Thorax 1999;54:390-395 ( May )

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

Stefano Nava, Fiorenzo Rubini

Respiratory Intensive Care Unit, Fondazione S. Maugeri, Centro Medico di Montescano, 27040 Montescano (PV), Italy

Correspondence to: Dr S Nava.

Received 3 July 1998; Returned to authors 10 September 1998; Revised version received 18 November 1998; Accepted for publication 24 November 1998

BACKGROUNDIdiopathic pulmonary fibrosis is an inflammatory disease which leads to chronic ventilatory insufficiency and is characterised by a reduction in pulmonary static and dynamic volumes. It has been suggested that lung elastance may also be abnormally increased, particularly in end stage disease, but this has not been systematically tested. The aim of this study was to assess the respiratory mechanics during mechanical ventilation in patients affected by end stage disease.
METHODSRespiratory mechanics were monitored in seven patients with idiopathic pulmonary fibrosis being ventilated for acute respiratory failure (PaO₂/FiO₂ 5.8 (0.3); pH 7.28 (0.02); PaCO₂ 8.44 (0.82) kPa; tidal volume 3.4 (0.2) ml/kg; respiratory rate 35.1 (8.8) breaths/min) using an oesophageal balloon and airway 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 pressure (PEEPi), static (Est) and dynamic (Edyn) elastances, total respiratory resistance (Rrs), interrupter respiratory resistance (Rint,rs), and additional respiratory resistance (Rrs).
RESULTSPEEPi was negligible in all patients. Edyn,rs and Est,rs were markedly increased (60.9 (7.3) and 51.9 (8.0) cm H₂O/l, respectively), and this was 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. Rrs 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 significantly 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).
CONCLUSIONSThe elastances and resistances of the respiratory system are significantly altered in ventilated patients with end stage idiopathic pulmonary fibrosis. These features are almost totally due to abnormalities in lung mechanics. These profound alterations in elastic and resistive mechanical properties at this stage of the disease may be responsible for the onset of hypercapnia.


Keywords: idiopathic pulmonary fibrosis; mechanical ventilation; pulmonary mechanics

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© 1999 by Thorax
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