- Critical Care of H1N1 Influenza A Patients.
The scenario most feared in planning for pandemic influenza involves shortages—of ventilators, intensive care unit (ICU) beds, antiviral drugs, and vaccines. Reports now emerging from the Southern Hemisphere, where the flu season is over, and a few other areas, are beginning to paint a clearer picture of both the clinical manifestations of severe H1N1 influenza disease and actual utilization of critical care resources. This picture suggests that as H1N1 influenza spreads in the U.S., the best approach for managing ICU resources may be to create regional centers equipped to deal with the minority of patients who are too ill to be managed by conventional ICU measures.
Utilization of Critical Care Services in the Southern Hemisphere
- 92.7% were under 65 years of age; this confirms the known age distribution of infection.
- 9.1% were pregnant women.
- 65% required mechanical ventilation.
- 20% had a bacterial co-infection.
- 14% died and 16% remained hospitalized, as of September 7, 2009.
- Median length of stay was 8 days.
A separate report, published in JAMA, details the experience in Australia and New Zealand with 68 influenza patients who were treated with extra corporeal membrane oxygenation (ECMO).2 These patients were the most severely ill, and 14 (21%) succumbed to their illness—a mortality rate lower than the 30% to 48% mortality rate seen in other ARDS cases requiring ECMO.
The Mexican ICU Experience
An observational study of 58 critically ill Mexican patients—comprising 6.5% of hospitalized patients at 6 centers—was also published in JAMA.4 As with other studies, several features in common were noted, including a median patient age of 48 years and obesity in 36% of patients. Medical histories revealed the following:
- 95% of patients received antibiotics; 78% received targeted antiviral therapy.
- 2 patients received activated protein C.
- 54 of 58 patients (93%) required mechanical ventilation; 2 patients required prone positioning.
- 1 patient required HFOV (other rescue therapies were not used).
- 4 patients had secondary bacterial pneumonia.
- Excluding those who died within 72 hours, survivors were 7.4 times more likely to receive appropriate antiviral therapy
- 41% of patients had died by 60 days from admission.
The Canadian ICU Experience
In addition to the data from Mexico, JAMA also published details on 168 critically ill patients with probable and confirmed cases of 2009 H1N1 influenza A disease from 38 Canadian ICUs. Important features include the following:
- Median age was 32 years.
- 25% of patients were Aboriginal Canadians, a community that was similarly disproportionately affected by the 1918 influenza pandemic.
- 24% of patients were morbidly obese.
- 81% required mechanical ventilation on the first day of ICU admission.
- 31% were administered inhaled nitric oxide; 12% required HFOV; 4% required EMCO, and 3% prone positioning.
- 33% of patients were administered vasopressors on their first day in the ICU.
- 91% received antiviral therapy; 99% received antibiotics.
- 51% received corticosteroids.
- 17% (29) of patients died.
The Michigan ICU Experience
In July, the MMWR reported on the University of Michigan’s experience with 10 patients with ARDS due to 2009 H1N1 influenza virus. Important aspects of these cases include:
- All patients initially required sophisticated mechanical ventilation strategies, including bilevel ventilation or high frequency oscillatory ventilation (HFOV). ECMO was initiated in 2 of those patients.
- 60% required continuous renal replacement therapy.
- 100% required tracheostomy.
- 90% required vasopressors.
- No bacterial co-infections were identified.
- 30% of case patients died.
- How Will Critical Care be Delivered?
- Bacterial Co-infection seen in only 30% of Cases
Unlike its predecessor, the 1918 H1N1 influenza virus, the 2009 H1N1 virus does not carry an alarmingly high rate of bacterial co-infection, according to a report published in the MMWR. Of 77 fatal cases studied by the CDC, 29% displayed evidence of bacterial co-infection. Several organisms were isolated (see table). Most notably, pneumococcus was the most prevalent pathogen isolated underscoring the potential importance of both the Pneumovax and Prevnar vaccines.
|Pathogen||Percentage of Cases of Co-infection|
|Streptococcus pneumoniae (pneumococcus)||45%|
| Streptococcus pyogenes
(Group A streptococcus)
| Streptococcus mitis
(viridians group streptococci)
- In the 1918 influenza pandemic, the majority of victims succumbed to bacterial superinfection with community-acquired pneumonia pathogens. In the modern era in which multi-drug resistant pathogens are a major concern, a report from Hong Kong describing a fatal case of influenza complicated by ca-MRSA is particularly noteworthy.
- Another alarming development is the report of mutations in the PB2 gene of influenza detected in Netherlands, a hallmark of increasing transmission fitness.
- In the weeks ahead tracking both ca-MRSA co-infection as well as the accumulation of virulence enhancing mutations will be important components of managing the pandemic.
- Many institutions have now begun to roll out their seasonal flu vaccine–which does not contain the 2009 H1N1 strain–but the Canadian province of Quebec has decided against this campaign and has decided to put all flu vaccination efforts towards the 2009 H1N1 vaccine. This is an interesting development because it reflects the difficulty of vaccine planning as the 2009 pandemic has, for all intents and purposes, rendered other flu strains obsolete for this season.
- The Southern Hemisphere, which is just emerging from their flu season, has received word from the WHO regarding the strain selection for the 2010 vaccine.
- As the spread of H1N1 continues, China has begun rolling out a vaccination campaign (alertnet.org) while new data from the US pediatric vaccine recipients has been released (Medical News Today).
- Other interesting clinical developments include the findings of increased rates of myocardial infarctions in influenza patients (The Lancet).
Friday, Sept 18, 2009