Flashcards in Acid base balance 2 Deck (29):
What is the normal range for plasma pH?
What is the normal range for plasma bicarbonate?
What is the normal range for arterial partial pressure of carbon dioxide
What is the difference between compensation and correction?
Compensation - aims to get the body pH back within a normal range at the expense of bicarbonate and carbon dioxide levels
Correction - aims to get the body pH back within a normal range and simultaneously have normal buffer levels
What happens immediately after a pH change? How quick is this response?
Buffering (dilution of acid or base) by blood (Hb, bicarbonate) or ECF (largely bicarbonate) buffers. Very quick
To get a patients pH status what should be performed?
Blood gas analysis
What is respiratory acidosis? Give examples
Carbon dioxide retention of respiratory origin
Anaesthesia (respiratory depression)
Airway restriction (asthma, tumour, etc)
How do respiratory disorders cause acidosis?
Carbon dioxide retention drives the buffer equation to the right causing a rise in hydrogen ions and bicarbonate. The hydrogen ion rise has more effect
When would you diagnose uncompensated respiratory acidosis?
Clinical picture fits
How is respiratory acidosis compensated for?
No extracellular buffering as respiratory system is the cause so purely renal compensation.
Increased partial pressure of carbon dioxide drives hydrogen secretion within the kidney which causes reabsorption of filtered bicarbonate and secretion of acids hence "new" bicarbonate addition to the blood
What does renal compensation for respiratory acidosis cause (biochemically speaking)?
Rise in blood bicarbonate. Rise in blood pH
How does correction of respiratory acidosis occur?
The partial pressure of carbon dioxide must be lowered restoration of normal respiratory function
What is respiratory alkalosis? Give some examples
Excess removal of carbon dioxide from the body by the respiratory system.
Hyperventilation as a result of hypoxia at altitude (i.e altitude sickness)
Hyperventilation (fever, brainstem injury, etc)
How do respiratory disorders cause alkalosis?
Excess removal of carbon dioxide drives the equilibrium of the buffer reaction to the left. Hydrogen and bicarbonate fall but it is the decreased hydrogen which causes the alkalosis
When would you diagnose uncompensated respiratory alkalosis?
pH > 7.45
How is respiratory alkalosis compensated for by the kidney?
Fall in partial pressure of carbon dioxide decreases hydrogen secretion by the tubules meaning it cannot reabsorb all the bicarbonate and this thus increases excretion of bicarbonate (alkaline urine). No titratable acid is formed either.
What does renal compensation of respiratory alkalosis cause (biochemically speaking)?
Fall in bicarbonate thus decrease in pH
What is metabolic acidosis? Give examples
Excess hydrogen ions arising from sources other than carbon dioxide
- Ingestion of acid
- Excessive metabolic production (DKA, lactic acid from exercise)
- Excessive loss of base (diarrhoea)
How would you diagnose uncompensated metabolic acidosis (biochemically speaking)? Why does this occur?
How is metabolic acidosis compensated for?
Respiratory compensation occurs when peripheral chemoreceptor sense the fall in pH and stimulate an increase in respiration. Increased respiration causes removal of carbon dioxide and thus the equilibrium of the buffer system shifts to the left. Hydrogen and bicarbonate levels both fall
How is metabolic acidosis corrected?
Filtered bicarbonate is low and readily reabsorbed by the kidneys. Hydrogen ions being secreted form titratable acids which get excreted in the urine (acidic urine). These two mechanisms allow bicarbonate to return to normal
What occurs after metabolic acidosis has been corrected?
Ventilation returns to normal
How important is respiratory compensation in metabolic acidosis?
Very important as renal correction is delayed!
Which is more common metabolic acidosis or metabolic alkalosis?
What is metabolic alkalosis? Give examples
Excess loss of hydrogen from the body.
- Excessive vomiting (loss of HCL from stomach)
- Ingestion of alkali
- Aldosterone hyper secretion
How does aldosterone hyper secretion cause metabolic alkalosis?
Increased activity of the hydrogen sodium exchanger at the apical membranes of tubular cells causes increased excretion of acid
How would you diagnose metabolic alkalosis (biochemically speaking)? Why does this occur?
pH > 7.45
H2CO3 > 27
Clinical picture fits
Decreased hydrogen or addition of base causes bicarbonate rise
How is metabolic alkalosis compensated for?
Rise in pH is detected by peripheral chemoreceptors and ventilation slows. This causes carbon dioxide retention (increase in partial pressure) and shifts equilibrium of the buffer equation to the right. Hydrogen and bicarbonate both rise