Respiratory failure

Question 1

Define respiratory failure

Answer 1

Impaired pulmonary gas exchange resulting in hypoxaemia with or without hypercapnia.

PaO2 <8kPa
PaCO2 <6.7kPa

Question 2

Classify the types of respiratory failure

Answer 2

Type 1: PaO2 <8kPa, normal or low PaCO2

Type 2: PaO2 <8kPa, plus PaCO2 >6.7kPa

Question 3

Describe the pathophysiology of type I respiratory failure

Answer 3

Disease damages the lung tissue. Hypoxaemia is due to right-to-left shunts or diffusion defects causing V/Q mismatch.

Question 4

List 5 causes of type 1 respiratory failure

Answer 4

Pneumonia
ARDS
Cardiogenic pulmonary oedema
Pulmonary fibrosis
Asthma
COPD
Pneumothorax
PE
Obesity

Question 5

Describe the pathophysiology of type 2 respiratory failure

Answer 5

Ventilatory failure results in insufficient ventilation to remove CO2. Respiratory muscle fatigue is a factor. Causes respiratory acidaemia.

Question 6

List 5 causes of type 2 respiratory failure

Answer 6

Failure to compensate for increased dead space and/or CO2 production: COPD*, severe asthma
Reduced ventilatory effort

Chest-wall deformities: scoliosis, kyphosis, flail chest
Respiratory muscle weakness: Guillain-Barre, DMD
Depression of respiratory centres: drugs, trauma, CVA

Question 7

List 5 clinical features of respiratory failure

Answer 7

Use of accessory muscles
Intercostal recession
Tachypnoea*: most sensitive of increasing difficulty
Tachycardia
Sweating
Inability to speak, unwilling to lie flat
Agitation, restlessness, reduced consciousness
Asynchronous respiration
Paradoxical respiration: abdomen and thorax move in opposite directions
Respiratory alternans: breath-to-breath alteration in the relative contribution of intercostal/accessory muscles and the diaphragm
Pulsus paradoxus: decrease in BP of 10mmHg or more during inspiration

Question 8

What investigations are required in suspected respiratory failure?

Answer 8

Blood gas analysis* to assess PaCO2

Pulse oximetry
Capnography if mechanically ventilated

Question 9

How is respiratory failure managed?

Answer 9

Oxygen therapy for type 1 respiratory failure
Assisted ventilation for type 2 respiratory failure

Treatment of distal airway obstructions
Measure to limit pulmonary oedema
Control of secretions
Treatment of pulmonary infection

Correct any abnormalities that lead to respiratory muscle weakness e.g. malnutrition

Question 10

What types of oxygen therapy are available?

Answer 10

High-flow oxygen*: 100% O2 at 15 L/min using non-rebreather mask. Used in acutely unwell patients.

Controlled oxygen therapy: variable fixed-rates using venturi mask. Used in COPD (88-92%), chronic type II respiratory failure, and ACS .

Nasal cannulae: 24-30% O2 at 1-4 L/min. Used in non-acute situations or mild hypoxia

Question 11

What are the indications for using controlled oxygen therapy

Answer 11

COPD: maintain sats 88-92%, to prevent over-oxygenation and loss of hypoxic drive.
Chronic T2RF: prevent loss of hypoxic drive.
MI if hypoxic: high-flow O2 has been linked to increased mortality

NB. Severe hypoxaemia is more dangerous than hypercapnia.

Question 12

What types of assisted ventilation are available?

Answer 12

Non-invasive ventilation via a positive-pressure face mask, nasal mask, or hood: esp in exacerbation of COPD with T2RF and pH 7.25-7.35

• CPAP: acute pulmonary oedema, sleep apnoea
• BiPAP: COPD exacerbation, ARDS

Invasive ventilation via ET tube or tracheostomy

ECMO

Question 13

What are the benefits of mechanical ventilation?

Answer 13

Relief from respiratory muscle exhaustion
Stent of aiways: decreases atelectasis
Improves CO2 elimination

Question 14

When is NIV used in COPD management?

Answer 14

Management of exacerbation of COPD if T2RF develops with pH between 7.25-7.35.

Question 15

Name 3 complications of assisted ventilation

Answer 15

Pneumothorax
Gastric insufflation
Aspiration
Ventilator-associated pneumonia: affects up to 1/3 of patients on mechanical ventilation. Gram -ve bacilli (P. aeruginosa, K. pneumoniae, E. coli, Acinetobacter spp.) and Staph aureus/MRSA.

Tracheal intubation: trauma, tube in oesophagus, tube in one bronchus, migration of tube, obstruction of tube, laryngeal injury, mucosal ulceration

Tracheostomy: tracheal intubation complications , plus death, haemorrhage, hypoxia, hypotension, arrhythmias, tracheal stenosis, cosmetic

NIV:
Related to pressure: Sinus pain
Related to airflow: dryness, nasal congestion, eye irritation
Other: Claustrophobia, pressure sores

Question 16

Explain the importance of weaning from assisted ventilation

Answer 16

Weaning is important to ensure the patient is capable of spontaneous ventilation once assisted ventilation has stopped.

Combination of catabolic response to critical illness, and reduction in respiratory work (disuse atrophy) results in weakness and wasting of the respiratory muscles.

Patients can experience difficulties in resuming unsupported spontaneous ventilation. Neuropathy and/or myopathy can develop after prolonged respiratory support.

NB. patients on assisted ventilation for <24-48hr can usually resume spontaneous respiration, and do not require weaning.