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Clinical Aspects Bhavani Shankar Kodali MD |
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Capnometry
Various factors result in either increased or decreased/absent PETCO2.
PETCO2 increased
| CO2 output | Pulmonary perfusion | Alveolar Ventilation | Technical errors
Machine faults |
| Fever
Malignant hyperpyrexia Sodium bicarbonate Tourniquet release Venous CO2 embolism |
Increased cardiac output
Increased blood pressure |
Hypoventilation
Bronchial intubation Partial airway obstruction Rebreathing |
Exhausted CO2
absorber
Inadequate fresh gas flows Leaks in breathing system Faulty ventilator Faulty valves
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PETCO2 decreased
| CO2 output | Pulmonary perfusion | Alveolar Ventilation | Technical errors
Machine faults |
| Hypothermia | Reduced cardiac output
Hypotension Hypovolemia Pulmonary embolism Cardiac arrest |
Hyperventilation
Apnea Total airway obstruction Partial airway obstruction Accidental tracheal extubation
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Circuit disconnection
Sampling tube leak Malfunction of ventilator |
The
table
above shows various factors that influence PETCO2 measurements
at the lips. However, it is strongly recommended that capnometry be used always
in conjunction with capnography as the latter, besides furnishing
diagnostic and therapeutic information, is the only way to confirm the
adequacy of CO2 sampling. Inadequate CO2 sampling leads to
falsely low PETCO2 values
which may be erroneously interpreted.
References:
1. Bhavani Shankar K, Moseley H, Kumar AY, Delph Y. Capnometry and anaesthesia. Review article. Canadian J Anaesth 1992;39:6:617-32.
