Deadspace free ventilatory measurements in newborns during mechanical ventilation.
OBJECTIVE
To improve the accuracy of ventilatory measurements in ventilated newborns by means of a numerical correction when a deadspace free differential measuring method using two pneumotachographs (PNTs) is applied and to investigate the clinical usefulness of this correction procedure.


METHODS
In vitro study and prospective animal study.


METHODS
Research laboratory of the Clinic of Neonatology and the Animal Research Laboratory, Charité Hospital Berlin.


METHODS
Ten newborn piglets, weighing 610-1340 g (median, 930 g), age <12 hrs.


METHODS
The accuracy of both the deadspace free method and the endotracheal flow measurements (conventional method) was investigated using mechanical lung models. A correction procedure for the deadspace free method was developed considering signal delay time and tube compliance between both PNTs. This method was applied to the piglets measured during partial liquid ventilation (PLV). Measurements were done before and after lung lavage and during 30 and 120 mins of PLV (30 mL/kg body weight perfluorocarbon).


RESULTS
In vitro measurements showed volume differences between both methods of 8%, 12%, 16%, and 17%, respectively, depending on the distance between the PNTs of 10, 60, 120, and 180 cm. After applying the correction algorithm, the differences decreased to 3%, 0%, -2%, and -8%, respectively. The piglets were measured with 120-cm tube length between the PNTs. The correction algorithm reduced the measured tidal volume before lavage by 7%, after lavage by 14%, 30-min PLV by 12%, and 120-min PLV by 10%, corresponding to the changes in respiratory compliance of 1.2, 0.6, 1.0, and 1.1 mL/cm H2O.


CONCLUSIONS
The deadspace free method can be advantageously used for continuous measurements in newborns despite much higher technical expense. The correcting procedure improved the accuracy of the volume measurement remarkably, especially for lower respiratory compliance.
Humboldt-University Berlin, Clinic of Neonatology (Charité), Berlin, Germany.
B
B
Foitzik
M
M
Schmidt
H
H
Proquitté
G
G
Schmalisch
D000465:Algorithms; D000818:Animals; D000831:Animals, Newborn; D015982:Bias; D002138:Calibration; D004195:Disease Models, Animal; D006801:Humans; D007231:Infant, Newborn; D007442:Intubation, Intratracheal; D021061:Liquid Ventilation; D008176:Lung Volume Measurements / Q000295:instrumentation / Q000379:methods*; D009716:Numerical Analysis, Computer-Assisted; D011446:Prospective Studies; D012126:Respiratory Dead Space; D012815:Signal Processing, Computer-Assisted; D013552:Swine; D013990:Tidal Volume