[The influence of endotracheal tube size on the airway flow resistance and work in infants analyzed using a...

The respiratory flow velocity of 74 infants under halothane-nitrous oxide-oxygen anesthesia was measured, and the statistical relationship between the age in months and the flow velocity was obtained with least square method. The flow resistance of endotracheal tubes (size of 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 mmI.D.) with the flow velocity below 45 ml.sec-1 was also measured in in vitro experiments. The standard respiratory flow velocity of 6, 12, 24, 36, 48 and 60 month old infants was estimated by the recurrent formula. The mean flow resistance and respiratory work with each size of endotracheal tube were calculated by simulation technique using these data. These data coincided well with the data obtained by calculation based on in vitro experiments.