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J Appl Physiol 87: 36-46, 1999;
8750-7587/99 $5.00
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Vol. 87, Issue 1, 36-46, July 1999

Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes

Pierre-Henri Jarreau1,2, Bruno Louis2, Gilles Dassieu3, Luc Desfrere1, Perre W. Blanchard1, Guy Moriette1, Daniel Isabey2, and Alain Harf2,4

1 Service de Médecine Néonatale, Centre Hospitalier Universitaire Cochin-Port Royal, Assistance Publique-Hôpitaux de Paris-Université Paris V, 75014 Paris; 2 Institut National de la Santé et de la Recherche Médicale (INSERM) U 492, 94000 Créteil; 3 Service de Réanimation Néonatale, Centre Hospitalier Intercommunal, 94000 Créteil; and 4 Service de Physiologie-Explorations Fonctionnelles, Centre Hospitalier Universitaire Henri Mondor, Assistance Publique-Hôpitaux de Paris-Université Paris XII, 94000 Créteil, France

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (Delta PETT) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, Delta PETT is given by the Blasius formula (F. Lofaso, B. Louis, L. Brochard, A. Harf, and D. Isabey. Am. Rev. Respir. Dis. 146: 974-979, 1992). Here, we also propose a general formulation for neonatal and pediatric ETTs on the basis of adimensional analysis of the pressure-flow relationship. Pressure and flow were directly measured in seven ETTs (internal diameter: 2.5-7.0 mm). The measured pressure drop was compared with the predicted drop given by general laws for a curved tube. In neonatal ETTs (2.5-3.5 mm) the flow regime is laminar. The Delta PETT can be estimated by the Ito formula, which replaces Poiseuille's law for curved tubes. For pediatric ETTs (4.0-7.0 mm), Delta PETT depends on the following flow regime: for laminar flow, it must be calculated by the Ito formula, and for turbulent flow, by the Blasius formula. Both formulas allow for ETT geometry and gas properties.

fluid mechanics; laminar flow; turbulent flow; Ito formula; Blasius formula


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