Arterial Blood Gas (ABGs)

Question 1

What sites of placement do we use to insert arterial lines?

Answer 1

Radial artery
Brachial artery (watch out for embolis)
Femoral artery
Dorsalis pedis (foot) artery

Question 2

What are the main components of an ABG analysis?

Answer 2

pH 
pO2
pCO2
HCO3
BE (base excess)
SaO2
AG (anion gap)

Others:
Glucose
Lactate
Hct
Electrolytes (Na+, K+, Ca++, Cl-)

Question 3

What is the normal range of blood pH?

Answer 3

7.35-7.45

Question 4

What are 3 indicators on an ABG reading that may indicate general acidosis?

Answer 4

Blood pH < 7.35
PaCO2 > 45
HCO3 < 22
BE < -3

Question 5

What are 3 indicators on an ABG reading that may indicate general alkalosis?

Answer 5

Blood pH > 7.45
PaCO2 < 35
HCO3 > 26
BE > +3

Question 6

What is the respiratory buffer response and how long does it take to kick in?

Answer 6

Blood pH changes in response to varying levels of H2CO3; body responds by either hypoventilating (compensation for alkalemia) or hyperventilating (compensation for acidemia) –> so PaCO2 will be affected by this response.

This response occurs within 1-3 minutes of blood pH shift in normal physiology.

Question 7

What is the difference between acidemia and acidotic?

Answer 7

AcidEMIA refers to an acid state of blood.

Acidotic refers to a generally acidic state of the patient.

Question 8

What is the renal buffer response and how long does it take to kick in?

Answer 8

The kidney can retain or excrete HCO3 (bicarbonate). It will do either in response to changes in blood pH - for example, if blood pH decreases, kidneys will retain HCO3.

This buffer system takes hours to days to correct the imbalance so cannot be relied on clinically - we must help pt compensate.

Question 9

What is the difference between respiratory and metabolic acidosis/alkalosis?

Are they mutually exclusive?

Answer 9

Respiratory acidosis = pCO2 > 45

Metabolic acidosis = HCO3 < 22

Respiratory alkalosis = pCO3 < 35

Metabolic alkalosis = HCO3 > 26

No, patient can have both respiratory and metabolic acidosis.

Question 10

What are some causes of respiratory acidosis?

Answer 10

CNS depression
Pleural disease (think pleural space of lungs)
COPD
ARDS
Musculoskeletal disorders (that may affect lung function)
Compensation for metabolic alkalosis
Hypoventilation

Question 11

What is base excess?

Answer 11

Indicates the amount of excess or insufficient level of bicarbonate -2 to +2mEq/L

Question 12

H+ value that corresponds with pH of 7.4? 7.3? 7.5?

Answer 12

7.4 = 40, 7.3 = 50, 7.5 = 30

Question 13

What is the respiratory buffer response?

Answer 13

The blood pH changes according to the level of H2CO3 present, triggering the lungs to increase or decrease the rate and depth of ventilation.

This response occurs within 1-3 minutes.

Question 14

How does the body compensate for chronic respiratory acidosis?

Answer 14

Renally via synthesis and retention of HCO3.

Also by excreting more Cl to balance charges (causing hypochloremia).

Question 15

How does the body respond to acute and chronic respiratory alkalosis?

Answer 15

Acute - decreases HCO3 2mEq/L for every 10mmHg decrease PCO2

Chronic - decreases HCO3 4mEq/L for every 10mmHg decrease in PCO2

Question 16

A 1mEq/L decrease in HCO3 causes how much of a change in PCO2?

Answer 16

Decreases PCO2 by 1.2mmHg

Question 17

Causes of Metabolic Gap Acidosis?

Answer 17

MUDPILES - Methanol, Uremia, DKA, Paraldehyde, INH, Lactic acidosis, Ethylene glycol, Salicylate

Also non-gap metabolic acidosis - hyperalimentaiton, acetazolamide, RTA, diarrhea, pancreatic fistula

Question 18

Stepwise Approach to ABG

Answer 18

1. Acidemic or alkalemic?
2. Respiratory or metabolic?
3. Assess PaO2. Below 80mmHg = hypoxemia. For respiratory, is it acute or chronic?
4. For metabolic acidosis, is anion gap present?
5. Assess normal compensation by respiratory system for a metabolic disturbance.

Question 19

How do you tell if hypoxemia is acute?

Answer 19

If the change in PaCO2 is associated with a change in pH

Question 20

If pH is acidotic, but the PaCO2 decreases, what does this indicate?

Answer 20

The lungs are compensating for a metabolic acidosis by blowing off excess CO2.

Question 21

If pH and HCO3 are moving in opposite directions, what does this indicate?

Answer 21

The kidneys are compensating for a respiratory disorder by holding or releasing HCO3

Question 22

What are some possible causes of respiratory acidosis?

Answer 22

• CNS depression
• Pleural disease
• COPD/ARDS
• Musculoskeletal disorders
• Compensation for metabolic alkalosis

Question 23

What is the effect of respiratory alkalosis on chloride electrolyte levels?

Answer 23

Cl- will increase to balance charges

Question 24

What are some possible causes of respiratory alkalosis?

Answer 24

• Intracerebral hemorrhage
• Anxiety that decreases lung compliance
• Liver cirrhosis
• Sepsis
• Salicylate and progesterone drug usage

Question 25

How does the body compensate in chronic respiratory alkalosis?

Answer 25

Decreased bicarb (acid) reabsorption and ammonium excretion to normalize pH

Question 26

How long does it take for complete activation of respiratory compensation (alkalosis) for metabolic acidosis?

Answer 26

12-24 hours

Question 27

Causes of non-gap metabolic acidosis?

Answer 27

- Diarrhea - Pancreatic fistula - Hyperalimentation (overconsumption of food, can be through tube) - RTA (renal tubular acidosis) - Acetazolamide

Question 28

Causes of metabolic alkalosis?

Answer 28

- Vomiting - Chronic diarrhea - Diuretics - Hypokalemia - Renal failure

Question 29

In multiple ABG readings, your patient's pH is decreasing along with his PaCO2. Is this a primary respiratory or metabolic problem?

Answer 29

a primary metabolic problem

Question 30

In multiple ABG readings, your patient's pH is decreasing and HCO3- is dropping. Is this a primary respiratory or metabolic problem?

Answer 30

a primary metabolic problem

Question 31

What does base excess (BE) estimate?

Answer 31

Estimates the amount of strong acid or base needed to correct (METABOLIC component) an acid-base abnormality

Question 32

What is the formula for estimating how much HCO3- to give a patient undergoing metabolic acidosis?

Answer 32

0.3 x BE x body weight in kg

Question 33

When the pt's pH and paCO2 moves in the same direction, the problems is primarily metabolic/respiratory?

Answer 33

Metabolic