Lung and chest wall mechanics in ventilated patients with end stage idiopathic pulmonary fibrosis

Background-Idiopathic pulmonary fibrosis is an inflammatory disease which l eads to chronic ventilatory insufficiency and is characterised by a reducti on in pulmonary static and dynamic volumes. It has been suggested that lung elastance may also be abnormally increased, particularly in end stage dise ase, but this has not been systematically tested. The aim of this study was to assess the respiratory mechanics during mechanical ventilation in patie nts affected by end stage disease. Methods-Respiratory mechanics were monitored in seven patients with idiopat hic pulmonary fibrosis being ventilated for acute respiratory failure (Pao( 2)/Fio(2) 5.8 (0.3); pH 7.28 (0.02); Paco(2) 8.44 (0.82) kPa; tidal volume 3.4 (0.2) ml/kg; respiratory rate 35.1 (8.8) breaths/min) using an oesophag eal balloon and all-way occlusion during constant flow inflation. The total respiratory system mechanics (rs) was partitioned into lung (L) and chest wall (w) mechanics to measure static intrinsic positive end expiratory pres sure (PEEPi), static (Est) and dynamic (Edyn) elastances, total respiratory resistance (Rrs), interrupter respiratory resistance (Rint,rs), and additi onal respiratory resistance (Delta Rrs). Results-PEEPi was negligible in all patients. Edyn,rs and Est,rs were marke dly increased (60.9 (7.3) and 51.9 (8.0)cm H2O/l, respectively), and this w as due to abnormal lung elastance (dynamic 53.9 (8.0) cm H2O/l, static 46.1 (8.1) cm H2O/l) while chest wall elastance was only slightly increased. Rr s and Rint,rs were also increased above the normal range (16.7 (4.5) and 13 .7 (3.5) cm H2O/l/s, respectively). RL and Rint,L contributed 88% and 89%, on average, to the total. Edyn,rs, Est,rs, Rrs and Rint,rs were significant ly correlated with the degree of hypercapnia (r = 0.64 (p<0.01), r = 0.54 ( p<0.05), r = 0.84 (p<0.001), and r = 0.72 (p<0.001), respectively). Conclusions-The elastances and resistances of the respiratory system are si gnificantly altered in ventilated patients with end stage idiopathic pulmon ary fibrosis. These features are almost totally due to abnormalities in lun g mechanics. These profound alterations in elastic and resistive mechanical properties at this stage of the disease may be responsible for the onset o f hypercapnia.