The Other ACS: Acute Chest Syndrome
A 25-year-old male with sickle cell SS disease, well-known to your emergency department for vaso-occlusive pain crises, presents with his typical shoulder and knee pain. As you examine him and formulate a plan for analgesia, he has a coughing fit. Further probing reveals that this cough has been present for three days and is associated with mild dyspnea, but not with fevers, chills, or sick contacts. Your exam is significant for hypoxia to 90% and right-sided crackles and wheezing. What should you be concerned about?
What is ACS, and who is at risk for it?
Acute chest syndrome (ACS), formally defined as a new infiltrate on chest XR in the setting of new respiratory symptoms, is an important cause of morbidity (i.e. respiratory failure requiring mechanical ventilation, multiorgan failure) and mortality in patients with sickle cell disease (SCD). Any individual with SCD can get ACS, but patients with homozygous disease are at highest risk. Know your SCD patient’s genotype. Other risk factors include prior episodes of ACS, leukocytosis, infection, asthma, increased hemoglobin, smoking, and an active vaso-occlusive pain crisis.
Why is vaso-occlusive pain crisis a risk factor?
There is a great deal of overlap between these two entities; a pain crisis often precedes the development of ACS. When you see a patient in a pain crisis, screen for respiratory symptoms and signs during your history and physical. Imagine sickled cells getting stuck everywhere... including the pulmonary microvasculature. Imagine your patient with bone marrow ischemia releasing fat emboli into the venous system, where they cause occlusion and inflammation inside the pulmonary microvasculature. There begins a cycle of respiratory distress, hypoxia, inflammation, acidosis, and potential cardiac arrest.
A different kind of PE
Remember that SCD patients are hypercoagulable, and thus at risk for PE. But sickle cells can also occlude the pulmonary vasculature all by themselves, essentially acting like in-situ thrombi.
Couldn’t this just be pneumonia?
Absolutely - but making that differentiation won’t change your management plan. They look too similar.
What do I order?
Start with a CBC with differential, reticulocyte count, chest XR, blood and sputum cultures, an EKG, and troponins. Depending on the case, you may add a CT to investigate for PE and/or troponins.
Avoid uncontrolled pain, hypovolemia, and hypoxia with analgesia, IV fluids (until oral intake improves), and supplemental oxygen (including BiPAP in some cases) to achieve an O2 saturation of at least 92%.
Initiate transfusion (either simple or exchange, depending on the severity of the ACS) as needed to achieve a hemoglobin of 10 g/dL.
Treat empirically for atypical pathogens, S. pneumoniae, and H. influenza - in other words -- ceftriaxone and azithromycin -- but remember that viruses can also cause ACS.
Consider albuterol, especially in asthmatics.
Start venous thromboembolism prophylaxis.
Encourage incentive spirometry to prevent atelectasis.
ACS is deadly. Actively seek it out, especially in SCD patients with prior episodes of ACS, homozygous disease, leukocytosis, infection, asthma, increased hemoglobin, smoking, and an active vaso-occlusive pain crisis.
SCD patients can have PEs, too -- but they can come in two flavors. The first is the “traditional” PE, which arises from a DVT. The other happens when sickled cells occlude the pulmonary vasculature all by themselves, acting like in-situ thrombi.
Management is about so much more than just analgesia. In addition to analgesia, good supportive care means fluid resuscitation, supplemental oxygen, albuterol (in some cases), venous thromboembolism prophylaxis, and incentive spirometry. In addition to these measures, transfuse to a hemoglobin of 10 g/dL and treat empirically with ceftriaxone and azithromycin.
Sonika Raj, MD, MS is a current third year resident at Stony Brook Emergency Medicine.
Edited by Bassam Zahid, MD