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Physics > 5. Measurement of Oxygen, CO2 & Anaes > Flashcards

5. Measurement of Oxygen, CO2 & Anaes Flashcards

1
Q

Capnograph 4 phase

Gap Paco2 & ETCo2
Increased gap?

A
  1. Baseline - Inspiration
  2. Rapid upstroke - expiration
    - COPD - sloped up as unit empty diff / obstruction
  3. Plateau at end expiraton - mix alveolar gas
  4. Rapid decline - Inspiration

Usually 0.4- 0.7
PP gradient Gas exhchange
If reverse - CO2 Not leave alveoli
V/Q mismatch

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2
Q 
Transcutaneous method of O2 measure
1. Define
2. Describe how
3. Risks & minimised
What temperature
A
  1. Contin measurement of capillary PO2~~ pAo2
  2. Skin heathed 44’C
    Vessels dilate, O2 usage negligable w/ total o2
    = skin o2 approx art
    O2 diffuse thru skin - electrode skin
    Polgraphic electrode Plat or gold cathode & silver anode - electroylte soln

45’ localised burn - skin temp thermistor
controls heating power
second thermistor as safety - switch off if malfunction
Move 3-6 hourly

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3
Q

Pulse oximetry

inaccurate - with what
high
low
unaffected

Accuracy
Curve when sats plotted ppo2
4 causes of Right shift hb dissoc curve

A

NIV - meas O2 sats & HR
Reduced by causes of perfusion reduction
70-100% accuracy +/-2%
CO overstimates

inacc low
- methaem
methylen blue
icg

bili sulp hb fetal hb - dont alter accuray

PPO2 vs Sat curve - sigmoidal 
Right shift  
Reduced pH
Increased temperature
Partial pressure of carbon dioxide and
2,3-diphosphoglycerates.

300hz

red 660
ir 940

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4
Q

Sats probe
requires
Whats a plethysmograph

A

Pulsatile flow

measures changes in volume with time within an organ - trace from finger represent change volume

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5
Q

How does a sats probe work

A 
Measure relative absorb 2  WL 
660 red
940 IR
differentiate oxy  deoxy
Ratio absorb 2 lights calibrated nomogram  convert to sats
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6
Q

Methaemoglobin
Phsiological effects
absorb light
what cause sats to run

A

more IR than either O2Hb or HH
Absorbance of red light ~ HHb,
patients with significant methemoglobinaemia can appear cyanotic.
red and IR light equally well at both wavelengths used in conventional pulse oximetry
high MetHb levels will cause the SpO2 to trend toward 85%

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7
Q

Capnography based on

A

Infrared absorption

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8
Q

CO2 absorb IR @

A

4.28 µm

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9
Q

Etco2 is normally how much higher or lower than PACo2

A

ETCO2 0.6-0.7 kPa lower than the arterial partial pressure.

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10
Q

Mainstream analyser

A

the patient’s breathing system and therefore increases dead space but allows rapid analysis. The IRMATM mainstream probes (manufactured by the company Masimo) are comercially available. They can measure CO2, N2O and five volatile anaesthetic agents (halothane, enflurane, isoflurane, sevoflurane and desflurane).

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11
Q

Sidestream

A

Small diameter tubing that samples gases at 150-200 mL/min. It can cause sampling delay but multiple gases and anaesthetic vapours can be analysed from the same sample.

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12
Q

Oxygen crit temp

A

-118.6

annot be liquefied no matter how much pressure is applied.

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13
Q

O2 @ altitude

A

PP falls

Fi same

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14
Q

Clark electrode

A

Platinum cathode

silver anode

K OH or K Cl

O2
slow response time
Requires a battery

halothane - false high

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15
Q

Galvanic fuel cell

A

gold cathode

a lead anode.

slow response time
O2

Nitrous oxide - reacts lead - N - alter pressure damage
not affected by halothane

both liverate Electrons at anode

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16
Q

pH electrode

A

Glass electrode - responds H+
Measuring - bulb - pH sense glass - silver/sliver chloride in buffer
potential diff dep ph in & out

Ref -merc/merc cl - KCl buffer soln - semi perm membrane reduces contam protein

Blood sample sep H+ ion sens glass - gradient accross = potential difference

Create circuit - pot diff displayed

Both maintained at 37
Linear output 60mV per unit pH

17
Q

Pulse Ox principle

nm absorbeds

A

Differential absorption light Oxy & Deoxy

Oxy absorbs @ 940 (IR)
Deoxy  660 (red)

590 805 Isobestic
590

18
Q

Explain how pulse ox works

A

The light absorbed by non-pulsatile tissues is constant (DC),

non-constant absorption (AC) is the result of arterial blood pulsation

The DC and AC components at 660 and 940 nm are then analysed by the microprocessor and the result is related to the arterial saturation.

0ulse oximeter provides a continuous non-invasive measurement of the arterial oxygen saturation.

The light emitting diodes (LEDs) produce beams of red and infrared light at 660 nm and 940 nm respectively (not 640 and 960 nm), which travel through a finger (toe, ear lobe or nose) and are then detected by a sensitive photodetector.

19
Q

Oxygenated blood abosorbs at

A

940

20
Q

Deoxy absorbs at

A

660

21
Q

Store abg sample cold can lead to

A

False Low ongoing metabolism in white blood cells) or a falsely high reading d/t bubbles dissolving

22
Q

What is the base excess

A

base excess is the amount of strong acid required to return the pH of 1 litre of blood to 7.40 at a PaCO2 of 5.3 kPa and37°C

23
Q

excessive heparin errors on abg

A

w PaCO2 and low PaO2, though the pH is little affected).

24
Q

Side stream analser

flow min min

how long

A

syphon gas at 150ml min

flow < than above - slow transit time
effects rise time

High flow - incorrect - decreased pressure in sample line

<2m in length

25
Q

metacresol dye change what to what

what is it

A

purple to yellow - emergency when no capnograph

26
Q

Mass spec

how sub analysis

whats process

what can aid ID

is it quick

A

sub analysed according to mol mass

knowledge cracking pattern - aid identification

process
drawn in
E hot cathode
charged accell out - genertating fied
charged particles pass thru magnetic field
different deflection - mass moment = ID

can be used for gas anaylsis - fast response time

27
Q

Regarding paramagnetism

analysers are how accurate

A

used with null deflection arr acc +- .01%

28
Q

diamagnetic substances

A

repelled magnetic field

29
Q

Paramagnetic

A

attracted to magnetic

oxygen - unpair electrons make it so

Nitric oxide
not nitrous

30
Q

Severinghaus electrode

A

tension co2 blood paco2

h ion mesasure - direct related pac2o

co2 blood diffsued sem membrane - react water = carbonic acid dissoc h andbic

react h - sense glass - bath bic

31
Q

Oxygen measured

A

1 Fuel cell
2 paramagnetic
3 chemically
4 polarographically

Physics (11 decks)

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