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Basic Principles of Anesthesia > Monitoring > Flashcards

Monitoring Flashcards

1
Q

What is the goal of the ASA standards for monitoring?

A

To reduce patient morbidity and mortality. Not following them may lead to patient injury and provider liability.

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2
Q

We are required to monitor oxygenation in what two ways during every surgery or procedure?

A

Oxygen Analyzer and Pulse Oximeter

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3
Q

How is ventilation monitored?

A

End-tidal CO2, chest rise, condensation in airway device, auscultate breath sounds, touch, smell, listening, monitor reservoir bag, and pulse ox. Ventilator must be able to detect disconnection in the circuit.

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4
Q

How often is the BP checked?

A

At least every 5 minutes but is usually done every 3-5 minutes

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5
Q

Of all the standards, which is the only one that is not required to be present, unless when applicable?

A

Temperature! Temp should always be used during active warming or cooling or with long or GA cases.

Temp not necessary for a short MAC case (like a colonoscopy)

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6
Q

Continuous monitoring of CV status is a requirement for any patient receiving an anesthetic; this includes what 4 things?

A

HR
Rhythm
ST segment changes
T waves

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7
Q

What is the most common required diagnostic tool in the OR?

A

ECG monitoring

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8
Q

1/3 patients scheduled for non-cardiac surgery have risk factors for what?

A

CAD and postoperative MI

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9
Q

When is postop MI 3x as frequent?

A

Pt’s with hx of ischemia

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10
Q

What is a major cause for cardiac morbidity?

A

Prolonged ischemia (ST depression)

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11
Q

ST segment monitors:

A

Sensitivity and specificity nearing 75% in detecting ischemia

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12
Q

ST segment identification: the degree of elevation or depression is relative to what?

A

The isoelectric line (PR segment)

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13
Q

Where is the PR segment?

A

Extends from the end of the P wave to the start of the ventricular depolarization

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14
Q

Where is the ST junction (J point)?

A

Where the QRS ends and the ST segment begins

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15
Q

ST segment deviation thresholds account for what factors?

A

Influence of gender, ECG lead, age, race & position of the ST segment

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16
Q

What leads are typically the outliers for ST segmentation deviation?

A

V2 and V3

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17
Q

Threshold values for ST-segment elevation are 1mm for men or >1 mm for females. What would V2 and V3 have to be in order to count as elevation?

A

Male - 2mm
Female - 1.5mm

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18
Q

ST depression thresholds are -1mm in all leads except for what two leads?

A

Again, V2 and V3! They will be -0.5mm.

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19
Q

When ST segment threshold values are met, what may exist?

A

Injury or ischemia

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20
Q

The AHA, American College of Cardiology Foundation, and the Heart Rhythm Society recommend measuring ST segment changes where?

A

J point!

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21
Q

Why is the mean or the ST point not a good place to measure ST segment changes?

A

They can lead to:
1) false positives (reads as ST elevation in a normal EKG)
2) false negatives (reads as normal in an ST depression)

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22
Q

A falsely elevated ST segment that suggests an MI is a _____ ______

A

False positive

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23
Q

Masking of a significant ST segment depression is a ______ _______

A

False negative

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24
Q

What procedures make it hard to place ECG leads in the proper placement?

A

Burns, ICD, abdominal, cardiac, spine

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25
Q

Where does the white lead go?

A

RA - white, right!

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26
Q

Where does the green lead go?

A

RL - grass under clouds

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27
Q

Where does the black lead go?

A

LA - smoke over fire

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28
Q

Where does the red lead go?

A

LL - fire under the smoke

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29
Q

Where does the brown lead go?

A

The center!

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30
Q

What can result in improper selection of ECG leads?

A

Unrecognized MI, injury or infarction

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31
Q

Is a single ECG lead for ischemic monitoring in patients with CAD acceptable?

A

No! Need multiple leads. Used derived leads if available.

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32
Q

In a patient with a history of stent or MI, where should you monitor their rhythm?

A

In the leads, that will reflect their area of injury! You need to know where their injury occurred.

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33
Q

In patients with no pre-op ECG or unremarkable history, where should you monitor the ST segment?

A

V3
Others listed: V4, V5, III, or aVF

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34
Q

In patients with no pre-op ECG or unremarkable history, where should you assess narrow QRS complex rhythms, particularly if the P wave is significant for diagnostic criteria?
Ex: Afib, Aflutter

A

Lead II

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35
Q

In a 3-electrode ECG system, what 3 leads will you have?

A

RA (white), LA (black), and LL (red)

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36
Q

What are your Lateral leads?

A

I, aVL, V5-V6

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37
Q

The lateral leads show what coronary artery anatomy?

A

LCx or diagonal of LAD

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38
Q

What are your inFerior leads?

A

II, III, aVF

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39
Q

The inferior leads should what coronary artery anatomy?

A

RCA and/or LCx

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40
Q

What are your anterior/ septal leads?

A

V1-V4

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41
Q

The anterior/ septal leads show what anatomy?

A

LAD

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42
Q

Where does the tip of a central line sit?

A

Junction of the Venae Cavae and Right Atrium

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43
Q

Where is the most common site to place a central line?

A

Right IJ

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44
Q

What is the distance from the right IJ to the junction of the venae cavae and right atrium?

A

15 cm

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45
Q

What is the distance from the right IJ to the right atrium?

A

15-25 cm

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46
Q

What is the distance from the right IJ to the right ventricle?

A

25-35 cm

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47
Q

What is the distance from the right IJ to the pulmonary artery?

A

35-45

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48
Q

What is the distance from the right IJ to the pulmonary artery wedge position?

A

40-50

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49
Q

What are the normal pressures for the CVP/ MRAP?

A

Range: 1-10
Absolute Value: 5

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50
Q

What are the normal pressures for the RV?

A

Range: 15-30/0-8
Absolute Value: 25/5

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51
Q

What are the normal pressures for the PA?

A

Range: 15-30/5-15
Absolute Value: 25/10

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52
Q

What is the normal MPAP?

A

Range: 10-20
Absolute Value: 10

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53
Q

What is the normal PAOP/ wedge pressure?

A

Range: 5-15
Absolute Value: 10

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54
Q

What is the normal MLAP?

A

Range: 4-12
Absolute Value: 8

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55
Q

What is the normal LVEDP?

A

Range: 4-12
Absolute Value: 8

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56
Q

What are normal oxygen saturations on the right side of the heart?

A

75%

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57
Q

On a right atrial pressure waveform, what does the a wave indicate?

A

Contraction of the RA

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58
Q

On a right atrial pressure waveform, what does the c wave indicate?

A

Early systole - closure of the tricuspid valve. The valve bulges into the RA during RV contraction.

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59
Q

On a right atrial pressure waveform, what does the x wave indicate?

A

Atrial relaxation

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60
Q

On a right atrial pressure waveform, what does the v wave indicate?

A

Passive filling of the RA, encompassing a portion of RV systole

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61
Q

On a right atrial pressure waveform, what does the y wave indicate?

A

Early diastole - ventricular filling

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62
Q

Why is the a wave larger in the RAP waveform?

A

Because that’s where the catheter tip sits

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63
Q

Why should a PAC with the distal balloon inflated remain in the RV for as little as possible?

A

It can tickle the ventricle and cause ectopy!

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64
Q

The downstroke of the PA catheter waveform in the pulmonary artery contains what identifiable mark?

A

Dicrotic notch - sudden closure of the pulmonic valve leaflets (the beginning of diastole)

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65
Q

The pulmonary artery occlusion pressure (PAOP) waveform is similar to what other waveform?

A

CVP

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66
Q

In a PAOP waveform, the a wave represents what?

A

LA systole

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67
Q

In a PAOP waveform, the c wave represents what?

A

Closure of the mitral valve

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68
Q

In a PAOP waveform, the v wave represents what?

A

Filling of the LA, upward displacement of the MV during LV systole

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69
Q

Why is it less common to detect a c wave on a PAOP tracing?

A

Retrograde transmission of LA pressure attenuated within the pulmonary circulation

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70
Q

When/ where do you measure a wedge pressure?

A

At end-expiration!

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71
Q

What waveforms appear after the beginning of ventricular depolarization (QRS complex)?

A

C and V waves

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72
Q

What factors can cause the loss of a waves or only v waves on a CVP or PAOP?

A

Loss of a P wave - afib, ventricular pacing in the setting of asystole

remember a wave represents atrial contraction

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73
Q

What factors can cause giant a waves or “cannon” a waves on a CVP or PAOP?

A

Junctional rhythms
Complete AV block
PVCs
V pacing (asynchronous)
Tricuspid or mitral stenosis
Diastolic dysfunction
MI
Ventricular hypertrophy

remember a wave represents atrial contraction

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74
Q

What factors can cause large v waves on a CVP or PAOP?

A

Tricuspid or mitral regurgitation
Acute increase in intravascular volume

remember the v wave represents the filling of the atrium

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75
Q

What can a low CVP correlate with?

A

Hypovolemia
CVP serves as an estimate of PV preload

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76
Q

An elevated RVP can correlate with what?

A

PHTN, VSD, pulmonary stenosis, RV failure, constrictive pericarditis, cardiac tamponade
*RVP is assessed INDIRECTLY from the CVP and the PA pressure recordings

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77
Q

What is more concerning - an elevated RV pressure from PHTN or pulmonary stenosis?

A

PHTN! Pulmonary stenosis is a fixed lesion and not as unpredictable as pulmonary hypertension.

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78
Q

How can the LVEDP be measured?

A

Indirect measurement is estimated by measuring the pressure value that exists just prior to the upstroke of the PA waveform. The mitral valve must be open.

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79
Q

What can cause a false high value on the PAP?

A

Catheter whip - exaggerated oscillation of the PA tracing

Occurs with catheter coiling if the tip of the PA catheter is near the pulmonic valve.

It also occurs in pts with dilated pulmonary arteries, PHTN

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80
Q

What are the potential causes of an elevated CVP?

A

RV failure
Tricuspid stenosis or regurgitation
Cardiac tamponade
Constrictive pericarditis
Volume overload
PHTN
LV failure (chronic)

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81
Q

What are the potential causes of an elevated PAP?

A

LV failure
Mitral stenosis or regurgitation
L to R shunt
ASD or VSD
Volume overload
PHTN
Catheter whip

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82
Q

What are the potential causes of an elevated PAOP?

A

LV failure
Mitral stenosis or regurgitation
Cardiac tamponade
Constrictive pericarditis
Volume overload
Ischemia

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83
Q

How do you calculate the pulmonary vascular resistance index (PVRI)?

A

(MPAP - PAOP) / CI x 80 = 45-225

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84
Q

How do you calculate the systemic vascular resistance index (SVRI)?

A

(MAP - RAP) / CI x 80 = 1760-2600

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85
Q

How do you calculate cardiac index (CI)?

A

CO/BSA = 2.8-3.6 L/min m2

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86
Q

Cardiac Output and Thermodilution:
The computer plots a time-temperature curve, with the area under the curve being _________ proportional to the CO

A

Inversely

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87
Q

Cardiac Output and Thermodilution:
If the curve increases, what happens to the CO?

A

It decreases

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88
Q

Cardiac Output and Thermodilution:
If the curve decreases, what happens to the CO?

A

It increases

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89
Q

What variables may cause an overestimated CO using thermodilution?

A

Low injectate volume
Injectate that is too warm
Thrombus on the thermistor of the PAC
Partially wedged PA

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90
Q

What variables may cause an underestimated CO using thermodilution?

A

Excessive injectate volume
Injectate that is too cold

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91
Q

What causes unpredictable values while using thermodilution?

A

R –> L VSD
L –> R VSD
Tricuspid regurgitation

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92
Q

How do you assess preload?

A

Indirectly by CVP

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93
Q

How can you assess fluid responsiveness?

A

Stroke volume variation (SVV) &
Pulse pressure variation (PPV)

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94
Q

What is normal SVV?

A

10-13%

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95
Q

What does an SVV > 13% present?

A

Patients will respond positively to an increase in preload

96
Q

What is a con to noninvasive CCO monitoring?

A

It does not represent real-time data. Depict the average CO from the prior 3 to 6 minutes.

97
Q

SvO2 presents what?

A

Mixed venous & central venous O2

98
Q

SvO2 is a ________ monitor of oxygen delivery

A

Indirect. It is the amount of O2 left after tissue extraction.

99
Q

What is the normal SvO2?

A

60-80%

100
Q

Where do you draw the SvO2 from?

A

The tip of the PA catheter

101
Q

You must assume that a decrease in SvO2 reflects a change in what?

A

Increased O2 delivery or tissue consumption or presumably via a reduction in CO

102
Q

If a venous oxygen saturation is decreased, what two things may be happening?

A

Increased oxygen need/ demand (increased metabolic activity)
OR
Decreased oxygen supply

103
Q

If a venous oxygen saturation is decreased because of an increased in oxygen demand, what factors may be happening?

A
  • Fever
  • Shivering
  • Pain
  • Stress
  • Anxiety
104
Q

If a venous oxygen saturation is decreased because of a decreased oxygen supply, what factors may be happening?

A
  • Decreased cardiac output
  • Hemodilution
  • Hypoxemia
  • Anemia
  • Heart disease
105
Q

If a venous saturation is increased, what two things might be happening?

A

Increased oxygen supply
OR
Decreased oxygen need (decreased metabolic activity)

106
Q

If a venous oxygen saturation is increased because of increased oxygen supply, what factors may be happening?

A
  • High CO
  • Early sepsis
  • Cyanide poisoning
  • AV shunts
107
Q

If a venous oxygen saturation is increased because of a decreased oxygen need, what factors may be happening?

A
  • Analgesia
  • Sedation
  • Mechanical Ventilation
  • Hypothermia
108
Q

BP cuffs should have a bladder dimension of approximately _____ of the circumference of the extremity

A

40%

109
Q

When auscultating a BP, what are the sounds called that are produced by turbulent blood flow within an artery during cuff deflation?

A

Korotkoff

110
Q

What are some risks of a NIBP?

A

Damage to peripheral nerves (ulnar)
Compartment syndrome
Interference w/ delivery of drugs through an IV line –> sedation with propofol!!
Will loose pulse ox pleth during inflation

111
Q

What can happen to a BP if it is taken on the forearm with a patient supine or sitting with the HOB elevated at 45 degrees?

A

It can OVER estimate BP

112
Q

If BP is taken on the forearm of an obese patient, the real BP will be a little lower. Ex: if a diastolic forearm pressure is 80 mmHg, what would the adjusted DBP be?

A

72.4 mmHg

113
Q

If BP is taken in the thigh or calf, what would happen to the SBP?

A

SBP is greater in the thigh or calf compared to the arm

114
Q

If BP is taken in the thigh or calf, what would happen to the DBP and MAP?

A

DBP and MAP are lower in the thigh or calf compared to the arm

115
Q

What is the gold standard for monitoring arterial blood pressure?

A

Arterial line

116
Q

Where is the most common placement of an arterial line?

A

Radial artery
Others include ulnar (common in peds or down syndrome), brachial, axillary, femoral, and dorsalis pedis

117
Q

What are indications for an arterial line?

A
  • potential for acute changes in hemodynamics
  • SSEP monitoring
  • pts with comorbidities may be at substantial risk for a stroke or heart attack during periods of acute stress (laryngoscopy or emergence)
118
Q

Where do you zero the aline transducer?

A

Phlebostatic Axis!
4th intercostal space, mid anterior/ posterior chest wall

119
Q

If the aline transducer is positioned below the heart, how can that affect your results?

A

False increase in BP (overestimates)

120
Q

What does a positive Allen test represent?

A

You can proceed with arterial line placement because there is adequate flow in the opposite artery.

121
Q

What can an underestimated aline, with a dampened waveform represent?

A

Flexed wrist
Low pressure in transducer system (the bag is deflated)
Air bubbles in tubing
Clot in catheter

122
Q

What can a transesophageal echocardiogram (TEE) tell you?

A

Systolic wall motion abnormalities
Vascular aneurysms
EF and ventricular preload
Measurement of blood flow within heart chambers and across valves

123
Q

How does a TEE work?

A

Uses sound waves to define anatomic structures in the body

124
Q

True or false - is it okay to turn off the audible sound on the pulse ox machine?

A

False! Audible warning systems should be used!

125
Q

What is more catastrophic - failure to successfully intubate or failure to recognize misplacement?

A

Failure to recognize misplacement is catastrophic!

126
Q

What is crucial to ensuring the adequacy of minute ventilation, as well as interpreting patient response to pharmacologic agents and surgical stimuli?

A

RR and tidal volume

127
Q

What is the most common means of monitoring carbon dioxide levels in anesthesia?

A

Capnography

128
Q

How does ETCO2 work?

A

Through infrared analysis. Each gas in the mixture absorbs infrared radiation at a different wavelength. Detects its absorbance at specific wavelengths.

129
Q

ETCO2 is about 2 to 5 torr ______ than arterial CO2 in patients who have no cardiac or pulmonary abnormalities

A

LOWER

130
Q

Pathologies that result in an increased dead space (PE) and alterations in hemodynamic stability will __________ the variance seen between ETCO2 and arterial measurements

A

INCREASE!
ETCO2 will be even LOWER than normal

131
Q

What type of ETCO2 is more common - nondiverting or diverting?

A

Diverting - extracts gas from sample tubing attached near the patient end of the circuit and pumps it to the monitor

132
Q

If using a sampling line of a diverting ETCO2 in an awake or sedated, spontaneously breathing patient receiving O2 via a simple mask or NC, what may happen to the ETCO2 results?

A

ETCO2 results will be lowered because of the dilution of room air

133
Q

Where is ETCO2 measured?

A

The end of the third phase or point D
It is measured at the end of the plateau just prior to the beginning of phase four

134
Q

When might ETCO2 be inaccurate?

A

In the presence of significant V/Q mismatching
- increase in dead space causes a low concentration of ETCO2
- small TV, reflecting inadequate alveolar ventilation, may produce ETCO2 recordings that significantly underestimate arterial CO2 levels

135
Q

What might you see on the ETCO2 monitor during esophageal intubation?

A

Initial slight upstroke from excess air blown into the stomach followed by a measurement of 0 and loss of waveform

136
Q

On the ETCO2 monitor, you notice that the waveform fails to return to baseline during phases one and four. What does this indicate?

A

Rebreathing of CO2
This can be the result of inadequate fresh gas flow in the non-rebreathing system OR a depleted/ ineffective CO2 absorber

137
Q

If you are observing rebreathing on the ETCO2 monitor, how might you fix this?

A

Increase flow
Change CO2 absorber

138
Q

What does sloping of the plateau phase on ETCO2 monitoring represent?

A

Progressive prolongation of expiration

139
Q

What may be happening if you observe sloping during ETCO2 monitoring?

A

Obstruction
Chronic obstructive lung disease (COPD)
Kinking of the ETT or circuit tubing

140
Q

How might you fix sloping on ETCO2 monitor?

A

Unkink tubing
Decrease I:E ratio (this increases expiratory time)

141
Q

If you observe regular, saw-tooth waves that equal the HR on the expiratory phase of ETCO2 monitoring, what might this indicate?

A

Cardiac Oscillations - contraction of the heart and great vessels forcing gas in and out of the lungs

142
Q

What population are cardiac oscillations commonly seen in?

A

Pediatric patients

& old, frail, skinny patients

143
Q

What are anesthesia implications for cardiac oscillations?

A
  • May need to deepen anesthesia
  • May need to skip pressure support (because the oscillations can trigger a breath, and it may look like the patient is initiating breaths, but their not) and may need to place pt directly on spontaneous mode from volume control. Monitor for apnea!
144
Q

Curare cleft on ETCO2 monitoring represents what?

A

Spontaneous respiratory effort if anesthetic depth is insufficient to prevent respiration or when inadequate muscle relaxation is present

145
Q

True or false - irregular asynchronous waveform (curare cleft) on ETCO2 can only occur with the mechanically ventilated wave

A

False! It can occur within the mechanically ventilated wave OR separate from it

146
Q

If you observe a curare cleft, how can you fix it?

A
  • put the pt on pressure support
  • breathe them down (decrease their CO2) to take away their drive to breathe
  • could put on nitrous oxide (it has a quick on and off!)
147
Q

What causes a high ETCO2?

A
  • Increased CO2 delivery/ production (malignant hyperthermia, fever, sepsis, seizures, bicarb administration, lap surgery, clamp/ tourniquet release)
  • Hypoventilation (COPD, paralysis, CNS depression, med s/e, metabolic alkalosis)
  • Equipment problems (CO2 absorbent exhaustion, vent leak, breathing, inspiratory or expiratory valve malfunction)
148
Q

What causes a low ETCO2?

A

Decreased CO2 delivery/ production (hypothermia, low CO, PE, hemorrhage, hypotension, hypovolemia, V/Q mismatch, shunt, auto-PEEP)

Hyperventilation (pain, anxiety, light anesthesia)

Equipment problems (disconnect, esophageal intubation, bronchial intubation, obstruction, apnea, kink)

149
Q

What can you observe that can provide rapid evaluation of changes in lung compliance and resistance?

A

Spirometry loops

150
Q

What are spirometry loops?

A

A graphic representation of a dynamic relationship between two respiratory variables: flow and volume OR pressure and volume

151
Q

What can pressure-volume loops show?

A

Provide insight into LUNG COMPLIANCE and show volume on a vertical axis and airway pressure on the horizontal axis

152
Q

What can flow-volume loops show?

A

Provide information on PULMONARY RESISTANCE and show flow on the vertical axis and volume on the horizontal axis

153
Q

What is the first monitor you should put on?

A

Pulse ox

154
Q

What does pulse oximetry tell you?

A

HR and % of oxygen saturation (SaO2) of hgb continuously and noninvasively

155
Q

How does pulse ox work?

A

Oxygenated hgb absorbs light at different wavelengths than unoxygenated hgb

156
Q

At a red wavelength between 650 nm and 750 nm, what happens?

A

Reduced oxygen hgb absorbs more light than oxyhemoglobin

157
Q

In the infrared wavelengths of 900 nm to 1000 nm, what happens?

A

Oxygenated hgb absorbs better

158
Q

How do pulse oximeters distinguish arterial blood from venous blood?

A

By measuring the change in transmitted light during pulsatile flow
The pulse ox converts the detected light to a plethysmographic signal that measures the drop in light intensity with each beat

159
Q

How is the majority of O2 transported in the body?

A

Bound to hgb –> oxygen-carrying capacity is mainly dependent on the amount of hgb!

160
Q

What determines the amount of O2 that binds to Hgb?

A

The PO2 of the plasma

161
Q

What causes a left shift on the oxygen-hemoglobin dissociation curve?

A

Decreased pCO2
Decreased H+ (alkalosis)
Decreased temperature
Decreased 2,3-DPG
HgbF

162
Q

A left-shift on the curve indicates what?

A

Left-Love! A higher affinity of O2 to hgb = decreased release to tissues

163
Q

What causes a right shift on the oxygen-hemoglobin dissociation curve?

A

Increased pCO2
Increased H+ (acidosis)
Increased temperature
Increased 2,3 - DPG

164
Q

A right-shift on the curve indicates what?

A

Right-Release! A decreased affinity to O2 - more is release from the Hgb at the tissue level

165
Q

True or false - the pulse oximeter is more accurate when oxygen saturation is between 80-100%

A

True! When saturation drops below 80%, it is not as accurate

166
Q

How does methemoglobin affect pulse ox?

A

Methemoglobin absorbs light equally to oxyhemoglobin; pulse ox measurements are:

Falsey underestimated when oxygen sat is > 85%
Falsey overestimated when oxygen sat is < 85%

167
Q

What limitations are there with the pulse ox?

A

Methemoglobin
Carboxyhemoglobin
Sickle cell anemia
Injectable dyes (methylene blue or indigo carmine)

168
Q

How do injectable dyes affect pulse ox?

A

Will result in a significant, but transient, decrease in the measured oxygen saturation by pulse ox, BUT O2 IS NOT ACTUALLY DROPPING

169
Q

Cerebral oximetry is also referred to as what?

A

Near Infrared Spectroscopy (NIRS)

170
Q

What does cerebral oximetry measure?

A

The ratio of oxygenated hgb to total hgb within a region - expressed as a %

171
Q

When is cerebral oximetry helpful?

A

During cardiac bypass surgery

172
Q

When should temperature be measured?

A

On all pediatric patients receiving GA
Surgery > 30 mins
Use of a forced-air warmer

173
Q

What is the goal tempearture

A

36 degrees C

174
Q

What is the gold standard for monitoring temperature?

A

PA catheter

175
Q

How is hypothermia as a core temperature defined?

A

Less than 36 degrees C

176
Q

What are risks of hypothermia?

A
  • wound infection/ delayed healing
  • increased O2 consumption/ shivering
  • increased risk of CV incidents and MI
  • increased rate of sickling in sickle cell patients
177
Q

What are the 3 components of temperature regulation?

A

1) afferent input (anterior spinal cord)
2) central control
3) efferent response

178
Q

Heat and warmth receptors travel through what fibers?

A

Unmyelinated C fibers

179
Q

Cold receptors travel along what fibers?

A

A-delta

180
Q

How is ascending sensory thermal input transmitted?

A

To the hypothalamus (primary thermoregulatory control center) via the anterior spinal cord

181
Q

Efferent responses activate what effector mechanisms?

A
  • Increase metabolic heat production
  • Alter environmental heat loss
182
Q

What is the body’s response to heat?

A

Sweating
Cutaneous vasodilation - divert blood to the periphery where heat can be dissipated

183
Q

What is the body’s response to cold?

A

Vasoconstriction
Shivering - involuntary muscular activity that increases metabolic heat production

184
Q

Why do newborns have inadequate thermoregulation?

A

Large surface area
Lack of SQ tissue
Inability to shiver

185
Q

What is non-shivering thermogenesis (NST)?

A

SNS stimulation enhances the metabolism of brown fat to increase heat production
- Metabolic byproducts are produced

186
Q

What are the temperature effects of GA?

A

0.5C to 1.5C drop over 30 mins followed by a slower linear decrease of about 0.3C per hour until plateau

187
Q

Why is there such a large initial temp drop in the beginning of surgery?

A

Increased heat loss during prepping and draping
Redistribution of body heat from anesthesia-induced vasodilation

188
Q

How does GA eliminate behavioral responses to temperature change?

A

Vasoconstriction is impaired by anesthetic agents (prop and volatile anesthetics)

Muscle relaxants reduce heat production and prevent shivering

Central regulation of temp is depressed

189
Q

Can regional anesthesia effect temperature?

A

Yes! Induced vasodilation, resulting in redistribution of perfusion from the core to the periphery

190
Q

What are the effects on temperature when general and regional anesthesia are used?

A

The effects are additive! No plateau phase - the temp will continue to decrease throughout surgery

The threshold for vasoconstriction during combined regional/GA is centrally decreased by 1 degree C MORE than with GA alone

191
Q

What are the four mechanisms of intraoperative heat loss?

A

1) radiant
2) conduction
3) convection
4) evaporation

192
Q

How does the majority of heat loss occur?

A

Radiation

193
Q

What is radiant heat loss?

A

Loss to environment (air)

194
Q

What is conductive heat loss?

A

Heat transfer to OR table

195
Q

What is convective heat loss?

A

Moving air currents

196
Q

What is evaporative heat loss?

A

Vaporization of liquid from body cavity or respiratory tract

197
Q

What happens to the body when core temperature falls below 36 degrees C?

A

Coagulation - defect in platelet function occurs, and the activity of enzymes involved in the coagulation cascade is impaired

Wound infections - vasoconstriction decreases O2 delivery to the wound site

3x increase in morbid myocardial outcomes

Shivering - increases O2 requirements by 135-468%

Drug metabolism is decreased

198
Q

At what temperature can you extubate a patient?

A

36!

199
Q

How do you define hyperthermia?

A

Core temp > 38 degree C

200
Q

What is the most common reason for intraoperative hyperthermia?

A

Iatrogenic overwarming (particularly in children)

Excessive heat via convective warmer (bair huggar) that can not dissipate because the patient is covered

201
Q

What are other causes of hyperthermia?

A

Malignant hyperthermia
Post-op development of infection

202
Q

How can you decrease the initial 0.5-1.5 degree C temperature drop at the beginning of surgery?

A

Active prewarming for as little as 30 mins prevents redistribution

203
Q

How does giving 1 unit of blood or 1 L of room temperature crystalloids affect the body temperature?

A

Decreases temperature by about 0.25 degrees C

204
Q

What is the most basic approach to prevent heat loss during anesthesia?

A

Warm blanket - a single cotton blanket reduces heat loss by approximately 30%. It does not ADD heat; just reduces heat loss.
Adding more layers does not help with heat loss for short procedures.

205
Q

What is the most common perioperative warming system used?

A

Forced Air Warmer - CONVECTIVE warming (air to surface)

206
Q

What heating method uses heat produced by passing a low-voltage electric current through fabric coated with a semiconductive polymer?

A

Conductive fabric warming technology - Hot Dog Patient Warming System

207
Q

What can conductive warming methods decrease the risk of?

A

Infection from eliminating air blowing around the sterile field

208
Q

How does IV temperature management work?

A

Catheter inserted into the CV system via femoral, subclavian or IJ.

Venous blood is warmed as it passes over balloon, exchanging heat without infusing saline

209
Q

In the case of MH, how do you treat hyperthermia?

A

Dantrolene!

210
Q

The temperature of pulmonary arterial blood correlates well with what three areas?

A

1) tympanic membrane
2) distal esophageal
3) nasopharyngeal

211
Q

Why is the tympanic membrane a good place to check a temperature?

A

It is close to the carotid artery and approximates that at the hypothalamus

212
Q

What risks are associated with obtaining a temperature via the tympanic membrane?

A

Perforation
Bleeding

213
Q

How do you measure a nasopharyngeal temperature?

A

Nare to ear

214
Q

Why is the nasopharyngeal temperature accurate?

A

May reflect same blood supply as the hypothalamus

215
Q

Why is the nasopharyngeal temperature subject to error?

A

Displacement or leakage of respiratory gases and resultant cooling

216
Q

What is a risk of nasopharyngeal temperature monitoring?

A

Epistaxis

217
Q

Where is a great place to monitor temp in a patient under GA with ETT?

A

Esophageal - safe, easily accessible, accurate core temp

218
Q

Where is the optimal position for the esophageal temp sensor in adults?

A

45 cm form the nose (in line w/ the heart)

Must be measured in the distal third or quarter of the esophagus to avoid cooling by respiratory gases in the trachea

219
Q

Can you use an esophageal temp probe with an LMA?

A

No! You can use a nasopharyngeal probe instead.

220
Q

When is a bladder temperature mostly correlating with core body temperature?

A

When urine flow is high

221
Q

Is a bladder temperature good for cardiopulmonary bypass surgery?

A

No - temp changes too rapidly for bladder temp to follow core temp

222
Q

When is axillary temperature mostly accurate?

A

Infants and small children

223
Q

When is it okay to use skin temperature?

A

MAC sedation - it reflects peripheral perfusion rather than core temp. It is a fair estimate of core temp EXCEPT in rapidly changing conditions

224
Q

Where is skin temperature commonly measured?

A

Forehead

225
Q

How can a skin temperature monitor be affected?

A

ambient temp, skin surface warming devices & regional vasoconstriction

226
Q

When is a PA temperature not reliable?

A

During open chest procedures

227
Q

What does a Bispectral Index (BIS) monitor show?

A

Depth of anesthesia

228
Q

What is the BIS goal during general anesthesia?

A

40-60

229
Q

What does a BIS reading of 100 show?

A

Consciousness

230
Q

Where does burst suppression on the BIS monitor occur?

A

20

231
Q

On the BIS monitor, where might you see a flat EEG?

A

0

232
Q

BIS levels below 40 indicate a deep hypnotic state and increased ________

A

Mortality
Oversedation –> hemodynamic changes

233
Q

How do you set up a BIS monitor?

A

Application of four electrodes on the forehead

Clean forehead w/ alcohol swab

Digital pressure applied over sensor leads for 2-5 seconds

234
Q

What are indications of the BIS monitor?

A

High-risk populations - trauma or OB (that will have hemodynamic instabilities - helps prevent giving too much sedation)

TIVA - there is no MAC value with TIVA like with volatile agents

Aid in emergence

May decrease PONV if it helps decrease narcotic use

Decrease LOS - save money!

235
Q

What are the limitations of the BIS?

A

Anesthetic agents (ketamine and nitrous oxide - BIS is increased)

Hypothermia (BIS goes down by 1.12 units/ C reduction in body temp)

Age < 6 months

Neuro impairment (BIS usually lower)

Cautery

Bair hugger

Basic Principles of Anesthesia (2 decks)

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