Idiopathic Postpneumonectomy Pulmonary Edema: 1.Hyperinflation Of The Remaining Lung Is An Aetiological Factor 2. Abolished By Use Of Balanced Pleural Drainage
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Objective:
Pneumonectomy remains associated with considerable risk. Idiopathic Post-Pneumonectomy Pulmonary Edema (PPE) is considered, by some, the leading cause of mortality post pneumonectomy. As ARDS is the final result of this syndrome, it is often misdiagnosed.
Postoperative hyperinflation of the remaining lung is implicated as an aetiological factor. We demonstrated the abolition of PPE solely by changing our management of the pneumonectomy space to a balanced drainage system.
We therefore developed an animal model to test the hypothesis that:
1. Postoperative induced hyperinflation of the remaining lung can cause PPE.
2. A balanced drainage system would prevent PPE compared to traditional management of the pneumonectomy space.
Methods:
We performed 37 right-sided pneumonectomies in adult sheep, using a single lumen endotracheal tube, tidal volumes of 6-8ml/kg; total perioperative intravenous crystalloid given was 6oomL/sheep. Nine sheep, (placebos), had right thoracotomy alone. All sheep, according to protocols, were euthanased five days post surgery. All (right and left) lungs underwent standardised analyses for pulmonary edema by two clinically blinded pathologists.
Experiment 1: 10 sheep, from completion of surgery, had continuous suction (5kpa) applied via an intercostal catheter placed in the empty hemithorax to induce mediastinal shift and hyperinflation of the left lung; no adverse haemodynamic sequelae occurred.
Experiment 2: 27 sheep were randomly allocated, prior to pneumonectomy, into 3 equal groups: A: balanced drainage B: no intercostal drainage and C: a clamp-release intercostal underwater drainage. The clamp release occurred for two minutes six times a day from surgery to euthanasia. The balanced drainage system (-13cmH20-+1cm H2O) was applied from surgery to euthanasia.
Results:
All sheep tolerated their surgery uneventfully. All right lungs were normal histologically.
Experiment 1: There was significant mediastinal shift at autopsy in all sheep, 60 % (n=6) developed PPE in the left lung, p=0.003 (compared to placebo and/or group A).
Experiment 2: the incidence of PPE was: group A:0, B: 3 (30%), C:3 (30%) ( p=0.003, Fisher exact test)
Only the 12 sheep developing PPE developed respiratory distress, the rest had uneventful recoveries.
Conclusions:
In a sheep model of PPE
- Hyperinflation from mediastinal shift is an aetiological factor.
- A balanced drainage system abolished PPE.
- This is the first time such a cause and effect relationship has been demonstrated.
These results support our continued use of balanced drainage post-pneumonectomy
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