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Respiratory > Acid-base Regulation > Flashcards

Acid-base Regulation Flashcards

1
Q

What measurements could you expect to find in an arterial blood gas test

A 
pO2 + pCO2
pH
HCO3
Base excess
Hb
Haematocrit
FHbO2 + FHbCO
SaO2
FMetHb (Hb in the ferric methaemoglobin state)
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2
Q

What is base excess

A

Concentration of bases (bicarbonate) compared with the expected concentration assuming no renal or metabolic disturbance (due to CO2)

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3
Q

What is the importance of pH regulation

A

Proteins (ion channels, enzymes, hormones, receptors) can be altered by changes in pH
Impaired function and processes
Drug metabolism and clotting affected

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4
Q

What is a strong acid

A

Fully ionised/dissociated

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5
Q

What is a base

A

Anionic molecule capable of reversibly binding to protons

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6
Q

Describe the dynamic equilibrium of acids

A

Acids exist as either a complete molecule or a dissociated proton and anion
In standard conditions the preferred direction of the dynamic equilibrium is denoted by k

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7
Q

Give an example of acid dynamic equilibrium in the body

A

H2CO3 - H+ + HCO3-

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8
Q

What is the pH of the fluid intracellularly, extracellularly, in the arteries, veins and stomach

A 
intra - 7.0
extra - 7.4
arterial blood - 7.4
venous blood - 7.36
stomach - 2.4
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9
Q

Where are the following acids produced: carbonic acid, HCl, Ketoacids, Phosphoric acids, lactic acids, pyruvic acid

A 
Carbonic - CO2 in respiration
Hydrochloric - stomach
Keto - Fatty acid metabolism 
Phosphoric - incomplete phospholipid oxidation
Lactic - energy production
Pyruvic - energy production
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10
Q

Which acid is most important in evaluating acid-base status

A

Carbonic acid
Due to the rate of its production in cellular respiration
CO2 = respiratory acid (while lactic acid is metabolic)

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11
Q

What does acidemia and alkalaemia refer to compared to acidosis and alkalosis

A 
acidaemia/alkalaemia = pH in the blood
acidosis/alkalosis = circumstances that affect pH balance
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12
Q

What is the ratio of respiratory acids to metabolic acids

A

100:1

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13
Q

How is pH calculated

A

pH = -log [H+] (Sorensen)

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14
Q

What is the Henderson equation

A

Calculates dissociation constant

K = [H+][HCO3-] / [CO2][H2O]

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15
Q

What is the Henderson-Hasselbach equation

A

Combines Sorensen and Henderson

pH = pK + log10 [HCO3-] / [CO2]

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16
Q

What is the principal organ responsible for acid clearance

A

Lungs

Changes in ventilation can stimulate a rapid compensatory response to change CO2 elimination to alter pH

17
Q

Which organs reuse or clear the acid

A

Liver or kidneys

Changes in HCO3 and H+ retention can stimulate a slow compensatory response to alter pH

18
Q

How can hyper/hypoventilation affect acid-base balance

A

Increasing or decreasing the amount of CO2 eliminated in the lungs

19
Q

What is the effect of non-hypercapnic hyperventilation

A

Voluntary or panic attack
Reduced PCO2
May cause alkalosis

20
Q

Describe the buffers in the blood

A

Bicarbonate, phosphate and protein chains act s a buffers. The N- and C- terminals have the potential to liberate or gain

21
Q

What is the normal base excess range

A

-2 to +2

22
Q

What us the significance of base excess

A

Changes in bicarbonate that are due to pCO2 changes are eliminated
Any changes are therefore due to either metabolic acid base disturbance or change in renal excretion

23
Q

What is the cause and effect of a rise in base excess

A

Due to an increase in renal excretion of acid, ingestion, or administration of base
May be due to acid loss from vomiting
Causes metabolic alkalosis

24
Q

What is the cause and effect of a decrease in base excess

A

Overproduction of metabolic acids (E.g. lactic) or ingestion of acid
May be due to reduction in/ failure of acid excretion by the kidneys or excessive loss of alkali from the intestine with diarrhoea
Causes metabolic acidosis

25
Q

What is the reporting procedure for acid-base disturbance

A 
DACO
Disturbance (acidosis or alkalosis)
Aetiology (resp or met)
Compensation (un-, partially, fully)
Oxygenation

Name is in the order CADO e.g. uncompensated respiratory alkalosis with moderate hyoxaemia

26
Q

How do you distinguish between metabolic and respiratory aetiology

A

Acidosis
PCO2 high = respiratory
PCO2 normal/low = Metabolic

Alkalosis
PCO2 high/normal = metabolic
PCO2 low = respiratory

27
Q

What is suggested if both paCO2 and BE are low (abnormal pH)

A

Partially compensated metabolic acidosis

Partially compensated respiratory alkalosis

28
Q

What is suggested if both paCO2 and BE are high (abnormal pH)

A

Partially compensated respiratory acidosis

Partially compensated metabolic alkalosis

29
Q

What are the suggested conditions with acidosis, a high paCO2 and varying levels of BE

A

low BE = uncompensated mixed acidosis
normal BE = uncompensated respiratory acidosis
high BE = partially compensated respiratory acidosis

30
Q

What are the suggested conditions with acidosis, a low paCO2 and low BE

A

partially compensated metabolic acidosis

31
Q

What are the suggested conditions with alkalosis, a high paCO2 and high BE

A

high BE = partially compensated metabolic alkalosis

32
Q

What are the suggested conditions with alkalosis, a low paCO2 and varying levels of BE

A

Low BE = Partially compensated respiratory alkalosis
normal BE = Uncompensated respiratory alkalosis
High BE = uncompensated mixed alkalosis

33
Q

What is the general rule for identifying mixed acidosis/alkalosis

A

Abnormal CO2 and BE in opposite directions

34
Q

What is the general rule for identifying a fully compensated distubance

A

CO2 and BE are abnormal in the same direction

35
Q

Which disturbances can coexist

A

Respiratory acidosis and respiratory alkalosis cannot coexist
Metabolic acidosis and respiratory alkalosis can coexist

Respiratory (16 decks)

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