JC20 - Cor Pulmonale and respiratory failure

Question 1

Define Cor Pulmonale

Answer 1

Enlargement of right ventricle/ Right heart hypertrophy due to increased right ventricular afterload from lung/ airway diseases, chest wall disorder, poor ventilation control or pulmonary circulation

Associated with pulmonary hypertension

Manifests as right heart failure

Question 2

Pathophysiology of cor pulmonale

Answer 2

1) Respiratory diseases with Hypoxia > Hypoxic vasoconstriction and polycythaemia > Increased pulmonary vascular resistance
2) Disorders of pulmonary vessels > Increase pulmonary vascular resistance

>> Pulmonary Hypertension
>> Right ventricular hypertrophy/ dilatation due to increased RV workload
>> RV failure

Question 3

Clinical features of Cor Pulmonale

Answer 3

□ Underlying lung condition

□ Pulmonary hypertension: SOB, loud P2

□ Right ventricular hypertrophy and RH failure: oedema, chest pain, fatigue, syncope, palpitation, ↑JVP, parasternal heave, RV S3

→ Often manifest during acute exacerbation of chronic respiratory problem
→ Also prone to LV failure (reason unknown, may be due to pro-inflammatory state)

Question 4

First-line investigations for diagnosis of Cor Pulmonale

Answer 4

□ Arterial blood gas: hypoxaemia ± hypercapnia

□ CXR:
→ Dilated pulmonary trunks with peripheral pruning
→ RV dilatation

□ ECG: p pulmonale, right atrial dilatation, right ventricular hypertrophy

□ Echocardiography – doppler for pulmonary hypertension, right ventricular function

Question 5

Management of Cor pulmonale

Answer 5

□ Treat underlying respiratory disease
□ Diuretics for Right heart failure, Low salt diet and fluid restriction
□ Anticoagulation for ↓risk of thromboembolism
□ Digoxin if atrial tachyarrhythmia

Question 6

Underlying diseases that cause Cor Pulmonale

Answer 6

1. Respiratory diseases with hypoxia causing pulmonary hypertension
   - COPD
   - Bronchiectasis
   - ILD
2. Disorder of pulmonary circulation:
   - Chronic pulmonary thromboembolism
   - Massive acute PE
   - Primary PHTN
3. Chest wall dysfunction: - Kyphoscoliosis, Obesity hypoventilation syndrome
4. Acute exacerbations of chronic respiratory diseases

Question 7

Define respiratory failure and define gas tension in arterial blood gas

Answer 7

Respiratory failure = Failure of the lungs to meet the metabolic demands of the body
□ Hypoxaemia → failure in tissue oxygenation
□ Hypercapnia → failure in carbon dioxide homoeostasis

Type 1: ↓pO2 <60mmHg (8kPa) + ↓/-pCO2 ≤ 50mmHg (6.5kPa)

Type 2: ↓pO2 <60mmHg (8kPa) + ↑pCO2 > 50mmHg (6.5kPa)

Question 8

Define normal limits of PaO2, PaCO2 and pH

Answer 8

PaO2 10.6-14.0 kPa
PaCO2 4.7-6.0 kPa
pH 7.35-7.45

Question 9

3 main pathophysiological causes of Type 1 respiratory failure

List examples of respiratory diseases a/w each pathophysiological process

Answer 9

V/Q mismatch: hypoxaemia and CO2 retention

e.g. COPD, asthma, bronchiectasis, pulmonary embolism

Shunting: Mixed venous blood passes through lungs without oxygenation (alveoli not ventilated)

e.g. pneumonia, collapsed lung, ARDS, acute pulmonary oedema

Diffusion impairment: = failure of pulmonary capillary blood to fully equilibrate with alveolar gas

e.g. ILD, pulmonary oedema, emphysema

Question 10

4 main pathophysiological causes of Type 2 respiratory failure

Answer 10

Depressed respiratory drive (TV and RR increase): e.g. sedative overdose, CNS depression, metabolic alkalosis, hypothermia, hypothyroidism

Neuromuscular (Low TV, High RR): spinal cord injury, GBS, phrenic nerve injury, myasthenia gravis…

Thoracic cage disorder (Low TV High RR): kyphoscoliosis, flail chest, OHS

Global lung hypoventilation: upper airway obstruction, decompensated diffuse lower airway disorder (COPD, asthma)

Question 11

Clinical features of Type 2 respiratory failure

Answer 11

Hypercapnia/ CO2 retention: headache (from vasodilation), altered mentation, flushing, papilloedema, HTN, flapping tremor

Acidosis: Kussmaul breathing, gasping

Question 12

Clinical features of Type I respiratory failure

Answer 12

Hypoxia and Hypocapnia

• *Increase respiratory effort**: tachypnoea, use of accessory respiratory muscles
• *Diaphragmatic fatigue**: paradoxical breathing of abdomen
• *Sympathetic discharge**: ↑HR, ↑BP, sweating, agitation
• *Hypoxaemia**: central cyanosis, confusion

Question 13

Pathophysiology of respiratory failure

Answer 13

respiratory failure is defined in terms of gas tension
of blood leaving the lungs i.e. arterial blood gases

Question 14

Formulas for oxygen saturation, DO2 and Minute Volume

Answer 14

Minute ventilation or minute volume = tidal volume (TV) x respiratory rate (RR)

O2 delivered to body / mls/min (DO2): (O2 binding capacity of Hb x SaO2) x cardiac output = 1.34 x Hb x SaO2 x C.O.

Oxygen saturation = Oxy Hb / (Oxy Hb + reduced Hb) = % of oxy Hb

Question 15

Causes of increased respiratory load

Answer 15

Airway resistive loads: Bronchospasm; Airway edema, secretions, scarring; Upper airway obstruction; OSA

Lung elasticity: Alveolar edema, atelectasis, infection…etc

Chest wall elasticity: Pneumothorax, rib fracture, effusion, tumor, ascites…etc

Minute ventilation load: Sepsis, PE, hypovolemia

Question 16

Causes of decreased respiratory strength

Answer 16

Depressed respiratory drive: drug, brainstem lesion, hypothyroidism

Neuromuscular diseases: spinal cord lesion, GBS, ALS, MG, Botulism…etc

Muscle weakness: Fatigue, Electrolyte disturbance, Malnutrition, Myhopathies…etc

Question 17

Clinical picture:

Long history of cough and exertional dyspnea

bilateral leg swelling for one day

Physical examination:
o Cyanotic, tachypnoeic
o Bilateral pitting ankle oedema
o Inspiratory retraction of intercostal muscles

Hyperinflated chest with diffuse expiratory rhonchi

Oxygen saturation on
supplemental oxygen at 1 L/min
through nasal cannula: 94%

Interpret following profile

Answer 17

Clinical diagnosis:
o Chronic obstructive pulmonary disease (COPD) – chronic bronchitis, pulmonary emphysema
o Acute on chronic type 2 respiratory failure – hypoxaemia ± hypercarbia, respiratory acidosis with inadequate renal metabolic compensation

o Cor pulmonale (right heart failure)

o Precipitated by respiratory infection

Question 18

Pathophysiology of chronic bronchitis and emphysema (COPD)

Answer 18

1. Destruction of alveoli - loss of capillary bed and loss of elastic support of airways
2. Inflammation of airway - collapse of distal poorly supported airways
3. Excess secretion with mucus plugging
4. Increased airway smooth muscle contraction - Airflow obstruction, gas trapping, hyperinflation

Question 19

Describe the lung function test profile for COPD

Answer 19

o Obstructive: LOW FEV1 / FVC
o Air trapping: High residual volume
o Hyperinflation: High total lung capacity
o Destroyed capillary bed: Low DLCO

Question 20

Pathophysiology of respiratory failure in COPD

Answer 20

Mixed type 1 and 2 Respiratory failure:_

V/Q mismatch:
 Destruction of alveoli: loss of capillary bed
 Airflow obstruction

Alveolar hypoventilation:

 Respiratory muscle fatigue: Increase work of breathing due to increased airway resistance

 Blunted central drive: severe hypoxaemia and hypercarbia

Shunting: pneumonia or congestive heart failure

Question 21

Management of acute (on chronic) respiratory failure in COPD

Answer 21

1. Treat airflow obstruction in COPD:

 Inhaled bronchodilators (beta-agonists, anticholinergics)
 Systemic steroids in acute exacerbation of COPD

2. Identify the trigger of exacerbation and treat, e.g. infections, pneumothorax
3. Supportive measures for respiratory failure:
    Oxygen supplement
    Ventilatory support (invasive or non-invasive)
4. Treat heart failure – diuretics
5. Identify any other comorbidities e.g. arrhythmia, ischemic heart disease

Question 22

Long-term management of COPD with chronic respiratory failure

Answer 22

1. Stop smoking
2. Treat airway obstruction and inflammation - Bronchodilator and ICS
3. Pulmonary rehabilitation
4. Influenza and pneumococcal vaccines
5. Long-term home oxygen/ LTOT
6. Home nocturnal ventilation

Question 23

A COPD patient was admitted for acute onset of shortness of breath. He has an oxygen saturation of 75% on 3 liters/min of oxygen supplement, and arterial blood gas confirms severe hypoxemic respiratory failure with no carbon dioxide retention. CXR shows hyperinflation and a 3 cm lung mass in RLZ suspicious of lung malignancy. What is the cause of this severe hypoxaemia?

A. Acute exacerbation of COPD
B. Pulmonary embolism
C. Pleural effusion

Answer 23

B: CXR shows lung mass in this patient with COPD (likely heavy smoking history) suspicious of lung cancer. Malignancy predisposes to deep vein thrombosis and pulmonary embolism which gives rise to further hypoxemia.

Question 24

Severe kyphoscoliosis may lead to type 2 respiratory failure with high carbon dioxide retention due to the pathophysiologic mechanism of:

A. Ventilation:perfusion mismatch
B. Shunting
C. Hypoventilation

Answer 24

(C: Chest wall restriction leads to limited lung expansion and hypoventilation)

Question 25

Which of the following among the three is the first line treatment in COPD, and why?

A. Inhaled bronchodilator
B. Oral beta agonists
C. Inhaled corticosteroids

Answer 25

(A: COPD only has partial and limited reversibility of airways obstruction, given the structural destruction of alveolar tissue. But the small degree of bronchodilatation can lead to less air-trapping and lung hyperinflation, thus resulting in lower work of breathing and less dyspnea and better exercise tolerance.)