Relationship between arterial and end-tidal carbon dioxide pressure during controlled ventilation in porcine neonates

To investigate the validity of ETCO(2) in porcine neonates, which have been frequently used as an experimental model for human neonates, the relationship between arterial (PaCO2) and end-tidal PCO2 (ETCO(2)) in porcine neonates was examined under different respiratory conditions by regulating both inspiratory flow and positive end expiratory pressure (PEEP). The difference between PaCO2 and ETCO(2) widened significantly, according to the significant decrease in tidal volume/body weight ratio (TV/BW) caused by the increase of PEEP. A lower correlation between PaCO2 and ETCO(2) was observed in <6 ml/kg than in greater than or equal to 6 ml/kg TV/BW. It therefore seems reasonable to conclude that, in porcine neonates, the valid ETCO(2) measurements corresponding to PaCO2 would be obtained at greater than or equal to 6 ml/kg TV/BW.