Acid Base and Oxygen

Question 1

Define the Henderson Hasselbach’s Equation

Answer 1

pH=pKₐ+log₁₀([Base]/[Acid])

Question 2

The Bohr Effect describes what?

Answer 2

Hb releases oxygen in less oxygenated environments and this effect is facilitated by acidic environments

Question 3

What is the respiration (anaerobic vs aerobic) in red blood cells?

Answer 3

Anaerobic

Question 4

In the red blood cell, which electrolyte ion is exchanged for bicarbonate when bicarbonate enters of leaves the cell?

Answer 4

Chloride

Question 5

What contribution do plasma proteins make to the buffering capacity?

Answer 5

Up to a 1/3 in chronic acidosis especially bone

Question 6

Explain why lactated ringers solution is actually an alkaline-type fluid

Answer 6

The lactate is metabolism which generates bicarbonate ions.

Question 7

What is the key amino acid required for removal of H+ in the form of ammonium ions?

Answer 7

Glutamine

Question 8

How does phosphate help remove H+ ions?

Answer 8

Monohydrogen phosphate combines with H+ to fomr dihydrogen phosphate.

Question 9

The acid dissociation constant Ka is approximately what in the body?

Answer 9

800mmol/l

Question 10

Is the Ka in the body fixed?

Answer 10

No there is evidence it can change which is important as several gas analyzers rely on this. It changes in severe illness.

Question 11

What is ‘bicarbonate’ actually measuring when a bicarbonate result is given in blood results

Answer 11

It is actually measuring the total CO2. Admittedly, the vast majority of this will be bicarbonate, but it also measures dissolved CO2, Carbonic acid and carbamino compounds in amino acids.

Question 12

What is a standard bicarbonate?

Answer 12

It gives a value for the bicarbonate if the PCO2 was to be normal. In other words, if the standard bicarbonate is normal, theoretically there is a non-respiratory cause impacting on the hydrogen concentration in the blood.

Question 13

Define base excess

Answer 13

This is the amount of acid in mmol needing to be added to 1l of that patients blood in vitro to restore the patients blood to normal in an alkalosis state

Question 14

What is standard base excess?

Answer 14

Base excess extended to the entire extra cellular compartment correcting for anaemia of 5g/dl i.e. haemoglobin needs to be inputted.

Question 15

Which enzyme is increased in synthesis in the kidneys in states of acidosis?

Answer 15

Glutaminase (which generates ammonium ions from glutamine). Excretion of ammonium contributes to raising pH in acidosis (it prevents the body from having to deal with ammonia by putting into urea molecules as ureogenesis generates H+ ions, direct ammonium excretion does not

Question 16

What effect does acidosis have on the CVS?

Answer 16

Vasodilation of arteries, constriction of peripheral veins and probably is negative ionotropic but only if severe

Question 17

How does an increase in H+ concentration affect levels of 2,3 DPG? Why is this important if bicarbonate is being given IV to correct acidosis?

Answer 17

2,3 DPG will fall in the presence of H+ ions, causing a left shift in the Hb dissociation curve. This is important because if suddently the acidosis is corrected too quickly, there is rapid right shift in the curve. This can be balanced by 2,3 DPG changes but this takes a few hours, hence the need to correct slowly. (2,3 bisphhosphoglyceric acid)

Question 18

What is the cause of K+ rises in acidosis felt to be due to?

Answer 18

Likely decreased activity of ATPases

Question 19

What is the effect of acidosis on bone?

Answer 19

More free ionised calcium. The bone can neutralise a significant amount of H+ ions but long term leads to osteodystrophy

Question 20

What is the cut off at which bicarbonate treatment should be considered (excluding dangerous hyperkalaemia in renal failure)?

Answer 20

> 100nmol/l

Question 21

Whick ketoacid do urine dipsticks not pick up?

Answer 21

2 OH-butryrate (beta-ketone)

Question 22

Sodium and potassium are lost in the urine in DKA. Why?

Answer 22

Up to 50% of beta ketones and acetoacetate can be extreted in the urine as cations. This is useful because it helps get rid of them but unfortunately a corresponding anion is also needed, which is usually both Na+ and K+.

Question 23

How does alcoholic ketoacidosis develop?

Answer 23

Alcoholics send to neglect food and be in fasting state. As a result, insulin levels are suppressed and there is increased lipolysis and ketone production. They tend to be dry, leading to poor renal removal of ketones and decreased insulin secretion.

Question 24

Give examples of a type a lactic acidosis and type b

Answer 24

type a: shock, hypoxia, exercise (i.e. hypoxia is the primary event). Tpe B (biguanides esp phenformin, ethanol, fructose, IMD (Fructose 1,6 disphostase, pyruvate, G6PD, liver failure, thiamine deficiency)