Respiratory System

Abnormal Ventilation/Perfusion (V/Q) Ratio

Shunt [↓ V/Q]

  • Anatomic shunt
    • Intracardiac shunt
    • Pulmonary arteriovenous malformation (AVM)
    • Hepatopulmonary syndrome
  • Physiologic shunt
    • Obstructive lung diseases
    • Alveolar lung diseases

Dead Space [↑ V/Q]

  • Shock
  • Pulmonary embolism
  • Pulmonary vascular diseases

Etiology of Increased A-a Gradient

  • Interstitial lung diseases
  • V/Q mismatch

Etiology of Hypoventilation

  • ↓ Respiratory drive
  • ↓ Tidal volume
    • Neuromuscular disorders
    • Chest wall deformities

Abnormal Physical Examination Findings

Finding Mechanism Conditions
Hyperresonant percussion ↓ Density Pneumothorax
Emphysema
Dull percussion ↑ Density Pleural effusion
Lung consolidation
↓ Fremitus Accumulation in pleural space Pleural effusion
↑ Fremitus Accumulation in lung Lung consolidation

Abnormal Breathing Patterns

Etiology of Kussmaul Breathing {KUSSMAUL}

  • Ketoacidosis
  • Uremia
  • Sepsis
  • Salicylate
  • Methanol
  • Aldehyde
  • Uricemia
  • Lactic acidosis

Etiology of DLCO Changes

Decreased DLCO

  • Emphysema
  • Interstitial lung diseases

Increased DLCO

  • Asthma

Light Criteria for Pleural Fluid (PF)

PF PF ÷ Serum TP PF ÷ Serum LDH PF LDH
Transudate < 0.5 < 0.6 < 2/3 Serum LDH upper limit
Exudate > 0.5 > 0.6 > 2/3 Serum LDH upper limit
  • Total protein (TP)
  • Lactate dehydrogenase (LDH)

Comparison Between Obstructive and Restrictive Lung Diseases

  Obstructive Restrictive
TLC
FEV1
FVC -
FEV1/FVC -

Types of Obstructive Lung Diseases

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
    • Chronic bronchitis
    • Emphysema
      • Centriacinar emphysema
      • Panacinar emphysema
  • Bronchiectasis
    • Central bronchiectasis
    • Peripheral bronchiectasis

Etiology of Obstructive Lung Diseases

Disease Etiology
Asthma Hypersensitivity
Chronic bronchitis Smoking
Centriacinar emphysema Smoking
Panacinar emphysema α1-antitrypsin deficiency
Central bronchiectasis Allergic bronchopulmonary aspergillosis (ABPA)
Peripheral bronchiectasis Cystic fibrosis
Primary ciliary dyskinesia
Immunodeficiency

Classification of Asthma Severity

Asthma Attacks Awakenings SABA Uses FEV1 FEV1/FVC
Intermittent < 2 days/week ≤ 2/month ≤ 2 days/week > 80% Normal
Mild persistent 2 ~ 7 days/week 3 ~ 4/month 2 ~ 7 days/week > 80% Normal
Moderate persistent Daily > 1/week Daily 60 ~ 80% ↓ < 0.05
Severe persistent Throughout Daily Throughout < 60% ↓ > 0.05

Medications for Asthma

Mechanism Medication
β2 agonists Albuterol
Salmeterol
Formoterol
M antagonists Ipratropium
Tiotropium
NF-κB inhibitors Corticosteroids
LOX inhibitors Zileuton
LTD4 antagonists Montelukast
Zafirlukast
Mast cell inhibitors Cromolyn
Nedocromil
IgE inhibitors Omalizumab

Treatment of Asthma

Acute Asthma

  • Nebulized β2 agonists
  • Intravenous magnesium
  • Intravenous corticosteroids

Chronic Asthma

GOLD Staging of Chronic Obstructive Pulmonary Disease (COPD)

Stage Severity FEV1
1 Mild > 80%
2 Moderate 50 ~ 80%
3 Severe 30 ~ 50%
4 Very severe < 30%

Types of Pneumoconioses

Type Deposit Location Findings Associations
Asbestosis Asbestos Lung base Calcified pleural plaques
Ferruginous bodies
Bronchogenic carcinoma
Mesothelioma
Coal worker's disease Coal dust Lung apex - -
Silicosis Silica Lung apex Eggshell calcifications Tuberculosis
Berylliosis Beryllium Hilum Hilar adenopathy -

Types of Lung Cancers

Type Location Paraneoplastic Syndromes
Small cell carcinoma Central ACTH & SIADH
Lambert-Eaton myasthenic syndrome
Paraneoplastic myelitis/encephalitis
Squamous cell carcinoma Central PTHrP
Adenocarcinoma Peripheral -
Large cell carcinoma Peripheral β-hCG

Modified Wells Criteria for Pulmonary Embolism

Criteria Points
DVT symptoms/signs 3
Clinical suspicion 3
Tachycardia 1.5
Immobilization 1.5
Previous PE/DVT 1.5
Hemoptysis 1
Malignancy 1

Management of Suspected Pulmonary Embolism

Score Risk Management
0 ~ 1 Low D-dimer
2 ~ 6 Intermediate CT angiography
V/Q scan
Bedside echocardiography
≥ 7 High Treatment

Evaluation for Pulmonary Embolism

  • D-dimer
  • CT angiography
  • Ventilation/Perfusion (V/Q) scan
  • Bedside echocardiography

Treatment of Pulmonary Embolism

  • Anticoagulants
  • IVC filter
  • Revascularization
    • Thrombolysis
    • Thrombectomy

Lower Respiratory Tract Infections

Infection Pathogens Management
Epiglottitis Haemophilus influenzae Antibiotics
Intubation
Laryngotracheobronchitis [Croup] Parainfluenza virus Corticosteroids
Nebulized epinephrine
Bronchitis
Bronchiolitis
Virus Supportive care
Pneumonia Any Antimicrobials

Sputum Sample Acceptable for Gram Stain

  • PMNs > 25/HPF
  • Epithelial cells < 10/HPF

Pathogens of Bronchitis & Bronchiolitis

  • RSV
  • Rhinovirus
  • Parainfluenza virus
  • Influenza virus
  • Adenovirus
  • Coronavirus

Pathogens of Pneumonia

Lobar Pneumonia & Bronchopneumonia

  • Staphylococcus aureus
  • Streptococcus pneumonia
  • Haemophilus influenzae
  • Klebsiella pneumoniae
  • Pseudomonas aeruginosa
  • Anaerobes
  • Virus

Atypical Pneumonia {LCM}

  • Legionella
  • Chlamydia
  • Mycoplasma

Empirical Antibiotics for Pneumonia

Patient Antibiotics
CAP & Outpatient Amoxicillin
Macrolides / Doxycycline
CAP & Outpatient & Complicated Amoxicillin & (Macrolides / Doxycycline)
Fluoroquinolones
CAP & Inpatient Anti-pneumococcal β-lactams & (Macrolides / Doxycycline)
Fluoroquinolones
CAP & Inpatient & Complicated Anti-pneumococcal β-lactams & Fluoroquinolones
HAP Anti-MRSA & Anti-pseudomonal β-lactams & Fluoroquinolones

Complicated Outpatients

  • Age > 65 years
  • Antibiotics within 3 months
  • Commorbid

CURB-65 Score for Inpatient

  • Confusion
  • Uremia :: BUN > 19
  • Respiratory rate > 30
  • Blood pressure :: SBP/DBP < 90/60 mm Hg
  • Age > 65 years

Respiratory Failure

Type PaO2 PaCO2 A-a Gradient Etiology
1 - V/Q mismatch
2 - Hypoventilation
3 Mixed
4 - Sepsis

Indications for Mechanical Ventilation

  • GCS ≤ 8
  • PaCO2 > 50 mmHg
  • PaO2 < 60 mmHg
  • SpO2 < 90%

Ventilator Modes

Sequence Control Trigger Mode
Continuous mandatory Presure (PC)
Volume (VC)
Time Assist-control ventilation (ACV)
Intermittent mandatory Presure (PC)
Volume (VC)
Time
Patient
Synchronized intermittent mandatory ventilation (SIMV)
Continuous spontaneous - Patient Pressure support ventilation (PSV)

Etiology of Post-intubation Desaturation {DOPE}

  • Displacement
  • Obstruction
  • Pneumothorax
  • Equipment failure

Ventilation Weaning Parameters

Parameter Normal Adult Range Weaning Threshold
Respiratory Rate (RR) 14 ~ 18 < 40
Tidal Volume (VT) 5 ~ 7 mL/kg 5 mL/kg
Rapid shallow breathing index (RSBI) = RR ÷ VT < 50/min/L < 105/min/L
PF Ratio = PaO2 ÷ FiO2 > 400 > 200
Max Inspiratory Pressure < -90 cm H2O < -25 cm H2O