| Manifestations | - Abnormal capnogram shape with elevated baseline
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- Abnormal motion of one-way valves
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| Potential causes | |
- High respiratory rate, small tidal volume in pediatrics
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- Open self-sealing CO2 canister connection (ie, quick-connect)
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- Intentional CO2 administration (eg, single ventricle neonates)
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- Excessive apparatus deadspace relative to tidal volume (eg, neonate)
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- Incompetent (stuck open) inspiratory valve
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- Incompetent (stuck open) expiratory valve
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- Low levels of inspired CO2 occur with rebreathing circuits such as Mapleson D or Bain circuits
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- Breathing system disconnect (during spontaneous breathing)
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| Suggested responses | - Increase fresh gas flow rate to above minute ventilation (inspired CO2 will disappear if absorbent is exhausted or decrease with Mapleson breathing system)
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- Replace CO2 absorbent and check that canister is properly connected
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- Increase minute ventilation (to compensate for rebreathing)
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- Inspect, vibrate, dry, and/or repair one-way valves
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- Switch ventilator mode (spontaneous-manual versus mechanical) if incompetent one-way valve on fresh gas decoupled breathing system
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