Monitoring Flashcards
1
Q
What does anesthesia produce in a patient?
A
- CNS depression (hypnosis)
- CV depression (hypotension, +/- bradycardia, arrhythmias)
- Resp depression (hypoventilation, +/ hypercapnia, hypoxemia)
- Impairs thermoregulation (hypothermia, +/- hyperthermia)
2
Q
What are the Big 5 of anesthetic monitoring?
A
- ECG
- Blood pressure
- Pulseoximetry
- Capnography
- Temperature
3
Q
What are the most common causes of perioperative death in small animals?
A
CV or respiratory causes
4
Q
What should you be monitoring for during each step of the anesthesic process?
A
- After pre-med: regurg/vomiting, hypoventilation, hypoxemia, arrhythmias
- During induction: regurg/aspiration, hypoventilation/apnea, arrhythmias, hypotension
- During maintenance: the Big 5
- During recovery: airway protection, hypothermia, oxygenation, pain
5
Q
What are some general considerations to have during the post-operative period?
A
- Residual resp depression may lead to hypoxemia in animals breathing room air
- Ability to protect airway against aspiration
- Analgesics? - animal may be painful
- Adequate body temp until they are able to thermoregulate normally
47% of anesthesia-related deaths occur in post operative period!!
6
Q
How do you monitor the CNS in your anesthetic patient?
A
Clinical evaluation of reflexes:
- Swallowing: important during extubation - patient can protect airway
- Palpebral: light plane when present, can become fatigued
- Corneal: presence of reflex is NO indicator of anesthetic depth and may still be present for short time after cardiac arrest
- Muscular (jaw) tone
7
Q
Describe the Guedel’s classification scheme for CNS monitoring
A
- Stage I: Awake
- Stage II: loss of consciousness, Involuntary movements (central normal pupil, irregular breath-holding, present palpebral, lacrimation, and response to surgical stim)
- Stage III:
- LIGHT plane (regular breathing, ventral miotic pupil, present palpebral, lacrimation, response to Surg stim)
- MEDIUM plane (regular, shallow breathing, ventral miotic pupil, absent palpebral)
- DEEP plane (jerky breathing, dilated central pupil, present corneal)
- Stage IV: extreme CNS depression, cardiac arrest
8
Q
What is the bispectral index (BIS)?
A
- Combo of several electrical signals from the brain
- Dimensionless number: indicates patient’s level of consciousness
- ranges from 100 (awake) to 0 (isoelectric EEG)
- 55 in humans = adequate depth for surgical anesthesia
9
Q
What is MAP made up of?
A
Stroke volume and SVR
10
Q
What is cardiac output made up of?
A
HR and SV (preload, afterload [SVR] and contractility)
11
Q
How is the CV system monitored for anesthesia?
A
Clinically
- Auscultation
- Pulse rate/quality
- CRT
Instrumentally
- ECG
- BP
- Pulse pressure variation
- Lactate
12
Q
What is the normal blood pressure in awake animals?
A
- Systolic: 140-160 mmHg
- MAP: 95-110 mmHg
- Diastolic: 80-95 mmgHg
13
Q
What is the definition of hypotension?
A
- MAP <65 mmHg
- Untreated severe/prolonged hypotension => cardiac arrest or blindness or renal failure after recovery
14
Q
What is the definition of hypertension?
A
- MAP >140 mmHg or SAP >180 mmHg
- Increases cardiac after load
- Can lead to retinopathy, renal DZ, encephalopathy
15
Q
What does pulse palpation tell you?
A
it’s a subjective estimation of pulse pressure (SAP-DAP); can be high with low pressure associated with vasodilation —> NOT ACCURATE
16
Q
What are the various methods of measuring BP?
A
- Non Invasive: Oscillometric, Doppler
- Invasive (direct): arterial catheter
17
Q
What value is the most accurate for oscillometric readings?
A
the MAP; SAP and DAP are calculated values
18
Q
How does the placement and size of the cuff used change the accuracy of the oscillometric BP readings?
A
- Larger cuff (too loose) = false low pressure
-
Smaller cuff (too tight) = false high pressure
- cuff should be 40-60% circumference of extremity
- placed above/below heart level = wrong readings
- arrhythmias might affect readings
19
Q
What is HDO?
A
- High definition oscillometric device
- recognizes artifacts, ultra precise, high sensitive at low amplitudes
- good for MAP and DAP
20
Q
Describe how Dopplers work
A
- Application of piezoelectric ultrasound crystals over artery distal to cuff
- cuff pressure at which the first audible flow sound is heard approximates SAP
21
Q
T or F: there is good correlation between the MAP and SAP values calculated by Dopplers and indirect/direct BP methods
A
False; there is poor agreement between the two methods (particularly in small animals)
22
Q
Describe direct blood pressure monitoring
A
- Gold standard
- beat to beat measurement (useful when giving vasoactive drugs)
- Waveform and pulse contour analysis
- should be positioned at level of R atrium
- allows for frequent blood sampling
- measures SAP and DAP and calculated MAP
23
Q
What are the best arteries to use for direct BP monitoring in small animals?
A
- Dorsal metatarsal (dorsopedal)
- lingual
- radial/carpal
- coccygeal
- femoral
- auricular (dogs with large ears)
24
Q
What does damping do to direct BP monitoring?
A
- It reduces accuracy
-
Overdamping
- results in lower SAP and higher DAP
- MAP not affected
- due to long tubes, air bubbles, clots
-
Underdamping
- results in higher SAP and lower DAP
- MAP not affected
25
How does direct BP monitoring relate to fluid responsiveness?
* It monitors the ability of the CV system to increase CO when a fluid volume is administered
* **Should have incr in CO in response to bolus of fluids**
26
What is an alternative method of direct BP monitoring?
* Improvised method using an aneroid manometer
27
What are the principles of monitoring using capnography?
* Used to assess _adequacy of ventilation_
* **Estimates PaCO2** by measuring concentration of expired CO2 (ETCO2)
* **Differences b/t PaCO2 and ETCO2** can be d/t dead space (**2-5 mmHg**)
* also useful for diagnosis of mechnical problems, airway obstruction, and cardiogenic shock
28
What are the advantages and disadvantages of using side stream capnography?
**Gas sampled from Y piece**
Adv:
* can sample other gases (anesthetic agents)
* away from patient
* inexpensive
Disadv:
* delayed response
* eccessive sampling in patients w/ small TV (underestimates ETCO2)
* need for scavenger
29
What are the advantages and disadvantages of using main stream capnography?
**Sensor located between ET tube and breathing circuit**
Adv:
* real time measurements, no delay
* less disposable parts
* no need for scavenger
Disadv:
* sensor is heavy and can kink small tubes
* fragile
* adds dead space
* only measures CO2 and O2
30
What does each phase of the capnograph mean?
* Phase I: inspiration
* Phase II: expiratory upstroke (transition from dead space gas to alveolar gas)
* Phase III: expiratory plateau (gas coming from alveoli)
* **D point represents ETCO2**
* If there is no plateau —\> might not be actual ETCO2
* Phase IV: inspiratory downstroke
31
What does this capnograph suggest?
**Low ETCO2**
hyperventilation
32
What does this capnograph suggest?
**High ETCO2**
Hypoventilation
33
What does this capnograph suggest?
Spontaneous breathing during IPPV
34
What does this capnograph suggest?
Cardiac oscillations
35
What does this capnograph suggest?
**Airway obstruction**
progressive increase in alfa angle
36
What does this capnograph suggest?
**Large leak from the ET tube**
Decrease in plateau due to room air contamination
37
What does this capnograph suggest?
**Rebreathing CO2**
exhausted CO2 absorbent
incompetent **expiratory** valve
38
What does this capnograph suggest?
**Rebreathing CO2**
incompetent **inspiratory** valve
39
What does this capnograph suggest?
**Abrupt loss ETCO2**
Disconnection
Apnea
40
What does this capnograph suggest?
**Gradual and significant decrease in ETCO2**
Sudden blood pressure drop
Sudden CO drop
Cardiac arrest
PTE
41
What does pulse oximetry tell you?
* **Hemoglobin saturation with oxygen**
* normal range =98-99%
* hypoxemia = \<95%
* severe hypoxemia = \<90%
42
What are the downsides of pulse oximetry?
* Cannot measure carboxyhemoglobin
* Several sources of interference:
* vasoconstriction, ambient light, electrocautery
43
Pulse ox’s can be placed where?
* Tongue
* lips
* vulva
* prepuce
* base of tail
* rectum
44
Describe PaO2
* _Measure of the ability of the lungs to move oxygen from the atmosphere to the blood_
* Measured using a **blood gas analyzer (requires arterial sample)**
* normal PaO2 at sea level (breathing 21% oxygen) ranges between 80-110 mmHg
**Hypoxemia = PaO2 \<80 mmHg**
**Severe hypoxemia = PaO2 \<60 mmHg**
45
What are the 5 causes of hypoxemia?
1. Low FiO2
2. Hypoventilation
3. Ventilation-perfusion mismatch
4. Diffusion impairment
5. Shunt
46
What are some important principles in monitoring body temp during anesthesia?
* Body heat is unevenly distributed: **core temp is 2-4\*C higher than the peripheral**
* General **anesthesia inhibits vasoconstriction**, allows redistribution of body heat and **affects thermoregulatory mechanisms**
47
When is the max period of body temperature loss under anesthesia?
within the first hour
48
What are the consequences of hypothermia?
**90-94F**
* **Marked CNS depression**
* **Little** or no **anesthetic requirement**
* Atrial arrhythmias
* **50% reduction on O2 consumption**
* **HR and CO reduced by 40%**
* BP reduced by 60%
49
Describe hyperthermia during anesthesia
* Rare during anesthesia
* **Most commonly iatrogenic**
* often large **heavy coated animals**
* **Opioid associated** hyperthermia - **most common in cats and ferrets**
50
What should you suspect (and aggressively treat) in a patient that is hyperthermic and demonstrates other **signs of hypermetabolism** (increased ETCO2, metabolic acidosis, hypoxia)?
malignant hyperthermia or thyrotoxicosis
