Respiratory JC020: A Cyanotic, Dyspneic Elderly Man With Ankle Edema: Respiratory Failure, Cor Pulmonale

Question 1

Case:

• 70yo chronic smoker
• long history of cough, exertional dyspnea
• seen intermittently by GP
• prescribed inhaler medications once but did not continue to use
• admitted for ↑ dyspnea for 2 days with ↑ cough + purulent sputum
• bilateral leg swelling for 1 day

Answer 1

PE:

• Cyanotic
• Tachypneic
• Bilateral pitting ankle edema
• Inspiratory retraction of intercostal muscles + use of SCM muscle
• Hyperinflated chest with diffuse expiratory rhonchi
• SaO2 on supplemental O2 at 1L/min through nasal cannula: 94%

CXR:

• Cardiomegaly
• ↑ Lung markers esp. lower zone
• No frank consolidation
• Hyperinflation of chest

ECG:

• Right axis deviation
• Large right atrium, P Pulmonale
• RV hypertrophy

ABG (on supplemental O2):

• pH 7.1 (7.35-7.45) —> Respiratory acidosis
• pO2 6.5 (10-13) —> Hypoxaemia
• pCO2 8.1 (4.5-6) —> CO2 retention / Hypercapnia
• Base Excess +8 (+/- 2) —> Renal compensation
• HCO3 32 (24-28) —> Renal compensation

Clinical diagnosis:

• COPD: chronic bronchitis + pulmonary emphysema
• Acute exacerbation of COPD
• Acute on chronic type 2 respiratory failure (Inadequate alveolar ventilation): Respiratory acidosis + Hypoxaemia + Hypercapnia + Renal compensation (but inadequate)
• Cor pulmonale (RH failure)
• Precipitated by respiratory infection

Question 2

Definition of Respiratory failure

Answer 2

Failure of lungs to meet metabolic demands of the body

1. Tissue oxygenation
2. CO2 homeostasis

Respiratory failure defined in terms of ***gas tension of blood leaving the lungs i.e. Arterial blood gases

Question 3

Chronic bronchitis, Emphysema

Answer 3

1. ***Destruction of alveoli (e.g. smoking) with loss of capillary bed + loss of elastic support of airways
2. ***Inflammation of airway wall —> collapse of distal poorly supported airways
3. **Glandular hyperplasia in airway epithelium with **excess secretion + mucus plugging
4. ***↑ Airway smooth muscle contraction (esp. during acute exacerbation)

End result: Airflow obstruction

Emphysema:
Critical narrowing occurs at terminal bronchial level (quite distally) (early closure of airway during expiration due to loss of radial traction / elasticity)
—> Air-trapping in already enlarged non-elastic alveolar sacs (distal to narrowed site)

Question 4

Lung function test in COPD

Answer 4

• Obstructive airway disease pattern
• Only partial reversibility (with BD) (Asthma: very good reversibility)

Obstructive: ↓ FEV1/FVC ratio
Air trapping: ↑ RV (air trapping)
Hyperinflation: ↑ TLC
Destroyed capillary bed: ↓ DLCO

Question 5

***Pathophysiology of Respiratory failure in COPD

Answer 5

1. **V/Q mismatch
   - destruction of alveoli with **loss of capillary bed —> deranged Q
   - airflow obstruction: ***non-uniform distribution of inspired air + air-trapping —> deranged V
2. ***Shunting (alveoli perfused but no ventilation to supply perfused area: V/Q = 0)
   - pneumonia / CHF

1+2: Early stage manifestation: Contribute to ***Type 1 respiratory failure (齋gaseous exchange 有問題)

3. **Alveolar hypoventilation (esp. during acute exacerbation)
   - **Respiratory muscle fatigue
   —> ↑ work of breathing (∵ ↑ airway resistance + hyperinflation (stretch diaphragm, not in optimal tension)) (mechanical disadvantage)
   —> inadequate supply of fuel to respiratory muscles (∵ hypoxaemia, poor nutrition, catabolism)

• **Blunted central drive: severe hypoxaemia + hypercapnia (usually should stimulate breathing)
  3: Late stage manifestation: Contribute to **Type 2 respiratory failure (連ventilation都有問題)

Question 6

Arterial blood gases in COPD

Answer 6

Hypoxaemia +/- Hypercapnia

Acute on Chronic respiratory failure:
- **Respiratory acidosis (∵ CO2 retention) with **inadequate metabolic compensation

Question 7

Oxygen saturation

Answer 7

OxyHb / (OxyHb + reduced Hb)
—> % of OxyHb

Oxygen saturation curve:
Sigmoid shape
—> flattened as pO2 ↑
—> takes a lot of O2 to further ↑ SaO2
—> ∴ usually takes 90% as target

Question 8

Amount of O2 delivered to body / DO2 (ml/min)

Answer 8

DO2:
CaO2 (O2 content of arterial blood) x CO
= (**O2 combined with Hb + **O2 dissolved in plasma) x CO
= [(O2 binding capacity of Hb x SaO2) + O2 dissolved in plasma)] x CO
= [(1.34 x Hb x SaO2) / 100 + (pO2 x 0.0027)] x CO

Question 9

Cor pulmonale

Answer 9

RH hypertrophy due to respiratory disease
- Acute (e.g. massive PE) / Chronic (usually)

Pre-requisite:
- ***Pulmonary hypertension

Manifestations:

• RV hypertrophy
• RH failure

Question 10

***Pathogenesis of Cor pulmonale

Answer 10

1. Hypoxia
   —> Polycythaemia + ↑ Pulmonary vascular resistance

—> Polycythaemia —> ↑ Pulmonary vascular resistance
—> Hypervolaemia
—> ↑ CO

—> ↑ Pulmonary vascular resistance + ↑ CO
—> Pulmonary hypertension
—> ↑ RV workload
—> Cor pulmonale

2. Obliteration / Occlusion of blood vessels (in COPD, emphysematous lungs with enlarged air sacs, no intervening normal alveolar wall structure)
   —> Pulmonary hypertension
   —> ↑ RV workload
   —> Cor pulmonale

Question 11

Diagnosis of Cor pulmonale

Answer 11

1. Clinical features of
   - Pulmonary hypertension
   - RH hypertrophy
   - RH failure
   (e. g. ***ECG features)
2. Underlying lung condition
   - usually chronic e.g. COPD
3. RH failure manifest when acute exacerbation of chronic respiratory problem
   - e.g. ankle edema

N.B. These patients are also prone to CHF (Left + Right HF)
- e.g. Left heart suffering from IHD

Question 12

***Investigations of Cor pulmonale

Answer 12

1. ***Hypoxaemia +/- Hypercapnia (Respiratory failure)
2. ***CXR
   - dilated pulmonary trunks at hila
   - RV dilation
3. **ECG
   - P pulmonale
   - **right axis deviation
   - RVH
4. Echocardiogram
   - doppler for pulmonary hypertension, RV function (usually not done if clinical manifestations are straight forward)

Question 13

***Management of Acute (on Chronic) Respiratory failure in COPD

Answer 13

記: CSIAN (Controlled O2, Systemic steroid, Inhaled BD, Antibiotics, NIV) + Diuretics

1. Treat airflow obstruction in COPD
   - **Inhaled BD (β-agonists, Anti-cholinergics)
   - **Systemic steroids (in ***acute exacerbation of COPD, not for long term use in stable COPD)
2. Identify trigger of exacerbation and treat
   - e.g. infection (***Antibiotics), pneumothorax
3. Supportive measures (for respiratory failure)
   - **O2 supplement
   - **Ventilatory support (Invasive / Non-invasive)
4. ***Diuretics
   - treat HF
5. Identify other comorbidities which may complicate condition
   - e.g. arrhythmia, IHD

Question 14

***Chronic management of COPD

Answer 14

1. Smoking cessation
2. ***Treat airflow obstruction
   - BD (prominent role)
   - ICS (for airway inflammation, lesser role vs Bronchial asthma)
3. Pulmonary rehabilitation
   - not improve lung function but maximise ADL
4. ***Influenza, Pneumococcal vaccines
5. ***Long term home O2 (LTOT)
   - for hypoxaemia (use esp. during sleep / exertion where further desaturation occurs)
6. Home nocturnal ventilation
   - benefit “selected” patients

Question 15

Pathophysiologic mechanisms of Respiratory failure in clinical context

Answer 15

• Normal ABG tension (breathing atmospheric air at sea level)
• Concept of A-a gradient (A: Alveolar, Inspired O2 tension; a: Arterial O2 tension)
• ***NOT all blood gas abnormalities are respiratory failure (e.g. Congenital cyanotic heart disease)
• ***NOT all respiratory failure are due to lung diseases (e.g. Narcotic overdose depress respiration)

Question 16

Balance between Load upon and Strength of respiratory system

Answer 16

Determines progression / resolution of ACRF

Load:

1. Resistive loads (bronchospasm, OSA)
2. Lung elastic loads (alveolar edema, atelectasis)
3. Chest wall elastic loads (pleural effusion, pneumothorax)
4. Minute ventilation loads (sepsis, PE)

Strength:

1. Muscle weakness (electrolyte derangement)
2. Impaired neuromuscular transmission (phrenic nerve injury, MG)
3. Depressed drive (drug overdose, hypothyroidism)

Question 17

***Mechanisms of respiratory failure

Answer 17

1. V/Q imbalance
2. Shunting
3. Dead space
4. Hypoventilation
5. Diffusion impairment

• may have >=1 mechanism involved in an individual with several pathologies
• may have >=1 mechanism involved in 1 disease condition

Question 18

1. V/Q imbalance

Answer 18

Non-uniform Alveoli
—> **Non-uniform Ventilation (e.g. destroyed alveolar wall in COPD) + **Non-uniform Perfusion (e.g. destroyed capillary wall)
—> Poor oxygenation of blood

Affects both O2 uptake, CO2 elimination
—> but ↑ V/Q mismatch affects O2 uptake > CO2 elimination (∵ sigmoid O2 dissociation vs linear CO2 dissociation)
—> Hypoxaemia > CO2 retention

(↓ PaO2, ↑ PaCO2 —> ↑ V —> ↑ CO2 elimination —> ↓ PaCO2 —> ∴ PaCO2 tends to “normalise” / less elevated)

Characteristic abnormality in most conditions affecting lung parenchyma (gas exchange apparatus):

1. ***Chronic bronchitis + Emphysema
2. ***Asthma
3. Pulmonary edema

Question 19

2. Shunting

Answer 19

Mixed venous blood passes through lung **without being oxygenated ∵ some alveoli are **not ventilated (collapsed, fluid-filled etc.)

• V/Q = 0
• extreme form of V/Q mismatch

Result:
Hypoxaemia with **Normal / Low pCO2 (∵ stimulation of ventilation by hypoxaemia)

• ↑ FiO2 (supplemental O2) ***not as effective
  —> ∵ shunted blood does not come into contact with alveolar gas (O2 supplement)

Normal shunt: Unoxygenated blood in the bronchial, mediastinal, thebesian veins emptying directly into LV

Clinical conditions:

1. ***Pulmonary edema
2. ***ARDS
3. ***Lung collapse / Pneumonia

Question 20

3. Dead space

Answer 20

Lung units that are ventilated but ***not perfused

“Effective” alveolar ventilation ↓
—> ↑ Minute ventilation (RR x TV) to compensate
—> If a cause of hypoxaemia is present e.g. Lung units with V/Q imbalance units
—> manifest as ***hypoxaemia

Question 21

4. Hypoventilation

Answer 21

Minute ventilation / Minute volume = TV x RR
- ↓ in Hypoventilation

Alveolar ventilation

• Volume effectively ***entering alveoli
• Effective gas exchange part of lungs

Insufficient fresh air breathed in

• cannot provide enough O2 to ↑ pulmonary capillary pO2 to normal levels
• cannot allow sufficient CO2 to leave blood stream

Result:
- Hypoxaemia + ***Hypercapnia

In clinical scenarios, ↑ pCO2 often reflect an element of hypoventilation

Clinical conditions:
“Normal lungs”
- Depressed CNS (e.g. drug overdose —> both TV, RR ↓)
- Neuromuscular / Skeleton deformity with restriction of chest wall movement (e.g. MG, kyphoscoliosis —> ↓ TV with ↑ RR initially until respiratory muscle fatigue)

—> Hypoventilation despite normal gas exchange
—> ***not sufficient by just giving supplemental O2
—> only allow pCO2 to ↑ (respiratory acidosis)

Question 22

5. Diffusion impairment

Answer 22

• Failure of pulmonary capillary blood to fully equilibrate with alveolar gas
• Rarely a cause of significant hypoxaemia because equilibration time takes only about 1/3 of time blood uses to pass through capillaries
• May contribute to **hypoxaemia in conditions with **very thick diffusion barrier e.g. interstitial lung disease / ***severe loss of diffusion surface e.g. Severe pulmonary emphysema

Clinical conditions:

1. ***Interstitial lung disease
2. Severe pulmonary ***emphysema

Question 23

***Type 1 Respiratory failure

Answer 23

***Hypoxaemia

Predominant V/Q imbalance:

1. ***COPD
2. ***Acute asthma
3. ***Interstitial lung disease - IPF

Predominantly Shunting:

1. ***Pulmonary edema
2. ***ARDS
3. Major lung collapse

Question 24

Type 2 Respiratory failure

Answer 24

***Hypoxaemia + Hypercapnia

Elevation of pCO2:

• cannot be detected by pulse oximetry, need high awareness
• **Early feature in respiratory failure due to diseases causing **Hypoventilation e.g. neuromuscular disease, narcotic overdose
• **Late feature in respiratory failure due to diseases with **V/Q imbalance e.g. severe COPD / acute exacerbations (severe V/Q imbalance + respiratory muscle fatigue)

Treat Hypercapnia:

• cannot just give O2 supplements
• ***need to support Ventilation