Acid Base Flashcards
What is the henderson hasselbach equation for Carbonic Acid
pH = 6.1 + log[HCO3/0.03(PaCO2)]
How does the body react to metabolic acidosis
1. instantaneous: ECF: bicarb ICF: bicarb and phosphates 2. Short term: tachypnea to blow off CO2 3. Long latency: renal compensation
How does renal compensation for Metabolic acidosis work?
PCT, TAL, DCT: Na-H exchange = excrete H+, carbonic anhydrase activity
CD:
alpha-intercalated cells = H+ pump
H-K exchange pumps
What do alpha-intercalated cells excrete and absorb?
excrete: H+
absorb: Bicarb
through the activity of Carbonic Anhydrase
How and where is H+ renally excreted (as what molecule)
Ammonia in mainly the PCT as a response to acidosis
Where is ammonia reabosored in the kidney and what happens to it?
ammonia is reabsorbed in the TAL then:
- excreted in the thin descending limb
- absorbed in CD and H+ is excreted by alpha intercalated cells
- reabsorbed and processed by liver
What is the renal response to alkalosis (and where)
reduction in PCT H+ excretion
Increased CD excretion of HCO3- (by PENDRIN in B-intercalated cells)
Pendrin = Cl-HCO-3 exchanger
Cl is reabsorbed, HCO3 is excreted
How do you calculate the Anion Gap? what is the normal Anion Gap?
Anion gap = [Na+] - [HCO3- + Cl-]
normal AG = 8-12 meq/L
What are the two types of Metabolic acidosis.
Anion gap and Non-anion gap
What is the pH, Bicarb, pCO2 criteria for a Non-anion gap acidosis
pH<7.38, Bicarb <22mm/L, Normal pCO2 = 40mmHg
occurs due to excess or reduced availability of K+ or Cl-
How do you interpret an Anion Gap? in presence of metabolic acidosis (if >12, if normal
If >12 = then there is an anion gap (extrinsic acid present = unmeasured anions)
if normal = increased H+ or loss of bicarb+
What is happening physiologically during a non-anion gap metabolic acidosis? and how is this compensated for?
increased of Cl- in the ECF is causing a compensatory loss of HCO3- = metabolic acidosis
kidneys will try to excrete H+ in the form of NH4+
How do you distinguish a renal and nonrenal cause of metabolic acidosis?
Normal kidney = will excrete NH4+
renal disease = impaired NH4+ excretion
ESTIMATED BY URINE OSMOLALITY GAP:
Renal cause>40 osmole gap>non-renal cause
What two things cause a non-Anion gap metabolic acidosis
- loss of bicarb (diarrhea, GI problems)
2. Renal Disease (Cant Excrete H+) from meds (lithium, topiramte, acetazolamide)
How do you estimate if there is respiratory compensation for a metabolic acidosis?
PaCO2 = 1.5 [HCO3] + 8 ± 3 (winter’s formula)
if pCO2 is above or below estimation - primary resp acidosis or alkalosis is present
What is the pH and HCO3- criteria for a metabolic alkalosis?
pH >7.42, [HCO3-] > 26mmol/L
What are the causes of metabolic alkalosis?
- ECF volume contraction (body keep Na in xchange for H and K)
- excess glucocorticoids/mineralocorticoids (increase bicarb resorption)
- Loss of H+ (vomiting, nasogastric suction)
- Depletion of ECF chloride ions
- Hypercapnia - chronic lung disease (CO2 retainer)