Some Fundamentals
Arterial-Alveolar Gradient
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A-a Gradient = Measured PaO2 - Calculated PaO2
Quick A-a formula: 150 – (PaCO2 x 1.2 + PaO2)
- Normal: 10-15mm Hg (increases with age)
- Increased:
MECHANISM EXAMPLE PATHOLOGY Shunt ASD, AV Fistula VQ Mismatch PE, COPD, Pneumonia ? Diffusion Interstitial Disease
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Some Fundamentals
Cyanosis
- Central cyanosis only clinically apparent with >5g/dL desaturated Hb
- Cannot be both anemic and cyanotic because cyanosis requires >5g/dL of desaturated Hb (e.g. having >5g/dl desaturated Hb with a total Hb of 8 is clinically impossible)
- Cyanosis is more likely if also polycythemic (e.g. the blue bloater) – (e.g. easy to have >5g/dl of desaturated Hb with a total Hb of 18
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Some Fundamentals
Pitfalls of the Pulse Oximeter
- Anemia
- Pulse ox does not consider Hgb level
- Supplemental O2
- Can mask severe pulmonary process (i.e. when there is an ? A-a gradient)
- Carboxyhemoglobinemia (CO)
- Looks like 100% oxyhemoglobin (e.g. false sat of 100%)
- Methemoglobinemia
- Looks like 85% oxyhemoglobin (e.g. false sat of 85%)
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Asthma (1)
Epidemiology
- Mortality greater in:
- African American and Latinos
- Females
- Adults
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- Factors associated with asthma prevalence
- Developed nations
- Urban areas
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- Factors associated with mortality/morbidity:
- Poverty / lack of access
- Overuse of OTC inhalers / episodic treatment
- Under use of early steroids
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Asthma (2)
Pathophysiology
- Asthma is a chronic inflammatory disease
- Reduced airway diameter 2º to:
- Bronchial constriction
- Bronchial edema
- Mucous plugging
- Increased goblet cells
- Bronchial muscle hypertrophy
- Airway remodelling
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Asthma (3)
Pathophysiology
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Asthma (4)
Pathophysiology
Asthma (5)
Clinical Features
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Precipitants
- URI (#1)
- Allergy
- Respiratory irritants (smoke, chemicals)
- Cold
- Exercise
- GERD
- Beta blockers (even eye drops)
- Methacholine
- ASA, NSAIDs (triad with nasal polyps)
- Menstruation
- Psychological
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- Decreased expiratory flow
- Air trapping & barotrauma
- Pneumothorax
- Pneumomediastinum
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- Decreased venous return
- Hypotension
- Pulsus paradoxus
- Hypercarbia hypoxemia
- Muscle fatigue
- Respiratory failure
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Asthma (6)
Diagnosis
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- Bedside spirometry (PEFR, FEV1)
- Measures large airway obstruction
- Measures severity and response to therapy
- Predicts need for admission
- Pulse oximetry
- Does not aid in predicting clinical outcome
- O2 saturation may paradoxically drop in improving patient due to transient VQ mismatch
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Asthma (7)
Diagnosis
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- Arterial Blood Gases (ABGs)
- Not generally indicated
- Should not be used to determine therapy
- Chest X-ray
- Not generally indicated
- Obtain if:
- Complications suspected (pneumothorax or pneumonia)
- Not improving
- Requiring admission
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Asthma (8)
Asthma Phases
Asthma (9)
Phases
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Asthma (10)
Death Risk Factors
- Hx of sudden severe exacerbations
- Prior intubation
- Prior ICU admit
- >1 admission or >2 ED visits in past year
- ED visit in past month
- >2 adrenergic MDIs per month
- Current/recent systemic steroid use
- "Poor perceivers"
- Concomitant disease – cardiopulmonary or psychosocial
- Illicit drug use
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Asthma Therapy (1)
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Aerosolized ?2 agonists
- 1st line therapy
- Bronchodilators (via adenyl cyclase)
- Selective ?2 agonists have less unwanted ?1 effects (tachydysrhythmias)
- Evidence
- Inhaled superior to oral and parenteral routes, fewer side effects
- Intermittent equal to continuous administration
- MDIs equal to nebulizers
- Racemic equal to "R" enantiomer preparations (levalbuterol)
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Asthma Therapy (2)
Steroids
- Dual Action
- Delayed (hours)
- Principal Mechanism
- Immunomodulatory
- Up-regulate ?-receptors
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- Principal Mechanism
- Immediate (minutes)
- Vasoconstriction (“Blanching Effect")
- Delayed (hours)
- Evidence
- Oral equal to IV administration
- Systemic (PO and IV) superior to inhaled route
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Asthma Therapy (3)
Indicated for Severe Exacerbations
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- Aerosolized Anticholinergics
- Ipratropium bromide (Atrovent)
- Block tone in bronchial smooth muscle
- Modest effect when added to ?-agonists
- Magnesium
- IV infusion (2-3g IV over 10 minutes)
- Smooth muscle relaxant
- Incremental benefit in most severe presentations
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Asthma Therapy (4)
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Not Indicated for Acute Treatment
- Theophylline
- No benefit over ?2 agonists
- Narrow therapeutic index
- Long-Acting ?2 agonists (Salmeterol)
- Long term treatment only
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- Leukotriene modifying agents (Montelukast) and mast cell stabilizers
- Long term preventive treatment only
- Heliox
- Balance of studies find no benefit
- More convincing role in upper airway obstruction
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Asthma Therapy (5)
Intubation and Beyond
- Mechanical Ventilation
- Does not treat obstruction (e.g. the 1° problem!)
- Barotrauma is big concern
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- IV Ketamine
- Sedation and bronchodilation
- Increases secretions
- Anesthetic gases/ECMO
- Transfer to the OR!
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Asthma Therapy (6)
Intubation and Beyond
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Preventing and Managing Barotrauma
- May use paralytics initially to facilitate ventilation
- Continue aggressive in-line nebulizer therapy
- Increase time for expiratory phase (e.g. ? inspiratory flow rate, ? respiratory rate, ? I:E ratio)
- Permissive hypercapnia (allow pCO2 to rise), pOx>88%
- Diligent pulmonary toilet, may need bronchoscopy
- External chest compression
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Asthma Arrest
1 Disconnect ventilator 2 Compress chest
3 Bilateral chest tubes 4 Fluid bolus
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Bronchiolitis
- Presentation and Diagnosis
- Presents like URI-triggered asthma exacerbation in small children (<2 years old, peak age=6 months)
- Clinical diagnosis
- Etiology
- Viral - usually respiratory syncytial virus (RSV)
- Nasal swab for hospital epidemiology
- Treatment
- Supportive, symptomatic care
- Trial of beta-agonists
- Steroids ineffective
- Ribavirin for congenitally ill children
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COPD (1)
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- Definition
- Chronic, inflammatory disease
- Airflow limitation that is not fully reversible and is progressive
- Pathophysiology
- Different inflammatory markers from asthma (e.g. neutrophils, not eosinophils)
- Proteases and oxidants result in tissue destruction
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COPD (2)
- Natural History
- Hypoxemia and hypercapnia
- Destruction of pulmonary vascular bed and thickened vessel walls
- Pulmonary hypertension
- Polycythemia
- Right sided heart failure (cor pulmonale)
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COPD (3)
Clinical Phenotypes
COPD (3)
Clinical Phenotypes
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COPD (4)
Acute Exacerbations
- Definition
- ? Dyspnea
- ? Sputum volume
- ? Sputum purulence
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- Causes
- Viruses
- Role of bacteria controversial
- Environmental
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- Consider Mimics
- Progressive onset
- Pneumonia
- CHF
- Sudden onset
- Pneumothorax
- PE
- Lobar atelectasis
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- Progressive onset
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COPD (5)
Differential Diagnosis of Acute Exacerbation
COPD (6)
CT of Anterior Pneumothorax
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COPD (7)
Bleb Mimicking a Pneumothorax in COPD
COPD (8)
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Another Bleb in COPD Patient
COPD (9)
CT Confirmation of Bullous Disease (Pneumothorax ruled out)
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COPD (10)
Lobar Atelectasis
- Sudden decompensation
- Volume loss distinguishes from pneumonia
- May require emergent bronchoscopy following intubation
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COPD (11)
Therapy for Acute Exacerbations
- Aerosolized ?-agonists and anticholinergics
- First line therapy
- Steroids
- Systemic steroids (IV in ED followed by PO course) reduce rates of relapse and improve dyspnea following ED visit
- Antibiotics
- Indicated in cases with ?sputum volume and purulence
- Non-Invasive ventilation
- Highly effective at avoiding intubation if initiated early
- Not appropriate in patients with respiratory arrest or hemodynamic instability
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COPD (12)
Long Term Interventions
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- Disease Altering Interventions
- Only 2 interventions proven to reduce mortality:
- Smoking cessation
- Home oxygen (for PaO2 < 55 or signs of cor pulmonale)
- Only 2 interventions proven to reduce mortality:
- Pneumococcal Vaccination
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Acute Respiratory Distress Syndrome (1)
- Definition
- Acute Lung Injury (ALI) and ARDS are clinical diagnoses along a spectrum
- Pathogenesis
- Noncardiogenic pulmonary edema due to leaky alveolar capillary membranes
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- Diagnostic criteria
- Hypoxia
- PaO2 < 60 mm Hg with FiO2 > 0.5
- Normal ventricular function
- PCWP < 18 mm Hg
- Diffuse alveolar infiltrates
- With normal heart size
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- Hypoxia
Acute Respiratory Distress Syndrome (2)
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- Causes
- Sepsis (most common)
- Trauma
- Near-drowning
- Aspiration
- Toxicologic (ASA, opiates, hydrocarbons)
- Pancreatitis
- Environmental (high-altitude)
- Fat or amniotic fluid embolus
- CNS catastrophe (e.g. SAH)
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Acute Respiratory Distress Syndrome (3)
- Treatment
- Supportive
- Maintain O2 sat >85% while minimizing FiO2 and airway pressures
- PEEP or CPAP
- Pressure controlled or high frequency ventilation
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- Recent Literature
- Lower mortality with low tidal volume ventilation (6mL/kg)
- Prone position improves oxygenation
- Supportive
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Pneumonia
Critical Mimics Not to Miss
- Cancer
- Tuberculosis
- Pulmonary embolus
- Toxicologic / environmental
- Chlorine gas, Farmer's lung (allergic reaction to inhalation of moldy crops – hay, grain, tobacco)
- ARDS
- e.g. from chronic ASA toxicity or other treatable cause
- Atelectasis
- Right-sided endocarditis
- Septic emboli
- Diffuse alveolar hemorrhage
- Low hemoglobin, immune disease
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Bacterial Pneumonias
| ORGANISM | TYPICAL PATTERN | TYPICAL HOST |
|---|---|---|
| Streptococcus pneumoniae | Lobar (Rusty sputum,Single Rigor) | Everyone Community-acquired Most common overall |
| Haemophilus influenzae | Lobar or patchy | COPD Smokers |
| Staphylococcus aureus (including MRSA) | Pleural Effusion Necrotizing (Abscesses, Cavitation, Empyema) | Post-viral IVDA |
| Klebsiella pneumoniae | Lobar (esp. RUL) Bulging minor fissure (Currant jelly sputum) | Alcoholics COPD, Diabetics |
| Pseudomonas and Enterobacter | Patchy, multilobar, necrotizing, fulminant (sickly sweet odor) | Hospital acquired Immunocompromised Cystic fibrosis |
| Anaerobes | Patchy(esp. lower lobes) (foul smelling sputum) | Alcoholics Poor dentition |
Lobar Pneumonia
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Pneumonia with Effusion
Pneumonia
- Strep. pneumo, H. flu, Staph. aureus
- TB
Non-Infectious Effusions
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- PE
- Abdominal process e.g. pancreatitis
- Aortic dissection
- Boerhaave's syndrome (esophageal rupture)
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Lung Cavitation
Cavities
- Staph
- Pseudomonas
- TB
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Atypical Pneumonias
| ORGANISM | CLINICAL FEATURES | SPECIAL FEATURES |
|---|---|---|
| Mycoplasma pneumoniae | "Walking pneumonia” Young adults CXR: Patchy interstitial | Extrapulmonary findings Guillain-Barré, encephalitis, hemolysis, cold agglutinins, bullous myringitis, erythema multiforme |
| Chlamydia pneumoniae | Non-toxic appearing Infants at 3-20 weeks Outbreaks in young adults CXR: Patchy interstitial | Staccato cough Conjunctivitis (in infant group) |
| Legionella pneumophilia | Contaminated water sources, air conditioning Older, sickly men Toxic patients, altered with relative bradycardia CXR: Unilateral lobar infiltrates | GI symptoms (N,V,D) Low serum sodium Abnormal LFTs No person-to-person transmission No organisms on standard smear |
Interstitial Infiltrates
Interstitial infiltrates
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- Mycoplasma
- Chlamydia
- Viral
Mycoplasma Pneumonia
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Legionella Pneumonia
Really Atypical Pneumonias
| ORGANISM | RISK GROUPS | CLINICAL FEATURES |
|---|---|---|
| Fungi | Southwest US (Coccidioidomycosis) Mississippi River Valley (Histoplasmosis) Southeast US (Blastomycosis) CXR: Hilar adenopathy Diffuse patchy infiltrates | Chest pain Erythema nodosum |
| Q fever (Coxiella burnetii) | Vets, farmers Sheep, goats, cattle CXR: Highly variable | Hepatitis Endocarditis |
| Psittacosis (Chlamydia psittaci) | Bird handlers CXR: Highly variable | Epistaxis Relative bradycardia Sepsis and shock Low WBC count |
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Fungal Pneumonia
Pneumonia: Gram's Stain
| Gram's Stain | Organism |
|---|---|
| Gram positive diplococci | Streptococcus pneumoniae |
| Gram positive cocci in chains | Group A streptococcus |
| Gram positive cocci in clusters | Staph. aureus |
| Gram positive rods | Bacillus anthracis (anthrax) |
| Small Gram neg rods | H. Influenza |
| Short, fat Gram neg paired rods | Klebsiella pneumonia |
| Gram neg rods | Pseudomonas, Enterobacter Yersinia pestis (plague) |
| Intracellular, Gram negative | Chlamydia |
| No bacteria, large PMNs only | Legionella |
| No bacteria, mononuclear cells | Mycoplasma |
Strep Pneumoniae Sputum Gram Stain
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Pneumonia Treatment
| Organisms | Antibiotics | |
|---|---|---|
| Outpatient <60 years old | Strep. pneumoniae Atypicals | Macrolide or Doxycycline |
| Outpatient >60 years old | Strep. pneumoniae H. flu Gram negatives | Macrolide + Cephalosporin or Fluoroquinolone |
| Inpatient, Ward | Same as above | Same as above |
| Inpatient, ICU or Health Care Associated | Add: 1 Pseudomonas 2 Drug resistant Strep. pneumo 3 MRSA coverage | Antipseudomonal cephalosporin or aminoglycoside + Vancomycin |
Pneumonia in Children
| Organisms | Antibiotics | |
|---|---|---|
| Birth-3 weeks | Group B strep E. coli Listeria monocytogenes | Ampicillin + gentamicin or Cefotaxime |
| 3 weeks-3 months | Strep. Pneumoniae Chlamydia trachomatis Bordetella pertussis RSV / Parainfluenza virus 3 | Erythromycin or Cefotaxime |
| 4 months-4 years | Viruses Strep. pneumoniae Mycoplasma pneumoniae | Erythromycin or Cefotaxime |
| 5 years-15 years | Mycoplasma pneumoniae Strep. pneumoniae | Erythromycin/Doxycycline (>8y) or Cefotaxime (sicker) |
| All ages (sick) | Staph. aureus | Vancomycin |
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Uncommon but Deadly
- Hantavirus pulmonary syndrome
- In Southwest US, from aerosolized rodent excreta
- Pulmonary edema with cardiac and renal failure
- Supportive therapy only
- Plague (Yersinia pestis)
- Spread by fleas on rodents (bubonic), bioterrorism (pulmonary)
- Very contagious person-to-person, strict respiratory isolation
- Bilateral, multilobar pneumonia
- Rx: doxycycline, fluoroquinolones, aminoglycosides
- Anthrax (Bacillus anthracis)
- Inhaled (bioterror Class A agent)
- No person-to-person transmission
- Hemorrhagic mediastinitis (prominent mediastinum on x-ray)
- Rx: penicillin, doxycycline or fluoroquinolone
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Uncommon but Deadly (2)
SARS/MERS
Severe Acute Respiratory Syndrome
- Coronavirus
- Person-to-person spread
- Originated from civet cat in Asia (aerosolized fecal material)
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AIDS: Pulmonary Manifestations (1)
- Infectious
- Bacterial: Most common Same pathogens as non-AIDS
- Mycobacterial: TB, Mycobacterium avium complex (MAC)
- Parasitic: Toxoplasmosis
- Viruses: CMV, HSV
- Fungal: PCP Often disseminated Cryptococcosis, histoplasmosis, aspergillosis, candidiasis
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This download link is referred from the post: MBBS 2025 Lecture Notes for all subjects
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