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Principles I > Basic Intraoperative Monitoring > Flashcards

Basic Intraoperative Monitoring Flashcards

1
Q

Which standard states that the CRNA must monitor the patient’s physiologic condition as appropriate for the type of anesthesia and specific patient needs?

A

Standard V

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2
Q

What are the 5 components of monitoring stated in Standard V?

A

Monitor ventilation continuously
Monitor cardiovascular status continuously
Monitor body temperature continuously
Monitor neuromuscular function continuously
Monitor and assess patient positioning

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3
Q

When did the AANA create standards of monitoring for the CRNA?

A

1974

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4
Q

What does vigilance mean in anesthesia?

A

a state of clinical awareness whereby dangerous conditions are anticipated or recognized and promptly corrected

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5
Q

What is the most important monitor in anesthesia?

A

the vigilant anesthetist

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6
Q

What is the fundamental goal of ventilation and oxygenation?

A

avoidance of hypoxia

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7
Q

How can we determine if the patient has optimal oxygenation?

A 
Oxygen analyzer
Pulse oximetry
Skin color
Color of blood
ABG (when indicated)
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8
Q

Where does the oxygen analyzer work?

A

Measures inspired gas on the inspiratory limb of the circuit, determines if pipeline is truly O2

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9
Q

When does the oxygen analyzer alarm?

A

Should alarm of concentration <30%

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10
Q

At what oxygen percentages do you calibrate the oxygen analyzer?

A

21% and 100%

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11
Q

Is the oxygen analyzer required for any general anesthetic?

A

Yes

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12
Q

What is the O2 percentage on the O2 analyzer useful for calculating?

A

PaO2

Alveolar gas equation: PAO2 = FiO2 x (BP - 47) - PaO2

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13
Q

What type of sensor is the oxygen analyzer and how does it work?

A
  • electrochemical
  • has cathode and anode embedded in electrolyte gel separated from gas by O2-permeable membrane
  • O2 reacts with electrodes and generates electrical signal proportional to O2 pressure (mmHg) in sample gas
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14
Q

Which component of oxygenation monitoring provides early warning of hypoxia?

A

pulse oximetry

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15
Q

How does the pulse oximeter work?

A
  • measures arterial oxygen saturation combining principles of oximetry and plethysmography (pulsatile measurement)
  • requires pulsatile arterial bed
  • continuous measurement of pulse rate and oxygen saturation of peripheral hemoglobin (SpO2)
  • produces SpO2 measurement by changes in light absorption during arterial pulsations
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16
Q

Which law applies to pulse oximetry?

A

Beer-Lambert Law of spectrophotometry, oxygenated and reduced Hgb differ in their absorption of red and infrared light; comparison of absorbances of these wavelengths enables oximeter to calculate O2 saturation (ratio of infrared and red transmitted to a photodetector)

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17
Q

At what wavelength does HgbO2 (saturated Hgb) absorb infrared light?

A

960 nm

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18
Q

At what wavelength does Hgb (unsaturated) absorb red light?

A

660 nm

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19
Q

What are factors that can affect the accuracy of the pulse oximeter?

A
  • high intensity light
  • patient movement
  • electrocautery
  • peripheral vasoconstriction
  • hypothermia
  • cardiopulmonary bypass (no pulsatile bed)
  • presence of other Hgbs (COHgb or MetHgb)
  • IV injected dyes (dec. with methylene blue)
  • Hgb < 5 (will not register)
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20
Q

What is the rule of thumb for estimating PaO2 from pulse oximeter percentages?

A

PaO2 30 = SaO2 60
PaO2 60 = SaO2 90
PaO2 40 = SaO2 75

(30 is 60…60 is 90…45 is 75)

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21
Q

What are different ways to monitor ventilation?

A
  • Continuous auscultation
  • Observation of chest excursion
  • End-tidal capnography
  • Spirometry
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22
Q

What is the purpose of the precordial stethoscope?

A

Easily detect changes in breath sounds or heart sounds; ability to quickly detect airway/circuit disconnect, endobronchial intubation, and anesthetic depth (increased heart rate or contractility means decreased anesthetic depth)

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23
Q

Where do you listen with the precordial stethoscope?

A

suprasternal notch or apex of left lung

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24
Q

What is the purpose of the esophageal stethoscope?

A

Allows better quality heart and breath sounds with incorporated temperature probe

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25
Q

What must a patient have in order to use an esophageal stethoscope?

A

ETT

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26
Q

Where is correct placement of the esophageal stethoscope?

A

distal 1/3 of esophagus

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27
Q

What are some of the primary principles of capnography?

A
  • confirms ETT placement
  • Confirms adequate ventilation
  • average adult produces 250 mL CO2/min that changes with patient’s condition, anesthetic depth, and temperature
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28
Q

How does capnography work?

A

Uses sidestream sampling (most common) and aspirates airway gas and pumps it through measuring device

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29
Q

What are the sampling flow rates of capnography?

A

50-250 mL/min

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30
Q

What are some limitations of capnography?

A
  • H2O condensation can contaminate the system and falsely increase readings
  • lag time between sample aspiration and reading
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31
Q

What is the normal PACO2 - PaCO2 gradient?

A

2-10 mmHg

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32
Q

What are some causes for an abnormal PACO2 - PaCO2 gradient?

A
  • gas sampling errors
  • prolonged expiratory phase
  • VQ mismatch
  • airway obstruction
  • embolic states
  • COPD
  • hypoperfusion
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33
Q

What does phase 1 of the capnograph correspond to?

A
  • inspiration

- at baseline (should be 0 unless rebreathing) and indicates anatomic/apparatus dead space devoid of CO2

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34
Q

When would the baseline be elevated on capnography?

A
  • CO2 absorbent exhausted
  • Expiratory valve incompetent/missing
  • Bain circuit
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35
Q

What does phase 2 of the capnograph correspond to?

A
  • early exhalation, steep upstroke

- mixing of dead-space with alveolar gas

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36
Q

What does a prolonged upstroke of phase 2 indicate on a capnograph?

A
  • mechanical obstruction, kinked ETT

- slow emptying of lungs due to COPD or bronchospasm

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37
Q

What does phase 3 of the capnograph correspond to?

A
  • horizontal plateau with mild upslope
  • CO2 rich alveolar air
  • steepness is function of expiratory resistance (COPD or bronchospasm)
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38
Q

What does phase 4 of the capnograph correspond to?

A

Steep decline, inspiration of fresh gas, return to baseline

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39
Q

What is the purpose of the anesthetic gas analysis?

A

Measures volatile agents

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40
Q

How does the anesthetic gas analysis work?

A

Obtains sample with sidestream sampling, uses mass spectrometry to ionize gas sample by electron beam and pass it through magnetic field; ions are then identified by own unique trajectory across magnetic field

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41
Q

What are different alarms on the ventilator that alert you to inadequate ventilation?

A
  • tidal volume (integrated spirometry)
  • airway pressure (in-circuit pressure gauge, peak inspiratory pressure, sustained elevated pressure)
  • disconnect alarm (low airway pressure)
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42
Q

How can you monitor adequate circulation/cardiovascular status?

A
  • BP
  • HR
  • EKG
  • heart sounds
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43
Q

What abnormalities can an EKG detect?

A
  • cardiac dysrhythmias
  • conduction abnormalities
  • MI / ST depression
  • electrolyte changes
  • pacemaker function/malfunction
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44
Q

What lead do we typically monitor in a three lead EKG?

A

Lead II

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45
Q

What is a disadvantage of monitoring a three-electrode EKG?

A

limited in detection of MI

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46
Q

What leads does a five electrode EKG monitor?

A

Six standard limb leads (I, II, III, aVR, aVL, aVF) and one precordial lead (usually V5)

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47
Q

What are some advantages of using a five electrode EKG monitor?

A
  • Better in detecting myocardial ischemia

- Allows better differential diagnosis of atrial and ventricular dysrhythmias

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48
Q

What are the 2 most commonly used EKG leads?

A

Lead II and V5

49
Q

Why is lead II a commonly monitored lead?

A
  • Yields max P wave voltages
  • Superior detection of atrial dysrhythmias
  • Detects inferior wall ischemia/ST depression
50
Q

Why is lead V5 a commonly monitored lead?

A
  • 5th ICS/anterior axillary line

- Allows detection of anterior and lateral wall ischemia

51
Q

What are some advantages of automated indirect blood pressure monitoring (NIBPM)?

A
  • easy and accurate
  • versatile in children and obese
  • may be used on calf or thigh
52
Q

How does noninvasive arterial blood pressure monitoring work?

A

Is oscillometric device that uses air pump (microprocessor) to inflate cuff and then deflation valve opens to sample oscillations

53
Q

What can cause errors in oscillometric blood pressure monitoring?

A
  • surgeon leaning on cuff
  • inappropriate cuff size (small cuff –> high reading; large cuff –> low reading)
  • shivering/excessive motion
  • atherosclerosis and HTN (systolic low; diastolic high compared with invasive arterial pressure)
54
Q

What are some indications for invasive arterial BP monitoring?

A
  • any patient requiring BP measurement more frequently than minute to minute
  • critically ill
  • anticipated rapid blood loss
  • major procedures (cardiopulmonary bypass, aortic cross-clamping, intracranial surgery, carotid sinus manipulation)
  • frequent ABG sampling
55
Q

Where are possible sites for arterial lines?

A
  • radial artery (most common)
  • ulnar artery (not often used, could compromise circulation in hand, technically more difficult)
  • brachial artery (complications may risk limb, predisposed to kinking/location)
  • femoral artery (prone to pseudoaneurysm and atheroma formation)
  • dorsalis pedis (may have distorted waveform)
  • axillary artery (potential for plexus/nerve damage from hematoma or traumatic cannulation)
56
Q

What are some indications for CVP monitoring?

A
  • fluid management of hypovolemia and shock
  • infusion of caustic drugs
  • aspiration of air emboli
  • insertion of pacing leads
  • TPN
  • venous access in patients with poor peripheral veins
57
Q

Where are possible sites for CVP monitoring?

A
  • internal jugular (right preferred)
  • subclavian
  • external jugular
  • antecubital (requires special kit with long catheter)
58
Q

What are some indications for a PA cath?

A
  • poor LV function (EF < 2L/min)
  • valvular heart disease
  • recent MI
  • ARDS
  • massive trauma
  • major vascular surgery
  • evaluate response to fluid administration, vasopressors, vasodilators, inotropes
59
Q

What are some factors affecting temperature?

A 
Ambient room temperature
Scope and length of surgery
Hypothalamic depression
Intraoperative fluid replacement (not warming fluids)
Vigiliance in maintaining core temp
60
Q

What are the 4 mechanisms of heat loss?

A

Convection, conduction, radiation, evaporation

61
Q

What is radiation heat loss?

A

heat radiated from patient into room

62
Q

What is convection heat loss?

A

Heat loss due to air velocity over patient

63
Q

What is conduction heat loss?

A

Heat lost by contact with OR table

64
Q

What is evaporative heat loss?

A

heat loss due to dry inspired gases

65
Q

What is hypothermia?

A

Environmental heat loss outpaces metabolic heat production

66
Q

Who is at greatest risk for hypothermia?

A

elderly, burn patients, neonates, and patients with spinal cord injuries

67
Q

What are some adverse effects of hypothermia?

A

Delay awakening or cause shivering that increases body’s O2 need by 400%

68
Q

At what temperature would you consider the patient hypothermic?

A

<36 degrees Celsius

69
Q

What is mild hypothermia and what can it cause?

A

Mild: 33-36 degrees celsius (reduced enzyme function and coagulopathy)

70
Q

What is moderate hypothermia and what can it cause?

A

Moderate: </= 32 degrees Celsius (fibrillatory threshold)

71
Q

Is hyperthermia usually seen under anesthesia?

A

No, and it is a late sign of malignant hyperthermia

72
Q

What are some other causes of hyperthermia under anesthesia besides malignant hyperthermia?

A
  • Endogenous pyrogens
  • Thyrotoxicosis or pheochromocytoma (increased metabolic rate)
  • Anticholinergic blockade of sweating
  • Excessive environmental warming
73
Q

Where are some monitoring sites for temperature?

A
  • Esophagus (lower 1/3) accurately reflects body temperature
  • Nasopharynx
  • Rectum
  • Bladder (integrated into Foley)
  • Tympanic membrane (risk of perforation)
  • Blood (PA cath)
  • Skin
74
Q

What are some superficial warming modalities?

A
  • Forced air warmer (Bair hugger; most effective because decreases radiant and convective heat loss; decreases postoperative shivering and PACU stay)
  • Warming blanket (minimally effective; Arctic sun water circulating)
  • Radiant heat unit (no role in OR; no impact on mean body temp)
  • Heated liquids (iv bags or bottles on patient; very dangerous and can cause burns)
75
Q

What are some core warming modalities?

A
  • IV fluid warmers
  • Gastric lavage (warms body core but impractical to perform during surgery)
  • Peritoneal irrigation (encourage use of warm irrigation during intraabdominal procedures)
76
Q

What are some passive warming modalities?

A
  • Increase ambient temperature (has greatest effect on maintaining body heat; if >24 degrees Celsius most adults remain normothermic without requiring other measures)
  • Insulation (extremities and head)
  • Heat and moisture exchanger (“artificial nose”; retains moisture)
  • Coaxial breathing circuit (“King” circuit; warms and humidifies inspiratory gases)
77
Q

What is a peripheral nerve stimulator?

A

monitors status of neuromuscular junction when using NM blocking drugs
delivers electrical stimulation to a peripheral motor nerve mechanically evoking a response
permits titration of drug to optimal effect
quantifies recovery from NMB

78
Q

What is the onset sequence of a NMB drug?

A 
Eyes
Extremities
Chest
Abdominal muscles
Diaphragm
79
Q

Where are the monitoring sites for a PNS?

A

Ulnar nerve
Facial nerve
Posterior tibial nerve
Peroneal nerve

80
Q

What muscle does the ulnar nerve innervate?

A

Adductor pollis

81
Q

Where are electrodes placed to innervate ulnar nerve?

A

placed at wrist or elbow with the negative (depolarizing) mode placed distally

82
Q

If monitoring ulnar nerve, what is it not an accurate reflection of?

A

degree of diaphragm or airway muscles (muscles are less sensitive to NMB)
could have adductor pollis paralysis but still have coughing, breathing, and vocal cord movement

83
Q

Where does the facial nerve lie?

A

Within the parotid gland, if doing excision of that gland should not use NMB

84
Q

Where do you place the electrodes to monitor the facial nerve?

A

infront of tragus of ear and below; avoid direct muscle stimulation

85
Q

What is the facial nerve a better indicator of?

A

NM blockade of diaphragm and airway; better to use facial nerve for induction

86
Q

What muscle does the facial nerve innervate?

A

orbicularis oculi

87
Q

Where do you place the electrodes to monitor the posterior tibial nerve and what do you see when nerve is innervated?

A

behind medial malleolus of tibia; plantar flexion

88
Q

Where do you place the electrodes to monitor the peroneal nerve?

A

lateral aspect of knee with response of dorsiflexion of the foot

89
Q

What are the patterns of stimulation for a PNS?

A 
Single 0.5-1 second twitch (0.5-1 Hz)
TOF ratio
Tetanic stimulation
Post-tetanic stimulation
Double-burst stimulation
90
Q

What is single twitch stimulation?

A

Single pulse delivered every 10 secs; increasing block results in diminished response

91
Q

What is TOF stimulation?

A

most common
4 repetitive stimuli
ratio of responses to 1st and 4th twitches are sensitive indicator of ND relaxation

92
Q

What are the T4:T1 ratios and what do they mean?

A

Loss of 4th twitch = 75% of receptors blocked
Loss of 3rd twitch = 80% of receptors blocked
Loss of 2nd twitch = 90% of receptors blocked

93
Q

How many receptors need to be blocked for clinical relaxation?

A

75-95% blocked

94
Q

What type of NMBD would you see fade on a TOF?

A

non-depolarizers

95
Q

What is tetanic stimulation?

A

Tetany at 50-100 Hz
5 seconds at 50 Hz evoked tension approximates tension developed during maximal voluntary effort
Sustained response occurs when TOF >70%

96
Q

When is post-tetanic count used?

A

when all twitches are suppressed

97
Q

What is post-tetanic count?

A

applies tetanus at 50 Hz for 5 seconds, waits 3 seconds then applies single twitches every second up to 20

98
Q

What is the relation between number of twitches and depth of block with post-tetanic count?

A

inversely related, less anesthetic means more twitches present

99
Q

What is double burst stimulation?

A

less painful than tetany

3 short 50 Hz impulses followed by 750 msec then another 3 bursts

100
Q

When is double burst stimulation more helpful than TOF?

A

more sensitive for visual evaluation of fade

101
Q

What modes on the PNS are used during induction?

A

single twitch

TOF

102
Q

What modes on the PNS are used during maintenance?

A

TOF

post-tetanic count

103
Q

What modes on the PNS are used during emergence?

A

TOF

double-burst stimulation

104
Q

Which nerves do you monitor for onset and recovery of NM monitoring?

A

onset - facial

recovery - ulnar

105
Q

How long will reversal take with 1 out of 4 twitches?

A

30 minutes

106
Q

How long will reversal take with 2-3 out of 4 twitches?

A

10-12 minutes with long-acting relaxants, 4-5 minutes after intermediate relaxants

107
Q

How long will it take to recover with 4 out of 4 twitches?

A

Within 5 mins of Neostigmine, 2-3 mins of edrophonium

108
Q

What is the bispectral index score (BIS)?

A

used to assess depth of anesthesia

109
Q

Is BIS monitoring required or optional?

A

optional, not currently under standard of care

110
Q

What are some advantages of using BIS monitoring?

A
  • Reduced risk of awareness
  • Better management of responses to surgical stimulation
  • Faster wake up (controversial)
  • More cost effective use of anesthetics
111
Q

What is the BIS range and what does it mean?

A

EEG signal with index ranging from 0-100
0 = isoelectric EEG
100 = awake CNS

112
Q

What does a BIS of 80-100 mean?

A

responds to normal voice

113
Q

What does a BIS of 60-80 mean?

A

Can respond to loud commands or mild shaking

114
Q

What does a BIS of 40-60 mean?

A

*General anesthesia

low probability of explicit recall and unresponsive to verbal stimulus

115
Q

What does a BIS of 20-40 mean?

A

Deep hypnotic state

116
Q

What does a BIS of 0-20 mean?

A

Burst suppression or flat line EEG

117
Q

What affects BIS readings?

A 
electro-cautery
EMG
pacer spikes
EKG signal
patient movement
118
Q

What numbers on EEG monitoring are associated with recall?

A

no absolute or guarantees, but research indicates that levels >70 have increased risk of recall

119
Q

What are routine monitors?

A 
NIBP
stethoscope
EKG
pulse ox
O2 analyzer
EtCO2
Et agent

Principles I (5 decks)

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