Respiratory Failure

Question 1

Hypoxia

Answer 1

Defined as PaO2 <8kPa; Breathlessness, Agitation, Confusion and Central Cyanosis
o Long standing Hypoxia can lead to ↑PCV, PH and RHF

Question 2

Hypercapnia

Answer 2

PaCO2 >6kPa; Headache, Peripheral vasodilation, Tachycardia and Bounding
pulse, Tremor and CNS symptoms
o Headache due to Hypercapnia-induced Cerebral Hyperperfusion (due to Vasodilation)

Question 3

Type 1 Respiratory Failure

Answer 3

Hypoxia with normal/low PaCO2
Causes: Pneumonia, Pulmonary Oedema and Embolism,
Asthma, Emphysema, Pulmonary Fibrosis and
Acute Respiratory Distress

Question 4

Type 2 Respiratory Failure

Answer 4

Hypoxia with Hypercapnia
Causes: Severe Pulmonary diseases which cause T1RF
↓Respiratory Drive – CNS depression
NMJ Diseases and Issues with Thoracic wall
T2RF is due to Alveolar Hypoventilation (only cause of Hypercapnia) ± VQ Mismatch

Question 5

Investigations

Answer 5

FBC, U&E, CRP, ABG, CXR, Microbiology if indicated, Spirometry

Question 6

Control of Breathing

Answer 6

Hypercapnic (stronger) and Hypercapnic drive through Central, and Peripheral Chemoreceptors in the Carotid and Aortic bodies; Stimulation of Breathing centre
o ↑PaCO2 leads to Respiratory Acidosis; H+ stimulates
Peripheral Chemoreceptors
o Central Chemoreceptors only sensitive to CO2 as H+
unable to cross BBB

Question 7

Mechanical Process of Ventilation

Answer 7

o At end Inspiration and Expiration, PAlv = 0; PAlv becomes
positive during Expiration and negative during Inspiration
o PIP is negative during quiet respiration – More negative
during Inspiration and less negative in Expiration

Question 8

Mechanical Ventilation: Non-invasive methods

Answer 8

o Continuous Positive Airway Pressure (CPAP) – Applies mild air pressure on a
continuous basis to keep airways continuously open; BiPAP used if CPAP increases the
work of breathing
o Positive End-Expiratory Pressure (PEEP)
o Bilevel Positive Airway Pressure (BiPAP) – Two different strength continuous positive
airway pressure during expiration and inspiration

Question 9

Mechanical Ventilation: Invasive Methods

Answer 9

o Tracheal Intubation – Oral or Nasal route, typically administered while sedated
o Tracheostomy – Surgical opening of the Trachea
o Cricothyroidotomy – Surgical opening of the Cricothyroid membrane, reserved for
emergency access only
o Laryngeal Mask Airway (LMA) – Supraglottic, forms a tight seal over the Glottis; less
invasive and damaging than other Invasive methods of ventilation

Question 10

Pharmacological Respiratory stimulant

Answer 10

(Doxapram) – Stimulation of Chemoreceptors

Question 11

Oxygen Therapy

Answer 11

• Nasal Prongs/Cannula – 1-4L/min = 24-40%
• Simple Face Mask – Do not use if hypercapnia; Risk of rebreathing CO2 at low flow rates
o Hypercapnic patients might require have lost Hypercapnic drive and dependent on
Hypoxic drive for respiration

• Venturi Mask – Precise FiO2 at high flow rates; start with 24-28% (Blue or White) in COPD
• Non-Rebreather Mask – Delivery of high concentrations of O2; used in Emergencies
• Treatment of Anaemia, Improvement of Cardiac Output and Physiotherapy can improve
efficacy of Oxygen therapy

Question 12

Palliative Care

Answer 12

• End-of-life care by withholding/withdrawing Ventilatory support may be appropriate
• E.g. Advanced Medical Directive, DNACPR order by competent patients
o DNACPR might also be in patient’s best interest if the outcome of resuscitation does
not outweigh the risks and adverse effects