INDICATIONS/CONTRAINDICATIONS

Single lung transplantation is suitable for the two most common causes of end-stage lung disease, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). The first successful single lung transplant was performed for IPF in 1983 at Toronto General Hospital. Initially, patients with COPD were considered to be poor candidates for single lung transplantation, as it was thought that preferential ventilation of the native emphysematous lung would complicate allograft function. This concern was overstated and only a few years later single lung transplantation for COPD was proven to be feasible. Single lung transplantation was the most common form of pulmonary transplantation until the late 1990s, when bilateral (or double) lung transplantation became more common. In 2011, the most recent year with available registry data, bilateral lung transplants were performed 3.8 times as often as single lung transplants.

The most significant attribute of single lung transplantation is its ability to maximize donor supply and utilization. Presently, the donor pool for pulmonary allografts is severely constrained, with a severe mismatch in supply and demand. Single lung transplantation affords two recipients an opportunity to undergo transplantation from a single suitable donor, maximizing a valuable resource.

Another attribute of single lung transplantation is that it is technically simpler and associated with less early postoperative morbidity than bilateral lung transplantation, when patients are selected appropriately. This is relevant for the elderly or frail patient, for whom a prolonged anesthetic time results in increased postoperative complications.

Presently, 10% to 15% of patients listed for transplantation die on the waiting list, due to lack of donor availability. Listing patients for both single and bilateral lung transplantation, when appropriate, reduces waitlist deaths. This is especially relevant for a patient with IPF, for whom disease progression can be quite rapid and a prolonged waiting time is to be avoided. A single lung transplant may be lifesaving, if it means more prompt transplantation.

Single lung transplantation is contraindicated in patients with cystic fibrosis or other conditions with suppurative lung disease, such as bronchiectasis. Bilateral pneumonectomy is necessary to prevent contamination of the pulmonary allograft by native lung sepsis. Although there are a few reports of cystic fibrosis patients undergoing single lung transplantation and contralateral pneumonectomy (either synchronous or previously), the vast majority of patients are best served by bilateral lung transplantation.

Severe pulmonary hypertension is another contraindication to single lung transplantation. A single allograft may not provide enough unloading of the strained right heart. Significant right heart dysfunction can complicate recovery from single lung transplantation. In addition, the single lung allograft may be exposed to almost the entire cardiac output when significant pulmonary hypertension remains in the native lung, increasing the risk of primary graft dysfunction. Although it is uncertain what degree of pulmonary hypertension precludes safe single lung transplantation, a mean pulmonary artery (PA) pressure greater than 50 mm Hg is often cited as a contraindication.

Extended donor criteria including age >55 and smoking history >20 pack-years are increasingly used to expand the donor pool. There is some uncertainty as to the appropriateness of using marginal lungs in single lung transplantation. Both early and late outcomes may be compromised when a single marginal lung is transplanted. There are possibly interactions with the recipient’s diagnosis and condition as well and it remains to be seen how extended criteria lungs function in both single and bilateral transplant settings.

PREOPERATIVE PLANNING

Beyond routine preoperative assessment, a potential single lung recipient requires careful cardiovascular evaluation. Severe pulmonary hypertension, as revealed on echocardiography and right heart catheterization, is a contraindication to single lung transplantation. Moreover, evidence of significant left or right heart dysfunction on echocardiography can predict the requirement for cardiopulmonary bypass (CPB) and appropriate cannulation strategy is selected ahead of time. A right-sided transplant may be preferable in a patient expected to require CPB, as cannulation of the aorta and atrium is straightforward after right thoracotomy. CPB is almost never necessary for single lung transplantation in patients with obstructive lung disease and is necessary in about 15% to 25% of patients with fibrotic disease. Regardless, a CPB circuit and perfusionist should be on stand-by for all single lung transplants.

A quantitative ventilation–perfusion (V/Q) scan determines whether there is differential perfusion between the native lungs. If the option is available, the less perfused lung is transplanted, barring any other requirements for laterality (e.g., chest size, pathology in native lung, etc.). When the recipient is suffering from obstructive lung disease, the native left lung is less prone to hyperinflation after right lung transplant. In contrast, patients with fibrotic lung disease may be better suited to left lung transplantation, as the liver is not a fixed impediment to allograft expansion. In spite of these observations, there are no hard and fast rules to guide selection of the side to transplant and reasonable outcomes can be expected regardless of side transplanted.

Donor lung characteristics may also dictate the laterality of single lung transplantation. When pneumonia or pulmonary contusion is severe in one lung, the contralateral lung may still be suitable for transplantation. Thorough radiographic assessment, including liberal use of computed tomography, helps assess donor lungs, especially when extended criteria are used. Bronchoscopy determines whether or not hemorrhage or purulence localizes to one lung. Even with such testing, suitability of a lung may not be determined until after donor sternotomy. Blood gas analysis of pulmonary venous blood tests whether or not one lung has improved function and is performed if there is any question of which side to procure.

SURGERY

Positioning and Incision

Single lung transplantation may be performed through either a posterolateral thoracotomy or a muscle-sparing anteroaxillary incision. While a full lateral decubitus position is required for posterolateral thoracotomy, an anteroaxillary approach is performed with the patient positioned 60 degrees forward from the horizontal axis. For a posterolateral incision, the latissmus is divided and the serratus is retracted and vice versa for an anterolateral or anteroaxillary approach. Exposure and draping of the ipsilateral groin, especially when left-sided transplantation is performed, permits femoral cannulation for CPB. A fourth intercostal space thoracotomy facilitates aortic cannulation and access to the pulmonary hilum.

Technique

Single lung ventilation is established through a left-sided double-lumen endotracheal tube. Significant hypoxemia with single lung ventilation may develop, which may be an indication for CPB. Careful anesthetic management avoids CPB in almost all patients with obstructive lung disease and in the majority of patients with fibrotic disease undergoing single lung transplantation. On occasion, clamping of the PA of the lung to be explanted is performed to improve oxygenation, as this eliminates the shunt through the deflated lung.

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