Lecture 3 Monitoring the Anesthetized Patient 1 Flashcards
Why do we monitor?
to WARN anesthetist of changes in depth or status of patient to facilitate an early response
When does monitoring begin?
- Begins preop => recovery
- peri-op mortality within 1st 3 hours
Individualized Anesthesia Plan Provides basis for
- Drug selection
- Monitoring & support
- Anticipated complications & plan of action to address them
Why is the The Anesthesia Record important?
- Legal record of events
- Prompts to observe, evaluate & record patient status
- *Irreversible CNS & cellular changes occur within 3-5 min of cessation of blood flow*
- Trends can be recognized
What are the safest anesthetic agents?
“There are no safe anesthetic agents, there are no safe anesthetic procedures. There are only safe anesthetists”
What is the Best/Most expensive Monitoring Equipment
- Is an attentive anesthetist: YOU!!! (or vet tech that is educated)
- LOOK at/touch your patient
- Use your senses
What do we monitor?
- Anesthetic Depth
- Body Temperature
- Circulation
- Ventilation
- Oxygenation
Why do we monitor anesthetic depth
- Too light – arousal, awareness, movement, pain
- Too deep – anesthetics are DOSE DEPENDENT cardiovascular and respiratory depressants
proper oxygenation will require what 2 systems to be working
circulatory + respiratory function
How can you use eye position to check anesthetic depth for dogs, cats and cattle
- Eye Position:
- Rolls ventrally @ surgical plane
- Centered @ light/deep planes
- Differentiate with palpebral
- Dogs, cats & cattle
How can you use eye position to check anesthetic depth for horses
- Horses – medial position
- May be unreliable
- Different positions in each eye
- Nystagmus/tearing => TOO LIGHT!!!
How can you use eye position to check anesthetic depth for Sheep, goats, camelids
globe does NOT rotate
How do you test the palpebral reflex for anesthetic depth for:
- Small animals
- Horses (add about horses being on back blood to head)
- Ruminants/ swine
- Small Animals
- tap medial canthus
- absent @ surgical plane
- Horses
- gently brush cilia, slow closure of eyelids
- Present @ surgical plane
- Ruminants/swine
- Absent @ surgical plane
- How can you use the corneal reflex for anesthetic depth
- Withdrawl relfex
- Corneal
- ALWAYS present
- Never use in patient believed to be alive!!
- Withdrawal
- Toe pinch withdrawal will be present if too light
How can you use Jaw Tone for anesthetic depth
- Varies with depth
- Subjective
- Not reliable with dissociative anesthetics
- Ketamine will cause muscle regidity
- What is Minimum Alveolar Concentration (MAC)
- What is it used for?
- is the concentration of inhalant in the lungs needed to prevent movement (motor response) in 50% of animals in response to a noxious or surgical (pain) stimulus.
- MAC is used to compare the strengths, or potency of inhalant anesthetic
- What is the MAC for isoflurane in dogs, cats and horses
- for sevoflurane for dogs and cats
- ISOFlurane:
- Dog 1.28%,
- Horse 1.3%
- Cat 1.63%,
- MAC for SEVOflurane:
- Dog 2.3%,
- Cat 2.6%
- 95% patients adequately anesthetized at what MAC number
- Why dont you keep all patients at the same MAC?
- 1.5 MAC
- Not as same MAC because:
- Pre-med/intra-op analgesia ↓ MAC
- MAC reflects population not individual
- Need to titrate to patient
- Typically at what % will we start the iso setting on and what flow (high or low)?
- For how long in a circle system?
- Why?
- start patients on 2% iso with high flow
- first 15 min
- to get the iso concentration higher in the circuit
Will all the % of iso be absorbed?
- a certain amount will be soluble in the blood and tissue
- that is why the expired % iso and inspired % is different
How can we use End tidal inhalant Concentration (Et-inhalant) for anesthetic depth
- Is the concentration of inhalant gas expired at the End of expiration
- Et-iso concentration gas reflects brain concentration
- End-tidal inhalant % more precise than vaporizer setting
What is the primary driver for respiration
CO2
How can you use EtCO2 for anesthetic depth
Normal respiration controlled primarily by blood levels of carbon dioxide (PaCO2)
EtCO2 monitors exhaled CO2 noninvasively
Indirect measure of arterial CO2 (PaCO2)
EtCO2 3-5mmHg < PaCO2
Because EtCO2 is an indirect measure of arterial CO2, what would the PaCO2 be?
EtCO2 3-5mmHg < PaCO2
Inhalants: dose-dependent respiratory depressants
How does this affect EtCO2
An anesthetized patient will take a breath at a higher EtCO2
- Normal awake ~40 mmHg
- Anesthetized < 55 - 57mmHg
If PaCO2 gets high, what will happen to the body generally?
blood will become acidodic
What is the equation for delivery of oxygen (DO2)
DO2 = CO x CaO2
What is the equation for cardiac output (CO)
CO = HR x SV
What is the equation for oxygen content of blood (CaO2)
CaO2 = HbO2 + PaO2
What does capillary refill time (CRT) read?
- Normal < 2 seconds
- Prolonged CRT => poor tissue perfusion or dehydration
capillary refill time (CRT) is not very useful during anesthesia, why?
- Drugs and ↑ PaCO2 cause vasodilation
- Dexmedetomidine => vasoconstriction
What are 4 different ways to measure circulation in the anesthetized patient
- Clinical Evaluation
- palpation of pulses
- Auscultation of heart – stethoscope
- Auscultation of heart/pulse
- Esophageal stethoscope, Doppler
- Electrocardiogram (ECG)
- Blood Pressure
- Indirect, direct
When you auscult the heart, what is also important to do?
simultaneous palpation of peripheral pulses
- What are the different areas you can palpate pulses in dogs and cats?
- Horses?
- Dog & Cat: Femoral, dorsal pedal, lingual
- Horse: Facial, trans. Facial, metacarpal/tarsal, coccygeal
- What do you want the heart rate to be for dogs?
- cats?
- Horses?
- >60 dogs
- >80 cats
- HR constant in horses
Does the pulse preasure indicate mean arterial pressure?
- PP= SAP – DAP
- SAP = systolic arterial pressure
- DAP = diastolic arterial pressure
- MAP = mean arterial pressure
- PP does not indicate MAP!
How far do you try and place an esophageal stethoscope?
Tip @ level of heart
- What are the advantages to an Esophageal Stethoscope
- disadvantages?
- Advantage:
- inexpensive
- also monitor resp rate
- Disadvantage:
- difficult to use in certain cases (endoscopy)
- can disconnect
- Need amplifier ($150 on ebay) or dedicated person
There is an adible beep on an ECG when?
with each R wave
What are limitations of an Electrocardiogram (ECG)
- Electrical activity only, no info about mechanical function
- pulseless electrical activity (PEA)/ electromechanical dissociation (EMD) => cardiac arrest, normal electrical activity but no pulses
- so ECG can still be going and the patient is dead
- ECG should not be used alone
When looking at the ECG leads, what do the following abreviations mean
- RA
- LA
- LL
- Arm
- Leg
- RA = Right Arm
- LA = Left Arm
- LL = Left Leg
- Arm = forelimb
- Leg = hindlimb
When you have 3 limb leads (RA, LA, LL) what option should the ECG be on for lead types (Lead I, II, III)
Lead II
- When using an Esophageal ECG, where do you place the leads
- What option do you change the ECG to (Lead I, II, III)
- RA & LL placed on esophageal probe
- LA on ear or neck
- select lead II on ECG
Advantage of esophageal or base-apex lead placement
- avoids attachment to hindquarters
- accessible by anesthetist
- minimize motion artifact
When using the Base apex Electrocardiogram, where do you place the leads?
- RA & LL electrodes attach to right (preferred) or left jugular furrow
- LA electrode attach to opposite thoracic wall caudal to heart
- Lead I (negative deflection)
- Lead III (positive deflection)
What are the 2 types of indirect blood pressure monitors and what do they measure
- Doppler - SAP only
- Oscillometric – SAP, MAP, DAP
SAP = systolic arterial pressure
DAP = diastolic arterial pressure
MAP = mean arterial pressure
What are the 3 types of direct blood pressure monitors and what do they measure
- arterial catheter, transducer & monitor
- measures MAP, SAP, DAP
- Continuous beat-to-beat pulse waves
SAP = systolic arterial pressure
DAP = diastolic arterial pressure
MAP = mean arterial pressure
When you use an Ultrasonic Doppler what are you measuring
blood flow & SAP
Explain how you take a blood pressure with an Ultrasonic Doppler
- Probe + gel placed over peripheral artery – limb or tail
- BP cuff placed proximal to ultrasonic probe, inflated until it exceeds SAP, which silences Doppler signal
- Cuff gradually deflated until first signal is audible
- BP on sphygmomanometer is SAP
- What are the advantages of using the Ultrasonic Doppler
- disadvantages
- Advantages:
- Cost, systolic BP
- Disadvantages:
- Proficiency of use
- Not automatic
- Accuracy dependent on cuff**
- Size, fit, excessive hair
- Weak signal with vasoconstriction/hypotension
How do you set up an Oscillometric BP
- Cuff size 40% of limb circumference
- BP cuff on peripheral limb or tail base
- Hindlimb – above or below tarsus
- Forelimb – above carpus
MAP, SAP, DAP taken at set time interval
What are the advantages of using an Oscillometric BP
- Advantages:
- easy to use, set for automatic measurements
- Disadvantages:
- Technology is motion sensitive
- ↓ accuracy at low BP, low/high HR or arrhythmia
- accuracy dependent on cuff size – 40% limb circumference
- Too small overestimates BP
- Too large, loose underestimates BP
What is the Gold standard for measuring MAP, SAP, DAP
- Direct BP
- Uses arterial catheter, BP transducer & monitor for continuous beat-to-beat pulse waves
- What are the advantages of using a Direct BP measurement
- disadvantages?
- Advantages:
- accurate, continuous
- Arterial blood gas sampling
- Ideal for critical patients
- Disadvantages:
- Cost, skill
- Complications:
- infection, thrombosis, hematoma
- air embolism, exsanguination
- drug injection
- What are the common sites for arterial catheter placement in dogs and cats?
- Horses?
- Dogs & Cats
- Dorsal pedal, lingual
- Horses
- Facial, ear, metatarsal, transverse facial
