L2: Arterial Blood Gasses

What is an arterial blood gas?

Invasive physiologic assessment tool that measures the acid-base balanace, alveolar ventilation, and oxygenation status

In laymans terms, what info do we get from an arterial blood gas?

• pH

• pCO2

• HCO3 (bicarbonate)

How much arterial blood is taken for an ABG?

2 mL

How quickly should an ABG be completed/analyzed?

Best if analyzed/completed in 10 minutes

What are the PT implications of ABG? In other words, what is it used for?

• Monitor respiratory status

• Assess effectivenes of treatment and progress of disease

• Drives clinical decision making

What is considered a normal pH?

7.35 - 7.45

"If the pH is lower than the ""normal"" pH level, this indicates ________"

Acidosis

"If the pH is higher than the ""normal"" value, this indicates ________"

Alkalosis

What is the true middle value of pH?

7.4

What is the normal value of pCO2?

35 - 45 mmHg

"If the pCO2 is lower than the ""normal"" value, this indicates ________"

Alkalosis

"If the pCO2 is higher than the ""normal"" value, this indicates ________"

Acidosis

What is the normal value of HCO3?

22 - 28 mEq/L (milliequivalents per liter)

"If HCO3 is lower than the ""normal"" value, this indicates ________"

Acidosis

"If HCO3 is higher than the ""normal"" value, this indicates ________"

Alkalosis

HCO3 (bicarbonate) is a ________

Base

Normal Hypoxia:

PO2 = ________ mmHg
SpO2 = ________

80-100, >93%

Mild Hypoxia:

pO2 = ________ mmHg
SpO2 = ________

60-80, 90-90%

Moderate Hypoxia:

pO2 = ________ mmHg
SpO2 = ________

40-60, 75-89%

Severe Hypoxia:

pO2 = ________ mmHg
SpO2 = ________

<40, <75%

If someone has low pCO2 levles in the alveoli, they are ________ventilating

Hyper
They are blowing off the CO2 at a fast rate

If someone has high pCO2 levels in the alveoli, they are ________ventilating

Hypo
They are not blowing off CO2 at a regular rate (and so CO2 builds up in the body)

What are some examples of pathologies that would cause hypoventilation?

• Rib fx

• Mucus Plug

• TBI

• Muscular Dystrophy

• ALS

• Obesity

• Pregnancy

What condition does someone have if they are hypoventilating?

What causes this?

Respiratory Acidosis

Increased CO2

How does someone with hypoventilation compensate?

Retain HCO3-

(Known as Metabolic Alkalosis)

What are some examples that cause hyperventilation?

• Anxiety

• Pain

• Congestive Heart Failure

• Altitude (less pO2 available)

What condition does someone have if they are hyperventilating?

What causes this?

Respiratory Alkalosis

Decreased CO2

How does someone with hyperventilation compensate?

Excrete HCO3-

(AKA - Metabolic Acidosis)

What might cause decreased base or increased acid in the body?

• Ketoacidosis (common in T1DM)

• Kidney Failure

• Diarrhea

What condition does someone have if they have decreased base or increased acid in the body?

What causes this?

Metabolic Acidosis

Decrease in HCO3- or Increased H+

How does someone with decreased base or increased acid in their body compensate?

Increase respiratory rate (to blow off CO2)

(AKA - Respiratory Alkalosis)

What might cause increased base or decreased acid in the body?

• Stomach Pumping

• Diuretic

What condition does someone have if they have increased base or decreased acid in the body?

What causes this?

Metabolic Alkalosis

Increased HCO3- or Decreased H+

How does someone with increased base or decreased acid in their body compensate?

Decreased the respiratory rate (retain CO2)

(AKA - Respiratory Acidosis)

What is the chemical equation to turn CO2 into H+?

CO2 + H2O ↔ H2CO3 ↔ H+ +HCO3

What are the three systems that regulate the pH of extracellular fluid (ECF)?

• Buffer System

• Respiratory System

• Kidney System

What does the buffer system handle in regulating the pH? How does it handle pH changes?

• Quick

• Handles small changes

• Available all the time

• Combines with excess acids or bases

What does the respiratory system handle in regulating the pH? How does it handle pH changes?

• pH changes that the buffer system can't handle

• Takes 0-12 minutes from initiation of pH imbalance

• Increase or decrease respiration to increase or decrease CO2

What do the kidneys handle in regulating the pH? How does it handle pH changes?

• Takes the longest / slowest acting

• Most powerful 
  

• Responsible for long-term changes

• Acts by excreting H+ (acid) or retaining/producing new HCO3- (base)

Define SpO2. How is it measured?

• ""Peripheral Oxygen Saturation""

• Measure of oxygen bound to Hg compared to total Hg

• Measured via pulse oximetry; non-invasive

Define SaO2. How is it measured?

• ""Arterial Oxygen Saturation""

• Measure of oxygen bound to Hg compared to total Hg

• Measured via arterial blood gas; invasive

• (Basically same as SpO2 -- just invasive)

Define pO2 (or PaO2).

The pressure exerted by unbound oxygen in a volume if alone

Define pCO2.

Partial pressure of carbon dioxide in the blood