Acid-Base Disorders DSA and CIS Flashcards
What is normal arterial pH?
Intracellular?
arterial: 7.35 - 7.45
intracellular: 7.0 - 7.3
Bicarbonate buffer sys equation
Henderson-Hasselbach equation
How do the lungs affect bicarbonate buffering?
control concetnration of PCO2
incr respiration = incr CO2 blown off = incr pH
(the more PCO2, the lower the pH
What are the 4 kinds of acid-base disturbances?
metabolic acidosis = low serum bicarb
metabolic alkalosis = high serum bicarb
respiratory acidosis = high PCO2
respiratory alkalosis = low PCO2
What is normal anion gap metabolic acidosis also called?
hyperchloremic acidosis
What are the two types of metabolic alkalosis?
saline-responsive (hypovolemia) aka contraction alkalosis or chloride deficiency alkalosis
saline-non-responsive (euvolemia)
What is winter’s fomula and what is it used for?
PCO2 = 1.5[HCO3] + 8 +/- 2
used to calculate compensation in metabolic acidosis?
How do you calculate the compensation for metabolic alkalosis?
PCO2 will incr by 0.7 mmHg for each 1.0 mEq/L incr in HCO2 from normal
How do you calculate compensation for respiratory acidosis (acute and chronic)?
acute: HCO3 will incr by 1 mEq/L for every 10 mmHg incr in PCO2 from normal (40)
chronic: HCO3 will incr by 3.5 mEq/L for every 10 mmHg incr PCO2 from normal
How do you calculate the compensation for respiratory alkalosis (both acute and chronic)?
acute: HCO3 will decrease by 2 meq/L for every 10 mmHg decrease in PCO2 from normal (40)
chronic: HCO3 will decrease by 5 mEq/L for every 10 mmHg decrease in PCO2 from normal
How many acid-base disturbances can be present at once?
3 total
What are common cations in the body?
Na+, K+, Ca+, Mg+
protein, but not many
What are common anions in the body?
Cl-, HCO3-
Proteins (esp albumin)
HpO4-
SO4-
organic ions
What is an anion gap?
fabricated concept in clinical medicine
in the body cations and anions equal each other
What are the most prominent anions and cations?
Na+
Cl-
How do you calculate an anion gap?
Na+ - (HCO3 + Cl-)
normal = 12 +/- 2
Why does renal tubular acidosis or diarrhea result in NAGMA?
we do not know
thought that loss of HCO3 in these conditions along w/ its cation Na+ produces a volume contraction –> NaCl retention w/in the kidney
How does hypoalbuminemia affect the anion gap?
will falsely lower AG and thus must be corrected
for every 1 g/dL drop in albumin –> AG drops by 2.5 mEq/L
(the AG will actually be higher and they can have HAGMA that isn’t apparent at first)
What is normal serum albumin?
~3.5 g/dL
What is the equation for calculated serum osmolality and what is the normal range?
2(Na) + (glucose/18) + (BUN/2.8)
normal = 275 - 290 mosm/L
How do you calculate an osmolar gap and what is the normal range?
osmalar gap = measured serum osmolality - calculated serum osmolality
normal < 10 mosm/L
im osmolar gap > 10 mosm/L, suggestive of additional solutes to blood
What is calculating the osmolar gap useful for?
screening for alcohol ingestions, particularly in HAGMA cases
AG > 20, should be highly suspicious for alcohol ingestion
screening for ketoacidosis and lactic acidosis
What is the delta-delta gap and what is it useful for?
used in pts w/ HAGMA to determine if there is a coexistent NAGMA or metabolic alkalosis present
delta gap = calculated AG - normal AG (12)
delta HCO3 (expected) = normal HCO3 - delta gap
(if measured HCO3 is less than delta HCO3 –> NAGMA is also present)
What are the normal blood values for pH, bicarb, CO2, anion gap, and osmolality gap?
pH: 7.35 - 7.44
HCO3 = 24 mEq/L
PCO2 = 40 mmHg
Anion Gap = 12
osmolality gap = 10 mmol/L
What is the acronym to remember Ddxs for high anion gap metabolic acidosis?
GOLD MARK
Glycols (ethylene and propylene)
Oxoproline (Pyroglutamic acid; acetaminphen toxicity)
L-Lactic acidosis
D-Lactic acidosis (bacteria in colon metabolizing carbs; seen in short bowel syndromes)
Methanol
Aspirin
Renal Failure
Ketoacidosis
What is pyroglutamic acidosis?
seen when acetaminophen depletes glutathione –> get buildup of pyroglutamic acid
Dx: urinary organic acid screen
Tx: discontinue acetaminophen, IVF, N-acetylcysteine
What are the Ddxs of increased osmolar gap?
MEDIE
Methanol
Ehtanol
Diethylene glucol (mannitol)
Isopropyl Acohol (not assoc w/ metabolic acidosis)
Ethylene glycol
(also propylene glycol, ketoacidosis, and lactic acidosis (smaller increase in osmolar gap))
How are acidosis/alkalosis and serum potassium related?
acidosis assoc w/ hyperkalemia –> caused by shift of H+ out of cells for K+ so that cellular electroneutrality is maintained
(in acidosis, H+ enters cells and K+ exits)
alkalosis associated w/ hypokalemia
(in alkalosis, H+ ions exit cells and K+ enters)
What are the DDxs for normal anion gap metabolic acidosis?
DURHAAM
Diarrhea
Ureteral diversion or fistula
Renal tubular acidosis
Hyperalimentation (enteral nutrition or total parenteral nutrition)
Acetazolamide
Addision’s Dz
Miscellaneus (toluene toxicity - glu sniffing, pancreatic fistula, meds)
What is type 2 RTA?
proximal tubular
normally 80-90% of filtered HCO3 is reabsorbed in PT
in Proximal RTA, decr capacity to reabsorb bicarb –> bicarb loss in urine and low serum bicarb
eventually serum bicarb decreases to the point that kidney’s reabsorptive capacity not overwhelmed –> bicarb stabilizes, but at lower level
What do alpha intercalated cells in the DT and colelcting duct do?
Principle cells?
Alpha: H+/ATPase and H+/K+ - ATPase
principle: ENaCs create net - lumin –> favors H+ secretion
What is the most common cause of type 2 TRA in children?
cystinosis
What is fanconi syndrome most often due to?
most adults w/ it have a secondary cause like multiple myeloma
however, some pts have an isolated reanl defect resulting in fanconi syn
What are the clinical manifestations of Proximal RTA (type 2) and how do you diagnose it?
NAGMA with or w/out proximal tubular dysfunction
hypokalemia (mild compared to distal RTA)
Dx: urine pH can be high or low; if < 5.5, normal H+ secretion in distal nephron
urine anion gap can be positive or negative
What is urine anion gap?
used to differentiate renal from non-renal causes of NaGMA
marker of NH4Cl excretion = appropriate urinary acidification
UAG = (urine Na + Urine K+) - Urine chloride
if negative –> appropriate distal nephron urinary acidification
if positive –> distal nephron fcked up
What is type 1 renal tubular acidosis?
distal RTA
unable to acidify urine
decreased net H+ secretion in DCT
abnormally permeable distal tubule and CD allows H+ back into tubular cells
*amphotericin*
What are two significant causes of distal RTA?
sjogren’s syndrome
glue sniffing - toluene
What are the clinical manifestations of distal RTA and how do you diagnose it?
assoc w/ nephrolithiasis or nephrocalcinosis
Dx: unable to acidify urine pH < 5.5
hypokalemia, usually severe
UAG is positive
What is type 4 RTA?
hyperkalemic RTA
distal nephron dysfunction from impaired excretion of H+ and K+ –> NAGMA and hyperkalemia
What are the most common causes of hyperkalemic RTA (type 4)
deficiency of circulating aldosterone (DM, drugs)
aldosterone resistance in collecting ducts (interstitial renal dz, drugs)
either case leads to impaired Na reabsorption in principle cells –> decr luminal negativity –> impaired acidification bc lower driving force for H+ secretion
results in hyperkalemia
What are clinical manifestations of type 4 RTA and how do you dx it?
usually asymptomatic, NAGMA, hyperkalemia; most pts in 50s-70s w/ hx of DM or CKD
Dx: variable urine Ph, usually > 5.5; UAG is +
What are the 5 top causes of metabolic alkalosis?
hypokalemia (shift of H+ and K+)
vomiting or nasogastric tube suctioning (GI loss of HCl)
diuretics (thiazide and loop)
volume depletion
mineralocorticoid excess (appropriate and inappropriate)
What do beta-intercalated cells in the CD do?
mirror image of alpha-intercalated cell
generate bicarb and secrete bicarb into lumen in exchange for Cl-
(in contraction alkalosis, must replete Cl- to help w/ HCO3- secretion)
What causes repiratory alkalosis and acidosis?
alkalosis: anything that increases respiratory rate or tidal volume
acidosis: anthing that lowers RR or tidal volume, incr dead space, or worsens airway obstruction
What should be your sequence of evaluation in a possible acidosis or alkalosis case?
acidotic or alkalotic?
metabolic or respiratory?
anion gap?
osmolar gap?
appropriate compensation?
UAG normal?
How can a pulmonary embolus present (acidosis or alkalosis)?
can present as respiratory acidosis or alkalosis
if inadequate ventilator settings –> will not have high enough RR to blow of CO2 –> resp acidosis
What does serum K+ look like in each type of RTA?
type 1 and 2: HypOkalemia
(type 1: dysfunction in H+ ATPase –> secrete K+ instead)
Type 4: HypERkalemia
What type of RTA can be caused by heparin?
type 4
