Risks/Mortality/Outcomes
Clinical characteristics and outcomes of patients with 2009 influenza A(H1N1) virus infection with respiratory failure requiring mechanical ventilation

https://doi.org/10.1016/j.jcrc.2010.05.031Get rights and content

Abstract

Purpose

The purpose of the study was to describe the clinical characteristics and outcomes of critically ill patients with 2009 influenza A(H1N1).

Methods

An observational study of patients with confirmed or probable 2009 influenza A(H1N1) and respiratory failure requiring mechanical ventilation was performed.

Results

We studied 96 patients (mean age, 45 [14] years [mean, SD]; 44% female). Shock and acute respiratory distress syndrome were diagnosed during the first 72 hours of admission in 43% and 72% of patients, respectively. Noninvasive positive pressure ventilation was used in 45% of the patients, but failed in 77% of them. Bacterial pneumonia was diagnosed in 33% of cases, 8% during the first week (due to community-acquired microorganisms) and 25% after the first week (due to gram-negative bacilli and resistant gram-positive cocci). Intensive care unit mortality was 50%. Nonsurvivors differed from survivors in the prevalence of cardiovascular, respiratory, and hematologic failure on admission and late pneumonia. Reported causes of death were refractory hypoxia, multiorgan failure, and shock (50%, 38%, and 12% of all causes of death, respectively).

Conclusions

Patients with 2009 influenza A(H1N1) and respiratory failure requiring mechanical ventilation often present with clinical criteria of acute respiratory distress syndrome and shock. Bacterial pneumonia is a frequent complication. Mortality is high and is primarily due to refractory hypoxia.

Introduction

The emergence of pandemic influenza caused by the novel 2009 influenza A(H1N1) virus has posed enormous challenges to the public health system and to clinicians. It is estimated that about 0.3% of infected cases require hospital admission and 20% of them will require intensive care unit (ICU) admission, with the subsequent strain on critical care resources in the affected areas [1], [2], [3], [4].

The disease spectrum caused by this virus in humans is still not well known, and it seems to differ importantly from that of seasonal influenza. Previous reports have analyzed clinical characteristics of patients with infection by the 2009 influenza A(H1N1) virus that required critical care [1], [2], [5], [6], [7]. Information on the clinical profile of critical illness is of great importance to identify risk factors, define the time course of organ dysfunction in survivors vs nonsurvivors, compare outcomes between centers, monitor mortality changes over time, and describe geographical differences in the clinical features of the disease.

We here report the clinical characteristics, treatments, and outcomes of critically ill adults with the diagnosis of 2009 influenza A(H1N1) necessitating ICU admission because of respiratory failure requiring mechanical ventilation.

Section snippets

Patients and methods

We included in the study patients older than 18 years with the diagnosis of confirmed or probable 2009 influenza A(H1N1) virus infection, as defined by the World Health Organization [4], admitted to ICUs from 10 centers in Chile and Uruguay with respiratory failure requiring mechanical ventilation. Ethics Committee approval was granted by Hospital Universitario de Getafe and by all of the 10 recruiting centers.

Characteristics of study patients and laboratory findings on admission

During the study period, 96 patients (65 [68%] from Chile, 31 [32%] from Uruguay) were admitted to the participating ICUs with the diagnosis of confirmed (n = 77) or probable (n = 19) 2009 influenza A(H1N1) virus infection and respiratory failure requiring mechanical ventilation (Table 1). There were no differences in demographic or outcome measurements between patients with confirmed or probable infection. Patients were young adults, only 7% of patients being older than 65 years (Fig. 1). Most

Discussion

In our study, patients with 2009 influenza A(H1N1) and respiratory failure requiring mechanical ventilation were characteristically young adults, often presenting some serious comorbidity, with a high prevalence of obesity and a time course characterized by severe acute respiratory failure and often shock. Mortality is high and is most frequently due to refractory hypoxia.

The clinical profile of patients with 2009 influenza A(H1N1) seems to differ from seasonal influenza [9], [10], [11], [12],

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