β(2)-Adrenoreceptor blockade improves early posttrauma hyperglycemia and pulmonary injury in obese rats

Pathophysiology of Hemorrhage as It Relates to the Warfighter

Saving lives of wounded military Warfighters often depends on the ability to resolve or mitigate the pathophysiology of hemorrhage, specifically diminished oxygen delivery to vital organs that leads to multi-organ failure and death. However, caring for hemorrhaging patients on the battlefield presents unique challenges that extend beyond applying a tourniquet and giving a blood transfusion, especially when battlefield care must be provided for a prolonged period. This review will describe these challenges and potential strategies for treating hemorrhage on the battlefield in a prolonged casualty care situation.

A novel rat model of extremity trauma for prehospital pain management research

BACKGROUND

Pain management is important in prehospital care of patients with extremity trauma (ET). The goal of this study was to establish a rat model of ET for prehospital pain research and validate it using pain behaviors and analgesics.

METHODS

Rats were anesthetized using isoflurane, and ET was induced in one hindlimb via clamping retrofemoral tissues for 30 seconds, followed by closed fibula fracture. Rats regained consciousness after ET. Pain responses in the injured hindlimb to thermal hyperalgesia (paw withdrawal latency [PWL]), mechanical allodynia (paw withdrawal pressure [PWP]), and weight bearing (WB) were determined before and 90 minutes after ET. Morphine (2 mg/kg), fentanyl (10 μg/kg), sufentanil (1 μg/kg), ketamine (5 mg/kg), or vehicle (saline) were then administered via intravenous (i.v.) injection, followed by PWL, PWP, and WB assessments at 10 minutes, 40 minutes, 80 minutes, and 120 minutes after analgesia.

RESULTS

After ET, PWL, PWP, and WB were significantly decreased by 61 ± 4%, 64 ± 8%, and 65 ± 4%, respectively, compared with pre-ET values. These pain behaviors were maintained for 3 hours to 4 hours. Compared with the saline group, opioid analgesics significantly increased PWL for at least 80 minutes, with sufentanil exhibiting the highest analgesic effect. An increase in PWL was only observed at 10 minutes after ketamine. The PWP was transiently increased with opioid analgesics for 10 minutes to 40 minutes, but was not changed with ketamine. Weight bearing was improved with opioid analgesics for at least 2 hours, but only for up to 80 minutes with ketamine.

CONCLUSION

Our ET model includes long bone fracture and soft tissue injury, but no fixation surgery, mimicking prehospital ET. Our model produces acute, steady, and reproducible trauma-related pain behaviors, and is clinically relevant regarding the pain behaviors and established responses to common analgesics. This model of acute pain due to ET is ideal for prehospital pain management research.

Early treatment with GLP-1 after severe trauma preserves renal function in obese Zucker rats

Early posttrauma hyperglycemia (EPTH) is correlated with later adverse outcomes, including acute kidney injury (AKI). Controlling EPTH in the prehospital setting is difficult because of the variability in the ideal insulin dosage and the potential risk of hypoglycemia, especially in those with confounding medical comorbidities of obesity and insulin resistance. Glucagon-like peptide-1 (GLP-1) controls glucose levels in a glucose-dependent manner and is a current target in antidiabetic therapy. We have shown that after orthopedic trauma, obese Zucker rats exhibit EPTH and a later development of AKI (within 24 h). We hypothesized that GLP-1 treatment after trauma decreases EPTH and protects renal function in obese Zucker rats. Obese Zucker rats (~12 wk old) were fasted for 4 h before trauma. Soft tissue injury, fibula fracture, and homogenized bone component injection were then performed in both hind limbs to induce severe extremity trauma. Plasma glucose levels were measured before and 15, 30, 60, 120, 180, 240, and 300 min after trauma. GLP-1 (3 μg·kg^-1·h^-1, 1.5 ml/kg total) or saline was continuously infused from 30 min to 5 h after trauma. Afterwards, rats were placed in metabolic cages overnight for urine collection. The following day, plasma interleukin (IL)-6 levels, renal blood flow (RBF), glomerular filtration rate (GFR), and renal oxygen delivery (Do₂) and consumption (V̇o₂) were measured. EPTH was evident within 15 min after trauma but was significantly ameliorated during the 5 h of GLP-1 infusion. One day after trauma, plasma IL-6 was markedly increased in the trauma group and decreased in GLP-1-treated animals. RBF, GFR, and Do₂ all significantly decreased with trauma, but renal V̇o₂ was unchanged. GLP-1 treatment normalized RBF, GFR, and Do₂ without affecting V̇o₂. These results suggest that GLP-1 decreases EPTH and protects against a later development of AKI. Early treatment with GLP-1 (or its analogs) to rapidly, effectively, and safely control EPTH may be beneficial in the prehospital care of obese patients after trauma.

Effect of beta-blocker therapy on early mortality after emergency colonic cancer surgery

Background

Emergency colorectal cancer surgery is associated with significant mortality. Induced adrenergic hyperactivity is thought to be an important contributor. Downregulating the effects of circulating catecholamines may reduce the risk of adverse outcomes. This study assessed whether regular preoperative beta-blockade reduced mortality after emergency colonic cancer surgery.

Methods

This cohort study used the prospectively collected Swedish Colorectal Cancer Registry to recruit all adult patients requiring emergency colonic cancer surgery between 2011 and 2016. Patients were subdivided into those receiving regular beta-blocker therapy before surgery and those who were not (control). Demographics and clinical outcomes were compared. Risk factors for 30-day mortality were evaluated using Poisson regression analysis.

Results

A total of 3187 patients were included, of whom 685 (21·5 per cent) used regular beta-blocker therapy before surgery. The overall 30-day mortality rate was significantly reduced in the beta-blocker group compared with controls: 3·1 (95 per cent c.i. 1·9 to 4·7) versus 8·6 (7·6 to 9·8) per cent respectively (P < 0·001). Beta-blocker therapy was the only modifiable protective factor identified in multivariable analysis of 30-day all-cause mortality (incidence rate ratio 0·31, 95 per cent c.i. 0·20 to 0·47; P < 0·001) and was associated with a significant reduction in death of cardiovascular, respiratory, sepsis and multiple organ failure origin.

Conclusion

Preoperative beta-blocker therapy may be associated with a reduction in 30-day mortality following emergency colonic cancer surgery.

β-Blockade use for Traumatic Injuries and Immunomodulation: A Review of Proposed Mechanisms and Clinical Evidence

Sympathetic nervous system activation and catecholamine release are important events following injury and infection. The nature and timing of different pathophysiologic insults have significant effects on adrenergic pathways, inflammatory mediators, and the host response. Beta adrenergic receptor blockers (β-blockers) are commonly used for treatment of cardiovascular disease, and recent data suggests that the metabolic and immunomodulatory effects of β-blockers can expand their use. β-blocker therapy can reduce sympathetic activation and hypermetabolism as well as modify glucose homeostasis and cytokine expression. It is the purpose of this review to examine either the biologic basis for proposed mechanisms or to describe current available clinical evidence for the use of β-blockers in traumatic brain injury, spinal cord injury, hemorrhagic shock, acute traumatic coagulopathy, erythropoietic dysfunction, metabolic dysfunction, pulmonary dysfunction, burns, immunomodulation, and sepsis.

Perioperative "remote" acute lung injury: recent update

Perioperative acute lung injury (ALI) is a syndrome characterised by hypoxia and chest radiograph changes. It is a serious post-operative complication, associated with considerable mortality and morbidity. In addition to mechanical ventilation, remote organ insult could also trigger systemic responses which induce ALI. Currently, there are limited treatment options available beyond conservative respiratory support. However, increasing understanding of the pathophysiology of ALI and the biochemical pathways involved will aid the development of novel treatments and help to improve patient outcome as well as to reduce cost to the health service. In this review we will discuss the epidemiology of peri-operative ALI; the cellular and molecular mechanisms involved on the pathological process; the clinical considerations in preventing and managing perioperative ALI and the potential future treatment options.

OBESITY AND CRITICAL ILLNESS: INSIGHTS FROM ANIMAL MODELS

Critical illness is a major cause of morbidity and mortality around the world. While obesity is often detrimental in the context of trauma, it is paradoxically associated with improved outcomes in some septic patients. The reasons for these disparate outcomes are not well understood. A number of animal models have been used to study the obese response to various forms of critical illness. Just as there have been many animal models that have attempted to mimic clinical conditions, there are many clinical scenarios that can occur in the highly heterogeneous critically ill patient population that occupies hospitals and intensive care units. This poses a formidable challenge for clinicians and researchers attempting to understand the mechanisms of disease and develop appropriate therapies and treatment algorithms for specific subsets of patients, including the obese. The development of new, and the modification of existing animal models, is important in order to bring effective treatments to a wide range of patients. Not only do experimental variables need to be matched as closely as possible to clinical scenarios, but animal models with pre-existing comorbid conditions need to be studied. This review briefly summarizes animal models of hemorrhage, blunt trauma, traumatic brain injury, and sepsis. It also discusses what has been learned through the use of obese models to study the pathophysiology of critical illness in light of what has been demonstrated in the clinical literature.

β2-adrenergic regulation of stress hyperglycemia following hemorrhage in the obese Zucker rat

Stress hyperglycemia following trauma has been shown to potentiate morbidity and mortality. Glucose control in obese patients can be challenging due to insulin resistance. Thus, understanding the mechanisms for glucose generation following hemorrhage may provide important insights into alternative options for glycemic control in obesity. Obesity is characterized by elevated glycogen and increased hepatic β₂‐adrenergic activity, which play major roles in glucose production after hemorrhage. We hypothesized that, in obesity, hepatic glycogenolysis is enhanced during stress hyperglycemia due to increased hepatic β₂‐adrenoceptor activation. Hemorrhage was performed in conscious lean Zucker (LZ) and obese Zucker rats (OZ) by withdrawing 35% total blood volume over 10 min. Liver glycogen content and plasma levels of glucose, insulin, and glucagon were measured before and 1 h after hemorrhage. The hyperglycemic response was greater in OZ as compared to LZ, but glycogen content was similarly reduced in both groups. Subsequently, OZ had a greater fall in insulin compared to LZ. Glucagon levels were significantly increased 1 h after hemorrhage in LZ but not in OZ. To test the direct adrenergic effects on the liver after hemorrhage, we treated animals before hemorrhage with a selective β₂‐adrenoceptor antagonist, ICI‐118,551 (ICI; 2 mg/kg/h, i.v.). After hemorrhage, ICI significantly reduced hyperglycemia in both LZ and OZ, independent of hormonal changes, but there was a significantly decreased hepatic glycogenolysis in OZ. These results suggest that the hemorrhage‐induced hepatic glycogenolysis is likely glucagon‐dependent in LZ, whereas the β₂‐adrenoceptor plays a greater role in OZ.

This figure demonstrates that hemorrhage does not result in an increase in glucagon levels in the obese Zucker rat, but does increase in the lean Zucker rat. These results suggest that the hemorrhage‐induced hepatic glycogenolysis is likely glucagon‐dependent in LZ and not in obese Zucker.

Oxidative stress contributes to orthopedic trauma-induced acute kidney injury in obese rats

After trauma, obese patients have an increased risk of developing acute kidney injury (AKI). We have demonstrated that obese Zucker (OZ) rats, but not lean Zucker (LZ) rats, develop AKI 24 h after orthopedic trauma. ROS have been implicated in the pathophysiology of AKI in models of critical illness. However, the contribution of ROS to trauma-induced AKI in the setting of obesity has not been determined. We hypothesized that AKI in OZ rats after trauma is mediated by increased oxidative stress. Male LZ and OZ rats were divided into control and trauma groups, with a subset receiving treatment after trauma with the antioxidant apocynin (50 mg/kg ip, 2 mM in drinking water). The day after trauma, glomerular filtration rate, plasma creatinine, urine kidney injury molecule-1, and albumin excretion as well as renal oxidant and antioxidant activity were measured. After trauma, compared with LZ rats, OZ rats exhibited a significant decrease in glomerular filtration rate along with significant increases in plasma creatinine and urine kidney injury molecule-1 and albumin excretion. Additionally, oxidative stress was significantly increased in OZ rats, as evidenced by increased renal NADPH oxidase activity and urine lipid peroxidation products (thiobarbituric acid-reactive substances), and OZ rats also had suppressed renal superoxide dismutase activity. Apocynin treatment significantly decreased oxidative stress and AKI in OZ rats but had minimal effects in LZ rats. These results suggest that ROS play an important role in AKI in OZ rats after traumatic injury and that ROS may be a potential future therapeutic target in the obese after trauma.