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Lab Medicine > ABGs > Flashcards

ABGs Flashcards

1
Q

An arterial blood gas is a test that measures _______, _________, ____________, and ____________.

A

Acidity (pH);
Oxygen Tension (PaO2);
Carbon Dioxide Tension (PaCO2);
Bicarbonate Concentration (HCO3)

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2
Q

Common sites to get arterial blood for an ABG

A
  1. Radial
  2. Brachial
  3. Femoral (sometimes)

Rarely:

  1. Dorsalis Pedis
  2. Axillary Artery
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3
Q

T/F: It is important to draw blood from the radial or brachial arteries because the results of the ABGs will be more accurate to the rest of the body.

A

False, there is NO evidence that one site is better than another.

The radial artery is typically the easiest and most used access site.

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4
Q

This is the process used to collect radial arterial blood defined by the following process:

  1. The patient’s hand is initially held upright with the fist closed and both the ulnar and radial arteries compressed (allowing blood to drain from the hand).
  2. The hand is then lowered, fist opened, and pressure is released only from the ulnar artery.
A

Modified Allen Test

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5
Q

In the Modified Allen Test, the color should return to the hand within ________ after releasing the ulnar compression.

A

Six Seconds

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6
Q

What is the difference between the Allen Test and the Modified Allen Test?

A

Allen Test has you releasing the ulnar artery and then the radial artery on two different occassions testing the patency of both arteries.

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7
Q

What is the equation for the Bicarbonate-Carbon Dioxide Buffering System in the Blood?

A

Dissolved CO2 + H2O H2CO3 HCO3- + H+

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8
Q

How do you calculate the serum bicarb level/concentration?

A

Using the CO2 and pH measured by the ABG machine, you use the Henderson-Hasselbach Equation.

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9
Q

What is the Henderson Hasselbach equation?

A

pH = 6.1 + log( [HCO3-] / [0.03 x PCO2] )

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10
Q

Normal Range of pH

A

7.35 - 7.45

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11
Q

Normal Range of HCO3-

A

21 - 27 meq/L

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12
Q

Normal Range of PCO2

A

35 - 45 mmHg

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13
Q

Normal Range of PaO2

A

Varies because the treshold below which tissue hypoxiaoccurs is not an exact value and has not been defined.

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14
Q

This is the term for an arterial pH below the normal range ( < 7.35)

A

Acidemia

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15
Q

This is the term for a disorder that INCREASES the pH and REDUCES the PCO2

A

Respiratory Alkalosis

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16
Q

This is the term for an arterial pH above the normal range ( > 7.45)

A

Alkalemia

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17
Q

This is the term for a disorder that REDUCES the pH and REDUCES the HCO3-

A

Metabolic Acidosis

18
Q

This is the term for a disorder that REDUCES the pH and INCREASES the PCO2

A

Respiratory Acidosis

19
Q

This is the term for a disorder that INCREASES the pH and INCREASES the HCO3-

A

Metabolic Alkalosis

20
Q

Step-Wise Approach for looking at ABGs:

A
  1. Look at the pH
  2. Determine the process that led to the acidemia or alkalemia. Look at the HCO3- and PCO2
  3. Calculate the Anion Gap
  4. Determine if a compensatory process is present
  5. Determine if a Mixed Acid-Base Disorder is Present
21
Q

If we see a patient with acidemia (pH < 7.35) and we see that the PCO2 is also elevated (>45), what is this condition?

A

Respiratory Acidosis

22
Q

If we see a patient with alkalemia (pH > 7.45) and we see that the HCO3- is elevated (>27), what is this condition?

A

Metabolic Alkalosis

23
Q

If we see a patient with acidemia (pH < 7.35) and we see that the HCO3- is low (< 21), what is this condition?

A

Metabolic Acidosis

24
Q

If we see a patient with alkalemia (pH > 7.45) and we see that the PCO2 is low (<35), what is this condition?

A

Respiratory Alkalosis

25
Q

How do you calculate the Anion Gap?

A

AG = Na+ - (Cl- + HCO3-)

26
Q

What does an elevated Anion Gap (>12) imply?

A

Implies that the Patient has a Primary, Wide-Anion Gap Metabolic Acidosis

27
Q

For primary respiratory acidosis (high PCO2), the compensatory process is ?

A

Metabolic Alkalosis

Rise in serum HCO3-

28
Q

For primary respiratory alkalosis (low PCO2), the compensatory process is ?

A 
Metabolic Acidosis
(Decrease in serum HCO3-)
29
Q

For primary metabolic alkalosis (high HCO3-), the compensatory process is ?

A 
Respiratory Acidosis
(High PCO2)
30
Q

For primary metabolic acidosis (low HCO3-), the compensatory process is ?

A

Respiratory Alkalosis

Low PCO2

31
Q

When a metabolic acidosis (reduction in serum HCO3-) or metabolic alkalosis (increased serum HCO3-) occurs, there should be an appropriate degree of respiratory compensation.

How can we see this degree of respiratory compensation?

A

Moving PCO2 in the SAME direction as the serum HCO3-

32
Q

When a respiratory acidosis (increased PCO2) or respiratory alkalosis (decreased PCO2) occurs, compensation occurs in two phases.

What are these two phases?

A
  1. Immediate Small Change in HCO3- (same direction as PCO2)
  2. If the respiratory disorder continues for more than minutes to hours, the kidneys respond by producing larger changes in serum HCO3-. (same direction of PCO2)
33
Q

How long can it take the kidneys to compensate to resolve respiratory acidosis in the body?

A

3-5 days

34
Q

How do you determine if there is a mixed Acid-Base disorder?

A

Calculate the Delta-Delta.

The change in Anion Gap compared to the change in bicarb

35
Q

How do you calculate the Delta-Delta?

A
  1. Calculate the Delta Anion Gap: Measured AG – Normal AG(12).
  2. Calculate the Delta-Delta: Add the Delta Gap (#1) to the measured HCO3 ˉ(from the chemistry panel).
  3. Compare the Delta-Delta to a normal bicarbonate (22-26).
36
Q

If the Delta-Delta is < 22 or if the Delta Anion Gap is less than the Delta HCO3-, this is called

A

Non-Anion Gap Acidosis

37
Q

If the Delta-Delta is > 26 or if the Delta Anion Gap is greater than the Delta HCO3-, this is called

A

Metabolic Alkalosis

38
Q

If the Delta Anion Gap is EQUAL to the Delta HCO3-, then the wide Anion Gap Acidosis is termed:

A

Pure

39
Q

DDx for Metabolic Acidosis

MUDPILES

A 
M - Methanol
U - Uremia
D - DKA/AKA
P - Paraldehyde
I -  Iron/INH
L - Lactic acidosis
E - Ethylene glycol
S - Salicylates
40
Q

DDx of Respiratory Acidosis

A
  1. Acute narcotic or other sedative overdose
  2. Severe metabolic encephalopathy
  3. Obesity hypoventilation
  4. Severe COPD
  5. Neuromuscular disorders (eg. Guillan Barre, Myasthenia Gravis, Botulism, ALS)
  6. Later stages of a severe asthma exacerbation (patient is tiring out)
  7. Inappropriately low minute ventilation settings on mechanical ventilation
41
Q

DDx of Respiratory Alkalosis

A
  1. Early stages of an asthma exacerbation
  2. Anxiety attack
  3. Acute hypoxia (hypoxic ventilatory response)
  4. Pregnancy or other cases of elevated progesterone
  5. Cirrhosis and/or hepatic encephalopathy
  6. Salicylate intoxication
  7. Central nervous system disease

Lab Medicine (7 decks)

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