Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes.

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (DeltaP(ETT)) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, DeltaP(ETT) 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 DeltaP(ETT) can be estimated by the Ito formula, which replaces Poiseuille's law for curved tubes. For pediatric ETTs (4.0-7.0 mm), DeltaP(ETT) 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.

[1]  A. Harf,et al.  Acoustic method to monitor the longitudinal area profile of neonatal endotracheal tubes. † 194 , 1997, Pediatric Research.

[2]  J BIMAR,et al.  Pediatric Anesthesia , 1996, Agressologie: revue internationale de physio-biologie et de pharmacologie appliquees aux effets de l'agression.

[3]  L. Brochard,et al.  Efficacy of dead-space washout in mechanically ventilated premature newborns. , 1996, American journal of respiratory and critical care medicine.

[4]  A. Mohanna,et al.  Patient-triggered ventilation decreases the work of breathing in neonates. , 1996, American journal of respiratory and critical care medicine.

[5]  J. Fredberg,et al.  Pulmonary airway area by the two-microphone acoustic reflection method. , 1994, Journal of applied physiology.

[6]  Josef Guttmann,et al.  Continuous Calculation of Intratracheal Pressure in Tracheally Intubated Patients , 1993, Anesthesiology.

[7]  J. Ornato,et al.  Guidelines for cardiopulmonary resuscitation and emergency cardiac care, VI: Pediatric advanced life support , 1992 .

[8]  B Louis,et al.  Use of the Blasius resistance formula to estimate the effective diameter of endotracheal tubes. , 1992, The American review of respiratory disease.

[9]  H. Lorino,et al.  Inspiratory pressure support compensates for the additional work of breathing caused by the endotracheal tube. , 1991, Anesthesiology.

[10]  G R Bernard,et al.  In vitro versus in vivo comparison of endotracheal tube airflow resistance. , 1989, The American review of respiratory disease.

[11]  E. Gonzalez,et al.  Guidelines for cardiopulmonary resuscitation and emergency cardiac care. , 1987, Clinical pharmacy.

[12]  D. Altman,et al.  STATISTICAL METHODS FOR ASSESSING AGREEMENT BETWEEN TWO METHODS OF CLINICAL MEASUREMENT , 1986, The Lancet.

[13]  F. Bowen,et al.  Mechanics and energetics of breathing helium in infants with bronchopulmonary dysplasia. , 1984, The Journal of pediatrics.

[14]  A. C. Bryan,et al.  Passive respiratory mechanics in newborns and children. , 1984, The American review of respiratory disease.

[15]  D Isabey,et al.  Steady and unsteady pressure-flow relationships in central airways. , 1981, Journal of applied physiology: respiratory, environmental and exercise physiology.

[16]  M. Wall.  Infant endotracheal tube resistance: effects of changing length, diameter, and gas density , 1980, Critical care medicine.

[17]  M Sullivan,et al.  Endotracheal tube as a factor in measurement of respiratory mechanics. , 1976, Journal of applied physiology.

[18]  F. Plum.  Handbook of Physiology. , 1960 .

[19]  H. Itō,et al.  Friction Factors for Turbulent Flow in Curved Pipes , 1959 .

[20]  J. Womersley.  Method for the calculation of velocity, rate of flow and viscous drag in arteries when the pressure gradient is known , 1955, The Journal of physiology.

[21]  I. E. Idel'cik.  Memento des Pertes de Charge , 1999 .

[22]  J. Fredberg,et al.  Acoustic method to estimate the longitudinal area profile of endotracheal tubes. , 1994, American journal of respiratory and critical care medicine.

[23]  D. Bratlid,et al.  Effects of endotracheal tube size and ventilator settings on the mechanics of a test system during intermittent flow ventilation , 1991, Pediatric pulmonology.

[24]  J. Bates,et al.  Noninvasive determination of respiratory mechanics during mechanical ventilation of neonates: A review of current and future techniques , 1988, Pediatric pulmonology.

[25]  A. C. Bryan,et al.  Total resistance of the respiratory system in preterm infants with and without an endotracheal tube. , 1984, The Journal of pediatrics.

[26]  S. Sorokin,et al.  The Respiratory System , 1983 .

[27]  H. Itō,et al.  Laminar Flow in Curved Pipes , 1969 .

[28]  I. E. Idelchik.  Memento des pertes de charge - coefficients de pertes de charge singulières et de pertes de charge par frottement , 1969 .