Ventilatory response to CO with Read's rebreathing method in normal infants.

Background: Methods of evaluating the ventilatory response to CO (VRCO ) of the respiratory center include the steady-state and the rebreathing method. Although the rebreathing method can evaluate the ventilatory response continuously to gradually increasing CO , the rebreathing method has been rarely performed in infants. The aim of this study was to investigate whether we could perform the VRCO with the rebreathing method in normal infants.

Methods: The subjects were 80 normal infants. The gestational age was 39.9 (39.3-40.3) weeks, and the birth body weight was 3142 (2851-3451) grams. We performed the VRCO with Read's rebreathing method, measuring the increase in minute volume (MV) in response to the increase in EtCO by rebreathing a closed circuit. The value of VRCO was calculated as follow: VRCO (ml/min/mmHg/kg) = ΔMV/ΔEtCO /body weight.

Results: We performed the examination without adverse events. The age in days at examination was 3 (2-4), and the examination time was 150 ± 38 s. The maximum EtCO was 51.1 (50.5-51.9) mmHg. The value of VRCO was 34.6 (29.3-42.8). The intraclass correlation coefficient of the VRCO of cases with multiple measurements was 0.79.

Conclusion: This study suggests that the rebreathing method can evaluate the ventilatory response to high blood CO in a short examination time. We conclude that the rebreathing method is useful even in infants. In the future, we plan to measure the VRCO of preterm infants, and evaluate the respiratory center of infants in more detail.