Bridging to lung transplantation for severe pulmonary hypertension using dual central Novalung lung assist devices

Abstract

This case describes the technique of using dual Novalungs (a pumpless extracorporeal system) to bridge a patient with idiopathic pulmonary hypertension to bilateral lung transplantation. A 41-year old lady with idiopathic pulmonary hypertension (with a possible veno-occlusive element) presented with symptoms of end-stage heart and lung failure. This was refractory to medical management with iloprost, sildenafil and bosentan. The patient was placed on the urgent waiting list for lung transplantation and central pulmonary artery to left atrial Novalung insertion was performed. Local anaesthetic was given before performing peripheral cardiopulmonary bypass due to the high risk of cardiac arrest. Two days later, donor organs became available and the patient was taken for double-lung transplantation. The pulmonary artery cannula was removed leaving a large defect. This was then closed using a bovine pericardial patch. Due to the damaged right superior pulmonary vein from Novalung cannulation, cardioplegia was given to facilitate an open atrial anastomosis. After 13 days in the intensive therapy unit, she was transferred to the ward. There were no further complications and she has been discharged home.

INTRODUCTION

Venoarterial pump-driven extracorporeal membrane oxygenation (ECMO) is routinely used as a bridge to lung or heart–lung transplantation in those deteriorating secondary to idiopathic pulmonary hypertension. Complications including haemolysis, sepsis and renal failure often limit therapy to around 2 weeks [1]. The scarcity of donor lungs means novel bridging techniques, minimizing complications, must be sought.

Novalung has been successful as a bridge to transplantation. Conventionally peripheral cannulation is utilized to connect a single Novalung system. In patients with idiopathic pulmonary hypertension connecting the pulmonary arterial main trunk to the left atrium can act as a shunt through a low-resistance gas exchange device, the near systemic pressure in the pulmonary arteries means no pump is required.

This case describes the operative steps and pitfalls for surgeons undertaking lung transplantation with dual central Novalung.

CASE DESCRIPTION

A 41-year old woman with idiopathic pulmonary arterial hypertension (iPAH) was admitted due to worsening right heart failure refractory to medical management.

Investigations revealed mean pulmonary artery pressures of 56 mmHg, and right atrial pressures of 13 mmHg. Electrocardiogram demonstrated P-pulmonale and T-waves in V1, with right axis deviation. Chest X-ray showed cardiomegaly with increased interstitial markings in both lung fields.

The forced expiratory volume in 1 second, forced vital capacity and transfer factor of the lung for carbon monoxide were 81, 77 and 35% predicted, respectively. Arterial blood gas analysis on 7 L oxygen demonstrated pH of 7.51, PCO₂ of 3.1 kPa, PO₂ of 4.5 kPa. Echocardiography revealed severely dilated and impaired right ventricle (RV), and D-shaped flattening of the intraventricular septum with left ventricle function compromised by RV.

Her rapidly deteriorating condition meant central pulmonary artery to left atrial dual Novalung (Novalung, Talheim, Germany) insertion was performed as imminent cardiac arrest was likely. This aimed to improve right heart function by creating a pumpless right to left shunt of low resistance across a gas diffusion membrane.

Insertion of the Novalung was undertaken on cardiopulmonary bypass due to the high risk of cardiac arrest on induction of anaesthesia.

Bypass was instituted via the femoral artery and vein under local anaesthetic before induction. After sternotomy, a size 9 pulmonary artery cannula (Berlin Heart) was inserted and a 34-mm angled cannula (Medtronic, Inc.) was placed into the left atrium via the left superior pulmonary vein. See Fig. 1.

Figure 1:

Intraoperative photograph showing size 9 pulmonary artery cannula for a Berlin Heart and 34-mm angled cannula inserted into the left atrium.

The two Novalung lung assist devices were placed in parallel. Bovine pericardium was used over the cannulae to protect them at redo sternotomy for lung transplantation.

The patient was extubated the next day with off-loading of the right ventricle evident on echocardiography.

Two days later, a suitable donor was found. The sternotomy was reopened uneventfully. Cardiopulmonary bypass was established via ascending aortic and two-stage right atrial cannulation.

Due to the inevitable damage to the left superior pulmonary vein from Novalung cannulation, cardioplegia was given to facilitate the atrial anastomosis at lung transplantation which was then performed open.

The pulmonary artery (PA) cannula removal left a large defect in the main pulmonary artery, and a bovine pericardial patch was used for reconstruction (Fig. 2). The patch was sized to avoid tension or obstruction of the main pulmonary artery. A pulmonary artery vent was placed through the suture line before trying to facilitate the transplant. After lung implantation on each side, the vent was removed and the suture line completed. The transplant concluded satisfactorily with uneventful weaning from cardiopulmonary bypass.

Figure 2:

Intraoperative photograph showing the Novalung cannulation defect to the pulmonary artery, later repaired with bovine pericardium.

The patient was extubated 12 h after transplantation but reintubated 3 days later for respiratory failure. Good RV function was shown on echocardiogram. Bronchoscopy demonstrated healthy anastomosis but inflamed distal airways. Extubation occurred 4 days later. No further complications occurred. She continues to improve 9 months post transplantation.

CONCLUSIONS

ECMO is a more complex technique than Novalung with increased risk of complications and greater expense. Complications increase after 2 weeks and may threaten fitness for subsequent transplantation. Novalung relies on mean arterial pressure to drive flow, requires limited anticoagulation and has the capacity for oxygenation and carbon dioxide removal.

Previously, it has been demonstrated that this is a safe option for mid- to long-term bridge to lung transplantation for spontaneously ventilating patients with hypercapnia and respiratory acidosis [2, 3].

iPAH provides an alternative to the conventional option of Novalung insertion into the femoral vessels as the high pulmonary pressures drive flow through the dual Novalung systems to the left atrium. Dual systems reduce resistance and create a passive shunt through the gas diffusion membranes. More recently, there has been a report of minimally invasive cannulation in this setting but access may be limited and risks bleeding complications [4].

This case describes the importance of utilizing peripheral bypass established under local anaesthesia to prevent sudden deterioration prior to commencing the Novalung insertion, thus decreasing the risk of cardiopulmonary arrest.

Central cannulation and dual Novalung systems provide a viable bridging option for severe pulmonary artery hypertension with probable decreased risk of complications compared with ECMO.

Centrally inserted Novalung systems allow patients to mobilize. However, further large-scale analysis is needed to confirm Novalung is a better long-term option than ECMO with fewer complications.

Novalung explantation leaves a large defect in the PA, which needs reconstruction with a bovine pericardial patch at lung transplantation. The cannulation site in the superior pulmonary vein means that an open atrial anastomosis may be required under cardioplegic cardiac arrest and should be prepared for.

Conflict of interest: none declared.