Pulmonary sequelae of severe H1N1 infection treated with high frequency oscillatory ventilation

During the recent influenza A (H1N1) pandemic, due to severe respiratory failure many patients required treatment with alternative ventilator modalities including High Frequency Oscillatory Ventilation (HFOV). We present four such patients treated with HFOV at an academic, tertiary referral hospital in Ireland. We detail outcomes of clinical examination, pulmonary function testing, quality of life assessment and radiographic appearance on CT Thorax at follow-up at 6 months. Further clinical assessment and pulmonary function testing were performed at median 19 months (range 18-21 months) post-discharge. At initial review all patients were found to have reduced gas transfer (median predicted DLCO 74%) with preservation of lung volumes and normal spirometrical values at 6 months (median FVC 5.42L [101% predicted] and FEV14.5L [101.2% predicted] respectively), with improvements in gas transfer (median predicted DLCO 83%)at subsequent testing. Post-inflammatory changes on CT thorax at 6 months were seen in all 4 cases. To our knowledge this is the first report to document the long-term effects of severe H1N1 infection requiring high frequency oscillation on respiratory function. We conclude that the effects on respiratory function and pulmonary radiological appearance are similar to those observed following conventional treatment of Acute Respiratory Distress Syndrome [ARDS].