Module 5 Section 4

Question 1

acid-base disorders

Answer 1

• any change in [H+] is directly related to the ratio of [HCO3-] to [CO2]
• this ratio is normally 20:1, and that according to the henderson-hasselbalch equation, this ratio should result in a pH of 7.4
• determining the concentration of HCO3- and CO2 provides much more information on the source of the acid-base imbalance than simply calculating the conc of H+ within a solution

Question 2

first rule when examining acid-base imbalances

Answer 2

• a change in pH caused by the respiratory system will have an abnormal [CO2], which in turn causes a change in carbonic acid-generated H+
• a change in pH caused from metabolism will have an abnormal [HCO3-], resulting from an inquality in the amount of HCO3- available and the amount of H+ generated from non-carbonic acid sources that the HCO3- must buffer

Question 3

second rule when examining acid-base imbalances

Answer 3

a change in [HCO3-]:[CO2] ratio
- when it falls below 20:1 it will cause acidosis as the pH will be less tha 7.4
- when the ratio rises above 20:1 this will cause alkalosis as the pH will be greater than 7.4

Question 4

respiratory acidosis

Answer 4

• occurs when there is a buildup of CO2 in the plasma, whihc causes the [HCO3-]:[CO2] ratio to be below 20:1
• it is caused when there is hypoventilation and less than normal amounts of CO2 are removed through the lungs
• such situations can occur with emphysema, chronic bronchitis, asthma, sever pneumonia and metabolic acidosis

Question 5

uncompensated respiratory acidosis

Answer 5

• there is an increase in [CO2]
• this leads to the formation of H+ and HCO3-
• the H+ will lead to acidosis yet there is little change in the [HCO3-]
• while this seems counterintuitive, the concentration of [HCO3-] is normally 600000 times greater than [H+] so even a modest increase in [CO2] can lead to acidosis but the rise in HCO3- is negligible compared to its plasma concnetration

Question 6

compensated respiratory acidosis

Answer 6

• the chemical buffers immediately start taking up the extra H+ and the kidneys secrete more H+ while both reabsorbing HCO3= and generating new HCO3-
• even though CO2 may remain high, the body will continue these compensations until [HCO3-] elevates enough to restore the ratio to 20:1 and bring the pH back to 7.4
• the respiratory system cannot play a role in the compensation as it is a respiratory issue that caused it in the first place

Question 7

respiratory alkalosis

Answer 7

• occurs when there is an increase in ventilation that causes the [CO2] in the plasma to decrease below normal
• examples of what can cause this are fever, anxiety, and severe infections

Question 8

uncompensated respiratory alkalosis

Answer 8

the decrease in [CO2] increase the [HCO3-]:[CO2] ratio (since there is little change in [HCO3-]), thus resulting in an increased pH

Question 9

compensated respiratory alkalosis

Answer 9

• the chemical buffer systems release H+ and the respiratory system responds by decreasing ventilation
• both [CO2] and the [H+] are the driving forces behind increased ventilation so when both decrease during respiratory alkalosis, the respiratory centre usually responds by decreasing ventilation
• if the respiratory alkalosis persists for a few days, the kidneys will eventually compensate by decreasing H+ secretion and increasing HCO3- secretion
• when fully compensated, the [HCO3-] is reduced to restore the [HCO3-]:[CO2] ratio of 20:1

Question 10

metabolic acidosis

Answer 10

• also known as non-respiratory acidosis, metabolic acidosis describes anything that causes acidosis besides that due to excess CO2, and is always characterized by a decrease in [HCO3-] and a normal [CO2]
• this decrease can be caused by excessive loss of HCO3- or from the buildup of non-carbonic acids, which also decreases [HCO3-] due to buffering

Question 11

to determine cause of metabolic acidosis

Answer 11

• measure the anion gap
• normally the plasma is electro-neutral meaning that the number of cations equals the number of anions
• if you measure and subtract the cations from the anions in the plasma, you can get as estimate of the amount of non-measured anions (such as phosphate, citrate, sulphate, proteins, lactate, and keto acids)

Question 12

low anion gap

Answer 12

a low anion gap (<8 mEq/L) is uncommon and generally results from the loos of plasma albumin, such as during haemorrhage

Question 13

normal anion gap

Answer 13

• a normal anion gap (8-16 mEq/L) means that there is a loss of HCO3-, which can be caused by diarrhea and some renal diseases
• there is generally a compensatory increase in [Cl-] to conserve electrical neutrality

Question 14

high anion gap

Answer 14

high anion gap (>16 mEq/L) indicates that the metabolic acidosis is caused by an increase in the unmeasured anions, which causes a decrease in [HCO3-] as it is used up for buffering the acids

Question 15

4 common causes of metabolic acidosis

Answer 15

1. severe diarrhea
2. diabetes mellitus
3. strenuous exercise
4. uraemic acidosis

Question 16

severe diarrhea causing metabolic acidosis

Answer 16

• the digestive juices are rich in HCO3- that is secreted to aid in digestion but later reabsorbed
• during diarrhea, this HCO3- may be eliminated before it can be reabsorbed, which causes a drop in [HCO3-], decreasing the buffer capacity of the plasma as well as causing more bicarbonate to dissociate and release H+

Question 17

diabetes mellitus causing metabolic acidosis

Answer 17

• without insulin, glucose does not enter most cells, so they revert to fat metabolism to generate ATP
• this causes an increase in keto acids, which raises the anion gap

Question 18

strenuous exercise causing metabolic acidosis

Answer 18

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

Question 19

uraemic acidosis causing metabolic acidosis

Answer 19

• uraemia is sever renal failure
• with decreased renal function, the kidneys cannot excrete the excess H+ produced from metabolism so the [H+] increases
• there is generally a loss of HCO3- as well, causing an increased anion gap

Question 20

uncompensated metabolic acidosis

Answer 20

• metabolic acidosis is characterized by a decrease in [HCO3-] and a normal [CO2]
• this decrease can be caused by excessive loss of HCO3- or from the buildup of non-carbonic acids, which also decreases [HCO3-] due to buffering

Question 21

compensated metabolic acidosis

Answer 21

• for all of these except uraemic acidosis, compensation can occur by the buffers taking up the extra H+, the lungs blowing off extra CO2, and they kidneys secreting more H+ and conversing HCO3-
• the respiratory system can only partially compensate for metabolic acidosis
• this means that someone with uraemic acidosis cannot fully compensate the metabolic acidosis due to decreased kidney function

Question 22

metabolic alkalosis

Answer 22

• a reduced [H+] caused by a decrease in non-carbonic acids
• while uncompensated, it is generally associated with an increase in [HCO3-] and no change in [CO2], which increases the [HCO3-]:[CO2] to above 20:1

Question 23

metabolic alkalosis - vomiting

Answer 23

• hydrochloric acid is secreted into the stomach during digestion
• the HCl secretion results i HCO3- being transported into the plasma
• this increased plasma [HCO3-] is generally not a problem as most of the secreted H+ will be reabsorbed in the digestive tract and therefore reduce free HCO3-
• with vomiting, there is a loss of stomach H+, meaning it cannot be reabsorbed so plasma pH increases and [HCO3-]. remains elevated

Question 24

metabolic acidosis - ingestion of alkaline drugs

Answer 24

• drugs that are used for treating excess gastric acid generally contain HCO3-, which relives the symptoms by neutralizing H+
• these drugs usually contain very high amounts of HCO3- and excess HCO3- is absorbed in the digestive tract, raising [HCO3-] and decreasing plasma H+ by binding it

Question 25

uncompensated metabolic alkalosis

Answer 25

the [HCO3-]:[CO2] ratio is increased by excess [HCO3-]

Question 26

compensated metabolic alkalosis

Answer 26

- the chemical buffer systems immediately liberate H+, ventilation reduces to raise plasma CO2, and if it persists over several days, the kidneys decrease H+ secretion and increase HCO3- secretion - when fully compensated, both [HCO3-] and [CO2] are elevated above normal but the [HCO3-]:[CO2] ratio is again 20:1