73. Sickle cell Flashcards
An unbooked Afro-Caribbean primagravida arrives on the ward in
advanced labour. Fetal distress is diagnosed and the obstetricians wish
to do an emergency caesarean section. Her full blood count shows an Hb
of 8.3 g/dl with a microcytic picture (normal platelets). Time will not
permit electrophoresis.
What may explain the blood picture?
A haemoglobin concentration of less than 10.5 g/dl is due to something other
than the dilutional anaemia of pregnancy. Some causes of a microcytic
anaemia with normal platelets are:
Iron deficiency
Hb SS (Sickle cell disease) – the patient would know this diagnosis
Hb AS (Sickle cell trait)
Hb SC
a-Thalassaemia
b-Thalassaemia (less common in Africans)
Some anaemias of chronic disease.
The blood film should be examined and electrophoresis should be organised
because it may influence future management.
Sickle cell trait (AS)
Usually no clinical abnormality unless exposed to extreme hypoxia
(sickling if PaO2 < 15 mmHg).
Increased risk of pyelonephritis during pregnancy.
Sickle cell haemoglobin C (SC) disease
Less severe clinical course than SCD but can suffer the same complications.
Prevalent in West Africans.
May not develop symptoms until late pregnancy
(splenic sequestration and marrow necrosis).
Can develop proliferative retinopathy.
How would you manage anaesthesia for the Caesarean section?
Pregnancy exacerbates the complications of sickle cell anaemia. Maternal
mortality of 1% is due to pulmonary infection and infarction.
Blood transfusions are indicated for:
Severe anaemia
Hypoxaemia
Pre-eclampsia
Septicaemia
Renal failure
Acute chest pain syndrome
Anticipated surgery.
A haemoglobin concentration of 10 g/dl is commonly aimed for in patients
having a caesarean section.
Either regional or general anaesthesia is acceptable. Principles of
management are
Oxygen
Crystalloids for intravascular volume
Transfusion to maintain oxygen carrying capacity
Venous stasis prophylaxis
Normothermia.
Anaesthetic problems with Sickle cell disease
Avoidance of precipitants of sickle crises
Difficult i.v. access
Pain/opioid tolerance
Anaemia and high output failure
Infection (salmonella)
Psychiatric problems
Intra-operative crisis/thrombo-embolic phenomena
Acute chest syndrome
Renal impairment
Pulmonary hypertension
Precipitants of a Sickle crisis
Dehydration
Hypoxia
Cold
Alcohol
Stress
Infection
Menstruation
Vascular stasis
Acidosis.
Surgery proceeds uneventfully, but post-operatively she develops acute
pleuritic chest pain. What may be causing this
Possible causes
Pulmonary embolus
Acute chest syndrome
Pneumothorax
Pneumonia.
If this were a Sickle crisis, how would you manage the case?
The mainstays of management of a Sickle crisis are:
Analgesia
Fluid replacement
Avoidance of hypoxia.
Types of Sickle crisis:
Aplastic
Sequestration
Infarctive
Aplastic
Depression of erythropoiesis secondary to infection
(esp. parvovirus) or folate deficiency in pregnancy
Sequestration
This can result from massive pooling in the spleen
(esp. with SC disease).
Infarctive
These are vaso-occlusive events, often in the
abdomen, back or long bones.
Pain
Can be very severe (and often underestimated).
Treat with: High dose opioids (PCA may be used)
NSAIDs
Epidural
Paracetamol
Fentanyl patches
Tricyclic antidepressants
Benzodiazepines for spasms and anxiolysis.
Dehydration
Causes increased haematocrit and increased sickling.
If fever is present
Search for focus of infection
(cultures of blood, sputum and urine).
It may be due to the crisis itself.
Broad-spectrum antibiotics, which must cover strep. Pneumonii (hyposplenism).
If refractory:
Exchange transfusion
Steroids have been used (Methylprednisolone
Acute chest syndrome
Cause
Unknown exactly
? Hypoventilation due to pain from rib infarcts
? infarcted marrow embolism
? PE
Signs Acute chest pain
Fever
Cough
Basal X-ray changes
↓SaO2
Treatment O2/CPAP/IPPV
Exchange transfusion with HbS < 30% causes a response within 1–2 days
Sickling mechanism
The HbS tetramer
undergoes a conformational change in the deoxygenated state
and leaves hydrophobic residues (valine instead of glutamic acid) exposed.
These react with other globin chains forming an insoluble polymer.
Hb S begins to aggregate at a PO2 of less than 50 mmHg.
The process is also time dependent.
When exposed to oxidant stress,
HbS produces free radicals that damage
the erythrocyte membrane proteins.
Abnormal adhesion to endothelium then occurs.
Infection or minor sickling events cause leucocytes to produce IL-6, IL-1
and TNF that up-regulate cell adhesion molecules (CAMs) on the vascular
endothelium.
These cause activation of the haemostatic mechanism.
Platelets and sickle reticulocytes bind easily to CAMs causing clot
formation and vascular occlusion → hypoxia → more sickling
