Am. J. Respir. Crit. Care Med., Volume 158, Number 2, August 1998, 526-531

Total Lung Capacity by N₂ Washout from High and Low Lung Volumes in Ventilated Infants and Children

JÜRG HAMMER, ANDREW NUMA, and CHRISTOPHER J. L. NEWTH

Division of Pediatric Critical Care, Children's Hospital of Los Angeles, University of Southern California School of Medicine, Los Angeles, California

Although there is a strong rationale for the assessment of the subdivisions of lung volume, lung function testing has focused on the measurement of FRC alone in ventilated infants and children. To assess the feasibility, reproducibility, and accuracy of measurements of total lung capacity (TLC), FRC, and their ratio, we determined both lung volumes in 50 critically ill, intubated, and paralyzed infants (mean age [SEM]), 19.9 [4.6] mo) with a variety of lung diseases, by a modified N₂ washout technique from end-exhalation and from +40 cm H₂O inspiratory pressure, respectively. In the same infants, we also defined TLC by adding inspiratory capacity, measured by pneumotachograph during a passive exhalation from +40 cm H₂O to FRC measured by N₂ washout. Respiratory mechanics were measured by single-breath occlusion, and the patients were classified according to clinical picture and lung function into groups without lung disease or with restrictive or obstructive disease. The TLC data obtained by both methods showed good agreement for the infants without lung disease or restrictive disease (limits of agreement [LOA]: 3.8/4.6 and 2.9/3.2 ml/kg, respectively). The agreement was less in the infants with airflow obstruction where the N₂ washout gave slightly higher values (LOA: 7.1/11.3 ml/kg). Mean FRC/TLC was significantly elevated in the obstructive group, whereas mean FRC alone did not differ from the group without lung disease. Our results suggest that TLC can be measured by both methods in intubated infants, but with limited agreement in obstructive disease. FRC/TLC ratios allow an estimation of the degree of pulmonary hyperinflation.

This article has been cited by other articles:

				B. S. von Ungern-Sternberg, D. Trachsel, T. O. Erb, and J. Hammer Forced expiratory flows and volumes in intubated and paralyzed infants and children: normative data up to 5 years of age J Appl Physiol, July 1, 2009; 107(1): 105 - 111. [Abstract] [Full Text] [PDF]

				R. Kraemer, A. Blum, A. Schibler, R. A. Ammann, and S. Gallati Ventilation Inhomogeneities in Relation to Standard Lung Function in Patients with Cystic Fibrosis Am. J. Respir. Crit. Care Med., February 15, 2005; 171(4): 371 - 378. [Abstract] [Full Text] [PDF]

				C. J. DAKIN, A. H. NUMA, H. WANG, J. R. MORTON, C. C. VERTZYAS, and R. L. HENRY Inflammation, Infection, and Pulmonary Function in Infants and Young Children with Cystic Fibrosis Am. J. Respir. Crit. Care Med., April 1, 2002; 165(7): 904 - 910. [Abstract] [Full Text] [PDF]

				M.G. Morris, P. Gustafsson, R. Tepper, M. Gappa, and J. Stocks The bias flow nitrogen washout technique for measuring the functional residual capacity in infants Eur. Respir. J., March 1, 2001; 17(3): 529 - 536. [Abstract] [Full Text] [PDF]