SINGLE, DOUBLE, OR HEART-LUNG TRANSPLANT

For most conditions in which lung transplantation is indicated, either a single or a bilateral sequential lung transplant may be performed. Outcomes of bilateral sequential lung transplantation are slightly better, but single-lung transplantation represents the most economic use of available organs. For conditions associated with pulmonary sepsis (cystic fibrosis, bronchiectasis), bilateral sequential lung transplant is required. For pulmonary hypertension, either single or bilateral sequential lung transplant may be performed, although bilateral sequential lung transplant is the preferred option worldwide.^4,5 Even in the presence of significant right ventricular dysfunction, patients with pulmonary hypertension do not usually require heart-lung transplantation.⁶ The number of patients with primary pulmonary hypertension who undergo lung transplantation is becoming smaller with the development of more effective medical therapy.

Heart-lung transplantation is an uncommon operation that is performed in only a few centers. The procedure is reserved for patients with end-stage pulmonary and cardiac disease (e.g., Eisenmenger syndrome in association with an uncorrectable intracardiac defect or left ventricular dysfunction).

Preoperative Recipient Optimization

Nutritional status has an important bearing on the outcomes of lung transplantation. Patients with pretransplant body mass indexes less than 17 kg/m² or more than 25 kg/m² are at increased risk for early postoperative death.⁸ Patients with low body mass indexes should receive nutritional supplements. Enteral feeding via a percutaneous gastrostomy tube is commonly used for patients with cystic fibrosis and should be continued during the postoperative period. Compliance with a pulmonary rehabilitation program is a prerequisite for lung transplantation in patients with chronic obstructive pulmonary disease (COPD) and has been shown to improve outcomes of surgery.⁹ Corticosteroids should be discontinued or weaned to doses less than 20 mg/day of prednisone at the time of listing for transplantation because of their adverse effects on bone and muscle mass and the increased risk for colonization or infection by an opportunistic organism.¹⁰ Lung transplant recipients with cystic fibrosis and bronchiectasis may require regular courses of intravenous antibiotics to control pulmonary infection.

Donor Criteria

The optimal donor criteria^11–14 for lung transplantation are summarized in Table 13-3. However, because of the limited number of suitable organs, there is substantial pressure to use marginal donors. Although good outcomes have been obtained with graft ischemic times longer than 6 hours, data indicate a reduction in survival rates when the ischemic time exceeds 5.5 hours.¹⁵ Donor lungs with a positive gram stain on tracheal aspirate or bronchial washings may be considered for transplantation depending on other factors, such as the chest radiograph appearances and the gas exchange. Marginal oxygenation in the donor can be managed with various ventilatory strategies to improve gas exchange (see Chapter 29). If there is evidence of unilateral chest sepsis in a potential donor, a single-lung transplant using the noninfected donor lung may be considered. The decision to use a marginal organ is difficult and depends not only on donor factors but also on the sickness of the potential recipient and the likelihood of another organ becoming available.

Table 13-3 Ideal Donor Criteria for Lung Transplantation

PEEP, positive end expiratory pressure; P_aO₂, arterial partial pressure of oxygen.

From Orens JB, Boehler A, de Perrot M, et al: A review of lung transplant donor acceptability criteria. J Heart Lung Transplant 22:1183-1200, 2003.

Recipient-Donor Matching

The matching of donors and recipients of thoracic organs (heart and lungs) is based on compatibility, geographic location, and medical urgency, as outlined in Chapter 14. For lung transplantation, a number of criteria are used to ensure size matching, including height, thoracic circumference, and chest radiograph dimensions. A recent study has shown that predicted total lung capacity based on height and gender provides more accurate size matching than height alone.¹⁶

Living Lobar Lung Donors

Living lobar lung transplantation was introduced in 1993 for individuals too unwell to await cadaveric organs. In this procedure, right and left lower lobes from two healthy donors are implanted in the recipient in the place of the whole right and left lungs. A recent review of the outcomes of this technique in a single center showed survival rates at 1 year of 70%, at 3 years of 54%, and at 5 years of 45%.¹⁷ These rates are comparable to those obtained in conventional lung transplantation.

Intraoperative Management

Patient monitoring during lung transplantation includes an arterial line, central venous and pulmonary artery catheters, and a transesophageal echocardiogram (TEE). Strict attention to aseptic technique is essential for all invasive procedures. The patient should be kept as warm as possible: the room should be heated (>20°C), and a fluid warmer and forced-air warming blanket should be used.

For single-lung transplantation, surgical access is obtained by means of a lateral thoracotomy incision, with the patient placed in the lateral position. Because two patients may receive transplants from a single donor, the choice of operative side may be limited, but in general the recipient side with the worst lung function is preferred. Surgical technique varies, but typically a standard pneumonectomy is performed and the donor lung is implanted by performing the anastomoses in a posterior-to-anterior sequence: the bronchus first, the pulmonary artery second, and the pulmonary veins third.

Surgical access for bilateral sequential lung transplant is usually made by performing a transsternal bilateral thoracotomy (a “clamshell” incision) with the patient in a supine position. The procedure involves performing two single-lung transplants, one after the other. The side with the worse lung function is typically resected first.

In patients with COPD or interstitial lung disease, lung transplantation (either single or bilateral-sequential) can usually be performed without the use of cardiopulmonary bypass (CPB) by using selective lung ventilation via a double-lumen endotracheal tube. However, in certain situations CPB is required. Patients with severe pulmonary hypertension typically do not tolerate the increase in pulmonary vascular resistance associated with the clamping of one pulmonary artery. Therefore, CPB is used electively in this patient group. CPB may also be required as an emergency intervention due to an acute deterioration in cardiac or respiratory function. Cardiac dysfunction may arise from incessant arrhythmias or acute right ventricular failure, both of which are provoked by acidosis, hypercarbia, hypoxemia, and surgical manipulations. The adverse hemodynamic effects of surgical manipulations are more pronounced in the presence of dense adhesions, such as those that occur in patients with cystic fibrosis or bronchiectasis. Also, patients with suppurative lung disease may not tolerate one-lung ventilation because of the recurrent plugging of the double-lumen tube by thick secretions. Emergency CPB also may be required during a bilateral sequential transplantation if a severe reperfusion injury develops in the first transplanted lung.

There are clear advantages in avoiding CPB, but they should not occur at the cost of prolonged periods of hypotension, hypoxemia, and acidosis. Ideally, CPB is used on an elective basis in appropriately selected patients rather than as a rescue maneuver in impending cardiac arrest.

Heart-lung transplantation is performed via a median sternotomy or clamshell incision with the use of CPB. During explantation of the native heart and lungs, it is essential to identify and preserve both phrenic nerves and to secure hemostasis of the bronchial vessels in the subcarinal space, because subsequent exposure of this region is extremely difficult. The donor heart-lung block is sutured in via tracheal, atrial, and aortic anastomoses. Prior to decannulation, the heart and pulmonary circulation must be fully de-aired.

For all transplant procedures, the times at which reperfusion occurs should be noted so the total ischemic time of the organs can be calculated. Methylprednisolone is typically administered at the time of reperfusion.

At the completion of surgery, the bronchial anastomoses are inspected bronchoscopically. Unless independent lung ventilation is being considered, the double-lumen tube is exchanged for a single-lumen tube prior to the patient’s transfer to the cardiothoracic intensive care unit (ICU).

Immunosuppression

Standard immunosuppression¹⁸ in lung transplantation consists of triple therapy, including a calcineurine inhibitor (cyclosporine, tacrolimus), an antiproliferative agent (azathioprine, mycophenolate mofetil), and a corticosteroid (methylprednisolone, prednisone). In a recent survey of North American practice, the most commonly used regimen consisted of tacrolimus, mycophenolate mofetil, and prednisone.⁵ The first doses of immunosuppression are given prior to surgery and continued postoperatively. If there is evidence of postoperative acute renal dysfunction, the calcineurine inhibitor may be withheld for a few days or another class of drug may be substituted. In some centers, induction therapy that is commonly either an anti-lymphocyte antibody or interleukin 2 (IL-2) blocker is administered during the early postoperative period.