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ACVN - ANAESTHESIA > Blood Gas Analysis recap > Flashcards

Blood Gas Analysis recap Flashcards

1
Q

What does blood gas measure?

A

partial pressure of gasses in the blood,incorportates pH analysis and consideration of various electrolytes that affect pH

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2
Q

What does ACID mean in acid base?

A

proton donor

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3
Q

What does BASE mean in acid base?

A

proton acceptor

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4
Q

What is normal pH?

A

7.4 / 7.35-7.45

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5
Q

What happens as pH falls?

A

hydrogen increases in bigger and bigger steps

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6
Q

Why are we interested in blood gas analysis?

A
  • effects rate of enzymatic reactions
  • has a big impact on physiology
  • often deranged in disease
  • iatrogenic pH derrangements
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7
Q

What occurs if pH is less than 6.8 or greater than 7.6?

A

death

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8
Q

What is it called when pH is less than 6.8?

A

acidaemia

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9
Q

What is it called when pH is more than 7.6?

A

alkalaemia

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10
Q

What determines pH in the body?

A

body must be electroneutral and all negative and positive charges must add up

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11
Q

Whar works together to minimise pH changes?

A

chemical buffers, respiratory and renal systems

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12
Q

What is Henderson Hasselbalch Equation?

A

the relationship between pH and bicarbonate and carbon dioxide levels

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13
Q

What elements are most important for maintenance of normal pH?

A

phosphates, proteins and bicarbonate/carbonic acid system most important

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14
Q

What are capable of accepting or donating hydrogen?

A

any particle

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15
Q

What do buffers do?

A

act to soak up excess hydrogen and release it when necessary

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16
Q

What are examples of buffers?

A

bicarbonate (HCO3-), haemoglobin, blood proteins, phosphate and lactate

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17
Q

What can cause pH derangements?

A
  • respiratory acidosis or alkalosis
  • metabolic acidosis or alkalosis
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18
Q

What causes respiraotry acidosis or alkalosis?

A

a change in PCO2 leading to a change in pH

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19
Q

What causes metabolic acidosis or alkalosis?

A

a change in anything else that can affect pHand usually see a change in HCO3- due to loss or gain

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20
Q

What does hyperventilation cause?

A

a fall in PaCO2

21
Q

What does hypoventilation cuase?

A

increase in PaCO2

22
Q

What does the renal system play a role in?

A

regulating the amount of bicarbonate in the body and regulates the levels of many ions

23
Q

What causes acute respiratory acidosis?

A

hypoventilation

24
Q

What is respiratory acidosis in response to?

A

increased HCO3-

25
Q

What happens with chronic respiratory acidosis?

A

more acid excreted and HCO3- retained

26
Q

What is arespiratory alkalosis?

A

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

27
Q

What is metabolic acidosis signified by?

A

decreased HCO3-

28
Q

What is metabolic acidosis caused by?

A

direct loss of bicarbonate or its consumption due to excess levels of acid

29
Q

What is respiratory alkalosis signified by?

A

increased HCO3-

30
Q

What is metabolic alkalosis caused by?

A

compensatory increase due to loss of chloride ions or albumin

31
Q

What can derangements can occur at the same time?

A

respiratory and metabolic

32
Q

What is an example of a mixed disorder?

A

horse with colicmay have metabolic acidosis and a respiratory acidosis

33
Q

What is base excess?

A

amount of acid required to titrate 1L of blood to a pH of 7.4 at 37 degrees and a PaCO2 of 40mmHg whcih can be positive or negative

34
Q

What are the normalarterial values for oxygen?

A

90-100mmHg when breathing room air and 21% oxygen

35
Q

What are the normal venous values for oxygen?

A

40-50mmHg

36
Q

What is hypoxaemia defined as?

A

oxygen at less than 80mmHg

37
Q

What do blood gas machines measure?

A

electrolytes, lactate, haematocrit, glucose

38
Q

What test can you do if you are interested in acid base?

A

arterial or venous sample

39
Q

What test do you need if wanting to know about gas exchange?

A

arterial sample

40
Q

What is a glass syringe or?

A

impermeable to gas, best is sample analysis delayed but must be kept on ice

41
Q

What are plastic syringes used for?

A

purpose designed blood gas syringe for short term (5-10 minutes) storage at room temperature

42
Q

How do you handle a blood gas sample?

A
  • heparinised syringes
  • prevent clotting by rolling syringe in hand between sampling and analysis
  • discard the first drop of blood as often clotted
43
Q

What artifacts are often seen?

A
  • air contamination leading to low co2
  • saline contamination leading to high chloride often seen with samples from catheters
  • clotting - low PCV/HCT
44
Q

What is anion gapnormally?

A

15-25mmol/L

45
Q

What is decreased anion gap?

A

hypoproteinaemia

46
Q

What is normal anion gap?

A

GI bicarbonate loss

47
Q

What is increased anion gap?

A

lactic acidosis, ketoacidosis

48
Q

What PaO2 will you expect to see under anaesthesia?

A

400-500mmHg as given 100% oxygen

ACVN - ANAESTHESIA (12 decks)

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