BACKGROUND

Carbon-dioxide elimination during high-frequency oscillatory ventilation (HFOV) is thought to be proportional to the carbon dioxide diffusion coefficient (DCO ) which is calculated as frequency x (tidal volume) . DCO can be used to as an indicator of CO elimination but values obtained in different patients cannot be directly compared.

OBJECTIVES

To analyze the relationship between DCO , the weight-corrected DCO (DCO corr) and blood gas PCO values obtained from infants receiving HFOV.

METHODS

DCO data were obtained from 14 infants at 1/s sampling rate and the mean DCO was determined over 10 min periods preceding the time of the blood gas. DCO corr was calculated by dividing the DCO by the square of the body weight in kg.

RESULTS

Weight-correction significantly reduced the inter-individual variability of DCO . When data from all the babies were combined, standard DCO showed no correlation with PCO but DCO corr showed a weak but statistically significant inverse correlation. The correlation was better when the endotracheal leak was <10%. There was significant inverse but weaker correlation between the HFOV tidal volume (VThf) and the PCO . In any baby, DCO corr >50 mL /sec/kg or VThf > 2.5 mL/kg was rarely needed to avoid hypercapnia.

CONCLUSIONS

Weight-correction of DCO values improved its comparability between patients. Weight-corrected DCO correlated better with PCO than uncorrected DCO but the correlation was weak.