Lect 11

Question 1

What are the three lines of defense against acid/base disturbances

Answer 1

• buffers
  
  • mainly HCO3-/H2CO3; very fast
• respiratory compensation
  
  • adjusts CO2 levels
  • very fast but incomplete
• renal compensation
  
  • adjusts HCO3- levels
  • slow but potent

Question 2

which compensation is always active when primary problem is metabolic

Answer 2

respiratory compensation

Question 3

which compensation will compensate for respiratory problems and metabolic problems if they do not involve the kidney

Answer 3

reanl compensation

Question 4

Problem

• pH= 7.52
• HCO3- = 22
• PCO2 = 28

Answer 4

1. alkalosis
2. there is a respiratory component: (PCO2 <35)
3. expected HCO3- = 22 (since PCO2 is 12 mmHg below normal which will depress HCO3- by 2 due to mass action)
4. actual HCO3- = 22, so there is no renal compensation
5. this is an uncompensated (pure) respiratory alkalosis

Question 5

Problem

• pH = 7.43
• HCO3- = 18
• PCO2 = 28

Answer 5

1. normal pH
2. primary disturbance is respiratory
3. expect HCO3- = 22, but it = 18; therefore, 4 was removed by kidneys
4. completely componsated respiratory alkalosis

Question 6

problem

• pH=7.25
• HCO3- = 12
• PCO2 = 28

Answer 6

• pH = acidosis
• expected HCO3- = 22, but it =12; therefore must be a primary metabolic acidosis that reduced HCO3- by 10
• partly compensated metabolic acidosis

Question 7

Problem

• pH = 7.30
• HCO3- = 25
• PCO2 = 52

Answer 7

1. acidosis
2. there is a respiratory acidosis
3. expected HCO3- = 25, which it is
4. uncompensated (pure) respiratory acidosis

Question 8

H+ loss or HCO3- gain is consistent with

Answer 8

metabolic alkalosis

Question 9

Hyperaldosteronism and ECF volume contraction can lead to what condition

Answer 9

• metabolic alkalosis

Question 10

how can ECF volume contraction due to vomiting or extensive use of diuretics maintain metabolic alkalosis?

Answer 10

• increase in renin-angiotensin II-aldosterone system
  
  • angiotensin II stimulates Na+-H+ antiporter and HCO3- reabsorption
  • aldosterone stimulates secretion of H+ (H+-ATPase) from type A intercalated cells and K+ from principle cells

Question 11

metabolic alkalsosis is often linked with what

Answer 11

hypokalemia

• volume contraction stimulates aldosterone which intensifies both alkalosis and hypokalemia

Question 12

hypokalemia has what effect on H+ secretion

Answer 12

• stimulates H+ secretion by type A intercalated cells (H+/K+ ATPase) and can increase NH4+ secretion, both intensify alkalosis

Question 13

metabolic alkalsos can present with hypochloremia. why?

Answer 13

• due to loss in gastric fluids or urine (diuretics)
• without Cl- available for co-transport with Na+, the collecting duct lumen develops a more negative potential with respect to the cytoplasms which facilitates the excretion of K+ and H+

Question 14

how is metabolic alkalosis treated

Answer 14

• repletion of Cl- deficit with saline (NaCl or KCl)
  
  • corrects saline-responsive forms
  • will adjust the RAAS system
  • Cl- transport with Na+ reduces negativity of CD lumen, H+ and K+ loss reduced
  • result in excretion of bicarbonate

Question 15

aldosterone excess (secreting tumor) is an example of saline-resistant metabolic alkalosis. What is the treatment

Answer 15

• ECF volume is increased, and [Cl-] is okay
• administering saline does not help as patient is already volume expanded
• excess aldosterone increases H+ secretion and Na+ reabsorption
• treatment: remove tumor or aldosterone antagonist (spironolactone)

Question 16

a gain of H+ or loss of HCO3- causes

Answer 16

metabolic acidosis

Question 17

what are the three types of metabolic acidosis from diminished tubular H+ secretion

Answer 17

1. type I (distal)
   
   • H+-ATPase activity is reduced
2. type II (proximal)
   
   • Na+-H+ antiporter is reduced
3. type IV
   
   • reduced formation of NH4+
     
     • often due to hyperkalemia secondary to aldosterone deficiency

Question 18

what is a anion gap? what is the normal value?

Answer 18

• in the body, the concentration of anions must equal the concentration of cations
  
  • major anions: Cl = 100; HCO3- = 24; total = 124
  • major cation: Na+ =140
• anion gap = [Na+] -([Cl-] +[HCO3-])
  
  • normal gap = 8-16

Question 19

the anion gap often increases in what state? why?

Answer 19

• increases in acidosis where there is an excess of other non-volatile (fixed) acids
  
  • ​AG is often nml is acidosis due to simple bicarb loss due to Cl- increase
• fixed acids liberate H+ which is buffered by HCO3- w/o changing Cl- levels, this increases the anion gap
• **anions associated with these acids (lactate, oxalate) take the place of HCO3-; so Cl- levels do not change

Question 20

name some clinical causes of increased anion gap

Answer 20

• lactic acidosis: due to lactic acid
• ketoacidosis: acetoacetic acid
• renal failure: accumulation of phosphoric, sulfuric acid
• salicylate poisoning

Question 21

high altitude, anxiety, and hypoxemia can cause what state

Answer 21

• respiratory alkalosis
• due to decrease in PaCO2 via increases alveolar ventilation

Question 22

impairment of central respiratory regulation, chest wall dysfunction, impaired airway mechanisms can cause what state

Answer 22

• respiratory acidosis
• due to impaired pulmonary excretion of CO2