Module 5: Section 4

Question 1

what are the 2 rules when examining acid-base imbalances before compensation takes place

Answer 1

1) change in pH
2) change in [HCO3-]:[CO2] ratio

Question 2

Rule 1: change in pH

Answer 2

• caused by respiratory system
• change in [CO2] causes change in carbonic acid generated H+
• a change in pH from metabolism will have abnormal [HCO3-]
  – causes inequality in amount of HCO3- available and amount of H+ generated from non-carbonic acid sources

Question 3

rule 2: change in [HCO3-]:[CO2] ratio

Answer 3

• when the ratio falls below 20:1 it will cause acidosis (pH <7.4)
• when ratio is above 20:1 it will cause alkalosis (pH>7.4)

Question 4

respiratory acidosis

Answer 4

• occurs when buildup of CO2 in plasma
• causes [HCO3-]:[CO2] ratio to go below normal
• caused by hypoventilation (less than normal amount of CO2 removed thru lungs)
• can occur w/ emphysema, chronic bronchitis, asthma, sever pneumonia and metabolic acidosis

Question 5

uncompensated respiratory acidosis

Answer 5

• increase in CO2 conc
• causes formtation of H+ and HCO3-
• H+ causes the acidosis but little change in HCO3- conc change

Question 6

Compensated respiratory acidosis

Answer 6

• to compensate , chemical buffers immediately start taking up the extra H+ and kidneys secrete more H+ which reabsorbing and secreting more HCO3-
• will continue until HCO3- conc increases to the 20:1 ratio and pH= 7.4
• respiratory tissue can’t help because they caused the issue

Question 7

uncompensated respiratory alkalosis

Answer 7

• the decrease in CO2 conc causes increase in [HCO3-]:[CO2] ratio
  – since little change in HCO3- conc
• results in increased pH

Question 8

compensated respiratory alkalosis

Answer 8

• chemical buffers will release H+ and respiratory system decreases ventilation
• if persists fro a few days, kidneys will compensate by decreasing H+ secretions and increase HCO3- secretion
  – once fully compensated the ratio will be 20:1 again

Question 9

metabolic acidosis (non-respiratory acidosis)

Answer 9

anything that causes acidosis besides that due to excess CO2 and is always characterized by decrease in HCO3- conc and normal CO2 conc
- can be caused by excessive loss of HCO3- or buildup of non-carbonic acids (which also decrease HCO3- conc bc of buffering)

Question 10

how do we determine the cause of metabolic acidosis

Answer 10

measure the anion gap

Question 11

what is the plasma normally?

Answer 11

electro-neutral
- #cations = #anions

Question 12

anion gap calculation

Answer 12

([Na+] + [K+]) - ([Cl-] + [HCO3-]) = anion gap

normally shortened to…
[Na+] - ([Cl-] + [HCO3-]) = anion gap

Question 13

what does it mean to have a low anion gap

Answer 13

• <8 mEq/L
• uncommon
• generally results from loss of plasma albumin
  – eg draining a hemorrhage

Question 14

what does it mean to have a normal anion gap

Answer 14

– 8-16 mEq/L
- means a loss of HCO3-
- can be caused by diarrhea and some renal diseases
- generally a compensatory increase in Cl- conc. to conserve electrical neutrality

Question 15

what does it mean to have a high anion gap

Answer 15

• > 16 mEq/L
• indicates metabolic acidosis
• caused by increased in unmeasured anions
  – which causes decrease in HCO3- conc since its used for buffering the acids

Question 16

causes of metabolic acidosis

Answer 16

• severe diarrhea
• diabetes mellitus
• strenuous exercise
• uraemic acidosis

Question 17

causes of metabolic acidosis: severe diarrhea

Answer 17

• HCO3- will be eliminated before it can be reabsorbed
  – causes from in HCO3- conc
  – decreasing buffer capacity of plasma and causing more bicarbonate to dissociate and release H+

Question 18

causes of metabolic acidosis: diabetes mellitus

Answer 18

• w/ out insulin, glucose doesn’t enter most cells so they revert to fat metabolism to generate ATP
  – causes decrease in keto acids which raises anion gap

Question 19

causes of metabolic acidosis: strenuous exercise

Answer 19

• when muscles resort to anaerobic metabolism, excess lactate is produced which raises plasma H+
• lactic acid will also raise anion gap

Question 20

causes of metabolic acidosis: Uraemic acidosis

Answer 20

• uraemia = severe renal failure
• w/ decreased renal function, kidneys can’t excrete excess H+ from the metabolism so H+ conc increases
• a loss of HCO3- also occurs causing increased anion gap

Question 21

Uncompensated metabolic acidosis

Answer 21

• decreased HCO3- conc and normal CO2 conc
• the decrease is caused by excessive loss of HCO3- OR buildup of non carbonic acids which also decreases its conc bc of buffering

Question 22

compensated metabolic acidosis

Answer 22

• compensation can occur by buffers taking up extra H+, the lungs blowing off extra CO2, and kidneys secreting more H+ and conserving HCO3-
• someone with ureamic acidosis cannot fully compensate due to decreased kidney function and that the respiratory system can only do so much

Question 23

what are the 2 primary causes of metabolic alkalosis?

Answer 23

1) vomiting
2) ingestion of alkaline drugs

Question 24

metabolic alkilosis cause: vomiting

Answer 24

when vomiting there’s a loss of stomach H+ meaning it can’t be reabsorbed so plasma pH increases and HCO3- conc stays high

Question 25

metabolic alkilosis cause: ingestion of alkaline drugs

Answer 25

- the drugs often contain high amounts of HCO3- and excess HCO3- HCO3- is absorbed into digestive tract -- raises HCO3- conc and decreases plasma H+ by binding to it

Question 26

Uncompensated metabolic alkalosis

Answer 26

- theres an increase in HCO3- conc in the ratio

Question 27

compensated metabolic alkalosis

Answer 27

- to compensate, chemical buffer systems immediatly liberate H+ - ventilation reduces to raise plasma CO2 - if persists for several days the kidneys decrease H+ secretion and increase HCO3- secretion - when fully compensated both HCO3- conc and CO2 conc are above normal but ratio is still 20:1