Comparison of ventilation and gas exchange in anaesthetized infants and children during spontaneous and artificial ventilation

Measurements of minute and alveolar ventilation (VE and VA), respiratory frequency, end-tidal carbon dioxide concentration (E'CO2), deadspace (VD) and carbon dioxide output (VCO2) were made in 22 anaesthetized infants and young children during spontaneous (SV) and intermittent positive pressure ventilation (IPPV). In the children who had been given an opioid premedication, E'CO2 concentrations were significantly greater during SV than the predetermined value set for IPPV. In infants premedicated with atropine alone, E'CO2 during SV was only slightly greater than during IPPV, and VA was not changed. A mean tidal volume (VT) of 9.8 +/- 2.5 ml kg-1, and a mean VE of between 225 and 250 ml min-1 kg-1, were required to produce E'CO2 4.5% during IPPV. Despite a decrease in respiratory frequency, VD/VT and VD per minute were both decreased by IPPV in infants. VCO2 was unchanged in both groups. The decrease in wasted ventilation seen during IPPV in infants supports its use in clinical practice.