Acid base I

Question 1

what are the clinical decision making steps to assessing acid base disorders?

Answer 1

1. history
2. pH: acidemic or alkalemic?
3. metabolic or respiratory?
4. anion gap?
5. appropriate compensation?
6. if metabolic acidosis, is it a mixed disorder?
7. diagnosis?
8. treatment?

Question 2

what is the pH range compatible with life?

Answer 2

6.80 - 7.80

Question 3

can a respiratory acid base disorder be both alkalosis and acidosis?

Answer 3

no

Question 4

what is the range of normal blood pH?

Answer 4

7.35 - 7.45

Question 5

what is the conceptual cause of metabolic alkalosis?

Answer 5

increased serum HCO3-

Question 6

what maintains metabolic alkalosis?

Answer 6

condition resulting in inability to secrete HCO3- by the kidneys

Question 7

what value indicates a primary metabolic alkalosis?

Answer 7

over 40 mmol / L [HCO3-]

Question 8

what is the compensatory mechanism for metabolic alkalosis?

Answer 8

respiratory acidosis - hypoventilation, increased pCO2

Question 9

what are the etiologies of metabolic alkalosis?

Answer 9

• GI proton loss
• renal proton loss
• intracellular shift of hydrogen
• alkali administration
• contraction alkalosis

Question 10

what should be considered the normal value for bicarb?

Answer 10

25 mmol / L

Question 11

although contraction alkalosis can be caused by diuretics, it is maintained by ___________

Answer 11

hyperaldosteronism

Question 12

what is the mechanism for contraction alkalosis?

Answer 12

• diuretics trigger secretion of H+ and K+ with loss of volume
• to counteract this hypovolemia, aldosterone is released which promotes Na+/H2O/HCO3- and secretion of K+/H+

Question 13

what are two major reasons why metabolic alkalosis can be maintained?

Answer 13

• chloride depletion (also decreases bicarb secretion)

- hypokalemia

Question 14

which two drugs can cause renal hydrogen loss leading to metabolic alkalosis?

Answer 14

• loop diuretics

- thiazide diuretics

Question 15

what are the treatment options for metabolic alkalosis?

Answer 15

• correct underlying cause and maintainers

- correct electrolyte abnormalities (NaCl or KCl resuscitation)

Question 16

what are maintainers of metabolic alkalosis?

Answer 16

• hypovolemia
• hypokalemia
• reduced GFR
• chloride depletion
• aldosterone excess

Question 17

what drug interferes with bicarb reabsorption?

Answer 17

acetazolamide

Question 18

what value of [HCO3-] indicates a primary metabolic ACIDOSIS?

Answer 18

under 15 mmol/L

Question 19

what is the compensation for metabolic acidosis?

Answer 19

respiratory alkalosis - hyperventilation, decreased pCO2

Question 20

usually an increase in the anion gap is caused by an increase in the unmeasured _____________ (cations / anions)?

Answer 20

unmeasured anions

Question 21

what is the concept behind anion gap? what is its purpose?

Answer 21

• the total number of cations and anions must be equal to maintain neutrality
• however, the ions measured by the lab (Na, Cl, HCO3) are NOT equal
• purpose: differentiates different causes of metabolic acidosis (high vs normal / non-anion gap)

Question 22

what are the scenarios that lead to a normal anion gap metabolic acidosis?

Answer 22

1. loss of substantial amounts of measured anion HCO3-, leading to a hyperchloremic state
   - sum total of measured anions remains the SAME, and in turn the anion gap remains the same, but hyperchloremic
2. defective renal acidification resulting in failure to excrete normal quantities of metabolically produced acid
   - hyperchloremic state occurs because conjugate base is excreted as sodium salt and sodium chloride is retained

Question 23

what are the causes of high anion gap metabolic acidosis?

Answer 23

Methanol 
Uremia (chronic renal failure) 
Diabetic ketoacidosis (most common reason) 
Propylene glycol 
Infection / Iron / Isoniazid 
Lactic acidosis 
Ethylene glycol 
Salicylates (aspirin)

Question 24

diabetic ketoacidosis is a triad of:

Answer 24

• hyperglycemia
• high anion gap metabolic acidosis
• ketonemia

Question 25

what is the serum osmolal gap?

Answer 25

measured serum osmolal - calculated serum osmolal

Question 26

what are two common causes of an increased serum osmolal gap?

Answer 26

- methanol intoxication | - ethylene glycol intoxication

Question 27

what are the signs and symptoms of methanol toxicity?

Answer 27

- CNS / retinal injury - pancreatitis - high anion gap - increased serum osmolal gap

Question 28

ethylene glycol is metabolized to ______ and _________ are these measured or unmeasured compounds?

Answer 28

oxalate, hippurate (unmeasured anions)

Question 29

what are the signs and symptoms of ethylene glycol poisoning?

Answer 29

- neuro / cardiopulmonary collapse - calcium oxalate crystals in urine - high anion gap - increased serum osmolal gap

Question 30

what are the early symptoms of salicylate (aspirin) poisoning?

Answer 30

EARLY: - tinnitus - vertigo - nausea - vomiting - diarrhea LATE: - altered mental status - hyperpyrexia - noncardiac pulmonary edema - coma

Question 31

how do you characterize the acid-base progression in aspirin poisoning? what is the net effect?

Answer 31

- initially: respiratory alkalosis - later: high anion gap metabolic acidosis NET EFFECT: mixed disorder - primary respiratory alkalosis + primary metabolic acidosis

Question 32

what explains the early respiratory alkalosis in aspirin poisoning?

Answer 32

salicylates stimulate the respiratory center directly, resulting in an early fall in pCO2

Question 33

what explains the late high anion gap metabolic acidosis seen in aspirin poisoning?

Answer 33

accumulation of organic acids, including lactic acid and ketoacids

Question 34

what is the management for aspirin poisoning?

Answer 34

- GIVE BICARBONATE IMMEDIATELY | - activated charcoal if caught early

Question 35

what level of serum salicylate concentration is associated with increased morbidity and mortality? this is an absolute indication for what treatment?

Answer 35

- 100 mg/dL | - hemodialysis