Figure 1.

Correlation between transcutaneous carbon dioxide (Tcco₂) and partial pressure of carbon dioxide (Paco₂). The correlation between Paco₂ and Tcco₂ for all measurements of patients requiring high-frequency oscillatory ventilation/high-frequency percussive ventilation, conventional mechanical ventilation, and noninvasive ventilation is high with Pearson’s correlation coefficient (PCC) = 0.82, concordance correlation coefficient (CCC) = 0.81, and repeated measures correlation coefficient (RMC) = 0.80. The increased number of samples plotted with a Paco₂ above 100 mm Hg is due to limitations of laboratory measurement (i.e., maximum level in the blood gas device is > 110 mm Hg) and may actually be higher.