M103 T4 L5

Question 1

Why is ABG testing done from the arteries instead of the veins?

Answer 1

allows us to assess the acid-base balance in the blood and the ventilatory status in ways in which accessing venous blood does not allow us to reliably assess

the acid base balance is linked with the ventilatory status - the pressure of CO2 in the blood

Question 2

Why is co2 considered an acid even though it doesn’t have a H?

Answer 2

it nearly always reacts with water in the body, especially in the presence of co2, to make carbonic acid
90% of the acids that we produce in the body are from co2 mlcs

Question 3

How are fixed acids removed from the body?

Answer 3

lactate is converted into glucose

urine is filtered out by the kidney and excreted

Question 4

Why can patients with kidney failure develop acidosis?

Answer 4

they’re kidneys are no longer functioning effectively so fixed acids aren’t being filtered out properly

Question 5

If there is so much fixed acids being produced in the body, why is our pH not acidic?

Answer 5

fixed acids are removed

there are buffers that work to keep pH at 7.4

Question 6

What are the three most important buffers in our body?

Answer 6

bicarbonate
proteins
phosphates

Question 7

How do protein buffers work to eliminate acids?

Answer 7

they have a histamine residue that circulate in the blood
this histamine residue can either combine with a proton or eliminate a proton or give up a proton
so they act as either a conjugate base or as an acid

Question 8

How do phosphates work to eliminate acids?

Answer 8

they can accept or give off three protons per ion

Question 9

How do we detect if there’s an abnormal acute accumulation of fixed acids?

Answer 9

ion imbalance - blood in a normal healthy body is not ionically charged - the amount of positive charge is equal to the amount of negative charge so they cancel out
in a body struggling to eliminate acids, +ve will not equal -ve, and there will be an imbalance
so it’s the Anion Gap that is measured

Question 10

When testing for an abnormal acute accumulation of fixed acids, is there a test that measures the level of every acid type directly?

Answer 10

no bc there’s a variety of different types of acid, would require lots of tests

Question 11

When calculating the anion cap, which ions come under anions and which under cations?

Answer 11

anions (-ve); chlorine- and bicarbonate

cations (+ve); sodium (and sometimes potassium)

Question 12

What is the normal anion gap?

Answer 12

12 mEq/L

Question 13

What are the main physiological causes of an anion gap in acidosis?

Answer 13

GOLD MARK
* most common causes

Glycols (ethylene and propylene)
Oxoproline 
L-lactate*
D-lactate 
Methanol 
Aspirin
Renal failure*
Ketoacidosis*

Question 14

What are the two types of metabolic acidosis?

Answer 14

addition of acid acid (anion gap acidosis)

loss of bicarbonate (non anion gap acidosis)

Question 15

Why will a loss of bicarbonate lead to metabolic acidosis?

Answer 15

in the carbonic anhydrase reaction, bicarbonate and H+ are the products of this reaction
if bicarbonate is removed, the EQL will try to compensate by driving the right side of the reaction for EQL, creating more protons
this accumulation of protons will lead to metabolic acidosis

Question 16

How does the body lose bicarbonate?

Answer 16

kidney tubules

pancreatic ducts

Question 17

Why does the body lose bicarbonate through the kidney tubules?

Answer 17

the kidneys, by poor design, filter a lot of bicarbonate out when the glomeruli in in the kidneys first starting to make urine
by the time the urine is ready to leave the kidneys, most of that bicarbonate has been reabsorbed
so failure to reabsorb that bicarbonate can lead to inappropriate loss of bicarbonate

Question 18

Why does the body lose bicarbonate through the pancreatic ducts?

Answer 18

the pancreas actually makes quite a bit of bicarbonate and secretes it into the lumen of both the pancreatic duct and that of the intestines

Question 19

What are the two causes of bicarbonate loss in non-anion gap metabolic acidosis?

Answer 19

RTA - when there’s a dysfunction in teh kidney
GI losses
excessive chloride administration in the body

Question 20

When and how is chloride administered to the body?

Answer 20

to patients with hypotension via IV fluids containing NaCl

Question 21

What happens if too much chloride is adminstered to the body?

Answer 21

If the patient receives many litres of blood, they will have a build up of chloride in the blood
to manage this, the body will compensate by eliminating / storing it within the cells of the body
AAR the blood levels will be will appear depressed
the patient will then lose the ability to buffer their pH as effectively, because they’ll lose bicarbonate that way

Question 22

What two reasons might there be for acidemic blood?

Answer 22

too much volatile acid

not enough bicarbonate

Question 23

What pHs are required to meet the diagnosis of acidaemia / alkalaemia?

Answer 23

acidaemia - less than pH 7.38

alkalaemia - higher than pH 7.42

Question 24

What are the main three lung receptor types?

Answer 24

C-fiber nociceptors
Mechanically sensitive receptors
Lung stretch receptors

Question 25

How are central chemoreceptors different to other chemoreceptors?

Answer 25

They are much more limited - can only sense the presence of protons
indirect measure of pH

Question 26

What can cause respiratory depression?

Answer 26

Opioids / narcotics (heroin, legal prescription narcotics)
Alcohol
Anaesthesia and other sedatives
Cerebral diseases: ex. cerebral vascular accident

Question 27

Where is the medulla oblongata located?

Answer 27

in the hind brain in the Pons and the medulla

Question 28

Where is the Dorsal Respiratory Group located?

Answer 28

they extend most of the length of the dorsal medulla. They are near to the central canal of the spinal cord, and just behind the ventral group

Question 29

What is the function of the Dorsal Respiratory Group?

Answer 29

to set and maintain the rate of respiration

Question 30

When can apneusis occur?

Answer 30

if the pons is lesioned

Question 31

What are the three classes of nerve fibre in the C&P NS?

Answer 31

group A-C

Question 32

What are the physical features of Group C nerve fibers?

Answer 32

unmyelinated, low conduction velocity

small diameter

Question 33

What is the difference between Group A&B nerve fibres and those of Group C?

Answer 33

Groups A and B are myelinated while C is unmyelinated

Question 34

What types of fibers are included in Group C fibres?

Answer 34

postganglionic fibers in the ANS

nerve fibers at the dorsal roots (IV fiber), carry sensory information

Question 35

What type of information is carried by nerve fibers at the dorsal roots (IV fiber)?

Answer 35

sensory information

Question 36

How is lactate removed from the body?

Answer 36

it’s taken up by the liver and converted into glucose

Question 37

How is urine removed from the body?

Answer 37

it’s filtered out by the kidney and disposed of as a waste product

Question 38

What is the role of Lung stretch receptors?

Answer 38

they help terminate inspiration and initiate exhalation when the lungs are adequately inflated

Question 39

What happens to bicarbonate produced by the pancreas?

Answer 39

it’s secreted into the gut IOT balance out the acidic gut contents coming from the stomach

Question 40

What is the normal pH in the stomach?

Answer 40

around 3

Question 41

What is the normal pH in stool?

Answer 41

6.6

Question 42

What happens to bicarbonate levels if a patient has diarrhoea?

Answer 42

high output of stool = more bicarbonate will be lost

Question 43

Where are central chemoreceptors located?

Answer 43

in the ventrolateral surface of the medulla oblongata and other areas of the brain such as the NST

Question 44

What is the role of central chemoreceptors?

Answer 44

they detect pH changes in the CSF as a reflection of changes in the PAco2