Blood Gas Analysis recap

Question 1

What does blood gas measure?

Answer 1

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

Question 2

What does ACID mean in acid base?

Answer 2

proton donor

Question 3

What does BASE mean in acid base?

Answer 3

proton acceptor

Question 4

What is normal pH?

Answer 4

7.4 / 7.35-7.45

Question 5

What happens as pH falls?

Answer 5

hydrogen increases in bigger and bigger steps

Question 6

Why are we interested in blood gas analysis?

Answer 6

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

Question 7

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

Answer 7

death

Question 8

What is it called when pH is less than 6.8?

Answer 8

acidaemia

Question 9

What is it called when pH is more than 7.6?

Answer 9

alkalaemia

Question 10

What determines pH in the body?

Answer 10

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

Question 11

Whar works together to minimise pH changes?

Answer 11

chemical buffers, respiratory and renal systems

Question 12

What is Henderson Hasselbalch Equation?

Answer 12

the relationship between pH and bicarbonate and carbon dioxide levels

Question 13

What elements are most important for maintenance of normal pH?

Answer 13

phosphates, proteins and bicarbonate/carbonic acid system most important

Question 14

What are capable of accepting or donating hydrogen?

Answer 14

any particle

Question 15

What do buffers do?

Answer 15

act to soak up excess hydrogen and release it when necessary

Question 16

What are examples of buffers?

Answer 16

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

Question 17

What can cause pH derangements?

Answer 17

• respiratory acidosis or alkalosis
• metabolic acidosis or alkalosis

Question 18

What causes respiraotry acidosis or alkalosis?

Answer 18

a change in PCO2 leading to a change in pH

Question 19

What causes metabolic acidosis or alkalosis?

Answer 19

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

Question 20

What does hyperventilation cause?

Answer 20

a fall in PaCO2

Question 21

What does hypoventilation cuase?

Answer 21

increase in PaCO2

Question 22

What does the renal system play a role in?

Answer 22

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

Question 23

What causes acute respiratory acidosis?

Answer 23

hypoventilation

Question 24

What is respiratory acidosis in response to?

Answer 24

increased HCO3-

Question 25

What happens with chronic respiratory acidosis?

Answer 25

more acid excreted and HCO3- retained

Question 26

What is arespiratory alkalosis?

Answer 26

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

Question 27

What is metabolic acidosis signified by?

Answer 27

decreased HCO3-

Question 28

What is metabolic acidosis caused by?

Answer 28

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

Question 29

What is respiratory alkalosis signified by?

Answer 29

increased HCO3-

Question 30

What is metabolic alkalosis caused by?

Answer 30

compensatory increase due to loss of chloride ions or albumin

Question 31

What can derangements can occur at the same time?

Answer 31

respiratory and metabolic

Question 32

What is an example of a mixed disorder?

Answer 32

horse with colicmay have metabolic acidosis and a respiratory acidosis

Question 33

What is base excess?

Answer 33

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

Question 34

What are the normalarterial values for oxygen?

Answer 34

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

Question 35

What are the normal venous values for oxygen?

Answer 35

40-50mmHg

Question 36

What is hypoxaemia defined as?

Answer 36

oxygen at less than 80mmHg

Question 37

What do blood gas machines measure?

Answer 37

electrolytes, lactate, haematocrit, glucose

Question 38

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

Answer 38

arterial or venous sample

Question 39

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

Answer 39

arterial sample

Question 40

What is a glass syringe or?

Answer 40

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

Question 41

What are plastic syringes used for?

Answer 41

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

Question 42

How do you handle a blood gas sample?

Answer 42

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

Question 43

What artifacts are often seen?

Answer 43

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

Question 44

What is anion gapnormally?

Answer 44

15-25mmol/L

Question 45

What is decreased anion gap?

Answer 45

hypoproteinaemia

Question 46

What is normal anion gap?

Answer 46

GI bicarbonate loss

Question 47

What is increased anion gap?

Answer 47

lactic acidosis, ketoacidosis

Question 48

What PaO2 will you expect to see under anaesthesia?

Answer 48

400-500mmHg as given 100% oxygen