acid/base imbalance and disturbance Flashcards
What is an acid?
A molecule that releases a hydrogen ion.
What is a base?
A molecule that accepts a proton.
What is the normal pH of ECF?
7.35-7.45.
Is intracellular or extracellular pH higher?
Extracellular.
How does the body deal with daily acid load?
- Buffers
- Lungs via alveolar ventilation
- Kidneys via renal excretion of H+.
What is the buffer system in the ECF?
Carbonic acid.
What is an important buffer system in the renal tubular and intracellular fluids?
Phosphate buffer system.
What is responsible for most intracellular fluid buffering?
Protein buffer system.
How does systemic acidosis impact breathing?
It stimulates the respiratory system to increase ventilation to blow off CO2.
Where is most bicarb reabsorbed?
Proximal tubule.
What is necessary for the kidney to generate acids?
- Reabsorbing all the filtered HCO3
- Excrete ammonium
- Excrete titratable acids.
What bicarb CO2 level indicates metabolic alkalosis?
Greater than 30.
What bicarb CO2 level indicates metabolic acidosis?
Less than 22.
Give the equation for metabolic acidosis in assessing if someone’s lungs are responding to a kidney problem.
pCO2 = [(1.5 x HCO3] + 8 +/- 2).
How do we calculate the anion gap?
AG = Na – (Cl + HCO3). Should equal around 12.
What is the formula for osmolar gap?
2 x Na + (BUN/2.8) + (glucose/18).
What should the osmolar gap be?
Less than 10.
Describe metabolic acidosis.
Low bicarb, low pH, low pCO2 (from hyperventilation).
What causes metabolic acidosis?
Loss of bicarb, addition of acid, or rapid addition of non bicarb solutions to the ECF.
What is the difference between type A and B lactic acid diagnosis?
Type A always has hypotension and edema, and type B is just inappropriate formation of lactic acid that may be caused by things like drugs, liver problems, and mitochondrial disorders.
Describe ketoacidosis.
Absent or low levels of insulin cause the body to use alternate energy sources like free fatty acids. These convert to ketoacids, causing more acid in the body.
What is alcoholic ketoacidosis?
Often due to nausea/vomiting causing a decrease in the insulin to glucose ratio, leading to more ketoacid production and lower body pH. Can also happen in withdrawal with volume depletion and starvation leading to ketoacid production.
How can renal failure lead to acidosis?
Lower number of functioning nephrons leads to a lowered ability to excrete acids. This leads to an accumulation of anions due to metabolic adjustments, leading to an elevated anion gap.
What poisons impact serum osms?
Methanol and ethylene glycol.
What do we use to measure non-gap metabolic acidosis?
Urine anion gap.
What is the formula for urine anion gap?
Una + Uk – Ucl.
What is a normal urine anion gap?
20-50.
What should happen to the urine anion gap in non-gap metabolic acidosis?
It should become more negative due to increased NH4Cl excretion.
In terms of acid-base, what happens with diarrhea?
We lose a lot of bicarb, leading to metabolic acidosis.
What causes RTA?
Either an inability to reabsorb filtered bicarb or impaired excretion of ammonium chloride.
What is proximal RTA (type 2)?
Inability to reabsorb bicarb in the proximal tubule; leads to non-gap metabolic acidosis.
What is Fanconi syndrome?
Proximal tubular dysfunctions associated with proximal RTA.
What is a common cause of proximal RTA in adults?
Multiple myeloma.
What is distal RTA (type 1)?
Inability to secrete excess protons as ammonium chloride or sodium dihydrogen phosphate.
What factors can be involved in a distal RTA?
- Inability to generate ammonium
- Inability to do medullary recycling of ammonia
- Inability to generate a negative tubular potential in the CCD
- Inability to secrete acid into the tubule.
What is Sjogrens syndrome?
Disease in adults that can impact the proton ATPase and lead to distal RTA.
A patient walks in and seems totally fine. You find they have a super low bicarb. What could it be?
Distal RTA; this RTA is not systemic so they will have very pronounced metabolic acidosis but seem ok.
What is RTA caused by hyperaldosteronism?
Inability for aldosterone to facilitate excretion of H+ bound to ammonia.
Type 4 RTA (hyperaldosteronism) is always associated with…
Hyperkalemia.
Type 4 RTA is common in…
Diabetics and those with renal impairment.
In metabolic alkalosis, how do the lungs respond?
With hypoventilation to hold onto more CO2 and drop pH.
Describe the pathophysiology of metabolic alkalosis.
- There is either an intake of excess exogenous alkali or loss of H+ via vomiting or diuretics.
- The kidneys are unable to handle this high amount of HCO3, either through low GFR, low volume, low potassium, or high aldosterone.
- Low GFR causes a low filtration and excess HCO3 in the body; low volume can lead to increased HCO3 reabsorption or increased H+ secretion; low potassium leads to increased H+ secretion; increased aldosterone increases NH4+ excretion.
How do we assess volume status in metabolic alkalosis?
Urine chloride! Bicarb binds to sodium to be excreted so sodium isn’t reliable.
What does a urine chloride less than 15 indicate?
Metabolic alkalosis due to volume loss; Gastric fluid loss or post-diuretic therapy.
What does a urine chloride more than 20 indicate?
Metabolic acidosis with some outside cause that has caused us to gain some fluid back after a volume loss; could be hyperaldosteronism, Cushing’s syndrome, steroids.
What are the most common causes of metabolic alkalosis?
Vomiting, diuretics, primary hyperaldosteronism.
