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Intro to Anesthesiology > Monitoring the Anesthetized Patient > Flashcards

Monitoring the Anesthetized Patient Flashcards

1
Q

T/F: heart rate speeds up when animals are light and decreases as animals get deeper

A

False

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2
Q

Monitoring

A

Is an imprecise art

  • combo of subjective and objective signs
  • balancing act between too much and too little
  • low therapeutic index for most anesthetics
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3
Q

Depth of anesthesia

A

Theoretical construct to conceptualize anesthetic effects on CNS as discrete or continuous phases or states

  • sedation and amnesia that prevents explicit recall (humans)
  • no movement or hemodynamic responses to surgical stimuli
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4
Q

Insufficient unconsciousness

A
  • purposeful, directed movement

- treat with a drug that produces unconsciousness (any GABA agonist)

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5
Q

Insufficient antinociception

A
  • nonpurposeful movement associated with surgery

- treat with a drug that provides antinociception (opioids)

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6
Q

Components of anesthesia

A
  • amnesia
  • unconsciousness
  • immobility
  • analgesia
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7
Q

Analgesia is the absence of _____

A

Pain

  • unconscious patients can not experience pain, so analgesia is unnecessary
  • anesthetized patients can and do respond physiologically and autonomically to noxious stimuli
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8
Q

Inhalants

A

Minimum alveolar concentration

  • medial ED50 response to supramaximal stimulation
  • permits comparisons between agetns at equipotent levels
  • MAC used to define endpoints
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9
Q

Consciousness is usually lost at _____

A

0.25-0.4 MAC

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10
Q

_____ is the endpoint often used in animal studies

A

Loss of righting reflex

- transition between Guedel stage 1 and 2

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11
Q

Unconsciousness occurs at anesthetic concentrations _____ those preventing movement

A

Below

- noxious stimulation can cause movement in unconscious animals

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12
Q

Movement does not equal _____

A

Consciousness

  • anesthetized animals may move in response to noxious stimuli
  • unconscious animals can produce complex movements at the level of the brainstem or spinal cord
  • -> connection to cerebral cortex not required, movement during light anesthesia is generated in spinal cord rather than brain
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13
Q

Anesthetic-induced amnesia

A

Memory formation in humans blocked at MAC awake

  • 0.25-0.4 MAC
  • new memory formation in animals blocked at similar levels
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14
Q

Anesthetic-induced analgesia

A

Pain assessment can only occur at concentrations below MAC awake

  • reflex responses to noxious stimuli reduced or lost at 1 MAC
  • hyperalgesia occurs with some anesthetics at low levels (0.1-0.2 MAC, 0.1 - 0.3 ED50 for injectables)
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15
Q

Anesthetics cause ______

A

Dose-dependent cardiorespiratory depression

  • reduce CO and bp
  • reduce respiratory rate and volume
  • reduce delivery of O2 to tissues
  • anesthetic effects may exaggerate concurrent dz
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16
Q

What is required to monitor anesthetized patients?

A
  • pre-existing and current physiologic status
  • subjective and objective methods
  • ability to assess multiple parameters and integrate them into a general assessment of patient’s current status
  • means to document and track changes in real time
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17
Q

ACVAA monitoring recommendations

A
  • assessment of circulation
  • assessment of ventilation
  • maintenance of an anesthetic record of events
  • assignment of a responsible person to be aware of the patient’s status and prepared to intervene
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18
Q

Subjective

A

Open to individual interpretation

  • simple, no special equipment
  • educated guesses
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19
Q

Objective

A

Quantifiable

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20
Q

Subjective assessments

A
  • reflex activity
  • eye position
  • muscle relaxation
  • heart rate, pulse quality and strength
  • respiratory rate, volume, character
  • mucous membrane color and refill time
  • response to noxious stimuli
21
Q

Guedel’s stages of anesthesia

A
  • 1: voluntary movement (awake or asleep, can be aroused)
  • 2: involuntary excitement (loss of consciousness to onset of regular breathing)
  • 3: surgical anesthesia (light, medium, deep)
  • 4: medullary depression (extreme CNS/CV depression, death)
22
Q

What is a major problem with subjective parameters?

A

Non-specific!

23
Q

Differentials for tachycardia

A
  • sympathetic stimulation or pain
  • hypotension
  • hypovolemia
  • hypoxemia or anemia
  • hypercarbia
  • hyperthermia
  • acute anaphylactoid response
  • drugs (ketamine, thiobarbiturates, antimuscarinics)
  • electrolyte disturbances
24
Q

Differentials for bradycardia

A
  • excessive sympathetic depression
  • increased vagal tone
  • hypothermia
  • hyperkalemia
  • elevated intracranial pressure
  • hypoxemia
  • drugs (opioids, alpha2 agonists)
25
Q

Differentials for tachypnea

A
  • sympathetic stimulation
  • hypoxemia
  • hypercarbia
  • hyperthermia
  • CSF acidosis
  • drug effects (doxapram)
26
Q

Differentials for bradypnea or apnea

A
  • excessive respiratory depression
  • recent hyperventilation
  • hypothermia
  • musculoskeletal weakness or paralysis
27
Q

Lacrimation, pupil size, eye position

A

Unreliable

  • varies with anesthetic type
  • influenced by concurrently administered drugs
28
Q

Common objective monitoring methods

A
  • ECG
  • bp
  • hemoglobin saturation
  • CO production/elimination
29
Q

Less common objective monitoring methods

A
  • inhaled anesthetic concentration
  • neuromuscular responses
  • EEG
  • temporally processed data
  • pleth volume index
30
Q

ECG

A

Monitoring device that produces a continuous waveform representing the summation of electrical activity of the heart for a given axis or plane

31
Q

All diagnostic ECGs in dogs are done in ______

A

Right lateral recumbency

32
Q

ECG pros

A

Non-invasive

  • provides HR and cardiac electrical rhythm in real time
  • used to diagnose chamber enlargement and defects in cardiac impulse origin and conduction
33
Q

ECG cons

A
  • limited to assessment of changes in the x-axis
  • does not provide info on cardiac pumping activity
  • useful when combined with other methods that assess perfusion
34
Q

Blood pressure

A

Q x R

  • systolic: 100-160 mmHg
  • diastolic: 60-90 mmHg
  • mean arterial pressure: 60-80 mmHg
35
Q

Direct blood pressure

A

Catheter inserted into an artery and connected to a pressure transducer
- changes in pressure converted to proportional changes in voltage and displayed on monitor

36
Q

Direct arterial pressure pros

A

Provides systolic, diastolic, and mean arterial bp and hr

  • gold standard of arterial pressure monitoring
  • reliable under wide range of perfusion pressures
37
Q

Direct arterial pressure cons

A
  • invasive
  • specialized equipment
  • accuracy depends on calibration and selected artery
  • does NOT measure flow or perfusion
  • requires skill for placement
  • potential for hematoma formation, air embolism, exsanguination, sepsis
38
Q

Indirect blood pressure

A

Occlusive cuff is placed over accessible artery and inflated until artery is occluded
- pressure slowly released while noting the reappearance of perfusion in the artery

39
Q

Indirect arterial pressure pro

A
  • non-invasive
  • doppler gives systolic bp and hr
  • oscillometric provides systolic, diastolic, mean arterial pressures, hr
  • easy
  • assess trends
40
Q

Indirect arterial pressure cons

A
  • specialized equipment
  • accuracy directly related to cuff fit
  • doppler only gives systolic value (15-25 mmHg low in cats and small dogs)
  • not reliable in presence of reduced peripheral perfusion, or patient movement
  • does not quanify flow or perfusion
  • not accurate or repeatable
41
Q

Blood pressure

A

Useful for indirect assessment of adequacy of organ perfusion

  • arterial bp = hr x sv x svr (**3 independent variables affecting bp!!)
  • useful in monitoring anesthetic depth, assess IV fluid loading, inotrope efficacy
42
Q

Pulse oximeter

A

Dual wavelength spectrophotometer
- arterial Hbg saturation by determining the difference in light absorption between oxyhemoglobin and total hemoglobin during pulsatile flow

43
Q

Pulse oximeter pros

A
  • non invasive
  • simple to operate
  • indicates presence of pulsatile flow and hemoglobin saturation
  • normal SpO2 breathing air (21% O2) 92-95%
  • increases to 98-100% when breathing 100% oxygen
44
Q

Pulse oximeter cons

A

Slope of Hgb dissociation curve when SpO2 <90% makes pulse ox a brink of disaster monitor due to rapid fall in PaO2

  • adversely affected by vasoconstriction, probe motion, and hypotension
  • large number of false alarms
  • limited probe placement locations
  • misleading in face of severe anemia
45
Q

Pleth variability index

A

Patient’s position of the Frank-Starling curve

  • during mechanical ventilation, transpulmonary pressure increases during inspiration thus increasing preload on the heart
  • not enough fluid positions your patient on the steep end of curve, making them more susceptible preload induced by the vent
  • observed on pulse ox
46
Q

PVI calculation

A

Automated measurement

  • changes in plethysmographic waveform amplitude over the respiratory cycle
  • percentage from 1 to 100% –> 1 = no pleth variablity, 100 = max pleth variability
47
Q

Capnograph

A

Infrared spectrophotometer that determines CO2 levels in the last gas exiting the lungs during normal tidal expiration, where ETCO2 < PACO2 < PaCO2

48
Q

Capnograph pros

A
  • non invasive
  • verifies ET placement
  • provides rr
  • verifies normal function of anesthetic circuit with lack of rebreathing
  • verifies presence of circulation thru CO2 delivery to lungs
  • accurate predictor of arterial PCO2 in ventilated patients
49
Q

Capnograph cons

A
  • expensive
  • reduced accuracy in spontaneously breathing patients due to dead space ventilation (large difference between ETCO2 and PaCO2)
  • false low readings with non-rebreathing circuits and high fresh gas flows due to sample dilution

Intro to Anesthesiology (10 decks)

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