Sickle cell acute complications: Viva

This is acute chest syndrome complicating a vaso-occlusive pain crisis in a child with sickle cell disease. The structured oral runs from the diagnosis through the immediate resuscitation, the transfusion strategy, the avoidance of harm, and the prevention, and it ends with the parallel emergencies of the stroke and the sequestration. [4]

Opening: make the diagnosis

Examiner. The boy was admitted for a pain crisis and now has a fever, a cough, and a saturation of 89 percent on room air. What is the diagnosis, and why did it appear now? [4]

Candidate. The diagnosis is acute chest syndrome, defined by the new pulmonary infiltrate on the chest radiograph together with the fever, the breathlessness, the cough, and the hypoxia, and the saturation of 89 percent marks a moderate-to-severe episode. It appeared after admission because the rib and chest pain of the crisis caused splinting and atelectasis, which seeded the lung, and this is the typical pattern in which the acute chest follows the pain crisis by a day or two. The acute chest syndrome is the leading cause of death in sickle cell disease, so I act now. [4]

Branch 1: the immediate resuscitation

Examiner. What do you do immediately? [1]

Candidate. I give oxygen to keep the saturation at or above 92 percent, and I inform the intensive care team early because the deterioration can be rapid. I take the blood cultures and start a third-generation cephalosporin such as cefotaxime combined with a macrolide such as azithromycin, covering the bacteria and the atypicals. I continue the analgesia for the underlying pain crisis with intravenous morphine at 0.1 mg per kg, because the relief of the rib pain lets the child breathe deeply, and I give the fluids at maintenance rather than as boluses, because over-hydration worsens the lung. [1]

Examiner (probe). Why the macrolide? [4]

Candidate. Because Mycoplasma and Chlamydia are among the infectious causes of the acute chest syndrome, alongside the pyogenic bacteria, and the fat embolism from the infarcted marrow is the other principal mechanism. The macrolide covers the atypicals that the cephalosporin misses. [4]

Branch 2: the transfusion strategy

Examiner. When do you transfuse, and by which method? [7]

Candidate. The transfusion is guided by the severity and the haemoglobin trend. For the moderate episode with a falling haemoglobin or a rising oxygen requirement, I give a simple transfusion, kept cautious and never pushing the haemoglobin above about 100 g per litre, because the higher haematocrit causes hyperviscosity and worsens the sickling. For the severe or progressive episode with worsening hypoxia or multilobar infiltrates, I use an exchange transfusion to bring the haemoglobin S under 30 percent, the same target used after a stroke, and the exchange removes the sickled blood and replaces it with donor blood. [7][4]

Examiner (probe). And why is over-transfusion dangerous? [1]

Candidate. Because raising the haemoglobin too high with a simple transfusion increases the viscosity of the blood, and in sickle cell disease the viscosity worsens the sickling and the vaso-occlusion. The haemoglobin is raised cautiously, and the exchange transfusion is used when the goal is a low haemoglobin S rather than a high haemoglobin. [1]

Branch 3: the parallel emergencies

Examiner. Suppose instead the boy had presented with a sudden hemiparesis. What would change? [2]

Candidate. That would be an acute stroke, and the management is an urgent exchange transfusion to bring the haemoglobin S under 30 percent, and thrombolysis is not used, because the mechanism is the sickling vasculopathy and not a thromboembolism. The stroke is the highest-stakes complication, and the child is committed after the event to a lifelong chronic transfusion programme to prevent the recurrence. [2]

Examiner (probe). And if the patient were an infant with pallor and an enlarging spleen? [1]

Candidate. That would be acute splenic sequestration, a hypovolaemic emergency in the infant, and the management is volume resuscitation followed by a cautious transfusion to a haemoglobin of about 70 g per litre, deliberately below normal, because the sequestered blood returns to the circulation when the spleen shrinks and the over-transfusion causes hyperviscosity. After a major episode, the recurrence rate is high, so I plan a chronic transfusion programme or a splenectomy to prevent the next event. [1]

Closing: the prevention and the evidence

Examiner. How do you prevent the recurrence, and what is the evidence? [4]

Candidate. The prevention is the disease-modifying therapy. Hydroxyurea, started at 20 mg per kg per day and escalated to the maximum tolerated dose, raises the fetal haemoglobin and reduces the frequency of the pain crises and the acute chest syndrome, and the Multicenter Study of Hydroxyurea established the benefit. The Vichinsky study defined the causes and the outcomes of the acute chest syndrome and set the modern management, and the NHLBI 2014 report and the ASH 2020 guidelines codify the care. With this package of oxygen, antibiotics, transfusion, hydroxyurea, and the surveillance, the boy has the best chance of surviving the acute chest and of avoiding the next one. [4][1]