Ch. 8 - Acid-Base Balance and ABGs

Pathophysiology Exam 2

What is the normal blood pH?

7.35-7.45

What is the normal PaCO2?

35-45mmHg

What is the normal HCO3?

22-26 mEq/L

What is the normal PaO2?

80-100 mmHg

What is the normal oxygen saturation (SaO20)?

95-100%

What is an acid?

A substance that donates hydrogen ions (H+), lowering pH

What is a base?

A substance that accepts hydrogen ions or releases bicarbonate (HCO3), increasing pH

What happens when pH falls below 7.35?

Acidosis develops

What happens when pH rises above 7.45?

Alkalosis develops

What are the three mechanisms that regulate pH?

Chemical buffer systems (seconds), respiratory system (minutes), kidneys (hours to days)

What is the fastest pH regulation system?

Chemical buffer systems

Which organ regulates carbon dioxide?

The lungs

Which organ regulates bicarbonate?

The kidneys

Why is CO2 considered an acid?

CO2 combines with water to form carbonic acid (H2CO3)

How do the lungs compensate for acidosis?

Hyperventilate to remove CO2

How do the lungs compensate for alkalosis?

Hyperventilate to retain CO2

How do the kidneys compensate for acidosis?

Retain HCO3 and excrete H

How do the kidneys compensate for alkalosis?

Excrete HCO3 and retain H

Which ABG value reflects respiratory function?

PaCO2

Which ABG value reflects metabolic function?

HCO3

Which ABG value determines whether the patient is acidotic or alkalosis?

pH

What is the first step when interpreting an ABG?

Look at the pH

What is the second step?

Determine whether PaCO2 or HCO3 matches the pH change

What is the third step?

Determine whether compensation is occuring

pH - 7.30

PaCO2 - 52

HCO3 - 24

Respiratory acidosis

pH - 7.50

PaCO2 - 30

HCO3 - 24

Respiratory alkalosis

pH - 7.28

PaCO2 - 40

HCO3 - 32

Metabolic acidosis

pH - 7.48

PaCO2 - 40

HCO3 - 32

Metabolic alkalosis

What causes respiratory acidosis?

Hypoventilation causing CO2 retention

What happens to CO2 in respiratory acidosis?

CO2 increases (>45 mmHg)

What happens to pH in respiratory acidosis?

pH decreases

List four causes of respiratory acidosis?

COPD

Pneumonia

Drug overdose

Airway obstruction

What are the signs and symptoms of respiratory acidosis?

Confusion

Headache

Drowsiness

Warm, flushed skin

Dyspnea

What can severe respiratory acidosis lead to?

Respiratory failure, coma, and death if untreated

What causes respiratory alkalosis?

Hyperventilation causing excessive CO2 loss

What happens to CO2 in respiratory alkalosis?

CO2 decreases (<35 mmHg)

What happens to pH in respiratory alkalosis?

pH increases

List four causes of respiratory alkalosis

Anxiety

Pain

Fever

Pulmonary embolism

What are the signs and symptoms of respiratory alkalosis?

Dizziness

Lightheadedness

Tingling

Numbness

Muscle cramps

Tetany

What causes metabolic acidosis?

Loss of bicarbonate or excess acid production

What happens to bicarbonate during metabolic acidosis?

HCO3 decreases (<22 mEq/L)

List four causes of metabolic acidosis?

Diabetic ketoacidosis (DKA)

Lactic acidosis

Renal failure

Severe diarrhea

Why does diarrhea cause metabolic acidosis?

It causes loss of bicarbonate-rich intestinal fluids

What are the signs and symptoms of metabolic acidosis?

Kussmaul respirations

Weakness

Hypotension

Confusion

Nausea

What are Kussmaul respirations?

Deep, rapid breathing that removes CO2 to compensate for metabolic acidosis

What causes metabolic alkalosis?

Excess bicarbonate or loss of hydrogen ions

List four causes of metabolic alkalosis

Vomiting

NG suction

Diuretics

Excess antacid use

Why does vomiting cause metabolic alkalosis?

Vomiting causes loss of hydrochloric acid (HCL) from the stomach

What are the signs and symptoms of of metabolic alkalosis?

Muscle cramps

Weakness

Tetany

Confusion

Cardiac arrhythmias

What is compensation?

The body’s attempt to restore pH using another organ system

Which compensates faster: lungs or kidneys?

Lungs

What happens to potassium during acidosis?

Potassium shifts out of the cells, causing hyperkalemia

What happens to potassium during alkalosis?

Potassium shifts into cells, causing hypokalemia

Why are potassium imbalances dangerous?

They can cause muscle weakness and life-threatening cardiac dysrhythmias

What does the ROME mnemonic stand for?

Respiratory = Opposite

pH down/ CO2 up = Respiratory acidosis

pH up / CO2 down = Respiratory alkalosis

Metabolis = Equal

pH down / HCO3 down = Metabolic acidosis

pH up / HCO3 up = Metabolic alkalosis