Acid base balance Flashcards
What is an acid?
Electrolytes that release H+ when dissolved
What is a base?
Electrolytes that release ions that combine with H+
What is normal serum pH?
7.35-7.45
What is a volatile acid?
Gas, produced via cellular metabolism and excreted by lungs as CO2
What is a non-volatile acid?
Liquid, produced via cellular metabolism excreted by the kidneys such as:
Lactic acid (anaerobic breakdown) Keto acid (fat breakdown) Sulphuric/phosphoric acid (Protein breakdown)
What is the function of buffers?
Minimize changes in pH
Chemical and physiological buffers
What are the 3 chemical buffers?
1) Carbonic acid-bicarbonate buffer system
2) Phosphate buffer system
3) Protein buffer system
What is the first line of defense against pH changes?
Chemical buffers, specifically the carbonic acid-bicarbonate buffer system
How does the carbonic acid bicarbonate buffer system work?
Acid: Base ratio is 1:20 with pH 7.40, so strong acids are neutralized by HCO3- and strong bases are neutralized by H2CO3+
More common to have more strong acids than strong bases enter the body
How does the phosphate buffer system work?
PO4 is able to bind to 2 H+ ions or release them to maintain pH
Becomes H2PO4 or HPO4
How does the protein buffer system work?
Blood buffer, is most abundant buffer in the body.
Majority of CO2 travels in blood as H+ and HCO3-, H+ can bind to hemoglobin/RBCs which seal of H+ and prevent changes to serum pH
What are the 2 physiological buffers?
1) Lungs
2) Renal system
How do the lungs act as a physiological buffer?
Takes mins to react, regulates CO2.
In acidosis –> Respiratory centers in the medulla triggers increase RR to blow off CO2
In alkalosis –> Medulla triggers decrease RR to retain CO2
How do the kidneys act as a physiological buffer?
Directly eliminate H+ by controlling HCO3- and H+ secretion and reabsorption. Is the most effective buffer, but takes longest.
What happens when the kidneys move H+ from blood to urine?
It exchanges with another positive ion (e.g. K+)
Therefore risk of hyperkalemia in pts with profound acidosis.
What happens when nephrons have to move too much H+ out into urine?
When nephron pH < 4.5 (too much secretion of H+), tubular necrosis and kidney damage occurs
What happens when the kidneys move HCO3- from blood to urine?
Cl- is exchanged.
Recall lasix blocks Cl- reabsorption at the ascending LOH so urinary losses of Cl- eventually exceeds bicarbonate losses leading to metabolic alkalosis.
What causes metabolic acidosis?
PH < 7.35, pHCO3- < 22
1) Accumulation of non-resp acids (lactic acid, DKA, renal failure, ingestion of acids, ASA)
2) Loss of base (diarrhea, prolonged vomiting)
How is metabolic acidosis treated?
Underlying cause, sodium bicarb, HD
What causes respiratory acidosis?
pH < 7.35, pCO2 > 45
Accumulation of volatile acids (CO2 retention, resp depression, airway obstruction, resp failure)
How is respiratory acidosis treated?
Treat cause, ventilate increase RR, assess sedation
What causes metabolic alkalosis?
pH > 7.45, HCO3- > 28
1) Accumulation of bases (antacids, diuretics causing loss of Cl-, blood transfusions due to citrate breaking down to HCO3-)
2) Loss of non-volatile acids (vomiting stomach contents, NG suction)
How is metabolic alkalosis treated?
Usually not treated but acetazolamide can be used to decrease HCO3- production (low evidence)
What causes respiratory alkalosis?
pH > 7.45, pCO2 < 35
Loss of volatile acids (alveolar hyperventilation decreases CO2, hypoxemia, over ventilation)
How is respiratory alkalosis treated?
Underlying cause, sedation, if ventilated then correct RR and Vt
