Types of respiratory failure

• No disease is always associated with one type of failure - can be commonly associated

Type 1 respiratory failure

• Short of oxygen - hypoxemia
• Under 8 kPa

Type 2 respiratory failure

• Short of oxygen - hypoxemia AND
• Too much carbon dioxide - hypercarbia
  • Over 6 kPa

Prescribing oxygen

• Give no oxygen if SaO2 > 90%
• In patients at risk of CO2 retention, give oxygen to maintain SaO2 at 88-92%
  • If too much oxygen given there is a risk of acidosis because as pO2 rises pCO2 rises
• In patients not at risk of CO2 retention give oxygen to maintain SaO2 at 90-94%

V/Q mismatching

• Areas of poor ventilation have reactive vasoconstriction
• High concentrations of O2 will promote vasodilation - perfusion improves BUT ventilation is still poor
  • Dilated pulmonary vessels bring back larger quantities of CO2 - alveolar pCO2 increases
  • Ventilation is poor so CO2 cannot be exhaled, which increases arterial pCO2 → type II respiratory failure

pCO2 and haemoglobin

Haldane effect

• O2 can displace CO2 from Hb
• Chronically hypoxemic patients without CO2 retention can still become acidotic with too much O2

Bohr effect