Long-term membrane oxygenator use to support an infant with acute respiratory distress syndrome on biventricular assist device

Abstract

Ventricular assist devices (VADs) are used in children with severe heart failure as a bridge to heart transplantation or recovery. Severe pulmonary dysfunction may preclude their use, leaving extracorporeal membrane oxygenation (ECMO) as the most frequently used option for combined cardiac and respiratory failure. There are few case reports describing the use of an oxygenator in combination with VAD support, but none that describes long-term utilization. We report the successful use of a low-resistance oxygenator placed into the right-sided VAD (RVAD) circuit of an infant with life-threatening respiratory failure. The oxygenator enabled immediate reversal of hypoxaemia and hypercarbia and recovery of the RVAD function. The oxygenator remained within the VAD circuit for 15 days, facilitating complete lung recovery. An oxygenator used in conjunction with a VAD may be a life-saving therapy, allowing adequate oxygenation and ventilation in severe respiratory and cardiac failure. Extended use may facilitate the prevention of ventilator-associated lung injury and organ dysfunction. This therapy may be an attractive intermediate step in the transition from, or alternative to ECMO, in patients requiring VAD placement with associated acute lung injury.

INTRODUCTION

Ventricular assist devices (VADs) are used in children with severe heart failure as a bridge to heart transplantation or recovery. Severe pulmonary dysfunction may preclude their use, leaving extracorporeal membrane oxygenation (ECMO) as the most frequently used option for combined cardiac and respiratory failure. There are a few case reports describing the use of an oxygenator in combination with VAD support [1–3], but none that describes long-term utilization. We report the successful use of a low-resistance oxygenator placed into the right-sided VAD (RVAD) circuit of an infant with intractable hypercarbia, hypoxaemia and pulmonary hypertension—facilitating the recovery of lung and VAD function.

CASE REPORT

The patient was born with transposition of the great arteries and single intramural coronary artery, with the status of postarterial switch operation complicated by coronary insufficiency upon reimplantation and resultant chronic heart failure. At 11 months, she underwent a cardiac catheterization revealing severe biventricular dysfunction. She had escalating inotropic support requiring emergent placement on veno-arterial ECMO. One week later, her biventricular failure had not improved; she was listed for cardiac transplantation and transitioned to a Berlin Heart EXCOR^® biventricular assist device with 25-cc RVAD and left-sided VAD (LVAD) that stabilized her haemodynamics. Three weeks later, she had pulmonary haemorrhage leading to intractable hypercarbia (PaCO₂ >120 mmHg) and hypoxaemia (PaO₂ <40 mmHg) despite FiO₂ 1.0 and peak inspiratory and mean airway pressures of 60 and 35 cm H₂O, respectively. Associated pulmonary hypertension caused RVAD outflow obstruction and cardiovascular collapse secondary to acute decrease in left atrial venous return. She was resuscitated with nitric oxide, colloid boluses, toxic ventilator settings and a sodium bicarbonate infusion. At this point, a paediatric Quadrox-iD oxygenator (Maquet Cardiopulmonary, Hirrlingen, Germany) was interposed into the outflow cannula of the RVAD circuit (Fig. 1). Transduced pre- and postoxygenator pressures revealed a 10-mmHg pressure decrease, thus systolic outflow pressure of the RVAD driver was increased by 10 mmHg (5%) to overcome the oxygenator resistance, achieving adequate RVAD emptying. A near infrared spectroscopy (NIRS) sensor was placed on the circuit tubing before the oxygenator as surrogate of mixed venous oxygen saturations. Oxygenation and ventilation immediately normalized and pulmonary hypertension resolved upon placement of the oxygenator. The patient was placed on lung rest settings with rate 10, peak inspiratory pressure 24, positive end expiratory pressure 8 and FiO₂ 0.4 and underwent frequent bronchoscopy and exogenous surfactant therapies over the next few days. The oxygenator enabled her to be extubated for rigid bronchoscopy to remove large blood clots from her airways. Anticoagulation was provided by 10 units/kg/h heparin infused directly into the port on the premembrane side of the oxygenator in addition to systemic warfarin and aspirin as per protocol for Berlin Heart EXCOR^®. Transmembrane pressure never increased, and there was no thrombus formation on the oxygenator. She remained on the oxygenator for 15 days without complications while her acute lung injury healed. She was in spontaneous breathing mode when the oxygenator was removed and, after 2 weeks of rehabilitation, she was extubated to bilevel positive airway pressure. She was reintubated 24 h later due to sepsis from peritonitis, from which she eventually died.

Figure 1.

Left: paediatric Quadrox-iD oxygenator interposed into the outflow cannula of the right-sided ventricular assist device (RVAD) circuit. Right: oxygenator interposed into the outflow cannula of the RVAD for clarity. A: RVAD: B: left-sided ventricular assist device (LVAD); C: oxygen line; D: preoxygenator pressure line and heparin infusion port; E: postoxygenator pressure line; F: paediatric Quadrox-iD oxygenator; G: NIRS sensor; H: flow probe; I: pulmonary artery cannula; J: right atrium cannula.

DISCUSSION

Veno-arterial ECMO is the standard of care for cardiac support in paediatric patients with severe heart failure, but VADs offer a longer-lasting solution when bridge to heart transplantation is considered [2]. ECMO has the conventional advantage of additionally supporting oxygenation and ventilation if severe respiratory failure accompanies cardiac failure. More recently, low-resistance oxygenators placed within VAD circuits have been used to support respiratory function in a few patients with severe cardiac failure who developed acute respiratory distress syndrome [1–3].

Our patient had life-threatening respiratory decompensation that could not be stabilized with maximal ventilator and medical therapies. Oxygenator placement proved life-sustaining, immediately normalizing the infant's ventilation and oxygenation, while facilitating the reversal of pulmonary hypertension and return of RVAD function. Furthermore, complete respiratory support afforded by the oxygenator allowed us to extubate the patient on the first day for the removal of large blood clots from the airways; and later perform therapeutic bronchoscopy and exogenous surfactant administration per institutional ECMO protocols. Our case differs from other reports, as the duration of therapy was significantly longer than that described previously (<72 h) [1, 2]. Our case demonstrates that it is possible to use an in-line oxygenator longer than 2 weeks without complications. While we could have removed the oxygenator sooner, the extended treatment course helped to decrease the likelihood of developing the ventilator-associated lung injury and multiple organ dysfunction syndrome associated with aggressive ventilator settings [4]. Our patient remained on very minimal rest settings as her lungs healed, weaning to a spontaneous breathing ventilator mode prior to the oxygenator being removed. She had no further respiratory setbacks.

Our case is also unique, as we placed the oxygenator in the outflow cannula of the RVAD such that blood flow was from the right atrium to the RVAD to the oxygenator to the pulmonary artery. Previous case reports describe placing the oxygenator in-series with the LVAD [1, 2]. Membrane oxygenators are known to be thrombogenic, thus placement of the oxygenator in the RVAD circuit may avoid increasing the risk of embolic strokes that complicate up to 29% paediatric patients in the recent EXCOR^® IDE trial [5]. In addition, with the oxygenator in this orientation, oxygenated blood is delivered directly to the pulmonary arteries, which along with decreased ventilator support helped ameliorate elevated pulmonary vascular resistance [4].

It is unclear whether an in-line oxygenator requires additional anticoagulation to standard VAD protocols [1–3]. Extrapolating from our right ventricle to pulmonary artery conduit antithrombosis protocol, we infused 10 units/kg/h of heparin directly into the oxygenator, changing the patient's partial thromboplastin time minimally. With this strategy, there was no deterioration in oxygenation capacity or thrombus formation noted on the oxygenator after removal.

In conclusion, an oxygenator used in conjunction with a VAD may be a life-saving therapy, allowing adequate oxygenation and ventilation in combined respiratory and cardiac failure. Extended use may facilitate the prevention of the ventilator-associated lung injury and organ dysfunction accompanying toxic ventilator settings. This therapy may be an attractive intermediate step in the transition from ECMO, or an alternative to ECMO, in patients requiring VAD placement who also have acute lung injury.

FUNDING

This work was supported by the University of Alabama at Birmingham Division of Pediatric Critical Care Departmental Funds.

Conflict of interest: none declared.