Swine flu patients risk pulmonary emboli, study finds

Swine flu patients are at risk of developing severe complications, such as pulmonary emboli, according to University of Michigan researchers. Most chest x-rays come back normal, so it's especially important for radiologists to look closely for risks of blocked arteries in the lungs.

In June the World Health Organization declared a global pandemic of H1N1, more commonly known as swine flu, and raised its alert level to Phase 6. Considering its infectious nature, knowledge of H1N1's radiologic features and complications is crucial, the researchers said.

They reviewed the cases of 222 patients with H1N1, 66 of whom underwent chest radiographs, more than half of which came back normal. But in 14 patients who were admitted to the ICU and scanned with chest CT, five showed PE (AJR 2009;193:1-6).

H1N1 is confirmed with a blood test but CT exams may be useful for patients for whom the clinical symptoms are worse than expected or are unusual, said Dr. Prachi P. Agarwal, an assistant professor of radiology at the University of Michigan Medical School and lead author of the study.

"Patients in whom the clinical symptoms and lung function are out of proportion to those usually seen with the flu, and who are in the ICU in particular, should have pulmonary embolism suspected as a secondary diagnosis," she said.

The high incidence of pulmonary embolism was noted only in severely ill patients admitted to the ICU and who were using advanced mechanical ventilation. The radiologists identified a large saddle embolus straddling the bifurcation of the main pulmonary artery, lobar emboli, segmental emboli, and subsegmental emboli.

"Chest radiographs are often normal, and even when abnormal, underestimate the extent of disease found on CT examinations," she said. "Any chest CT examination done in H1N1 patients using intravenous contrast should be scrutinized for pulmonary embolism, even if that was not the reason the CT was specifically requested."

Suspicion of PE should be raised for patients in the ICU who require advanced mechanical ventilation and experience clinical deterioration not otherwise explained, Agarwal said.

The patients involved in the study were admitted between May and July. Clinical manifestations of H1N1 are flulike symptoms such as fever, cough, sore throat, body aches, headache, chills, and fatigue. Nausea, vomiting, and/or diarrhea have also been reported.