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ABGs Basics

pH: The Picky Princess

pH = "picky princess" - it wants things its way.
The pH scale ranges from 0 to 14, with 7 as neutral.
- Less than 7 is acidic.
- Greater than 7 is alkaline (basic).
Pure water/blood is around 7.
Examples of common items on the pH scale:
- Doctor Pepper and sodas are acidic.

Acid-Base Balance

Metabolic processes maintain a balance between acids and bases in the body.
Lungs:
- Think respiratory (PaCO2)
- Exhale CO2 $($ CO2 is an acid).
Kidneys:
- Think metabolic (HCO3)
- Involve $HCO_3$ (bicarbonate, a base).
The body works to stay compensated.
Losing stomach acid (e.g., through vomiting or NG tube suction) leads to losing acid, resulting in becoming more basic (alkalosis).

Memorizing ABG Values

Lab ranges will be provided in exam questions, but they may not always be helpful if multiple values are off.
Normal pH: $7.35 - 7.45$
- pH less than 7.35: Acidosis (acidity going down).
- pH greater than 7.45: Alkalosis (kicking pH up).
"Princess" (pH) determines the problem, so acidic pH means acidosis is part of the answer.
Test-taking strategy: Identify if pH is acidic or alkalotic to narrow down answer choices.

$CO_2$ (Carbon Dioxide)

Normal $CO_2$ : $35 - 45$
$CO_2$ is an acid; the more you have, the more acidic you are.
- $CO_2$ greater than 45: Acidosis.
- $CO_2$ less than 35: Alkalosis.
Think lungs/respiratory when you see $CO_2$ .

$HCO_3$ (Bicarbonate)

Normal $HCO_3$ : $21 - 28$
Some resources may say $22-26$ , but $21-28$ is the standard for this course and board exams.
$HCO_3$ is a base; the more you have, the more alkalotic you are.
- $HCO_3$ greater than 28: Alkalosis.
- $HCO_3$ less than 21: Acidosis.

Additional Values (Not Required for Now)

PaO2 normal: $80 - 100$ (hypoxemia if less than 80)
SaO2 normal: $95 - 100$

ABG Interpretation Steps

Look at the pH first (low or high).
Assess $PaCO_2$ (low, normal, or high).
Assess $HCO_3$ (low, normal, or high).
Match the pH imbalance with either $CO<em>2$ or $HCO</em>3$ imbalance.
If the issue is $CO<em>2$ , think respiratory; if it's $HCO</em>3$ , think metabolic.

Quick Method: ROME

ROME = Respiratory Opposite, Metabolic Equal.
Respiratory: pH and $CO_2$ arrows will move in opposite directions.
Metabolic: pH and $HCO_3$ arrows will move in the same direction.

Practice Problems

Example 1

pH: 7.30 (Low = Acidic).
$CO_2$ : 40 (Normal).
$HCO_3$ : 19 (Low = Acidic).
Since $HCO_3$ is low (acidic), it's metabolic acidosis.

Example 2

pH: 7.30 (Low).
$CO_2$ : 50 (High).
$HCO_3$ : 24 (Normal).
Arrows are opposite (pH down, $CO_2$ up) = Respiratory.
Low pH = Acidosis.
Result: Respiratory Acidosis.

Example 3

pH: 7.50 (High).
$CO_2$ : 40 (Normal).
$HCO_3$ : 30 (High).
Equal arrows = Metabolic.
High pH = Alkalosis.
Result: Metabolic Alkalosis.

Respiratory Alkalosis

pH > 7.45 and $CO_2$ < 35
Hyperventilation is a key cause (breathing off too much $CO_2$ ).
Other causes: anxiety, high altitudes, pregnancy, fever, hypoxia, early pulmonary emboli.
Asthma:
- Early stages: Respiratory Alkalosis (breathing fast).
- Late stages (if untreated): Respiratory Acidosis (tiredness, poor gas exchange).
COPD: Typically Respiratory Acidosis (retaining $CO_2$ ).

Metabolic Alkalosis

Loss of gastric juices (e.g., vomiting, NG tube) removes stomach acid.
Other causes: potassium-wasting diuretics, overuse of antacids.
Treatment: Address the underlying cause (e.g., antiemetics for vomiting, fluids, treat the flu).

Lab Trick

"If it comes out the as $=$ idosis".
Diarrhea $=$ Metabolic Acidosis.
Vomiting $=$ Metabolic Alkalosis.

Respiratory Acidosis

Low respiratory rate/hypoventilation (not exhaling enough $CO_2$ ).
Causes: drug overdose, chest trauma, airway obstruction.

Metabolic Acidosis

Diarrhea (losing base).
Organ failure (kidney, liver).
Sepsis.
Diabetic ketoacidosis.
Treatment: Address the underlying cause (e.g., Narcan for drug overdose, CPR if not breathing, fluids for diarrhea).