END-TIDAL VERSUS TRANSCUTANEOUS CO2 MEASUREMENT IN THE CRITICALLY ILL NEONATE

Both end-tidal (PetCO2) and transoutaneous (PtoCO2) estimates of PaCO2 have limitations in the critically ill neonate. To determine whether the site of PetCO2 sampling is important, 47 measurements of distal and proximal PetCO2, PtoCO2 and PaCO2 were compared. Twenty-eight intubated neonates, 35±1 wks post-conceptual age with a mean weight of 2.32±0.9 kg were studied. Distal and proximal PetCO2 were measured at the tip and connector of the endotraoheal tube using a Puritan-Bennett capnometer. Distal PetCO2 was significantly greater than proximal measurements in all patients (p<0.001) and more accurately estimated PaCO2. The correlation coefficient, r, for PtcCO2 and PaCO2 was 0.86 and for distal PetCO2 and PaCO2 was 0.63. The response time of this capnometer limits its accuracy at respiratory ratea >75/min, and PetCO2 is known to be inaccurate In severe lung disease (FiO2>0.7). Excluding these neonates, the r value for distal PetCO2 and PaCO2 was .83. Both PtcCO2 and distal PetCO2 provide accurate estimates of PaCO2 in neonates although PtcCO2 is superior in severe lung disease. Distal sampling of PetCO2 increases the accuracy of end-tidal measurement.