Type I Respiratory Failure.
Type I refers to hypoxaemia, in which there is a decrease in the oxygen supply to a tissue. Hypoxaemia is mainly caused by a disturbance between the ventilation (gas) and perfusion (blood) relationship within the lungs. Levels of carbon dioxide in the blood can remain normal or reduce as the amount of gas breathed in and out each minute increases to compensate for lack of oxygen.
Conditions affecting oxygenation:
- Ventilation-perfusion mismatch (parts of the lung receive oxygen but not enough blood to absorb it).
- Alveolar hypoventilation (decreased minute volume due to reduced respiratory muscle activity).
- Diffusion problem (oxygen cannot enter the capillaries due to lung disease).
- Shunt (oxygenated blood mixes with deoxygenated blood from the venous system).
Common causes of type I respiratory failure include:
- Atelectasis: a collapse of lung units (diffusion problem).
- Pneumonia: an inflammation of the lung tissue, often of infective origin (diffusion problem).
- Pulmonary oedema: an accumulation of fluid in the lungs.
- Pulmonary embolism (ventilation-perfusion mismatch).
- Neurologic problems: head injury or opiate overdose could be the cause of this problem (alveolar hypoventilation).
Type II Respiratory Failure.
Type 2 refers to hypoxaemia with hypercapnia, the presence of an abnormally high level of carbon dioxide in the circulating blood, which can occur with or without hypoxia. This type of respiratory failure is primarily caused by a reduction in the amount of gas inhaled and exhaled over time (minute ventilation), usually expressed as hypoventilation.
The inability to excrete carbon dioxide results in a systemic acidosis, which has negative effects on organ performance and metabolism, ultimately leading to cellular death. In chronic situations the body responds to the acidosis by producing more buffers, thus ‘compensating’ for the failure. This process is typically seen in patients with COPD and can be exacerbated by acute illness, such as chest infection.
Common causes of type 2 respiratory failure include:
- Depression of the respiratory centre such as opiate overdose;
- Acute chest disease: infection, asthma, pneumonia;
- Increased airways resistance: COPD, asthma.
- Decrease in lung area for gas exchange: chronic bronchitis.
- Spinal injury;
- Acute neuromuscular disease: myasthenic crisis, Guillain-Barre syndrome;
- Pneumothorax or haemothorax;
- Airway obstruction: foreign bodies or swelling/oedema.
Signs and Symptoms of Respiratory Failure.
- Increased rate of breathing- as the patient makes efforts to either compensate for hypoxaemia or hypercapnia their rate of breathing will increase.
- Increased effort of breathing- either due to low oxygen levels or high airway resistance or poor compliance within the lung the patient may need to increase their tidal volumes, which may require them to work harder. This then adds to their problem as they can then tire making their breathing even more difficult.
- Use of accessory muscles- in an attempt to improve their respiratory function the patient in respiratory distress will often utilise the accessory muscles to aid in increasing the size of the thoracic cavity. These muscles include the sternomastoid and the scalenes.
- Tachycardia- partly due to the sympathetic response and partly due to the hypoxaemia the heart rate will also increase in an attempt to supply the tissues with more oxygen.
- Cyanosis- as the levels of oxygen may be low in the blood this is often manifested in the peripheral circulation as cyanosis. So the fingers or hands may well have a blue tinge. If the tongue or the lips have this blue tinge then the patient may well be cyanosed both peripherally and centrally which is an alarming sign and needs to be treated very promptly.
- Confusion- due to the effects of low oxygen or higher carbon dioxide levels in the blood which serves the brain confusion may ensue.
- Reduced level of consciousness- both severe hypoxaemia and hypercapnia will cause a reduced level of consciousness.
- Low oxygen saturations- a low oxyhaemoglobin will manifest itself with low oxygen saturations. You do need to be aware however, that if the patient is peripherally shut down and therefore cold, the oxygen saturations may not be very reliable.