Forced Deflation PFT: A Novel Method to Evaluate Lung Function in Infants and Young Children

Pretransplant pulmonary function test (PFT) abnormalities are correlated with risk of early respiratory failure and mortality in adults and older children. While there is an increasing use of allogeneic BMT in infants and young children with metabolic and immune deficiency disorders, lung function has not been systematically studied in this age group. We describe use of forced deflation PFT (dPFT), a novel technique for assessment of lung function in a series of infants and young children and those unable to perform cooperative testing.

Forced dPFT studies were coordinated with other procedures requiring general anesthesia and performed according to previously published techniques¹. Briefly, a specially constructed forced deflation device was inserted between the endotracheal tube and anesthesia breathing circuit via a 3-way slide valve (Figure). The lungs were inflated three times to 40 cm H₂O (total lung capacity) and then rapidly deflated to -40 cmH₂O via a pneumotachograph (to residual volume). Raw flow or volume measurements were normalized and converted to %predicted and standard deviation scores using data obtained in healthy children.

Between October 2008 and April 2014, 52 dPFT studies were performed in 26 transplant recipients. Indications for BMT were inherited metabolic disease (42%), malignancy (31%), primary immune deficiency (15%) and bone marrow failure (12%). Median age of 21 patients who had pretransplant studies was 0.9±1.3 y (0.1 – 4.9 y); nine of them (43%) had one or more prior lung diseases (respiratory failure [n=7]; pneumonia [n=7]; ARDS [n=3]; bronchopulmonary dysplasia [n=1]; and bronchitis [n=1]). Forced vital capacity (FVC) and forced expiratory flow (FEF₇₅) were normal in all but respiratory system compliance (Crs) was reduced in 5/21 cases. Six out of nine (66.7%) patients with clinical resp. issues pre-BMT also had respiratory complications post-BMT compared with 3/12 (25%) that had no pre-transplant respiratory issues.  There were no significant differences in pre-transplant FVC, FEF₇₅ and Crs between those patients who did and who did not have post-transplant pulmonary complications with median follow-up of 1.7±1.5 y (p=0.435, p=0.305, and p=0.301 respectively). There were no complications during the procedures and dPFT studies could be safely done in coordination with other procedures requiring anesthesia.

In this pilot study, pre-transplant PFTs were not predictive of post-transplant pulmonary complications, and most patients had normal volume and flows. A larger study would be required to determine prevalence and significance of lung function abnormalities in infants and toddlers undergoing transplantation.

1. Motoyama, E. K., et al. (1987). "Early onset of airway reactivity in premature infants with bronchopulmonary dysplasia." Am Rev Respir Dis 136(1): 50-57.