Respiratory Failure

Question 1

Definition of respiratory failure.

Answer 1

PaO2 < 8kPa

Question 2

Subdivisions of respiratory failure.

Answer 2

Type 1 respiratory failure

Type 2 respiratory failure

Question 3

Define type 1 RF.

Answer 3

Hypoxia -> < 8kPa PaO2

with a normal or low PaCO2.

Question 4

Main causes of type 1 RF.

Answer 4

V/Q mismatch

Hypoventilation

Abnormal diffusion

Right to left cardiac shunts

Question 5

Examples of V/Q mismatches.

Answer 5

Pneumonia

Pulmonary oedema

PE

Asthma

Emphysema

Pulmonary fibrosis

ARDS

Question 6

Define type 2 RF.

Answer 6

Defined as hypoxia PaO2 < 8 kPa and hypercapnia of PaCO2 > 6 kPa.

Caused by alveolar hypoventilation with or without V/Q mismatch.

Question 7

Causes of type 2 RF.

Answer 7

Pulmonary disease like asthma, COPD, pneumonia, end-stage pulmonary fibrosis and obstructive sleep apnoea.

Reduced resp drive like sedatives, CNS tumour or trauma.

Neuromuscular disease like cervical cord lesion, diaphragmatic paralysis, poliomyelitis, myasthenia gravis, Guillain-Barré syndrome.

Thoracic wall disease like flail chest or kyphoscoliosis.

Question 8

Clinical features of hypoxia.

Answer 8

Dyspnoea

Restlessness

Agitation

Confusion

Central cyanosis

Tachycardia

Long-standing;

Polycythaemia

Pulmonary hypertension

Cor pulmonale

Question 9

Clinical features of hypercapnia.

Answer 9

Headache

Peripheral vasodilation

Tachycardia

Bounding pulse

Tremor/flap - asterixis

Papilloedema

Confusion

Drowsiness

Coma

Question 10

Investigations in respiratory failure.

Answer 10

Blood tests like FBC, U&Es, CRP and ABG.

Pulse oximetry

Capnography

CXR

Microbiology like sputum and blood cultures if indicated.

Spirometry

PaO2/FiO2 ratio

CXR

Question 11

Clinical features of acute respiratory distress/failure.

Answer 11

Tachypnoea (respiratory rate >24 breaths per minute in adults)

Use of accessory breathing muscles

Cyanosis

Tachycardia

Intercostal recession

Sweating

Pulsus paradoxus

Inability to speak and unwillingness to lie flat

Question 12

Management of type 1 RF.

Answer 12

Treat the underlying cause.

Give O2 24-60% by facemask

Assisted ventilation if PaO2 < 8kPa despite 60% oxygen

Question 13

Management of type 2 RF.

Answer 13

Remember there might be only a hypoxic drive causing tachypnoea.

Treat underlying cause

Controlled oxygen therapy starting at 24% O2. The oxygen therapy should be given with care. However remember that severe hypoxaemia is more dangerous that severe hypercapnia.

Recheck ABG after 20 min -> If PaCO2 is steady or lower then increase O2 to 28%.
If PaCO2 has risen > 1.5kPa and the patient is still hypoxic consider assisted ventilation like NIPPV.

If this fails consider intubation and ventilation.

Question 14

What is capnograph?

Answer 14

A continuous breath-by-breath analysis of the expired carbon dioxide concentration.

Question 15

What is capnography used for?

Answer 15

Confirm tracheal intubation

Continuously monitor end-tidal PCO2 to assess effectiveness of ventilation.

Detect acute airway problems

Detect acute alterations in cardiorespiratory function.

Question 16

What can happen if you give too much oxygen apart from CO2 retention?

Answer 16

Oxygen toxicity where hyperoxia causes pulmonary dmaage due to oxygen free radical and oxidative damage to the lung tissue.

Question 17

Give examples of techniques for respiratory support.

Answer 17

Controlled mechanical ventilation (CMV)

Synchronised intermittent mandatory ventilation (SIMV)

Pressure support ventilation (PSV)

Biphasic positive airway pressure (BiPAP)

Non-invasive ventilation (NIV)

Continuous positive airway pressure (CPAP)

Extracorporal techniques

Question 18

What does NIV encompass?

Answer 18

Nasal mask/cannula

Face mask

Hood

Question 19

What does CPAP encompass?

Answer 19

Mask

Hood

High-flow nasal prongs

Question 20

Indications for mechanical ventilation.

Answer 20

Acute respiratory failure with signs of severe respiratory distress.

Acute ventilatory failure like MG, GB-syndrome, high spinal cord injury when vital capacity has fallen to 10ml/kg or less.

Post-OP ventilation in high-risk patients

Head injury to avoid hypoxia or hypercarbia

Trauma to chest or high spinal cord

Severe left ventricular failure with pulmonary oedema

Coma with airway compromise or breathing difficulties.

Question 21

Complications of tracheal intubation.

Answer 21

Trauma to upper airways

Tube goes into oesophagus

Tube in one or other main bronchus - need to be in both.

Migration of tube out of trachea

Leaks around tube

Obstruction of tube

Sinusitis

Mucosal oedema and ulceration

Laryngeal injury

Tracheal narrowing and fibrosis

Tracheomalacia

Question 22

Complications of tracheostomy.

Answer 22

Death, pneumothorax, haemorrhage, hypoxia, hypotension, cardiac arrhythmias, subcut emphysema

Mucosal ulceration, erosion of tracheal cartilages, erosion of innominate artery, stomal infection, pneumonia

Failure of stoma to heal, tracheal granuloma, treacheal stenosis, collapse of tracheal rings at level of stoma, cosmetic factors.

Question 23

General complications associated with mechanical ventilation.

Answer 23

Disconnection, failure of gas or power supply.

CVS complications - pulmonary HTN -> fall in cardiac output.

Respiratory complications like venilator-associated pneumonia and tension pneumothorax.

Question 24

Types of controlled mechanical ventilation.

Answer 24

Volume-controlled ventilation

Pressure-controlled ventilation

Question 25

How is oxygen delivered in CPAP?

Answer 25

a tightly fitting face mask or a hood

Question 26

Indications for NIV.

Answer 26

Acute exacerbation of COPD (H+ > 44nmol/L or pH < 7.35)

Cardiogenic pulmonary oedema

Chest wall deformity/neuromuscular disease

Obstructive sleep apnoea

Severe pneumonia

Asthma

Weaning patients from invasive ventilation

Question 27

Contraindications of NIV.

Answer 27

Facial or upper airway surgery

Reduced conscious level

Inability to protect the airways.

Question 28

What is a venturi mask?

Answer 28

A mask providing precise percentage or fraction of O2 (FiO2) at high flow rates.

This is what you can use in COPD and start off at 24% to 28%.

Question 29

When to consider ABGs.

Answer 29

Any unexpceted deterioration in an ill patient.

Anyone iwth an acute exacerbation of a chronic chest condition

Anyone with impaired cosncioussness or impair resp effort.

Signs of CO2 retention such as bounding pulse, drowsy, tremor, headache.

Cyanosis, confusion and visual hallucinations

To validate measurements from transcutaneous pulse oximetry.