Anesthesia MonitoringSarah Ouellette CVT.

Anesthesia and MonitoringGoals:

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

Why we monitor?Anesthetic emergencies/complications:

Difficult to predictHappen quickly Become life threatening quickly

It is better to be proactive than reactive

Prevention is key!

MonitoringRemember:

No monitoring device can take the place of constant human observation

The equipment we use only enhances our ability to monitor a patient

Monitoring Starts when animal is dropped off

Pre-anesthetic evaluation includes History, Physical Exam

Ends after recovery period even day after

Pre-anesthetic EvaluationHistory: what you want to know

Individual risk factors/underling problemsAge – certain risks for pediatric and geriatric

patientsBreed – brachiocephalic (long recovery) Temperament – aggressive/fractious (pre-med early)

Physical Exam – TPR, heart murmurs, lung sounds

Procedure – invasiveness, pain level

Stages of AnesthesiaStage 1: Pre-medication

Stage 2: Induction

Stage 3: Maintenance Planes: 1 – 4

Stage 4: Recovery

Stages1. 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

StagesPre-medication:

Decreases need for increased induction agents and inhalant anesthetics

Aids for smoother induction and recovery

Place IV catheter during this stageMay start fluids or pain management CRI at

this time

Stage 1: Pre-medicationWhat we monitor:

Heart rate

Respiratory rate

Perfusion – MM color/CRT

Pulses

Drooling/vomiting

Level of sedation

Reactions to medications

Stages2. 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

Stage 2: InductionWhat we monitor:

HR/RR

Perfusion - MM color/CRT

Pulses

CNS reflex's – depth

Stages3. Maintenance:

Unconscious + pain free

Inhalant anesthetic used to maintain unconsciousnessEx. Isoflurane, sevoflurane

Procedure is performed+/- IV fluids+/- Pain management CRI (fentanyl, MKL)

Procedure dependant

Stage 3: MaintenanceWhat we monitor:

HR/RR

Perfusion - MM color/CRT

Pulses

CO2/O2 concentrations

Blood Pressure

CNS reflex's – depth

Temperature

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

Stage 4: RecoveryWhat we monitor:

HR/RR

Perfusion – MM color/CRT

Pulses

Temperature

CNS signs – consciousness

+/- Blood pressure

Planes of AnesthesiaPlanes are used to describe depth of anesthesia

during the maintenance stage

Plane 1: light

Plane 2: medium

Plane 3: deep

Plane 4: too deep

Planes of Anesthesia Plane 1 (light):

Regular HR

+/- irregular RR

Swallowing reflex decreases

Limb movements decrease

CNS signs present

Pain sensitive

Considerable jaw tone

Planes of AnesthesiaPlane 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

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

Planes of anesthesiaPlane 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

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

MonitoringParameters we monitor during

anesthesia:

1. Central nervous system

2. Cardiovascular system

3. Respiratory system

4. Temperature

Monitoring CNSVaries 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

Common CNS reflexesEye 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 drugEx. Ketamine - eyes are fixed centrally

Eye Positioning

Common CNS reflexesPalpebral 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

CNS common reflexesPupil 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

Common CNS reflexesNystagmus:

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

Common CNS reflexesSwallowing:

• Spontaneous when awake

• Lost plane 1

• Regains after consciousness

• Important in recovery stage• Must be present before extubation to prevent

aspiration

CNS common reflexesLaryngeal reflex:

Monitored during intubation

Arytenoids close to protect trachea

Elicited by tube stimulation

Induction decreases this reflex Lost plane 1Cats may need deeper plane to avoid

laryngospasms

Larynx/Arytenoids

DO NOT TOUCH ARYTENOIDS Can cause laryngospasms

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

CNS common reflexesPedal reflex:

• Pinching digit or pad looking for withdrawal

• Lost by plane 2

• Movement = inadequate depth for surgery

• Shouldn’t be present with inhalant anesthesia

CNS common reflexesEar/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

CNS common reflexesMuscle 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

CNS common reflexesResponse to surgical stimulus:

Movement

Lost by plane 2

Dramatic increase in HR and RR

Late indicator of inadequate depth

Monitoring CirculationGoal:

Ensure adequate blood flow to tissues and vital organs

How we monitor Circulation

Heart rate

Blood pressure

Tissue perfusion

Monitoring HRHeart 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

Monitoring HRBradycardia: Low HR

< 60 dogs< 120 cats

Common causes:

Drugs/inhalants (have depressant effect) If patient is too deep

Monitoring HRTachycardia: High HR

> 180 dogs> 220 cats

Common causes:PainDrugs

Ex. Atropine, gycopyrrolate, ketamine

Monitoring HRHow we monitor heart rate:

1. Palpation

2. Auscultation

3. Pulse Oximeter

4. Electrocardiogram (ECG)

Monitoring HRPalpation of chest for heart rate:

Difficult to feelLess reliable

Palpation of peripheral artery: Femoral, metacarpal, dorsal pedal, cranial tibial, lingual most common Count a rate Note the quality – normal, bounding, weak

Common Palpable Arteries

Monitoring HRAuscultation of the heart:

• Hand held stethoscope• Count rate• Detect murmurs

Monitoring HREsophageal 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

Esophageal Stethoscopes

Monitoring HRPulse 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

Monitoring HRElectrocardiography (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

Monitoring HRElectrocardiography (ECG)

Has 4 leads (most have 3): placed on armpit and flankWhite: Right frontBlack: Left frontRed: Left hindGreen: Right hind*

* this lead is commonly left out

Monitoring HR

Monitoring HRECG 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

Monitoring HR

ECG leads

Monitoring HRElectrocardiograph: waveform

Provides regional information about the heartP waveQRS complexT wave

Each letter represents a location and function of heart

Abnormal waveform called arrhythmia

Monitoring HR

Monitoring HRCommon causes of arrhythmias:

Heart dz #1

Pain

Drugs - (atropine and glycopyrrolate)

Electrolyte imbalances

Poor oxygenation

Monitoring HR

ECG RhythmsNormal:

Abnormal ECG RhythmsAtrioventricular Block (AV block)

Absence of QRS complex and T wave (dropped beat)

Abnormal ECG RhythmsVentricular Premature Contractions (VPC’s)

Extra beat originating from from ventricles

Monitoring Blood PressureBlood 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

Monitoring Blood Pressure Further defined:

Systolic pressure – SAP

Diastolic Pressure – DAP

Mean Pressure – MAP

Monitoring Blood Pressure Normal ranges under anesthesia:

Systolic 80-150mmHg

Diastolic40-80mmHg

Mean - More important/accurate parameter Dogs: 60-100mmHgCats: 60-120mmhg

Monitoring Blood Pressure Hypotension: low blood pressure

MAP < 60mmHgTissue perfusion is compromised

Common complication under anesthesiaDrugs/inhalants depressant

Tx/prevent: Lower inhalant, start fluids – give boluses, certain drugs

Monitoring Blood Pressure Hypertension: high blood pressure

MAP > 175mmHg

Causes:

Underling Heart disease

Pain

Monitoring Blood PressureDependent 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

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

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

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)

Monitoring Blood Pressure Oscillometric technique:

Monitoring Blood Pressure Doppler:

Indirect method

non-invasive

**ONLY used to

measure SAP**

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

Monitoring Blood Pressure Arterial monitoring: (gold standard)

Yields most accurate results

Direct method – Invasive method

IVC placed in dorsal pedal or metacarpal ARTERIESNeed a highly skilled technician Risks of infection and hemorrhage are high

Because of these reasons it is not common technique

Monitoring Blood PressureArterial monitoring:

Catheter connected to electronic pressure transducer via extension tubing and transmits signal to monitor

Displays: SAP, DAP, MAP and constant waveform

Arterial Catheter

Arterial Catheter

Monitoring Blood PressureCentral 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)

Monitoring Tissue Perfusion

How we monitor tissue perfusion:

1. Palpation Artery

2. Mucus membrane color

3. Capillary refill time

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)

Monitoring Tissue perfusion

Mucus membrane color:

Should be pink and moist

Abnormal:Pale = vasoconstriction, blood loss or anemiaPurple or blue = cyanosisDry/sticky = dehydrated (dugs)Red/injected = heat stroke, sepsis, carbon

monoxide poisoning Yellow (icteric) = liver disease

Mucus Membrane Colors

Normal

Pale

Icteric

Cyanotic

Monitoring Tissue Perfusion

Capillary refill time:

Touch gums note time it takes for color to returnshould be < 2 sec

Prolonged = poor perfusion

RespirationGoal:

Move O2 into the lungs and expel CO2 out

Ensure adequate O2 and CO2 concentrations in blood

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!

Anatomy of RespirationAlveolar sac:

Blue – venous blood from body high levels of CO2

Red – arterial blood high in O2 going back to the body

Anatomy of Respiration

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

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

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

Monitoring RespirationVaries between patients

Normal resting rates:Dogs 10 – 20 Cats 15 – 25

Under anesthesia:8-20 both spp.

Monitoring RespirationCauses of decrease in respiration:

Drugs we give

Too deep

Heavy drapes or instruments on small patients

Dr. hand over patients chest

Low CO2 concentration

Monitoring Respiration Causes of increase respiration:

Surgical stimulation

Too light/pain

Lung diseasePulmonary edema, pneumothorax, masses, ect.

Monitoring RespirationHow we monitor respiration/ventilation:

1. Visual/listening

2. Monitoring CO2

3. Monitoring O2

Monitoring RespirationVisual/listening:

Observe chest movements

Watch breathing bag

Handheld stethoscope

Listen to breathing sounds with esophageal

stethoscope gives rate and quality

Monitoring CO2Respiratory Rate:

Can correlate to amount of CO2 in bloodNormal 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

Monitoring CO2How we monitor CO2:

1. Blood Gas Analysis

2. Capnography

Monitoring CO2Blood Gas: “GOLD STANDARD”

Most accurate determinant of CO2 levels in blood

Direct – invasive method

Need:Arterial blood sampleBlood gas analyzerSkilled technician Patient dependent – size, age

**Not common method**

Monitoring CO2However…

Measuring end tidal CO2 (EtCO2) using capnography is useful alternative to estimate levels in blood (PaCO2) without invasive techniques

Monitoring CO2Capnography:

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

Monitoring OxygenationCapnoGRAPH tells us:

Graphical display CO2 that is exhaled

EtCO2 concentration

Resp rate

CapnoMETER tells us:

EtCO2 concentration

Resp rate

Capnography

Capnometer

Capnograph

Monitoring Oxygenation

Capnograph:

Monitoring CO2Why is capnoGRAPH preferred?

Graphical display useful for determining:Airway obstruction Leak in endotracheal tube

Normal CapnographGraphical display

Abnormal Capnograph

Inadequately inflated endotracheal tube cuff

Damaged or leaking endotracheal tube cuff

Abnormal Capnograph

Obstruction of endotracheal tubeBlood or mucus buildupKinked tube

Monitoring CO2CO2 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**

Monitoring O2SpO2:

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

Monitoring O2O2 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)

Monitoring O2How we monitor O2:

1. Blood Gas Analysis

2. Pulse Oximeter

Monitoring O2Blood Gas: “GOLD STANDARD”

Most accurate determinant of O2 levels in blood

Direct – invasive method

Need:Arterial blood sampleNeed blood gas analyzerSkilled technician Patient dependant – size, age

*Not commonly used*

Monitoring SpO2Pulse 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

Pulse Oximeter machines

Pulse OximetrySurgi-Vet Monitor

Monitoring SpO2Probes:

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

Pulse OximetryProbes

Pulse Ox equipmentRectal probe:

Rectum must be free of excess foreign material

Light positioned dorsally

Anchor it to the tail with tape

Monitoring SpO2Causes 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

Monitoring SpO2High readings:

Falsely increased

Florescent lightsPlace 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**

TemperatureGoal:

Maintain a body temperature adequate for normal metabolic functions

Avoid accidental hypothermia or malignant hyperthermia

TemperatureNormal:

99.5 – 102.5F

Hypothermia: low temp

Hyperthermia: high temp

Monitoring temperatureHypothermia:

Common complication under anesthesia

Loose heat rapidlyFirst 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

Monitoring TemperatureWhy 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

Monitoring TemperatureTreating hypothermia:Prevention. Prevention. PreventionWarm IVF Hot water pads/blanketsBubble wrap feetWarm blankets Bair huggers

Monitoring TemperatureTreating hypothermia:

Hot water bottles/fluid bags in towels

** NEVER direct contact with patient**

heat + pressure + time = necrosis

Monitoring TemperatureCauses of hyperthermia:

Excessive application of heat in attempt to prevent hypothermia

Infections

Cats – adverse reaction to hydromorphone

Ketamine

Monitoring temperatureTreating hyperthermia

Remove blankets from cage

Place ice packs in towels in cageNot directly on the patient

** REMEMBER: if methods are being used to treat hyperthermia, the temperature should be monitored

closely to prevent subsequent hypothermia **

How We Monitor Temperature

Manually – hand thermometer

Esophageal probe

Rectal probe

Thermometer probes

Record Keeping

How we keep it all together

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

Record KeepingUseful 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

Record KeepingAnesthesia 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

Record KeepingTypes of anesthesia sheets

1. Graphical

2. Numerical

Graphical

Numerical

In ConclusionNo 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!