17 de maio de 2013

Artigo recomendado: A practical approach to anaesthesia for paediatric liver transplantation


J Thomas, M McCulloch, W Spearman, T Butt, A Numanoglu
Departments of Paediatric Anaesthesia, Nephrology, Surgery, Medicine, University of Cape Town, South Africa

Southern African Journal of Anaesthesia & Analgesia • March 2006

ABSTRACT
Anaesthesia for paediatric liver transplantation requires meticulous attention to detail, an understanding of the disease process leading up to the need for transplantation, and an awareness of the haematological, biochemical, and multi-organ consequences of this operation. In the past 20 years, significant advances in surgical techniques, organ procurement and preservation, immunosuppression, anaesthetic management and monitoring, and postoperative care in the intensive care unit have contributed to improved outcomes of both the graft and the patient. In more recent years, the use of reduced size and living related organs has increased the donor pool for infants and children. Paediatric liver transplantation in South Africa, up until the present time, has been centered at the Red Cross Children’s Hospital in Cape Town, and survival rates here are comparable with international figures. This paper highlights the preoperative problems which face the anaesthetist, emphasises the importance of good planning and preparation for the intraoperative procedure, simplifies the surgical technique of the operation, and stresses the value of a multidisciplinary approach to the child requiring liver transplantation.

Introduction
The first liver transplant in children was performed by Starzl in Pittsburg, Philadelphia, in 1967. Cyclosporine and steroid therapy were introduced in 1980, after which survival has significantly improved. The first paediatric liver transplant in South Africa was performed at the Red Cross Children’s Hospital in December 1987. Despite limited resources, this transplant program has performed 79 transplants in 76 patients with excellent patient and graft survival figures.
The actual liver transplantation in children is the culmination of a long pre-transplant program. Most paediatric liver transplants are the consequence of liver failure due to biliary atresia, inborn errors of metabolism of liver origin such as alpha1-antitrypsin deficiency, autoimmune disorders, or cirrhosis. Less commonly, an acute event such as mushroom poisoning or an adverse drug reaction may precipitate fulminant liver failure. This latter group of children and their families have very little time to prepare for this life-changing event, compared with those who have had an agonising wait for an appropriate donor. A shortage of donors due to infections with hepatitis B virus and the human immunodeficiency virus contributes to the waiting list mortality and infrequent transplantation.
Anaesthesia for paediatric liver transplantation is a challenging event, and although many anaesthetists will not be involved in the actual operation, a working knowledge of this procedure is important. Many of the survivors may present for surgery unrelated to their transplantation.

Preoperative assessment
Important factors to consider include:
1. The general health of the child. Document the age, weight, and height.
2. Bruising, signs of encephalopathy, and stigmata of liver disease may be present.
3. The cause of the liver failure: is this acute hepatic failure or end-stage liver disease? This will impact on the presence or absence of the consequences of chronic liver failure – varices, and portal hypertension, as well as on the general nutritional status of the child i.e. healthy as opposed to chronically ill. The liver disease should be regarded as fulminant, sub-acute, or chronic.
4. Liver disease may occur as part of well-recognised syndromes such as Alagille’s syndrome, and the child may have other features, especially cardiac, in keeping with that particular syndrome. These need to be identified and documented.
5. Causes of renal dysfunction may be multi-factorial. Polycystic liver disease is associated with polycystic kidneys, and primary oxaluria may present initially with renal calculi. Hepato-renal syndrome, pre-renal azotaemia, and acute tubular necrosis may each be a factor.
6. Hepato-pulmonary or porto-pulmonary disease may result in a child who is oxygen-dependent. It is advisable that these children have a cardiac echo prior to surgery to assess heart function and the degree of pulmonary hypertension. A cardiac catheterisation may also be necessary. Pre-existing right to left shunts in the pulmonary vascular bed increase the risk of intraoperative systemic air emboli at the time of venous anastomosis. Preoperative hypoxaemia may be due to intrapulmonary arteriovenous shunting, ventilation-perfusion mismatch, restrictive lung disease from ascites and raised intraabdominal pressure, and a decreased pulmonary diffusing capacity. The oxygen dissociation curve is shifted to the right.
7. A hyperdynamic circulation is usually present, with an increased heart rate, cardiac output, and stroke volume, but a decreased systemic peripheral vascular resistance, and low blood pressure.
8. Arteriovenous shunts may be present, which result in increased venous saturations and a decreased arteriovenous difference in oxygen content. These patients are prone to supraventricular tachycardias, cardiomyopathies, valvular lesions (Alagilles), and occasionally biventricular failure. They are often anaemic preoperatively, especially if they have associated renal disease and/or bleeding varices.
9. Presence of varices: gastric, oesophageal, abdominal wall, or rectal. The date of the most recent sclerotherapy should be documented, as well as the date and type of the antibiotics most recently given.
10. Previous surgery. Has the child had previous abdominal surgery such as a Kasai portoenterostomy for biliary atresia or shunts for control of varices. If so, when was the surgery performed? This will impact on the complexity of the surgery, the amount of bleeding encountered in the pre-anhepatic phase, and the length of time before the diseased liver is removed.
11. Document any allergies, as well as the details of previous anaesthetics the child has had. The size of the endotracheal tube last used may be useful in the planning for the anaesthetic.
12. Most of these children have had an appropriate time for starvation before surgery starts, so are usually nil by mouth.
13. Confirm that blood bank and the haematology and biochemistry laboratories have been informed about the operation.
14. Plan for postoperative care; alert the Intensive Care Unit that the child will return to them after surgery.

Investigations
• Blood results required include a full blood count for haemoglobin, platelets, and white cell count, INR, clotting profile with fibrinogen and PTT. An arterial blood gas is not usually necessary and is a painful procedure, so only request this if it forms a useful baseline for management.
Electrolytes are important, especially if there is concomitant renal disease, and calcium, phosphate and magnesium levels should be available. These patients may be alkalotic with low sodium, potassium, calcium, magnesium, and glucose measurements, and may be hyperphosphataemic.
Acidosis usually reflects poor perfusion, liver necrosis, orrenal tubular acidosis.
• Liver function tests results, especially albumin, should be documented. Low albumin may result in poor drug binding, ascites, and a low colloid oncotic pressure.
• Renal function: urea and creatinine levels are necessary.
• Baseline cytomegalovirus and Epstein Barr virus status is required.
• Blood cultures are performed in these children prior to transplantation.
• A chest X ray (CXR) is necessary to identify fluid overload, infection, and to exclude tuberculosis.
• Echo cardiography will be required for the patient who has hepato-pulmonary syndrome and/or pulmonary hypertension.

Preoperative medication
These drugs are usually administered under the instruction of the liver transplant medical team as per program for each individual child. In general this would include:
1. Tacrolimus 0.2mg/kg per os (po), or Cyclosporine 5mg/kg po. The choice of drugs will depend on the current regimen.
2. Mycostatin 2-5 mls per os stat (depending on the child’s age).
3. Glycerine suppositories: 1 per rectum stat.
4. Depending on the coagulation status, a preoperative fresh frozen plasma infusion may be necessary.

Premedication
Anxiolysis is generally all that these children require, and oral midazolam 0.25-0.5 mg/kg half an hour preoperatively is satisfactory. If the child has hepato-pulmonary syndrome with significant shunts and is cyanosed, supplemental oxygen via face mask or nasal cannulae preoperatively is advised.

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