Arterial Blood Gas Analysis

Question 1

Respiratory system:
2 things the resp. system needs

kPa values of normal O2 and CO2 in the blood

Answer 1

1) adequate pulmonary capillary blood flow for perfusion
2) adequate ventilation of alveoli

O2= 13.3 kPa 100 mmHg
CO2= 5.3 kPa 40 mmHg

Question 2

Ventilation-Perfusion Mismatch

Physiology Shunting
what is it? (ratio) 
leads to
because...
eg. 
compensation = (key word) 
what is this?

Physiology Dead Space 
what is it? (ratio) 
because...
eg. 
compensation = (key word) 
what is this?

Answer 2

Physiology shunting
Dec. in ventilation so dec. in perfusion -> low V/Q ratio
leads to low PaO2
Due to obstructive pulmonary disorder/ obstructed airway
eg. Asthma or COPD
compensation= Hypoxic vasoconstriction
This is where blood vessels to well ventilated lung areas dilate and inc. flow and vasoconstriction to poorly vent. areas.

Physiology Dead Space
Ventilation but no perfusion! High V/Q ration
leads to low PaO2
Blood vessel blocked
Eg. PE
compensation= Bronchoconstriction + dec. surfactant
directs air to well perfused areas

Question 3

Both types of Resp. Failure
Both names!
what happens?

Answer 3

Type 1 (Hypoxaemia) -> low PO2 (V/Q mismatch) and normal PCO2

Type 2 (hypercapnic) -> Low PO2 AND HIGH PCO2

Question 4

If Inc. PCO2, pH of blood will Dec. -> this is Chronic Resp. Acidosis
what will the body do to combat this drop in pH?
1) kidney
2) liver
3) liver
4) kidney EXPLANATION IS KEY
5) key one!! (type of….)

Answer 4

1) Inc. in plasma HCO3- from kidneys
2) Liver Dec. LESS urea
3) Liver. Inc. glutamine
4) Kidneys inc. in gluatmase dehydrogenase which catalyses glutamine -> NH4- + HCO3- in PCT
Therefore increase in HCO3-
5) KUSSMAL breathing (inc. in tidal and minute vol. to expel more CO2)

Question 5

How does the body combat Chronic Resp. Alkalosis
1) cells in kidneys

metabolic factors that affect:
HCO3- levels (3)
H+ levels (2)

ALSO….

Answer 5

1) Inc. no. of type B intercalated cells in collecting duct-> excrete more HCO3- so dec. HCO3- plasma levels

HCO3-

• kidney failure
• ketone bodies
• alkaline tide

H+

• vom
• exercise therefore lactic acid

Question 6

what does KUSSMAL breathing stand for? (causes for inc. in minute and tidal vol. to do with acidosis)

Answer 6

K- Kentone bodies
U- Uremia 
S - Sepsis 
S- Salicytes
M- Methanol
A- Aldehydes
L- Lactic acid/ acidosis

Question 7

Detection and Reflex to Inc. Ventilation rate:
1
2-> both types that detect and what nerves they use… also goes to
3 (brainstem)
4
5
6

Answer 7

1) Peripheral and central chemoreceptors detect inc. in H+/ dec. in pH
2) peripheral: aorta -> vagus nerve and carotid sinus-> glossopharangeal nerve BOTH to NTS (nucleus tractus saltori)
3) central pattern generator in brainstem
4) inc. freq of impulses down phrenic nerve + intercostals
5) inc. force and freq. of contraction of diaphgragm, intercostals and accessories
6) inc. depth and ventilation rate (inc CO2 expel and inc. pH)

Question 8

Interpreting AGG 
normal levels:
PO2
pH
PCO2
[HCO3-]
Acid base balance

Stop O
What are we looking at?
if too low= ….. -> then look at… which indicates…
if too = ….. -> then look at… which indicates…

Answer 8

PO2: 10- 13.3 kPA 
pH: 7.35-7.45
PCO2: 4.7- 6kPa
[HCO3-]: 20mM-28mM
Acid base balance: -2 to +2mM

Look at PO2:
Too LOW <10 kPa
means resp. problem 
then look at CO2:
Normal= Type 1 Resp. failure (hypoxaemia)
High= Type 2 Resp. failure (hypercapnea)

Question 9

Step A, B and C
What are we looking at?
if too low= ….. -> then look at… which indicates…

if too = ….. -> then look at… which indicates…

Answer 9

Look at pH:
Too low< 7.35 = acidosis
now determine if resp or metabolic by looking at Buffers (eg. CO2 and HCO3-)

High CO2 (> 6kPa) indicates resp. acidosis meaning cannot expel enough CO2 so inc. [H+] -> Acute= normal [HCO3-] and chronic would show [HCO3-] > 28mM

Low HCO3- (> 20mM) inidcates metabolic acidosis meaning kidney is not producing or retaining enough HCO3- -> Acute= normal change in PCO2 and chronic would show > 4.7 kPa change in PCO2

Too high > 7.45 = alkalosis
now determine if resp or metabolic by looking at Buffers (eg. CO2 and HCO3-)

Low CO2 (<4.7 kPa) indicates Resp. Alkalosis meaning blowing off too much CO2 -> Acute= normal [HCO3-] and chronic would show [HCO3-] < 20mM

High HCO3- (>28mM) indicates metabolic alkalosis eaing kindey is producing too much HCO3- -> Acute= normal change in PCO2 and chronic would show > 6 kPa change in PCO2