Acid Base Flashcards
What is normal pH?
7.35-7.45
Must be tightly regulated (ECF) for enzymes and proteins to work
What distinguishes acidosis/alkalosis from acidaemia/alkalaemia?
Acidaemia/alkalaemia is when the pH of the BLOOD is out of the normal range.
Acidosis/alkalosis is the underlying pathological causing abnormal pH
severe for both is 7.2 and 7.6
incompatibility is 6.9 and 7.9
What is a buffer?
A weak acid or base that minimises pH changes due to addition or removal of H+.
Only removes H+ ions temporarily
the pK of a buffer si the pH at which the acid (HA) and base (A-) are equal
What are the body’s buffer systems?
Bicarbonate and proteins like albumin and haemogloibn
What determines our blood pH?
Using the henderson hesselbach equation
pH= 6.74 (pK) + log ([HCO3-]/[pCO2])
How is pCO2 controlled by the respiratory system?
We produce a lot of CO2 by metabolism all the time. This would increase acid (due to equilibrium).
Due to breathing we expel the CO2. If we have a low pH this will stimulate ventilation to remove the CO2 and thus reducing the ‘acidosis’.
Ventilation rate controls the pCO2
How do CO2 retention/hypoventilation and hyperventilation alter blood pH?
CO2 retention will hift equilibrium to more acid. respiratory acidosis, due to maybe an asthma attack where less air can be expelled.
hyperventilation lowers CO2 reducing the H+ ion conc due to equilibrium causing resp. alkalosis
What is occuring in metabolic pH changes?
- If you decrease bicarbonate (likely by addition of acid) you will be under metabolic acidosis (less buffer)
- If you increase bicarbonate will be in metabolic alkalosis (more base lol)
What is a clinical example of metabolic acidosis?
Diabetic ketoacidosis as a result of anaerobic metabolism. More acid, buffered by HCO3-. lowers the bicarbonate and causes acidosis.
Note body tries to respond by secreting more H+
What is the role of the kidney in acid base balance?
Renal hydrogen excretion by use of urinary buffers such as phosphoric acid and ammonium ions
What are some causes of metabolic acidosis?
- lactic acidosis, due to hypoxia, poor perfusion as a result of hypotension or CO poisoning.
- decreased renal H+ excretion due to renal failure or tubular acidosis
- loss of bicarboate due to diarrhoea or iliostomies
How does vomiting cause metabolic alkalosis?
Lowers H+, more bicarbonate formed from CO2 due to equilibrium shift
How can respiration quickly compensate for metabolic pH changes?
MAC: the low pH and bicarbonate can be chnaged by hyperventilated (acidotic breathing) to reduce the CO2 in blood increasing the H+ and the pH thus
MAL: the high pH by increased bicarbonate would cause hypovent. increasing the pCO2 lowering the pH
What are the three roles the kidney has in acid base balance?
Bicarbonate reabsoprtion in the proximal tubule, bicarbonate generation here and H+ secretion in distal tubule
What does acetazolamide do?
Will block carbonic anhydrase. As a result less bicarbonate is made, and will cause metabolic acidosis. Used to counteract alkalosis as a result of hyperventilation
How does renal compensation occur?
NB occurs over a longer time.
RAC: decreased vent. causes increased pCO2, thus increasing pH. the kidney will generate more bicarbonate to offset this acidosis. Occurs over days.
RAL: hyperventilates, lowers pCO2, causes alkalosis (higher pH). Kidney will lower bicarbonate secretion and increase H+ excretion to compensate (this will decrease pH)
What is base excess?
amount of acid or base required to restore pH to normal.
Normal is 0 (-2 to +2)
As rule it is positive in metabolic alkalosis, and negative in metabolic acidosis
What is the anion gap?
Serum cation concs - anions conc. (normal is 14-18)
Normal AG reflects mainly protein anions.
Thus if more acid, more anions when dissociates
If it is increased, then there are less anions (such as bicarbonate) such as in metabolic acidosis.
ONLY useful in MAC
Main causes: lactic acid and ketoacidosis as well as renal failure (more phosphates and sulphates)
What are common causes of anion gap acidoses?
Why are they hyperchloremic?
- GI bicarbonate loss
- RTA: defects in acid secretion, no increased urine ammonium
due to the low bicarbonate excess Cl- is reabsorbed to balance the sodium absorption
What is the link between potassium and acid base?
vague rule
H+ and K+ will drive each other into and out of cells
Acidosis and hyperkalaemia:If acidosis, H+ into cells causes K+ out and vice versa.
Alkalosis and hypokalaemia: if alkalosis, K+ will go in and H+ out or low potassium will cause H+ to go in and K+ out to counter
What are exceptions to the rule of potassium and acid-base balance?
1) diarrhoea- loss of bicarbonate and potassium (usually an acidosis but can be either)
2) RTA: distal and proximal types both associated with hypokalaemia
What are some common causes of metabolic alkalosis?
vomiting- due to loss of H+ and Cl- (need chloride to get rid of bicarbonate?)
- secondary to hypokalaemia (laxatives/chronic diarrhoea)
- ingestion of alkali’s (need something else)
What is Chloride depletion alkalosis?
- Normally in alkalosis body tries to increase bicarbonate loss
- if chlroide depletion is present, bicarbonate reabs. must occur to balance sodium
- can not correct until chloride balance is restored
