Addition of lactic acid levels improves the accuracy of quick sequential organ failure assessment in predicting mortality in surgical patients with complicated intra-abdominal infections: a retrospective study

Sepsis has been a major cause of death for many decades in critically ill patients worldwide [1, 2]. Despite its high morbidity and mortality, there is no diagnostic gold standard test for sepsis. For the past decade, sepsis had been defined as a systemic inflammatory response syndrome (SIRS) by the host to an infection [3]. Owing to advances in our understanding of the pathophysiology of sepsis, a 2016 consensus conference redefined sepsis as “life-threatening organ dysfunction caused by a dysregulated host response to infection” [4].

Based on this new definition, sepsis is now diagnosed when a ≥ 2-point change occurs in the sequential organ failure assessment (SOFA) score because of an infection. However, due to the complex nature of the SOFA score, the 2016 task force introduced quick SOFA (qSOFA) for the rapid identification of patients at a high risk of mortality in the setting where all components of the SOFA score cannot be measured [4]. The qSOFA score includes (1) systolic blood pressure (SBP) ≤ 100 mmHg, (2) respiratory rate (RR) ≥ 22 breaths/min, and (3) an altered mental status (AMS). The total qSOFA score ranges from 0 to 3. Despite its simplicity, qSOFA showed better accuracy than SIRS criteria for predicting patient mortality in non-intensive care unit (ICU) settings in many studies [5‐7]. However, others have questioned its utility as a quick screening tool due to its poor sensitivity [8‐10].

Because of the limited sensitivity of qSOFA, we performed this study based on three assumptions. First, qSOFA alone has a poor sensitivity for predicting mortality in patients with complicated intra-abdominal infections. Second, plasma lactate levels have been shown to have a strong association with mortality in critically ill patients [11‐13]. Therefore, the combination of the qSOFA score with a score based on lactate levels should have a better prognostic performance than qSOFA alone. Finally, the combination score should have a prognostic performance comparable to that of the full SOFA score. The aim of this study was to compare the performance of qSOFA with a combined score derived from qSOFA and serum lactate levels for predicting in-hospital mortality in surgical patients with complicated intra-abdominal infections.

Our study results showed that the qSOFA alone has a poor sensitivity and a modest predictive performance. There are rising concerns on the poor sensitivity of qSOFA, despite its high specificity, and potential delays in identification and resuscitation for patients at a high risk of mortality [16]. The addition of one point for hyperlactatemia (plasma lactate level > 2.0 mmol/L) resulted in improved sensitivity with a slightly decreased specificity. The addition of the use of serum lactate levels to the qSOFA improved the predictive performance significantly, increasing it to a level comparable to that of the full SOFA. The strengths of the qSOFA include its simplicity, rapidity, and ease of performance for all health care providers without requiring complicated equipment or laboratory results. However, after the qSOFA was introduced, we observed that surgical patients who required emergency gastrointestinal surgery rarely presented to the ED with AMS. In a study of ED patients with suspected infection conducted by Williams et al. [8], only 5.1% of patients had AMS, while 21.1% of patients had a respiratory rate ≥ 22 breaths/min, and 26.8% had a systolic blood pressure ≤ 100 mmHg. Our study also demonstrates that only 15 patients (3.3%) in our study population (457 patients) had AMS. In this population of patients, the most common presentation was abdominal pain with hypotension and tachypnea. The tachypnea was thought to be because of shallow respirations caused by diffuse peritoneal irritation in some patients. Because so few patients presented to the ED with AMS, only 17% of our patients had a qSOFA score ≥ 2, making it difficult to identify and screen patients at a high risk of mortality. In our study group, 27 patients with a qSOFA score < 2 did not survive. Other studies have emphasized the poor sensitivity of qSOFA as a screening test for sepsis [8, 9].

To improve the sensitivity of qSOFA, we analyzed several combination scores including qSOFA and diagnostic markers of inflammation, such as C-reactive protein, white blood cell count, delta neutrophil index, and plasma lactate concentration. As suggested in many studies, plasma lactate concentration is an important predictor of mortality in critically ill patients [11‐13]. Plasma lactate concentration alone with a cutoff value of 2 mmol/L did not show a good predictive performance in our study, but when combined with qSOFA, it was the best predictor of in-hospital mortality in our study population.

The rapid point-of-care measurement and accuracy of plasma lactate levels is an important advantage [17]. Singer et al. reported that an early bedside point-of-care (POC) lactate evaluation in the ED was associated with the early administration of intravenous fluid resuscitation and improved mortality in patients with suspected sepsis [18]. The use of plasma lactate levels improves the discriminatory ability of qSOFA without complicating its use as a quick and simple screening method.

The association between full SOFA scores and patient mortality has been confirmed in previous studies [5, 19‐21]. However, the calculation of the full SOFA score is time-consuming since many laboratory values and a significant amount of clinical information are needed. Therefore, the use of full SOFA scores is only suited for patients in an ICU environment. The use of the qSOFA + lactate score is a simple and rapid way to screen patients at high risk of mortality in pre-ICU, such as in the ED, or even in pre-hospital settings with a predictive performance comparable with that seen with the full SOFA score. The use of the qSOFA + lactate score will assist clinicians in immediately assessing the risk of mortality in patients with suspected intra-abdominal infection, allowing more rapid resuscitation and control of the infective source and reducing patient mortality.

The qSOFA score alone has poor sensitivity in screening surgical patients presenting to the ED with a high risk of mortality. Combining the qSOFA score with an additional one point for hyperlactatemia has a better predictive performance with higher sensitivity for patient mortality than that seen with qSOFA alone and comparable to that seen with full SOFA.