4. Breathing System

4.1 Calibrate O₂ monitor(s)

• Calibrate to read 21% (sensor in room air)
• Set low O₂ alarm limit to more than 21% and make sure an alarm occurs
• Reinstall sensor - flush circuit with O₂ flush; verify monitor reads close to 100%

• cannot calibrate - faulty fuel cell

• crossover between O₂ supply and other gas - hospital piping or in gas machine
• wrong gas in central supply / cylinder

4.2 Check initial status of breathing system

• Circuit complete, undamaged, unobstructed
• Verify CO₂ absorbent is adequate
• Install PEEP valve if needed
• Attach gas sampling line to circuit
• Set all flows to zero (or minimum)

• manufacturing defects causing leaks or obstruction
• foreign object obstructing e.g. sampling port cap inside elbow

• PEEP valve on inspiratory side

4.3 Check function of unidirectional valves

• Temporarily remove circuit from absorber
• Check inspiratory valve
  • Attach a spare reservoir bag to the inspiratory outlet of the absorber and occlude expiratory inlet with thumb
  • Fill bag with O₂ flush until pressure gauge reads 40 cm H₂O - pressure holds
  • Squeeze and release test bag - pressure rises but returns to 40 cm H₂O - no loss

• missing, incompetent valves or incorrectly seated

• Check expiratory valve
  • Attach spare reservoir bag to the expiratory inlet of the absorber and occlude inspiratory outlet with thumb
  • Pressurize with O₂ flush to 40 cm H₂O and bag on expiratory inlet stays deflated