Breathing Flashcards
Breathing in A-E refers to recognising respiratory failure. So what are the two types of respiratory failure and the differences between the two?
Type 1 - low pO2 (<8kPa on or off oxygen) and low/normal pCO2
Type 2 - low pO2 (<8kPa) and high pCO2 (>7kPa)
What is the difference between hypoxaemia and hypoxia?
- Hypoxaemia - pO2 <8kPa or spO2<94% (presence of hypoxaemia indicates respiratory failure)
- Hypoxia - reduced oxygen at the tissue level
What are the signs of hypoxaemia?
- Central cyanosis - due to presence of desaturated haemoglobin
- Signs of hypoxaemic hypoxia may also be present e.g. reduced CNS due to ischaemia of the brain
Type 2 respiratory failure is hypoxaemia and hypercapnia. Is seeing these results on an ABG always worrying and indicative of a critically ill patient?
- Not always - the patient may be in chronic type 2 respiratory failure due to COPD (blue bloater)
- However, do not dismiss the blood gas just because they have COPD as they may have an acute CO2 retention on top of their chronic retention due to an acute exacerbation.
A patient with COPD presents to the emergency department. A blood gas shows a low pO2 and a high pCO2.
- acute type 2 respiratory failure requires urgent treatment, usually ventilation
- chronic type 2 respiratory failure is not acutely life-threatening and patients manage years without ventilation
How would you determine which category this patient falls under?
- Examination:
- Signs of chronic CO2 -retention - asterixis, warm extremities, bounding pulse, confusion
- It is likely to be a chronic problem if they are cyanosed but not acutely SOB (their central chemoreceptors have become sensitised to the chronic hypercapnia). (Blue bloaters rely on hypoxic drive to maintain adequate ventilation and often go on to develop cor pulmonale)
- Look at pH:
- Chronic CO2 retention is compensated for by an increase in bicarbonate, so pH will be normal
- A metabolic acidosis will be present in an acute on chronic retention
- Look at bicarbonate:
- Assessing HCO3- in conjunction with the CO2 with the 1 for 10 rule
- Acute - for every rise of 10 of the PaC02 above 40, bicarb rises by 1
- Chronic - for every rise of 10 of the PCO2 above 50, the bicarb rises by 4
- Compare current ABG with previous ABGs if possible
What are the main 3 mechanisms of respiratory failure?
- Hypoventilation (always results in Type 2 respiratory failure)
- V/Q mismatch (usually starts with Type 1 and progress to Type 2)
- Diffusion impairment (usually starts with Type 1 and progress to Type 2)
What are the causes of hypoventilation?
- Poor respiratory drive caused by CNS depression (stroke, head injury, drugs)
- Poor respiratory effort due to muscle weakness (chronic malnourishment) or nerve damage (myasthenia gravis, GBS, MS, MNS, myelopathy)
- Restrictive abnormalities due to chest wall abnormalities (kyphoscoliosis, pain from fractured ribs) or severe pleural disease (pulmonary fibrosis, large pleural effusion/haemothorax)
What is meant by V/Q mismatch?
- Gas exchange is optimal when alveolar ventilation and perfusion are matched, with V/Q = 1.
- Mismatch occurs when there is inadequate alveolar ventilation or inadequate perfusion.
Which conditions commonly cause a V/Q mismatch due to inadequate alveolar ventilation and how?
- Airway narrowing not uniform throughout the lungs - Asthma, COPD
- Exudate in some alveoli - Pneumonia
- Fluid in some alveoli - Pulmonary oedema
- Some alveoli collapsed due to inadequate surfactant - ARDS of newborn
Which condition most commonly causes a V/Q mismatch due to perfusion problems? How does this cause type 1 respiratory failure?
Pulmonary embolism
- The alveoli distal to the thrombus are poorly perfused.
- Blood is diverted to the alveoli proximal to the thrombus.
- If this extra blood (increased Q) cannot be matched by the ventilation (V) of the alveoli, then there is a reduced V/Q ratio and a drop in PaO2
When making an assessment of Breathing in a conscious patient, a brief history is appropriate. What information would you hope to gain from this?
- Level of consciousness
- a fully conscious pt will complain of SOB and will be distressed
- confusion, lethargy and reduced consciousness may be caused by hypoxaemia and hypercarbia
- Focussed questioning to determine the underlying cause of the problem
Is cyanosis an early or late sign of a breathing problem?
LATE
What signs suggest a breathing problem?
- LOOK FOR RESP DISTRESS - Tachypnoea (>25 breaths/min), use of accessory muscles, chest deformity, conscious level, remember cyanosis is a late sign
- LISTEN - noisy breathing, breath sounds
- FEEL - expansion, percussion and tracheal position
Describe how you would approach B in the A-E assessment.
“I would assess the respiratory system using a look, listen and feel approach –
- looking at chest expansion and respiratory effort;
- listening for air entry and added sounds
- feeling for chest expansion, tracheal deviation and percussing.
In terms of basic observations I would check oxygen saturations and respiratory rate.
If the respiratory system was compromised I would sit the patient up and deliver 15L high-flow O2 through a non-rebreathe mask and consider an ABG and portable CXR for further assessment.”
What step-wise approach would you use for managing a breathing problem?
- Ensure the airway is clear and maintained.
- Give oxygen, initially high flow and once stable aim for an SpO2 of 94-98%.
- Treat the underlying cause e.g. thoracocentesis for tension pneumothorax
- If breathing becomes inadequate it must be supported (e.g. ventilate with a bag-mask).
