Blood gas interpretation Module 6

Question 1

Why is arterial blood used to assess respiratory function?

Answer 1

its oxygen and CO2 levels are determined primarily by the lungs.

Question 2

Why is the radial artery the preferred site for ABG sampling?

Answer 2

It’s easy to access, has good collateral circulation, and is easy to stabilize post puncture.

Question 3

how is collateral circulation assessed before puncturing to do the arterial blood sample?

Answer 3

using the ALLEN TEST. if the collateral circulation is adequate, the hand should return to pink within 10 - 15 seconds after release of the ulnar artery.

Question 4

How long should you hold the puncture site after taking blood sample if clotting problems exist.

Answer 4

3-5 minutes longer

Question 5

what does the PaO2 reflect?

Answer 5

The ability of the lungs to allow the transfer of oxygen from the environment to the circulating blood

Question 6

What does a PaO2 below the predicted range for a patient breathing room air regardless of the actual FiO2 mean?

Answer 6

hypoxemia

Question 7

Hypoxia

Answer 7

a condition in which tissue oxygenation is inadequates

Question 8

What amount of PaO2 would be considered hypoxemia at any age?

What amount would be considered severe hypoxemia?

Answer 8

1. <65mm Hg is hypoxemia at any age
2. <40mm Hg is considered severe hypoxemia

Question 9

List 5 things that would cause hypoxemia to occur, ie’ it is secondary to these things.

Answer 9

1. ventilation/perfusion (V/Q) mismatch
2. shunt
3. diffusion defect
4. hypoventilation
5. reduced partial pressure of oxygen in the inhaled gas (PiO2)

Question 10

What is the most common cause of hypoxemia?

Answer 10

V/Q mismatch

Question 11

What is V/Q mismatch?

Answer 11

1. a defect in which ventilation (the exchange of air between the lungs and the environment) and perfusion (the passage of blood through the lungs) are not evenly matched.
2. typical in COPD
3. it is the most common cause of hypoxemia
4. and a component of most causes of respiratory failure

Question 12

ventilation

Answer 12

The air that reaches the alveoli

Question 13

What defines ventilation? (blood gas results?)

What determines Ventilation

Answer 13

1. PaCo2 and pH
2. Alveolar minute ventilation

Question 14

Perfusion (Q)

Answer 14

is the blood which reaches the alveoli

Question 15

V/Q ratio

Answer 15

1. the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli

Question 16

Oxygenation 3points

Answer 16

1. is separate from ventilation
2. defined by PaO2 and SaO2
3. a is arterial
4. determined by

• spontaneously breathing: FiO2
• PPV: FiO2 and mean airway pressure

Question 17

PPV

Answer 17

positive pressure ventilation

Question 18

List the Normal ranges and goal ranges for

1. pH
2. PaCO2 mmHg
3. PaO2 mmHg
4. HCO3 mmol/L
5. Base Excess
6. SaO2

Answer 18

Normal: Goal:

1. 7.35-7.45 pH 7.35-7.45
2. 35-45 PaCO2 35-45mmHg
3. 80-100 PaO2 60-100mmHg
4. 22-26 HCO3
5. +-2 Base Excess
6. 95-100% SaO2 >=90%

Question 19

How do sudden changes in PaCO2 impact pH?

Answer 19

1. Sudden changes in PaO2 = changes in pH
2. when PaO2 increases, pH decreases
3. for every 10mmHg increase in PaO2, there is a corresponding decrease in pH by 0.06
4. when PaO2 decreases pH increases
5. For every 10 mmHg decrease in PaO2, there is a corresponding increase in pH by 0.10

Question 20

What disorders in a patient would shift the oxyhemoglobin curve to the left , resulting in HIGHER SaO2 values at the SAME PaO2

Answer 20

1. Alkalosis
2. hypocapnia
3. hypothermia
4. fetal Hb
5. HbCO

Question 21

Which disorders in a patient would shift the oxyhemoglobin curve to the right and result in LOWER SaO2 values for the same PaO2?

Answer 21

1. Acidosis
2. hypercapnia
3. fever

Question 22

How does an oxyhemoglobin shift to the left impact Oxygenation of the tissues?

Answer 22

shifts to the left cause O2 to be more tightly bound to Hb, and make unloading of oxygen at tissues more difficult.

Question 23

How does an oxyhemoglobin shift to the right impact oxygenation of the tissues?

Answer 23

results in decreased O2 affinity for Hb, and allows easier unloading of O2 at the tissues

Question 24

what is the pH a reflection of?

Answer 24

the acid-base status of arterial blood

Question 25

What is the most reliable measure for evaluating the effectiveness of ventilation? and what should be taken into account when interpreting it?

Answer 25

1. PaCO2 2. should be interpreted in light of the patients minute volume VE

Question 26

what is the HCO-3 level a reflection of? how is HCO-3 level regulated

Answer 26

1. Primarily a reflection of the metabolic component of acid-base balance 2. it is regulated by the renal system

Question 27

What is the Henderson-Hasselbalch equation?, what does it demonstrate?

Answer 27

1. Demonstrates that arterial blood pH is determined by the ratio of HCO-3 to PaCO2 2. the ratio is normally 20:1

Question 28

When would we consider a pt to have respiratory acidosis?

Answer 28

When the PaCO2 is elevated above normal OR when it is higher than the expected level of compensation

Question 29

When would we consider a patient to have METABOLIC ACIDOSIS?

Answer 29

when plasma HCO-3 or BE falls below normal

Question 30

When would we consider a patient to have **respiratory Alkalosis?**

Answer 30

PaCO2 below the expected level this indicates that ventilation is exceeding the normal level

Question 31

When would we consider a patient to have Metabolic alkalosis?

Answer 31

when there is an above normal elevation of the plasma HCO-3

Question 32

Describe what is happening with the blood gases in a **MIXED ACID-BASE DISORDER?**

Answer 32

When **metabolic acidosis** is accompanied by a PaCO2 that is lower than the predicted level for the degree of acidosis, a respiratory alkalosis is occuring simultaneously.

Question 33

What would a pH of 7.40 occuring simultaneously with significant abnormalities in PaCO2 and plasma HCO-3 indicate? and why?

Answer 33

1. indicates a mixed disorder 2. normal compensation of a single disorder NEVER returns the pH to 7.40 3. The body will NOT overcompensate

Question 34

What impact does a change in PaCO2 have on the level of HCO-3 in the blood?

Answer 34

1. As PaCO2 levels change so will the bicarb 2. for every **10 mmHg increase in PaCO2 the HCO-3 increases 1mmol/L** 3. foe every **10 mmHg decrease in PaCO2 the HCO-3 decreases by 2mmol/L** Based on the Hydrolysis equation do not confuse this normal relationship with compensation

Question 36

What would the systematic approach to blood gas interpretation be?

Answer 36

1. Acid-base assessment * acidemia, alkalemia or normal? * respiratory of metabolic in origin? * is it compensation occurring? * simple vs. mixed disorder? 2. Assess Oxygenation * adequacy of oxygenation? for all ABG interpretation you need to consider the patient history and current clinical status.

Question 37

What are the normal values for pH? what would be considered Acidemia? What would be considered Alkalemia?

Answer 37

1. 7.35-7.45 2. \<7.35 3. \>7.45

Question 38

What other than normal could a pH in the normal range of 7.35-7.45 indicate?

Answer 38

it could indicate a norma, fully compensated disorder, or a mixed disorder.

Question 39

what values would indicate that the respiratory system is the primary cause of an Acid-Base disorder?

Answer 39

1. if **PaCO2 is abnormal** and in the **OPPOSITE** direction of the pH then the respiratory system is the primary cause.

Question 40

what ABG values would indicate that an Acid-base disorder is metabolic

Answer 40

1. **If HCO3- is abnormal** and in the SAME direction of the pH, then the disorder is metabolic (primarily)

Question 42

How do we know compensation is occuring when the original problem is respiratory?

Answer 42

1. the **metabolic** system compensatesby either increasing or decreasing the HCO3- levels to "correct" the pH back to normal

Question 43

How do you determine if the original problem is metabolic when compensation is occuring in an acid-base disorder?

Answer 43

1. the **respiratory system r**esponds by either increasing or decreasing minute volume resulting in decrease or increase of PaCO2 respectively 2. this new PaCO2 counteracts the metabolic problem and "corrects" the pH 3. this results in both PaCO2 and HCO3- being abnormal but the end result is a pH that is normal or closer to normal. Important to note: the body does NOT overcompensate.

Question 44

How would we determine if an acid base disorder is simple or mixed?

Answer 44

* for every 10mmHg increase in PaCO2, there is a decrease in pH by 0.06 * for every 10mmHg decrease in PaCO2, there is a corresponding increase in pH by 0.10 Calculate the predicted pH: if PaCO2 = 40: predicted pH=measured pH PaCO2\>40: predicted pH=7.40-[(PaCO2-40)\* .006] PaCO2\<40: Predicted pH=7.40+[(40-PaCO2)\*.01] Compare the predicted pH to the actual: if the actual pH does not = the predicted pH, then a mixed disorder is occuring.