Acute Chest Syndrome (Sickle Cell Disease)

The newest edition of the Skeptics’ Guide to Emergency Medicine “Hot Off The Press” covers this article on sickle cell acute chest syndrome: 

http://onlinelibrary.wiley.com/doi/10.1111/acem.13048/abstract

The Hot Off The Press series allows you to comment and ask questions of the authors of the paper. The best comments will be included in the summary that accompanies the paper in Academic Emergency Medicine. Before we get to the paper, let’s do a quick review.

What is acute chest syndrome?

Acute chest syndrome is a common and potentially deadly complication of sickle cell disease. Acute chest syndrome is defined as a new pulmonary infiltrate of at least one lung segment (not atelectasis) with accompanying symptoms of fever, chest pain and/or respiratory signs or symptoms.¹

What causes acute chest syndrome?

There are three major causes to consider: infection, fat embolization from bone marrow, and vaso-occlusion of the pulmonary vasculature by sickled RBCs.²

Can acute chest syndrome be prevented?

Almost 50% of patients develop acute chest syndrome during a hospitalization for another illness, such as an acute pain crisis.3 The Canadian guidelines suggest the following measures to promote early detection and prevention:¹

• Pulse oximetry should be a routine part of every medical assessment to identify changes from a patient’s baseline oxygen saturation level.

• Patients admitted for a febrile or vaso-occlusive episode should be carefully examined and have continuous oxygen saturation monitoring for early detection of clinical symptoms and/or changes in oxygenation.

• Hydroxyurea therapy should be considered for patients after a single episode of acute chest syndrome.

• There is conflicting evidence about the benefit of chronic red blood cell (RBC) transfusions for the prevention of ACS, and they and are not routinely recommended.
• Asthma management for children and adults with both sickle cell disease and asthma should be optimized, and a referral to an asthma specialist should be considered.

Other recommendations include incentive spirometry and patient controlled analgesia (to help avoid over sedation and hypoventilation).

How is acute chest syndrome treated?

All children with acute chest syndrome should be admitted to hospital.¹ These patients can get be very sick, so start with the ABCs. The management is primarily supportive.³ Titrate oxygen therapy to an oxygen saturation ≥95%.1 Respiratory therapy is important, including incentive spirometry and pulmonary toilet.^1,3 Febrile patients should have blood cultures drawn and be given broad spectrum antibiotic coverage.¹ Treat pain and maintain hydration.¹ Transfusion of packed red blood cells may be required, but is probably best done in consultation with a hematologist.¹ If the patient presents with wheeze or other signs of reactive airway disease, treat with inhaled bronchodilators and steroids.¹ Noninvasive positive pressure ventilation may also have a role.¹

Hot off the Press

This paper for this edition is:

Eisenbrown K, Nimmer M, Ellison AM, Simpson P, Brousseau DC. Which Febrile Children With Sickle Cell Disease Need a Chest X-Ray?. Acad Emerg Med. 23(11):1248-1256. 2016. [article]

This is a retrospective chart review looking at children with sickle cell disease aged 3 months to 21 years presenting to one of two pediatric emergency departments with a fever. They were looking at the accuracy of history, physical, and laboratory findings for identifying acute chest syndrome on chest x ray. Overall, they identified 1837 visits made by 697 children for fever. Acute chest syndrome was diagnosed in 185 visits (10%). Of course, this is a chart review, so it is possible that some children may have been missed (if, for example, they were coded as pneumonia but not sickle cell disease). They then use a CART (classification and regression tree) analysis to identify the most discriminatory variables in their data set.

• Doing x rays only in patients with respiratory signs or symptoms (shortness of breath, tachypnea, cough, and/or rales) or chest pain had a sensitivity of 87.6% and a specificity of 45.9%. It would have missed 23 cases of ACS while avoiding 781 chest x rays.

• Adding a white blood cell count over 18.75 to the above criteria increased sensitivity to 93.5% but specificity was 35.2%. It would have missed 12 cases of ACS while avoiding 593 chest x rays.
• Adding a past history of ACS to all of the above increases sensitivity to 97.8% but dips specificity to 25.8%. It would have missed 4 patients with ACS (out of 185 or 2.2%) while avoiding 430 chest x rays.

My thoughts:

Fever is a reasonable variable for a chart review, as it will be objectively recorded, but shortness of breath may been difficult to determine from a chart. Similarly, how often is the exam finding of rales accurately recorded on the chart?  

This is a retrospective derivation. This model should not be used without prospective validation. Looking at the data, you get the idea that the decision tool is highly fit to this specific group when you recognize that the white blood cell cut-off used is 18.75. It is highly unlikely that the exact same numbers would be replicated in a second data set.

I am not sure sure how good chest x ray is as a gold standard. This is a surrogate outcome, and it’s not clear that every patient who has an infiltrate identified on x ray will have similar outcomes or will require the same treatment. Also, we know that x ray lacks sensitivity for infiltrates. Would we be better off using ultrasound or CT?

Finally, we need to consider what is an acceptable miss rate for ACS? Even using criteria retrospectively fit to this specific group of patients, we would have still missed 2% of ACS cases, while only avoiding chest x rays in 23% of visits.

Bottom line: For me, this is interesting data, but given the importance of diagnosing acute chest syndrome, I will continue to order a chest x ray on all febrile children with sickle cell disease until I see stronger prospective data.

Time to comment

Those are my thoughts, but we want to know what you think. Do you have and thoughts or questions about this data. Please head on over to the SGEM and leave them in the comments. Or comment on twitter using the hashtag #SGEMHOP. Remember, the best questions or comments will be included in an upcoming publication in Academic Emergency Medicine.

Enjoy keeping up with the emergency medicine literature and reading quick critical appraisals? Click here for many more.

Other FOAMed Resources

Acute Chest Syndrome on Pediatric EM Morsels

EMCases best case ever #38: sickle cell acute chest syndrome

References

1. The Canadian Hemoglobinopathy Association. Consensus Statement on the Care of Patients with Sickle Cell Disease in Canada.
2. Gladwin MT, Vichinsky E. Pulmonary complications of sickle cell disease. The New England journal of medicine. 359(21):2254-65. 2008. [pubmed]
3. Crabtree EA, Mariscalco MM, Hesselgrave J. Improving care for children with sickle cell disease/acute chest syndrome. Pediatrics. 127(2):e480-8. 2011. [pubmed]
4. Chang TP, Kriengsoontorkij W, Chan LS, Wang VJ. Clinical factors and incidence of acute chest syndrome or pneumonia among children with sickle cell disease presenting with a fever: a 17-year review. Pediatric emergency care. 29(7):781-6. 2013. [pubmed]
5. Eisenbrown K, Nimmer M, Ellison AM, Simpson P, Brousseau DC. Which Febrile Children With Sickle Cell Disease Need a Chest X-Ray?. Acad Emerg Med. 23(11):1248-1256. 2016. [article]