The paradoxical effect of obesity on outcome in critically ill patients

The impact of obesity on sepsis mortality: a retrospective review

Background

Recent sepsis guidelines have focused on the early identification and risk stratification of patients on presentation. Obesity is associated with alterations in multiple inflammatory regulators similar to changes seen in sepsis, suggesting a potential interaction between the presence of obesity and the severity of illness in sepsis.

Methods

We performed a retrospective chart review of patients admitted with a primary billing diagnosis of sepsis at a single United States university hospital from 2007 to 2010. Seven hundred and ninety-two charts were identified meeting inclusion criteria. Obesity was defined as a body mass index (BMI) ≥ 30 kg/m². The data recorded included age, race, sex, vital signs, laboratory values, length of stay, comorbidities, weight, height, and survival to discharge. A modified APACHE II score was calculated to estimate disease severity. The primary outcome variable was inpatient mortality.

Results

Survivors had higher average BMI than nonsurvivors (27.6 vs. 26.3 kg/m2, p = 0.03) in unadjusted analysis. Severity of illness and comorbid conditions including cancer were similar across BMI categories. Increased incidence of diabetes mellitus type 2 was associated with increasing BMI (p < 0.01) and was associated with decreased mortality, with an odds ratio of 0.53 compared with nondiabetic patients. After adjusting for age, gender, race, severity of illness, length of stay, and comorbid conditions, the trend of decreased mortality for increased BMI was no longer statistically significant, however diabetes continued to be strongly protective (odds ratio 0.52, p = 0.03).

Conclusions

This retrospective analysis suggests obesity may be protective against mortality in septic inpatients. The protective effect of obesity may be dependent on diabetes, possibly through an unidentified hormonal intermediary. Further prospective studies are necessary to elaborate the specific mechanism of this protective effect.

Reporting the methodology of height and weight acquisition in studies of body mass index-based prognosis in critically ill patients

PURPOSE

Conflicting findings were reported on the body mass index (BMI)-based prognosis of critically patients. Errors in source weight and height data can confound BMI group allocation. The aim of the present work was to examine investigators' reporting on the methods of height and weight acquisition (HWA).

MATERIALS AND METHODS

PubMed and Embase databases were searched for studies describing BMI group-based risk of death in critically ill patients. Eligible studies were examined for reporting on (1) the use of measured and/or estimated HWA, (2) details of measuring devices, (3) device accuracy, and (4) methods of adjustment for acute and chronic fluid-related weight changes.

RESULTS

Thirty studies met the eligibility criteria, including 159,565 patients. No data were provided in 13 studies (52% of reported patients) on whether estimates or measurements were used for HWA. Measured HWA was used exclusively in 6 studies (3% of patients), and an unspecified combination of estimated and/or measured HWA was reported for the remainder. Only 1 study reported the specific devices used. None of the studies provided data on the bias and precision of measuring devices. Adjustment for chronic and/or acute fluid-related weight changes was addressed in 2 studies for each.

CONCLUSIONS

These findings demonstrate the prevalent risk for BMI group misallocation in the reviewed studies, which may confound BMI-based prognosis, raising concerns about the validity of reported BMI-related prognostic impact.

Effects of acute and chronic low density lipoprotein exposure on neutrophil function

Mounting evidence suggests that obesity and the metabolic syndrome have significant but often divergent effects on the innate immune system. These effects have been best established in monocytes and macrophages, particularly as a consequence of the hypercholesterolemic state. We have recently described defects in neutrophil function in the setting of both obesity and hypercholesterolemia, and hypothesized that exposure to elevated levels of lipoproteins, particularly LDL its oxidized forms, contributed to these defects. As a model of chronic cholesterol exposure, we examined functional responses of bone marrow neutrophils isolated from non-obese mice with diet-induced hypercholesterolemia compared to normal cholesterol controls. Chemotaxis, calcium flux, CD11b display, and F-actin polymerization were assayed in response to several chemoattractants, while neutrophil cytokine transcriptional response was determined to LPS. Following this, the acute effects of isolated LDL and its oxidized forms on normal neutrophils were assayed using the same functional assays. We found that neutrophils from non-obese hypercholesterolemic mice had blunted chemotaxis, altered calcium flux, and normal to augmented CD11b display with prolonged actin polymerization in response to stimuli. In response to acute exposure to lipoproteins, neutrophils showed chemotaxis to LDL which increased with the degree of LDL oxidation. Paradoxically, LDL oxidation yielded the opposite effect on LDL-induced CD11b display and actin polymerization, and both native and oxidized LDL were found to induce neutrophil transcription of the monocyte chemoattractant MCP-1. Together these findings suggest that chronic hypercholesterolemia impairs neutrophil functional responses, and these defects may be in part due to protracted signaling responses to LDL and its oxidized forms.

Obesity is associated with neutrophil dysfunction and attenuation of murine acute lung injury

Although obesity is implicated in numerous health complications leading to increased mortality, the relationship between obesity and outcomes for critically ill patients appears paradoxical. Recent studies have reported better outcomes and lower levels of inflammatory cytokines in obese patients with acute lung injury (ALI)/acute respiratory distress syndrome, suggesting that obesity may ameliorate the effects of this disease. We investigated the effects of obesity in leptin-resistant db/db obese and diet-induced obese mice using an inhaled LPS model of ALI. Obesity-associated effects on neutrophil chemoattractant response were examined in bone marrow neutrophils using chemotaxis and adoptive transfer; neutrophil surface levels of chemokine receptor CXCR2 were determined by flow cytometry. Airspace neutrophilia, capillary leak, and plasma IL-6 were all decreased in obese relative to lean mice in established lung injury (24 h). No difference in airspace inflammatory cytokine levels was found between obese and lean mice in both obesity models during the early phase of neutrophil recruitment (2-6 h), but early airspace neutrophilia was reduced in db/db obese mice. Neutrophils from uninjured obese mice demonstrated diminished chemotaxis to the chemokine keratinocyte cytokine compared with lean control mice, and adoptive transfer of obese mouse neutrophils into injured lean mice revealed a defect in airspace migration of these cells. Possibly contributing to this defect, neutrophil CXCR2 expression was significantly lower in obese db/db mice, and a similar but nonsignificant decrease was seen in diet-induced obese mice. ALI is attenuated in obese mice, and this blunted response is in part attributable to an obesity-associated abnormal neutrophil chemoattractant response.

The impact of comorbid [corrected] conditions on critical illness

OBJECTIVE

To review the current knowledge of common comorbidities in the intensive care unit, including diabetes mellitus, chronic obstructive pulmonary disease, cancer, end-stage renal disease, end-stage liver disease, HIV infection, and obesity, with specific attention to epidemiology, contribution to diseases and outcomes, and the impact on treatments in these patients.

DATA SOURCE

Review of the relevant medical literature for specific common comorbidities in the critically ill.

RESULTS

Critically ill patients are admitted to the intensive care unit for various reasons, and often the admission diagnosis is accompanied by a chronic comorbidity. Chronic comorbid conditions commonly seen in critically ill patients may influence the decision to provide intensive care unit care, decisions regarding types and intensity of intensive care unit treatment options, and outcomes. The presence of comorbid conditions may predispose patients to specific complications or forms of organ dysfunction. The impact of specific comorbidities varies among critically ill medical, surgical, and other populations, and outcomes associated with certain comorbidities have changed over time. Specifically, outcomes for patients with cancer and HIV have improved, likely related to advances in therapy. Overall, the negative impact of chronic comorbidity on survival in critical illness may be primarily influenced by the degree of organ dysfunction or the cumulative severity of multiple comorbidities.

CONCLUSION

Chronic comorbid conditions are common in critically ill patients. Both the acute illness and the chronic conditions influence prognosis and optimal care delivery for these patients, particularly for adverse outcomes and complications influenced by comorbidities. Further work is needed to fully determine the individual and combined impact of chronic comorbidities on intensive care unit outcomes.

Endocrine system and obesity

Obesity is associated with significant alterations in endocrine function. An association with type 2 diabetes mellitus and dyslipidemia has been well documented. This article highlights the complexities of treating endocrine system disorders in obese patients.