22/04/2017
PEDIATRIC LIVER TRANSPLANT
Medical treatment, surgery, and postsurgical care can be broken into 4 basic steps:
1.Candidate evaluation
2.Waiting period
3.Surgery
4.Postsurgical care
A. Pretransplantation care
Pretransplantation care needs to take into consideration potentially prolonged waiting periods and to project far in advance when transplantation might be required. By initiating the pretransplant workup early, one can work toward maximizing the nutritional status.
Nutritional status impacts both pretransplant and posttransplant outcomes, especially in the pediatric population, because of an increased incidence of cholestatic liver diseases. Cholestatic liver diseases lead to fat malabsorption, which causes a deficiency of calories as well as fat-soluble vitamins.
Pediatric patients can greatly benefit from caloric assessments and supplemental tube feedings as indicated. Furthermore, parenteral feedings are sometimes warranted in the most nutritionally deprived patients with end-stage liver disease. The optimization of nutritional status in pediatric patients has translated into improved survival after transplantation, fewer infections, and a reduction of surgical complications.
B. Neonatal liver transplantation
Liver transplantation has been successfully extended to neonates. Acute liver failure from hemochromatosis, leading to a histologic diagnosis of giant-cell hepatitis, is the primary indication for liver transplantation in the neonatal population. Because of size discrepancies between the recipient and the donor pool, partial liver grafts are usually used for this population of patients.
Although neonates appear to be more immunotolerant to transplanted organs, their immature immune systems combined with immunosuppression increases the risk for infectious complications. Among neonatal transplant recipients, vascular thrombosis is the major complication, dramatically reducing survival.
C. Indications for pediatric liver transplantation
About 50% of the pediatric patients who require a liver transplant have biliary atresia. Other disease states that progress to end-stage liver disease among pediatric patients and require liver transplantation include metabolic disorders and progressive intrahepatic cholestasis.
Examples of metabolic derangements include Wilson disease, alpha 1-antitrypsin deficiency, tyrosinemia, and hemochromatosis. Other metabolic disease states leading to hepatic dysfunction include the following :
Crigler-Najjar syndrome
Glycogenosis
Hyperoxaluria
Metabolic respiratory chain deficiencies
Familial hypercholesterolemia
Methylmalonyl aciduria
D. Contraindications to pediatric liver transplantation
Transplantation is not indicated if an acceptable alternative is available or if contraindications, such as malignancy, a terminal condition, or poor expected outcome exist.
E. Candidate evaluation
Once a liver transplant is considered, a team of specially trained staff usually evaluates the patient to establish whether the patient would be a good candidate for a liver transplant. The team includes the following specialists:
Hepatologists (medical liver specialists)
Transplant surgeons
Social workers
Psychologists, psychiatrists, or both
Nurses
Transplant coordinators
When a pediatric patient is likely to require a liver transplantation, the medical management is generally divided into pre-transplant and post-transplant periods, with the post-transplant follow-up further separated into early and late periods.
F. Waiting period
Once a pediatric patient is found to be a suitable candidate for a liver transplant, the patient's name is placed on a waiting list for an organ. Unfortunately, many more potential recipients are on the waiting list than there are organs available each year.
At most transplantation centers, the decision to be placed on a waiting list is determined by a multidisciplinary committee. Although not pediatric specific, an observational multicenter study reported that the decision process primarily involves reviewing possible reasons for patient exclusion, which may include patients who are not sick enough, too sick, or too old; other reported factors were the presence of non-hepatic comorbid conditions, substance abuse problems, or other psychosocial barriers.
G. Need stratification
Candidates waiting to receive donor livers are stratified according to the severity of their illness and blood type. Organ allocations are generally based on medical urgency more than the length of time a person has been on the waiting list. Candidates with fulminant hepatic failure (status 1) are allocated organs ahead of all other waiting patients.
The stratification system uses a risk determination based on a 3-month pretransplant assessment risk profile to assign priority and organ allocation to the most severely ill patients.
Patients who qualify for liver transplantation are assigned a score based on a nationwide ranking system. This system is called the Model for End-Stage Liver Disease (MELD) for adults and the Pediatric End-Stage Liver Disease (PELD) for patients younger than 12 years.
H. Care during the waiting period
Pretransplantation care needs to take into consideration the possibility that the patient will be facing a prolonged waiting period and to project far in advance when transplantation might be required. Unfortunately, the number of children with liver deficiencies necessitating liver transplantation far exceeds the availability through donation. The mortality rate for children on the UNOS waiting list is estimated at 17%.
By initiating the pretransplant workup early, one can work toward maximizing the nutritional status, a factor impacting both the pretransplant and posttransplant outcome, especially in the pediatric population, because of an increased incidence of cholestatic liver diseases such as biliary atresia. Malabsorption of fat-derived calories and fat-soluble vitamins in the setting of chronic disease causes various metabolic and disease progression problems.
I. PREPARATION
Anesthesia in pediatric liver transplantation
Living donors receive general anesthesia and immediate transplantation of a portion of their liver into the recipient. Therefore, the patient receiving the transplant is prepared for surgery within the same time frame as the donor.
A liver from a deceased donor must be transplanted into the recipient within 12-18 hours. A team of surgeons and anesthesiologists performs an operation to remove the liver from the donor. The liver is then preserved and packed for transport. These procedures are performed using standard surgical practices and sterile techniques. Upon completion of the operation, the incisions are closed, and the donor's body is prepared for funeral or cremation. If desired, an open-casket funeral remains possible.
J. Overview of liver transplantation
Most liver transplants are orthotopically performed, meaning the new liver is placed in the same location as the diseased liver. This requires that the diseased liver be removed. This portion of the operation is critical and can take several hours, depending on the extent of previous surgery and the adhesions and scar tissue that developed.
If the new liver is a whole liver, the intrahepatic portion of the inferior vena cava can be removed as well, or it can be left in the recipient and the new liver "piggybacked" onto the cava. If the new liver is coming from a living donor or is the result of a reduction or splitting of the deceased donor's liver, then the inferior vena cava must be left in place and the new liver will be anastomosed to the native vena cava. The preferred preservation time for the new liver is less than 12 hours, although the maximum time is reported to be 24 hours.
The implantation requires the reestablishment of blood flow to the liver via the portal vein and hepatic artery and the reestablishment of blood flow away from the liver via the hepatic veins. After the blood flow has been restored, the bile duct's continuity with the GI tract must be established. In pediatric transplantation, this is usually via a hepaticojejunostomy.
A significant advance in transplantation has been the use of living donor and split-liver grafts. Technical challenges include vascular anatomy, sufficient volume for metabolic demands of the patient, and biliary drainage.
The use of split livers from deceased donors and partial grafts from living donors has yielded encouraging results in terms of graft viability. A careful donor and recipient selection process has been advocated to decrease the risk of primary nonfunction in split-liver grafts. The use of living donation in pediatric transplantation is well established and has been shown to be associated with excellent results in the child and is generally safe for the donor (20% morbidity, 0.01% mortality).
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