Letter re: Letter to the Editor: Obesity Does Not Increase Risk for Mortality in Severe Sepsis Trauma Patients

We read with great interest the study by Tay-Lasso et al regarding the impact of obese body habitus on outcomes in trauma patients with severe sepsis. ¹ This study offers impactful findings with a thoughtful discussion of the potential influence of these findings. We commend the authors’ contributions through their excellent efforts in exploring a crucial topic in trauma research. With this letter, we intend to offer our thoughts, raise a few concerns, and suggest recommendations about this study to guide future research efforts.

Regarding the methods of this study, Tay-Lasso et al collected data from the American College of Surgeons Trauma Quality Improvement Program (ACS-TQIP) dataset but elected to only include data from the year 2017. Including additional years would have allowed for an overall larger sample size across all groups and greater statistical power for analyses. Regarding inclusion and exclusion criteria, patients were included in the study if they met the criteria for severe sepsis. However, the investigators do not specify when or where the diagnosis of sepsis was made. Given that the timing of treatment initiation can significantly impact mortality in patients with sepsis, the lack of this data may have affected their findings. ² Additionally, the authors decided to exclude patients with an Abbreviated Injury Scale (AIS) grade for the head ≥3, thus potentially excluding patients with severe head trauma. It would have been preferential to either control for patients with severe head trauma or include this patients’ population and stratify by AIS head grade to observe the potential impact of severe head trauma in patients with severe sepsis.

The study also divided patients into 2 groups of trauma patients with severe sepsis: non-obese (BMI <30) and obese (BMI ≥30). If all patients with a BMI <30 were included in the non-obese group, then both underweight (BMI <18.5) and overweight (BMI 25–29.9) patients were included in this group for the primary analysis. It would have been more appropriate for the authors to stratify by traditional BMI categories (underweight, normal weight, overweight, obese, etc.) especially given that they have conducted subset analyses for morbidly obese patients as some studies have shown increased mortality rates in underweight patients with sepsis. ³ Also, the sub-analyses of this study observed mortality rates in differing BMI classes, however, they did not disclose the sample size for each of these subgroups. If these subgroups consisted of smaller sample sizes, it may have affected the overall reliability and validity of these findings. Thus, this information should be provided for clarity. Additionally, the investigators state that the primary outcome of this study is mortality, however, the type/timing of mortality (24-hour mortality, in-hospital mortality, 30-day mortality, etc.) is not specified. As the timing of mortality is critical to the interpretation of the investigators’ main findings that there was a similar risk for mortality among varying degrees of obesity when compared to non-obese patients, the type and timing of mortality should have been specified.

When conducting their statistical analyses, although vital signs were adjusted for, only the systolic blood pressure is defined in the methods, the parameters for heart rate and respiratory rate are not clearly defined. The systolic blood pressure used in this study was described as the lowest systolic blood pressure in 24 hours. Rather than using the lowest value in a 24-hour period, it may have added additional value to include initial emergency department vital signs in the assessment and definition of potential sepsis and progression to sepsis. Some comorbidities were also adjusted for, however, there is no mention of the use of the Charlson Comorbidity Index to ensure accurate controlling for the included comorbidities. Interestingly, although data were collected for age, chronic obstructive pulmonary disease, and smoking status, these variables were not adjusted for in the study analysis model. Had this been performed, it could have significantly impacted the validity of the results of this study. Recent evidence indicates that current smoking is associated with increased length of hospital stay, need for mechanical ventilation, and increased mortality in patients with severe sepsis. ⁴ As there were more smokers in the non-obese group, this could have severely impacted the outcomes in this group. Other variables that could have been adjusted for to eliminate any confounding bias include or may include sex, emergency medical services (EMS transport time), emergency department length of stay, whether patients underwent a surgical intervention or not, mechanism of injury (blunt or penetrating), and type of injury, most of which are available in the ACS-TQP PUF dataset. Furthermore, adjusting and controlling for Intensive Care Unit length of stay (ICU-LOS) in the analysis model, given that this was defined as one of the study’s main outcomes, may have significantly skewed the results. Rather than eliminating the effects of ICU-LOS on sepsis progression and outcomes, it would have been more appropriate to assess if ICU-LOS as an independent factor would influence sepsis and other associated outcomes among study groups.

In the discussion of their results, the authors omitted some findings that are worthy of mention. First, in their analysis of patients with severe sepsis who had a BMI <30 compared to those who had a BMI ≥30, it was found that the obese group had an increased incidence of complications, including acute kidney injury, acute respiratory distress syndrome, and cardiac arrest with cardiopulmonary resuscitation. Second, sub-analyses were conducted to compare mortality rates amongst different weight classes to patients with a normal BMI, defined as a BMI of 18.5–25. In the sub-analysis that included only patients with an ISS >15, morbidly obese patients (BMI ≥40) were found to have a significantly increased risk for mortality when compared to patients with a normal BMI (OR: 2.396, CI: 1.45–3.94, P = .001). The other sub-analysis conducted was a multivariate logistic regression analysis which although not statistically significant, still demonstrated an increased risk for mortality in morbidly obese patients when compared to patients with a normal BMI (OR: 1.448, CI: 1.01–2.07, P = .44). Despite these findings, the authors conclude that all weight classes of patients with severe sepsis are at a similar risk for mortality. Given these findings, it is not completely accurate to suggest that morbidly obese trauma patients are at a similar risk for mortality from severe sepsis compared to trauma patients with a lower BMI.

Lastly, although highlighted in the limitations, the inclusion of variables in the study analysis model such as the type and timing of antibiotics therapies administered in the emergency department or following hospital admission, the type, volume, and timing of fluid resuscitation, and whether patients underwent surgical intervention, some of which are available in ACS-TQP PUF dataset, and as the rapid administration of antibiotics in sepsis is associated with a decreased risk for in-hospital mortality, the inclusion of this data would have added significant value to the study findings and their clinical implications. ²

Despite these concerns, the study by Tay-Lasso et al still offers valuable insight into the impact of obesity on outcomes in trauma patients with severe sepsis. It is our hope that their investigation will encourage future studies to further investigate this important topic and ultimately improve the quality of care for these patients’ population.