12 Acid Base Disturbance Flashcards
Q: Compare oxygen levels in post alveolar venules and systemic arterial circulation to the venous side and pre alveolar arterioles.
A: much more to much less
Arterial pH = 7.4
Venous pH = 7.36
Q: Define acidaemia.
Define alkalaemia.
What does -aemia describe?
A: Refers to lower-than-normal pH of blood
Refers to high-than-normal pH of blood
at a point in time, the condition of the blood
Q: Define acidosis.
Define alkalosis.
What does -osis describe?
A: Describes circumstances that will increase [H+] and decrease pH
Describes circumstances that will decrease [H+] and increase pH
describes things causing change
Q: What’s an acid? What must be regulated? why? What is a base? Relationship?
A: molecule that has a loosely bound H+ ion (proton) that it can donate
The acidity of the blood must be tightly regulated, marked changes will alter the 3D structure of proteins (enzymes, hormones, protein channels)
anionic (negatively charged ion) molecule capable of reversibly binding protons (to reduce the amount that are ‘free’)
dissociation eqm:
(conjugated) H+A- H+ and A-
- > concentration of acid determines where eqm lies
Q: Application version of the dissociation eqm eqn. How can it be adjusted?
A: H2O + CO2 H2CO3 H+ + HCO3-
for inhalation of CO2 and movement of HCO3- around body (CO2 is considered an acid as it makes HCO3-)
(Increasing something on one side will push the equation in the opposite direction)
Q: What capacity does the blood have? can?
A: The blood has an ENORMOUS buffering capacity that can react almost IMMEDIATELY to imbalances
Q: What is pH related to? Unit? What’s wrong with this? Solution? (2) Summary eqn.
A: power of hydrogen/ concentration of H+ in blood
since it refers to charges-> use Eq/L (equivalence per L) (not mmol)
Eq system counts the charges
concentration of H+ in blood is actually so small= almost unmanageable -> [H+] = 0.00000004 Eq/L
solution= Sørensen scaled the data using a log10 transformation = much more manageable but negative -> easily fixed by applying a minus sign to the equation
-> -log10[H+] = 7.4
(inversa function of log) [H+] = 10^-pH
Q: What are the 2 sources of acid for the body? Ratio? Where is most coming from?
A: respiratory acid eg CO2 as it makes HCO3-
metabolic acid eg pyrvate, lactic acid
~99:1 (most is coming from CO2 as part of NRG production in cells)
Q: What does the Sørensen eqn allow? what is it? What does the Henderson eqn allow? what is it?
A: To calculate pH from proton concentration (or vice versa)
pH = - log10 [H+]
To calculate the dissociation constant (Ka) (compares how much was in the free form vs conjugated)
……..[H+][HCO3-]
K = ——————-
…………..[CO2]
Q: What does the Henderson-Hasselbalch equation allow? What is the eqn?
A: allows us to take into consideration the dissociation constant (ie how strong of an acid it is) when calculating pH
combines sorenson and henderson eqn
…………………………….[HCO3-]
pH= pK + log10 —————
………………………………[CO2]
Q: Estimate the volume of respiratory acid (i.e. CO2) produced in a typical adult over a 24-hour period. Explain.
A: ANS:
4 mL/dL (x50) = 200 mL/min (x60) = 1200 mL/h (x24) = 288 L/day = volume of CO2 produced everyday
WORKING:
CO2 flux is 4 mL/dL/min = for every 100 mL (1 dL) of blood that goes through the systemic capillaries, 4 mL of CO2 is added, on top of the CO2 already in there
Using this 4 mL value, we can extrapolate to a 5 L cardiac output (there are 50 decilitres (100 mLs) in 5 L of blood) by multiplying by 50. This gives us a CO2 production rate of 200 mL every minute
Q: Arterial blood gas (ABG).
H+ 35.2 nmol/L
pCO2 4.56 kPa
pO2 7.09 kPa
BE (B) 0.3 mmol/L
What does this patient have?
A: from H+ calculate pH -> in this case pH is high
PaCO2 assesses the respiratory component and in this case is low
PO2 is low
BE (B) is assessing the metabolic component and is normal (base excess= calculated variable that uses measured bicarbonate and compares it to estimated bicarbonate-> able to do so since CO2 and bicarb. are in eqm)
Uncompensated respiratory alkalosis with moderate hypoxaemia
Q: Basic guidelines for PaO2. What is normal? Mild hypoxaema? moderate hypoxaemia? severe hypoxaemia?
Threshold for BE (B)? higher than this? pH relation?
A: >10 kPa is normal
8-10 kPa is mild hypoxaemia
6-8 is moderate hypoxaemia
<6 kPa is severe hypoxaemia
-2 to 2 (over 2= more bicarbonate than there should be-> more protons bound-> pH will decrease)
Q: If there’s an issue with the lungs to change pH, what fixes it and how fast? What does hyperventilation do?
A: (resp problem)
slow compensatory response by kidneys by changing HCO3- and H+ retention/secretion
hyperventilation-> lose CO2-> lose acid-> increase pH (cause alkalosis)
Q: If there’s an issue with the kidneys to change pH, what fixes it and how fast?
A: (metabolic problem)
rapid compensatory response by lung to change CO2 elimination and therefore alter pH
Q: Draw graph between acidosis and alkalosis. Relationship? (2) Describe graph (4).
A: REFER
An acidosis will need an alkalosis to correct
An alkalosis will need an acidosis to correct
first points= normal
second= uncompensated disorders (situation is bad and compensatory mechanisms haven’t kicked in)
third= partially compensated response
forth= provided the stimulus is still there-> fully compensated disorder
Q: What would indicate uncompensated respiratory acidosis? (3) What needs to be done? how? Phases? (2) Result? Now called?
A: -high CO2 (possibly caused by low ventilation) causes
- increases H+ concentration
- BE (B) is normal as level of bicarb is normal for CO2
- reduce [H+]
- increasing bicarbonate to bind to some excess H+
- acute phase- CO2 moving into erythrocytes combines with H2O in presence of carbonic anhydrase to form bicarbonate -> moves out of cell via AE1 transporter
increased plasma bicarbonate concentration pushes eqm backwards so that more conjugated carbonic acid forms -> increases pH
- chronic phase- increase amount of bicarbonate reabsorbed in kidneys -> provides longer term mechanism to stabilise pH
- once corrective mechanisms are in action-> blood gases still show that pH is low (but closer to normal)
- pCO2 is still high if breathing has not changed
- BE (B) is now high
=> partially compensated resp acidosis
Q: What can indicate partially compensated resp acidosis? (3) Eventually? What does this look like? (3) Now called?
A: -blood gases still show that pH is low (but closer to normal)
- pCO2 is still high if breathing has not changed
- BE (B) is now high
eventually compensation is enough to return pH to normal range
- normal pH
- high BE (B)
- high pCO2
fully compensated resp acidosis
Q: What’s the interpretation procedure of an ABG? (4)
A: Type of imbalance?
Acidosis (or acidaemia) / Alkalosis (or alkalaemia) / Normal
Aetiology of imbalance?
Respiratory (acidosis or alkalaemia) / Metabolic (acidosis or alkalosis) / Mixed (respiratory and metabolic) / Normal
Any homeostatic compensation?
Uncompensated / Partially compensated / Fully compensated
Oxygenation?
Hypoxaemia / Normoxaemia / Hyperoxaemia
Q: Uncompensated (3). Uncompensated mixed.
A: -either have normal CO2 or normal BE
- normal BE but abnormal CO2= resp
- normal CO2 but abnormal BE= met
both lungs and kidneys are making it acidic or alk
Q: pH___CO2__BE
low\_\_\_high\_\_-- high\_\_low\_\_\_-- low\_\_\_--\_\_\_\_low high\_\_\_--\_\_\_high low\_\_\_high\_\_low high\_\_low\_\_\_high low\_\_\_low\_\_low high\_\_low\_\_\_low --\_\_\_\_low\_\_\_low --\_\_\_high\_\_\_high --\_\_\_--\_\_\_\_--
A: pH___CO2__BE
low\_\_\_high\_\_-- \_\_\_\_\_\_\_\_U resp acid high\_\_low\_\_\_-- \_\_\_\_\_\_\_\_U resp alk low\_\_\_--\_\_\_\_low \_\_\_\_\_\_\_U met acid high\_\_\_--\_\_\_high\_\_\_\_\_\_\_U met alk low\_\_\_high\_\_low\_\_\_\_\_\_\_U mix acid high\_\_low\_\_\_high \_\_\_\_\_\_U mix alk low\_\_\_low\_\_\_low\_\_\_\_\_\_\_PC met acid high\_\_low\_\_\_low \_\_\_\_\_\_\_PC resp alk --\_\_\_\_low\_\_\_low \_\_\_\_\_\_\_FC resp alk/ met acid --\_\_\_high\_\_\_high\_\_\_\_\_\_\_FC met alk/ resp acid normal
Q: Phases to fix uncompensated resp alkalosis. Result? (3) Next? Result? (3)
A: no acute phase, just chronic
decreases amount of bicarb reabsorbed in kidneys
-still high pH
-still low pCO2
-low BE (B) (was normal before)
=> partially compensated resp alk
eventually bicarb excretion and increase in dissociation to produce H+ will decrease pH
-normal pH
-low pCO2
-low BE (B)
=> fully compensated resp alk
Q: What can diarrhoea result in? 3 readings. What changes as you fix it?
Q: Excess secretion of HCO3- which means increase dissociation and therefore increase H+
-low pH
-normal pCO2
-low BE (B)
=>uncompensated metabolic acidosis
low pCO2
