Acid Base. Large Group 2 -Barnes Flashcards
What is the difference between acidemia and acidosis?
acidemia=pH in the blood shows that it is acidic
acidosis=PROCESS of becoming acidic. can be acidotic and alkaline
How do you calculate anion gap? What is a normal anion gap?
AG=(Na+) - (CL- + HCO3-)
normal=12 +/-2
What is your expected anion gap? How can this be calculated?
albumin x 3=expected anion gap
What happens when you have an anion gap metabolic acidosis?
increasing anions in the system will cause a decrease in bicarbonate–> acidosis
What are the causes of anion gap metabolic acidosis?
MUD PILES
Methanol Uremia* DKA* Polyethylene glycol Iron Lactic acidosis* Ethanol, ethylene glycol Salicylates*
*=most common
What is a Delta Gap? Why do we check it?
Measured AG-Expected AG then add to measured HCO3-
24=concomitant metabolic alkalosis
we check this to see if there is another metabolic process along with the Anion gap metabolic acidosis
What equation do we use to check for compensation in metabolic acidosis?
winters formula
expected pCO2=1.5 x [HCO3-] +8 +/-2
What equation do we use to check for compensation in metabolic alkalosis?
Expected pCO2 = 0.7 [HCO3-] + 20 mmHg (range: +/- 5)
What can initiate metabolic alkalosis? (3)
- net loss of H+
- Net addition of HCO3-
- external loss of fluid containing Cl-
What is necessary to maintain a state of metabolic alkalosis? What are some examples? (4)
maintenance: something in the kidneys causing a retention of HCO3-:
1. Cl- depletion
2. K+ depletion
3. Hypercapnea
4. Rarely; primary disorders of specific ion channels
How can we tell if a pt is Chloride Responsive? What type of pts do we check for this in?
Chloride responsive: give Cl- and the condition resolves.
-if the urine Cl- is low (<15-20) suspect that the Cl- in the blood is also low and that the pt is chloride responsive
check for this in metabolic alkalosis pts (high HCO3- in the urine can be from low Cl- in the urine)
If a pt has Chloride Non-responsive Metabolic Alkalosis, what is the likely diagnosis?
Urine Chloride >20
most common= primary hyperaldosteronism (excess mineralocorticoid) (pt will have HTN) (also presents the same as licorice abuse)
-Urine K+ laxative abuse or severe K+ depletion
can also be impairment of Cl-linked Na+ transporters (Bartter Syndrome or Gitelman syndrome)
What is Barnes’ shortcut for compensation?
Bicarb and PCO2 should be 13-15 away from each other is PCO2 is what you expect
When do we evaluate a urinary anion gap? What is Urinary Anion Gap?
What does a negative vs positive UAG indicate?
NAGMA pts!!!
UAG=(Na + K+) -Cl-
negative UAG: extra-renal origin of the metabolic acidosis (negative value=large amount of unmeasured extra NH4+ in the urine (Cl- increases with increasing NH4+) –> kidneys are responding appropriately)
Positive UAG: renal origin of metabolic acidosis –> RTA
What is Bicarb Reclamation? Where does this primarily take place?
90% in the Proximal Tubule
requires a Na+ dependent secretion of H+ into the lumen where it will combine with filtered bicarb.
with CA in the lumen==> becomes H2O and CO2 which is taken back up into the cells
reacts with CA in cell–> breaks down into H+ (back into lumen) and HCO3- (reabsorbed in the basolateral membrane)
What is Bicarbonate Regeneration? Where does it take place?
throughout the renal tubule but the CCD is the final site of urinary acidification
H+ secreted into the urine and combines with NH3 or phosphate as buffers –> excreted
creates “new” bicarb
What affect will chronic metabolic acidosis have on total ammonia excretion?
chronic metabolic excretion==> much greater total ammonia excretion
What happens to a normal kidney in response to acidosis? What effect will this have on UAG?
increased excretion of NH4+ which will cause an increase in Cl- ions in the urine
this causes an negative value in the UAG because NH4+ is not measured in UAG–> only Cl- is
Where is the problem in Type II RTA?
Proximal tubules
the apical membrane Na+/H+ exchanger
Where is the problem in Type I RTA? What will result?
Distal tubule
CCD -alpha intercalated cells (problem with K+/H+ ATPase?)
get a build up of intracellular H+ ions –> NAGMA
A patient with NAGMA, a positive UAG, urine pH of 7.3, and K+ =3.2 most likely has: A. Distal RTA B. Proximal RTA C. Type IV RTA D. RTA of Renal Failure
A. Distal RTA
What labs can be used to distinguish distal vs proximal RTA? Why?
urinary pH (both will have low K+)
proximal=lower urinary pH because distal tubule can compensate
distal RTA=higher urinary pH because nothing to acidify the urine after it
What will Type IV RTA present with?
hyperkalemia
urine pH 15
aldosterone deficiency
associated with DM
