Acute and chronic respiratory failure

Question 1

What are the two conditions NIV is usually justified?

Answer 1

• acute exacerbation of COPD complicated by respiratory acidosis
• APO

Question 2

List one absolute contraindication to NIV and 3 relative contraindications

Answer 2

Question 3

Describe the mechanism that NIV is thought to improve acute APO

Answer 3

• Increased alveolar pressure decreases the effects of pulmonary oedema on gas exchange

Increased intrathoracic pressure improves LV performance:
- decreased LV transmural pressure = decreased afterload
- decreased venous return = decreased preload

Improvement in pulmonary oedema and respiratory distress also indirectly decrease myocardial oxygen demand by moderating the sympathetic response and decreasing the effort of breathing

Question 4

How does NIV reduce preload and afterload?

Answer 4

• during systole, NIV increases the intrathoracic pressure -> reduction in venous return -> reduced afterload
• in diastole, NIV increases pericardial pressure -> reduces afterload

Question 5

Other than COPD and APO, list 4 indications for NIV

Answer 5

Question 6

What is the ideal patient for NIV?

Answer 6

• can maintain own airway!
• conscious
• can manage own secretions
• tolerates the NIV

Question 7

In a broad sense, how does NIV treat respiratory failure?

Answer 7

• induces increased inspiratory pressure -> decreases WOB due to improved lung compliance + recruitment of collapse alveoli
• Increased FRC due to increased closing capacity improves oxygenation
• Tight-fitting mask ensures accurate delivery of prescribed FiO2

Question 8

Broadly explain how NIV can treat severe COPD

Answer 8

• Increased end-expiratory positive pressure decreases work of breathing vs. intrinsic PEEP
• Increased expiratory air flow can improve CO2 clearance
• Increased minute volume can better compensate for the increased dead space of emphysema
• Splinting open of smaller airways allows better bronchodilator delivery

Question 9

Why is NIV not useful in a patient with CAP?

Answer 9

NIV does not tend to benefit this group of patients, because:
- It can impair secretion clearance
- It can increase shunt

However, the delivery of humidified oxygen by mask can improve secretion clearance
In patients with CCF or COPD and pneumonia, NIV can improve mortality