Insulin Resistance Heralds Positive Cultures after Severe Injury

Making sense of gut feelings in the traumatic brain injury pathogenesis

Traumatic brain injury (TBI) is a devastating condition which often initiates a sequel of neurological disorders that can last throughout lifespan. From metabolic perspective, TBI also compromises systemic physiology including the function of body organs with subsequent malfunctions in metabolism. The emerging panorama is that the effects of TBI on the periphery strike back on the brain and exacerbate the overall TBI pathogenesis. An increasing number of clinical reports are alarming to show that metabolic dysfunction is associated with incidence of long-term neurological and psychiatric disorders. The autonomic nervous system, associated hypothalamic-pituitary axis, and the immune system are at the center of the interface between brain and body and are central to the regulation of overall homeostasis and disease. We review the strong association between mechanisms that regulate cell metabolism and inflammation which has important clinical implications for the communication between body and brain. We also discuss the integrative actions of lifestyle interventions such as diet and exercise on promoting brain and body health and cognition after TBI.

Simulation and qualitative analysis of glucose variability, mean glucose, and hypoglycemia after subcutaneous insulin therapy for stress hyperglycemia

Background

The critically ill can have persistent dysglycemia during the “subacute” recovery phase of their illness because of altered gene expression; it is also not uncommon for these patients to receive continuous enteral nutrition during this time. The optimal short-acting subcutaneous insulin therapy that should be used in this clinical scenario, however, is unknown. Our aim was to conduct a qualitative numerical study of the glucose-insulin dynamics within this patient population to answer the above question. This analysis may help clinicians design a relevant clinical trial.

Methods

Eight virtual patients with stress hyperglycemia were simulated by means of a mathematical model. Each virtual patient had a different combination of insulin resistance and insulin deficiency that defined their unique stress hyperglycemia state; the rate of gluconeogenesis was also doubled. The patients received 25 injections of subcutaneous regular or Lispro insulin (0-6 U) with 3 rates of continuous nutrition. The main outcome measurements were the change in mean glucose concentration, the change in glucose variability, and hypoglycemic episodes. These end points were interpreted by how the ultradian oscillations of glucose concentration were affected by each insulin preparation.

Results

Subcutaneous regular insulin lowered both mean glucose concentrations and glucose variability in a linear fashion. No hypoglycemic episodes were noted. Although subcutaneous Lispro insulin lowered mean glucose concentrations, glucose variability increased in a nonlinear fashion. In patients with high insulin resistance and nutrition at goal, “rebound hyperglycemia” was noted after the insulin analog was rapidly metabolized. When the nutritional source was removed, hypoglycemia tended to occur at higher Lispro insulin doses. Finally, patients with severe insulin resistance seemed the most sensitive to insulin concentration changes.

Conclusions

Subcutaneous regular insulin consistently lowered mean glucose concentrations and glucose variability; its linear dose-response curve rendered the preparation better suited for a sliding-scale protocol. The longer duration of action of subcutaneous regular insulin resulted in better glycemic-control metrics for patients who were continuously postprandial. Clinical trials are needed to examine whether these numerical results represent the glucose-insulin dynamics that occur in intensive care units; if present, their clinical effects should be evaluated.

Insulin resistance increases before ventilator-associated pneumonia in euglycemic trauma patients

BACKGROUND

Hyperglycemia caused by stress-induced insulin resistance is associated with both infection and mortality in critically injured patients. The onset of infection may increase stress-induced insulin resistance, leading to hyperglycemia. Hyperglycemia has been shown to precede the diagnosis of ventilator-associated pneumonia (VAP) in critically injured adults and has been suggested to have potential diagnostic importance. However, glycemic control (GC) protocols in critically ill patients limit the development of hyperglycemia despite increasing insulin resistance. Our computer-assisted GC protocol achieves excellent GC, limiting infection-related hyperglycemia while capturing prospectively all glucose values, insulin infusion rates, and the multiplier (M) used to calculate the insulin rate. We hypothesized that surrogate measures of insulin resistance, the insulin infusion rate and multiplier M, would increase prior to the clinical suspicion of VAP, even in euglycemic critically injured patients.

METHODS

All critically injured patients (2,656) on the computerized glycemic control protocol were included in the analysis and categorized by those developing VAP and those without pneumonia on days 3-10 of their intensive care unit (ICU) stay. Median blood glucose concentration (BG), insulin infusion rate (IDR), and multiplier (M) [Insulin Drip Rate=M*(BG-60)] were determined for VAP patients (n=329) and non-infected ventilated (NIV) patients (n=2,327) on each day of mechanical ventilation. The day of VAP diagnosis according to U.S. Centers for Disease Control and Prevention (CDC) criteria was defined as day zero and VAP patients matched with NIV patients according to ventilator day from -10 to +10. Comparisons were conducted using the Mann-Whitney U test.

RESULTS

Baseline characteristics between VAP and NIV groups did not differ. Measures of insulin resistance increased from the time of injury in both groups. Patients with VAP had significantly greater change in both measures of insulin resistance, IDR and M, in the 48 hours preceding the diagnosis of VAP. These changes occurred despite the fact that the computer-assisted GC protocol achieved lower glucose values in VAP patients for the majority of study days.

CONCLUSIONS

Measures of insulin resistance increase in the two days prior to the clinical suspicion of VAP for critically injured patients on the GC protocol. These changes occur despite the protocol maintaining euglycemia. This data suggests that markers of insulin resistance may provide clinically useful information in the early diagnosis of VAP.

Insulin Resistance in Critically Injured Adults: Contribution of Pneumonia, Diabetes, Nutrition, and Acuity

PURPOSE

Changes in insulin resistance (IR) cause stress-induced hyperglycemia after trauma, but the numerous factors involved in IR have not been delineated clearly. We hypothesized that a statistical model could help determine the relative contribution of different clinical co-variates to IR in critically injured patients.

PATIENTS AND METHODS

We retrospectively studied 726 critically injured patients managed with a computer-assisted glycemic protocol at an academic level I trauma center (639 ventilated controls without pneumonia (VWP) and 87 patients with ventilator-associated pneumonia (VAP). Linear regression using age, gender, body mass index (BMI), diabetes mellitus, pneumonia, and glycemic provision was used to estimate M, a marker of IR that incorporates both the serum blood glucose concentration (BG) and insulin dose.

RESULTS

Increasing M (p<0.001) was associated with age (1.62%; 95% confidence interval [CI] 1.27%-1.97% per decade), male gender (9.78%; 95% CI 8.28%-12.6%), BMI (4.32% [95% CI 4.02%-4.62%] per 5 points), diabetes mellitus (21.2%; 95% CI 19.2%-23.2%), pneumonia (10.9%; 95% CI 9.31%-12.6%), and glycemic provision (27.3% [95% CI 6.6%-28.1%] per 100 g of glucose). Total parenteral nutrition was associated with a decrease in M of 10.3%; 95% CI 8.52%-12.1%; p<0.001.

CONCLUSIONS

Clinical factors can be used to construct a model of IR. Prospective validation might enable early detection and treatment of infection or other conditions associated with increased IR.

Stress hyperglycemia and surgical site infection in stable nondiabetic adults with orthopedic injuries

BACKGROUND

Hyperglycemia in nondiabetic patients outside the intensive care unit is not well defined. We evaluated the relationship of hyperglycemia and surgical site infection (SSI) in stable nondiabetic patients with orthopedic injuries.

METHODS

We conducted a prospective observational cohort study at a single academic Level 1 trauma center over 9 months (Level II evidence for therapeutic/care management). We included patients 18 years or older with operative orthopedic injuries and excluded patients with diabetes, corticosteroid use, multisystem injuries, or critical illness. Demographics, medical comorbidities (American Society of Anesthesiologists class), body mass index, open fractures, and number of operations were recorded. Fingerstick glucose values were obtained twice daily. Hyperglycemia was defined as a fasting glucose value greater than or equal to 125 mg/dL or a random value greater than or equal to 200 mg/dL on more than one occasion before the diagnosis of SSI. Glycosylated hemoglobin level was obtained from hyperglycemic patients; those with glycosylated hemoglobin level of 6.0 or greater were considered occult diabetic patients and were excluded. SSI was defined by a positive intraoperative culture at reoperation within 30 days of the index case.

RESULTS

We enrolled 171 patients. Of these 171, 40 (23.4%) were hyperglycemic; 7 of them were excluded for occult diabetes. Of the 164 remaining patients, 33 were hyperglycemic (20.1%), 50 had open fractures (6 Type I, 22 Type II, 22 Type III), and 12 (7.3%) had SSI. Hyperglycemic patients were more likely to develop SSI (7 of 33 [21.2%] vs. 5 of 131 [3.8%], p = 0.003). Open fractures were associated with SSI (7 of 50 [14%] vs. 5 of 114 [4.4%], p = 0.047) but not hyperglycemia (10 of 50 [20.0%] vs. 23 of 114 [20.2%], p = 0.98). There was no significant difference between infected and noninfected patients in terms of age, sex, race, American Society of Anesthesiologists class, obesity (body mass index > 29), tobacco use, or number of operations.

CONCLUSION

Stress hyperglycemia was associated with SSI in this prospective observational cohort of stable nondiabetic patients with orthopedic injuries. Further prospective randomized studies are necessary to identify optimal treatment of hyperglycemia in the noncritically ill trauma population.

LEVEL OF EVIDENCE

Therapeutic study, level III.

Undiagnosed medical comorbidities in the uninsured: a significant predictor of mortality following trauma

BACKGROUND

Lack of health care insurance has been correlated with increased mortality after trauma. Medical comorbidities significantly affect trauma outcomes. Access to health care and thereby being diagnosed with a pretrauma comorbidity is highly dependent on insurance status. The objective of this study was to determine whether rates of diagnosed or undiagnosed preexisting comorbidities significantly contribute to disparities in mortality rates observed between insured and uninsured trauma patients.

METHODS

Review of trauma patients admitted to a Level I trauma center during a 5-year period. Data extracted from the registry included age, sex, Injury Severity Score (ISS), comorbidities, mortality, and insurance status. Multivariate logistic regression analysis was performed using age, sex, and insurance status to predict comorbidities and age, sex, ISS, and insurance status to predict mortality.

RESULTS

Insured patients were older (54 years vs. 38, p < 0.001) and more likely female (41.3% vs. 22.5%, p < 0.001). When adjusting for age and sex, insured patients were more likely to have a pretrauma diagnosis of coronary artery disease (odds ratio [OR], 2.09; 95% confidence interval [CI], 1.54-2.83), diabetes mellitus (OR, 2.09; 95% CI, 1.61-2.72), hypertension (OR, 1.97; 95% CI, 1.65-2.35), asthma/emphysema (OR, 1.64; 95% CI, 1.32-2.04), neurologic problems (OR, 1.79; 95% CI, 1.31-2.44), and gastroesophageal reflux disease (OR, 2.03; 95% CI, 1.33-3.11), compared with patients without insurance. In the analysis to predict mortality, having insurance was protective (OR, 0.57; 95% CI, 0.45-0.71). Among patients with no diagnosed comorbidities, insured patients had the lowest mortality risk (OR, 0.5; 95% CI, 0.38-0.67). When analyzing only patients with diagnosed comorbidities, insurance status had no impact on mortality risk (OR, 0.81; 95% CI, 0.53-1.22).

CONCLUSION

Undiagnosed preexisting comorbidities play a crucial role in determining outcomes following trauma. Diagnosis of medical comorbidities may be a marker of access to health care and may be associated with treatment, which may explain the gap in mortality rates between insured and uninsured trauma patients.

LEVEL OF EVIDENCE

Prognostic/epidemiologic study, level III.