Which area of the capnogram represents the portion of an exhaled breath most likely to contain expiratory gases exclusively from the anatomic dead space?

Capnography is now routinely used in the monitoring of patients undergoing general anesthesia. Understanding the different shapes and portions of the typical capnogram is vital to making adjustments in respiratory management of a patient when their clinical status is altered.

Capnograms are commonly divided into four phases (Figure 1). Phase 0 incorporates all of inspiration, and begins with an initial phase that contains a mix of the remnants of the previously expired alveolar gases that are being rapidly diluted by newly inspired fresh gas that is devoid of CO2.This leads to a steep decline in the capnogram followed by a baseline, where no CO2 is typically present unless unintentional rebreathing is occurring, perhaps because of a faulty unidirec-tional valve or exhausted...

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