This study evaluated the association between GluCV within 3 days after ICU admission and 28-day all-cause mortality, ICU mortality and hospital mortality in patients with ARDS. Our findings revealed that ARDS patients in high GluCV (> 22.80%) group had a higher risk of 28-day mortality compared to other two groups after covariate adjustments. Besides, the short-term mortality (28-day all-cause mortality, ICU mortality and hospital mortality) increased as the GluCV levels increased. In addition, subgroup analysis showed that high GluCV (> 22.80%) was associated with 28-day mortality compared to low tertile of GluCV in ARDS patients without diabetes or with lower levels of mean glucose within 3 days (< 140mg/dl) after ICU admission. These results indicated that GluCV is an independent risk factor for 28-day mortality in ARDS patients, especially in those without diabetes or with lower levels of mean glucose within 3 days (< 140mg/dl) after ICU admission.
In this study, hyperglycemia (> 140 mg/dL) at ICU admission was presented in 54.0% of ARDS patients, and 56.0% of those did not have a history of diabetes. This phenomenon is similar to that observed in critically ill patients. Farnoosh Farrokhi et al.[3] summarized that 40% of critically ill patients have hyperglycemia, and 80% of these patients were without history of diabetes. It suggests that stress-induced hyperglycemia is also common among patients with ARDS.
This study found that higher GluCV was an independent risk factor for short-term mortality in ARDS patients. This is consistent with the findings of two previous study. Chiara Lazzeri et al. [26]analyzed clinical data from 83 patients with COVID-19-related ARDS, and the results indicated that non-survivors of COVID-19-related ARDS exhibited significantly higher GV within the first 48 hours of ICU admission. Bojan Hartmann et al.[27] collected all fasting blood glucose measurement data from COVID-19-related ARDS patients during their ICU stay to calculate GluCV. They found that high GluCV during ICU admission was significantly associated with increased 30-day all-cause mortality in Covid-19 ARDS patients. However, these two studies were conducted in COVID-19-related ARDS patients. This may be different from the mechanism in this study. For patients with COVID-19, acute elevation of blood glucose promoted the binding of SARS-COV2 to ACE2, which facilitated viral invasion of cells and may lead to a more severe disease[28]. This study is a retrospective study based on the MIMIC-IV database, which contains clinical data of critically ill patients admitted to the ICU between 2009 and 2018. Therefore, this study could have a more accurate assessment of the relationship between GV and ARDS mortality for avoiding COVID-19-related potential confounding factors. The fluctuation in blood glucose levels is associated with endothelial cell apoptosis[20], endothelial dysfunction[15], oxidative stress[13], and inflammation-related processes[29], which exacerbate damage to the alveolar-capillary barrier in ARDS patients. This may be the reason why higher GluCV increased the risk of 28-day mortality in ARDS patients in this study. Furthermore, Bojan Hartmann et al.[27] calculated GluCV using all measurements of blood glucose during ICU stay. However, over an extended period, levels of blood glucose may be influenced by more clinical interventions, such as the use of insulin and supplementation of enteral and parenteral nutrition, resulting in less accurate predictive outcomes. In this study, GluCV was calculated using blood glucose measurements within 3 days after ICU admission. Therefore, it could be obtained simply and be more reproducible and accurate to predict the prognosis of ARDS patients in clinical practice. Besides, in this study we identified patients with ARDS by the new global definition and the 2012 Berlin definition and performed same data analyzed in these two cohorts. And the both of two results suggested that higher level of GluCV associated with worse 28-day survival. It indicated that GluCV may have great universality and stability for prognostic assessment in patients with ARDS.
In subgroup analysis, we found that GluCV was not associated with 28-day mortality in ARDS patients with average blood glucose levels within 3 days after ICU admission more than 140mg/dl or those with history of diabetes. Conversely, compared to low GluCV, high GluCV (> 22.80%) was positively associated with 28-day mortality in ARDS patients with average blood glucose levels within 3 days after ICU admission less than 140mg/dl or those without history of diabetes. This is consistent with previous studies. In a retrospective study, James Stephen Krinsley[30] investigated the impact of diabetes or its absence on GluCV as a risk factor for mortality and found that in critically ill patients without history of diabetes, high GluCV (> 50%) was associated with an increased risk of mortality [OR (95% CI), 2.12 (1.23–3.65)], while in the population with history of diabetes, high GluCV (> 50%) was not independently associated with mortality. It suggested that patients with diabetes may develop relative tolerance to cellular and microvascular complications associated with moderate to high levels of blood glucose. In contrast, the same degree of hyperglycemia may cause greater stress response in critically ill patients without history of diabetes. Additionally, GV reflects fluctuations in blood glucose, and high glycemic variability may lead to severe hyperglycemia or hypoglycemia. It is believed that hypoglycemia is more harmful than hyperglycemia[31], which may explain the differential effect of GluCV on mortality between patients with average blood glucose levels within 3 days after ICU admission below 140mg/dl and those above 140mg/dl. In summary, GluCV may be a better predictor of prognosis in ARDS patients with blood glucose levels below 140mg/dl or without history of diabetes.
This study is the first to report the association between GluCV and 28-day mortality in non-COVID-related ARDS patients identified respectively by two different definitions. The calculation of GluCV requires at least three blood glucose measurements. Repeated blood glucose measurements are often performed in critically ill patients during ICU stay. Therefore, GluCV is an available and simple indicator. This study explored the association between GluCV within 3 days after ICU admission and 28-day mortality, which allowed clinician for obtaining GluCV in a short period of time. This study provides additional information for ARDS prognosis prediction. However, this study has several limitations. Firstly, due to database limitations, we were unable to attain the fasting time of the patients. Thus, each blood glucose record in this study should be considered as random blood glucose. Secondly, MIMIC-IV database lacks data on biomarkers of inflammation, endothelial damage, and oxidative stress. Therefore, we explained the reason for association between high GluCV and increased risk of 28-day all-cause mortality in ARDS patients based on previous literature, and it is still hypothetical and requires further investigation through appropriately designed studies. Finally, this study is a single-center, retrospective cohort study. Our findings need to be validated in external populations.