There are an estimated 571,000 cases of severe sepsis that present to United States emergency departments (EDs) each year, with an unacceptably high mortality rate between 20% and 50% (1
). Early identification of the “at-risk” patient represents a challenge to the ED physician, as the presentation of sepsis is often subtle and difficult to assess. Although there is no universally accepted gold-standard screening test, the measurement of serum lactate level is useful for the identification of ED patients at increased risk of mortality from sepsis (3
). The Surviving Sepsis Campaign, an international, multidisciplinary consensus effort, endorses obtaining a serum lactate as one of its core sepsis bundles (6
). Additionally, the use of similar markers of hypoperfusion, namely low pH and base excess, have been proposed but not previously well studied. The identification process of patients at increased risk of adverse outcome is important, as septic patients benefit from early and aggressive resuscitation protocols (1
In order for a blood lactate level to provide utility for clinical decision-making, an accurate result must be readily available in a timely fashion. A major problem in obtaining accurate blood lactate levels relates to sample handling before analysis. Once the blood sample is drawn, lactate levels continue to rise in the sample as the result of red blood cell metabolism. If the sample can be analyzed immediately, the effect is minimal. But, if the sample needs to be transported to a central laboratory or requires centrifugation before analysis, the delay results in falsely elevated lactate levels. From a practical standpoint, one may divide the currently available lactate methods into three groups: 1) standard enzymatic spectrophotometric methods, performed with blood collected in special preservative tubes, requiring centrifugation; 2) electrode-based amperometric methods, performed on anticoagulated whole blood but which may require transport to a laboratory (see Methods); 3) electrode-based amperometric methods, performed on whole blood at the bedside (see Methods) For the first method, delays are unavoidable, thus the recommendation that samples be collected in tubes that minimize red cell metabolism (e.g., so-called “gray-top” tubes containing NaF). Due to the need for transportation, centrifugation, and typical instrument analysis times, turnaround times are often 2–3 h (or longer). For the electrode-based methods, centrifugation is not required and analysis time is minimal (<5 min). For the second method, though, actual turn-around time may be prolonged significantly by transportation delay; during those delays, lactate levels will rise, potentially significantly. As a result, there are criticisms of this methodology, but it was, in fact, the method used in many of the studies establishing blood lactate as a valuable ED risk stratification tool for patients with infection (3
). With a turnaround time of typically 30 min or less, this is within a time frame that is useful for clinical decision-making. The third method, point-of-care lactate, offers the advantage of rapidly available results at the bedside with reduced time-to-assay that would potentially reduce time for in vitro metabolism; however, its feasibility and reliability is relatively unproven in this setting.
Because conventional measurement in a central laboratory is not available in all institutions, or may be associated with significant delays, a rapid and accurate point-of-care (POC) test could contribute to improved and timely care of the septic patient. Accordingly, we undertook this study to determine if a POC device would be reliable in the ED for identification of patients at risk for adverse outcomes in sepsis. The objective of this investigation was to study the feasibility and accuracy of a POC analyzer capable of performing bedside serum lactate measurements in patients with suspected infection, and to determine if other POC acid-base measurements (pH, base excess) hold similar predictive ability.