Pulmonary function testing in infants with tetralogy of Fallot and absent pulmonary valve syndrome

Absent pulmonary valve syndrome (APVS) is found in 3-6% of patients with Tetralogy of Fallot (TOF). Along with findings of TOF, absence of pulmonary valve tissue results in aneurysmal dilatation of the main and branch pulmonary arteries compressing the trachea, main-stem, and intrapulmonary bronchi leading to obstructive airways disease. Our objective was to review pulmonary function tests (PFT) in TOF-APVS patients.

Eight PFT were performed on five mechanically ventilated TOF-APVS patients in the intensive care unit. Tidal volume, forced vital capacity (FVC), maximal expiratory flow 25%, resistance and compliance of the respiratory system were measured.

Pre-operative PFTs showed markedly elevated airways resistance (RRS) (median 0.45 cmH2O/mL/sec, range 0.17-0.66) and marked variability of the static compliance of the respiratory system (CRS) (median 0.6 mL/cmH2O/kg, range 0.25-2.6). Flow-volume loops measured by forced deflation showed flow limitation within the medium to small airways. Post-operative FVC was reduced in four of the five patients (median 46 mL/kg, IQR 42.9 - 48.8 mL/kg). Patients studied with various levels of positive end expiratory pressure (PEEP) showed improvement in tidal volume and reduced obstruction with PEEP greater than 10 cmH2O. For three patients with pre-operative data available, surgical correction resulted in near-normal post-operative CRS and improved, but still elevated RRS (median 0.14 cmH2O/mL/sec, interquartile range [IQR] 0.11-0.31).

For our patients with TOF-APVS, airway resistance was elevated. Flow limitation was seen in the medium to small airways with a mild reduction of FVC. PFTs may help guide management of mechanical ventilation for TOF-APVS patients.