Respiratory failure Flashcards
Define type 1 & type 2 respiratory failure
Type 1=hypoxic
Type 2=hypercapnic
Describe the different pathways causing respiratory failure
- ) Lung failure leading to hypoxic respiratory failure- results in hypoxic respiratory failure
- ) respiratory muscle pump failure leading to hypercapnic respiratory failure
Define Hypoxaemia
PaO2<8kPa
-refers to oxygen in the blood
What are the causes of hypoxaemia?
- Ventilation-perfusion mismatch
- Impaired diffusion
- Alveolar hypoventilation
- Low partial pressure of inspired oxygen
- Anatomical R-L shunt e.g PAVM lobar pneumonia
What should the relationship between ventilation and perfusion be?
-They should be exactly matched
-VA=Q
Normal value should be 0.8
Describe the different Va/Q scenarios and state the values of their ratios
1.)Shunt alveolar unit. Va/Q=0 Q>>Va Wasted perfusion 2.) Ideal alveolar unit Va/Q=1 Q=Va idealized matching 3.)Dead space alveolar unit Va/Q=infinity? Q<
Define hypercapnia
PaCo2>6kPa
State the equation to work out alveolar ventilation (Va)
minute ventilation(Ve) - dead space ventilation(Vd)
How do you work out minute ventilation
Tidal volume(Vt) x respiratory rate(RR)
How do you work dead space ventilation?
Dead space volume x RR
How is blood flow increased to well ventilated alveoli and decreased to poorly ventilated alveoli in the healthy lung
via reflex mechanisms
What are the two possible responses to oxygen therapy
- Patients PaCo2 and clinical state may improve or not change
- Patients PaCo2 rises(hypercapnia), becomes drowsy or unconscious
Why do some patients develop hypercapnia on oxygen therapy?
- Patients with COPD rely on their hypoxic ventilatory drive due to blunted sensitivity to Co2 and H+
- Hypercapnia results from a suppression of the hypoxic ventilatory drive causing alevolar hypoventilation
- Patients ‘stop breathing’
What are the 3 factors governing blood gas levels
- Drive (cortical, brainstem)
- Load( resistive forces)
- Capacity( spinal cord, peripheral nerves, NMJ,muscles)
What factors influence respiratory failure?
- ) Drive failure
- Cortical &brainstem lesions (incl.trauma), encephalitis, ischaemia,Haemorrhage, Cheyne-Stokes respiration (CHF)
- Drugs(sedatives,opiods)
- Metabolic alkalosis (loop diuretics) - ) Transmission failure: (spinal cord lesion, poli,MND,myasthenia gravis)
- ) Threshold (intrinsic PEEP, dynamic hyperinflation)