Buffering Response to AB IMbalance- 2 Week 2 Flashcards
What is the HH equation
pH= 6.1 + {HCO3-]/(.03 x PCO2)
This relates bicarb conentaion, pH, and PCO2… If iknow i can always get the others.
why is CA an effective buffer
- Adding acid would increase CO2
- So we would expect a decreaes in pH according to HH equation
- But the respiratory system blows of CO2 shifting the carbonic acid equation further to the right, buffering more H+
H+ + HCO3 → H2CO3 → CO2 + H2O (3)
When can we use the dvaenport nomogran
When we hold PCO2 constant. At any constant value we can draw a line that would tell us all possibly values of HCO3- and pH at that constant PCO2.
We can make isobars at other constant PCO2 values
What tw
o things happen when buffering a non carbonic aci
- Most is buffered through the bicarb.. so plasma H+ would increase and bicarb plasma leevls would decrease
- Respiratory system holds PCO2 constant (so we w
ould be on a davenport nomogram)
What happens in buffering of carbonic acids
** PCO2 is changin so our pH and bicarb values are no longer on the isobar of davenport**
- CA is titrated with NC buffers mainly Hb.
- Each time we buffer an H+ with Hb we shift the equation towards H+ and bicarb, increasing the amount of bicarb in the plasma . The amount of new bicarb= the amount of Hb- that was lost
What is the normal buffering abilites of Hb
The normal buffer capacity of Hb is about –11 slykes (sl).
increase in HCO3 by 11 results in decrease of pH by 1
What changes happen in resperatory system in carbonic acidosis
PCO2 increases to the value that the individual’s abnormal respiratory system establishes and will be constant when that value is reached until the problem is reversed or eliminated.
When PCO2 changes
• CA increases or decreases and
• pH and HCO3 – change by sliding up or down a line with
slope –11 in the Davenport nomogram. (The slope of this line
depends of [Hb], but we will assume –11 for this class.)
What happens when you add HNC to PCO2? bicarb?
Adding CA does what to PCO2? bicarb?
- Adding HNC doesn’t affect PCO2. Reduces bicarb (used as buffer)
- Adding CA increase PCO2. Increase bicarb
Both situation woudl decrease pH
4 keys buffering rules
- what do buffers do
- Which buffers work with CA NCA acids
- Affects on bicarb
- pH changes is on what line
- Buffering decreases the magnitude of the pH change, but it doesnot prevent pH from changing.
- Non-carbonic acids are buffered by all buffer systems.
Carbonic acid is only buffered by NCA buffers. - When non-carbonic acids are buffered, [HCO3–] decreases.
When carbonic acid is buffered, [HCO3–] increases. - When a change in respiratory function causes a pH change, the
trajectory of that change is on a line with a slope of –11 sl.
What ions are considering in the anion gap? what are there values and what is the gap?
What is it actually considering?
Cations- CL-(100mM) and bicarb (24mM)
Anions- Na+ (140)
140- (100+24)= 16mM
Remember that cation and anion i are equal in body fluids.
This difference of 16 mM represents the difference between the unmeasured cations and anions.
The unmeasured cations are less than the unmeasured anions, and the difference is called the
anion gap. The anion gap is used to show changes in the concentration of unmeasured ions.
Explain why the anion gap gets larger in buffering
- We have an increae in H+ and NC-
- The H+ is buffered by bicarb decreasing out total measured anions
- While NC- (an anion) is produced it isn’t measured so the anion gap gets larger
Causes of the anion gap
Endogenous acids that can increase the anion gap:
• HSO4– accumulates in renal failure
• lactic acid accumulates in hypoxemia
• ketones accumulate in diabetes mellitus
Exogenous methanol/ethylene glycol poisioning
What buffer system causing increase in anion gap?
What does an increas gap mean?
CA buffering– giving up those bicarbs to the H+.
increased anion gap may indicate a metabolic acidosis
(it is not definitive)
