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Anesthesia MM/TL > Physics, monitors, machine > Flashcards

Physics, monitors, machine Flashcards

1
Q

What is the equation for the time left before the cylinder is depleted

A

Divide the pressure left (psig) by 3 and then divide by the flow rate

Example: 500 psig left and 10 L/min
166.67/10 = 16 minutes

2200 psig left and 10 L/min
733.3/10 = 1 hour 13 minutes

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2
Q

Fresh gas flow must be equal to at least what to prevent rebreathe get during spontaneous ventilation while using a Mapleson A circuit?

A

Minute ventilation

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3
Q

What is a Mapleson A circuit?

A

Semi-open breathing system at relies on fresh gas flow for CO2 rebreathing

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4
Q

How does a Mapleson A circuit work?

A

Fresh gas flows to the patient, the APL valve is closed and reservoir bag deflated
Patient exhales and it goes out the APL valve, fresh gas accumulates in the reservoir bag and travels proximally to eliminate all exhaled gas

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5
Q

What is the safest flowmeter arrangement

A

One with oxygen tube down stream from all gases to prevent hypoxic mixtures

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6
Q

Which gas cylinders have to be measured by weight instead of pressure?

A

Carbon dioxide

Nitrous oxide

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7
Q

Why do carbon dioxide and nitrous oxide have to be measured by weight?

A

Because according to the ideal gas law, every time a gas is removed, liquid is vaporized to restore equilibrium

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8
Q

How much does a full e-cylinder of nitrous oxide weigh?

A

8.8 kg

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9
Q

How much does an empty nitrous oxide cylinder weigh

A

5.9 kg

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10
Q

What does a capnograph of an incompetent expiratory valve look like?

A

Looks like rebreathing CO2

The inspiratory segment is elevated

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11
Q

What does the capnograph look like with an incompetent inspiratory valve

A

Prolonged plateau phase

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12
Q

How is left ventricle contractility measured by echo?

A

dP/dT = rate of rise of ventricular pressure

The greater the force, the faste the rise

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13
Q

Which of the most commonly used gases has the lowest vapor pressure?

A

Sevoflurane

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14
Q

What is vapor pressure?

A

The pressure exerted by the vapor phase of a substance in equilibrium with solid and liquid phases at a given temperature in a closed system

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15
Q

What does a higher vapor pressure mean?

A

It means that substance is more likely to evaporate at a given temperature

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16
Q

What is the vapor pressure of desflurane

A

669 mm hg

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17
Q

What is the vapor pressure of isoflurane?

A

238 mm Hg

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18
Q

What is the vapor pressure of sevoflurane?

A

157 mm Hg

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19
Q

Fresh gas flows must be greater than or equal to what to prevent rebreathing during controlled ventilation using a Mapleson D circuit?

A

2-3 times minute ventilation

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20
Q

Fresh gas flows must be greater than or equal to what to prevent rebreathing during controlled ventilation using a Mapleson D circuit?

A

2-3 times minute ventilation

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21
Q

What causes an abrupt drop to zero in the ETCO2?

A
  1. Circuit disconnect
  2. Kinking of the ETT
  3. Esophageal intubation
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22
Q

What causes a sudden drop in ETCO2?

A

Partial airway obstruction

Circuit leak

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23
Q

What would cause a rapid decrease in ETCO2?

A

Pulmonary embolism

Circuit leak

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24
Q

What would cause a gradual decrease in ETCO2?

A

Hypothermia

Hyperventilating

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25
Q

What would cause a sudden increase in ETCO2?

A

Release of tourniquet

Sodium bicarbonate administration

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26
Q

What would cause a gradual increase in ETCO2?

A 
Decrease in minut ventilation
Faulty unidirectional valve
CO2 absorbent exhausted 
Thyroid storm
Malignant hyperthermia 
Insufficiency fresh gas flow
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27
Q

Which valve is better visualized with TTE?

A

Pulmonic due to its anterior position

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28
Q

What are pulse oximetry a poor monitor of?

A

Ventilation

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29
Q

What does pulse oximetry measure?

A

Functional hemoglobin saturation

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30
Q

Which color light does oxyhemoglobin absorb?

A

Blue - less red because this is what is reflected back to us

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31
Q

What gas property influences the flow rate around the annular space of a conventional flowmeter at low fresh gas flows

A

Viscosity

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32
Q

What is the annular space in the machine?

A

The space between the float and the wall of the flowmeter tube

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33
Q

What is the Hagen-Poisseuille equation?

A

Q= (change in Pressure X pi X r4)/8Ln

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34
Q

What gas property influences the flow rate around the annular space at high gas flows?

A

Density

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35
Q

What happens to partial pressures of gases as temperature decreases?

A

They decrease because they become more soluble in solution and the partial pressure depends on the amount go gas in gaseous form

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36
Q

What happens to ph with every degree of temperature decrease?

A

It increases by 0.017

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37
Q

During oscillometric non-invasive BP monitoring, how is the MAP determined?

A

By the point of maximal amplitude of oscillations

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38
Q

How are systolic and diastolic pressures determined in an oscillometric bp measurement?

A

By equations that detect the rate of change in oscillations

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39
Q

Which bp measurement is the least accurate?

A

Diastolic because it is most affected by movement

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40
Q

How many liters of nitrous oxide is in a full tank?

A

1590L

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41
Q

Why is oxygen always downstream?

A

Because if there is a leak in the flow meter, gas could leak out of the air flowmeter toward the oxygen flowmeter and patient. If oxygen was upstream it would leak out and be lost to the patient

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42
Q

If there was a leak in the oxygen flowmeter, what would happen if the anesthesia was used?

A

A lower than expected FiO2 would be delivered if using nitrous oxide too

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43
Q

When does the fail safe alarm go off?

A

When pressure of oxygen falls below 20-30 psig

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44
Q

What is absolut humidity?

A

The actual mass of water vapor in a volume of air

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45
Q

What is relative humidity?

A

The ratio of actual mass of water vapor in a given volume to the maximum it can hold

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46
Q

What does the negative pressure leak test do?

A

Differentiates between leaks in the machine and breathing system

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47
Q

How much does the BP per 10 cm of height change in comparison with the transducer?

A

7.5 mmHg per 10 cm of change

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48
Q

How much current does the Line isolation monitor detect?

A

Greater than 2 mA

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49
Q

Is it possible to deliver a micro shock with a working line isolation monitor.

A

Yes because it doesn’t detect anything under 2 mA

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50
Q

What are the two causes of the LIM system alarming?

A
  1. A faulty piece of electrical equipment was just plugged in
  2. Too many normal things are plugged in that are leaking current
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51
Q

What happens resistance and compliance of vessels as you get further and further from the aorta?

A

Resistance increases

Compliance decreases

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52
Q

What does a radial arterial waveform have in comparison with an aortic arterial waveform.

A

Higher systolic pressure
Wider pulse pressure
More delayed and slurred dicrotic notch
A more pronounced diastolic wave

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53
Q

Why does a radial arterial line have a higher systolic pressure than an aortic arterial line?

A

Due to all the branch points which reflect centrally and add to the pulse wave

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54
Q

What happens to the delivered concentration of anesthetic gas at higher altitudes through a variable bypass vaporizer?

A

It increases

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55
Q

What is Dalton’s law?

A

It states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases

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56
Q

How do variable bypass vaporizers work?

A

They are set to deliver fixed partial pressure of gas for a given level of barometric pressure

So as you ascend and barometric pressure drops, the vaporizer will correct for the barometric pressure and still deliver the same partial pressure, but give a higher concentration of gas

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57
Q

What is a good measure of volatile potency?

A

Partial pressure

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58
Q

How does a desflurane vaporizer work?

A

It heats the gas to 39 Celsius to create a certain vapor pressure independent of barometric pressure and then delivers the gas by concentration not partial pressure

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59
Q

What is the saturated vapor pressure of isoflurane?

A

238

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60
Q

What is the saturated vapor pressure of sevo?

A

157

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61
Q

What is the saturated vapor pressure of desflurane?

A

669

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62
Q

What is the concentration of agent inside the vaporizer equation?

A

Saturated vapor pressure/ barometric pressure

Note: the gas will always be saturated with agent inside the canister

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63
Q

How does pulse oximetry work?

A

It uses 2 different wavelengths of light to measure oxygenated and deoxygenated blood to give an estimate of SaO2

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64
Q

When the bellows go up, what air is filling them?

A

The exhaled gases from the patient

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65
Q

When the bellows go down, what air is being expelled and what part of respiration does that correspond with in the patient?

A

Gases and oxygen from the circuit to the patient

Inspiration

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66
Q

What should you do if the pipeline supply fails?

A

Turn the gas flows down because driving the bellows with the E-cylinders causes more consumption of gas

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67
Q

Why does a closed circuit machine cause more PONV.

A

Because of increased inhalation of noxious gases

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68
Q

Is there more heat loss with a closed circuit and why?

A

No, because each inspired breath has a higher humidity (due to the majority of inhaled gas being what was just exhaled) and lower fresh gas flows can be run in a closed circuit so there is less cool, dry air mixing.

Fresh gas flow is minimized in a closed circuit

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69
Q

How do the inspiratory valves work?

A

The inspiratory valve opens to let fresh gas flow into the patient while the expiratory valve closed to prevent rebreathing of gases

During exhalation, the expiratory valve opens to allow exhaled gas to flow to the absorb and the inspiratory valve closed to prevent exhaled gas from flowing retrograde into the inspiratory limb

70
Q

What would you do if you have an incompetent inspiratory valve?

A

Increase your flows

71
Q

How can you suspect an incompetent inspiratory valve?

A

CO2 not going back to baseline on the capnograph
Prolonged expiratory plateau
Gradual inspiratory stroke
Exhaled tidal volumes lower than expected as set on ventilator

72
Q

How should MRI compatible ECG cable be positioned?

A

Straight and insulated from the patient because can cause thermal injury to a patient

73
Q

What is acoustic impedance?

A

A tissue’s capacity for transmitting sound

High = greater ability to reflect sound

74
Q

When is reflection highest using ultrasound?

A

When the angle of incidence is 90 degrees

75
Q

What are the to factors that influence acoustic impedance?

A

Density and propagation of speed of sound

76
Q

What are the specifics of pulse oximetry?

A

It depends on the absorption of red and infrared light
Deoxyhemoglobin absorbs more light than oxyhemoglobin at red wavelengths
Oxyhemoglobin absorbs more light at infrared wavelengths

77
Q

What IV dye doesn’t mess with pulse oximetry?

A

Fluorescein because it absorbs light at similar wavelengths as hemoglobin

78
Q

Why do blue dyes affect pulse oximetry?

A

Because they absorb significantly more light at 940 nm which is interpreted as a greater concentration of deoxyhemoglobin

79
Q

Why does red nail polish not mess with the pulse oximetry?

A

Because it is the color that is pulsed through the tissue at 660 nm as is infrared

80
Q

Why are closed circuits so much better?

A
  1. They allow for less rebreathing
  2. They allow for low fresh gas flow
  3. They help conserve heat and humidity
81
Q

In thermodilution, what are the 2 axes for the graph?

A 
X= time
Y= temperature

And remember, by convention, the temperature is a positive deflection even though it represents a decrease in temperature from baseline

82
Q

What does low cardiac output look like on a thermodilution graph?

A

High, wide peak

83
Q

How does thermodilution work?

A

10 ml of cooled saline is injected into the right atrium and temperature is sensed in the pulmonary circulation

3 measures are taken and averaged due to variability with breathing

84
Q

What material should not be used with CO2 lasers around?

A

Polyvinylchloride > silicone > rubber

85
Q

What ETT materials are most resistant to ignition when using an Nd : YAG laser?

A

Silicone

Rubber with silver foil and sponge coating

86
Q

What are the best ETT tubes to use with CO2 laser?

A

Metal wrapped

Flexible metal

87
Q

What is the advantage of a microlaryngeal tube?

A

Same diameter as an ETT, longer, less flexible, large cuff volume, lower pressure

88
Q

What happens to desflurane partial pressure as the barometric pressure drops?

A

It decreases

89
Q

How does the desflurane vaporizer work?

A

It is heated on the inside to maintain a constant temperature of 39 degrees Celsius so that the same concentration of gas is always delivered at any level above sea level

90
Q

What is the equation for resetting the dial at a different atmospheric pressure to maintain constant partial pressure of gas?

A

% concentration X 760 mm Hg/ambient pressure

91
Q

What happens with variable bypass vaporizers at different altitudes?

A

They always deliver the same partial pressure of gas because they are not internally pressurized.

92
Q

What happens to the amount of gas delivered above sea level in a normal vaporizer?

A

It increases but the partial pressure delivered is the same.

93
Q

Why does barium hydroxide produce more carbon monoxide?

A

Less water in the absorbent

CO2 combines with water to form carbonic acid

94
Q

Which absorbent allows better CO2 absorption?

95
Q

Why does carbon monoxide form from the absorbents?

A

It is an exothermic reaction that happens with the volatile agents and the strong bases within the absorbents in the setting of decreased water content

96
Q

Which inhalational anesthetic produces the most carbon monoxide with absorbents?

A

Desflurane

97
Q

Which inhalational anesthetic produces the most heat with absorbents

A

Sevoflurane

98
Q

Which absorbent is more likely cause fire and compound A accumulation with sevoflurane?

A

Barium hydroxide due to its lower water content therefore makes more heat with sevo

99
Q

How does absorbent work?

A
  1. CO2 combines with water in the absorbent to make carbonic acid
  2. Carbonic acid reacts with NaOH (strong base) to form sodium bicarb, water, and heat
  3. Then sodium bicarb reacts with CaOH to form calcium carbonate and sodium hydroxide
100
Q

What does the PADSS use? (Post anesthesia discharge scoring system?

A

Scores from 0-2 for all categories

  1. Pain
  2. Hemodynamic stability
  3. Surgical site bleeding
  4. PONV
  5. Activity level
101
Q

Why does helium create laminar flow?

A

It is the least dense

102
Q

What is the viscosity of helium compared to air and oxygen?

103
Q

Why is helium used as a treatment for reactive airway disease?

A

It’s low density allows for more laminar flow

104
Q

What is Boyle’s law?

A

For a given mass, at constant temperature, the pressure time the volume is constant
PV= C

105
Q

What is Charles and Gay Lussac’s law?

A

For a given mass, at constant pressure, the volume is proportional to the temperature

106
Q

What is Dalton’s law of partial pressures?

A

In a mixture of gases, the pressure exerted by each gas is the same as if each gas occupied the volume alone

107
Q

What does laminar flow depend on?

A

Viscosity

Hence annular flow depends on viscosity at low flow gas

108
Q

When does ETCO2 show signs of VAE?

A

0.5 ml/kg of air

109
Q

How much does N2O increases the bubble at 50% nitrous?

A

It doubles it

110
Q

How much does N2O increases the bubble at 75% nitrous?

A

It quadruples it

111
Q

What are the NIOSH regulations for N2O scavenging?

A

Must be less than 25 ppm

112
Q

What are the NIOSH scavenging guidelines for halogenated agents with N2O?

113
Q

What are the NIOSH scavenging guidelines for halogenated agents without N2O?

114
Q

What does a time constant equal?

A

Volume of the container/flow through the container

115
Q

What is the % change of 1 time constant?

116
Q

What is the % change of 2 time constants?

117
Q

What is the % change in 3 time constants?

118
Q

What does the time constant of the circuit?

A

Volume of the circuit/FGF

119
Q

What does a line isolation monitor do?

A

Continually monitors the impedance from all lines to ground and indicates wha

120
Q

How is ETCO2 measured?

A

Infrared spectrophotometer where a wavelength of infrared light is passed through a gas sample and the amount of energy detected is inversely proportional to gas partial pressure

121
Q

What does a Ground fault current interrupter do?

A

Shuts off the power to the faulted machine to prevent electric shock to a person standing in the field (who offers a low resistance pathway for the current).

122
Q

What does a line isolation monitor do?

A

Alarms when one machine creates a current above 5 mA, this is called a first fault

Note: you need 2 faults to create a circuit and thus electrocution

123
Q

Do GFCI or LIM prevent microshock?

124
Q

Which Mapleson circuits require FGF to be 2-3X minute ventilation to prevent rebreathing?

A

Mapleson D, E, F

125
Q

What Mapleson circuit is the most efficient for spontaneous breathing?

126
Q

Which Mapleson circuits are most efficient for controlled ventilation?

127
Q

What is saturated vapor pressure?

A

The partial pressure of a substance at which the liquid and vapor states are in equilibrium

128
Q

How is end tidal CO2 measured?

A

By infrared spectrophotometer where a wavelength of infrared light is passed through a gas sample and the amount of energy detected is inversely proportional to the gas partial pressure

129
Q

Which gases are measured with infrared?

A

CO2, N2O, volatiles

130
Q

Which gases do not absorb infrared?

A

O2, N2, xenon

131
Q

What is a closed circuit?

A

Where all total fresh gas flow is equal to oxygen consumption and inhalational anesthetic metabolism.
No gas is vented to a scavenger
All gas is rebreathed
To minimize FGF - only oxygen is used

132
Q

What are semi-open circuits?

A

There are no expiratory/inspiratory valves, no CO2 absorbent

Rely on FGF to prevent rebreathing

133
Q

FGF has to be greater than or equal to what in controlled ventilation using Mapleson D circuit to prevent rebreathing?

A

1-2 times minute ventilation

134
Q

What should you do if a power failure happens during surgery?

A

Switch essential equipment to the red face plate electrical supply system

135
Q

What is different about the Bain circuit?

A

It has coaxial delivery of FGF
Requires higher gas flows to prevent rebreathing (2.5X minute ventilation)
Lower volume of tubing
Faster equilibration to changes in inspired gas concentrations

136
Q

What is Mapleson A better for?

A

Spontaneous respirations

137
Q

What is diluent flow?

A

The gas that bypassed the volatile chamber

138
Q

What happens to vaporizer output when it is moved from sea level to Denver?

A

Higher output

139
Q

What happens to vaporizer output when a vapor with higher pressure is put in a vaporizer set at a lower pressure (isoflurane for sevo)

A

Lower output

140
Q

How does using a Mapleson circuit speed the rate of rise of Fi?

A

Vc is lower and the smaller circuit causes less of a dilution all effect
No CO2 absorbent
Less plastic/rubber to absorb anesthetic

141
Q

What is the difference in a Mapleson A circuit?

A

The FGF enters near the breathing bag, not near the patient connection
Most efficient system in spontaneous breathing

142
Q

What is the difference in Mapleson E circuit?

A

Does not have a breathing bag, but a long piece of tubing that acts as a reservoir or expiratory limb
No rebreathing occurs during controlled ventilation because FGF fills the lungs

143
Q

WHat is the difference in Mapleson F circuit?

A

Allows for scavenging gas

Equally efficient of spontaneous and controlled ventilation

144
Q

What is the equipment ground wire for?

A

It is for prevent micro shocks from current leaks

145
Q

What is an equipment ground wire?

A

A low impedance wire that allows leakage current to pass through to prevent buildup of leakage current.

146
Q

What is the line isolation monitor useful for?

A

Preventing macro shock

147
Q

What does the line isolation monitor measure?

A

The total leakage current of the nongrounded isolate power circuit

148
Q

What is the ground fault circuit interrupter for?

A

Preventing macro shock

It monitors current imbalance in grounded circuits and interrupts them if there is an imbalance

149
Q

What is used to measure the partial pressure of oxygen and require a power source?

A

Clark electrode - polarographic

150
Q

What are the three ways you can measure the partial pressure of oxygen?

A
  1. Galvanic
  2. Paramagnetic (electromagnetic field that attracts oxygen molecules
  3. Polarographic
151
Q

What is the galvanic method?

A

Oxygen molecules enter th electrode and react with The lead anode.
The reaction produces electrons that move to the gold anode
The amount of electrons moving across is proportional to the oxygen concentration

152
Q

What is the polarographic method?

A

Oxygen molecules react with silver anode producing electrons and go toward a platinum cathode
- needs a battery (unlike Galvanic) so it’s faster

153
Q

What is the severinghaus electrode used for?

A

Measuring pCO2

  • has an internal ph sensor
154
Q

What is IR absorption used to detect?

A

Volatile, N2O, CO2

155
Q

Why are the unidirectional valves close to the Y piece?

A

To limit the amount of back flow there is if there is a leak

156
Q

Why is the APL valve positioned before the absorber?

A

To prevent the loss of fresh gas

157
Q

Why is the reservoir bag positioned on the expiratory limb?

A

To reduce expiratory resistance

158
Q

Why should the fresh gas outlet be positioned between the absorbed and the inspiratory valve?

A

So the patient always gets fresh gas that is not diluted

159
Q

What is a semi-open system?

A

High FGF with no rebreathing

160
Q

Where should the APL valve NOT be positioned to prevent rebreathing in a traditional circuit?

A

Between the patient and the inspiratory valve

161
Q

Where can the FGF not enter to prevent rebreathing in a traditional circuit?

A

Between the patient and the expiratory valve

162
Q

Where must a unidirectional valve be positioned to prevent rebreathing?

A

Between the patient and the inspiratory and expiratory limbs of the circuit

163
Q

How does the O2 analyzer work and what is it influenced by?

A

Paramagnetic analyzer

It is influenced by water vapor because water creates a magnetic field directly opposite of an imposed magnetic field –> reads O2 levels that are falsely low

164
Q

What is a semi-closed system?

A

Lower FGF with some rebreathing

165
Q

What is a closed system?

A

FGF matches patient consumption with complete rebreathing

166
Q

How do you decrease the time constant?

A

By decreasing the capacity of the circuit OR

Increasing the FGF

167
Q

What is the equation for the time constant?

168
Q

What is the time constant for isoflurane?

A

3-4 minutes, following first order kinetics, equilibration with the brain will take 10-15 minutes

169
Q

What is the time constant for N2O, Des, sevo?

170
Q

Why are newer absorbent so better than older?

A

They lack strong bases that react with volatile to make carbon monoxide

Anesthesia MM/TL (36 decks)

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