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Intensive Care Outcomes During the H1N1 Influenza Pandemic

By Amesh A. Adalja, MD, FACP

Knowledge of the clinical course of severe influenza and its management—which takes place almost exclusively in intensive care units (ICUs)—should inform planning and decisions about care delivery and resource allocation during pandemics. A new article by authors from the CDC1 provides detailed descriptions of ICU care provided to patients during the 2009 H1N1 influenza pandemic. The results provide information essential to planning for future pandemics and influenza seasons.  

Case Characteristics

The authors employed 2 national 2009 H1N1 case series that included data from 34 states. They selected 154 patients (30% of hospitalizations) with PCR-confirmed influenza who were admitted to ICUs for further study. Important subject features included the following:1

  • 77% were <50 years old

  • 40% were admitted to the hospital within 2 days of illness onset

  • 64% were admitted to the ICU on the same day as admission

  • 65% had at least one underlying medical condition, with neurologic disease most common in children and asthma in adults

  • 7% were pregnant, the majority were in the third trimester

  • 27% of adults were morbidly obese

  • Median ICU stay was 4 days

Not surprisingly, the majority (83%) of patients received antiviral therapy, almost exclusively with oseltamivir. However, the median time from onset of illness to receipt of antiviral therapy was 4 days, and 35% of patients were treated 6 or more days after illness onset.1

Mechanical Ventilation

Of those admitted to the ICU, 58% underwent mechanical ventilation and were, accordingly, more likely to have pneumonia and die as compared to those who did not require mechanical ventilation. Thirty-eight percent of the study subjects had ARDS, with the following features noted:

  • Longer time from disease onset to admission

  • More likely to be morbidly obese

  • More likely to have pneumonia

  • More likely to die

  • Less likely to have received antiviral therapy within 2 days after admission1

Early Antivirals Save Lives

Perhaps the most notable lesson to be learned from this study is the importance of initiating antivirals promptly to stave off development of ARDS. The patients in the study cohort who received treatment within 5 days of illness onset were less likely to develop ARDS; after 6 days, antivirals appeared to have had no effect in preventing ARDS. Prevention is of paramount importance because ARDS directly affects mortality: in this cohort, the mortality rate was 48% among patients who developed ARDS and 8% among those who did not. This finding reinforces the need for early administration of antiviral therapy to a wide segment of the population during an influenza pandemic (and likely during seasonal influenza as well) to prevent grave complications.

Regionalized Critical Care

The results of this study also lend credence to the notion of regionalizing care for the critically ill during pandemics. Most of the ICU patients in this study needed mechanical ventilation. There is evidence to suggest that patients' outcomes are improved with treatment in medical centers that manage a high volume of ARDS patients. Those centers provide the ready access to highly specialized critical care clinicians and technologies that are associated with lower mortality rates.2,3 Regionalization would guarantee that the sickest patients receive care at those centers with adequate levels of expertise to meet the needs of the critically ill.


  1. Bramley AM, Dasgupta S, Skarbinski J, et al. Intensive care unit patients with 2009 pandemic influenza A (H1N1pdm09) virus infection-United States, 2009. Influenza and Other Respiratory Viruses 2012. Accessed June 13, 2012.

  2. Kahn JM, Goss CH, Heagerty PJ, et al. Hospital volume and the outcome of mechanical ventilation. NEJM 2006; 355:41-50.

  3. Wallace DJ, Angus DC, Barnato AE, et al. Nighttime intensivist staffing and mortality among critically ill patients. NEJM 2012; 366:2093-2101.