Respiratory failure

Question 1

What is type 1 respiratory failure characterised by and what is the management?

Answer 1

Characterised by

• Low PO2 (<60mmHg / 8pKa)
• Low/normal PaCO2 (<50mmHg / 6pKa)

Management

• Provide high flow O2 to correct hypoxia!
• Can consider use of CPAP / PEEP if respi efforts are strong / present
• Can consider intubation & mechanical ventilation if respi efforts are weak / absent

Question 2

What is type 2 respiratory failure characterised by and why does it develop?

Answer 2

Characterised by:

• Low PO2
• High PaCO2 (>50mmHg / 6pKa)
• A-a gradient may be NORMAL or HIGH

Why T2RF develops?

• CO2 exchange is more efficient than O2 exchange
• Hence with increased parenchymal damage 🡪 poorer function 🡪 eventually CO2 exchange is impaired 🡪 hypercapnic RF

Question 3

Why do we not give CPAP in patients with type 2 respiratory failure?

Answer 3

• CPAP causes increased aeration of all regions within the lungs
• O2 is a Vasodilator 🡪 causes reversal of HPV of poorly functioning alveoli
• Hence worsening V/Q mismatch and worsening hypoxemia

Question 4

How do we manage type 2 respiratory failure?

Answer 4

• Can consider use of BiPAP if respi efforts are strong / present
• Can consider intubation & mechanical ventilation if respi efforts are weak / absent

Question 5

What is Positive End-Expiratory Pressure (PEEP)?

Answer 5

• Pressure imposed at the end of expiration: this ensures alveoli remain patent
• Improves oxygenation
• Used in type I respiratory failure

Question 6

What is Bi-level Positive Airway Pressure (biPAP)?

Answer 6

• Has pressure both during inspiration and expiration
• Inspiratory pressure: increases alveolar ventilation; reduces work of inhalation
• Expiratory pressure: prevents airway collapse during exhalation, prolonging expiration and increases elimination of CO2; opens up small airways improving ventilation
• Overall effect: improves tidal volume and minute ventilation
• Used in type II respiratory failure

Question 7

What are the advantages of non- invasive ventilation?

Answer 7

• Does not require sedation / paralytics = loss S/E from medications
• Lower risk of pneumonia due to lack of invasive procedure

Question 8

What are the potential complications of non- invasive ventilation?

Answer 8

• Air leaks 🡪 Pneumothorax – like all ventilation modalities
• Hypotension due to PEEP causing reduced venous return
• Gastric insufflation 🡪 N&V 🡪 aspiration
• Facial Abrasion / pressure sores / Skin breakdown

Question 9

What are the contraindications of non- invasive ventilation?

Answer 9

• Impaired mental status or drowsiness.
• Uncooperative or agitated patient.
• Cardiac or respiratory arrest.
• Inability to use a mask because of trauma or surgery.
• Excessive secretions.
• Haemodynamic instability or life-threatening arrhythmias.
• High risk of aspiration.
• Life-threatening refractory hypoxaemia.

Question 10

What are the indications of non invasive ventilation?

Answer 10

Diagnosis 
- Acute Pulmonary Edema
- Acute pneumonia in immunocompromised patients
- Acute COPD exacerbation
- NM abnormalities eg: MG
OSA

Blood gas findings

• Partial pressure of carbon dioxide in arterial gas (PaCO2) >45 mmHg
• Arterial pH < 7.35 but > 7.10
• Ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (PaCO2/FiO2) < 20

Clinical inclusion criteria

• Signs and symptoms of acute respiratory distress
• Moderate to severe dyspnea
• Respiratory rate greater than 24 breaths per minute
• Accessory muscle use
• Abdominal paradox

Question 11

What are the causes of hypoxemia with a normal A-a gradient?

Answer 11

1) Low FiO2 (e.g. high altitude)

2) Hypoventilation
- Associated with increased PCO2
- CNS depression (e.g. brainstem stroke, narcotic overdose)
- Obesity
- Scoliosis
- NMJ issues (MG), Myopathies, Peripheral neuropathies

Question 12

What are the causes of hypoxemia with an increased A-a gradient that responds to 100% FiO2?

Answer 12

1) V/Q mismatch
- obstructive lung disease
- PE
- Mild alveolar filling disease (blood, water, pus, protein)
- COPD
- Asthma

2) Diffusion impairment
- Interstitial lung disease
- Emphysema
- Pulmonary vascular disease
- increased cardiac output states (increased transit time through alveolar capillary membrane)

Question 13

What are the causes of hypoxemia with an increased A-a gradient that does not respond to 100% FiO2?

Answer 13

Large shunt that does not correct completely

• Atelectasis
• Pleural effusion
• Pneumothorax
• Haemothorax
• Severe ARDs/ Pneumonia? APO

Question 14

What is the formula for A-a gradient?

Answer 14

PAO2 - PaO2

PaO2 can be found from ABG

PAO2 = 7 x FiO2 - PaCO2 (from ABG)

A normal A-a gradient is 10-20mmHg, however inc w/ age

+3.5 mmHg for every decade of life, or use this formula: Normal Age/4 + 4.

Add 5 to 7 mmHg for every 0.1 increase in Fi02

Note that there is no correction for smokers