Monitoring---Anesthesia Flashcards
3 most important parameters monitored during surgery
- Anaesthesia depth
- Cardiovascular function
- Respiratory function
Anesthesia depth is used as a guide to tell us…
if we need more or less anesthetic
What’s the best monitor?
YOU
Physical signs used to determine anesthesia depth: (8)
– Palpebral reflex – Jaw tonicity – Movement – Cornea – Heart rate – Respiratory rate – Haemodynamic/ respiratory variations -- Eye movement
During anesthesia monitoring of a horse, you notice the palpebral reflex is still present. What do you do?
Nothing! It’s normal.
During anesthesia monitoring of a dog, you notice the palpebral reflex is still present. What do you do?
Crank up the anesthesia because that’s sooooo not normal. (same for cats)
What is stage 1?
Analgesia
What are the 7 components of stage 1/analgesia?
- Stage of voluntary movement
- From beginning of induction to loss of consciousness
- Motor function present
- Euphoria
- Ataxia
- Hallucinations
- Hyperacusis
What is stage 2?
Excitement
What are the 8 components of stage 2/excitement?
• Stage of delirium or involuntary movement • From loss of consciousness to onset of regular breathing • Salivation, vomiting • Dilated pupils • Tachycardia and hypertension • Nystagmus common in horses • Laryngeal spasm in pigs and cats • Avoid stimulation
What is stage 3?
Surgical anesthesia
What are the four components of stage 3/surgical anesthesia?
• Divided in plane 1-4 OR light, medium, deep • Progressive depression of reflexes • Plane 2: – moderate surgical anaesthesia – adequate muscle relaxation – stable respiration and pulse rate – strong corneal reflex • Plane 3: deep surgical anaesthesia; desired plane when muscle relaxants were not used; pupil dilation
What is stage 4?
Asphyxia
What are the components of stage 4/asphyxia?
- ἀσφυξία: without pulse
- CNS extremely depressed
- Respiration ceases, terminal gasps possible
- Blood pressure at shock level
- Pupils widely dilated
- Without intervention: death
Let’s say you’ve induced a patient without muscle relaxants on board…what plane of stage 3 do they need to be in before you start incising?
Plane 3
Let’s say you’ve induced a patient WITH muscle relaxants on board…what plane of stage 3 do they need to be in before you start incising?
Plane 2 is ideal
You’re monitoring induction of a cat and notice laryngeal spams. Is zi cat ready to be incised? What stage is she in?
Stage 2
Monitoring a cow during surgery and you notice elevated BP. how concerned should you be?
Not toooo concerned since increased BP is somewhat normal for cattle during anesthesia.
When should you check for corneal reflex?
Only if you think the patient is dying! Otherwise, this reflex should be present throughout stages 1-3. Remember stage 4 is death’s door so we probably would see little to no corneal reflex then.
How often do we monitor?
Continuously every 5 minutes. Not just every 5 minutes but continuously, every 5 mins. There is no such thing as over doing it.
Ways to monitor cardiovascular function:
• Capillary refill time, mucous membranes • Heart rate and rhythm • Blood pressure – non-invasive vs invasive – arterial BP – central venous BP • Cardiac output
What does it mean when you can’t really feel the femoral/metatarsal pulse?
Means BP is really low.
Ways to monitor the Heart Rate
- Auscultation
- Heart palpation
- Pulse palpation
- Doppler ultrasound
- Pulse oxymeter
- Blood pressure monitor
- Electrocardiogram (ECG)
Electrocardiogram (ECG)
1) it gives no information on the mechanical function of the heart
2) doesn’t tell you anything about cardiac output
3) just don’t use this as the sole monitor for CV fxn.
So we know that ECG sucks sometimes….but how can it be misleading?
1) It can look normal even if patient is hypovolemic
2) may be normal during cardiopulmonary
arrest
3) misinterpretation
What measurement does the prof find to be more important than ECG during monitoring?
Arterial blood pressure measurement
What HR is considered bradycardia in dogs?
Under 60 bpm..still, BP is more important as HR is relative
What HR is considered bradycardia in cat?
Under 100 bpm…still, BP is more important as HR is relative
What HR is considered bradycardia in horses?
Under 20 bpm…still, BP is more important as HR is relative
Non-invasive techniques for Arterial blood pressure measurement? (2)
– Oscillometric technique
– Doppler probe
**Dont’ forget we have invasive method as well
Why is the BP important??
MAP=driving force for blood flow through capillaries that supply O2 to organs and tissue beds.
Can we measure O2 content in the blood?
Yes
Can we measure Cardiac Output?
Yes but it’s not that practical especially to do on a daily basis.
What two parameters does Cardiac Output depend on?
SV and HR.
Remember, we can measure HR no problem. But SV?…
Another card for SV.
Can we measure Stroke Volume?
It’s not that easy to measure SV…definitely not practical to do on a daily basis.
It depends on after load, preload, contractility, etc
Since measure Cardiac Output isn’t practical, what’s the closest measurement we can use to get to figuring out what the CO is?
Blood pressure! BP gives us an idea about perfusion. BP depends on CO.
With BP being the closest measurement we can get to figuring out the CO, can we always assume BP will match CO? In other words, high BP=high CO and low BP=low CO?
NO!
If you have a rather high or almost high BP and PALE mucous membranes, that means VASOCONTRICTION. This means perfusion is low because Cardiac Output is low.
Pale mucous membranes with high blood pressure…what’s going on here?
Vasoconstriction due to low cardiac output.
What is the equation we use to calculate O2 content??
CaO2= (SaO2 x Hb x 1.34) + 0.003(PaO2)
Blood pressure is so important because hypotension can cause the following!!…:
hypotension can cause=
1) blindness
2) kidney failure
3) delayed recovery due to reduced hepatic metabolism
4) worsening of pulmonary perfusion
5) myopathy (esp in large animals if they are under perfused aka low BP!!!)
6) death
Equation for arterial blood pressure
ABP=HRxSVxSVR (systemic vascular resistance)
What do you do with a patient who has low HR and low BP?
Take action
What do you do with a patient who has pink mm, low HR and a good BP?
Everything might be irie
If you let the BP fall too low, what are you doing to the kidneys?
Pushing them into kidney failure.
Kidneys can tolerate a range of blood pressure but if you go lower than 50..60mmHg…you’re screwed. This is why monitoring is so important!
How do we monitor BP with invasive method and in which animal is this done most commonly?
Fluid filled extension line/Transducer/Monitor
Horses. Their arteries are easier to place catheters in. We do this in ruminants as well. With small animals, only do this in sick and critical patients.
Invasive is gold standard because you see real time changes!!
If you’re going to use the invasive approach to measure BP in a small anima, which vasculature are you gonna use?
dorsal metatarsal artery, femoral
artery, palmar artery
If you’re going to use the invasive approach to measure BP in a HORSE, which vasculature are you gonna use?
facial or transverse facial artery, digital artery
If you’re going to use the invasive approach to measure BP in a RUMINANTS, which vasculature are you gonna use?
Ear artery
With the ABP, the Systolic Arterial Pressure and Diastolic Arterial Pressure are measured and the MAP is then calculated. What’s the formula to calculate the MAP using the SAP and DAP?
MAP= DAP + 1/3 (SAP-DAP)
Which method of BP measurement is preferred for small animals?
Non-invasive
Oscillometric Blood Pressure—most accurate measurement?
mean BP
Oscillometric Blood Pressure—importnat technical stuff. What’s the deal with cuff size and accurate measurement?
Ideal cuff width: 40% of the circumference of the limb
- Wider cuff: underestimation
- Narrow cuff: overestimation
Where do we place the probe of the doppler ultrasound?
Small probe placed over peripheral artery…concave part touching the patient.
The only information the doppler ultrasound gives you?
Systolic BP and the pulse rate…can get a little idea about perfusion if you get a nice loud whoosh sound
The only information the Oscillometric Blood Pressure gives you?
Systolic, Mean and Diastolic
Pressure at which the pulse sound becomes audible
is defined as:
SAP (systolic arterial pressure)
What is the best BP we can get next to the invasive approach?
Doppler compared to Oscillometric
In which animal does the doppler measure falsely low?
CATS! So add 15mmHg
If you have low or high numbers with Oscillometric, use which method to confirm?
Doppler
When we’re interpreting BP results, which other parameters should we also take into account for the bigger picture? (2 things)
MM and CRT
What are the lowest acceptable values for BP during anesthesia?
– SAP: 90 mmHg
– MAP: 60 mmHg in SA, 70 mmHg in horses (horses have more muscles that need to be perfused or else myopathy!!. This is why it’s 70 and not as low as in SA.)
– DAP: 40 mmHg (the heart is being perfused during diastole so important to keep an eye on)
What are the two ways we can monitor respiratory function?
Physically and with monitors
Physical ways to monitor respiratory function: (4)
– chest excursions
– re-breathing bag
– rate, tidal volume, breathing pattern
– mm colour
Monitors to check on respiratory function: (5)
– oesophageal stethoscope – Pulse oximeter – Apnoea monitor – Capnograph – Blood gas analyser
What are the two things pulse ox combines?
oximetry with plethysmography
What are the two components of pulse ox?
– light-emitting diode
– photodiode detector
What is the Lambert-Beer law as it pertains to the functionality of the pulse ox?
The pulse ox emits two lights with different wavelength and oxygenated blood and deoxygenated blood detect those lights differently.
– OxyHb absorbs more infrared light
(940nm)
– DeoxyHb absorbs more red light (660nm)
What information can you get from pulse ox?
cardiopulmonary function! SpO2 and pulse rate
T/F
Pulse Ox gives us information about ventilation under anesthesia
Falseee
Can we use pulse ox to figure out patient’s CO2 elimination?
No. We just know about their oxygenation.
T/F
Pulse Ox does not give us information about Hematocrit.
True
Can we detect hypovolemia via pulse ox?
Yep!
Again, you see a reading of SpO2 < 90%. What comes to your mind?
Hypoxemia!
5 reasons for Hypoxemia (slightly different from what she said for clinical med but sorta the same)
– hypoventilation (most common) – hypoxic gas mixture (lowered FiO2) – kinked ET tube (leads to hypoxic gas mixture) – alveolar diffusion impairment – artefacts
Lowered SpO2 in a healthy patient. What’s the first thing you do?
Massage tongue, replace the probe and make sure you get back to normal reading.
What are some limitations with pulse ox?
- Motion or shivering
- Abnormal Hb
- Reduced perfusion (most common) due to probe compressing the vessels, hypothermia, hypotension, alpha2-adrenoceptor agonists
What’s the best thing you can use to monitor respiration in your patients?
Capnograph machine
What information does the capnograph give us? **
“Ultimate monitor” – indicates blood flowing to lung and patient ventilating and of course, CO2 levels.
Turning point: Capnograph Gives us info about ventilation and perfusion (bc where is CO2 coming from? metabolism in the tissue so there needs to be perfusion to bring the CO2 to the lungs so if you have low end tidal CO2 is from low BP, hypovolemia, shock? So if you have low CO2 due to cardiac arrest (it’s a bad sign in general), remember the ECG will still be normal with cardiac arrest.)
Normal values for end tidal CO2:
Normal values: ETCO2 of 35-45mmHg
If you have a dog with End tidal CO2 reading of 52, do we freak out?
Not really because we have to take into account the drugs given that could be causing hypoventilation so CO2 may be a little higher than the normal range.
What do we use as a good indicator of respiratory efficiency? Pulse Ox or Capnography?
Capnography
Two ways to capture capnography?
side stream—but with small animals and small volume of ‘breathing out’ can create a mismatch and you get lower values that aren’t accurate
main stream–more accurate. no time delay and no issues with the small animals
When patient is rebreathing CO2…what does the Capnograph look like?
It doesn’t touch Zero.
What are some reasons for rebreathing CO2?
- exhausted absorbent
- incompetent expiratory valve
- insufficient fresh gas flow
- problems with the inner tube of a Bain system
Is End Tidal 5% CO2 within normal range?? Turning point Q.
YES!
Atmospheric pressure is 760…1% of that is 7.6 multiplied by 5 is 38. 5% of 760 is also 38. There you go.
Curare Cleft….
If you use blocking agent and you have to breathe for them and then the blocking agent wears off and the patient starts breathing on its own, you’ll get a strange shape on the capnograph.
Possible causes for hypercapnia?
•High end tidal CO2 love 45mmHg
• Re-breathing (FiCO2 MUST be high as well to confirm this)
• Increase in metabolism
– Malignant hyperthermia (common in pigs)
– Skeletal muscle activity
– Hyperthermia
What’s more concerning? High end tidal CO2 or low end tidal CO2?
LOW.
Not high because if high you can just breathe for the patient.
Some cases of hypocapnia
- Hyperventilation
- Pulmonary embolism
- Hypoperfusion, hypovolaemia
- Hypometabolism
- Hypothermia
- Hypotension
- Cardiac arrest
If FiCO2 is 2, what does this indicate?
Rebreathing. Should be 0!!
You see a reading of PaO2 < 60mmHg. What comes to your mind?
Hypoxemia
What information can we gather from the use of blood gas analysis?
Respiratory function.
• Alveolar ventilation
• Oxygenation
What is gold standard for measuring gas exchange?
Blood gas analysis
The blood gas machine measures what? (3)
- PaO2
- PaCO2
- pH
What kind of sample do you need for arterial blood gas?
Arterial blood sample.
• PaO2 and PaCO2 would be different in venous blood sample.
Again, what’s A-a gradient and what information does it provide?
It is the difference between PO2 in alveoli and arteries
It tells us the efficiency of gas exchange and is also an indicator for lung function.
If it’s less than 15mmHg, then it’s normal!
