Investigating the Role of Nebulised Mucolytic Therapy During Lower Respiratory Tract Infections Post Lung Transplantation.

According to the International Society for Heart and Lung Transplantation (ISHLT), the incidence of lung transplants per annum worldwide is rising annually, with over 3000 transplants completed according to the latest registry(1). The Alfred is a state-wide, internationally renowned lung transplant service, transplanting between 59 - 79 patients over the last two calendar years, with a wait-list of more than 40 potential recipients. This makes it one of only 7 centres worldwide completing this volume of transplants(1).

Patients who have undergone lung transplantation for end-stage lung disease are subject to life-long immunosuppression to prevent allograft rejection. These patients are at a heightened risk of acquiring opportunistic lower respiratory tract infections (LRTI)(2), often characterized by sputum retention and / or production, which can have a negative impact on both morbidity and mortality(3). Patients post lung transplant often find it difficult to clear secretions due to an alteration in normal physiology. Transplanted lung tissue is denervated upon resection from the donor, which has been shown to lead to slower cilial beat frequencies(4), impaired muco-ciliary clearance (MCC) rates(4-6) and an impaired cough reflex(7). Devascularisation to lung tissue post ischaemic surgical time in the acute period can lead to an alteration in mucosal properties and structural changes around anastomoses, which may further impair the ability to clear secretions(3).

Inhaled, nebulised mucolytic agents are commonly used in the management of other suppurative chronic lung diseases characterized by excessive production of secretions. Dornase alfa acts by digesting the extracellular deoxyribonucleic acid (DNA) released by inflammatory cells during infection(8). It has been shown to have positive long-term effects on lung function in cystic fibrosis (CF)(8) and short-term benefits treating atelectasis and mucous plugging in acute, non-CF adult and pediatric cases(9-11). Yet shown to be safe in normal subjects(8), it has been shown to have a detrimental effect on pulmonary function in non-CF bronchiectasis(12).

Inhaled saline acts by restoring the airway surface liquid layer of the mucosa, favorably altering mucous properties, accelerating MCC and stimulating cough(13-14). Positive evidence exists for hypertonic saline (6-7%) in CF(13-14) and both hypertonic and isotonic (0.9%) saline in non-CF bronchiectasis(15). There is discussion of clinical use of saline as a mucolytic in the post transplant patient(16) with no evidence by way of randomized controlled trial to demonstrate effect. There is no current evidence on the use of inhaled mucolytics post transplant.

Currently, both dornase alfa and saline (isotonic / hypertonic) are used in the inpatient and outpatient setting at this institution as a reactive treatment strategy for LRTI characterized by excessive sputum production and / or retention. The investigators believe this warrants a short-term, randomized trial to assess the efficacy of current practice, and to evaluate whether dornase alfa is more effective than 0.9% saline, a cheaper, more accessible alternative.