Respiratory Failure

Question 1

Definition of respiratory failure

Answer 1

An arterial partial pressure of oxygen (at sea level, FiO2 0.21) at rest <8 kPa (60mmHg)

Question 2

What is type 1 respiratory failure?

Answer 2

Hypoxemic respiratory failure. PaO2 < 8kPa, PCO2 normal

Question 3

Causes of Type 1 respiratory failure

Answer 3

Right to left shunt or V/Q mismatch
Q: PE

V: chest infection, asthma, pulmonary oedema, ARDS, aspiration pneumonitis, airway obstruction, diffuse parenchymal lung disease

Question 4

What is type 2 respiratory failure?

Answer 4

Hypercapnic respiratory failure.

Hypoxemia with arterial PaCO2 > 6.5 kPa (50mmHg)

Question 5

Causes of type 2 respiratory failure

Answer 5

Reduced central drive: opioids, anasthetic agents, sleep apnea, stroke

Impaired peripheral respiratory system: airway obstruction, COPD, restriction due to pain/obesity/ascites, myopathy, chest wall abnormality)

Question 6

Principles of management in patient’s with respiratory failure

Answer 6

• Primary aim: treat hypoxemia
• Secondary aim: control paCO2 and respiratory acidosis
• Identify and treat underlying cause

Question 7

Indication for invasive ventilatory support

Answer 7

• Airway obstruction
• Airway protection
• Unconscious patient with impaired laryngeal reflexes
• Hypoxia or hypercapnea
• Anaesthesia (prolonged surgery, prone positioning, one lung ventilation)

Question 8

What are the clinical indicators of failure of basic respiratory support

Answer 8

• RR>30
• Increasing oxygen requirement to maintain SaO2
• PaO2 < 8KPa
• PaCO2 > 8 kPa with respiratory acidosis (pH <7.35)
• Low GCS/exhaustion/dyspnea

Question 9

How do we monitor respiratory function?

Answer 9

• Respiratory rate
• Oxygen saturation
• Oxygen requirement
• Conscious level
• End-tidal carbon dioxide
• Blood gas analysis

Question 10

What are signs of respiratory distress?

Answer 10

Tachypnea, mouth opening during inspiration

Pursed lips, expiratory grunting

Use of accessory muscles

Central cyanosis

Tachycardia, dilated pupils, sweat (sympathetic overactivity)

Question 11

Complications of mechanical ventilation

Answer 11

• Volume related
• Pressure related (barotrauma)
  
  • tension pneumothorax
  • pulmonary interstitial emphysema
  • pneumopericardium/mediastinum
• Oxygen
  
  • oxygen toxicity (lung endothelial injury)
  • ventilatory depression
  • absorption atelectasis

Question 12

What are types of non-invasive mechanical ventilation?

Answer 12

CPAP (continuous positive airway pressure)

BIPAP (bi-level positive airway pressure)

Question 13

What is CPAP?

Answer 13

Application of positive airway pressure through all phases of respiration.

Delivered gas flow must exceed peak inspiratory flow ( up to 60L/min)

Question 14

What are the advantages of CPAP?

Answer 14

• increases functional residual capacity by recruiting areas of atelectasis → improves oxygenation, reduced work of breathing
• increase pulmonary lymphatic flow
• improves mechanical function of heart to prevent further buildup

Question 15

Indications for CPAP

Answer 15

• Sleep apnea
• Pulmonary edema
• Hypoxemic respiratory failure

Question 16

What is BIPAP

Answer 16

Different set pressures for inspiratory and expiratory phase of respiration

Question 17

How to assess readiness to wean off ventilator

Answer 17

• Adequate cough
• Adequate mentation
• Resolution of underlying disease
• Stable cardiovascular status
• Adequate oxygenation (able to maintain with non-invasive measures)

Question 18

Satisfactory parameters that signify “adequate lung function”

Answer 18

RR > 35/min

PaO2 > 11 kPA

Minute volume < 10L/min

Tidal volume > 5ml/kg

Max inspiratory force > 20cm H2O

Question 19

How to adjust parameters to improve oxygenation?

Answer 19

increase FiO2

increase PEEP

increase I: E ratio

Question 20

How to adjust parameters to improve ventilation?

Answer 20

Increase respiratory rate

Increase tidal volume

Increase peak pressure

Question 21

What are the basic modes of ventilation?

Answer 21

• Pressure control
• Volume control
• Assisted modes
  
  • Pressure support ventilation
  • Synchronised Intermittent Mandatory Ventilation

Question 22

What is pressure control ventilation? Advantages and disadvantages

Answer 22

Pre-set inspiratory pressure delivered

Pros: less barotrauma

Cons: hypoventilation

Question 23

What is volume control ventilation? Advantages and disadvantages

Answer 23

Fixed tidal volume delivered and respiratory rate

Pros: ensures adequate minute ventilation to satisfy metabolic demand. Ideal for muscle rest

Cons: barotrauma

Question 24

What is plateau pressure? How to measure?

Answer 24

The equilibrated alveolar pressure at full volume / alveolar distending pressure

Question 25

What is the peak inspiratory pressure? How to measure

Answer 25

The dynamic pressure needed to fully inflate the lung. It is the peak of the wave form

Question 26

What does increase PIP and PPlat signify?

Answer 26

Decreased compliance of lung

Question 27

What does increased PIP and unchanged pPlat signify?

Answer 27

Airway obstruction: bronchospasm, ETT occlusion, secretions

Question 28

What is the most common primary initial mode of ventilatory support?

Answer 28

Volume assist control. It is ideal for muscle recovery (can trigger full tidal volume on an attempted breath)

Question 29

Draw the waveform that would appear on the monitor of a ventilator

Answer 29

Question 30

What is the A-a gradient?

Answer 30

PAO2-PaO2 Alveolar partial pressure oxygen minus the arterial partial pressure of oxygen

Question 31

What is a normal A-a gradient

Answer 31

5-10 mmHg

Question 32

Causes of raised A-a gradient

Answer 32

V/Q mismatch Right-to left shunt (intrapulmonary/cardiac Increase O2 extraction Diffusion defect (rare)

Question 33

Possible causes of hypotension while on ventilator

Answer 33

* Underlying cause of shock * Increases intrathoracic pressure * Tension ptx * PEEP and TV too high * Sedatives