TitelCondensation – an underestimated risk in the ventilation of extremely preterm infants

Measuring the correct tidal volume is playing an increasingly important role in mechanical ventilation of extremely preterm infants. Companies have developed several flow sensors based on a pressure differential. Condensation in the pneumotachograph can compromise the measurement accuracy that leads to hypoventilation of the infant. In an experimental study, three commercially used flow sensors were compared to determine how much they are affected by condensation and whether they provide consistent values over a long period.

Patient/en und Methoden

The measurements were carried out five times with each pneumotachograph, tested for two hours.
The experiment was conducted with the continuous flow ventilator Sophie (Stephan GmbH) connected to a pneumotachograph and a test lung, simulating a 1000 g preterm infant. Three pneumotachographs (A, B, Neo PNT) were exposed to simulated ventilation for two hours.
The tidal volume measured by the flow sensors every two seconds was recorded by the Sophie
Respirator and saved in log files. Based on these files, the progress of the tidal volume over
time was compared. Each trial was repeated five times with identical settings.


The measurement data showed an increase in the measured tidal volume of 0.5 ml for two flow sensors after 10 minutes and 4ml after two hours. The third sensor was able to maintain a constant measurement of tidal volume over two hours.


Condensation can significantly affect the measurements of the pneumotachograph. The measured tidal volume values may be incorrectly high due to the increasing differential pressure in pneumotachographs. Therefore, the measured values may also be questioned.

Erstautor*in ist unter 35 Jahre alt
Autor*in 1Linda Mur Paracelsus Medical University
Autor*in 2Martin Wald, MD, PD, Assoc. Prof. Division of Neonatology, Department of Paediatrics and Adolescent Medicine, Paracelsus Medical University, University Hospital Salzburg