Acid-Base

Question 1

Steps in determining the cause

Answer 1

1. Acidosis or alkalosis
2. Respiratory or metabolic
3. Pure or mixed

Question 2

How to know if an acid-base issue is respiratory or metabolic

Answer 2

• If pH and CO2 go SAME DIRECTION = METABOLIC

- If pH and CO2 go OPPOSITE DIRECTION = RESPIRATORY

Question 3

Respiratory problem:

Telling if it is pure or mixed

Answer 3

Pure - ∆pH = 0.08 per ∆10 paCO2 ± .02 (OPPOSITE DIRECTION)

Higher? – Metabolic alkalosis also
Lower? – Metabolic acidosis also

Question 4

Metabolic acidosis:

Telling if it is pure or mixed

Answer 4

Pure - CO2 is decreased

Mixed - CO2 is normal/high

Question 5

Telling compensation for a metabolic acidosis

Answer 5

pCO2 = 1.5(HCO3) + 8 ± 2

Question 6

Telling compensation for a metabolic alkalosis

Answer 6

∆pCO2 = 0.7 per ∆1 HCO3 (SAME DIRECTION)

Question 7

Anion gap equation

Answer 7

Na - Cl - HCO3

Question 8

Causes of high anion gap met. acidosis

Answer 8

Methanol
Uremia
Diabetic ketoacidosis
Paraldehyde
INH
Lactic acidosis
Ethanol, ethylene glycol
Salicylates

Question 9

3 general categories/causes of metabolic acidosis

Answer 9

1. HCO3 loss (GI, renal)
2. H+ loading (DKA, lactic acid)
3. Less H+ excretion (uremia, RTA)

Question 10

Causes of lactic acidosis

Answer 10

A = hypoxia (shock, anemia, HF, CO)
B1 = systemic Dz (DM, liver, sepsis, seizure)
B2 = drugs/toxins (EtOH, methanol, Eth. glyc)
B3 = cong. metab. error (G6PD def.)

Question 11

Tests for cause of pre-renal acidosis

Answer 11

EKG, lactic acid level, cardiac enzymes (HF, MI)

Question 12

Treatment for metabolic acidosis

Answer 12

Oxygen, loop diuretic (H+ secretion), fluid restriction (edema), HCO3, ACEI (cautious)

Question 13

Causes of normal anion gap (hyperchloremic) metabolic acidosis

Answer 13

Hyperalimentation
Addison's, acetazolamide (HCO3 loss)
RTA (low HCO3, high H+)
Diarrhea (low HCO3, low K)
Ureteral diversion
Pancreatic fistula (low HCO3, low K)
Spironolactone (H+ retention)

Question 14

Types of RTA

Answer 14

Proximal = Increased HCO3 excretion
- Myeloma, metal poisoning, Wilson’s
Distal = Decreased H+ secretion
- SLE, Sjogren’s, Toluene

Question 15

Causes of metabolic alkalosis

Answer 15

Contraction (volume loss -> RAAS -> H+ secretion)
Licorice
Endocrine 
Vomiting (loss of acid)
Excess base (increased H+ excretion)
Refeeding
Post hypercapnia
Diuretics (increased H+ secretion)

Question 16

Causes of chlorine LOSS (+ reabsorbed or not)

Answer 16

• Vomiting - will be reabsorbed
• N/G suction - will be reabsorbed)
• Diuretics - will be reabsorbed
• Endocrine - will NOT be reabsorbed
• Severe hypokalemia - will NOT be reabsorbed

Question 17

Drug to give in case of vomiting –> contraction alkalosis

Answer 17

Spironolactone (for excess aldosterone due to volume depletion)

Question 18

Weakness –> potential causes?

Answer 18

• Hypothyroid

- Electolyte imbalance (low Na, K, Mg, Ca)

Question 19

Hypokalemia on EKG

Answer 19

Flattened T wave –> ST depression (severe)

Question 20

Hyperkalemia on EKG

Answer 20

Elevated T wave –> QRS spacing (severe)

Question 21

HTN + hypokalemia + metabolic alkalosis = ?

Another clue?

Answer 21

Hyperaldosteronism (Conn’s disease)

Doesn’t respond to saline/fluids

Question 22

Causes of respiratory acidosis

Answer 22

Anything causing HYPOVENTILATION

- Drugs, CVA, obstruction, COPD, pneumonia, pulmonary edema

Question 23

Causes of respiratory alkalosis

Answer 23

Anything that causes HYPERVENTILATION:

CNS disease
Hypoxia
Anxiety
Mech. ventilation
Progesterone
Salicylates, sepsis

Question 24

Sepsis can cause what acid/base problems?

Answer 24

Lactic (metabolic) acidosis, respiratory alkalosis

Question 25

Bartter’s syndrome

Answer 25

TAL electrolyte transporter defect

• Polyuria, polydipsia
• Metabolic acidosis
• Hypokalemia, hypochloremia
• Nephrolithiasis (hypercalciuria)
• Hyper-renin-emia

Question 26

Calculating serum osmolality

Answer 26

2Na + BUN/2.8 + Glc/18