Is isolated Pulmonary Function Test (PFT), sufficient to asses the pulmonary status in scoliosis deformity correction cases?

Introduction: Scoliosis is a three-dimensional deformative abnormality of the spine. There is substantial interest in the relationship between spinal deformity and pulmonary function due to potentially high rates of morbidity and mortality. The deformed structures compress the lung parenchyma causing a decrease in lung volume and its compliance. These changes along with the increased effort to breathe may result in alveolar hypoventilation, hypercapnia, and hypoxemia leading to cor-pulmonale and right-sided heart failure. Since poor pulmonary function may lead to a higher incidence of postoperative pulmonary complications, preoperative pulmonary function tests (PFT) have commonly been used to predict postoperative complications concerning the severity of scoliosis. The objective of this study was to assess whether PFT was sufficient to evaluate the improvement in pulmonary function pre and post-deformity correction. Materials and methods: This was a retrospective analysis among patients with thoracic or thoracic lumbar scoliosis who were admitted to our institution for deformity correction between June 2014 to June 2019. The patients enrolled in the study were aged between 10-17 years, had a preoperative diagnosis of predominant thorasic scoliosis with a pre-operative PFTavailable for analysis. All the included patients were followed up radiographically along with the pulmonary function tests to measure total lung capacity (TLC), forced vital capacity(FVC), and forced expiratory volume in one second (FEV1) along with a functional assessment of the lung capacity. Each test was repeated three times and the single best effort was recorded. We focussed on percent predicted values of FVC and FEV1 to asses restrictive lung disease. Results: 17 patients were included in the study, with a mean age of 13.7 (10-17 years) at deformity correction. 8 patients had congenital scoliosis and 9 had adolescent idiopathic scoliosis. The mean preoperative FVC was 1.552 and percent predicted FVC was 63%. After posterior instrumentation corrective surgery, the mean FVC was 1.803 and percent predicted FVC was 66.5%. At 2years follow-up, PFT did not show any improvement for the correction of curves involving 5 levels or more. Patients with severe scoliosis with preoperative severe restriction showed a significant improvement of percent predicted FVC from 37% to 59% (P \textless .05). However, functional improvement was noted in the rest with significant improvement in right heart pressure with no significant improvement in PFT. Conclusion: Despite demonstrating a significant improvement in their functional status corresponding improvement in their pulmonary function was not noticed which raises the question that whether these cases had a lung compromise, to begin with, or whether pulmonary compensation was established before the surgery. Since PFT was the only measure utilized to assess the status of the lung, we probably could not essentially establish the extent of the lung compromise pre-operatively. We recommend additional measures to asses on going right heart compensation with echocardiography and pulmonary artery pressure to objectively establish the pre-operative pulmonary status beforehand.