Acid/base Disorders Flashcards
how do you create a proportionality for acid with HCO3- and CO2?
pH=HCO3-/CO2
just remember ABCD
Acidity=Bicarb/Carbon Dioxide
or just remember ROME:
Respiratory Opposite Metabolic Equal. When CO2 goes down, pH goes up, when bicarb goes down, pH does down.
What are the four primary acid/base disorders? what are they caused by?
metabolic acidosis
metabolic alkalosis
respiratory acidosis
respiratory alkalosis
metabolic means that HCO3-has changed; respiratory means that CO2 has changed.
compensation is always in the _____ direction as the primary change.
same
if primary change is that CO2 goes up, then bicarb goes up also to compensate and try to bring pH to normal level. If there is no compensation, an acid/base disorder is said to be simple.
how do we calculate respiratory compensation for metabolic acidosis/alkalosis?
metabolic acidosis:
deltaPCO2=(1.0 to 1.5) x deltaHCO3-
the fomulas very so she gave us a range. I think that 1.5 is most common.
metabolic alkalosis:
deltaPCO2=0.7 x deltaHCO3-
how do we calculate metabolic compensation for respiratory acidosis/alkalosis?
respiratory alkalosis: -acute: deltaHCO3-= inc. 1:10 ratio with PCO2 -chronic: deltaHCO3-= inc. 4:10 ratio with PCO2
respiratory alkalosis: -acute: deltaHCO3-= dec. 2:10 ratio with PCO2 -chronic: deltaHCO3-= dec. 4:10 ratio with PCO2
so if the patient is alkalotic and bicarb is up by 4 and the PCO2 is up by 10 then its chronic respiratory alkalosis.
metabolic (kidney; bicarb) compensation kicks in during respiratory disorders after about ______ (time).
3-5 days.
Note: renal compensation is what separates acute from chronic respiratory disorders.
What does this patient have?
c/o Shortness of breath, chest pain
Wheezing on exam
pH=7.5; PCO2= 20; HCO3= 20; PaO2=80
(normal: pH: 7.4; PCO2: 40; HCO3 24)
respiratory alkalosis. Acute compensation
What does this patient have:
c/o Shortness of breath, chest pain
Wheezing
pH=7.3; PCO2= 50; HCO3= 25; PaO2=58
normal: pH: 7.4; PCO2: 40; HCO3 24
respiratory acidosis. Acute compensation
In vomiting, which of the 4 disorders we’ve been talking about would you expect?
metabolic alkalosis. extrarenal loss of H+. Causes an inc. conc. of bicarb.
With mineralocorticoid or diuretic in excess, which of the 4 disorders we’ve been talking about would you expect?
metabolic alkalosis. mineralocorticoids (like aldosterone) act at the hydrogen ion ATPase pump. Every time you secrete H+ here you reabsorb bicarb which then enters the blood and causes alkalosis.
both diuretics and mineralocorticoids make kidney get rid of H+.
what things are typically associated with maintaining metabolic alkalosis?
- excess mineralocorticoid activity
- hypovolemia (aldosterone is released to hold on to salt and water which prevents excretion of bicarb.
How do you tell if the met. alkalosis is due to hypovolemia or something else?
If it is whats the treatment?
urine chloride test.
If hypovolemic, Cl will be low bc aldosterone is active which holds onto Na and water and Cl will hold on to Na. If Cl is low then you know that Na and Cl are being reabsorbed due to aldosterone action.
give NaCl to fix it.
what does this patient have? What would you give?
July 4th picnic, vomiting x 24 hrs, BP 90/40, HR125
c/o dizziness, nausea, can’t eat/drink
pH 7.5; PCO2: 50; HCO3-: 34 (nl: 7.4 / 40 / 24)
Urine Na: 25; Urine Cl: 9
normal urine chloride is 20.
metabolic alkalosis with appropriate respiratory compensationqq
urine Cl
how does the nephron handle the daily acid load?
PCT: reasorbs HCO3-
DT (collecting duct): secretes H+, makes HCO3-, acidifies urine, excretes daily acid load (notice how those four things are all the same really).
If there was something wrong with the PCT, which of the four disorders would you expect?
metabolic acidosis. PCT absorbs bicarb. if it is damaged then you can’t absorb bicarb and get acidotic. This is called a proximal RTA (renal tubular acidosis).
the distal tubule excretes H+. What options does H+ have once excreted?
- Can be free (H+)
- bound up in titratable acids (H2PO4-)
- Bound up in NH4+
how do we detect NH4+? how is this calculated?
The urine anion gap.
NH4+ + Na + K + Cl = urine anion gap.
The idea is that extra H+ gets excreted as NH4+ so that if H+ rises, then NH4+ will rise also. If NH4+ rises, then Cl rises to balance the positive charge. This is normal kidney fxn. Then when you sum Na, K and Cl, you will get a negative number. If you get a positive number then the kidney is not doing what its supposed to do bc chloride is not rising.
In conditions of metabolic acidosis: if positive urine ion gap= problem in kidney
How do we characterize a distal RTA?
failure to secrete H+ and generate bicarbonate. Thus, can’t bind to NH3 and so we see a positive urine anion gap.
metabolic acidosis.
metabolic acidosis is really characterized by ______. This can occur through what two ways?
loss of bicarb.
- Renal- RTA, urine anion gap is positive (kidneys are not working ok)
- GI- diarrhea, fistulas, etc… urine anion gap is negative (kidneys are working ok)
What is the serum anion gap? How do we calculate it? What’s a normal number?
different from the urine anion gap. This is a way to measure loss of bicarb in the serum. Any gap is just measuring something that’s not there.
Na – (HCO3- + Cl-) = 9±3
For metabolic acidosis what results would we expect for serum anion gap and urine anion gap in metabolic acidosis with:
- Renal loss of bicarb
- GI loss of bicarb
serum anion gap stays the same in both cases because as bicarb is lost, Cl- goes up (see formula on previous card).
Urine anion gap:
renal loss of bicarb: + UAG
GI loss of bicarb: - UAG
what does this patient have:
4th of July picnic, diarrhea for 3 days
pH: 7.2; PCO2: 26; HCO3- : 10
Serum Na: 140; Cl: 120; HCO3- : 10
Urine Na: 10; Urine K: 10; Urine Cl: 40
metabolic acidosis.
if its from loss of bicarb the serum Cl will go up. This is a normal serum anion gap metabolic acidosis so its due to bicarb loss.
There is a negative urine anion gap ((10 + 10) - 40)= -20. So this is due to GI loss of bicarb and the kidneys are working fine.
CO2 has gone down a little to compensate so that is good.
So this is a non-anion gap metabolic acidosis with appropriate respiratory compensation.
metabolic acidosis is typically caused by loss of bicarb (from GI or kidney). But it can also be caused by_______. This results in a _______.
- addition of acid.
- gap acidosis (as opposed to non-anion gap acidosis).
Serum anion gap will not be normal in this case bc bicarb is getting consumed by acid and Cl does not go up.
What H+ anions can be added?
KARL
Ketones
Aspirin and other toxins/ingestions
Renal failure
Lactic acid (most common one in the hospital)
if urine chloride is low its _____ responsive, if not then its not responsive.
chloride saline
Give a quick summary of metabolic acidosis.
its either anion gap (abnormal serum anion gap measurement) or non-anion gap (normal serum anion gap measurement)
non-anion gap is either renal loss of bicarb (+ UAG) or GI loss of bicarb (-UAG)
anion gap is due to the addition of acid.
