Acid/Base Physiology Dr. Burchette

Question 1

Normal values: pH, pCO2, HCO3(-)

Answer 1

pH = 7.35 - 7.45

pCO2 = 35 - 45 mmHg
higher than 45 -> acidic
lower than 35 -> basic

HCO3(-) = 22 - 26 mM
higher than 26 -> basic
lower than 22 -> acidic

Question 2

How fast do lungs and kidneys respond to a change in pH?

Answer 2

-fast: lungs (respiratory)

-several days for kidney (metabolic)

Question 3

How are Acid/Base levels measured?

Answer 3

Blood gas (ABG)

-Brachial artery
-Radial artery
-Femoral artery
-Dorsalis pedis artery

Question 4

Blood gas is measured on which type of blood vessels?

Answer 4

Arteries

-PaCO2, PaO2

Question 5

Where is HCO3(-) reabsorbed?

Answer 5

-mostly absorbed (80%) in the proximal tubule

-Bicarbonate HCO3(-) is freely filtered in the glomerulus and should be 100% reabsorbed

Question 6

Which enzyme is required for HCO3(-) reabsorption?

Answer 6

Carbonic anhydrase
-creates carbonic acid H2CO3
-> degraded into HCO3(-) and H(+)

-it also converts H2CO3 to H2O and CO2 (in the lumen) -> CO2 moves back to the epithelial cell

Question 7

What are the ways the kidney maintains bicarbonate HCO3(-)?

Answer 7

-bicarbonate reabsorption/excretion
-building new HCO3-

Question 8

Which drug affects the bicarbonate reabsorption?

Answer 8

-Carbon anhydrase inhibitor (acetazolamide)
(also used in altitude sickness)

-by blocking the carbonic anhydrase
-H2CO3 in the lumen will not be broken but excreted

Question 9

Common causes of respiratory acidosis

Answer 9

-Reduced breathing (retaining CO2)
-COPD, opioid overdose -> Hypoventilation
-Ventilation/perfusion mismatch

-Symptoms: SOB, shallow/fast breaths, headache, AMS, tachycardia, arrhythmias, drowsiness

Question 9

Common causes of respiratory alkalosis

Answer 9

-Hyperventilation

-decrease in CO2

-Symptoms: dizziness, MS, blurred vision, impaired
concentration, diaphoresis, arrhythmias,
respiratory collapse

Question 10

Which state causes respiratory alkalosis at baseline?

Answer 10

Pregnancy due to a shift in hormones and breathing

Question 11

How are respiratory issues treated?

Answer 11

Ventilator
Slow or increase breathing

Question 12

Causes of metabolic acidosis

Answer 12

-base deficit in the blood or excess of acids other than CO2

-Diarrhea/high output intestinal fistula (base goes down)
-Renal failure (they can’t balance their buffer the acid)
-diabetic ketoacidosis (DKA)
-tissue hypoperfusion
-salicylates (acid)
-EtOh
-starvation (increase in acid)

Question 13

Symptoms of metabolic acidosis

Answer 13

-MS,
-lethargy
-coma
-warm/flushed skin
-arrhythmias,
Kussmaul’s respirations
-N/V

Question 14

Anion Gap

Answer 14

only determined in metabolic acidosis, helps determine the type of metabolic acidosis

-Normal < 12 mEq/L
-Na+ – (Cl- + HCO3-) = anion gap

if above 12 –> gapped acidosis (HABMA - high anion gap metabolic acidosis)

Question 15

Which diseases cause a gapped anionic acidosis?

Answer 15

-MU
Methanol
Uremia
Diabetic ketoacidosis (DKA)
Paracetamol/Propylene glycol
Isoniazid, Iron, Inhaled toxins (CO)
Lactic acidosis
Ethylene glycol, ethanol (EtOH ketoacidosis)
Salicylates, solvents, starvation

Question 16

How is metabolic acidosis treated?

Answer 16

with sodium bicarbonate IV or tablets
-in CKD or ESRD -> dialysis

Question 17

How does the drug Tromethamine (THRAM) work?

Answer 17

-it is a proton acceptor (acid acceptor)
- so that H(+) doesn’t bind to HCO3(-) and HCO3(-) can act freely

-it is Na+ free (Na+ may increase BP)
-also acts as a diuretic
-no evidence of being more effective than sodium bicarbonate

Question 18

Causes of metabolic alkalosis

Answer 18

-excess of base in the blood or loss of acid other than CO2

-Antacids
-Bicarbonates
-lactate in dialysis (excess of base)
-Vomiting
-GI suction (stomach pumping, loss of acid)
-hypochloremia
-diuretics (contraction alkalosis)
-increased aldosterone (loss of acid)

Question 19

GI driven alkalosis/acidosis

Answer 19

Above: acid -> suction causes loss of acid -> metabolic alkalosis

Below: base -> diarrhea causes loss of base -> metabolic acidosis

Question 20

How do diuretics cause metabolic alkalosis?

Answer 20

-over diuresis (f.e. Lasix)
-loss of fluids -> activation of aldesterone -> Na+ and water retention -> taking away Na+ from the tubules results in an increase in HCO3(-) -> ALKALOSIS

-give fluids

Question 21

How to treat patients with metabolic alkalosis by producing too much aldosterone?

Answer 21

-aldosterone receptors antagonist
-Spironolactone, eplerenone, amiloride, triamterene

Question 22

How to treat metabolic alkalosis in patients with heart failure?

Answer 22

-these patients cant be treated with fluids (bc the heart is not working well, causing edema)

-carbonic anhydrase inhibitor
-acetazolamide (give for 24 to 48h and reassess to avoid overdosing -> metabolic acidosis)