Ox equipment
Rectal probe:
Rectum must be free of excess foreign material
Light positioned dorsally
Anchor it to the tail with tape
116. Monitoring SpO2
Causes of low readings:
Pigmented skin
Tissue thickness
Anemic animals
Poor perfusion
Check mm color and CRT for abnormal readings
Tylenol toxicities (destroys hemoglobin)
Reposition probe (every 5 - 10 min)
Probe itself can occlude vessels and decrease results
117. Monitoring SpO2
High readings:
Falsely increased
Florescent lights
Place drape or towel over probe
Important to check other parameters too!
MM/CRT
**if an animal has pale gums but a high SpO2 you may need
to troubleshoot**
118. Temperature
Goal:
Maintain a body temperature adequate for normal
metabolic functions
Avoid accidental hypothermia or malignant
hyperthermia
120. Monitoring temperature
Hypothermia:
Common complication under anesthesia
Loose heat rapidly
First 20 minutes most loss
Stay above 98 degrees for not to be detrimental to patient
Dramatically slows anesthetic recovery
Monitor every 15 – 30 min, as well as post-op until normal
121. Monitoring Temperature
Why they get so cold?
Shave fur
Scrub with fluids that cool as they evaporate
Take away their inability to shiver
Open body cavity to room air
Drugs/inhalants
124. Monitoring Temperature
Causes of hyperthermia:
Excessive application of heat in attempt to prevent
hypothermia
Infections
Cats – adverse reaction to hydromorphone
Ketamine
125. Monitoring temperature
Treating hyperthermia
Remove blankets from cage
Place ice packs in towels in cage
Not directly on the patient
** REMEMBER: if methods are being used to treat
hyperthermia, the temperature should be monitored closely
to prevent subsequent hypothermia **
126. How We Monitor Temperature
Manually – hand thermometer
Esophageal probe
Rectal probe
129. Record keeping
Goal:
Maintain a legal record of significant events during
the anesthetic period
Recognize trends or unusual values or parameters
and allow assessment of response to intervention
130. Record Keeping
Useful for 4 main reasons:
1. See trends in patient vitals address problems
2. Archive record to compare similar cases (statistical
analysis)
3. Reference for anesthesia in future
4. Legal document so it needs to be complete and easy to
read
131. Record Keeping
Anesthesia record/sheet should have:
Patient ID
Procedure
Pre-op findings
Drugs given – dose, time, route
Pre-op TPR
Vitals – 5 min during procedure
Unusual circumstances – arrhythmias, drug reactions,
regurgitation ect.
O2 and inhalant anesthetic rates
135. In Conclusion
No SINGLE criteria tells you how an animal is handling
anesthesia
Add up vitals and reflexes to determine a safe
anesthetic depth
Make sure anesthetic procedure is properly documented
NEVER be afraid to ask a Dr. or another technician
The only dumb question is the one not asked!
