Module 6 - ABG Interpretation Flashcards
ABG measures?
Acid base status
Oxygenation level in blood
Why arterial sample and not venus?
Oxygenated blood that is not carrying byproducts of metabolism
ABGs are mostly carried by the radial artery, what are other sites?
Brachial
Femoral
Pedal
An increase in pH indicates what?
A decrease in CO2
Acids release [H+] in solutions, if there is an increase in [H+], what happens to the solution?
It becomes more acidic
Do bases accept or release [H+]?
accept
What is a buffer?
[neutralize/stablize]
A solution that can resist pH change upon the addition of an acidic or basic component.
such as…[H+]
3 ways the body responds the acid-base balance.
Chemical buffer system
Respiratory response
Renal response
What formula is associated with the chemical buffer system
hint shifts correspond to change
H+ + HCO3- ↔ H2CO3 ↔ CO2 + H2O
HCO3 = bicarbonate
H2CO3 = Carbonic acid
What responds immediately to hydrogen ion balance?
Chemical buffer systems.
What is the purpose of chemical buffer systems?
Prevents excessive change in pH when either acid or base is added to the solution.
3 buffers in blood?
Bicarbonate system
Protein (hemoglobin)
Phosphate
[H+] + HCO3- <–> H2CO3
Bicarbonate system.
The most important buffer system in blood
Which is the most important buffer system in blood?
Bicarbonate system
[H+] + Protein <–> H.Pr
Protein (hemoglobin) buffer
[H+] + HPO4- <–> H2PO4
Phosphate buffer
Bicarbonate/Carbonic Acid Buffer System can be regulated by which systems?
The most important buffer for the overall regulation of pH
Regulated by both LUNGS and KIDNEYS
How is carbonic acid regulated?
Can be retained or exhaled by CO2
Bicarbonate management?
Retained or excreted by renal tubules
How does the Respiratory System Response regulate pH?
By breathing them off, altering ventilation can control acid-base levels.
what is a major end product of metabolism?
CO2 and Lactate.
CO2 is continuously inside cells.
CO2 diffuses out of the cells via interstitial fluid into the blood stream, what does it form when this happens?
Carbonic acid (H2CO3)
What is the average CO2 the lungs put out per minute?
240mL/min
why is carbonic acid important?
when it is buffered, it can be reformed back into CO2 in the lungs. From there, it is diffused into alveoli and exhaled.
Respiratory System Response: when is the respiratory system stimulated?
When there is imbalance in [H+] concentration.
Respiratory System Response: what does hyperventilation indiacte/do?
the body is attempting to get rid of excess acid
Respiratory System Response: what does hypoventilation indicate?
The body is trying to retain acid.
Equilibrium in lungs:
Hypoventilation vs hyperventilation responses?
Hypoventilation = retain acid
Hyperventilation = eliminate acids.
If CO2 production increases, what will also increase?
Bicarb
For every 10 mmHg increase in PaCO2, the HCO3 increases by how much?
1mmol/L
For every 10mmHg decrease in PaCO2, does HCO3 decrease by 1mmol/L?
No, they decrease by 2.
Is the Respiratory System Response fast or slow?
Very fast.
Why isn’t the Respiratory System Response efficient by itself?
When [H+] concentration reaches normal, the stimulus to the respiratory response stops.
They only adjust 50-75% of the [H+]
What assists the Respiratory System Response?
The kidney and buffering systems act to restore balance
Renal system = what?
Kidney response for the regulation of acids that cannot be “breathed” out.
i.e lactic acid
What are 2 types of acids that cannot the Respiratory System Response can’t get rid of?
Volatile or fixed acids.
Generally, how are Volatile acids dissociated?
They’re turned into free [H+] which are excreted by the kidneys?
What are the 2 renal system responses for regulation?
Acidosis and Alkalosis.
Alkalosis
Method to retain HCO3
by excreting more [H+] ions
Alkalosis
Method to retain [H+]
by excreting HCO3
Is the renal response fast or slow?
Slow
could take hours or days.
Why is pH deviation dangerous?
deterioration of enzyme systems and cellular function.
2 acid-base disorders?
Respiratory (ventilation)
Metabolic (non-respiratory)
What do respiratory disorders indicate?
Altered PaCO2
What do metabolic disorders represent?
Abnormalities in plasma HCO3
or other acid/bases
Henderson-Hasselbalch equation represents what?
The relationship between acid-base disorders and blood pH
Low pH indicated what?
Acidosis?
High pH indicates what?
alkalosis
High and low pH indicate what responses?
high = irritating
low = sedating.
Normal ABG values?
What is Ventilation defined by?
PaCO2 and pH
(circulation of air and corresponding blood pH)
What is ventilation determined by?
Alveolar minute ventilation
(RR x VT)
if PaCO2 increases, what does pH do?
pH decreases
10 mmHg increase = pH decrease by 0.06
if PaCO2 decreases, what happens to pH?
pH Increases
10 mmHg decrease = pH increase by 0.10
What is a buffer?
[neutralize/stabilize]
A solution that can resist pH change upon the addition of an acidic or basic component.
such as…[H+]
What is a buffer?
[neutralize/stabilize]
A solution that can resist pH change upon the addition of an acidic or basic component.
such as…[H+]
What is oxygenation determined by?
hint Hb is accounted for.
Spontaneously breathing: FiO2
Positive pressure ventilation: FIO2 and mean airway pressure.
How do you calculate arterial oxygen content [CaO2]?
CaO2=(1.34xHgb)SaO2+0.003(PaO2)
How do you calculate Delivered Oxygen [DO2]?
CaO2 x CO (cardiac output)
Normoxemic?
PaO2 = 80-100mHg
Mild Hypoxemia?
60-79mmHg
Severe Hypoxemia?
Anything below 40mmHg
Normal SaO2?
95-100%
What does Base Excess [BE]?
Measure of changes in total blood buffer base above or below normal.
[BE] is a pure measure of what component of the acid-base balance?
Metabolic
Why is [BE] taken into account ?
HCO3 isn’t the only buffer in the blood, so [BE[] is used to better understand blood buffers.
What does not affect [BE]?
PaCO2
A positive [BE] indicates which 2 things?
excess base OR
Excessive loss of acid
A negative [BE] indicates which 2 things?
excess acid OR
excessive loss of base.
Fully compensated disorder
The primary disorder accounts for the initial movement out of range, the opposing system works to pull the pH back into range
What is a primary respiratory problem opposed by?
The renal system
A primary metabolic respiratory system is counteracted by
A respiratory system
Combined disorder?
indicates both respiratory and metabolic components
Primary causes for a respiratory disorder?
Change in PaCO2
If PaCO2 is abnormal and opposite direction of the pH, it is the cause.
Normal PaCO2 = 35-45
What happens when PaCO2 is less than 35?
pH increase (alkalemia)
Normal PaCO2 = 35-45
What happens when PaCO2 is greater than 45?
What is the primary cause for a metabolic disorder
When HCO3 is abnormal and in the same direction of pH.
Normal HCO3: 22 - 26mmol/L
What happens when HCO3 is less than 22?
pH drops (acidemia)
[BE] decreases
Normal HCO3: 22 - 26mmol/L
What happens when HCO3 is greater than 26?
pH increases (alkalemia)
[BE] increases
How do you know when a response is compensated?
when the body is trying to maintain a normal pH.
How does the metabolic system compensate for a respiratory problem?
Either increasing or decreasing HCO3 in order to correct pH
Where does a metabolic response orginate?
Kidneys: either excreting or retaining bicarbonate
How does the respiratory system respond to a metabolic problem?
Increasing or decreasing minute volume.
The goal is to increase/decrease PaCO2.
Does the body over-compensate?
No.
General characteristics:
uncompensated (acute) respiratory acidosis?
PaCO2 is high -> low pH
HCO3- is normal
general description for a acute respiratory acidosis
a condition in which carbon dioxide builds up very quickly, before the kidneys can return the body to a state of balance.
General characteristics:
Partially compensated respiratory acidosis
PaCO2 is high ->low pH
pH isn’t as low as expected for the high PaCO2
HCO3 is high in an attempt to bring pH back to normal range
General characteristics:
Fully compensated (chronic) respiratory acidosis
pH is within normal range
PaCO2 is high
HCO3 is high (and successfully brought pH back to normal range)
Potential sources of respiratory acidosis (8)
CNS
Neuromuscular junction
Metabolism (tissue/cells)
O2 excess
Lungs
Drugs
Mechanical Ventilation
Muscle fatigue
General characteristics:
Uncompensated (acute) respiratory alkalosis
PaCO2 is low->high pH
HCO3 is nomral
General characteristics:
Uncompensated (acute) respiratory alkalosis
PaCO2 is low->high pH
HCO3 is normal
General characteristics:
Partially compensated respiratory terminology
PaCO2 is low->high pH
HCO3 is low in a attempt ot bring pH back to norm (but not yet)
General characteristics:
Fully compensated (chronic) respiratory alkalosis
pH is normal
PaCO2 is low
HCO3 is low (but pH is normal)
Potential sources for a respiratory alkalosis (6)
CNS
Cardiovascular system
Thoracic cage
Lungs
Drugs
Mechanical ventilation
Return and add slides 48 to 58
also add slide 59
Co-oximetry
Measures the oxygen carrying state of hemoglobin
(the types in the blood)
Co-oximetry measurement evaulate hemogoblin dowb by types via blood gas analysis, what are 4 hemoglobin types?
Metheglobin
Carboxyhemoglobin
fetal hemoglobin
sulfhemoglobin
Add slides 61 - 62
Combined Respiratory and Metabolic Acidosis
pH is low
Both the PaCO2 and HCO3- are contributing (high PaCO2 and low HCO3-)
Combined Respiratory and Metabolic Alkalosis
pH is high
Both the PaCO2 and HCO3- are contributing (low PaCO2 and high HCO3-)
Methemoglobin
Iron in ferric form Fe +++ causes reduced Hb carrying capacity
Normal range 0-3%
Symptoms grey-blue tint to skin
Treated with methylene blue
Carboxyhemoglobin
Normal .3-.8%
Tobacco users have higher than normal levels (3-8%)
Half life 4-6 hours in room air, as low as 35 minutes with HyperBaric Oxygen Therapy
Sulfhemoglobin
Rare
Increased sulfur atom blocks heme
Caused by some chronic drug use
