الفهرس 
Physiology of Oxygen TransportOnly 14 pages are availabe for public view
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Abstract
Sickle cell disease is a group of well-defined haemoglobinopathies involving abnormal alteration of the globin moiety under certain condition especially hypoxia, haemoglobin aggregates to give the red blood cells a crescent (sickle) and hence the name.
Sickle haemoglobin (HbS) is a result of a mutation in the betaglobin gene where valine substitutes glutamic acid in the amino acid of haemoglobin, nearly I of 350 African-Americans have some type of SCD.
Common genotypes include homozygous s mutation (sickle cell anaemia, Hb ss disease) and heterozygous cominations such as Hbs with Hb c (Hb sc disease) and Hb s with beta-thalassemia mutation (Hbs-beta thalassemia).
Sickle cell trait occurs in about 8% of African-Americans and it is used to describe a persons who is a heterozygote for a normal haemoglobin gene (A) with an abnormal gene (S). Persons with sickle trait lead to a normal life and do not present with symptoms, morbidity as mortality associated with SCD.
Sickle cell disease is most common among African-Americans, a though it has also been observed in persons native to the Mediterranean area.
The patients are young and present with the clinical picture of anaemia, obstructive or hemolytic jaundice, joint and bone pains, abdominal and chest pains, lymphadenopathy, chronic leg ulcers, haematuria epistaxis, priapism, finger clubbing and skeletal deformities the disease is characterized by periodic exaggeration of symptoms as sickle cell crisis.
Sickle cell crisis refers to the acute picture generally caused by sickling of red blood cells in vivo four clinical types of crisis haven been described they are as follows:
o Vascular occlusion crisis with organ infarction and pain.
o Haemolytic crisis with haematologic features of sudden haemolysis sequestration syndrome with sequestration of red blood cells in liver and spleen causing this massive, sudden enlargement and an acute fall in peripheral haematocirt.
o Aplastic crisis with bone marrow suppression.
Patients in painful crisis present with fever, anaemia, limb pain and abdominal pain. They are tachypneic and may have enlarged liver and spleen in addition to abdominal tenderness.
The pathogenesis of cell sticking involves the various factors that contribute to local hypoxia and acidosis.
Dehydration, hypothermia, over transfusion lead to increased viscosity and stasis which cause acidosis, hypoxic and cooling leading to sickling of RBC and result in vascular occlusion.
Also, infection, hypotension lead to acidosis, hypoxia and cooling and leading to sickling of RBC and result in vascular occlusion. Once sickling is initiated, it becomes a vicious cycle that causes more sickling unless proper remedial measures are undertaken.
A careful history and physical examination should be done and cardiopulmonary status should be thoroughly investigated in view of cardiac and pulmonary complications in these patients.
One should correct dehydration or infection in the preoperative evaluation laboratory tests that should be carried out are complete blood count, blood urea nitrogen (BUN). Serum creatinine, urine analysis specific tests should be carried out.
Peripheral smear for evidence of sickle cells
Sickle cell preparation.
Haemoglobin electrophoresis to determine HbS quantitatively.
Reticulocyte count.
Surgery, in sickle cell anaemia should be carried whilst the patients is in a steady state without evidence of ongoing crisis. Dehydration is a major hazard for there patients. They must be given intravenous fluid to cover the period of perioperative starvation.
Preoxygenation and prevention of acidosis aid in the prevention of sickling crisis.
There are no data to suggest which type of anaesthetic agents are best tolerated. Hypotension should be avoided patients with Hb ss or Hbsc disease.
The patient should be protected from chilling during surgery. Regional circulatory should be avoided.
The postoperative period is the most hazardous period for patients with sickle cell disease. Great care is required to make sure that the patient does not suffer from hypoxia, dehydration or cold during recovery. They should be given O2 by mask and I.V. fluids continued.
They should be carefully monitored for evidence of hypotension or circulatory slowing. Once the patients has fully recovered from the anaesthesia mobilization and other antithrombotic measures should be started as early possible.