Outcome of severe sepsis in the ICU is independent of haemoglobin levels

Introduction

In this observational cohort study we attempted to elucidate a haemoglobin (Hb) target that favours the mortality outcome in severe sepsis patients. The optimum level of Hb to influence outcome in severe sepsis is yet to be determined. Although the analysis of severe sepsis patients in the Canadian transfusion requirement in critical care study [1] did not find any mortality benefit with a Hb level of 10 g/dl or above, the early goal-directed therapy trial [2] showed significant mortality benefit by achieving haematocrit ≥ 30%, equivalent to a Hb value of 10 g/dl, during the early treatment period. This pilot study was therefore undertaken to look for any relationship between Hb levels and mortality in severe sepsis patients admitted to the ICU.

Methods

All patients 16 years or older with severe sepsis or septic shock who stayed longer than 24 hours between July 2006 and June 2007 were retrospectively included in the study. Patient demographics, Hb levels measured by the blood gas analyser during their period of severe sepsis and outcome data were collected. Binary logistic regression analysis was performed with ICU survival and 28-day survival as the dependent variables.

Results

Of the 62 patients enrolled in the study, the average age was 66.8 years (16 to 87 years), with mean admission APACHE II score and Simplified Acute Physiology Score II being 18 (8 to 30) and 58 (17 to 78), respectively. Their ICU and 28-day mortality rates were 35.5% and 41.9%, respectively. On analysis no significant relationship was found between average Hb, Hb variation, minimum Hb, maximum Hb, and number of units transfused with ICU or 28-day survival. In addition, no significant relationship was found between Hb falling below thresholds of 7, 8, 9, or 10 g/dl, or variation from an Hb of 7, 8, 9, 10 g/dl during severe sepsis and the ICU survival or 28-day survival.

Conclusion

While a haematocrit of 30% represents a physiological optimum between viscosity and oxygen carriage, the equivalent Hb from this pilot study shows no advantage in the outcome of severe sepsis. This study suggests that any effect Hb levels may have on the outcome from severe sepsis is likely to be small.