7.13
Respiratory failure
(7.13.1) Recognise a patient in respiratory failure
Presentation will be that of the cause for the failure (see 7.13.2) together with symptoms and
signs of either hypoxia (type 1 respiratory failure) or hypoxia and hypercapnia (type 2).
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Hypoxia: PaO2 <8 kPa
If long standing:
Dyspnoea
 Polycythaemia
Restlessness
 Pulmonary
Agitation
hypertension
Confusion
Central cyanosis  Cor pulmonale
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Hypercapnia: PaCO2 >6 kPa
Headache
 Tremor / flap
Peripheral
 Papilloedema
vasodilatation
 Confusion
Tachycardia
 Drowsiness
Bounding pulse
 Coma
(7.13.2) Assess the cause and severity of respiratory failure and initiate management
The purpose of the lungs is gaseous exchange – this process requires the following:
 Pumping of blood to the lungs by the heart
 Inspiration and expiration – powered by muscle and controlled by the respiratory centre of the
medulla. Impulses conveyed down the spinal cord and through peripheral nerves.
 A suitable environment for exchange at the alveoli (V:Q matching, no barriers to diffusion)
Causes
Type 1 resp failure
PaO2 <8 kPa; PaCO2 norm/
Type 2 respiratory failure: PaO2 <8 kPa; PaCO2 >6 kPa
Pneumonia
Pulm oedema
PE
Asthma
Emphysema
Fibrosing alveolitis
Pulmonary disease:
Asthma
COPD
Pneumonia
Pulm fibrosis
Obstructive sleep apnoea
Reduced Respir. drive
Right  left shunt
Sedative drugs
Cyanotic congenital heart
CNS tumour
disease
Trauma
Causes in italic may result in type I or II failure.
Neuromuscular:
Cervical cord lesion
Poliomyelitis
Gullaine Barré
Myasthenia gravis
Muscular dystrophies
Diaphragmatic paralysis
Thoracic wall disease
Flail chest
Kyphoscoliosis
The severity may be assessed by O2 SATS (pulse oximeter) and arterial blood gas.
Management
Investigations to ascertain cause:
Bloods: FBC, U&E, CRP, ABG
Radiology: CXR
Microbiology: Blood / sputum culture (if febrile)
Spirometry
Treat underlying cause
Give oxygen (see 7.13.5)
(7.13.3) Interpret arterial blood gas results
An arterial blood gas sample is taken usually from radial artery at wrist or brachial artery in cubital
fossa. Sample is kept in ice and must be processed within 30 minutes. Normal values are:
pH:
pCO2:
pO2:
[HCO3-]:
Base excess:
7.35 – 7.45
4.7 – 6.0 kPa
>10.6 kPa
22-25 mmol/L (standardised bicarbonate)
+/- 2 mmol/L
Base excess is the amount of acid (if negative) or alkali (if positive) that would be needed to bring
the pH to 7.4. It is therefore negative in acidosis and positive in alkalosis
If the problem is respiratory then pH and pCO2 change in the opposite directions (mnemonic
ROD)
 Respiratory acidosis:  pH,  pCO2
 Respiratory alkalosis:  pH,  pCO2
If the problem is metabolic then pH and [HCO3-] change in the same direction.
 Metabolic acidosis:  pH,  [HCO3-]
 Metabolic alkalosis:  pH,  [HCO3-]
It is also important to look at the FiO2 value – this is a value input by the user of the blood gas
machine. It is the concentration of O2 the patient was receiving at the time the sample was taken
(e.g. .21 in normal air)
Background box: useful facts about ABGs
 The blood gas syringe and needle – what is special about them: The syringe and needle
come in a package together – the syringe contains vacuum and heparin (in a small
rectangular piece of paper) – it will draw blood into itself with the heparin preventing clotting.
 Allens test can be performed before taking an ABG from the radial artery – it ensures patency
of the collateral supply from the ulnar artery: Press hard upon the patients radial and ulnar
arteries and get the patient to make a fist, hold for a few seconds then relax – the palm will go
white. If the grip on the ulnar artery is released and the palm goes red again then the
collateral supply is Ok and you may proceed to take blood from the radial artery.
 ABG results are printed on thermal paper – this fades with time. Always write the results
down and do not simply attach them to the notes.
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(7.13.4) Use and interpret results from a pulse oximeter
The pulse oximeter allows non-invasive measurement of peripheral O2 saturation (‘sats’) by way
of a probe attached to fingertip or earlobe. Results <90% require attention; <80% is clearly
abnormal and action is required unless this is normal for the patient (e.g. COPD). In children, any
result below 96% requires urgent action (oxygen).
Results from a pulse oximeter must be treated with caution – the following can result in erroneous
readings:
 Cold peripheries (poor perfusion)
 Skin pigmentation
Take an ABG when indicated
 Excess light
 CO poisoning (cherry red colour)
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Methaemaglobnaemia
Nail varnish
(7.13.5) Prescribe oxygen and oxygen delivery systems appropriately
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Oxygen is a drug – it must be prescribed. Use the normal cardex – there is often a dedicated
‘medical gas’ section on page 1. If not write as a normal drug and ring around all the time
slots to indicate continuous supply. Do not prescribe PRN – it is unlikely to be given.
Hypoxia kills faster than hypercapnia and CO2 retainers are rare (even in those with COPD) –
if in doubt start O2 at 40% and move from there.
If ABG shows >1.5 kPa increase in PaCO2, consider a respiratory stimulant (e.g. doxapram
1.5 – 4 mg / min IV) or assisted ventilation (e.g. NIPPV – non-invasive positive pressure
ventilation).
Oxygen delivery systems are divided into fixed and variable delivery systems:
A fixed performance device utilises the HAFOE principle (High Air Flow with Oxygen Enrichment).
O2 (A) flows into a jet (B) to entrain air through apertures (C) in the venturi barrel (D). The
resultant air/oxygen mixture containing the prescribed O 2 concentration flows into the face piece
(E) for patient breathing. Surplus gas leaves the mask through the holes (F) to flush out expired
CO2. When oxygen flow is increased, more air is entrained, to maintain a constant oxygen
concentration. This means that the exact FiO2 is known and does not vary.
One example of this type of mask is the Venturi
Mask in which the colour of the mask’s aperture
reflects the FiO 2 achieved (24%: blue; 28%:
white; 35%: yellow; 40%: red; 60%: green). The
flow rate of oxygen to be used with each colour is
printed on the Venturi barrel.
Changing the FiO2 means a new mask is needed.
This is a Hudson mask – a commonly used type of variable flow delivery
system.
The advantage of this system is that the FiO2 can be varied simply by
changing the flow rate of O2.
The disadvantage is that the exact FiO2
varies with the patient’s breathing pattern
and cannot be exactly known.
The last commonly used delivery system
is nasal cannulae (right) – these too are a
variable system – they may be used with
up to 4L of oxygen and are not likely to
achieve FiO2 greater than 28%. They are useful for patients who are
normally on low levels of home oxygen treatment.
So what system should I use?
Well but slightly low SATs
Nasal cannulae
Long term home oxygen
Hudson mask if required FiO2 <50% (approx 50% with 15L / min flow)
Asthma / LVF / pneumonia
Add a reservoir bag if required FiO2 >50-70% (at 15 L / min flow)
COPD
Venturi mask
More detail is available from:
http://www.studentbmj.com/issues/04/02/education/56.php
Nasal Cannulae
Venturi Mask
Hudson Mask
Hudson mask + reservoir
bag