Cyanosis

Definition

• Harrison's Principles of Internal Medicine 22E, p. 321

Pathophysiology

• Severe anemia: Even with marked arterial desaturation, cyanosis may be absent because total hemoglobin is too low to accumulate 5 g/dL of deoxygenated form.
• Polycythemia vera: Cyanosis appears at higher SaO2 levels due to the excess total hemoglobin available to become deoxygenated.
• Methemoglobin / Sulfhemoglobin: Even small quantities of these dysfunctional hemoglobin derivatives can produce cyanosis. Methemoglobin has an intense dark blue-purple color visible through the skin.

• Skin pigmentation and thickness (may not be apparent until SaO2 drops to 75% in dark-skinned individuals)
• State of the cutaneous capillaries
• Quality of lighting during examination
• Oxyhemoglobin dissociation curve
• Guyton and Hall Textbook of Medical Physiology, p. 548
• Harrison's Principles of Internal Medicine 22E, p. 321

Classification

Central Cyanosis

• SaO2 is reduced OR an abnormal hemoglobin derivative is present
• Both skin and mucous membranes are affected
• Best observed at the tongue and buccal mucosa (most sensitive sites)
• Not relieved by warming or massaging the extremity

• Harrison's Principles of Internal Medicine 22E, p. 322 (Table 42-1)
• Tintinalli's Emergency Medicine, p. 470

Peripheral Cyanosis

• Arterial blood is normally saturated but O2 extraction is abnormally high due to slowed blood flow
• Affects skin of extremities (nail beds, fingers, toes); mucous membranes are typically spared
• Relieved by warming or massaging the area

• Harrison's Principles of Internal Medicine 22E, p. 322
• Tintinalli's Emergency Medicine, p. 470

Key rule: All conditions causing central cyanosis also produce peripheral cyanosis. However, peripheral cyanosis can occur without central cyanosis.

Central vs. Peripheral Cyanosis - Quick Differentiation

Special Situations

Mixed Cyanosis

Neonatal Cyanosis

• Peripheral cyanosis (acrocyanosis) of hands/feet is normal in the first few days of life due to vasomotor instability - benign.
• Central cyanosis in a neonate is always pathological.
  • "Comfortably blue" (cyanosis without respiratory distress) - strongly suggests congenital heart disease.
  • Cyanosis that worsens with crying - cardiac origin.
  • Cyanosis that improves with crying - pulmonary origin.
  • Cyanosis that responds to supplemental O2 - pulmonary cause.
  • Cyanosis not responding to O2 - right-to-left cardiac shunt.
• Rosen's Emergency Medicine, p. 3202

Pseudocyanosis

• Drugs: chlorpromazine, minocycline, amiodarone
• Metals: gold, silver
• Features: mucous membranes are normal color, discoloration does not blanch with pressure, more intense in sun-exposed areas.
• Tintinalli's Emergency Medicine, p. 471

Approach to the Patient with Cyanosis

1. Time of onset: Cyanosis since birth/infancy - think congenital heart disease.
2. Central vs. peripheral differentiation: Examine mucous membranes; warm/massage the extremity.
3. Clubbing: Cyanosis + clubbing together = chronic central cause (congenital heart disease, pulmonary AV fistula, lung abscess). Peripheral cyanosis alone does NOT cause clubbing.
4. PaO2 and SaO2: Measure arterial blood gas; if mechanism is unclear, send spectroscopy for abnormal hemoglobin species.

• Harrison's Principles of Internal Medicine 22E, p. 322

Investigations

• Tintinalli's Emergency Medicine, p. 471

Management Principle

• Administer supplemental oxygen to all patients with central cyanosis.
• Failure to improve with O2 suggests: impaired circulation (shock), abnormal hemoglobin (methemoglobinemia - treat with IV methylene blue), or pseudocyanosis.
• Treat the underlying cause.
• Tintinalli's Emergency Medicine, p. 471

Vital Capacity

Definition

• Fishman's Pulmonary Diseases and Disorders, p. 576

Lung Volumes and Capacities - The Framework

The Four Basic Lung Volumes (do not overlap)

The Four Capacities (each = sum of 2 or more volumes)

• Costanzo Physiology 7th Edition, p. 200

Vital Capacity in Detail

• Larger body size / height
• Male sex
• Physical conditioning / athletic training

• Increasing age
• Female sex (relative to males)
• Obesity
• Restrictive lung diseases
• Extrapulmonary restriction (see below)
• Barash Clinical Anesthesia 9e, p. 1133
• Costanzo Physiology 7th Edition, p. 201

Forced Vital Capacity (FVC)

• Fishman's Pulmonary Diseases and Disorders, p. 585

FVC Maneuver

1. Patient inspires maximally to TLC
2. Forceful, rapid, complete expiration into a spirometer (to RV)
3. Normally completed within 6 seconds (in obstruction, may continue 10-12 s)

FEV1 and the FEV1/FVC Ratio - Clinical Core

FVC and FEV1 in Disease

• In severe asthma, FEV1/FVC can fall below 20%.
• In obstruction, the FVC curve is prolonged and flattened; in restriction, it is steep but low in volume.
• Costanzo Physiology 7th Edition, p. 203
• Guyton and Hall Textbook of Medical Physiology, p. 534

Clinical Significance of Vital Capacity

• Deep breathing ability
• Effective coughing (critical for airway clearance)
• Ability to sustain ventilation (relevant in neuromuscular disease)

Causes of Reduced Vital Capacity

• Pulmonary edema, atelectasis
• Pulmonary fibrosis / interstitial lung disease
• Pneumonia
• Emphysema (gas trapping reduces ERV)

• Pleural effusion
• Pneumothorax
• Pregnancy / large ascites
• Obesity (diaphragm elevation)
• Respiratory muscle weakness (e.g., Guillain-Barre, myasthenia gravis, muscular dystrophy)
• Quadriplegia / spinal cord injury

Critical threshold: FVC < 15 mL/kg is associated with increased risk of postoperative pulmonary complications and may indicate need for ventilatory support. This level is most often seen in quadriplegia or severe neuromuscular disease.

• Barash Clinical Anesthesia 9e, p. 1133-1134

Bedside Estimation

Summary

Atrial Septal Defect (ASD)

Definition

• Sabiston Textbook of Surgery 21e, p. 2563

Embryological Basis

Left: Blood flow in ASD (oxygenated "y" shunts L→R, increasing RA/RV load). Right: Locations of ASD types - Secundum (ASD 2°), Primum (ASD 1°), and Sinus venosus - Harrison's 22E

1. Septum primum grows down, partially closing the ostium primum
2. Before complete closure, ostium secundum opens posteriorly in septum primum
3. Septum secundum grows to cover ostium secundum, leaving the foramen ovale (a right-to-left channel in fetal life due to high pulmonary pressures)
4. At birth: lung expansion drops pulmonary pressure → left atrial pressure exceeds right → foramen ovale closes

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 503

Classification / Types

Important distinction: A patent foramen ovale (PFO) is NOT a true ASD - it is persistence of the flap valve of the fossa ovalis without a true septal deficiency. PFO persists in up to 20-25% of adults and does not cause right heart dilation. It has no resting shunt and is not detectable clinically, but can allow paradoxical embolism if right atrial pressures transiently rise.

• Harrison's Principles of Internal Medicine 22E, p. 2114
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 504

Pathophysiology

Congenital left-to-right shunt lesions: (A) ASD, (B) VSD, (C) PDA - Robbins Pathologic Basis of Disease

Left-to-Right Shunt

• Pulmonary vascular resistance < systemic vascular resistance
• Right ventricular compliance is greater than left ventricular compliance

Consequences of Chronic L→R Shunting

1. Right heart volume overload - RA and RV dilate
2. Increased pulmonary blood flow - pulmonary artery dilation
3. Atrial arrhythmias (AF, flutter) from RA enlargement
4. Pulmonary arterial hypertension - in ~10% of unrepaired ASDs
5. Eisenmenger syndrome - rare; when pulmonary hypertension causes shunt reversal to R→L, producing cyanosis

Significant Shunt Threshold

• Harrison's Principles of Internal Medicine 22E, p. 2113
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 504

Clinical Features

Symptoms

• Childhood: Often asymptomatic; occasional exercise intolerance or frequent respiratory infections
• Adults: Dyspnea on exertion, exercise intolerance, fatigue, palpitations
• Late/advanced: Right heart failure, atrial fibrillation, syncope, stroke (from paradoxical embolism)
• Aging factors: DM, hypertension, and atherosclerosis reduce LV compliance, worsening L→R shunt with age

Physical Examination

• Goldman-Cecil Medicine, p. 985
• Harrison's Principles of Internal Medicine 22E, p. 2113

Investigations

ECG

• Incomplete right bundle branch block (rSr' pattern in V1/V2) - characteristic finding, from RV volume overload
• Right axis deviation
• Right atrial enlargement (tall P waves)
• Prolonged PR interval (especially primum ASD)
• Atrial fibrillation or flutter (in older/advanced cases)

Chest X-Ray

• Pulmonary vascular plethora (increased pulmonary vascular markings bilaterally)
• Dilated main pulmonary artery and branches
• Right atrial and right ventricular enlargement
• Small aortic knuckle (reduced systemic output)

Echocardiography (Diagnostic Gold Standard)

• Transthoracic echo (TTE): Identifies secundum and primum ASDs; RV dilation; estimates PA pressures by Doppler
• Transesophageal echo (TEE): Required for sinus venosus defects and device sizing; agitated saline contrast (bubble study) demonstrates shunt
• Provides shunt ratio estimation (Qp/Qs)

Cardiac Catheterization

• "Step-up" in oxygen saturation at the right atrial level (confirms L→R shunt)
• Precise Qp/Qs measurement and pulmonary vascular resistance
• Indicated when PA hypertension is suspected or non-invasive data are inconclusive
• Goldman-Cecil Medicine, p. 986

Management

Indications for Closure

• Right heart dilation (with or without symptoms) - primary indication
• Qp/Qs ≥ 1.5 with attributable symptoms or signs
• In patients >40 years old: closure improves functional status and survival even with symptoms and large shunts
• Paradoxical embolism risk (prior stroke with PFO/ASD)

Contraindication

• Severe, irreversible pulmonary hypertension (Eisenmenger syndrome) - closure is harmful as it removes the "pop-off" valve

1. Transcatheter (Percutaneous) Device Closure

• Now preferred for secundum ASDs - currently accounts for >60% of all ASD interventions
• Suitable for centrally located defects up to ~3.5 cm with adequate tissue rims
• Amplatzer septal occluder (nitinol mesh) most widely used; placed under fluoroscopic + echocardiographic guidance
• Avoids sternotomy and cardiopulmonary bypass
• Limitations: Large defects, inadequate rims, anomalous pulmonary veins, or associated cardiac lesions requiring repair
• Complications: Device erosion through atrial wall/ascending aorta (rare but serious), conduction disturbances, endocarditis

2. Surgical Closure

• Required for: primum ASDs, sinus venosus defects, coronary sinus defects, large secundum ASDs unsuitable for devices, or when concomitant repairs needed
• Methods: direct suture closure, autologous pericardium patch, or prosthetic patch on cardiopulmonary bypass
• Very low mortality; postoperative survival comparable to general population
• Minimally invasive surgical approaches increasingly used

Timing

• Most centres recommend closure before school age for significant defects
• Earlier closure prevents pulmonary vascular disease; however, small ASDs may close spontaneously (less common than in VSD)
• Sabiston Textbook of Surgery 21e, p. 2563-2564
• Harrison's Principles of Internal Medicine 22E, p. 2114
• Goldman-Cecil Medicine, p. 986

Prognosis

• Small ASDs with minimal shunting: excellent prognosis, may not require intervention
• Surgically/percutaneously closed before pulmonary hypertension develops: life expectancy approaches that of the general population
• Unrepaired large ASDs: progressive right heart failure, atrial arrhythmias, pulmonary hypertension
• Eisenmenger syndrome (R→L shunt reversal): median survival ~40-45 years; managed medically with pulmonary vasodilators

ASD vs. PFO - Key Comparison

• Harrison's Principles of Internal Medicine 22E, p. 2114

Tetralogy of Fallot (TOF)

Overview

The Four Components

1. Ventricular Septal Defect (VSD)

• A large, unrestrictive, misaligned VSD - the aortic valve sits at its superior border
• Located in the perimembranous/subaortic region
• Results directly from the malaligned infundibular septum failing to close the interventricular communication
• The VSD is typically large enough that pressures in both ventricles are equal ("non-restrictive")
• Acts as the conduit for the right-to-left shunt

2. Right Ventricular Outflow Tract (RVOT) Obstruction - Pulmonary Stenosis

• Most often due to subpulmonic (infundibular/subvalvular) stenosis - narrowing of the muscular outflow tract below the pulmonary valve
• May also involve the pulmonary valve itself (valvular stenosis) in addition
• In the most severe form: pulmonary atresia - no forward flow to pulmonary arteries; survival depends on a PDA or bronchial collateral vessels
• The degree of RVOT obstruction is the single most important determinant of the severity of cyanosis and clinical presentation
• The pulmonary trunk is typically small/hypoplastic

3. Overriding Aorta (Dextroposition of the Aorta)

• The aorta is displaced anteriorly and to the right, so it straddles the VSD, receiving blood from both the right and left ventricles
• In a normal heart, the aorta arises entirely from the LV; in TOF, it "overrides" the ventricular septum
• The degree of override is variable - from mild to >50%
• Directly caused by the anterior malalignment of the infundibular septum
• Results in mixing of oxygenated and deoxygenated blood in the systemic circulation

4. Right Ventricular Hypertrophy (RVH)

• Secondary to the other three defects - not a primary developmental anomaly
• RVH develops because the RVOT obstruction causes chronic pressure overload on the right ventricle
• The VSD equalizes pressures between ventricles, so RV systolic pressure = LV systolic pressure = systemic pressure
• Macroscopically: the heart is enlarged and classically boot-shaped (coeur en sabot) due to prominent RVH lifting the cardiac apex, with a concave pulmonary artery segment
• Importantly, RVH protects the pulmonary vasculature from pressure overload (the stenosis acts as a barrier) - so unlike Eisenmenger's, pulmonary vascular disease is not a feature of TOF
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 505-506
• Rosen's Emergency Medicine, p. 3210

Embryological Basis

• Anterior shift → narrows the RVOT (causing stenosis)
• Anterior shift → displaces the aorta rightward (causing override)
• Anterior shift → VSD forms because the septum no longer aligns with the membranous septum
• RVH → develops secondarily from the pressure load

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 505
• The Developing Human - Clinically Oriented Embryology, p. 847

Summary Table: The Four Components

Pathophysiology of Cyanosis

• Degree of RVOT obstruction (increases R→L shunting)
• Systemic vascular resistance (SVR) (fall in SVR worsens R→L shunting)

"Pink Tet" vs Classic TOF

Associated Anomalies

• Right-sided aortic arch - present in ~25% (an important associated finding)
• Atrial septal defect (ASD) - creating a "pentalogy of Fallot" if both present
• Anomalous origin of the left coronary artery (from RCA crossing RVOT - surgically important)
• Partial anomalous pulmonary venous return

Tet Spells (Hypercyanotic/Hypoxic Spells)

1. Knee-to-chest position (increases SVR - most important first step)
2. Supplemental oxygen
3. Morphine 0.1-0.2 mg/kg IV/IM (reduces infundibular spasm and hyperpnea)
4. Sodium bicarbonate (1 mEq/kg IV) for metabolic acidosis
5. Ketamine (maintains/increases SVR)
6. Propranolol 0.1-0.2 mg/kg (reduces infundibular spasm)
7. Phenylephrine 0.01-0.02 mg/kg IV (pure vasoconstrictor, increases SVR)

• Rosen's Emergency Medicine, p. 3211

Investigations

Management

• Definitive treatment: Complete surgical repair - VSD patch closure + RVOT reconstruction (transannular patch to enlarge outflow tract), typically in early infancy
• Staged palliation: For severe cyanosis with very narrow RVOT or hypoplastic pulmonary arteries - modified Blalock-Taussig (BT) shunt (subclavian artery to pulmonary artery) as a bridge to full repair
• PGE1 infusion: For neonates with severe RVOT obstruction or pulmonary atresia - maintains ductal patency to preserve pulmonary blood flow

• Pulmonary regurgitation (most common) → progressive RV dilation → may require pulmonary valve replacement
• Residual RVOT obstruction or VSD
• Ventricular arrhythmias and sudden cardiac death (due to RV dilation/fibrosis)
• Aortic root dilation
• Grainger & Allison's Diagnostic Radiology, p. 303
• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 506

• P wave - small upright deflection; represents atrial depolarization (SA node → atria)
• Q wave - first small downward deflection of the QRS; septal depolarization
• R wave - tall upward spike; ventricular depolarization
• S wave - downward deflection after R; completion of ventricular depolarization
• T wave - broader upright wave after QRS; ventricular repolarization
• U wave - small wave after T (not always visible); possibly Purkinje repolarization

• Horizontal: 1 small square = 0.04 sec; 1 large square = 0.2 sec
• Vertical: 1 small square = 0.1 mV; 1 large square = 0.5 mV
• Paper speed: 25 mm/sec

Bronchiectasis

Definition

• Robbins & Kumar Basic Pathology, p. 455

Pathogenesis

Obstruction / Infection
        ↓
Impaired mucociliary clearance
        ↓
Mucus retention + bacterial colonisation
        ↓
Inflammatory cell recruitment
        ↓
Cytokines, proteases, bacterial toxins → bronchial wall destruction
        ↓
Airway dilation + peribronchial fibrosis
        ↓
Further impaired clearance → perpetuating cycle

1. Bronchial obstruction - impairs secretion clearance → superimposed infection → inflammatory destruction
2. Bronchial wall damage - direct necrotizing infection destroys wall structural components
3. Parenchymal fibrosis (traction bronchiectasis) - maturing fibrous tissue adjacent to airways retracts and pulls bronchi open

• Grainger & Allison's Diagnostic Radiology, p. 155
• Robbins & Kumar Basic Pathology, p. 455

Causes / Aetiology

Post-Infectious (most common worldwide)

Congenital / Hereditary

Airway Obstruction

• Foreign body aspiration (localized, single segment)
• Endobronchial tumour
• Mucus impaction (e.g., ABPA - allergic bronchopulmonary aspergillosis)
• Atopic asthma, chronic bronchitis (proximal)

Other Causes

• Rheumatoid arthritis (30% prevalence on CT - often clinically silent)
• Inflammatory bowel disease
• Post-lung transplant (obliterative bronchiolitis)
• Young's syndrome
• Recurrent aspiration
• Robbins & Kumar Basic Pathology, p. 455
• Murray & Nadel's Textbook of Respiratory Medicine, p. 1699

Pathological Types (Morphological Classification)

• Grainger & Allison's Diagnostic Radiology, p. 155

Macroscopic and Microscopic Pathology

Macroscopic

• Airways dilated up to 4x their normal diameter
• Can be traced almost to the pleural surface (in health, bronchioles cannot be followed within 2-3 cm of pleura)
• Lower lobes predominantly affected bilaterally (most vertical air passages)
• Localized disease when caused by obstruction or aspiration
• Airways filled with mucopurulent or purulent material

Microscopic

• Active phase: Intense acute and chronic inflammatory exudate within bronchial/bronchiolar walls; desquamation of lining epithelium; ulceration
• Mixed bacterial flora: staphylococci, streptococci, H. influenzae, Pseudomonas aeruginosa, anaerobes
• Chronic/healing phase: Fibrosis of bronchial walls; peribronchial fibrosis; goblet cell metaplasia; abscess cavity formation in severe cases
• Complete epithelial regeneration is unusual - structural damage persists
• Robbins & Kumar Basic Pathology, p. 455-456

Clinical Features

Symptoms

Signs

• Coarse crepitations (crackles) over affected areas - characteristically change with coughing and postural drainage
• Wheeze (from airway secretions or associated bronchoconstriction)
• Digital clubbing - in chronic severe bronchiectasis
• Signs of associated conditions (e.g., rheumatoid arthritis changes)
• In advanced disease: features of cor pulmonale (right heart failure from chronic hypoxia)

Complications

• Robbins & Kumar Basic Pathology, p. 456
• Murray & Nadel's Textbook of Respiratory Medicine, p. 875

Investigations

Chest X-Ray

• Tram lines - thickened bronchial walls seen as parallel lines (bronchi viewed longitudinally)
• Ring shadows - dilated bronchi seen end-on; poorly defined rings or curvilinear opacities
• Tubular opacities - mucus-filled dilated bronchi (gloved-finger shadows)
• Air-fluid levels - in cystic/saccular bronchiectasis
• Increased bronchial wall thickening; lower lobe predominance in idiopathic disease
• Overinflation in CF; atelectasis/volume loss in localized disease

HRCT Chest (Gold Standard)

• Grainger & Allison's Diagnostic Radiology, p. 155-156

Pulmonary Function Tests

• Obstructive pattern most common (FEV1/FVC reduced)
• Restrictive pattern in severe fibrotic disease
• Mixed pattern possible

Microbiological Investigations

• Sputum culture (routine and AFB): identify colonizing/infecting organisms
  • Common pathogens: H. influenzae, P. aeruginosa (associated with worse prognosis), S. aureus, Moraxella catarrhalis
• Sputum for NTM (non-tuberculous mycobacteria)

Aetiological Investigations (to identify the underlying cause)

• Serum immunoglobulins (IgG, IgA, IgM) - immunodeficiency
• Sweat chloride / CFTR gene testing - cystic fibrosis
• Nasal mucosal biopsy / ciliary beat frequency - primary ciliary dyskinesia
• Serum IgE, RAST for Aspergillus, total IgE - ABPA
• Alpha-1-antitrypsin level
• Autoantibodies (RF, ANA) - connective tissue disease

Management

Conservative / Medical

• Chest physiotherapy with postural drainage - essential; the basis of long-term management
• Active cycle of breathing techniques, oscillatory devices (Flutter, Acapella)
• Mucolytics (nebulized hypertonic saline, DNase in CF)

• Antibiotics guided by sputum culture and sensitivities
• H. influenzae: amoxicillin or co-amoxiclav
• Pseudomonas aeruginosa: ciprofloxacin (oral) or IV antipseudomonal penicillin/cephalosporin
• Duration typically 14 days (longer than standard pneumonia)

• Long-term macrolide therapy (azithromycin 3x/week) - reduces exacerbation frequency and improves lung function (anti-inflammatory + antibiotic effects)
• Inhaled antibiotics (tobramycin, colistin) for Pseudomonas-colonized patients

• Inhaled β2-agonists - improve mucociliary clearance and reverse bronchoconstriction
• Useful in patients with associated airflow obstruction

• Minor haemoptysis: usually managed with antibiotics
• Massive haemoptysis: bronchial artery embolization (interventional radiology)

• Annual influenza vaccine
• Pneumococcal vaccine

Surgical

• Reserved for localized bronchiectasis not responding to medical treatment
• Lobectomy or segmentectomy of the most severely affected lobe
• Low mortality in carefully selected patients
• Lung transplantation - for end-stage bilateral bronchiectasis (e.g., CF)
• Robbins & Kumar Basic Pathology, p. 456
• Murray & Nadel's Textbook of Respiratory Medicine, p. 875

Summary