Sickle cell crisis — acute chest syndrome

Diagnosis. Acute chest syndrome (ACS) — the leading cause of death in sickle cell disease — complicating a vaso-occlusive pain crisis. ACS is defined by a new pulmonary infiltrate on the chest radiograph accompanied by a respiratory symptom or sign (fever, cough, dyspnoea, pleuritic chest pain, hypoxia). The diagnosis is clinical and radiographic; the infiltrate may lag the symptoms, so a normal early film would not have excluded it.

Assessment and risk. Severity markers here include a respiratory rate of 30, hypoxia (90 per cent on room air), fever and a new infiltrate — this patient is at risk of rapid deterioration over hours and needs high-dependency-level care. Seek the precipitant (infection is the commonest, also fat embolism from marrow infarction, pulmonary infarction and hypoventilation from splinting). Send a full blood count and reticulocyte count, blood film, haemolysis markers (LDH, indirect bilirubin, haptoglobin), type and screen, blood cultures, venous gas, ECG, lipase and beta-hCG. Assess the pain score.^[2]

Immediate management — the universal backbone. Give supplemental oxygen targeting a saturation greater than 95 per cent. Establish intravenous access and, once euvolemic, give isotonic crystalloid at no more than maintenance — over-hydration risks pulmonary oedema and accelerates ACS. Start parenteral opioids within 30 minutes of triage and reassess every 15 to 30 minutes. Do not use meperidine (pethidine) unless it is the only effective opioid for that individual (NHLBI: neurotoxicity).^[1]

ACS-specific management. Start an intravenous cephalosporin plus an oral macrolide. Add bronchodilators if there is wheeze or a history of asthma. Prescribe incentive spirometry while awake. Escalate respiratory support (high-flow nasal cannula, non-invasive ventilation, or intubation) for worsening hypoxia.^[1]

Transfusion strategy. This patient's hypoxia and new infiltrate meet the threshold for transfusion. This patient already has hypoxia with a new infiltrate. NHLBI: simple transfusion (10 mL/kg) when haemoglobin is more than 10 g/L below baseline (may not be required if baseline is 90 g/L or higher); do not simple-transfuse SCA above 100 g/L. Escalate to urgent exchange transfusion for rapid progression — saturation below 90 per cent despite oxygen, increasing distress, progressive infiltrates, and/or haemoglobin falling despite simple transfusion. When exchange is performed, AABB usual goals are HbS not more than 30 per cent and haematocrit under 30 per cent. The STOP chronic programme keeps HbS below 30 per cent immediately prior to the next unit.^[1][3]

Disposition. Admit to high-dependency or intensive care given the hypoxia and tachypnoea. Involve haematology and the transfusion service early. Reassess the pain, the saturation and the respiratory rate at least every 30 minutes.^[1]

Differential. Pneumonia (treated identically as ACS plus the sickle-specific escalation, so the distinction is not waited upon), pulmonary embolism (sickle cell patients are prothrombotic; D-dimer is unhelpful as it is raised at baseline; CTPA if suspected), and pulmonary oedema from over-resuscitation.^[2]