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The Cool Observer: Monitoring Anesthesia with Confidence
Kristen Cooley BA, CVT, VTS (Anesthesia/Analgesia)
University of Wisconsin, School of Veterinary Medicine
Veterinary Anesthesia Support and Training
Madison, Wisconsin

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ANESTHESIA IS DEPRESSING...
Cardiovascular
Respiratory
Nervous

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ANESTHESIA IS CHALLENGING...
... to homeostasis
This requires our attention and support!

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SUCCESSFUL ANESTHESIA IS...
- Not the lack of mortality, but the lack of morbidity
- Mortality = death
- Morbidity = disease
- There are no safe anesthetics, only safe anesthetists!

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Monitoring devices don't replace TECHNICIANS & NURSES
(thank goodness)

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Veterinary Anesthesia
RISKS OF ANAESTHETIC & SEDATION RELATED DEATH IN HEALTHY AND SICK DOGS, CATS AND RABBITS
BRODBELT ET AL. (2008) THE RISK OF DEATH: THE CONFIDENTIAL ENQUIRY INTO PERIOPERATIVE SMALL ANIMAL FATALITIES

Dog Cat Rabbit
Healthy (ASA 1 & 2) 0.05%(90,618) 0.11%(72,473) 0.73% (7,652)
Sick (ASA 3-5) 1.33% (7,418) 1.4% (6,705) 7.37% (557)
Overall 0.17% 0.24% 1.39%

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Dog Cat Rabbit
After premed 1% 1% 0%
Induction 6% 8% 6%
Maintenance 46% 30% 30%
Post Operative 46% 61% 64%

* MOST WITHIN 3 HRS
BRODBELT ET AL. (2008) THE RISK OF DEATH: THE CONFIDENTIAL ENQUIRY INTO PERIOPERATIVE SMALL ANIMAL FATALITIES. VET ANAESTH ANALG #%; 365-3

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Monitoring...Philosophy 1
- When measuring things biological, one measurement gives a ‘window’ into a dynamic situation.
- Repeated measurements give some idea of the dynamic picture.

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Monitoring... Philosophy 2..
- All monitors have limited accuracy and reliability.
- Trends mean more than numerical values.

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Monitoring...Philosophy 3......
The best equipment is not a good job of monitoring.
Check the patient before checking the monitor.
Monitor the patient, not the monitor.
Monitors should not/cannot replace a skilled technician/nurse

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MONITORING AND SUPPORT
Anesthetic monitors are only as good as the person using them
You MUST know what is normal to be able to recognize abnormal

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ACVAA RECOMMENDS...
- Frequent, continuous monitoring of:
- Circulation
- Oxygenation
- Ventilation
- Temperature

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CIRCULATION
Adequate blood pressure is necessary
- Oxygen
- Nutrients
Hypotension is common!

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CIRCULATION
- Components of blood pressure
- Systolic
- Peak during contraction
- Stroke volume
- Arterial compliance (distensibility)
- Diastolic
- Lowest pressure during relaxation
- Heart rate
- Systemic vascular resistance (vessel size)
- Mean
- Driving pressure for organ perfusion

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Arterial Blood Pressure
Cardiac Output / Systemic Vascular Resistance
Heart Rate / Strake Volume /Vessel Diameter / Blood Viscosity
Lusitropy / Contractility / Preload / Afterload
Blood Volume

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MEASURING BLOOD PRESSURE
- Doppler Ultrasonic Blood Flow Detector
“Doppler”
- Audible blood flow
Great for monitoring heart rate in all species
- Blood pressure
Unfettered appendage with good blood flow
Sugar glider!

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MEASURING BLOOD PRESSURE
Cuff width = 40%
Too large
- Underestimation
Too small
- Overestimation
Bigger is better than smaller
- Greater error with a small cuff
Best sites:
- Forelimb between carpus and elbow
- Hindlimb above hock
- Hindlimb below hock
- Tail

- Snug fit
- At heart level
- Read q 3-5 min

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TROUBLESHOOTING

- NIBP
- Estimates BP
- Monitors trends
- Isolated abnormal readings?!

- Upward or downward trend
- Assess depth
- MM, CRT, HR, RR
- Jaw tone, eyes
- Make adjustments based on findings
- Deepen/lighten, analgesics, assist respirations...
- Sudden significant changes
- Evaluate patient
- Communicate with surgeon/DVM
- Recheck BP
- Make adjustments

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Direct Arterial Blood Pressure
- dABP most accurate method for determining BP
- Invasive = blood flow + SVR
- Non-invasive = blood flow
- Continuous physiological monitoring
- Aids in identification of physiological issues
- Can be used to guide treatment therapies
- Facilitate arterial blood sampling

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Indications
- Hemodynamically unstable patients
- Direct and continuous blood pressure monitoring
- Repeated arterial blood sampling

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Disadvantages
- Catheter placement can be challenging
- Equipment expensive
- Technical and mechanical issues can contribute to inaccuracy
- Catheter related complications

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Contraindications to placement of catheter
- Hemostatic abnormalities
- Severe thrombocytopenia
- Vitamin k rodenticide intoxication
- Hypercoagulable states
- IMHA
- Increased risk of thrombosis/embolism
- Insertion site compromise
- Pyoderma
- Burns
- Abrasions

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ABNORMALITIES
Hypotension = pathologic reduction in BP
- Systolic < 80 mmHg
- MAP < 60 mmHg
Consequences
- Hypoxemia, reduced drug metabolism, worsening of V/Q mismatch, delayed recovery, renal failure, CNS abnormalities, shock, arrest, death

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ABNORMALITIES
- Common causes
- Drugs
- Inhalants, acepromazine, rapid IV meds (abx, morphine), contrast, beta blockers - Decreased venous return
- Hemorrhage, fluid loss, compression of VC, increased intraabdominal pressure, mechanical ventilation

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ABNORMALITIES
- Cardiac disease
- Arrhythmias, valvular disease, cardiomyopathy, CHF, pericardial effusion
- Mechanical
- Closed pop-off valve, over-inflated bag
- Excessive depth
- Shock/vasoactive substance release

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HYPERTENSION
Less common
- Still important
- Greater swings in BP
- End-organ damage
Pre-anesthesia hypertension
- Maintain BP near awake values
- New set point for autoregulation

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HYPERTENSION
- Causes
- Mechanical error
- Sympathetic stimulation
- Hypercarbia, pain, light
- Drugs
- A-2’s, ketamine, inotropes, pressors
- Disease
- Pheo, CRF, hyperthyroid, increased intracranial pressure, heart disease...

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TREATING HYPOTENSION
- What is the cause?
Arterial blood pressure
Cardiac output / Systemic Vascular Resistance
Heart Rate / Stroke Volume / Vessel Diameter / Blood Viscosity
Contractility / Preload / Afterload
Blood Volume

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ELECTROCARDIOGRAPHY
Peripheral detection of electrical impulses
- No info on mechanical function
Arrhythmia diagnosis
Patient evaluation
Pre-op eval of high-risk patients
Intra-op all patients
Post-op to check stability

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CONDUCTION
P = atrial depolarization
QRS = ventricular depolarization and atrial repolarization
T = ventricular repolarization

Depolarization - Reduction in a cell's membrane potential caused by an influx of cations that can lead to an action potential (electrical impulse)
Repolarization - Restoration of a cell's membrane potential to its resting potential

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LEAD PLACEMENT
White - RF
Black - LF
Red - LH
Green - RH
Brown - Shoulder blades

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COMMON ARRHYTHMIAS
- AV Block
- 1st degree AV block
- 2nd degree AV block
- Type 1 and 2
- 3rd degree AV block

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COMMON ARRHYTHMIAS
VPC's
- Unifocal or multifocal
V-Tach
- Rate > 180 in dogs
- Rate > 220 in cats
SVT
- Rate > 180 in dogs
- Rate > 220 in cats
V-fibrillation
APC's

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OXYGENATION
Pulse Oximeter
- Pulse rate
- Hemoglobin saturation with oxygen

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PULSE OXIMETRY
How does it work?
- Red and infrared light
- Perfused tissue
- Must have a good pulse
Photodetectors
- Displays % oxygenated Hgb to total Hgb

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PULSE OXIMETRY
SpO2
- Hemoglobin oxygen saturation
- Non-invasive
PaO2
- Oxygen dissolved in plasma
- Invasive
Normal values depend on inspired O2 concentration
- Inspired X 5
PaO2(mmHg) / SpO2 (%)
100 /98
80 /95
60 / 90
40 /75

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OXYHEMO-WHAT?
Oxyhemoglobin Dissociation Curve
Does not discriminate high PaO2 values in areas where the curve is flat!

SpO2 = Pulse-ox reading
PaO2 = oxygen dissolved in plasma

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HYPOXEMIA
Pulse-ox is designed to alert to hypoxemia
- Decrease in blood oxygen levels
- PaO2 below 60 mmHg
There are 5 reasons for hypoxemia...
- Low inspired oxygen concentration
- Hypoventilation
- V/Q mismatching
- Diffusion impairment
- Shunting

PaO2 (mmHg) / SpO2 (%)
100 / 98 :)
80 / 95 :)
60 / 90 :(
40 / 75 :(

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LOW INSPIRED
Sedation
Anesthesia
- 100%
- Unlikely cause of hypoxemia
- Check supply and equipment
- NRB
- Check flow rates
- Mask
- Intubate
- Ventilate

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HYPOVENTILATION
Elevated EtCO2 and/or PaCO2
- Causes
- Drugs
- Positioning
- External forces
- Disease
Determine cause
Improve ventilation

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VENTILATION-PERFUSION MISMATCH
V/Q Relationship
- V= Ventilation
- Gas flow within the alveoli
- Q= Perfusion
- Cardiac output perfusing the alveoli

Alveolar deadspace ventilation
Alveoli are ventilated but not perfused
(Inadequate gas exchange)

Normal V/Q relationship
Alveoli are ventilated and well perfused
(Good gas exchange)

Shunt perfusion
Alveoli are perfused but not well ventilated
(Inadequate gas exchange)

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DIFFUSION IMPAIRMENT
Increase in the distance that oxygen has to travel to get to the capillaries
- Thickening of alveolar wall
- Pulmonary fibrosis
- Interstitial pulmonary edema

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SHUNTING
Oxygen bypassing alveolar exchange
- Heart
- Lungs
- VSD
- Tetrology of Fallot
- Reverse PDA
- Physiologic shunt
- Large atelectic areas

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ACCURACY OF PULSE OXIMETRY
Does not assess the adequacy of ventilation!
Estimation of oxygen
- Anemia
- 100% w/hypoxic tissues?
- Hb is largest contributor to AOC equation

Arterial Oxygen Content Equation
CaO2 = (1.34 x Hb x SaO2) + (PaO2 x 0.003)

Oxygen content of blood (CaO2) = The O2 binding capacity of hemoglobin (1.34) x Hemoglobin content (Hb) x Arterial hemoglobin saturation (SaO2) + Amount of
dissolved oxygen in arterial blood (PaO2) x Solubility constant for dissolved oxygen in plasma (0.003).
(Robertson, 2002)

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PHOTOPLETHYSMOGRAPHY
- Helps gauge accuracy of reading
- Strength, regularity of waveform
- Dysrhythmia detection
- Monitors without are inferior

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Perfusion Index PI
- Calculated by comparing the pulsatile and non-pulsatile signals
- Determines strength of pulse at site
- Helps find best site for pulse-ox
- Expressed as a percent
- 0.02% poor perfusion
- 20% very good perfusion

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Pleth Variability Index
- Calculates the respiratory variability in the pleth wave
- Tells us about patient fluid responsiveness
- PVI = PI max – PI min / PI max X 100%
- A low PVI = less variability in PI over the respiratory cycle
- A high PVI = more variability and patient is likely to respond to fluids with an increase in cardiac output

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VENTILATION
Carbon dioxide is a normal byproduct of cellular metabolism
Adequate...
- Aerobic cellular metabolism
- Tissue perfusion
- Pulmonary circulation
- Gas exchange
- Ventilation

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VENTILATION
- Cells produce CO2
- Aerobic cellular metabolism of nutrients to energy consumes oxygen and produces carbon dioxide
- The heart pumps blood to all tissues in the body
- Circulation picks up CO2 from the tissues and transports it to the lungs to be excreted
- The lungs provide an interface between circulation and ventilation
- The exchange of gases (oxygen and carbon dioxide) takes place within alveoli

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VENTILATION ADEQUACY
Arterial Blood Gas
- Gold standard
- PaCO2
- CO2 dissolved in plasma
End-tidal CO2
- Estimates PaCO2
- Amount of CO2 in alveoli

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HOW DOES IT WORK?
- Infrared absorption
- CO2 absorbs infrared light energy of specific wavelengths
- Amount absorbed is directly related to CO2 concentration
- CO2 monitor
- A beam of light passes across a gas sample to a photodetector
- The amount of CO2 present in that sample reduces the amount of light that reaches the sensor
- Circuit voltage is reduced and a volume is determined

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CLINICAL APPLICATIONS
- Intubation verification
- CPCR
- Procedural sedation
- Ventilation
- Ventilator setting/weaning
- Changes in CO

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HYPERCAPNIA
Elevations in EtCO2
- >55 mm Hg
- Hypoventilation
- Respiratory depression
- Drugs
- Depth
- Vent settings
- Machine
- Airway obstruction

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HYPOCAPNIA
Low EtCO 2
- < 20 mm Hg
- Hyperventilation
- Light
- Hypoxemia
- Pain
- Vent settings
- Over zealous hand ventilation
- Drop in CO

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INCO2
Inspired CO2
- 0-3 mm Hg
Excessive dead space
Exhausted soda lime
Inadequate fresh gas flows

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NOTEWORTHY GRAPHS
- Cardiogenic oscillations
- Leak in circuit
- Spontaneous breaths

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TEMPERATURE
Body temp is important!
- Anesthetics reset thermoregulation threshold
- Broader ranges tolerated without response

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TYPES OF HEAT LOSS
- Radiant
- Vasodilation
- Conductive
- Cool surgery table
- Convective
- Surgical scrub
- Open body cavity
- Evaporative
- Dry anesthetic gases

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HYPOTHERMIA
- Consequences
- Release of catecholamines
- Vasoconstriction, tachycardia, hypertension increases post-op morbidity
- Coagulation deficiencies
- Impaired platelet function
- Decreased coagulation pathways
- Decrease wound healing
- Impaired immune function
- Inhalant reduction
- Overdose potential
- Post -op shivering
- Increased oxygen consumption
- Residual respiratory depression

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HYPERTHERMIA
Identify cause
- Response to drugs
- Overuse of supplemental heating
- Heat dissipation inhibition
- Malignant Hyperthermia
Temp reducing techniques
- Oxygen
- Cool fluids

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MONITORING AND SUPPORTING
Convective warming units are best
Avoid
- Rice socks
- Hot water bottles
- Heating pads
- Direct contact with heat source

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Quick Review
- Monitors are only as good as the person using them
- Know what is normal!
- Monitor as many parameters as possible for the most complete picture
- Circulation
- BP, ECG, EtCO2
- Oxygenation
- SpO2
- Ventilation
- EtCO2
- Temperature
- All by someone who knows what they are doing!

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Questions?
Vastwise@gmail.com