Background:Transcutaneous CO2 (TCM) monitoring is the accepted standard in assessing carbon dioxide pressure (CO2) in the tissue and can be helpful in the management of newborns requiring ventilatory support. Infants with hypoxic ischemic encephalopathy (HIE) are routinely treated with therapeutic hypothermia (TH) to 33.5°C. It is well established that fluctuations in the partial pressure of CO2 in arterial blood (PaCO2) during TH is associated with poor neurodevelopmental outcomes, thus close monitoring of PaCO2 is key to good outcomes. TCM correlation is perfusion dependent. TCM heats the skin at the sensor site to arterialize the sample. The non-invasive device produces a PCO2 value corrected to 37°C (TcPCO2). The TCM is mostly regarded as a reliable noninvasive manner to continuously monitor tissue CO2. Our objective was to determine the accuracy and precision of TcPCO2values in newborns undergoing TH. Methods:We conducted a retrospective chart review of 10 neonates (3F/7M) undergoing TH for HIE requiring respiratory support. The weight of the neonates ranged from 2,230 to 3,810 g. We compared TcPCO2to PaCO2 values (all at 37°C) using a Bland-Altman plot for multiple measurements per patient. A Wilcoxon test for paired samples (non-normally distributed data), and a repeated measures ANOVA (rmANOVA: two types of measurements; five measurements per subject, eight subjects) was also used to aid in the analysis. IRB exempt status was gained through UC Davis. Results:Ninety paired samples were collected in 10 patients with a range of PaCO2 28–94 mm Hg. Median difference was 2 mm Hg higher in TcPCO2 (Wilcoxon test for paired samples P < 0.01). However, the precision was poor (95% CI was -13 to +18 mm Hg). The rmANOVA showed no main effect on measurement number (P = 0.38), method of comparison (P = 0.78), or the interaction (P = 0.67). Conclusions:TcPCO2 showed a strong median correlation to PaCO2 values at 37°C but lacked precision. TcPCO2may not be appropriate for estimating PaCO2 in patients undergoing TH. Care should be taken when utilizing TCM in these patients. TCM may prove to be a reliable trending tool but acute changes in values should be confirmed with PaCO2. Given our small sample size (N = 10) and the retrospective nature of our study, more investigation into the usefulness of TCM during TH is warranted. Discrepancy in TcPCO2and PaCO2 values during TH justifies further exploration in transcutaneous monitoring.
Smith et al. (Fri,) studied this question.