Influence of respiratory system impedance on volume and pressure delivered at the Y piece in ventilated infants.
OBJECTIVE
Tidal volume (VT) delivered to infants' airways are overestimated and pressure underestimated when measured in the ventilator and not at the Y piece. This study aimed at evaluating the influence of respiratory system impedance on expiratory VT (VTE) and pressure measurement difference.


METHODS
Prospective observational study.


METHODS
Pediatric intensive care unit at a university hospital.


METHODS
Data were collected between February 2000 and October 2001 for 30 infants (range, 1-23 months) ventilated in the pressure-controlled or volume-controlled mode.


METHODS
Measurements of VTE, pressure obtained at the same time at the Y piece and on the ventilator Servo 300, were collected in ventilated infants. Respiratory system impedance was calculated from data obtained at the Y piece. Circuit compliance was measured in vitro. VTEs were corrected for compressible volume.


RESULTS
VTEs were overestimated by the Servo 300 in the pressure-controlled and volume-controlled modes (from 5% to 62% of the value displayed on Servo 300). Maximal inspiratory pressures were underestimated by the Servo 300 in the pressure-controlled mode (difference from -2 to +19 cm H(2)O). Measurement difference increased with increasing respiratory system impedance. Ventilator VTE corrected for circuit compliance did not offer a sufficiently accurate estimation of VTE at the Y piece.


CONCLUSIONS
VT and pressure measurements must be performed at the Y piece, especially in infants with increased respiratory system impedance (i.e., decreased respiratory system compliance or increased resistance). Correcting VTE for circuit compliance cannot replace measurement of VT at the Y piece.
Nève
Véronique
V
Pediatric Intensive Care Unit and Pulmonary Function Testing Unit, Centre Hospitalier et Universitaire de Lille, Lille, France.
Leclerc
Francis
F
Noizet
Odile
O
Vernoux
Sandy
S
Leteurtre
Stéphane
S
Forget
Patricia
P
Sadik
Ahmed
A
Riou
Yvon
Y
D000403:Airway Resistance / Q000502:physiology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007223:Infant; D007442:Intubation, Intratracheal; D008170:Lung Compliance / Q000502:physiology*; D008297:Male; D008365:Manometry; D011175:Positive-Pressure Respiration / Q000295:instrumentation* / Q000379:methods; D011446:Prospective Studies; D013990:Tidal Volume