Gas Exchange Fundamentals

Gas Exchange

• Transports oxygen to cells and carbon dioxide away from cells
• Occurs through ventilation

Ventilation

• Movement of air in and out of the lungs

Diffusion

• Movement of gases between the alveoli and blood

Perfusion

• Arterial blood flow through tissues
• Blood is pumped by the heart to deliver oxygen to the tissues

Systems Involved in Gas Exchange

• Neuro
• Respiratory
• Cardiovascular
• Lungs deliver O2 to pulmonary capillaries
• Hemoglobin picks up O2 and transports it to cells
• Cell metabolism uses O2 to produce CO2 as byproduct
• Hemoglobin carries CO2 back to the lungs for exhalation

Oxygen Deprivation Conditions

• Ischemia: Insufficient oxygenated blood flow to tissues, can result in hypoxemia and cell damage/death
• Hypoxemia: Reduced oxygenation of arterial blood, low O2 levels can lead to hypoxia
• Hypoxia: Insufficient oxygen reaching cells and decreased tissue oxygenation
• Anoxia: Complete oxygen absence in body tissues

Respiratory Anatomy

• Nasal Cavity & Nares: Air enters and flows to the pharynx, moving down to the trachea
• Main Stem Bronchi: Branch off from the trachea, feeding air into the lungs
• Diaphragm: Located beneath the lungs, it allows for lung expansion during inhalation and contraction during exhalation

Airway Components

• Upper Airway: nasal cavity, oral cavity, pharynx, and larynx
• Lower Airway: trachea, bronchi, and bronchioles
• Lungs: Responsible for gas exchange
• Alveolar Air Sacs (Alveoli): Facilitate gas exchange, O2 enters blood and CO2 exits

Autonomic Nervous System

• The unconscious control center for vital functions regulates the breathing process automatically

Breathing Mechanics

• Body takes in air and sends signals to muscles around lungs
• Diaphragm flattens and intercostal muscles contract, creating more space for the lungs to expand

Air Pathway

• Air enters through nose or mouth
• Passes through the trachea, moving into the bronchi
• Travels through the bronchioles
• Reaches the Alveoli

Gas Exchange

• Oxygen diffuses from alveoli into hemoglobin in red blood cells
• Carbon dioxide diffuses from hemoglobin into alveoli

Exhalation Mechanics

• Diaphragm returns to a dome shape
• Intercostal muscles relax
• Chest cavity reduces, forcing air out of the lungs

Air Volume

• Approximately 10,000 liters of air are processed each day

Anatomy & Physiology of the Respiratory System

• Trachea (Windpipe): Surrounded by cartilaginous rings
• Pleural Cavity: Area where the lungs sit

Physiology of Breathing

• Primary Drive to Breathe: Depends on CO2 levels in arterial blood
• When CO2 levels rise, receptor sites in the medulla and pons stimulate increased ventilation rate/depth
• CO2 levels primarily drive breathing, not O2 levels
• Secondary Drive to Breathe: Receptor sites in aortic arch and carotid arteries monitor O2 levels

Breathing Quality

• Breathing effort and sounds that occur
• Effective breathing requires a patent airway

Oxygen Delivery

• Depends on inflated and well-oxygenated alveoli and well-perfused capillaries

Ventilation/Perfusion (VQ) Ratio

• Describes the concentration of O2/CO2 moving across membranes
• Ventilation issues: Blockages in alveoli (sputum, inflammation, atelectasis, fluid volume excess)
• Perfusion issues: Blood clots, plaque buildup, and emphysemic alveoli interfere with capillary blood flow

Oxygenation Components

• Requires proper lung function (ventilation)
• Requires Cardiovascular perfusion function (blood flow)

Dead Space (Air Trapping)

• When alveoli are too inflated, normal perfusion cannot take place

Assessment & Physical Exam

• History: cystic fibrosis, asthma, pneumonia, allergies, TB, diabetes, hypertension, heart disease
• Skin/Nail Beds: Pallor or cyanosis
• Nasal Flaring: Indicates difficulty breathing
• Work of Breathing: Dyspneic
• Neuro Exam: ALOC, difficulty speaking
• Respiratory Rate
• Pulse Oximetry
• Inspection: Breath Sounds, Accessory Muscle Use, Chest Symmetry
• Positioning: Tripod position, ask about orthopnea (use of pillows for sleeping)
• Cough: Productive or non-productive, Is it related to activity
• Sputum: Characteristics include color, thickness, amount

Early signs of Hypoxia

• Includes chest pain, restlessness, irritability, and fatigue

Labs & Diagnostics

• ABGs, Sputum Testing, RBC
• Imaging: Chest x-ray, thoracic CT, pulmonary angiogram, VQ scans
• Tests: Pulmonary function tests (PFTs), bronchoscopy, thoracentesis
• Tools: Incentive spirometry, peak expiratory flow rate (PEFR), exercise testing, capnometry and capnography

Normal Lung Sounds

• Bronchial Sounds: Loud, high-pitched, heard over the trachea, longer exhalation than inhalation
• Bronchovesicular Sounds: Medium loudness and pitch, heard over sternum and between scapulae - equal duration during inhalation and exhalation
• Vesicular Sounds: Soft and low-pitched, heard over peripheral lung fields, longer on inhalation than exhalation
• The left lung has 2 lobes and the right has 3
• Always listen anteriorly and posteriorly

Abnormal Breath Sounds

• Rhonchi: Coarse and low-pitched, continue through inspiration, indicating blockage of large airway passages
• Stridor: High-pitched sound in trachea/larynx, indicates narrowing, commonly seen in croup
• Crackles: High-pitched popping sounds, heard during inspiration, associated with fluid in alveoli
• Common in atelectasis, pneumonia, pneumothorax, or pleural effusion
• Wheezing: High-pitched whistling, usually during expiration, indicates narrowing of bronchi, seen in Asthma patients
• Pleural Rub: Low-pitched crackling during both inspiration and expiration, indicates pleural inflammation, TB and pneumonia

Sound Differentiation

• Wheezing persists after a cough
• Rhonchi disappear after a cough

Adventitious Breath Sounds

• Stridor: Continuous, high-pitched, crowing sound heard predominantly on inspiration
• Caused by partial obstruction of the larynx or trachea, foreign body obstruction and croup are common conditions
• Typically loudest over the anterior neck
• Wheeze: High-pitched, continuous, musical sound heard predominantly on expiration, caused by air passing through an obstructed narrow airway

Wheeze Types

• Sibilant Wheeze: High-pitched, whistle-like sound
• Sonorous Wheeze (Rhonchi): Deep, low-pitched, rumbling or coarse sound is caused by air moving through tracheal/bronchial passages, seen in asthma, emphysema, and chronic bronchitis

Crackles

• Fine, short, high-pitched, intermittent crackling sounds caused by air passing through fluid, pus, or mucus and commonly heard in the base of lung lobes during inspiration
• Coarse Crackles: Low-pitched and moist, caused by pulmonary edema and bronchitis
• Fine Crackles: Sound similar to hair rubbing near the ear, caused by congestive heart failure and pulmonary fibrosis
• Pleural Rub: Harsh, grating, or creaking sound caused by movement of inflamed pleural surfaces rubbing against each other during chest wall movement
• Lower anterior lungs and lateral chest during both inhalation and expiration in tuberculosis and pneumonia

Long-term Hypoxia Signs

• Nail Clubbing: often due to chronic cardiovascular or respiratory disease
• Barrel Chest: common in chronic respiratory conditions

Arterial Blood Gas (ABG)

• A blood specimen taken from an artery to measure O2 and CO2 levels
• pH: 7.35-7.45
• PaCO2: 35-45 mmHg
• PaO2: 80-100 mmHg
• HCO3: 22-26 mEq/L
• SpO2: 95-100%

Venous Blood Gas (VBG)

• Similar to ABG, but measures from a vein

CO2 Levels

• Hypercarbia (Hypercapnia): High CO2 levels
• Hypocarbia (Hypocapnia): Low CO2 levels

SaO2

• Measures the percentage of hemoglobin carrying oxygen
• Normal can vary with a patient’s health history

Kidney’s Role in Acid-Base Balance

• Increased pH (Alkalotic): Kidneys excrete bicarbonate (HCO3)
• Decreased pH (Acidotic): Kidneys retain bicarbonate to balance acids

Acid-Base Balance

• Respiratory Opposite: pH ↑ and PaCO2 ↓ = Respiratory Alkalosis, pH ↓ and PaCO2 ↑ = Respiratory Acidosis
• Metabolic Equal: pH ↑ and HCO3 ↑ = Metabolic Alkalosis, pH ↓ and HCO3 ↓ = Metabolic Acidosis

Nursing Interventions

• Monitor vital signs, lab values, and fluid status
• Assess activity tolerance (space periods of activity with rest)
• Promote secretion clearance (suctioning if necessary)
• Encourage deep breathing exercises and smoking cessation
• Assist with ADLs (activities of daily living)
• Positioning: High Fowler’s or Semi-Fowler’s

Oxygen Therapy

• Purpose: To relieve hypoxemia and hypoxia
• Goal: Use the lowest fraction of inspired oxygen (FIO2) to achieve acceptable oxygen levels without causing harm

Oxygen Delivery Devices

• Room Air: 21% FIO2
• Nasal Cannula: 24-45% FIO2, 1-6 L/min
• Simple Face Mask: 40-60% FIO2, minimum 5 L/min
• Partial Rebreather: 60-75% FIO2, 6-11 L/min
• Venturi Mask: 24-50% FIO2, 12-15 L/min (adjustable FIO2, ideal for COPD)
• CPAP: Continuous Positive Airway Pressure, used for sleep apnea
• High-Flow Nasal Cannula: 30-60 L/min, combines heat and humidity
• Non-Rebreather: >90% FIO2, 10-15 L/min
• Ambu Bag: Used in CPR to deliver forceful breaths