Differential effects of vasopressin and norepinephrine on vascular reactivity in a long-term rodent model of sepsis

Advances in the diagnosis of non-occlusive mesenteric ischemia and challenges in intra-abdominal sepsis patients: a narrative review

Non-occlusive mesenteric ischemia (NOMI) is a type of acute mesenteric ischemia (AMI) with a high mortality rate mainly because of a delayed or misdiagnosis. Intra-abdominal sepsis is one of the risk factors for developing NOMI, and its presence makes early diagnosis much more difficult. An increase in routine abdominal surgeries carries a corresponding risk of abdominal infection, which is a complication that should not be overlooked. It is critical that physicians are aware of the possibility for intestinal necrosis in abdominal sepsis patients due to the poor survival rate of NOMI. This review aims to summarize advances in the diagnosis of NOMI, and focuses on the diagnostic challenges of mesenteric ischemia in patients with intra-abdominal sepsis.

Cannabinoid Receptor 1 and 2 Signaling Pathways Involved in Sepsis

ABSTRACT

Sepsis is defined as a life-threatening organ dysfunction, caused by a dysregulated host response to an infection and can progress to septic shock, which represents a major challenge in critical care with a high mortality rate. Currently, there is no definitive treatment available for the dysregulated immune response in sepsis. Therefore, a better understanding of the pathophysiological mechanisms may be useful for elucidating the molecular basis of sepsis and may contribute to the development of new therapeutic strategies. The endocannabinoid system is an emerging research topic for the modulation of the host immune response under various pathological conditions. Cannabinoid receptors include the cannabinoid type 1 receptor (CB1) and the cannabinoid type 2 receptor (CB2). This review addresses the main functionality of CB1 and CB2 in sepsis, which can contribute to a better understanding about the pathophysiology of sepsis. Specifically, we discuss the role of CB1 in the cardiovascular system which is one of the biological systems that are strongly affected by sepsis and septic shock. We are also reviewing the role of CB2 in sepsis, specially CB2 activation, which exerts anti-inflammatory activities with potential benefit in sepsis.

The order of vasopressor discontinuation and incidence of hypotension: a retrospective cohort analysis

The optimal order of vasopressor discontinuation during shock resolution remains unclear. We evaluated the incidence of hypotension in patients receiving concomitant vasopressin (VP) and norepinephrine (NE) based on the order of their discontinuation. In this retrospective cohort study, consecutive patients receiving concomitant VP and NE infusions for shock admitted to intensive care units were evaluated. The primary outcome was hypotension incidence following discontinuation of VP or NE (VP1 and NE1 groups, respectively). Secondary outcomes included the incidence of acute kidney injury (AKI) and arrhythmias. Subgroup analysis was conducted by examining outcomes based on the type of shock. Of the 2,035 included patients, 952 (46.8%) were VP1 and 1,083 (53.2%) were NE1. VP1 had a higher incidence of hypotension than NE1 (42.1% vs. 14.2%; P < 0.001), longer time to shock reversal (median: 2.5 vs. 2.2 days; P = .009), higher hospital [29% (278/952) vs. 24% (258/1083); P = .006], and 28-day mortality [37% (348/952) vs. 29% (317/1,083); P < 0.001] when compared with the NE1 group. There were no differences in ICU mortality, ICU and hospital length of stay, new-onset arrhythmia, or AKI incidence between the two groups. In subgroup analyses based on different types of shock, similar outcomes were observed. After adjustments, hypotension in the following 24 h and 28-day mortality were significantly higher in VP1 (Odds ratios (OR) 4.08(3.28, 5.07); p-value < .001 and 1.27(1.04, 1.55); p-value < .001, respectively). Besides, in a multivariable model, the need for renal replacement therapy (OR 1.68 (1.34, 2.12); p-value < .001) was significantly higher in VP1. Among patients with shock who received concomitant VP and NE, the VP1 group was associated with a higher incidence of hypotension in comparison with NE1. Future studies need to validate our findings and their impact on clinical outcomes.

Pralidoxime improves the hemodynamics and survival of rats with peritonitis-induced sepsis

Several studies have suggested that sympathetic overstimulation causes deleterious effects in septic shock. A previous study suggested that pralidoxime exerted a pressor effect through a mechanism unrelated to the sympathetic nervous system; this effect was buffered by the vasodepressor action of pralidoxime mediated through sympathoinhibition. In this study, we explored the effects of pralidoxime on hemodynamics and survival in rats with peritonitis-induced sepsis. This study consisted of two sub-studies: survival and hemodynamic studies. In the survival study, 66 rats, which survived for 10 hours after cecal ligation and puncture (CLP), randomly received saline placebo, pralidoxime, or norepinephrine treatment and were monitored for up to 24 hours. In the hemodynamic study, 44 rats were randomly assigned to sham, CLP-saline placebo, CLP-pralidoxime, or CLP-norepinephrine groups, and hemodynamic measurements were performed using a conductance catheter placed in the left ventricle. In the survival study, 6 (27.2%), 15 (68.1%), and 5 (22.7%) animals survived the entire 24-hour monitoring period in the saline, pralidoxime, and norepinephrine groups, respectively (log-rank test P = 0.006). In the hemodynamic study, pralidoxime but not norepinephrine increased end-diastolic volume (P <0.001), stroke volume (P = 0.002), cardiac output (P = 0.003), mean arterial pressure (P = 0.041), and stroke work (P <0.001). The pressor effect of norepinephrine was short-lived, such that by 60 minutes after the initiation of norepinephrine infusion, it no longer had any significant effect on mean arterial pressure. In addition, norepinephrine significantly increased heart rate (P <0.001) and the ratio of arterial elastance to ventricular end-systolic elastance (P = 0.010), but pralidoxime did not. In conclusion, pralidoxime improved the hemodynamics and 24-hour survival rate in rats with peritonitis-induced sepsis, but norepinephrine did not.

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

Effects of epinephrine on heart rate variability and cytokines in a rat sepsis model

Catecholamines have both anti-inflammatory and vasoactive properties. A decreased cardiac response to catecholamines has been associated with a high risk of death in sepsis and septic shock. The aim of this study was to investigate the effects of epinephrine (EPI) on heart rate variability (HRV) and autonomic balance, as well as cytokine levels, in a rat sepsis model. Thirty-six male Sprague-Dawley rats were assigned to 4 experimental groups and 2 control groups of 6 rats each. The rats in the experimental groups were inoculated with a lipopolysaccharide (LPS, endotoxin) to establish a sepsis model. Group A received only LPS; group B received LPS, antecedent EPI and the nonselective β-blocker propranolol; group C received LPS and antecedent EPI; and group D received LPS, antecedent EPI and the selective β1-blocker esmolol. One control group received EPI and the other received saline placebo. Heart rate variability (HRV) was analyzed and tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) levels were measured. Measurements were carried out at baseline, at 0 hour after EPI infusion, and at 0.5, 2, and 4 hours after LPS inoculation. There were significant differences in HRV and cytokine levels between the groups, indicating that LPS infusion caused autonomic imbalance. Antecedent EPI significantly decreased the level of TNF-α in group C compared with group A in which TNF-α level peaked at 2 hours and then declined. Propranolol (group B) but not esmolol (group D) administration resulted in elevated TNF-α levels, comparable to those observed in group A. In conclusion, antecedent administration of EPI in a rat sepsis model inhibits the production of TNF-α possibly via the β2-adrenoceptor.

Contemporary Management of Acute Mesenteric Ischemia in the Endovascular Era

Objective:

Acute mesenteric ischemia is a rare disease entity associated with high morbidity and mortality. Disparate etiologies and nonspecific symptoms make the diagnosis challenging and often result in delayed diagnosis and intervention. Open laparotomy with mesenteric revascularization and resection of necrotic bowel has been considered the gold standard of care. With recent advances in percutaneous catheter-directed techniques, multiple retrospective studies have demonstrated the outcomes of endovascular therapy. Herein, we review the etiology, presentation, and diagnosis of acute mesenteric ischemia with contemporary outcomes associated with both open and endovascular treatments.

Methods:

The PubMed electronic database was queried in the English language using the search words mesenteric, acute ischemia, embolism, thromboembolism, thrombosis, revascularization, and endovascular in various combinations. Abstracts of the relevant titles were examined to confirm their relevance and the full articles then extracted. References from extracted articles were checked for any additional relevant articles. This systematic review encompassed literature for the past 5 years (between 2011 and 2016).

Results:

Early diagnosis and intervention improves acute mesenteric ischemia outcomes. Early restoration of mesenteric flow minimizes morbidity and mortality. In comparison to open laparotomy with mesenteric revascularization and resection of necrotic bowel, several retrospective studies using administrative data and single-center chart reviews demonstrate noninferior outcomes of an endovascular first approach in acute arterial mesenteric occlusion.

Conclusions:

For acute mesenteric arterial occlusive disease, both endovascular and open revascularization techniques are viable options. Although there is lack of level 1 evidence, single-center retrospective studies and administrative database studies demonstrated that an endovascular first approach may have improved outcomes in the immediate postoperative period. However, selection and other bias in these studies necessitate the need for definitive randomized prospective studies between endovascular and open mesenteric intervention. In contrast, mesenteric venous thrombosis may be treated with systemic anticoagulation without surgical revascularization. Catheter-directed thrombectomy and thrombolysis can be considered at the discretion of the clinician.

Association of Vasopressin Plus Catecholamine Vasopressors vs Catecholamines Alone With Atrial Fibrillation in Patients With Distributive Shock: A Systematic Review and Meta-analysis

IMPORTANCE

Vasopressin is an alternative to catecholamine vasopressors for patients with distributive shock-a condition due to excessive vasodilation, most frequently from severe infection. Blood pressure support with a noncatecholamine vasopressor may reduce stimulation of adrenergic receptors and decrease myocardial oxygen demand. Atrial fibrillation is common with catecholamines and is associated with adverse events, including mortality and increased length of stay (LOS).

OBJECTIVES

To determine whether treatment with vasopressin + catecholamine vasopressors compared with catecholamine vasopressors alone was associated with reductions in the risk of adverse events.

DATA SOURCES

MEDLINE, EMBASE, and CENTRAL were searched from inception to February 2018. Experts were asked and meta-registries searched to identify ongoing trials.

STUDY SELECTION

Pairs of reviewers identified randomized clinical trials comparing vasopressin in combination with catecholamine vasopressors to catecholamines alone for patients with distributive shock.

DATA EXTRACTION AND SYNTHESIS

Two reviewers abstracted data independently. A random-effects model was used to combine data.

MAIN OUTCOMES AND MEASURES

The primary outcome was atrial fibrillation. Other outcomes included mortality, requirement for renal replacement therapy (RRT), myocardial injury, ventricular arrhythmia, stroke, and LOS in the intensive care unit and hospital. Measures of association are reported as risk ratios (RRs) for clinical outcomes and mean differences for LOS.

RESULTS

Twenty-three randomized clinical trials were identified (3088 patients; mean age, 61.1 years [14.2]; women, 45.3%). High-quality evidence supported a lower risk of atrial fibrillation associated with vasopressin treatment (RR, 0.77 [95% CI, 0.67 to 0.88]; risk difference [RD], -0.06 [95% CI, -0.13 to 0.01]). For mortality, the overall RR estimate was 0.89 (95% CI, 0.82 to 0.97; RD, -0.04 [95% CI, -0.07 to 0.00]); however, when limited to trials at low risk of bias, the RR estimate was 0.96 (95% CI, 0.84 to 1.11). The overall RR estimate for RRT was 0.74 (95% CI, 0.51 to 1.08; RD, -0.07 [95% CI, -0.12 to -0.01]). However, in an analysis limited to trials at low risk of bias, RR was 0.70 (95% CI, 0.53 to 0.92, P for interaction = .77). There were no significant differences in the pooled risks for other outcomes.

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, the addition of vasopressin to catecholamine vasopressors compared with catecholamines alone was associated with a lower risk of atrial fibrillation. Findings for secondary outcomes varied.

Cardiovascular Responsiveness to Vasopressin and α1-Adrenergic Receptor Agonists After Burn Injury

The effects of burn injury on cardiovascular responsiveness to vasoactive agents are not well understood. The aims of this study were to determine whether burn injury alters cardiovascular reactivity to vasoactive drugs in vivo and intrinsic function of isolated mesenteric resistance arteries. Anesthetized Sprague-Dawley rats were subjected to sham procedure or 30% TBSA dorsal scald burn, followed by crystalloid resuscitation (Parkland Formula). At 24, 72, 96, and 168 hours post burn, rats were reanesthetized, and the mean arterial blood pressure (MAP) responses to various doses of the α1-adrenergic receptor agonist phenylephrine and arginine vasopressin were tested. Mesenteric arteries were harvested from uninjured animals and at 24 and 168 hours post burn. The responsiveness of arteries to phenylephrine and arginine vasopressin was tested by pressure myography. Dose response curves were generated and EC50 concentrations, Hill slopes, and maximal effects were compared. The potency of phenylephrine to increase MAP was reduced 2-fold 24 hours post burn (P < .05 vs sham) and gradually normalized at later time points. The reactivity of isolated arteries to phenylephrine was not significantly altered after burns. The potency of arginine vasopressin to increase MAP and to constrict isolated arteries was increased 2- to 3-fold at 24 hours post burn (P < .05) and normalized at later time points. Our findings suggest that burn injury differentially regulates vasopressor and blood pressure effects of α-adrenergic and vasopressin receptor agonists. Intrinsic vasopressin receptor reactivity of resistance arteries is sensitized early after burns. These findings will help to optimize resuscitation strategies and vasopressor use in difficult to resuscitate burn patients.

Combined use of high doses of vasopressin and corticosteroids in a patient with Crohn's disease with refractory septic shock after intestinal perforation: a case report

BACKGROUND

In this article, we present a clinical case of refractory septic shock resulting from intestinal perforation treated with high doses of vasopressin and hydrocortisone during emergency surgery. The use of such high doses of vasopressin for this type of shock is not described in the literature.

CASE PRESENTATION

A 49-year-old white woman with grade III obesity, Crohn's disease, and an intestinal perforation presented with refractory septic shock. Initially, a low dose of vasopressin was used. Then, the dosage was increased to 0.4 U/minute; in the literature, this is defined as "salvage therapy." This therapy consists of an initial load followed by a continuous infusion of hydrocortisone.

CONCLUSIONS

The significant increase in her cardiac index and stroke volume index resulted in an improvement in peripheral resistance, gas exchange, and urine output and a decrease in her heart rate, interleukin-6 level, and tumor necrosis factor-α level. The administration of high doses of vasopressin and corticosteroids was demonstrated to be safe for the immune system, to reduce the systemic inflammatory response, and to have direct cardiovascular effects. Further studies are required to examine the use of vasopressin as an initial vasopressor as well as its use in high dosages and in combination with corticosteroids.

Translational evidence for two distinct patterns of neuroaxonal injury in sepsis: a longitudinal, prospective translational study

Background

Brain homeostasis deteriorates in sepsis, giving rise to a mostly reversible sepsis-associated encephalopathy (SAE). Some survivors experience chronic cognitive dysfunction thought to be caused by permanent brain injury. In this study, we investigated neuroaxonal pathology in sepsis.

Methods

We conducted a longitudinal, prospective translational study involving (1) experimental sepsis in an animal model; (2) postmortem studies of brain from patients with sepsis; and (3) a prospective, longitudinal human sepsis cohort study at university laboratory and intensive care units (ICUs). Thirteen ICU patients with septic shock, five ICU patients who died as a result of sepsis, fourteen fluid-resuscitated Wistar rats with fecal peritonitis, eleven sham-operated rats, and three human and four rat control subjects were included. Immunohistologic and protein biomarker analysis were performed on rat brain tissue at baseline and 24, 48, and 72 h after sepsis induction and in sham-treated rats. Immunohistochemistry was performed on human brain tissue from sepsis nonsurvivors and in control patients without sepsis. The clinical diagnostics of SAE comprised longitudinal clinical data collection and magnetic resonance imaging (MRI) and electroencephalographic assessments. Statistical analyses were performed using SAS software (version 9.4; SAS Institute, Inc., Cary, NC, USA). Because of non-Gaussian distribution, the nonparametric Wilcoxon test general linear models and the Spearman correlation coefficient were used.

Results

In postmortem rat and human brain samples, neurofilament phosphoform, β-amyloid precursor protein, β-tubulin, and H&E stains distinguished scattered ischemic lesions from diffuse neuroaxonal injury in septic animals, which were absent in controls. These two patterns of neuroaxonal damage were consistently found in septic but not control human postmortem brains. In experimental sepsis, the time from sepsis onset correlated with tissue neurofilament levels (R = 0.53, p = 0.045) but not glial fibrillary acidic protein. Of 13 patients with sepsis who had clinical features of SAE, MRI detected diffuse axonal injury in 9 and ischemia in 3 patients.

Conclusions

Ischemic and diffuse neuroaxonal injury to the brain in experimental sepsis, human postmortem brains, and in vivo MRI suggest these two distinct lesion types to be relevant. Future studies should be focused on body fluid biomarkers to detect and monitor brain injury in sepsis. The relationship of neurofilament levels with time from sepsis onset may be of prognostic value.

Trial registration

ClinicalTrials.gov, NCT02442986. Registered on May 13, 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1850-7) contains supplementary material, which is available to authorized users.

Inhibition of complement C3 might rescue vascular hyporeactivity in a conscious hemorrhagic shock rat model

BACKGROUND

Vascular hyporeactivity in severe hemorrhagic shock could induce refractory hypotension and is an important cause of death. The global acute inflammatory response induced in shock triggers the over-expression of reactive oxygen species, NO, ET1 and TNF-α, which play essential roles in the pathology of vascular hyporeactivity. This leads to a hypothesis that inhibition of the complement system, the mediator of the inflammatory cascade, might be a promising therapeutic exploration for vascular hyporeactivity.

METHODS

We use cobra venom factor (CVF) and the soluble form of CR1 (sCR1) which deplete or inhibit complement C3 respectively to examine its role in vascular hyporeactivity in a conscious hemorrhagic shock rat model.

RESULTS

We first confirmed the over-activation of C3 during shock and the down-regulation effects of CVF and sCR1 on C3. Then, both CVF and sCR1 could significantly mitigate the over-expression of serum NO, ET-1, TNF-α and reactive oxygen species. Finally, the vascular reactivity of superior mesenteric arteries (SMA) was examined in vitro, which confirmed the massive reduction of vascular reactivity in shock, which was significantly rescued by both CVF and sCR1.

CONCLUSIONS

Inhibition of C3 might improve the reactivity of SMA to norepinephrine during hemorrhagic shock possibly through the downregulation of NO, ET1, TNF-α and reactive oxygen radicals.

Systemic inflammatory responses and multiple organ dysfunction syndrome following skin burn wound and Pseudomonas aeruginosa infection in mice

Burn wound-related sepsis is associated with the development of systemic inflammatory response syndrome and multiple organ dysfunction syndrome (MODS). This study is aimed at investigating the development and progression of SIS and MODS in a mouse model of skin burn sepsis. C57BL/6J mice were randomly divided into the sham, burn, Pseudomonas, and burn/Pseudomonas groups. The back skin of the sham, burn, and burn/Pseudomonas groups was burned about 10% of total area with using 37°C or 98°C water for 8 s, respectively, followed by inoculating with Pseudomonas aeruginosa. The Pseudomonas group was infected with P. aeruginosa without burn injury. Their body weights, mortality, organ histology, and function as well as systemic inflammation were measured longitudinally. The burn/Pseudomonas mice lost more body weights than did mice from the other groups and had a significantly higher mortality rate (P < 0.05). The burn/Pseudomonas mice exhibited significantly higher levels of bacterial loads in different organs and serum endotoxin, interleukin 1β, interleukin 6, tumor necrosis factor α, and C-reactive protein than those in mice from the other groups (P < 0.05). The burn/Pseudomonas mice also displayed more severe liver, lung, and kidney tissue damage and impaired organ functions, particularly at 72 h after inoculation than did the burn and Pseudomonas groups of mice. Our data indicate that burn and P. aeruginosa infection induced severe sepsis and rapidly progressed into systemic inflammatory response syndrome and MODS in mice.

Previous burn injury predisposes mice to lipopolysaccharide-induced changes in glucose metabolism

In mice, it has been demonstrated that at 7 days after burn injury, injection of lipopolysaccharide (LPS) is more lethal than the same dose at 1 day after injury. In the present study, we examined the effect of LPS injection to mice burned 7 days previously on glucose metabolism ([(18)F] 2-fluoro-2-deoxy-D-glucose [(18)FDG] uptake) in vivo. CD-1 male mice (25-28 g, Charles River Breeding Laboratories, Wilmington, MA) were anesthetized, backs shaven, and subjected to dorsal full thickness burn on 25% TBSA. Sham-treated animals were used as controls. Six days after burn injury, all mice were fasted overnight. One half of the burned and sham controls were subsequently injected IP with LPS (10 mg/kg; Escherichia coli). The remaining animals were injected with saline IP. Two hours later, all mice were injected IV with 50 μCi of (18)F FDG. One hour later, the animals were euthanized, and biodistribution was measured. Tissues were weighed, and radioactivity was measured with a well-type γ counter. Results were expressed as %dose/g tissue, mean ± SEM. The combination of burn 7 days previously and LPS significantly increased mortality compared to animals with burn alone, LPS alone, or sham controls. Burn injury 7 days previously caused a significant decrease in (18)FDG uptake by the brain compared to sham controls. The combination of LPS and burn injury 7 days previously produced a significant increase in (18)FDG uptake by brown adipose tissue and heart compared with either treatment separately. LPS produced a significant increase in (18)FDG uptake by lung, spleen, and gastrointestinal tract of the sham animals, changes that were different in mice burned 7 days previously and injected with LPS. The present results suggest that burn injury 7 days previously predisposes mice to alterations in (18)FDG uptake produced by LPS. These changes may relate, in part, to the increased lethality of LPS injection in previously burned mice.

Inhibition of vascular adenosine triphosphate-sensitive potassium channels by sympathetic tone during sepsis

OBJECTIVE

Excessive opening of the adenosine triphosphate-sensitive potassium channel in vascular smooth muscle is implicated in the vasodilation and vascular hyporeactivity underlying septic shock. Therapeutic channel inhibition using sulfonylurea agents has proved disappointing, although agents acting on its pore appear more promising. We thus investigated the hemodynamic effects of adenosine triphosphate-sensitive potassium channel pore inhibition in awake, fluid-resuscitated septic rats, and the extent to which these responses are modulated by the high sympathetic tone present in sepsis. Temporal changes in ex-vivo channel activity and subunit gene expression were also investigated.

DESIGN

In vivo and ex vivo animal study.

SETTING

University research laboratory.

SUBJECTS

Male adult Wistar rats.

INTERVENTIONS AND MEASUREMENTS

Fecal peritonitis was induced in conscious, fluid-resuscitated rats. Pressor responses to norepinephrine and PNU-37883A (a vascular adenosine triphosphate-sensitive potassium channel inhibitor acting on the Kir6.1 pore-forming subunit) were measured at 6 or 24 hrs, in the absence or presence of the autonomic ganglion blocker, pentolinium. The aorta and mesenteric artery were examined ex vivo for rubidium efflux as a marker of adenosine triphosphate-sensitive potassium channel activity, and for adenosine triphosphate-sensitive potassium channel subunit gene expression using quantitative reverse transcription-polymerase chain reaction.

MAIN RESULTS

A total of 120 rats (50 sham-operated controls, 70 septic) were included. Septic rats became hypotensive after 12 hrs, with a 24-hr mortality of 51.7% (0% in controls). At 6 hrs, there was an attenuated pressor response to norepinephrine (p < .01) despite blood pressure being elevated (p < .01). PNU-37883A had no pressor effect, except in the presence of pentolinium (p < .01). Kir6.1 subunit mRNA increased significantly in the mesenteric artery while rubidium efflux was increased in both the aorta and mesenteric artery at 24 hrs.

CONCLUSIONS

Despite evidence of increased adenosine triphosphate-sensitive potassium channel activity in sepsis, it appears to be inhibited in vivo by high sympathetic tone. This may explain, at least in part, the reduced efficacy of adenosine triphosphate-sensitive potassium channel blockers in human septic shock.

Bench-to-bedside review: Vasopressin in the management of septic shock

This review of vasopressin in septic shock differs from previous reviews by providing more information on the physiology and pathophysiology of vasopressin and vasopressin receptors, particularly because of recent interest in more specific AVPR1a agonists and new information from the Vasopressin and Septic Shock Trial (VASST), a randomized trial of vasopressin versus norepinephrine in septic shock. Relevant literature regarding vasopressin and other AVPR1a agonists was reviewed and synthesized. Vasopressin, a key stress hormone in response to hypotension, stimulates a family of receptors: AVPR1a, AVPR1b, AVPR2, oxytocin receptors and purinergic receptors. Rationales for use of vasopressin in septic shock are as follows: first, a deficiency of vasopressin in septic shock; second, low-dose vasopressin infusion improves blood pressure, decreases requirements for norepinephrine and improves renal function; and third, a recent randomized, controlled, concealed trial of vasopressin versus norepinephrine (VASST) suggests low-dose vasopressin may decrease mortality of less severe septic shock. Previous clinical studies of vasopressin in septic shock were small or not controlled. There was no difference in 28-day mortality between vasopressin-treated versus norepinephrine-treated patients (35% versus 39%, respectively) in VASST. There was potential benefit in the prospectively defined stratum of patients with less severe septic shock (5 to 14 μg/minute norepinephrine at randomization): vasopressin may have lowered mortality compared with norepinephrine (26% versus 36%, respectively, P = 0.04 within stratum). The result was robust: vasopressin also decreased mortality (compared with norepinephrine) if less severe septic shock was defined by the lowest quartile of arterial lactate or by use of one (versus more than one) vasopressor at baseline. Other investigators found greater hemodynamic effects of higher dose of vasopressin (0.06 units/minute) but also unique adverse effects (elevated liver enzymes and serum bilirubin). Use of higher dose vasopressin requires further evaluation of efficacy and safety. There are very few studies of interactions of therapies in critical care - or septic shock - and effects on mortality. Therefore, the interaction of vasopressin infusion, corticosteroid treatment and mortality of septic shock was evaluated in VASST. Low-dose vasopressin infusion plus corticosteroids significantly decreased 28-day mortality compared with corticosteroids plus norepinephrine (44% versus 35%, respectively, P = 0.03; P = 0.008 interaction statistic). Prospective randomized controlled trials would be necessary to confirm this interesting interaction. In conclusion, low-dose vasopressin may be effective in patients who have less severe septic shock already receiving norepinephrine (such as patients with modest norepinephrine infusion (5 to 15 μg/minute) or low serum lactate levels). The interaction of vasopressin infusion and corticosteroid treatment in septic shock requires further study.

Characteristics of clinical sepsis reflected in a reliable and reproducible rodent sepsis model

BACKGROUND

Sepsis models are frequently based on induction of peritonitis, with cecal ligation and puncture reflecting the prototypical model. However, there is an ongoing discussion about the limitations of these models due to their variability in progression and outcome. Since standardization is a cornerstone of experimental models, we aimed to develop a reliable and reproducible procedure for induction of peritonitis.

MATERIALS AND METHODS

A human stool batch was processed for -80° storage. For induction of peritonitis in fluid-resuscitated rats, a defined volume of stool suspension from this batch was injected intraperitoneally. For characterization of the model, physiologic and inflammatory changes were evaluated after sepsis induction. Survival analyses with the same batch were repeated in four independent experiments over a time period of 16 mo.

RESULTS

The polymicrobial infection resulted in severe peritoneal inflammation with a systemic increase in cytokines. The mortality rate at 15 h was 29% and this was reproducible over a 16 mo time period. If antibiotic treatment was applied, a 50% survival was achieved. Laboratory markers indicated a progressive multi-organ dysfunction, while blood gas analysis showed respiratory compensation of a metabolic acidosis, and maintenance of PaO(2). Intravital microscopy of the liver revealed an impaired microcirculation. A decreased hemostatic potential was demonstrated by rotational thromboelastometry. Despite clinical recovery within 3 d, surviving animals showed laboratory and histologic signs of persisting inflammation even after 2 wk.

CONCLUSIONS

This model reflects many features of human sepsis. Application of an infectious focus that is both quantitatively and qualitatively defined assures high reproducibility. Moreover, the procedure is simple and can be easily standardized.

Adrenergic support in septic shock: a critical review

The definition of septic shock includes sepsis-induced hypotension despite adequate fluid resuscitation, along with the presence of organ perfusion abnormalities, and ultimately cell dysfunction. To restore adequate organ perfusion and cell homeostasis, cardiac output should be restored with volume infusion plus vasopressor agents as indicated. Appropriate arterial pressure for each individual patient and proper arterial oxygen content are key elements to restoring perfusion. Tissue perfusion can be monitored by markers of organ and mitochondrial function, namely urine output, level of consciousness, peripheral skin perfusion, central or mixed venous oxygen saturation, and lactate. The hemodynamic effects of the different vasopressor agents depend on the relative affinity to adrenergic receptors. Those with predominant alpha-agonist activity produce more vasoconstriction (inoconstrictors) while those with predominant beta-agonist stimulation increase cardiac performance (inodilators). The debate about whether one vasopressor agent is superior to another is still ongoing. The Surviving Sepsis Campaign guidelines refer to either norepinephrine or dopamine as the first-choice vasopressor agent to correct hypotension in septic shock. However, recent data from observational and controlled trials have challenged these recommendations concerning different adrenergic agents. As a result, our view on the prescription of vasopressors has changed from a probably oversimplified "one-size-fits-all" approach to a multimodal approach in vasopressor selection.

Vasopressin synthesis by the magnocellular neurons is different in the supraoptic nucleus and in the paraventricular nucleus in human and experimental septic shock

Impaired arginine vasopressin (AVP) synthesis and release by the neurohypophyseal system, which includes the neurohypophysis and magnocellular neurons of the paraventricular and supraoptic nuclei, have been postulated in septic shock, but changes in this system have never been assessed in human septic shock, and only partially experimentally. We investigated AVP synthesis and release by the neurohypophyseal system in 9 patients who died from septic shock and 10 controls, and in 20 rats with fecal peritonitis-induced sepsis and 8 sham-operation controls. Ten rats died spontaneously from septic shock, and the others were sacrificed. In patients with septic shock, as in rats that died spontaneously following sepsis induction, AVP immunohistochemical expression was decreased in the neurohypophysis and supraoptic magnocellular neurons, whereas it was increased in the paraventricular magnocellular neurons. No significant change was observed in AVP messenger RiboNucleic Acid (mRNA) expression assessed by in situ hybridization in either paraventricular or supraoptic magnocellular cells. This study shows that both in human and experimental septic shock, AVP posttranscriptional synthesis and transport are differently modified in the magnocellular neurons of the supraoptic and paraventricular nuclei. This may account for the inappropriate AVP release in septic shock and suggests that distinct pathogenic mechanisms operate in these nuclei.

Continuous terlipressin versus vasopressin infusion in septic shock (TERLIVAP): a randomized, controlled pilot study

Introduction

Recent clinical data suggest that early administration of vasopressin analogues may be advantageous compared to a last resort therapy. However, it is still unknown whether vasopressin and terlipressin are equally effective for hemodynamic support in septic shock. The aim of the present prospective, randomized, controlled pilot trial study was, therefore, to compare the impact of continuous infusions of either vasopressin or terlipressin, when given as first-line therapy in septic shock patients, on open-label norepinephrine requirements.

Methods

We enrolled septic shock patients (n = 45) with a mean arterial pressure below 65 mmHg despite adequate volume resuscitation. Patients were randomized to receive continuous infusions of either terlipressin (1.3 μg·kg^-1·h^-1), vasopressin (.03 U·min^-1) or norepinephrine (15 μg·min^-1; n = 15 per group). In all groups, open-label norepinephrine was added to achieve a mean arterial pressure between 65 and 75 mmHg, if necessary. Data from right heart and thermo-dye dilution catheterization, gastric tonometry, as well as laboratory variables of organ function were obtained at baseline, 12, 24, 36 and 48 hours after randomization. Differences within and between groups were analyzed using a two-way ANOVA for repeated measurements with group and time as factors. Time-independent variables were compared with one-way ANOVA.

Results

There were no differences among groups in terms of systemic and regional hemodynamics. Compared with infusion of .03 U of vasopressin or 15 μg·min^-1 of norepinephrine, 1.3 μg·kg^-1·h^-1 of terlipressin allowed a marked reduction in catecholamine requirements (0.8 ± 1.3 and 1.2 ± 1.4 vs. 0.2 ± 0.4 μg·kg^-1·min^-1 at 48 hours; each P < 0.05) and was associated with less rebound hypotension (P < 0.05). At the end of the 48-hour intervention period, bilirubin concentrations were higher in the vasopressin and norepinephrine groups as compared with the terlipressin group (2.3 ± 2.8 and 2.8 ± 2.5 vs. 0.9 ± 0.3 mg·dL^-1; each P < 0.05). A time-dependent decrease in platelet count was only observed in the terlipressin group (P < 0.001 48 hours vs. BL).

Conclusions

The present study provides evidence that continuous infusion of low-dose terlipressin – when given as first-line vasopressor agent in septic shock – is effective in reversing sepsis-induced arterial hypotension and in reducing norepinephrine requirements.

Trial registration

ClinicalTrial.gov NCT00481572.

Recently published papers: predictors, pressors and poietins

Simple, sensitive and specific predictors of mortality in the critically ill remain elusive goals, and brain natriuretic peptide and venous lactate are the subjects of recent studies. The role of vasopressin in sepsis continues to be the focus of much research interest. Dose ranging studies, potential adverse effects, and selective V1 agonists are discussed below in recent trials. Finally the use of erythropoietin in the critically ill continues to be studied but many continue to urge caution for widespread use outside of clinical trials.