INTRODUCTION
The number of lung transplants performed worldwide has increased exponentially over the past 20 years. The availability of suitable organs has limited the number of patients who can undergo transplantation surgery as increasing numbers of patients are placed on waitlists for lung transplantation. Strategies to increase the donor pool have been diverse and have included increasing public awareness, use of extended donors, active donor management, and use of donation after cardiac death (DCD) donors.
SHORTAGE OF ORGANS
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Improved outcomes have led to an increased demand for lung transplantation surgery ( Fig. 36-1 ).
Figure 36-1
Number of lung transplants reported by year and procedure type.
(Adapted from Hertz MI, Aurora P, Christie JD, Dobbels F, Edwards LB, Kirk R, et al. Registry of the International Society for Heart and Lung Transplantation: a quarter century of thoracic transplantation. J Heart Lung Transplant 2008;27:937–983.)
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Trend toward bilateral rather than single lung transplants, among other factors, has led to a need for increased numbers of donors.
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In May of 2005, the lung allocation score (LAS) was developed by the United Network for Organ Sharing (UNOS) and Organ Procurement and Transplant Network (OPTN) networks to decrease the mortality rate of patients on the lung transplant waiting list. The high death rate of these patients is primarily a result of limited organ availability.
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LAS altered allocation of organs to recipients with the greatest need rather than to those with the longest time on the transplant list.
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Despite measures to increase rates of transplantation, significant numbers of patients die while on the waiting list.
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Very few lungs (15%–20%) are procured or used from potential donors, particularly when compared with procurement rates of other solid organs ( Figs. 36-2 and 36-3 ).
Figure 36-2
Lung offers translate to few transplants.
(Based on OPTN data as of February 2, 2007.)
Figure 36-3
Cadaveric donors by organ type.
(Based on OPTN data as of February 2, 2007.)
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Reasons for low use of lung allografts ( Fig. 36-4 ) :
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Perceived poor lung function in donor
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Medical or social history of donor
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No suitable recipient found
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Organ unsatisfactory
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Donor positive for human immunodeficiency virus/hepatitis/HTLV-1
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Cardiac arrest
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Abnormal findings of allograft biopsy
Figure 36-4
Reasons for non-recovery of consented organs, 2004.
(Based on OPTN/SRTR data as of May 2, 2005.)
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PHYSIOLOGY OF BRAIN DEATH
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The vast majority of lung allografts are from brain-dead donors.
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The process of brain death is referred to as coning.
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Central nervous system ischemia typically occurs in a stepwise fashion, progressing from the cerebrum and pons to hypothalamus and pituitary ( Fig. 36-5 ) :
Figure 36-5
Stepwise process of brain death and physiologic consequences.
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Autonomic and hypothalamic dysfunction results in a predictable fashion with direct implications for the lung.
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Hypernatremia
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Hypotension
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Pulmonary edema
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Systemic inflammation
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Procedures aimed at reversing these changes have been shown to increase rates of procurement.
DONOR MANAGEMENT
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On identification of a potential donor, management must often be done to maximize not only lung but other organs that may potentially be used for transplant surgery.
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Different organs often have very different, sometimes conflicting, management strategies.
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Use of a protocol published by the UNOS, entitled “Critical Pathway for the Organ Donor,” has provided general guidelines for management of organ donors, which take into account the specific needs of each potential organ and has been shown to improve procurement and transplantation rate (see the chapter appendix ).
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General management principles
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Invasive monitoring including arterial line and a pulmonary artery (PA) catheter or central venous catheter
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Central venous pressure (CVP) 6 to 8 mm Hg, or lowest CVP needed to maintain blood pressure (BP) and urine output, pulmonary capillary wedge pressure (PCWP) 8 to 12 mm Hg (if PA catheter placed)
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Appropriate use of antibiotics
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Vasopressor use to maintain BP greater than 90 mm Hg systolic
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Endocrine replacement
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Insulin drip, if needed
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Arginine vasopressin—1 unit bolus: 0.5 to 4.0 unit/h drip (titrate systemic vascular resistance [SVR] 800–1200)
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Methylprednisolone—15 mg/kg bolus (Repeat q 24 h PRN)
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Improves gas exchange
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Increases rate of procurement
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Tri-iodothyroxine (T 3 )—4 μg bolus: 3 μg/h continuous infusion
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Little data suggest that thyroid replacement is beneficial in lung recipients
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Ventilator management, not validated
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Tidal volume suggested 8 to 10 mL/kg
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Positive end-expiratory pressure (PEEP) is 5; ideally, it should be less than 10 cm H 2 O
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Maximize lung compliance (plateau pressure < 30 cm H 2 O)
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THE IDEAL LUNG DONOR
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Traditional criteria
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Age younger than 55 years
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ABO compatibility
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Clear chest radiograph
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Adequate oxygenation (PaO 2 > 300 mm Hg at FiO 2 = 1.0, or PaO 2 /FiO 2 > 250–300)
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No chest trauma
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No evidence of aspiration/sepsis
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Normal sputum gram stain
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Normal bronchoscopy
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No history of significant lung disease
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Limited smoking history (<20 pack-years)
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Very little data to support traditional criteria because extensive data now exists challenging their usefulness.
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Despite registry data suggesting worse early and late outcomes using lungs from older donors (>50 years), advanced donor age, in the absence of prolonged ischemic time (>6 hours) is associated with acceptable outcomes.
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Several studies have shown equivalent outcomes in donors with normal and abnormal chest x-ray studies (atelectasis or infiltrate).
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One published report suggested that as many as 41% of lungs rejected based on clinical criteria, including chest x-ray study, were actually suitable organs when examined pathologically.
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No data available linking donor smoking history with transplant outcomes.
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Markedly abnormal bronchoscopic evaluation of the potential lung donor is common despite normal radiographs and arterial blood gases.
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No strong evidence exists that has shown that the presence of significant airway secretions leads to unacceptably performing lung allografts, although this is frequently cited as a reason for lungs not being used.
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PaO 2 /FiO 2 ratio greater than 300 appears to be most important single factor in predicting outcomes after transplantation surgery.
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Little is known about the minimal acceptable PaO 2 /FiO 2 ratio as a modality to improve gas exchange (aspiration of secretions, diuresis, and use of corticosteroids can transform unacceptable organs to acceptable ones).
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There have been several reports of the successful use of lungs from donors with a PaO 2 /FiO 2 ratio of less than 300. This factor may affect outcomes only when accompanied by significant purulent secretions.
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Several published studies have challenged the notion of “ideal donor” as the use of “extended donors” has not been shown to impact significantly on early or late outcomes ( Fig. 36-6 )
