VENTILATION AND GAS EXCHANGE DURING ANAESTHESIA AND SURGERY IN SPONTANEOUSLY BREATHING INFANTS AND CHILDREN

Minute ventilation (VE) (mlmin^–1), respiratory frequency(f), mixed expired carbon dioxide fraction (FCO₂ and end-tidalcarbon dioxide concentration E'CO₂) (%) were measured, and alveolarventilation (VA), deadspace (VD), deadspace/tidal volume ratio(VD/VT) and carbon dioxide output (VCO₂) calculated in 58 anaesthetized,spontaneously breathing infants and children weighing 2.8–20.5kg.Although minute volumes varied, tidal volume correlated wellwith weight (r = 0.83), with a mean tidal volume (± ISD)of 5.2±1.2mlkg^–1. It was concluded that, by theuse of mean VT + ISD (approximated to 6 ml kg^–1) the freshgas flow in mlmin^–1 should be set at 2.5x6xkgxf(15xkgxf)to avoid rebreathing in various T-piece systems in anaesthetized,intubated and spontaneously breathing infants up to a body weightof 20 kg. End-tidal carbon dioxide concentration was lower inyounger patients who were premedicated with atropine alone thanin the older ones who received opioid premedication also. Respiratoryfrequency, VD/VT and total VD per minute were higher in theyounger age group, which explained the finding of a high VEin relation to VCO₂ for these patients. This inefficiency ofventilation emphasizes the need to minimize apparatus deadspacein breathing systems used for small infants. ^*Department of Anaesthesia, University Hospital, S-22185 Lund,Sweden. Department of Anaesthesia, St George's Hospital, Blackshaw Road,London SW17.