Monitoring Flashcards
What does anesthesia produce in a patient?
- CNS depression (hypnosis)
- CV depression (hypotension, +/- bradycardia, arrhythmias)
- Resp depression (hypoventilation, +/ hypercapnia, hypoxemia)
- Impairs thermoregulation (hypothermia, +/- hyperthermia)
What are the Big 5 of anesthetic monitoring?
- ECG
- Blood pressure
- Pulseoximetry
- Capnography
- Temperature
What are the most common causes of perioperative death in small animals?
CV or respiratory causes
What should you be monitoring for during each step of the anesthesic process?
- 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
What are some general considerations to have during the post-operative period?
- 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!!
How do you monitor the CNS in your anesthetic patient?
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
Describe the Guedel’s classification scheme for CNS monitoring
- 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
What is the bispectral index (BIS)?
- 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
What is MAP made up of?
Stroke volume and SVR
What is cardiac output made up of?
HR and SV (preload, afterload [SVR] and contractility)
How is the CV system monitored for anesthesia?
Clinically
- Auscultation
- Pulse rate/quality
- CRT
Instrumentally
- ECG
- BP
- Pulse pressure variation
- Lactate
What is the normal blood pressure in awake animals?
- Systolic: 140-160 mmHg
- MAP: 95-110 mmHg
- Diastolic: 80-95 mmgHg
What is the definition of hypotension?
- MAP <65 mmHg
- Untreated severe/prolonged hypotension => cardiac arrest or blindness or renal failure after recovery
What is the definition of hypertension?
- MAP >140 mmHg or SAP >180 mmHg
- Increases cardiac after load
- Can lead to retinopathy, renal DZ, encephalopathy
What does pulse palpation tell you?
it’s a subjective estimation of pulse pressure (SAP-DAP); can be high with low pressure associated with vasodilation —> NOT ACCURATE
What are the various methods of measuring BP?
- Non Invasive: Oscillometric, Doppler
- Invasive (direct): arterial catheter
What value is the most accurate for oscillometric readings?
the MAP; SAP and DAP are calculated values
How does the placement and size of the cuff used change the accuracy of the oscillometric BP readings?
- 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
What is HDO?
- High definition oscillometric device
- recognizes artifacts, ultra precise, high sensitive at low amplitudes
- good for MAP and DAP
Describe how Dopplers work
- Application of piezoelectric ultrasound crystals over artery distal to cuff
- cuff pressure at which the first audible flow sound is heard approximates SAP
T or F: there is good correlation between the MAP and SAP values calculated by Dopplers and indirect/direct BP methods
False; there is poor agreement between the two methods (particularly in small animals)
Describe direct blood pressure monitoring
- 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
What are the best arteries to use for direct BP monitoring in small animals?
- Dorsal metatarsal (dorsopedal)
- lingual
- radial/carpal
- coccygeal
- femoral
- auricular (dogs with large ears)
What does damping do to direct BP monitoring?
- 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
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
What is an alternative method of direct BP monitoring?
- Improvised method using an aneroid manometer
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
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
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
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
What does this capnograph suggest?
Low ETCO2
hyperventilation
What does this capnograph suggest?
High ETCO2
Hypoventilation
What does this capnograph suggest?
Spontaneous breathing during IPPV
What does this capnograph suggest?
Cardiac oscillations
What does this capnograph suggest?
Airway obstruction
progressive increase in alfa angle
What does this capnograph suggest?
Large leak from the ET tube
Decrease in plateau due to room air contamination
What does this capnograph suggest?
Rebreathing CO2
exhausted CO2 absorbent
incompetent expiratory valve
What does this capnograph suggest?
Rebreathing CO2
incompetent inspiratory valve
What does this capnograph suggest?
Abrupt loss ETCO2
Disconnection
Apnea
What does this capnograph suggest?
Gradual and significant decrease in ETCO2
Sudden blood pressure drop
Sudden CO drop
Cardiac arrest
PTE
What does pulse oximetry tell you?
- Hemoglobin saturation with oxygen
- normal range =98-99%
- hypoxemia = <95%
- severe hypoxemia = <90%
What are the downsides of pulse oximetry?
- Cannot measure carboxyhemoglobin
- Several sources of interference:
- vasoconstriction, ambient light, electrocautery
Pulse ox’s can be placed where?
- Tongue
- lips
- vulva
- prepuce
- base of tail
- rectum
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
What are the 5 causes of hypoxemia?
- Low FiO2
- Hypoventilation
- Ventilation-perfusion mismatch
- Diffusion impairment
- Shunt
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
When is the max period of body temperature loss under anesthesia?
within the first hour
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%
Describe hyperthermia during anesthesia
- Rare during anesthesia
- Most commonly iatrogenic
- often large heavy coated animals
- Opioid associated hyperthermia - most common in cats and ferrets
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
