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Gundeep S. Dhillon, MD
Ramona L. Doyle, MD
Heart-Lung and Lung Transplantation Program
Stanford University Medical Center
Stanford, California
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Lung or heart-lung transplantation is an acceptable therapeutic
option for patients with advanced lung diseases, including
patients with pulmonary hypertension in whom all other therapies
have been exhausted. However, the supply of donor lungs
is scarce relative to the demand.1 Among patients in the
United States awaiting lung transplantation, unlike among
those awaiting heart, liver, or kidney transplantation,
priority for organs as they become available has been based
on accumulated waiting time on the list, not on severity
of illness or clinical status. Under the old system, donor
lungs were allocated based on the time accrued while
on the waiting list, after taking ABO blood type, size,
and geographic location into consideration. Although this
method of allocation is simple and appears to be fair, it
can disadvantage patients who are sicker and/or have rapidly
progressive diseases. The death rate of potential lung recipients
on the waiting list is high and there have been observed
differences in waiting-list mortality based on diagnosis.
1,2 Therefore, survival after transplantation in the older
model could be suboptimal, resulting in a reduction in the
number of lives saved, the number of years of life saved,
and the quality of those lives.
In light of these concerns, and under a directive from
the Department of Health and Human Services to the United
Network for Organ Sharing (UNOS), a new lung allocation
system has been developed and recently implemented.3,4
The new system represents an attempt to improve on the
previous lung allocation scheme by balancing urgency of
need and likelihood of survival after transplantation,
ensuring
the optimal use of transplanted organs and the best possible
outcomes for individual patients.
The Lung Allocation Score
The new system is based on a lung allocation score. All
individuals in need of lungs who are over the age of 12
years will receive lungs on the basis of his or her lung
allocation score. The higher the score, the greater the
likelihood of being offered
donor lungs. The lung allocation score is derived from
multiple clinical variables. These clinical variables
(Table 1) are used to calculate
the following:
- The waitlist urgency measure (WLi), which predicts
the number of days an individual with a specific set
of characteristics is expected to live during the next
year on the waiting list (range 0-365).
- The post-transplant survival measure (PTi), which
predicts the number of days an individual is expected
to live during the first year after the lung transplantation
(range 0-365).
| Table
1. Clinical Variables Used for Lung Allocation Score
Calculation. |
| Characteristics for Waiting List Model |
Characteristics for Post-transplant Model |
Age (years)
Body mass index (kg/m2)
Diabetes
New York Heart Association functional class
Forced vital capacity (% predicted)
Pulmonary arterial systolic pressure for diagnosis
groups A, C, and D
Oxygen requirements at rest (L/min)
Six-minute walk distance (feet)
Continuous mechanical ventilation
Diagnosis groups*
Diagnosis detailed** |
Age at transplant (years)
Creatinine at transplant (mg/dL)
New York Heart Association functional class
Forced vital capacity for groups B and D (% predicted)
Pulmonary capillary wedge pressure mean ¡Ý20 mm Hg
for group D
Mechanical ventilation
Diagnosis groups*
Diagnosis detailed** |
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* Diagnosis groups
A = Obstructive lung disease
B = Pulmonary vascular disease
C = Cystic fibrosis or immunodeficiency disorder
D = Restrictive lung disease
** Diagnosis detailed
Bronchiectasis
Eisenmenger syndrome
Lymphangioleiomyomatosis
Obliterative bronchiolitis
Pulmonary fibrosis, other
Sarcoidosis and pulmonary arterial pressure mean
>30 mm Hg
Sarcoidosis and pulmonary arterial pressure mean
¡Ü30 mm Hg
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The raw allocation score is calculated using the following
equation:
Raw Score = PTi – 2WLi
The raw score can range from –730 to 365. A final
lung allocation score (0-100) is obtained by normalization
of the raw score.
Lung Allocation Score = 100[Raw Score – minimum]/Range
=
100[Raw Score – (–730)]/1095
=
100[Raw Score = 730]/1095
Under this system the clinical variables listed in Table
1 need to be updated once every 6 months in transplantation
candidates, but can be updated more frequently at the
discretion of the transplantation center.
Impact of the New Lung Allocation
System on Pulmonary Hypertension Patients
It is unclear how the new lung allocation system will
impact patients with pulmonary arterial hypertension without
or with congenital heart disease (Eisenmenger syndrome).
It is also not known how patients in need of combined
heart-lung transplantation will fare under the new system.
In addition, the lung allocation system does not account
for clinical events such as hemoptysis or syncope, generally
accepted poor prognostic factors in pulmonary hypertension.
In cases where the transplantation center feels that an
individual’s lung allocation score underestimates
his or her clinical severity, an appeal can be made to
a lung review board for adjustment of the score. Thus,
although the new system introduces greater uniformity
across transplantation centers, it does not replace the
need for centers to exercise clinical judgment regarding
the need for and timing of transplantation in individual
patients.
The old system of selecting patients for lung transplantation
required that physicians identify the “transplant
window,” the time when a patient is sick enough to
warrant lung transplantation yet well enough to survive
the transplant operation, and this still holds true. Under
the new system, the burden of factoring in nonclinical
decisions such as waiting time has, presumably, been eliminated.
Ideally the new lung allocation algorithm will reduce
variability among various centers as to the severity of
the illness of patients who receive transplantation thus
improving the fairness of the system.
A potential limitation of this new algorithm is that
it has not been prospectively
validated.6,7 However, the UNOS plans to update this algorithm
every 6 months using the most recent 3-year cohort of
patients on the waiting list and lung transplant recipients.
In conclusion, the need for change in the way donor lungs
are allocated in the United States has been recognized
and undertaken. It is hoped that this new system will
optimize the utilization of this precious resource. Its
impact on specific patient groups, including patients
with pulmonary hypertension, remains uncertain. Because
the system is being implemented in the absence of prospective
statistical validation, and in view of rapid advances
in nontransplant treatments for advanced lung diseases,
frequent reassessment of the process will be critical.
References
1. 2004 Annual Report of the US Organ Procurement and
Transplantation Network and The Scientific Registry of
Transplant Recipients. Rockville,
MD, and Richmond, VA: US Department of Health and Human
Services/Health Resources and Services Administration
(HHS/HRSA) and United Network for Organ Sharing (UNOS).
2004.
2. Hosenpud JD, Bennett LE, Keck BM, Edwards EB, Novick
RJ. Effect of diagnosis on survival benefit of lung transplantation
for end-stage lung disease. Lancet.1998;351(9095):24-7.
3. Department of Health and Human Services. Organ Procurement
and Transplantation Network; Final Rule. 42 CFRPart 121:
Federal Register; 1999:56649-61.
4. Organ Procurement and Transplantation Net-work. Policy
3.7. Allocation of Thoracic Organs. 2004.
5. Vongpatanasin W, Brickner ME, Hillis LD, Lange RA.
The Eisenmenger syndrome in adults. Ann Intern Med.1998;
128(9):745-55.
6. Justice AC, Covinsky KE, Berlin JA. Assessing the generalizability
of prognostic information. Ann Intern Med.1999;130(6):515-24.
7. McGinn TG, Guyatt GH, Wyer PC, Naylor CD, Stiell IG,
Richardson WS. Users’ guides to the medical literature:
XXII: how to use articles about clinical decision rules.
Evidence-Based Medicine Working Group. JAMA. 2000;284(1):79-84.
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