Patients with critical H1N1 pneumonia have more diffuse involvement of both lungs with greater prevalence of consolidation compared to patients with severe illness, according to a study published in the April 2023 issue of the Clinical Respiratory Journal.¹ The number of lobes affected was also higher in critical patients with more frequent involvement of the middle lobe.

To analyse the clinical and radiological differences between severe and critical illness, 27 patients who had been diagnosed with H1N1 pneumonia between October 2018 and March 2019 were enrolled in this retrospective study. Fifteen patients had severe pneumonia and 12 had critical pneumonia.

Patients with more than 3 days of high fever (>38.5°C) with severe cough with purulent or bloody sputum/chest pain; tachypnea, dyspnea, and cyanosis; dull reaction, hypersomnia, and restlessness; severe vomiting, diarrhea and dehydration; pneumonia and significant worsening of underlying disease were categorised as severely ill. Patients with respiratory failure, septic shock, multiorgan failure were considered as critical cases.

When the differences in clinical manifestations and laboratory parameters were analysed, dyspnea at rest was found to be more common in the critical patients than in the severe patients. The critical group also had higher neutrophil and lower lymphocyte percentages.

On imaging, both critically and severely patients had bilateral involvement of the lungs, although the number of lobes that were affected was higher in the critical group (vs severe group). Middle lobe involvement was significantly higher in the critical group (~92%) than in the severe group (~27%). Involvement of lungs was more diffuse in the critical group (83.30%), while the severe group had more peripheral involvement (40%).

Both groups of patients had ground-glass opacities and consolidation on chest CT. The prevalence of consolidation was higher in critical group vs severe group; 83.30% vs 33.3%, respectively. More critically ill patients had interlobular septal thickening but this difference was statistically nonsignificant. Both groups had comparable airway involvement, lymph node enlargement and pericardial effusion.

This study shows that clinical features, lab results and chest CT scan findings can together distinguish between severe and critical H1N1 pneumonia. Early identification of critical illness enables timely interventions before it becomes unsalvageable.

Reference

1. Yu M, et al. Differences in clinical characteristics and chest CT findings between severe and critical H1N1 pneumonia. Clin Respir J. 2023 Apr;17(4):277-285. doi: 10.1111/crj.13591.