Veterinary anesthesia (Monitoring Anesthetized Patients) Veterinary anesthesia continues to evolve as a science and specialty within the veterinary profession. The major drivers of change are advances in medical technology and pharmaceutical development for domesticated animals or those adapted from human anesthesiology; research in physiology, pharmacology, and clinical trials for human and veterinary patients that provide better evidence-based guidance for patient care; and socioeconomic and demographic changes in countries where animals serve evolving roles. Veterinary anesthesiologists will continue to be advocates for patient safety, humane care through education about pain management and quality of life, and educators of the profession and society at large about the current best practices in anesthesia, analgesia, and pain management. +++Cardiovascular system +++Pulmonary system +++Temperature By DR.Kambiz Yousefi Kambiz.u3fi@me.com

1. Monitoring Anesthetized Patients
Steve C. Haskins
School of Veterinary Medicine, University of California, Davis, California, USA
C ar diovas c ular s ys tem
Pulmonary s ys tem
Temper ature
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D R . K a m b i z Y o u s e f iP re s e n t e d B y :

2. The Primary Focus Of Monitoring Anesthetized Patients Is The Assessment Of
(1) Depth Of Anesthesia
(2) Cardiovascular And Pulmonary Consequences Of The Anesthetized State
(3) Temperature
Monitoring Anesthetized Patients
Too light a level of anesthesia fails to achieve all of the basic goals of anesthesia. Animals that
are too deeply anesthetized may suffer adverse cardiopulmonary consequences and death.
General anesthesia predisposes to hypothermia, which, in turn, predisposes to excess anesthetic
depth and a number of cardiopulmonary problems.
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3. The Purpose Of Assuring An Appropriate Level Of Anesthesia Is To Assure Lack Of Patient
 Awareness
 Recall
 Pain
 Movement
Anesthetic Depth Is Determined By
 The Amount Of Anesthetic Drug(s) In The Brain
 The Magnitude Of Surgical (Or Environmental) Stimulation
 Underlying Conditions That Have Synergistic CNS Depressant Effects (I.E., Hypothermia, Hypotension).
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4. A n esth etic D ep th Can Be F air ly Vo latile
I f Th er e A r e A b r u p t Ch an g es I n A n y O f Th e D eter min an ts
The specific anesthetic drugs used are important; some are good CNS depressants but poor analgesics
whereas others are good analgesics but poor CNS depressants
A lth o u g h A n esth etic I n f u sio n Rates Fo r I n tr av enou s D r u g s A n d En d ‐tid al
Co n cen tr ation s Fo r G aseo u s D r u g s A r e Tw o O f Th e Facto r s U sed To H elp Estimate
A n esth etic D ep th , Th ey D o N o t D ef in e A n esth etic D ep th
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5. Anesthetic Depth Has Traditionally Been Divided Into Stages And Planes
Stage I Is The Awake State Of Awareness, Including All Of The Levels Of Obtundation Down To Loss Of Consciousness,
Which Marks The Beginning Of Stage II
Stage II Is The Excitement Stage Heralded By Spontaneous Muscular Movement; The Cessation Of Spontaneous Muscle
Movement And Onset Of A Regular Pattern Of Breathing Marks The End Of Stage II And The Beginning Of Stage III
Stage III Is Divided Into Four Planes, Which Can Be Characterized By Changes In Readily Available Physical Signs And
Progressive Loss Of Reflexes
Stage IV Is Characterized By Extreme CNS Depression And Respiratory Arrest. Cardiac Arrest And Death Will Result If
The CNS Depression Is Not Reversed
U nf o rt unately, A nima ls Seldo m Beha v e A cco rding To The
Bo o ks A nd M a y Simult a neo usly Ex hibit Sig ns C o nsist ent
Wit h Two Or M o re Pla nes
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6. Physical Signs Of Anesthetic Depth Within Stage III
a PLR = pupillary light response
b Physiologic responses to nociception include increases in heart rate, blood pressure, or respiratory rate
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7. MACawake = minimum alveolar concentration (MAC) to prevent response to verbal command in 50% of patients
MACincision = MAC to prevent muscular movement in response to a strong surgical stimulus
MACBAR = MAC to block the autonomic response to skin incision
There Is No Obligatory Correlation Between Level Of Anesthesia And Physiologic
Consequence Of Anesthesia
Spontaneous Movement Is A Reliable Sign Of A Light Level Of Anesthesia With Most
Anesthetics.
Reflex Movement In Response To Surgical Stimulation Is A More Reliable Sign Of A Light
Level Of Anesthesia
An Abrupt Increase In Heart Rate, Blood Pressure, Or Breathing Rate In Response To Surgical Stimulation Is A
Reliable Sign Of A Light Or Light–medium Level Of Anesthesia
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8. In General, Physiologic Parameters Such As Heart Rate, Arterial Blood Pressure, Breathing Rate, And Minute
Ventilation Should Trend Downwards When An Animal Becomes More Deeply Anesthetized And Vice Versa.
In Small Animals, With Traditional Anesthetics, The Eyeball Position Is Central At Light And Deep Levels Of
Anesthesia And (Usually) Ventromedially Rotated In Planes 2 And 3
T h e E y e b a l l D o e s N o t R o t a t e W i t h K e t a m i n e
In Horses, The Eyeball Can Rotate, But Not Reliably So, And Spontaneous Nystagmus Can Occur
A Very Slow (‘Roving’) Eyeball Might Represent A Medium Level Of Anesthesia Whereas A Fast Nystagmus
Represents A Light Level Of Anesthesia.
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9. Nystagmus May Also Occur In Light Levels Of Anesthesia In Ruminants And Swine, But Disappears At
Deeper Levels As The Eyeball Rotates Ventrally
Nystagmus Does Not Normally Occur In Surgically Anesthetized Small Animals
The Presence Of A Palpebral Reflex Is A Reliable Indicator Of A Light Level Of Anesthesia; The Absence Of It
Suggests A Medium Or Deep Level
With K etamin e , The Palpebral Reflex Is Always Present And The Eyelids Remain Open
The Pupillary Light Reflex (PLR) (Pupillary Constriction In Response To A Bright Light) And A Dazzle Reflex
(A Blink In Response To A Bright Light) Are Reliable Indicators Of A Light To Light–medium Level Of
Anesthesia
Lacrimation (Tear Production) Decreases And Stops At Deeper Levels Of Anesthesia
The Presence Of Gag And Swallow Reflexes Indicates A Light Level Of Anesthesia In Nearly All Species
Lacrimation In Horses Is A Sign Of A Light Level Of Anesthesia
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10. Cardiovascular System
Heart Rate Is An Important Determinant Of Cardiac Output
Heart Rates (Bpm) In Normal Animals Are Highly Variable:
60–120 For Large Dogs
80–160 For Small Dogs
120–220 For Cats
35–45 For Horses
70–90 For Small Ruminants
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12. There Is No Consensus As To When Bradycardia Should Be Treated, But A Conservative Treatment
Trigger Guideline Might Be Something Like (Estimated As About 20–30% Below Low Normal)
<50 For Large Dogs
<60 For Small Dogs
<90 For Cats
<25 For Horses
<55 For Small Ruminants
Common Causes Of Bradycardia Which Are Not Responsive To Pharmacological Treatment Are
 Severe Hypothermia
 Cardiac Conduction Abnormalities
 Severe Myocardial Hypoxemia
In Most Cases, Treatment Involves The Administration Of An Anticholinergic And/or A
Sympathomimetic, Although An Underlying Cause Should Be Sought. 12

13. Similarly To Bradycardia, It Is Not Known Exactly When Tachycardia Should Be Treated.
In Dogs, A Pacing Rate Of Approximately 240 (For 2–3 Weeks) Has Been Used As A
Model For Inducing Heart Failure, But This Hardly Serves As A Guideline For Acute
Tachycardia During Anesthesia.
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14. Conservative Intervention Trigger Levels Might Be Something Like (Estimated As About 20% Above High Normal)
>150 For Large Dogs
>190 For Small Dogs
>260 For Cats
>55 For Horses
>110 For Small Ruminants
Tr eatmen t Mu st I n v o lv e
I d en tif ication A n d Co r r ectio n O f
Th e Un d erlyin g Diso rd er;
Beta ‐b lo ck er s A r e Rar ely I n d icated
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15. Arterial Blood Pressure
Arterial Blood Pressure Is Arterial Hydrostatic Pressure Compared With Atmospheric Pressure.
Arterial Blood Pressure Is Determined By The Arterial Compartment Blood Volume And The
Arterial Compartment Wall Tone.
Systolic Pressure Is The Highest Intra‐arterial Pressure Of
Each Cardiac Cycle.
Diastolic Pressure Is The Lowest Pressure Prior To The Next
Heart Beat
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16. Systolic, Diastolic, And Mean Blood Pressure Measurements In Normal Dogs And Cats Are Variable
Depending On The Level Of Stress, Body Position, And Measurement Technique, But Are
Approximately 100–160, 60–100, And 80–120 Mmhg, Respectively . Horses, Goats, And Sheep Have
Slightly Lower Values: 90–130, 60–90, And 70–110 Mmhg, Respectively.
In General, One Becomes Concerned About Excessive Hypotension When The Mean Blood Pressure
Decreases Below About 60 Mmhg Or The Systolic Blood Pressure Decreases Below About 80 Mmhg,
In Any Species.
In Ideal Situations, The Mean Blood Pressure Should Be Maintained Above 80 Mmhg And The
Systolic Blood Pressure Above 100 Mmhg.
Mean Arterial Blood Pressure Is Physiologically The Most Important To The Anesthetist
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18. 18

19. Arterial Blood Pressure Can Be Measured Indirectly By Sphygmomanometry Or Directly Via An Arterial Catheter.
Dorsal Metatarsal,
Radial/Carpal, Coccygeal,
Lingual, Femoral, And
Auricular Arteries
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20. Pulmonary system
Breathing Rate, Rhythm, And Effort
The Breathing Rate Can Vary Widely And, Except For Extreme Values, Is Of Limited Value As A Respiratory Parameter.
A Cheyne–stokes Breathing Pattern
(Cycling Between Hyperventilation And
Hypoventilation) May Be Seen In
Otherwise Healthy Anesthetized Horses
And An Apneustic Breathing Pattern
(Inspiratory Hold) May Be Seen In
Otherwise Healthy Dogs And Cats
Anesthetized With Ketamine.
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21. Ventilometry, Deadspace, And Compliance
Ventilation Volume Can Be Estimated By Visual Observation Of The Chest Or Rebreathing Bag
Or Measured By Ventilometry
Normal Tidal Volume Ranges Between About 6 And 15 Ml/Kg. A Small Tidal Volume May Be
Acceptable If The Breathing Rate Is Sufficiently Rapid To Accomplish Normal Alveolar Minute
Ventilation.
Normal Total Minute Ventilation Ranges Between 150 And 250 Ml/Kg/Min In Awake Patients.
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22. The Arterial PCO2 (Paco2) Is A Measure Of The Effective Alveolar Minute Ventilation And
Normally Ranges Between 35 And 45 Mmhg
Partial Pressure Of Carbon Dioxide (PCO2)
Acceptable Paco2 Values May Be Higher In Anesthetized Small Animals And Is Considerably
Higher (60–80 Mmhg) In Anesthetized Horses And Cattle.
A Paco2 In Excess Of 60 Mmhg May Be Associated With Excessive Respiratory Acidosis And Is
Usually Considered To Represent Sufficient Hypoventilation To Warrant Positive Pressure
Ventilation In Small Animals.
Paco2 Values Below 20 Mmhg Are Associated With Respiratory Alkalosis And A Decreased
Cerebral Blood Flow, Which May Impair Cerebral Oxygenation.
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24. Cyanosis
Grayish To Bluish Discoloration Of Mucous Membranes Signals The Presence Of Unoxygenated
Hemoglobin In The Observed Tissues.
The Observation Of Cyanosis Is Dependent Upon The Concentration Of Deoxygenated
Hemoglobin Present, The Visual Acuity Of The Observer
Lighting (It Is More Readily Detected In A Well‐lit Room Than In The Shadows Of A Cage)
Type Of Lighting Used (It Is More Readily Detectable With Incandescent As Opposed To
Fluorescent Lighting)
In General, It Requires An Absolute Concentration Of Unoxygenated Hemoglobin Of 5 G/Dl To
Manifest Sufficient Cyanosis To Be Observed Visually
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25. Hypoxemia
There Are Three Categorical Causes Of
Hypoxemia:
1. Low Inspired Oxygen Concentration
2. Hypoventilation
3. Venous Admixture
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26. A Fourth Cause Of Hypoxemia
Can Be A Reduced Venous
Oxygen Content Secondary To
Low Cardiac Output Or Sluggish
Peripheral Blood Flow ( Shock) Or
High Oxygen Extraction By The
Tissues (Seizures).
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27. Temperature
Hypothermia
Hypothermia During Anesthesia May Be Associated With Anesthetic Drug Depression Of
Muscular Activity, Metabolism, And Hypothalamic Thermostatic Mechanisms.
Heat Loss May Be Augmented By Evaporation Of Surgical Scrub Solutions From The Skin
Surface, By The Infusion Of Room Temperature Fluids, By Contact With Cold, Uninsulated
Surfaces, And By Evaporation Of Surface Fluid From An Exposed Body Cavity.
Core Temperature Can Be Measured With Either Esophageal Or Rectal Thermistors Attached To
A Continuously Displayed Thermometer.
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28. Core Body Temperatures Down To 36 °C (96 °F) Are Often Not Associated With Detrimental Effects, Although Immune
Function Impairment May Lead To Increased Risk Of Infection And Altered Enzyme Kinetics May Predispose To Coagulation
And Hemostatic Abnormalities
Body Temperatures Of 32–34 °C (90–94 °F) Are Associated With Reduced Anesthetic Requirements (Normothermic Amounts
Of Anesthetic Will Over‐anesthetize These Patients), And Recovery Will Be Prolonged.
Body Temperatures Of 28–30 °C (82–86 °F) Have A Marked CNS Depressant Effect (Little If Any Anesthetic Agent Is
Required), Atrial Arrhythmias May Occur. Oxygen Consumption Is Reduced To About 50% Of Normal, Heart Rate And
Cardiac Output To About 35–40% Of Normal, And Arterial Blood Pressure To About 60% Of Normal. Cerebral Metabolism Is
About 25% Of Normal
Body Temperatures Of 25–26 °C (77–80 °F) Are Associated With Prolongation Of The PR Interval And Widened QRS
Complexes, Increased Myocardial Automaticity, Decreased Tissue Oxygen Delivery Out Of Proportion To Decreases In
Oxygen Requirement Resulting In Anaerobic Metabolism, Lactic Acidosis, And Rewarming Acidemia. Blood Viscosity Is
About 200% Of Normal.
Body Temperatures Of 22–23 °C (72–74 °F) Are Usually Associated With Ventricular Fibrillation.
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29. Hyperthermia
Temperature
Fever Is A Reset Thermostat Caused By The Release Of Endogenous Pyrogens (Interleukin‐I)
From Monocytes In Response To Infections, Tissue Damage, And/Or Antigen–antibody Reactions.
Hyperthermia, Without A Reset Thermostat, Is Pathologic. It Can Occur In Large Dogs That Are
Cocooned On The Operating Table With Many Layers Of Drapes Or Overzealous Use Of
Supplemental Heat Sources.
Hyperthermia May Be Potentiated By Surface Vasoconstriction, Thick Coats (E.G., Newfoundland
Dogs), Light Levels Of Anesthesia, And Some Drugs (E.G., Ketamine And Opioids, Especially In
Cats).
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30. Mild degrees of hyperthermia are not harmful to the patient and may represent an appropriate fever. Mild
hyperthermia (less than 40 °C or 104 °F) does not normally require symptomatic treatment.
Cell Damage Starts To Occur At Body Temperatures Above 42 °C (108 °F), When Oxygen Delivery Can No
Longer Keep Pace With Increased Metabolism And Oxygen Consumption.
Severe Hyperthermia Causes Multiple Organ Dysfunction And Failure: Renal, Hepatic, Gastrointestinal
Failure, Myocardial And Skeletal Muscle, Cerebral Edema, Disseminated Intravascular Coagulation,
Hypoxemia, Metabolic Acidosis, And Hyperkalemia
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