Biphasic capnogram recorded in a patient after single lung transplantation. This is due to different populations of alveoli. The first peak represents expired carbon dioxide from an allografted lung, which has normal compliance, good perfusion, and good ventilation-perfusion ratios (V/Q). The second peak most likely reflects expired carbon dioxide from the native lung because of slanted upstroke or steeper plateau is characteristic of the mismatched V/Q ratios and differing alveolar time constants in emphysema. Independent of the perfusion characteristics of the two lungs, the differences in their compliance alone could account for the observed biphasic capnogram, with the transplanted lung emptying more rapidly than the native lung.
Williams EL, Jellish WS, Modica PA, Eng CC, Templehoff R. Capnography in a patient after single lung transplantation. Anesthesiology 1991;74:621-2 (with permission).
Biphasic capnograms can occur during sampling tube leaks, endobronchial intubation, and severe kyphoscoliosis.