Extracorporeal lung assist might avoid invasive ventilation in exacerbation of COPD

To the Editors:

Acute exacerbation of chronic obstructive pulmonary disease (COPD) requiring invasive mechanical ventilation (IMV) is associated with a very poor prognosis. Therefore noninvasive mechanical ventilation (NIV) with avoidance of endotracheal intubation should be preferred. However, NIV can fail and result in severe respiratory acidosis. If IMV becomes mandatory, the development of pulmonary dynamic hyperinflation with subsequent barotrauma and circulatory failure is the main pathophysiological alteration.

Extracorporeal CO₂ elimination, such as that provided by an arteriovenous extracorporeal lung assist system (avECLA), combined with NIV might be a therapeutic option in order to avoid IMV in patients with acute exacerbation of COPD (AECOPD). We present three cases with hypercapnic respiratory failure that were treated with NIV and extracorporeal lung assist for 2, 7 and 8 days, respectively. The combination of these two therapeutic approaches might be effective to prevent the potentially lethal side-effects of IMV in this group of multi-morbid patients.

COPD affects 4–7% of the general population and is the fourth leading cause of death in developed countries [1]. If patients with AECOPD require mechanical ventilation (MV), the mortality rate is 17–30% [2].

MV is mandatory in patients with AECOPD if decompensated hypercapnic respiratory failure is evident. NIV via face mask or helmet has been the evidence-based treatment of choice in AECOPD patients with hypercapnia for more than 20 yrs [3]. NIV has been shown to improve gas exchange and outcome when compared with IMV. However, in some cases NIV fails to eliminate CO₂ sufficiently and tracheal intubation and IMV are traditionally regarded as the last treatment option [4]. The prognosis of the affected patients still remains very poor and, therefore, measures that result in avoidance of IMV might be rational [5].

Over 10 yrs ago, a pumpless avECLA consisting of an extracorporeal membrane lung with a minimal resistance to blood flow, that was shown to remove CO₂ highly effectively in patients with acute respiratory distress syndrome, was introduced into clinical practice. AvECLA enables minute ventilation and peak inspiratory pressures to be reduced significantly following the rules of lung protective ventilation [6]. This was also shown for patients with asthma treated with IMV [7].

Thus, in AECOPD patients with decompensated respiratory acidosis that is refractory to NIV, the addition of avECLA might be able to avoid tracheal intubation and subsequent IMV. We report three AECOPD patients with decompensated respiratory acidosis treated with avECLA plus NIV.

The institutional review board approval to publish this patient data was obtained from the ethics committee of the University of Würzburg (Würzburg, Germany).

After ultrasonographic examination of the targeted vessels and exclusion of severe peripheral artery disease (PAD), avECLA was implanted using a 13-F cannula for the femoral artery and a 15- or 17-F cannula for the femoral vein, respectively. Anticoagulation was performed with a continuous heparin infusion resulting in a partial thromboplastin time of 40–60 s. With membrane lung blood flows ranging from 1.2 to 1.5 L·min⁻¹ and oxygen sweep gas flows through the membrane lung of 1–10 L·min⁻¹, the arterial carbon dioxide tension (P_a,CO2) was adjusted to values between 50 and 65 mmHg resulting in a pH of >7.2 (table 1). NIV was continued during avECLA treatment and positive end-expiratory pressure and pressure support were titrated to avoid tachypnoea and maintain oxygenation at an arterial oxygen tension (P_a,O2) between 50 and 60 mmHg.

An 85-yr-old morbidly obese male patient was admitted to the emergency room and subsequently to the intensive care unit (ICU) with shortness of breath. His past medical history (PMH) consisted of congestive heart failure and COPD with ambulant oxygen treatment for 8 h·day⁻¹. The chest radiograph and thoracic computed tomography (CT) scan showed cardiomegaly, basal pneumonic infiltrates and a known left indurative pleurisy. Assuming AECOPD, a calculated antibiotic therapy was initiated and piperacillin/tazobactam and prednisolone were administered. The patient developed decompensated respiratory acidosis. NIV via face mask did not result in amelioration of hypercapnia. 4 h after admission to the ICU avECLA was implanted. NIV via helmet combined with avECLA was performed for 8 days. Respiratory mechanics improved and signs of infection resolved. On day eight avECLA was removed uneventfully, NIV was continued for four more days without further decompensation of the respiratory acidosis. The patient was adapted to a home continuous positive airway pressure system and discharged home 4 days later.

A 66-yr-old male patient was admitted to the hospital with incremental deterioration of a chronic pulmonary infection. His main complaints were shortness of breath and continuously increasing adynamia. His PMH consisted of congestive heart failure, ventricular tachycardia with subsequent implantation of an automated cardioverter and COPD. The chest radiograph and the thoracic CT scan showed cardiomegaly, bilateral pneumonic infiltrates and right-sided bonchiectasis. Assuming AECOPD, a calculated antibiotic therapy was initiated and piperacillin/tazobactam and prednisolone were administered. The patient developed decompensated respiratory acidosis despite NIV via face mask. 12 h after admission to the ICU avECLA was implanted. NIV via face mask combined with avECLA was performed for 7 days. However, respiratory mechanics did not improve and after an initial phase of amelioration, oxygenation and haemodynamics deteriorated further (P_a,O2 40 mmHg, respiratory rate 35 breaths·min⁻¹ and need for vasopressors) and signs of infection increased due to recurrence of pneumonia. Antibiotic therapy was switched to ceftazidim/ciprofloxacin. The patient’s trachea was intubated and IMV in a lung protective mode was performed. AvECLA was discontinued uneventfully. Tracheostomy was performed on the same day. On day 17 the patient was transferred to a weaning clinic and subsequently to a nursing home providing long-term respiratory care with IMV.

A 52-yr-old cachectic female patient was admitted to the ICU in severe respiratory distress. Auscultation of the chest revealed wheezing and a prolonged expiration. Her PMH was remarkable for arterial hypertension, COPD and pneumococcus pneumonia infection requiring IMV that was accompanied by acute renal failure 1 yr ago. NIV via face mask and anti-asthmatic medication were started immediately but did not ameliorate the severe respiratory acidosis with a P_a,CO2 of 140 mmHg. The chest radiograph showed bilateral infiltrates and the typical radiological signs of COPD. Calculated antibiotic therapy was initiated and ceftriaxone and clarithromycin and a bolus of prednisolone were administered. After avECLA was started a pH >7.2 was quickly achieved. Bronchospasm subsided and avECLA was discontinued 2 days later uneventfully. Nevertheless, due to insufficiency of the respiratory pump the patient was adapted to an ambulatory NIV system and subsequently discharged home.

The longer IMV is performed, the higher the risk of death [8]. Thus, avoidance of IMV is a rational therapeutic goal. In all three patients the combination of avECLA and NIV unloaded the respiratory pump and brought the pulmonary gas exchange to acceptable values (table 1]). In two cases IMV was avoided, in one case the concept failed due to recurrence of pneumonia and subsequent weaning failure.

A prerequisite to put the presented treatment approach into practice is the concept of dissociating the pulmonary gas exchange into its two components: CO₂ elimination is provided with an extracorporeal lung and oxygenation is secured by an adequate level of mean airway pressure [9]. Whenever hypoxaemia occurs, the presented concept becomes obsolete, since O₂ transfer via avECLA does not suffice [6].

Looking at the risk–benefit ratio, complications and costs related to avECLA need to be addressed. It is well known that arterial cannulation with large bore cannulas can cause limb ischaemia especially in multi-morbid patients with a high risk of PAD [6] Without negatively influencing the CO₂ elimination rate, this risk can be reduced if cannulas with a diameter of >15-F are avoided. In addition, looking at the rapid progress in cannula and pump technology development, venovenous extracorporeal CO₂ removal with double lumen cannulas requiring only one vascular access port might also be combined with NIV in patients with AECOPD even when PAD is evident [10]. Obviously costs for extracorporeal systems must be considered as well as ventilator free days and length of ICU stay.

In conclusion, the combination of NIV and extracorporeal CO₂ elimination might be effective to prevent IMV and its potentially lethal side-effects in patients with AECOPD.

• ©ERS 2012