20 - Respiratory Failure Flashcards
Concentration of oxygen in air
20.94%
Barometric pressure (atmospheric pressure)
101.3kpa
PO2 of dry air at sea level
21.2kpa
o2 in air x atmospheric pressure
What is tracheal gas
PO2 after humidification
How to work out tracheal gas
• Fractional concentration of oxygen in the dry gas phase x (barometric pressure - SVP) FiO2 x (PB - SVP)
What effects alveolar PO2
Ventilation
O2 consumption/CO2 production
Alveolar PaO2
dry barometric pressure x (FiO2-VO2 / VA)
What is FiO2, VO2 and Va
o FiO2 – inspired oxygen concentration- 21/20.93
o VO2- oxygen consumption(round 250 ml/min)
o VA- alveolar ventilation
What is the alveolar to arterial PO2 difference determined by
Shunting
What is the normal A-A O2 difference
not normally greater than 2 kPa
What is shunting
An area of the lung that is perfused but not ventilated
Has blood supply but not oxygen
What is oxygen delviery
= [Hb] x Oxygen Saturation of Hb x 1.34 x 10 x Cardiac Output
o Round 1 litre per minute
Signs of respiratory compensation
Tachypnoea > 20
Use of accessory muscles
Nasal flaring
Signs of increased sympathetic tone
Tachycardia
Hypertension
Sweating
Signs of end-organ hypoxia
Altered mental status
Bradycardia and hypotension
Signs of haemoglobin desaturation
Cyanosis
Signs of CO2 retention
Flap
Bounding pulse
Type I respiratory failure
Hypoxaemia only- caused by shunting (hypoxia)
PaO2 < 8kpa
Causes of Type I resp failure
Pneumonia Pulmonary oedema Asthma/COPD PE Pneumothorax
Type II respiratory failure
o Hypoxaemia and hypercapnia
PaO2 <8kPa
PaCO2 > 6.5kPa
Symptoms of type I resp failure
Type I with fatigue
What can cause type 1 to turn into type 2
COPD
- After tired muscle
What causes type 2 resp failure
Brainstem Neuropathy Airway obstruction Depressant drugs Nerve root injury, or Chest wall compliance, nothing to do with lung
Indications for oxygen therapy
• Respiratory failure, cardiac or respiratory arrest, tachypnoea, cyanosis, hypotension, metabolic acidosis
Treatment for respiratory failure
Oxygen
When do you use oxygen mask, nasal cannulae
Patient with normal vital signs (post op)
When trauma mask
Higher o2 conc needed
Asthma attack, pneumonia, sepsis
(60% oxygen)
When to use venturi mask
Controlled treatment in long term resp failure e,g COPD
What does pulse oximetry tell us (SpO2)
oxygenation NOT ventilation
What is the critical threshold for pulse oximetry saturation
94%
Sources of error in pulse oximetry
Poor peripheral perfusion
Dark skin (oximeter over-reads slightly)
False nails or nail varnish
Lipaemia / hyperlipidaemia / propofol infusion
What is arterial blood gas monitoring for
• Arterial blood gas monitoring is used to keep the FiO2 to the minimum required to achieve adequate oxygenation
Too high O2 –> free radicals which damage the body
ABG also used to evaluate pH changes
What percentage of COPD patients are CO2 retainers
10%
What do do if unknown CO2 retainer
o Start high flow oxygen
o Monitor for drowsiness/signs of CO2 retention
o Check ABGs after 30 minutes
What to do if known CO2 RETAINER
o Controlled mask o Titrate – use lowest O2 possible o Aim for stats 90% - 92% (may need 85%+) o Measure ABGs ASAP o Repeat ABGs after 30mins of O2 change
When do you give ventilation
- Not for hypoxia
- Ventilation Used for hypercapnea
- i.e. give oxygen in hypoxia and ventilate in hypercapnea (= hypoventilation)
