Outcome of Critically Ill Patients With Influenza Infection: A Retrospective Study

Abstract

Background: Influenza causes significant morbidity and mortality in adults, and numerous patients require intensive care unit (ICU) admission. Acute respiratory distress syndrome (ARDS) is clearly described in this context, but other clinical presentations exist that need to be assessed for incidence and outcome. The primary goal of this study was to describe the characteristics of patients admitted in ICU for influenza, their clinical presentation, and the 3-month mortality rate. The second objective was to search for 3-month mortality risk factors.

Methods: This is a retrospective study including all patients admitted to 3 ICUs due to influenza-related disease between October 2013 and June 2016, which assesses the 3-month mortality rate. We compared clinical presentation, biological data, and outcome at 3 months between survivors and non-survivors. We created a predicting 3-month mortality model with Classification and Regression Tree analysis.

Results: Sixty-nine patients were included, 50 patients (72.5%) for ARDS, 5 (7.2%) for myocarditis, and 14 (20.3%) for acute respiratory failure without ARDS criteria. Non-typed influenza A was found in 30 cases (43.5%), influenza A H1N1 in 18 (26.1%), H3N2 in 3 (4.3%), and influenza B in 18 cases (27.5%). The 3-month mortality rate was 29% (n = 20). Extracorporeal membrane oxygenation (ECMO) was implanted in 23 patients, without any significant increase in mortality (39% vs 24% without ECMO, P = .19). A creatinine serum superior to 96 μmol/L, an aspartate aminotransferase level superior to 68 UI/L, and a Pao₂/Fio₂ ration below 110 were associated with 3-month mortality in our predictive mortality model.

Conclusion: Influenza in ICUs may have several clinical presentations. The mortality rate is high, but ECMO may be an effective rescue therapy.

Keywords: ARDS; ECMO; ICU; Influenza; acute respiratory failure; myocarditis.

Figure 1.

Kaplan-Meier survival curve at 3 months. Blue line indicates patient without ECMO; red line indicates patients with ECMO. Time in days. A value of P < .05 was considered statistically significant. ECMO indicates extracorporeal membrane oxygenation.

Figure 2.

Survival curve according to Cox model variable, 1 (red line): creatinine >96 μmol/L, AST >68 IU/L, and P/F ⩽110; 0 (blue line): creatinine <96 μmol/L, AST <68 IU/L, and P/F >110. Time in days. A value of P < .05 was considered statistically significant. AST indicates aspartate aminotransferase; P/F, O₂ partial pressure/O₂ inspired fraction ratio.

Figure 3.

Prediction model of 3-month mortality by segmentation tree (Classification and Regression Tree analysis) according to creatinine level, AST level, and P/F ratio. A value of P > .05 is significant and means predictive value improvement of the step. AST indicates alanine aminostransferase; NSv, 3-month non-survivors; P/F, O₂ partial pressure/O₂ inspired fraction ratio; Sv, 3-month survivors.