A simple method for estimating the ventilatory response to CO2 in infants.

We report a new noninvasive method for the estimation of CO2 response in uncooperative infants. By comparing the changes in inspired minus alveolar PO2 breathing air and 4% CO2, an indirect estimate of increase in alveolar ventilation can be obtained. This report is a comparison of 3 possible indirect methods: changes in inspired minus alveolar PCO2 (delta AIPCO2), changes in inspired minus alveolar PO2 (delta IAPO2), and changes in transcutaneous PO2 (TcPO2) with the standard steady-state method for ventilatory response to CO2. Twenty-one comparisons were made, 16 on 7 preterm infants, and 5 on an older child (at 2.5 and at 4 yr of age), with central hypoventilation syndrome. We found that changes in delta IAPO2 gave the best correlation with changes in minute ventilation (r = 0.83, p less than 0.001), that changes in delta AIPCO2 were less valid (r = 0.66, p less than 0.001), and that there was no correlation with changes in TcPO2. We conclude that changes in inspired PO2 minus alveolar PO2 can be used in uncooperative infants to estimate the ventilatory response to CO2.