Measurement of lung volume in mechanically ventilated monkeys with an ultrasonic flow meter and the nitrogen washout method.
OBJECTIVE
Measurement of functional residual capacity (FRC) during mechanical ventilation is important to standardise respiratory system compliance and adjust the ventilator settings to optimise lung recruitment. In the present study we compared three methods to measure FRC.


METHODS
The bias flow nitrogen washout technique (FRC(N2MC)), the multiple breath nitrogen washout (FRC(MBNW)) and the multiple breath sulphur-hexafluoride washout using the molar mass signal of an ultrasonic flow meter (FRC(MBSF6)) were compared in six adult monkeys after endotracheal intubation and during spontaneous breathing and mechanical ventilation at three different positive end-expiratory pressure (PEEP) levels of 0, 5 and 10 cmH2O.


METHODS
Animal research laboratory.


RESULTS
We found good agreement between all three methods and they all accurately measured changes in FRC when PEEP was increased. The coefficients of variance of the three measurement techniques were in the same range (1.3-9.2%).


CONCLUSIONS
The measurement of the tracer gas concentration with the molar mass signal of the ultrasonic flow meter provides a good and simple alternative to respiratory mass spectrometer for FRC measurements in ventilated subjects.
Schibler
Andreas
A
Paediatric Intensive Care, Mater Children's Hospital South Brisbane, QLD 4101 Brisbane, Australia. andreas_schibler@mater.org.au
Hammer
Jürg
J
Isler
Ruedi
R
Buess
Christian
C
Newth
Christopher J L
CJ
D000403:Airway Resistance; D000818:Animals; D001944:Breath Tests / Q000379:methods*; D045268:Flowmeters; D005652:Functional Residual Capacity; D008170:Lung Compliance; D008253:Macaca mulatta; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D023421:Models, Animal; D008991:Monitoring, Physiologic / Q000379:methods / Q000592:standards; D009584:Nitrogen; D009716:Numerical Analysis, Computer-Assisted; D011175:Positive-Pressure Respiration / Q000379:methods; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013459:Sulfur Hexafluoride; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods* / Q000592:standards
D009584:Nitrogen; D013459:Sulfur Hexafluoride