Defining segments and phases of a time capnogram

Area of Science:

• Anesthesiology
• Respiratory Physiology
• Medical Instrumentation

Background:

• Current methods for dividing time capnograms into inspiratory and expiratory phases are arbitrary.
• This arbitrary division hinders the immediate detection of rebreathing during ventilation.
• Lack of standardized nomenclature complicates the interpretation of time capnograms.

Purpose of the Study:

• To demarcate time capnograms into inspiratory and expiratory components using concurrent gas flow signals.
• To facilitate the prompt and accurate detection of rebreathing.
• To establish standardized nomenclature for improved understanding and interpretation of time capnograms.

Main Methods:

• Utilized a Novametrix((R)) CO(2)-SMO plus respiratory profile monitor for simultaneous CO(2) and respiratory flow waveform display.
• Recorded data during spontaneous and controlled ventilation in a circle system under conditions of no rebreathing and rebreathing.
• Compared CO(2) and flow waveforms, leveraging similar response times, to define capnogram segments (Phase 0, I, II, III).

Main Results:

• The end of expiration closely aligns with the CO(2) waveform downslope when rebreathing is absent.
• Rebreathing prolongs the alveolar plateau, incorporating a portion of inspiration (Phase 0) and the expiratory plateau (Phase III).
• Gas flow signals enable precise demarcation of inspiratory and expiratory segments, identifying rebreathing instantaneously.

Conclusions:

• The arbitrary division of time capnograms is suboptimal for detecting rebreathing.
• Demarcating capnograms using gas flow signals enables rapid identification of rebreathing causes.
• This approach enhances the clinical utility of time capnography through standardized interpretation.