2000 OPEN FORUM Abstracts
MEASURING AND PREDICTING FRC, TLC IN NONCOOPERATIVE, PEDIATRIC CANDIDATES FOR SCOLIOSIS CORRECTION SURGERY
Chris Meyer M.D., Alexander Adams RRT, Mary Stone RRT, Cathy Polley RRT, Carlos Milla M.D., University of Minnesota and Gillette/Regions Hospitals, St. Paul, MN
Background: Pulmonary function (PF) studies are difficult to obtain in children unable to cooperate with the instructions. Most predicted PF values for children are based on height, but in scoliosis the thoracic curvature reduces standing or sitting height. Therefore, armspan is often used as a surrogate for height to predict PF values. Children with scoliosis, arm contractions, and an inability to cooperate present an especially difficult problem with the measurement and prediction of PF values.
Methods: Immediately prior to surgery for partial correction of a thoracic curvature, FRC and TLC were measured after the patients were sedated and intubated. FRC was determined by helium dilution using 10 large tidal breaths via super syringe of a known helium concentration. The FIO2 of the tidal breaths was matched to the ventilator FIO2 and CO2/humidity were absorbed from the final helium mixture. Inspiratory capacity (IC) was determined by delivering a range of tidal volumes (VT) while tracking their plateau pressures (Pplat). Inspiratory flow was set to avoid autoPEEP. The VT that attained a Pplat of 30-33 cmH2O was considered the best estimate of IC.
Results: Complete evaluations were obtained on four patients at this time. Mean FRC and TLC were 57.5 ± 7.9% and 49.2 ± 5.5% of predicted, respectively. After adjustment for height gained by the corrective surgery (mean height gain of 6.8 cm), the calculation of mean predicted FRC and TLC decreased to 49.9 ± 6.0% and 43.0 ± 4.2%.
Conclusions: For these children undergoing a major corrective thoracic surgery, a restrictive lung impairment is evident yet comparisons to predicted values based on height are questionable. Repeat studies one year after surgery will require evaluation of changes in actual FRC, TLC values. Predicted values for these patients should be based on anthropometric correlates other than height or armspan. Possibilities to consider might be chest circumference or actual spine length.