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Applied Clinical Veterinary Nursing > Blood Gas Analysis > Flashcards

Blood Gas Analysis Flashcards

1
Q

what does blood gas analysis do?

A

measures the partial pressures of gases in the blood

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2
Q

what is an acid?

A

a proton donor

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3
Q

what is a base?

A

a proton acceptor

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4
Q

what is normal body pH?

A

7.35-7.45

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5
Q

what happens to [H+] when pH falls?

A

[H+] increases in bigger and bigger steps as pH falls

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6
Q

why is knowledge of a patients blood pH important?

A

effects rate of enzymatic reactions - has big impact on physiology

pH is often deranged in disease

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7
Q

what are the limits of pH change the body can cope with?

A

death usually occurs if pH is less than 6.8 (acidaemia) or greater than 7.6 (alkalaemia)

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8
Q

what does electroneutral mean?

A

all negative and positive charges in the body add up

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9
Q

how does the body try and mitigate any charge differences?

A

H+ is generated from water

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10
Q

what is classed as acidaemia?

A

blood pH less than 7.35

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11
Q

what is classed as alkalaemia?

A

blood pH more than 7.45

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12
Q

which systems does the body use to maintain a normal pH?

A

chemical buffers, respiratory and renal systems

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13
Q

what are the most key parts in the maintenance of normal pH?

A

phosphates, proteins and the bicarbonate/carbonic acid system

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14
Q

what is the bicarbonate/carbonic acid system?

A

H2O + CO2 <–> H2CO3 <–> H+ + HCO3-

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15
Q

what is a buffer?

A

any particle capable of accepting or donating H+

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16
Q

how do buffers work?

A

act to soak up any excess H+ and release it when necessary

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17
Q

how quickly do buffers work?

A

fast - seconds

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18
Q

give some examples of buffers in the body

A

bicarbonate (HCO3-)
haemoglobin
blood proteins
phosphate
lactate

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19
Q

what can cause pH derangements?

A

respiratory acidosis or alkalosis

metabolic acidosis or alkalosis

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20
Q

what is respiratory acidosis/alkalosis?

A

a change in PCO2 leading to a change in pH

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21
Q

what is metabolic acidosis/alkalosis?

A

a change in anything else that can affect pH (not pCO2)

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22
Q

which ion is usually involved in metabolic acidosis/alkalosis?

A

usually see a change in HCO3-, either due to loss/gain or its role as a buffer to other acids

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23
Q

what is the relationship between arterial CO2 (PaCO2) and ventilation?

A

inversely proportional

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24
Q

what type of breathing will cause PaCO2 to fall?

A

hyperventilation

25
Q

what type of breathing will cause PaCO2 to rise?

A

hypoventilation

26
Q

how quickly can the respiratory system change PaCO2?

A

rapidly - within seconds/minutes of sensing a pH change

27
Q

which parts of the brain/body sense changes in PaCO2?

A

medulla and carotid body

28
Q

what is the advantage of the quick response of the respiratory system to changes in pH?

A

allows the body to respond to sudden changes in pH e.g. exercise

29
Q

what is the main way of getting rid of excess acid from the body?

A

renal system

30
Q

how quickly does the renal system act to regulate ion levels in the body?

A

slowly - hours to days

31
Q

what is acute respiratory acidosis?

A

increased PCO2 due to hypoventilation

32
Q

what is the body’s response to acute respiratory acidosis?

A

compensatory response is to increase HCO3- (buffer to mop up excess H+)

33
Q

how do the kidneys react to chronic respiratory acidosis?

A

more acid is excreted and HCO3- retained

34
Q

what causes respiratory alkalosis?

A

a fall in PCO2 caused by increased ventilation (pain, stress, hypoxaemia)

35
Q

what signifies metabolic acidosis? why does this occur?

A

signified by decreased HCO3-

due to direct loss of bicarbonate or its consumption due to excessive levels of acids

36
Q

how does the body respond to metabolic acidosis?

A

respiratory compensation - a fall in PCO2 due to increased ventilation

37
Q

what signifies metabolic alkalosis? why does this occur?

A

signified by increased HCO3-

compensatory increase, usually due to loss of chloride ions or albumin

38
Q

how does the body respond to metabolic alkalosis?

A

respiratory compensation - an increase in PCO2 due to decreased ventilation

39
Q

what is base excess?

A

amount of acid required to titrate 1L of blood to a pH of 7.4 at 37C and a PaCO2 of 40mmHg

40
Q

is base excess positive or negative?

A

can be either

41
Q

what is the relevance of base excess in blood gas interpretation?

A

fixes the PaCO2 at 40mmHg - means any remaining pH change is due to metabolic processes

42
Q

what is normal PCO2 (mmHg)?

A

arterial 36-46
venous 38-48

43
Q

what is normal HCO3- (mmol/l)?

A

22-29 (arterial and venous)

44
Q

what is normal base excess (mmol/l)

A

2-5 (arterial and venous)

45
Q

what are normal arterial values for blood when breathing room air?

A

90-100mmHg

46
Q

what is the normal venous value for blood?

A

40-50mmHg

47
Q

what is hypoxaemia defined as?

A

less than 80mmHg oxygen in the blood

48
Q

what is the normal PaO2 under anaesthesia?

A

400-500mmHg (due to 100% oxygen being given)

49
Q

which samples can be used for acid-base balance?

A

arterial or venous

50
Q

which samples can be used for gas exchange values in the body?

A

ideally arterial sample, blood taken over a few breaths

samples should be collected anaerobically

51
Q

can glass syringes be used for sample collection?

A

yes - impermeable to gas

must keep sample on ice

52
Q

which type of syringe is best to use if blood sample analysis will be delayed?

A

glass - impermeable to gas

53
Q

how long can purpose-designed plastic syringes hold a sample?

A

5-10 mins at room temperature

54
Q

what do purpose-designed plastic collection syringes for blood gas analysis contain?

A

heparin

55
Q

why do we discard the first drop of blood from the sample?

A

often clotted

56
Q

what common artifacts are seen with blood gas analysis?

A

air contamination - CO2 unexpectedly low

saline contamination - high chloride

clotting - low PCV/HCT

57
Q

when is saline contamination of blood gas samples often seen?

A

when blood is sampled from an IV catheter

58
Q
A

Applied Clinical Veterinary Nursing (31 decks)

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