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)
What is the first thing to figure out when correcting metabolic alkalosis
if the cause if from:
1. renal wasting
or
2. retention of chloride
How do you differentiate from renal wasting and retention of chloride in metabolic alkalosis?
Spot urine-chloride
Cl- urine <25mmol = Chloride responsive
Cl- urine >40mmol = chloride unresponsive
What is the correction for chloride responsive alkalosis?
fluids NaCl + KCl
What is the cause and correction for chloride unresponsive alkalosis
chloride wasting (hyperaldosteronism, bartter, gitelman) correct Mg, Ca, find source of increased aldosterone
How do you tell if there is respiratory compensation for metabolic alkalosis?
PCO2=0.7 X [HCO3] + 20 ±5
if pCO2 is above or below then there is primary respiratory alkalosis or acidosis present
How do you tell if there is metabolic compensation for respiratory acidosis?
acute compensation (2-5 days): +1 mmol [HCO3-] for each 10mmHg above 40mmHg chronic compensation L +5mmol [HCO3-] for each 10mmHg above 40mmHg
How do you tell if there is metabolic compensation for respiratory alkalosis
Acute = ↓ 2mmol/L for PCO2 decrease per 10mm Hg below 40 Chronic = ↓ 5mmol/L for PCO2 decrease per 10mm Hg below 40
