This study evaluated whether serum lactic acid and cholesterol could predict mortality in patients with septic shock. The study cohort consisted of patients suffering from septic shock, as defined by the International Consensus on Sepsis-3. This study found that initial lactate levels are associated with 90-day mortality in patients with septic shock. This finding is consistent with other recent data [8, 13]. Based on the latest definition of septic shock, previous studies which evaluated the effect of cholesterol on the prognosis of patients with septic shock are limited and inconsistent. This study found that higher serum total cholesterol levels are beneficial to patients suffering from septic shock.
It is generally believed that low serum lipid levels are beneficial as the risk of cardiovascular disease is reduced. However, in recent years, studies have shown that low serum lipid levels are significantly correlated with patient mortality [14, 15]. In the early stages of a critical illness, the concentration and composition of lipids and lipoproteins in ICU patients change profoundly [16, 17]. Studies have shown that infection or inflammatory response syndrome can cause a significant decrease in total cholesterol levels along with LDL and HDL levels [18, 19]. This study found that the content of total cholesterol and the concentrations of LDLs and HDLs were significantly lower than the normal values in patients who met the definition of septic shock, according to Sepsis-3 [7]. In patients with sepsis and septic shock, rapid changes in serum lipid levels are closely related to clinical prognosis [20, 21]. Furthermore, HDL and LDL play an important role in removing bacterial toxins. In vitro studies have shown that lipopolysaccharides of gram-negative bacteria combine with HDL (60%) and LDL (25%). Therefore, low HDL and LDL concentrations increase the risk of a poor prognosis in sepsis patients due to the body’s inability to remove bacterial toxins from the bloodstream [9].
Interestingly, this study did not demonstrate that a low HDL concentration is associated with a poor 90-day prognosis in patients with septic shock. Contrary to the results of a previous meta-analysis, lower HDL levels are associated with higher mortality in adult patients suffering from sepsis [22]. Such results are not entirely surprising; a randomized controlled study demonstrated that raised HDL levels have no benefit in protecting patients with myocardial infarction [23]. At the same time, studies have shown that under some chronic inflammatory conditions, such as metabolic syndrome and rheumatoid arthritis, and acute some acute inflammatory conditions, such as sepsis and myocardial infarction, HDL function is dysfunctional and pro-inflammatory [24–28]. Current evidence suggests that HDL function may be more important than quantity. Daniel et al. found that hypocholesterolemia is an independent risk factor for death in critically ill patients [29]. Sérgio et al. also proved that total cholesterol concentrations ≤ 2.48 mmol/L are an independent risk factor for a poor prognosis in patients with acute kidney injuries [30]. The results of this study indicate that a reduction in total cholesterol levels is significantly associated with an increase in mortality in patients with septic shock. To the best of our knowledge, this study is the first to suggest that a total cholesterol level < 2.42 mmol/L is an independent risk factor for 90-day mortality in patients with septic shock.
Lactic acid levels in patients who died as a result of septic shock were significantly increased. Blood lactic acid levels were therefore determined as a predictor of mortality in patients with septic shock. Blood lactic acid levels ≥ 4.4 mmol/L were associated with a higher mortality rate in patients suffering from septic shock [13]. Studies have shown that septic shock, as defined by Sepsis-3, reduces the sample size by 50% and increases the 28-day mortality rate compared to the previous definition [31]. Therefore, the prognostic value of blood lactic acid levels in patients with septic shock, as defined by Sepsis-3, will be of great significance to clinicians in lactic acid-led resuscitation [8]. Previous research found that early, goal-directed therapy can reduce the mortality of adults with severe sepsis and septic shock, and lactate-guided therapy is more effective than early target-oriented therapy [32]. In fact, in the current study, when used alongside cholesterol to predict prognosis, patients with a lactate level above the median and a cholesterol level below the median accounted for only 10% of surviving patients.
In this study, serum albumin levels of non-surviving patients with septic shock were significantly reduced. Serum albumin levels below 25 g/L were found to be associated with a higher mortality rate in patients suffering from septic shock. Previous studies have shown that serum albumin levels are related to the prognosis of critical illness, and the relationship between hypoproteinemia, inflammation, and malnutrition is indissoluble [33, 34]. Furthermore, it is known that serum albumin levels can be reduced by stress. Clinical studies have shown that albumin replacement does not improve the 28-day and 90-day survival rates in patients with severe sepsis compared to crystalloids alone [35]. Therefore, serum albumin may not be an indicator that accurately reflects the prognosis of patients with septic shock.
A survey of sepsis severity demonstrated that patients with septic shock had an APACHE II score of ≥ 20. Furthermore, deaths in patients over 60 years of age were significantly higher than in those under the age of 60 with an APACHE II score of < 20. These findings are consistent with previous research [36, 37]; however, this study further quantified the severity of the disease and the risk of death in patients suffering from septic shock. Previous studies have demonstrated that the majority of sepsis cases originate from primary lung infections [38, 39]. Furthermore, that patients are more likely to develop septic shock if their infection originated from the urogenital tract, abdomen, or blood [40]. The mortality rate of those suffering from a primary bloodstream infection is higher than that of patients whose primary infections did not originate from the blood [41]. This study shows that the 90-day prognosis of patients with septic shock originating from a urogenital tract infection is better than that of patients with infections which originated from other regions.