Respiratory System Overview

Anatomy of the Respiratory System

The respiratory system is essential for gas exchange, supplying oxygen to the body and removing carbon dioxide. It consists of upper and lower airways, lungs, and associated structures.

• Upper Airways: Nose, mouth, pharynx, larynx

• Lower Airways: Trachea, bronchi, bronchioles, alveoli

• Muscles: Diaphragm, intercostal muscles, abdominal muscles

• Thoracic Cage: Ribs

• Pleura: Parietal and visceral layers

Conducting Airways

Conducting airways move air to and from the atmosphere and lungs. They humidify, filter, and warm air, and contain a mucociliary system to remove pathogens and foreign materials.

• Mucociliary System: Captures pathogens in mucus and transports them to the pharynx for elimination.

• Non-sterile Environment: Upper airways are non-sterile, important for nursing care.

Mechanics of Ventilation

Ventilation Process

Ventilation is the movement of air from the atmosphere to the alveoli, driven by contraction and relaxation of the diaphragm and intercostal muscles.

• Inspiration: Thorax expands, intrapulmonary pressure decreases, air flows in.

• Expiration: Thorax relaxes, pressure increases, air flows out.

Lung Compliance

Lung compliance measures the ease of lung expansion.

• High Compliance: Lungs stretch easily, optimal gas exchange.

• Low Compliance: "Stiff lungs" require more pressure to inflate, seen in restrictive lung diseases.

• PEEP (Positive End Expiratory Pressure): Used to keep alveoli open.

Lung Inflation and Surfactant

• Surfactant: Lipoprotein secreted by type II alveolar cells reduces surface tension, preventing alveolar collapse.

• Thoracic Structure: Rib cage and pleura help maintain lung inflation.

Gas Exchange and Diffusion

Pulmonary Gas Exchange

Gas exchange occurs at the alveolar-capillary membrane, where oxygen diffuses into blood and carbon dioxide diffuses out.

• External Respiration: Oxygen moves from alveoli to pulmonary capillaries; CO2 moves from capillaries to alveoli.

• Internal Respiration: Oxygen moves from blood to cells; CO2 moves from cells to blood.

Factors Affecting Diffusion

• Partial Pressures: PaO2, PaCO2, PvO2, PvCO2

• Pressure Gradient: Drives direction and rate of gas movement

• Surface Area: Greater area increases gas exchange

• Thickness of Membrane: Increased thickness decreases diffusion (e.g., pulmonary edema, fibrosis)

• Time: Exposure time for diffusion, affected by cardiac output

Oxygen Transport and Oxyhemoglobin Dissociation Curve

Hemoglobin and Oxygen Transport

Hemoglobin (Hgb) binds oxygen in the lungs and releases it to tissues. The oxyhemoglobin dissociation curve illustrates the relationship between O2 bound to Hgb and partial pressure of O2.

• Left Shift: Increased affinity, O2 tightly bound, less released to tissues (causes: alkalosis, hypothermia, hypocapnia, decreased 2,3-DPG)

• Right Shift: Decreased affinity, O2 loosely bound, more released to tissues (causes: acidosis, hyperthermia, hypercapnia, increased 2,3-DPG)

Pulmonary Perfusion and V/Q Relationship

Pulmonary Perfusion

Blood is pumped from the right heart to the lungs for oxygenation, then returned to the left heart for systemic circulation.

• Factors: Hemoglobin concentration, affinity of O2 to Hgb, gravity, cardiac output, blood flow, vasoconstriction

Ventilation-Perfusion (V/Q) Ratio

The V/Q ratio compares alveolar ventilation (V) to pulmonary capillary perfusion (Q).

• Normal Ratio: 0.8 (4L air : 5L blood)

• V/Q Mismatch: Seen in pulmonary embolism, shunting, and other disorders

Pulmonary Shunting

Pulmonary shunting refers to blood bypassing gas exchange, contributing to hypoxemia.

Ventilation Changes in the Older Adult

Age-Related Changes

Aging affects the respiratory system, decreasing lung compliance and gas exchange efficiency.

• Flattened diaphragm

• Stiffened chest wall

• Increased rib cage diameter

• Weakened respiratory muscles

• Air trapping and decreased gas exchange

Assessment and Diagnostics

Respiratory Assessment

• Vital Signs: Pulse, BP, respiratory rate, temperature

• Pulse Oximetry (SpO2): Measures oxygen saturation

• Capnography: Measures exhaled CO2 (etCO2)

• Physical Exam: Inspection, palpation, percussion, auscultation

Pulmonary Function Tests (PFTs)

PFTs assess ventilation, muscle strength, and disease progression.

• Tidal Volume: Air moved in/out per breath

• Vital Capacity: Maximum air expired after maximal inspiration

• Minute Ventilation: Total air expired in 1 minute

Common Pulmonary Disorders

Restrictive Pulmonary Disorders

Restrictive lung diseases limit lung expansion, reducing total lung capacity and oxygenation.

• Intrinsic: Pulmonary fibrosis, sarcoidosis, occupational lung diseases

• Extrinsic: Neuromuscular diseases, obesity

Obstructive Pulmonary Disorders

Obstructive diseases restrict airflow, causing air trapping and hypercapnia.

• Examples: COPD, bronchitis, asthma

• Symptoms: Dyspnea, wheezing, cough

Respiratory Medications

Beta Agonists

• Short-acting: Salbutamol (Ventolin), Albuterol

• Action: Bronchodilation via beta-2 adrenergic stimulation

• Adverse Effects: Tachycardia, hypokalemia, hypertension, tremors

Anticholinergic Bronchodilators

• Examples: Ipratropium bromide (Atrovent), Tiotropium (Spiriva)

• Action: Blocks cholinergic-induced bronchoconstriction

• Side Effects: Cough, dry mouth

Corticosteroids

• Forms: IV, PO, inhaled

• Action: Anti-inflammatory, reduces airway inflammation

• Side Effects: Delayed wound healing, GI upset, immune suppression, oral thrush (inhaled)

Acute Respiratory Failure and ARDS

Acute Respiratory Failure

Occurs when the cardiopulmonary system cannot meet oxygen demands, resulting in hypoxia and/or hypercapnia.

• Type 1: Hypoxemic (PaO2 ↓)

• Type 2: Hypercarbic (PaCO2 ↑)

• Symptoms: Dyspnea, tachypnea, cyanosis, altered LOC

Acute Respiratory Distress Syndrome (ARDS)

ARDS is a diffuse lung injury with severe inflammation and fluid accumulation, impairing gas exchange.

• Triggers: Pneumonia, sepsis, COVID-19

• Diagnostic Criteria: Rapid onset, bilateral opacities, PaO2/FiO2 < 300 mmHg

• Interventions: Neuromuscular blocking agents, prone positioning, ECMO

Pulmonary Embolism and Respiratory Infections

Pulmonary Embolism (PE)

PE is a blood clot blocking pulmonary vasculature, restricting blood flow and gas exchange.

• Risk Factors: Immobilization, surgery, smoking, malignancy, pregnancy

• Diagnosis: CT angiogram, ultrasound

• Interventions: Anticoagulants, thrombolysis, IVC filter

Respiratory Infections

• Aspiration Pneumonia: Oral/gastric secretions reach lungs

• Viral Pneumonia: Influenza, RSV, coronavirus

• Bacterial Pneumonia: Streptococcus pneumoniae, MRSA, E. coli

• Fungal Pneumonia: Aspergillus, Candida (immunocompromised)

Chest Trauma and Pleural Disorders

Rib Fractures and Flail Chest

Multiple rib fractures can cause flail chest, impairing ventilation and increasing risk for pneumonia and DVTs.

Pneumothorax

Pneumothorax is lung collapse due to loss of negative intrapleural pressure.

• Types: Spontaneous, traumatic, tension

• Interventions: Chest tube, needle decompression

Pleural Effusion, Hemothorax, Empyema

• Pleural Effusion: Fluid accumulation in pleural space (transudative or exudative)

• Hemothorax: Blood in pleural space

• Empyema: Pus in pleural space

• Interventions: Medications, chest tube

Summary Table: Key Pulmonary Terms

Formulas and Equations

Mean Arterial Pressure (MAP)

• MAP is used to assess organ perfusion. The formula is:

P/F Ratio

• P/F ratio is used to assess severity of respiratory failure:

Clinical Assessment and Nursing Interventions

• Assess airway, breathing, circulation, disability (ABCD)

• Monitor vital signs, SpO2, capnography

• Support ventilation and oxygenation (e.g., supplemental O2, PEEP, BiPAP, CPAP)

• Manage underlying conditions (infection, trauma, pulmonary disorders)

• Positioning: "Good lung down" to improve V/Q matching

References

• Wagner, K., Hardin-Pierce, M., & Welsh, D. (2018). High Acuity Nursing (7th ed.). Boston: Pearson.

• Venus, K., Munshi, L. and Fralick, M. Prone positioning for the patient with hypoxic respiratory failure related to COVID-19: Canadian Medical Association Journal, 192(47), E1532-E1537