Arterial Blood Gas Instrumentation

Question 1

Parameters measured

Answer 1

pH
pCO2
pO2
O2 sat
HCO3-
BE

Question 2

pH measured by

Answer 2

electrodes

Question 3

pCO2 measured by

Answer 3

electrodes

Question 4

pO2 measured by

Answer 4

electrodes

Question 5

O2 Saturation Measured

Answer 5

Calculation

Question 6

HCO3- Measured by

Answer 6

Calculated - ABG
Measured - electrodes - lytes

Question 7

BE Measured by

Answer 7

Calculated

Question 8

Electrodes Called

Answer 8

Potentiometry & Ion Selective Electrodes (ISE)

Question 9

Potentiometry Measures

Answer 9

the change in potential between measuring and reference electrode

Question 10

Application of Electrodes

Answer 10

ISEs select the ion measured by an ion selective surface designed to capture the “unknown” ion
ISEs are not specific but selective

Question 11

Change Potential Detected

Answer 11

Voltmeter and is proportional to concentration of ion in the unknown sample

Question 12

ISE Electrode: pH

Answer 12

Uses two probes
1) A calomel electrode: Hg/HgCl2 reference
2) ABG instruments: Ag/AgCl2 reference
Salt Bridge
1) Concentrated K+ or NaCl solution

Question 13

ISE Electrode: pH on ABG

Answer 13

ISE measuring and reference electrodes are combined
- Ag/AgCl2 reference electrode
- AgCl covered silver wire
- Glass electrode internal solution

Question 14

ISE Electrode: Measuring Other Ions

Answer 14

Common applications
- Potassium ISE
- Sodium ISE
- Calcium

Question 15

Potassium ISE

Answer 15

Valinomycin (an antibiotic)

Question 16

Sodium ISE

Answer 16

Lithium aluminum silicate

Question 17

Calcium ISE

Answer 17

Solid state poly vinyl chloride (PVC) polymer matrix membrane

Question 18

Modified ISE Electrode: pCO2

Answer 18

Modified pH electrode
Interior pH electrode pair
Outer jacket: weak Na+ and HCO3- solution
CO2 enters weak buffer and converted to H+

Question 19

Polarographic Electrode: pO2

Answer 19

Clark Electrode - Most common

Question 20

Principle of pO2 Electrode

Answer 20

Polarography flow between a cathode and anode during oxidation-reduction reaction O2
Cathode: Reduction half reaction (gain of electrons)
Anode: Oxidation half reaction (loss of electrons)

Question 21

pO2 Electrode Equation

Answer 21

Use of 0.6 V to cause oxidation
Anode
2 Ag + 4 Cl- = 2 AgCl2 + 4 e-
Cathode
1/2 O2 + H20 + 2 e- = 2 OH-

Question 22

Coulometry/Amperometry Electrode: Chloride

Answer 22

Measurement of Cl- ions for the sweat chloride test

Question 23

Principle of Chloride Electrode Coulometry

Answer 23

Measurement of amount of electricity passing between two electrodes per unit of time and titration amount of unknown
- Titrant (Ag+) is electrochemically generated

Question 24

Principle of Chloride Electrode Amperometry

Answer 24

Measures current flow produced by an oxidation-reduction reaction
- Analyte added to a dilute electrolyte of solution
- H2So4 = H+ + SO4-

Question 25

Chloride generator pair

Answer 25

Cl- is added to titration vessel
Combines with free Ag which comes from anode
- Ag+ + Cl- = AgCl2
Cathode reaction occurs
- 2e- + 2H+ = H2 gas

Question 26

Chloride indicator pair

Answer 26

Cl- is titrated, excess Ag is detected by indicator pair shutting off timer
- Ag+ + e- = Ag without charge

Question 27

Calculation of Chloride Concentration

Answer 27

Cl = ((time of titration) unknown/(time for titration) std) x STD
std and STD = standard

Question 28

ABG Measurement

Answer 28

Calibrated with gas and precision buffers

Question 29

Buffers for pH in ABG

Answer 29

6.838
7.384

Question 30

Levels of Gas for ABG

Answer 30

Two levels of gas
O2: Slope Gas = 0%, Cal Gas = 12%
CO2: Slope Gas = 5%, Cal Gas = 10%

Question 31

Gas Calibration

Answer 31

% gas converted by partial pressure of gas
pp of Gas = (BP mmHg - pWV at 37 C)/100 x % gas

Question 32

Partial Pressure of H2O Vapor

Answer 32

At 37 C = 47 mmHg

Question 33

ABG Parameters for Oxygen

Answer 33

Oxygen dissolved in Plasma
Oxygen saturation (O2 Sat) = % saturation of Hgb with O2
O2 Saturation increases as pO2 increases

Question 34

Oxygen Dissociation Curve

Answer 34

Non-linear relationship of pO2 to O2 Saturation
Explains O2 reserves in blood

Question 35

Normal Hgb O2 Levels

Answer 35

50% saturated at plasma pO2 of 27 mmHg

Question 36

Normal Venous Blood O2

Answer 36

Partial pressure O2 is 40 mmg Hg
O2 Saturation is 75%

Question 37

Normal Arterial Blood O2

Answer 37

Partial Pressure O2 is 97 mm Hg
O2 Saturation is 97% (sea level)

Question 38

Oxygen Dissociation Curve: p50

Answer 38

Measure of affinity of Hgb for O2
High p50 means low affinity of Hgb for O2 (right shift)
Low p50 means high affinity of Hgb for O2 (left shift)

Question 39

O2 Dissociation Right Shift

Answer 39

Decrease Hgb affinity for O2 and lower O2 content
Curve is shifted to right and O2 affinity of Hgb is decreased

Question 40

Causes of Right Shifts

Answer 40

Temperature increase (Hyperthermia = fever)
pH decrease (acidosis)
Increase in 2,3 DPG
Increase in pCO2

Question 41

O2 Dissociation Left Shift

Answer 41

Increased Hgb affinity for O2 at higher O2 content
Curve is shifted to left and O2 affinity of Hgb is increased

Question 42

Causes of Left Shifts

Answer 42

Temperature decrease (Hypothermia)
pH increase (alkalosis)
Decrease in 2,3 DPG
Decrease in pCO2

Question 43

Oxygen Status of Patient Affected By

Answer 43

Respiration
Cardiac
Anaerobic condition

Question 44

Problems with exposing Blood Gas to Air

Answer 44

Oxygen
pCO2
pH

Question 45

Temperature Corrections

Answer 45

> 37 C - Substrate 0.015/each degree
<37 C - Add 0.015/each degree

Question 46

Base Excess

Answer 46

Related to Total Buffer Capacity in Body
- Correlates strongly with HCO3 concentration
- Impacted by Proteins
Positive # - Excess Base Present
Negative # - Deficient in Base