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Bhavani Shankar Kodali MD

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Clinical uses of capnography

Bhavani Shankar Kodali MD

Capnometry
Various factors result in either increased or decreased/absent PETCO2.

PETCO2 increased

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

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
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.

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