Acid Base Disorders Flashcards
If serum Cl is low with respect to Na, what does that suggest?
metabolic alkalosis
chronic respiratory acidosis
If serum Cl is high with respect to Na, what does that suggest?
normal gap metabolic acidosis
chronic respiratory alkalosis
When will an increase in the anion gap occur?
increase in unmeasured anions
decrease in unmeasured cations
What is the most common cause of an increased anion gap?
metabolic acidosis from addition of non-Cl acid
What is the pathophysiology of an increased anion gap to due addition of a non-Cl acid?
HX combines with sodium bicarb and generates more NaX and H2CO3 - converted to CO2 and water and blown out
sodium bicarb has been replaced by NaX
What is the pathophysiology of a normal gap acidosis?
if you add more NaCl - sodium bicarb replaced by NaCl - removal of sodium bicarb causes water diuresis which leads to higher Cl concentration
In general, what will cause a normal gap acidosis?
addition of HCl
removal of sodium bicarb
Why is it important to always calculate the anion gap?
it may be the only indication of a metabolic acidosis
What are the five causes of a normal anion gap metabolic acidosis?
dilution with NaCl (saline) admin of Cl containing acid chronic ketoacidosis GI loss of bicarb: diarrhea, fistulae (most common) renal tubular acidosis (by exclusion)
How does dilution with NaCl cause a normal anion gap acidosis?
dilutes bicarb and CO2 but lungs return CO2 to normal quickly
What are the three types of renal tubular acidosis?
Type 1 - hypokalemic distal RTA - CD can’t acidify urine
Type 2 - proximal RTA - can’t reclaim bicarb
Type 4 - Hyperkalemic distal RTA - CCD can’t secrete H and K
How can the urinary acid excretion distinguish between extra renal and renal acidosis?
patients with extra renal have increased rates of renal acid excretion (>30-60)
renal have decreased rates of acid excretion
How does urinary ammonium help distinguish different types of normal gap acidosis?
elevated in metabolic acidosis of extrarenal origin
normal to decreased in RTA
How can urinary ammonium be estimated?
calculate urinary anion gap (UAG)
positive value indicates low rates of ammonium excretion and RTA
What are the causes of anion gap acidosis?
lactic acidosis
ketoacidosis (more acute than normal gap)
renal failure - more advanced CKD = uremic acidosis
overdoses
What can cause lactic acidosis?
circulatory collapse anemia hypoxemia metabolic blockade seizures
What can cause ketoacidosis?
diabetic
starvation
alcoholic
What can cause anion gap acidosis from overdoses and what clinical manifestations would be present?
methanol - formic acid causes visual impairment and hemodynmic instability
ethylene glycol - calcium oxalate crystals in urine
salicylates - tinnitus and respiratory alkalosis
first two also increase osmolar gap
What is the approach to a patient with increased anion gap metabolic acidosis?
aggressive
measurement of BUN and creatinine tells if due to renal failure
certain clinical findings can indicate overdose
measurement of blood lactate or ketoacids in plasma and urine
How can you tell if measured bicarb is equal to predicted bicarb?
bicarb should decrease the SAME amount of excess anion gap
What two things does the generation of metabolic alkalosis require?
generation of new bicarb
increased ability of kidney to reclaim filtered bicarb
generation can be renal or extrarenal
How is metabolic alkalosis maintained?
decreased EABV
K depletion: decreased GFR lowers filtered bicarb, stimulates proximal tube H secretion, increased ammonia synthesis, inhibits aldo release
increased aldo + distal delivery of Na and volume
What are the main mechanisms of renal generation of metabolic alkalosis?
increased distal Na delivery
mineralocorticoid excess
K deficiency
What is post-hypercapneic alkalosis?
chronic respiratory acidosis causes compensatory metabolic alkalosis
pCO2 suddenly corrected
What can generate metabolic alkalosis and what can maintain it?
exogenous admin of base, GI acid loss and renal acid loss
only kidney can maintain
What is the approach to the patient with metabolic alkalosis?
if maintenance due to contracted EABV - will respond to expansion with saline
urinary Cl 20 suggests maintenance by other mechanisms
How can you tell the difference between Barter’s and Gitelman’s clinically?
Barters has high urinary Ca
Gitelmans has low urinary Ca
What are the three causes of primary respiratory acidosis?
RARE
severe lung disease
CNS depression
Neuromuscular disease
What are common causes of primary respiratory alkalosis?
anxiety liver disease sepsis salicylate ingestion high progesterone levels (pregnancy)
