resp failure Flashcards
define
Respiratory failure occurs when pulmonary gas exchange is sufficiently impaired to cause hypoxaemia with or without hypercarbia.
Respiratory failure is present if PaO2 is less than 8 kPa - 60 mmHg.
types of resp failure
It is sub-classified into one of two types of respiratory failure based on the level of PaCO2:
type 1 respiratory failure:
- PaCO2 is less than 6.5 kPa
- PaO2 less than 8 kPa
type 2 respiratory failure:
- PaCO2 is greater than 6.5 kPa
- PaO2 is less than 8 kPa
causes of type 1 resp failure
Type 1 respiratory failure may occur in
- diseases that damage lung tissue
- conditions where there is a V/Q mismatch
- conditions where there is hypoxaemia due to right to left shunts
- It may be acute or chronic.
Acute type 1 respiratory failure may occur in conditions such as:
- asthma - in the acute phase the cause of respiratory failure in asthma is not the bronchoconstriction but rather the intense inflammation and oedema of the lungs which results in impaired oxygenation of the blood
- pulmonary embolus
- pulmonary oedema
- adult respiratory distress syndrome
Causes of chronic type 1 respiratory failure include:
- emphysema
- respiratory muscle disease, e.g. myasthenia gravis
- kyphoscoliosis
- thromboembolic pulmonary hypertension
- lymphangitis carcinomatosa
- pulmonary alveolar fibrosis
causes of type 2 resp failure
Type 2 respiratory failure occurs in conditions which cause alveolar hypoventilation, for example, where there is:
- a reduced ventilatory effort
- increased dead space
- increased carbon dioxide production
- a combination of these
- Type 2 respiratory failure may be acute or chronic.
acute type 2 respiratory failure
- severe acute asthma - as the patient becomes exhausted type 2 respiratory failure occurs
- acute epiglottitis
- respiratory muscle paralysis; a number of aetiologies including Guillain-Barre syndrome
chronic type 2 respiratory failure
- chronic bronchitis
- primary alveolar hypoventilation
- motor neurone disease
Clinical features of respiratory failure include?
clinical features of the underlying cause of the respiratory failure
hypoxia causing:
- restlessness,
- confusion and
- ultimately, coma
hypercapnia causing:
- drowsiness
- flapping tremor
- warm peripheries
- headaches
- bounding pulse
- papilloedema
investigations of resp failure
Initial patient assessment:
- assess the patient’s previous disability
- are there signs of deterioration?
Screening investigations:
- chest radiology
- blood gases
- peak expiratory flow rate
- ECG
- full blood count
- biochemistry
- sputum and blood culture
- store a blood sample for serology
Type 1 respiratory failure:
acute - PaO2 (\/ \/) PaCO2 (-) pH (-) bicarbonate (-)
chronic - PaO2 (\/) PaCO2 (-) pH (-) bicarbonate (-)
Type 2 respiratory failure:
acute - PaO2 (\/) PaCO2 (/) pH (\/) bicarbonate (-)
chronic - PaO2 (\/) PaCO2 (/) pH (\/ / /) bicarbonate (/)
Key:
\/ = decreased;
/\ = increased;
- = unchanged
management
- the administration of supplemental oxygen,
- the control of secretions,
- the treatment of any underlying pulmonary infection,
- the control of any bronchospasm and measures to limit pulmonary oedema.
Principles:
- treat the underlying disease
- physiotherapy
- oxygen therapy - try to maintain PaO2 > 8 kPa
- bronchodilators and steroids if there is airways obstruction
- in some circumstances, respiratory stimulants such as i.v. doxapram 1-4 mg / min, may be indicated if the PaCO2 begins to rise
- if arterial O2 continues to deteriorate or fails to improve then some form of respiratory support should be considered
- long-term management should be aimed at the underlying cause of the condition e.g. COAD
when should oxygen therapy be given?
In patients who are critically ill (anaphylaxis, shock etc) oxygen should initially be given via a reservoir mask at 15 l/min. Hypoxia kills. The BTS guidelines specifically exclude certain conditions where the patient is acutely unwell (e.g. myocardial infarction) but stable.
Oxygen saturation targets
acutely ill patients: 94-98%
patients at risk of hypercapnia (e.g. COPD patients): 88-92% (see below)
oxygen should be reduced in stable patients with satisfactory oxygen saturation
Management of COPD patients
- prior to availability of blood gases, use a 28% Venturi mask at 4 l/min and aim for an oxygen saturation of 88-92% for patients with risk factors for hypercapnia but no prior history of respiratory acidosis and do an ABG
- adjust target range to 94-98% if the pCO2 is normal ie <6kPa
- of pCO2 >6kpa: maintain target Spo2
Situations where oxygen therapy should not be used routinely if there is no evidence of hypoxia
:
- myocardial infarction and acute coronary syndromes
- stroke
- obstetric emergencies
- anxiety-related hyperventilation
mechanisms of oxygen therapy
- nasal prongs
* 1-4 L/min = 24-40% o2 - simple face mask
- non-rebreathe mask
- reservoir bag allows delivery of high concs of o2
- 60-90% @ 10-15L
- Venturi mask
- provides precise 02 concs @ high flow rates
- yellow- 5%
- white- 8%
- blue - 24%
- red - 40%
- green - 60%
