How to Read ABGs/ Everything with Airway

Question 1

Rule of 4s
Mnemonic to remember for Acid Base Disorders

Answer 1

Here’s how the “rule of 4s” works:
* pH: Remember that the normal pH is close to 7.40, which rounds off to 7.4 in the “rule of 4s.”
* pCO2: The normal pCO2 is approximately 40 mmHg, which also ends with a “4” in the “rule of 4s.”
* HCO3-: The normal bicarbonate level is around 24 mEq/L, which again has a “4” in the “rule of 4s.”
pO2: The normal pO2 is 80-100 mmHg, which is close to 80 and can be associated with the “rule of 4s.”

Question 2

What is the normal range for pH, PaCO2, HCO3-. What is metabolic acidosis/alkalosis and respiratory acidosis/alkalosis?

Answer 2

• Acidemia (pH < 7.35) indicates acidosis.
• Alkalemia (pH > 7.45) indicates alkalosis.
• High PaCO2 (> 45 mmHg) indicates respiratory acidosis.
• Low PaCO2 (< 35 mmHg) indicates respiratory alkalosis.
• High HCO3- (> 26 mEq/L) indicates metabolic alkalosis.
• Low HCO3- (< 22 mEq/L) indicates metabolic acidosis.

    · While many acid-base disorders involve complex pathology, they manifest themselves as deviations in levels of either arterial PCO2, bicarbonate, or both.
  
    · Four categories:
        · (1) high pCO2 is a respiratory acidosis
        · (2) low pCO2 is a respiratory alkalosis
        · (3) low bicarbonate is a metabolic acidosis (4) high bicarbonate is a metabolic alkalosis.

Hint: Just look at what is out of order, if it is the CO2 then it is respiratory if it is Bicarbonate then it is metabolic. Then look at the pH, if it is low it is acidosis and if it is high it is alkalosis.

Question 3

Do you know directional changes in arterial blood values how the body tries to compensate under acid or alkalotic conditions?

Answer 3

You should know

Question 4

Do you know how the body tries to compensate under acid or alkalotic conditions in terms of lab values?

Answer 4

Now you know

Question 5

Sample Problem #1
A patient’s arterial blood gas (ABG) results are as follows:
* pH: 7.30
* PaCO2: 50 mmHg
* HCO3-: 26 mEq/L
Interpret these results.

Answer 5

• pH is below the normal range (7.35-7.45), indicating an acidic pH
• PaCO2 is elevated (normal range: 35-45 mmHg), indicating respiratory acidosis
• HCO3- is within the HIGH normal range (22-26 mEq/L)
• the patient has respiratory acidosis with compensatory metabolic alkalosis (elevated
  HCO3- within normal range)
• The primary acid-base disorder is respiratory acidosis due to high PaCO2, and the metabolic alkalosis is the compensatory response to this acidosis

Question 6

Sample Problem #2
A patient’s arterial blood gas (ABG) results are as follows:
* pH: 7.49
* PaCO2: 30 mmHg
* HCO3-: 25 mEq/L

Interpret these results

Answer 6

• pH is above the normal range (7.35-7.45), indicating basic pH
• PaCO2 is decreased (normal range: 35-45 mmHg), indicating respiratory alkalosis
• HCO3- is within the normal range (22-26 mEq/L)
• Based on these results, the patient has respiratory alkalosis.
• There is no compensatory metabolic disorder present because the HCO3- level is within the normal range.
• Therefore, the primary acid-base disorder is respiratory alkalosis due to low PaCO2.

Question 7

What is the anion gap used to calculate?

Anion Gap = (Sodium) - (Chloride + Bicarbonate)

Answer 7

1. It evaluates and assess acid-base disorders
   • It represents the difference between the measured cations (positively charged ions) and the measured anions (negatively charged ions) in the blood
   • The anion gap is calculated using the following formula:
     Anion Gap = (Sodium) - (Chloride + Bicarbonate)

Question 8

What are the 2 types of Metabolic Acidosis Normal Anion Gap Acidosis

Answer 8

1. Normal Anion Gap Metabolic Acidocis or (Non-anion) Also known as hyperchloremic or non-anion gap acidosis (NAGMA)
2. High Anion Gap Metabolic Acidosis
   * This type of acidosis occurs when there is an increase in the levels of chloride ions in proportion to the decrease in bicarbonate ions (HAGMA)
   * Causes of normal anion gap acidosis include:
   * gastrointestinal losses (e.g., diarrhea)
   * Renal tubular acidosis
   * Administration of certain drugs (e.g., acetazolamide usually things that effect Na because Chloride follows sodium).

HAGMA* Also known as anion gap metabolic acidosis
* This type of acidosis occurs when there is an increase in unmeasured anions (such as lactate,
ketones, and sulfates) in relation to the decrease in bicarbonate ions
* Causes of high anion gap acidosis include:
* Diabetic ketoacidosis
* Lactic acidosis
* Renal failure
* Ingestion of toxins (e.g., methanol, ethylene glycol).

Question 9

What is High Anion Gap Acidosis

Answer 9

• Also known as anion gap metabolic acidosis
  * This type of acidosis occurs when there is an increase in unmeasured anions (such as lactate,
  ketones, and sulfates) in relation to the decrease in bicarbonate ions
  * Causes of high anion gap acidosis include:
  * Diabetic ketoacidosis
  * Lactic acidosis
  * Renal failure
  * Ingestion of toxins (e.g., methanol, ethylene glycol).

Question 10

How do the different anion gap issues present themselves

Answer 10

Question 11

What is Right Curve Oxygen dissociation

Answer 11

It is when you increase the relase of Oxygen from the Hemoglobin to the tissue

Question 12

What Is the Oxygen Dissociation Curve

Answer 12

Question 13

What is Left Curve Oxygen Dissociation

Answer 13

It is when you decrease the relase of Oxygen from the Hemoglobin to the tissue. Hence with Left shift, the tissue is Left Behind

Question 14

In the Oxygen Dissociation Curve what shifts the curve to the Right and what shifts it to the Left

Answer 14

The shifters are PCO₂, H⁺, decrease Temperature, Altitude, 2-3 BPG

The left shifters are a decrease in The shifters are PCO₂, H⁺, decrease Temperature, decrease in Altitude, and a decrease in 2-3 BPG

The right shifters are an increase in PCO₂, H⁺, Temperature, Altitude, and 2-3 BPG

Question 15

. Which of the following spirometric values measures the maximum volume of air exhaled after a deep breath in?
a) Forced expiratory volume in 1 second (FEV1)
b) Forced vital capacity (FVC)
c) Peak expiratory flow rate (PEFR)
d) Forced expiratory flow (FEF25-75)

Answer 15

Answer: b) Forced vital capacity (FVC). FVC measures the total volume of air exhaled forcefully after a deep inhalation.
The maximum volume of air exhaled forcefully after full inspiration.
Explanation: FVC measures how much air a person can exhale forcefully after taking a deep breath. It is an important marker of lung function.

Incorrect Choices:
a) FEV1 measures how much air can be exhaled in the first second, not the total volume.
c) PEFR measures the fastest speed of exhalation, not the total volume.
d) FEF25-75 -measures airflow in the middle 50% of exhalation. It is used to detect small airway disease because it captures airflow in the later phase of expiration when small airways contribute more resistance.

Question 16

What does a decreased FEV1/FVC ratio indicate?
a) Restrictive lung disease
b) Obstructive lung disease
c) Normal lung function
d) Increased lung compliance

Answer 16

Answer: b) Obstructive lung disease.
Explanation: A low FEV1/FVC ratio suggests an airflow obstruction, commonly seen in asthma, COPD, and other obstructive lung diseases.

a) Restrictive lung disease: These conditions (e.g., pulmonary fibrosis) cause reduced lung volumes but maintain a normal or increased FEV1/FVC ratio.
c) Normal lung function: A normal ratio suggests no obstruction.
d) Increased lung compliance: Increased compliance occurs in conditions like emphysema, but compliance itself does not determine the FEV1/FVC ratio.

FEV1/FVC Ratio:

This ratio measures how much air a person can exhale in one second (FEV1) relative to their total forced exhalation (FVC).
It is not compared to the population; rather, it reflects the patient’s own lung function.
A low FEV1/FVC ratio (<70%) indicates obstructive lung disease because patients struggle to push air out quickly due to narrowed airways.
A normal or high FEV1/FVC ratio with reduced lung volumes suggests restrictive lung disease (e.g., pulmonary fibrosis).

Question 17

Which of the following is most likely to cause inspiratory obstruction and noisy breathing?
a) Bronchiolitis
b) Upper airway obstruction
c) Small airway disease
d) Bronchiectasis

Question 18

Which condition is characterized by expiratory wheezing due to small airway obstruction?
a) Epiglottitis
b) Laryngotracheomalacia
c) Intrathoracic airway obstruction
d) Laryngeal cyst

Question 19

What is ventilation and perfusion or what is V/Q shunt mean?

Answer 19

Ventilation (V) = The movement of air into and out of the lungs (i.e., how much fresh air reaches the alveoli).
Perfusion (Q) = The blood flow to the lungs via the pulmonary circulation (i.e., how well oxygen is delivered to the blood).
Ventilation-Perfusion (V/Q) Mismatch occurs when:

Low V/Q (Shunt) → Blood reaches alveoli that aren’t ventilated (e.g., pneumonia, atelectasis).
High V/Q (Dead Space) → Air reaches alveoli that aren’t perfused (e.g., pulmonary embolism).

Question 20

Which of the following findings supports an asthma diagnosis?
a) FEV1/FVC ratio increased after bronchodilator
b) FEV1 decreases by >12% after exercise challenge
c) No change in lung function after bronchodilator
d) Oxygen saturation <85% at rest

Answer 20

Answer: (b) FEV1 decreases by >12% after exercise challenge.

(✅) b) Correct → Exercise-induced bronchoconstriction is a hallmark of asthma. A drop in FEV1 > 12% or PEF > 13% supports diagnosis.
(❌) a) Wrong → Asthma is obstructive, so FEV1/FVC decreases, not increases.
(❌) c) Wrong → Reversibility (increase in FEV1 > 12% after bronchodilator) confirms asthma. No change suggests a different cause (e.g., restrictive disease).
(❌) d) Wrong → Asthma usually doesn’t cause hypoxemia at rest; this is more common in severe lung disease (e.g., ARDS, COPD).

Question 21

Which patient is at the highest risk for life-threatening asthma exacerbations?
a) A child with occasional mild symptoms
b) A patient with well-controlled asthma on low-dose ICS
c) A patient with a history of ICU admission for asthma
d) A patient using an inhaled corticosteroid-formoterol as needed

Answer 21

Answer: (c) A patient with a history of ICU admission for asthma.

(✅) c) Correct → History of ICU admission or intubation is a major risk factor for severe asthma exacerbations.
(❌) a) Wrong → Mild, well-controlled asthma does not indicate high risk.
(❌) b) Wrong → ICS therapy reduces exacerbation risk.
(❌) d) Wrong → ICS-formoterol is now recommended as needed, reducing severe attacks.

Question 22

Which of the following is the most likely finding in a patient with a lung abscess?
a) Cavitary lesion with air-fluid level on chest X-ray
b) Diffuse ground-glass opacities
c) Steeple sign
d) Normal chest X-ray

Answer 22

Answer: (a) Cavitary lesion with air-fluid level on chest X-ray.

(✅) a) Correct → A lung abscess appears as a cavity with an air-fluid level due to necrosis and liquefaction.
(❌) b) Wrong → Ground-glass opacities are seen in interstitial pneumonia, ARDS, and viral infections.
(❌) c) Wrong → Steeple sign is seen in croup.
(❌) d) Wrong → A lung abscess is visible on imaging.

Question 23

Which condition is an example of a low V/Q mismatch?
a) Pulmonary embolism
b) Asthma exacerbation
c) Emphysema
d) Pneumothorax

Answer 23

Answer: (b) Asthma exacerbation.

(✅) b) Correct → Asthma causes air trapping and poor ventilation in some areas, leading to low V/Q mismatch (blood flows to poorly ventilated alveoli).
(❌) a) Wrong → Pulmonary embolism causes high V/Q mismatch (ventilation without perfusion).
(❌) c) Wrong → Emphysema causes both high and low V/Q mismatches due to alveolar destruction and capillary loss.
(❌) d) Wrong → Pneumothorax collapses the lung, leading to absent ventilation (extreme V/Q mismatch).

Question 24

What is the difference between obstructive, restrictive and increased lung compliance?

Answer 24

1️⃣ Obstructive Lung Disease: “Hard to Exhale”
🛑 Problem: Narrowed or blocked airways make it hard to get air out.

💨 Analogy:
Imagine breathing through a straw—you can get air in, but it’s tough to push it all out.

🫁 Examples:
Asthma (airways tighten & fill with mucus)
COPD (chronic bronchitis + emphysema)
Bronchiectasis
🩺 Key Features:
✔ Increased lung compliance (lungs stretch too easily, but don’t recoil well)
✔ Air trapping (lungs stay partially full even after exhaling)
✔ Increased residual volume (more air stuck inside)
===========
2️⃣ Restrictive Lung Disease: “Hard to Inhale”
🛑 Problem: Lungs are stiff or restricted, making it difficult to expand and take in air.

💨 Analogy:
Imagine trying to blow up a thick, stiff balloon—it’s hard to fill with air.

🫁 Examples:

Pulmonary fibrosis (scarring makes lungs stiff)
Sarcoidosis (lung inflammation)
Pleural effusion (fluid buildup around lungs)
Obesity-related lung restriction (extra weight compresses lungs)
🩺 Key Features:
✔ Decreased lung compliance (lungs resist stretching)
✔ Reduced lung volumes (TLC, FVC)
✔ Normal or high FEV1/FVC ratio (since both go down proportionally)
===============
3️⃣ Increased Lung Compliance: “Too Stretchy, Can’t Recoil”
🛑 Problem: Lungs inflate too easily but don’t snap back when exhaling.

💨 Analogy:
Imagine a grocery bag instead of a balloon—it stretches too much and doesn’t push air out well.

🫁 Example:

Emphysema (damaged alveoli lose elasticity)
🩺 Key Features:
✔ Increased total lung capacity (TLC)
✔ Air trapping & barrel chest
✔ Low elastic recoil → difficulty exhaling

Question 25

Why does severe asthma cause hypoxemia with respiratory alkalosis?
A) Air trapping prevents CO2 from being exhaled
B) Increased respiratory rate blows off CO2
C) Mucus production directly raises CO2 levels
D) Hypercapnia develops in mild asthma

Answer 25

✅ Correct Answer: B) Increased respiratory rate blows off CO2
🔹 During an asthma attack, patients hyperventilate due to hypoxemia, leading to low PCO2 (respiratory alkalosis).

❌ Why the others are wrong?

A) Air trapping prevents CO2 from being exhaled → This is true in late-stage or severe asthma, leading to respiratory acidosis (not alkalosis).
C) Mucus production directly raises CO2 levels → Mucus blocks airways, worsening hypoxia, but CO2 retention occurs later in severe cases.
D) Hypercapnia develops in mild asthma → No, mild asthma doesn’t cause CO2 retention; it only happens in life-threatening cases.

Question 26

Conditions that increase asthma severity include all EXCEPT:
A) Chronic hyperplastic sinusitis
B) Obesity
C) GERD
D) Type 2 Diabetes

Answer 26

✅ Correct Answer: D) Type 2 Diabetes
🔹 Diabetes affects metabolic function but does not directly worsen airway inflammation in asthma.

❌ Why the others are correct?

A) Chronic hyperplastic sinusitis → Chronic upper airway inflammation can trigger asthma flares.
B) Obesity → Increased abdominal pressure & systemic inflammation worsens asthma.
C) GERD → Acid reflux can irritate airways and trigger bronchospasms.

Question 27

Which of the following is a potential complication of asthma?
A) Generalized seizures
B) Airway wall remodeling
C) Pulmonary fibrosis
D) Cardiac arrhythmias

Answer 27

✅ Correct Answer: B) Airway wall remodeling
🔹 Chronic inflammation in asthma can lead to permanent structural changes in the airways, making treatment less effective.

❌ Why the others are wrong?

A) Generalized seizures → Asthma does not directly cause seizures, but hypoxia may contribute in severe cases.
C) Pulmonary fibrosis → More common in restrictive lung diseases (e.g., idiopathic pulmonary fibrosis).
D) Cardiac arrhythmias → Can occur secondary to hypoxia or beta-agonist overuse, but not a primary complication of asthma.

Question 28

What happens when you inhale or why does bp drop when you inhale?

Answer 28

Normal Physiology of Systolic BP During Inspiration
Inspiration Creates Negative Intrathoracic Pressure

When you inhale, your diaphragm contracts and moves downward, and your ribcage expands.
This expansion increases the volume inside your chest (thoracic cavity), causing the pressure inside the chest to drop (negative intrathoracic pressure).
Increased Venous Return to the Right Heart

Because of the lower pressure in the chest, more blood is pulled into the right atrium from the veins (superior & inferior vena cava).
This temporarily expands the right ventricle (RV) as it fills with more blood.
Interventricular Septum Shift & Reduced Left Ventricular Filling

The right ventricle (RV) now takes up a bit more space inside the heart.
The septum (wall between right and left ventricles) shifts slightly to the left, reducing the space available for the left ventricle (LV) to fill with blood.
As a result, less blood enters the LV, leading to a slight drop in stroke volume and a minor decrease in systolic blood pressure (BP).
Why is the Drop Normally <10 mmHg?

This process is normal and usually reduces systolic BP by less than 10 mmHg during each breath.
The effect is mild because the body maintains a balance between the right and left sides of the heart.