TRANSCUTANEOUS AND END-TIDAL CARBON-DIOXIDE PRESSURES SHOULD BE MEASURED DURING PEDIATRIC POLYSOMNOGRAPHY

Pediatric obstructive sleep apnea (OSAS) is characterized by partial a irway obstruction, alveolar hypoventilation, and elevated arterial CO2 (Pa-CO2). Thus, a reliable, practical method of estimating CO2 is nee ded for pediatric polysomnography. Therefore, we measured both transcu taneous CO2 (Ptc(CO2)) and end-tidal CO2 (PET(CO2)) in 15 pediatric po lysomnographic evaluations. Sleep state, the highest Ptc(CO2) and the highest PET(CO2) were recorded for 5,159 thirty-second epochs. Althoug h Ptc(CO2) and PET(CO2) were available for 78.5 and 73.0% of epochs, r espectively, at least one estimator was available for 92% of the epoch s. One infant who would not tolerate a nasal sampling catheter had no PET(CO2) data. For 13 of 14 studies there was a relatively constant di fference between Ptc(CO2) and PET(CO2). The difference between Ptc(CO2 ) and PET(CO2) was within 4 mm Hg in 63.9% of 3,072 epochs. Across 14 studies, mean Ptc(CO2) exceeded mean PET(CO2) by 2.8 +/- 3.0 mm Hg, an d it was within 4 mm Hg in 10 studies. In three subjects, PET(CO2) was intermittently or consistently less than Ptc(CO2) because of tachypne a, increased physiologic dead space, or severe partial airway obstruct ion; in one subject Ptc(CO2) exceeded PET(CO2) for undetermined reason s during one electrode application. The results of this study indicate that Ptc(CO2), as well as PET(CO2), should be measured during pediatr ic polysomnography. By utilizing both Ptc(CO2) and PET(CO2) there was a 70% reduction in the number of epochs that could not be assessed for hypoventilation. For an individual subject or electrode application t here was a constant, and usually close, relationship, between Ptc(CO2) and PET(CO2). Ptc(CO2) monitoring was particularly useful for childre n who would not tolerate a nasal sampling tube and for those with mode rate to severe partial airway obstruction, tachypnea, or increased phy siologic dead space in whom PET(CO2) underestimated Ptc(CO2).