Hemodynamic and metabolic effects of vasopressin blockade in endotoxin shock

Influence of innate immune activation on endocrine and metabolic pathways in infancy

Prematurity is the leading cause of neonatal morbidity and mortality worldwide. Premature infants often require extended hospital stays, with increased risk of developing infection compared with term infants. A picture is emerging of wide-ranging deleterious consequences resulting from innate immune system activation in the newborn infant. Those who survive infection have been exposed to a stimulus that can impose long-lasting alterations into later life. In this review, we discuss sepsis-driven alterations in integrated neuroendocrine and metabolic pathways and highlight current knowledge gaps in respect of neonatal sepsis. We review established biomarkers for sepsis and extend the discussion to examine emerging findings from human and animal models of neonatal sepsis that propose novel biomarkers for early identification of sepsis. Future research in this area is required to establish a greater understanding of the distinct neonatal signature of early and late-stage infection, to improve diagnosis, curtail inappropriate antibiotic use, and promote precision medicine through a biomarker-guided empirical and adjunctive treatment approach for neonatal sepsis. There is an unmet clinical need to decrease sepsis-induced morbidity in neonates, to limit and prevent adverse consequences in later life and decrease mortality.

Non-Hemodynamic Effects of Catecholamines

Circulatory shock is defined as an imbalance between tissue oxygen supply and demand, and mostly results from a loss of blood volume, cardiac pump failure, and/or reduction of vasomotor tone. The clinical hallmarks of circulatory shock are arterial hypotension and lactate acidosis. Since the degree and duration of hypotension are major determinants of outcome, vasopressor administration represents a cornerstone therapy to treat these patients. Current guidelines recommend the use of catecholamines as the drug of first choice. However, apart from their hemodynamic effects, which depend on the different receptor profile, receptor affinity, receptor density, and the relative potency of the individual molecule, catecholamines have numerous other biological effects as a result of the ubiquitous presence of their receptors. In shock states, catecholamines aggravate hypermetabolism by promoting hyperglycemia and hyperlactatemia, and further increase oxygen demands, which can contribute to further organ damage. In the mitochondria, catecholamines may promote mitochondrial uncoupling, and aggravate oxidative stress, thereby contributing to the progression of mitochondrial dysfunction. Immunological side effects have also gained specific attention. Although both pro- and anti-inflammatory effects have been described, current evidence strongly indicates an immunosuppressive effect, thereby making patients potentially vulnerable to secondary infections. Catecholamines may not only decrease splanchnic perfusion due to their vasoconstrictor properties, but can also directly impair gastrointestinal motility. This article reviews the non-hemodynamic effects of different catecholamines, both under physiologic and pathophysiologic conditions, with a special focus on energy metabolism, mitochondrial function, immune response, and the gastrointestinal system.

Resuscitation after cardiac arrest in a septic porcine model: adding vasopressin vs epinephrine alone administration

Background

Vasopressin administration has been tested in cardiac arrest. However it has not been tested when cardiac arrest occurs in certain circumstances, as in sepsis, where it may have a major role. The aim of the study was to investigate survival after cardiac arrest in a septic porcine model compared with healthy animals and to explore the effectiveness of adding vasopressin vs epinephrine alone administration.

Methods

Thirty five healthy piglets of both genders were studied. The piglets were randomly assigned into three groups: group A (n = 8), group B (n = 14), group C (n = 13). Animals of groups B and C were given endotoxin to mimic a septic state before arrest. We applied the same resuscitation protocol to all pigs but we replaced the first dose of epinephrine with vasopressin in pigs of group C. Following surgical preparation and 30 min resting period, baseline measurements were recorded. In order to assess tissue oxygenation, we implemented Near Infrared Spectroscopy (NIRS) with the vascular occlusion technique (VOT) in thirteen lipopolysaccharide (LPS)-treated animals, occluding abdominal aorta and inferior vena cava. Afterwards, LPS (100 μg/kg) was infused in a 30 min period to animals of groups B and C and normal saline to group A. New NIRS measurements were obtained again. Subsequently, we provoked ventricular fibrillation (VF). After 3 min of untreated VF, open chest cardiopulmonary resuscitation (CPR) was performed manually. Primary end point was the restoration of spontaneous circulation (ROSC).

Results

The chance of ROSC for the groups A, B and C was 75%, 35.7%, and 30.7% respectively. A significant difference in ROSC was established between septic (group B + C) and non septic piglets (group A) (P = 0.046). Vasopressin administration had no effect in outcome. LPS administration decreased oxygen consumption rate, as assessed by NIRS, in peripheral tissues (22.6 ± 7.2. vs 18.5 ± 7.2, P = 0.07).

Conclusion

Septic piglets have fewer chances to survive after cardiac arrest. No difference in outcome was observed when the first dose of epinephrine was replaced with vasopressin to treat cardiac arrest in the LPS-treated animals.

Vasopressin for the septic burn patient

BACKGROUND

Exogenous arginine vasopressin (VP) has been increasingly used in the hemodynamic management of critically ill patients with septic shock, but its use in septic burn patients has not been systematically examined.

PURPOSE

To review our experience with the use of VP in septic burn patients.

METHODS

Retrospective review of all patients who received VP at a tertiary care adult regional burn centre. Only patients who strictly met the American College of Chest Physicians/Society of Critical Care Medicine Consensus Criteria for sepsis at the time of VP initiation were analysed.

RESULTS

There were 30 septic burn patients treated on 43 distinct occasions with VP. This group had a mean (+/-S.D.) age of 49+/-19 years, a mean % TBSA burn of 41+/-15% and a 37% incidence of inhalation injury. A significant increase in mean arterial pressure (MAP), a significant decrease in heart rate (HR), and a trend towards increased urine output (UO) occurred following initiation of VP. When VP was added to an existing infusion of norepinephrine (NE), there was a significant NE sparing effect. VP was implicated in the death of one patient who developed diffuse upper gastrointestinal necrosis while on VP. Other complications in patients treated with VP included peripheral ischemia (2), skin graft failure (1) and donor site conversion (1). In all complications, VP had been administered in combination with prolonged NE infusions (mean of 10 microg/min over a mean of 177 h).

CONCLUSION

VP is a useful adjunctive pressor that spares NE requirements in septic burn patients, but its use is not without risks, particularly when VP is combined with sustained moderate to high infusions of NE.

Vasopressin: mechanisms of action on the vasculature in health and in septic shock

BACKGROUND

Vasopressin is essential for cardiovascular homeostasis, acting via the kidney to regulate water resorption, on the vasculature to regulate smooth muscle tone, and as a central neurotransmitter, modulating brainstem autonomic function. Although it is released in response to stress or shock states, a relative deficiency of vasopressin has been found in prolonged vasodilatory shock, such as is seen in severe sepsis. In this circumstance, exogenous vasopressin has marked vasopressor effects, even at doses that would not affect blood pressure in healthy individuals. These two findings provide the rationale for the use of vasopressin in the treatment of septic shock. However, despite considerable research attention, the mechanisms for vasopressin deficiency and hypersensitivity in vasodilatory shock remain unclear.

OBJECTIVE

To summarize vasopressin's synthesis, physiologic roles, and regulation and then review the literature describing its vascular receptors and downstream signaling pathways. A discussion of potential mechanisms underlying vasopressin hypersensitivity in septic shock follows, with reference to relevant clinical, in vivo, and in vitro experimental evidence.

DATA SOURCE

Search of the PubMed database (keywords: vasopressin and receptors and/or sepsis or septic shock) for articles published in English before May 2006 and manual review of article bibliographies.

DATA SYNTHESIS AND CONCLUSIONS

The pathophysiologic mechanism underlying vasopressin hypersensitivity in septic shock is probably multifactorial. It is doubtful that this phenomenon is merely the consequence of replacing a deficiency. Changes in vascular receptors or their signaling and/or interactions between vasopressin, nitric oxide, and adenosine triphosphate-dependent potassium channels are likely to be relevant. Further translational research is required to improve our understanding and direct appropriate educated clinical use of vasopressin.

Management of vasodilatory shock: defining the role of arginine vasopressin

The rationale for an arginine vasopressin (argipressin) infusion was put forward after it was discovered that patients in shock states might have an endogenous arginine vasopressin deficiency. Subsequently, several investigations impressively demonstrated that arginine vasopressin can successfully stabilise haemodynamics even in advanced vasodilatory shock. We report on physiological and pharmacological aspects of arginine vasopressin, and summarise current clinical knowledge on employing a continuous arginine vasopressin infusion in critically ill patients with catecholamine-resistant vasodilatory shock of different aetiologies. In view of presented experimental evidence and current clinical experience, a continuous arginine vasopressin infusion of approximately 2 to approximately 6 IU/h can be considered as a supplemental strategy to vasopressor catecholamines in order to preserve cardiocirculatory homeostasis in patients with advanced vasodilatory shock. Because data on adverse effects are still limited, arginine vasopressin should be reserved for patients in whom adequate haemodynamic stabilisation cannot be achieved with conventional vasopressor therapy or who have obvious adverse effects of catecholamines that result in further significant haemodynamic deterioration. For the same reasons, arginine vasopressin should not be used as a single, alternative vasopressor agent instead of catecholamine vasopressors. Future prospective studies will be necessary to define the exact role of arginine vasopressin in the therapy of vasodilatory shock.

Low-dose terlipressin improves systemic and splanchnic hemodynamics in fluid-challenged endotoxic rats

OBJECTIVE

Vasopressin has been used to treat arterial hypotension associated with hyperdynamic vasoplegic states, but detrimental effects on splanchnic circulation have been reported. We tested the effects of a low-dose vasopressin analogue, terlipressin (6 microg/kg), on systemic and splanchnic hemodynamics in fluid-challenged endotoxic rats (lipopolysaccharide, 30 mg/kg in 1 hr).

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

A total of 77 rats were divided into five groups: group C, control (17 rats); group E, LPS (18 rats); group EF, LPS plus fluid challenge (18 rats); group EFT, LPS plus fluid challenge plus terlipressin (18 rats); and group ET, LPS plus terlipressin (seven rats).

INTERVENTIONS

Rats were anesthetized, mechanically ventilated, and instrumented to measure heart rate, mean arterial pressure, and abdominal aortic and mesenteric vein indexed blood flows; ileal microcirculation was assessed by laser Doppler. After LPS infusion, rats experienced an endotoxic shock and were resuscitated after the allocation group. The fluid challenge was targeted to maintain mean arterial pressure of >90 mm Hg and aortic blood flow at baseline values.

MEASUREMENTS AND MAIN RESULTS

Terlipressin significantly (p <.05) increased mean arterial pressure without decreasing indexed aortic blood flow and heart rate in the fluid-challenged endotoxic rats (EFT) compared with EF rats and had detrimental effects in hypodynamic endotoxic rats (ET). Fluid challenge significantly (p <.05) increased mesenteric vein blood flow in both the EF and EFT groups, and terlipressin had no detrimental effect on mesenteric blood flow. Terlipressin significantly (p <.05) increased ileal microcirculation in fluid-challenged endotoxic rats (EF and EFT) but not in hypodynamic endotoxic rats (E and ET).

CONCLUSION

Low-dose terlipressin in fluid-challenged endotoxic rats improved systemic and splanchnic hemodynamics and improved the ileal microcirculation.

Vasopressin: new uses in critical care

The science of medicine has evolved dramatically over recent years, with better understanding of the mechanisms of disease leading to innovative new treatments. However, the critical care patient still suffers from a high mortality rate with few advances from the traditional modalities of therapy. Arginine vasopressin has been explored as a vasoconstrictor in the treatment of the hypotension associated with septic shock. This drug has also recently been added to the advanced cardiac life support protocol for the resuscitation of pulseless ventricular tachycardia and ventricular fibrillation. Studies of arginine vasopressin in these situations have been promising but still have yet to prove a survival benefit over traditional therapies. Newer and larger trials are necessary to determine whether any mortality benefit can be sustained from the use of arginine vasopressin in critical care patients with septic shock and cardiac arrest secondary to pulseless ventricular tachycardia and ventricular fibrillation.

Vasopressin and shock

Vasopressin (antidiuretic hormone) is emerging as a potentially major advance in the treatment of a variety of shock states. Increasing interest in the clinical use of vasopressin has resulted from the recognition of its importance in the endogenous response to shock and from advances in understanding of its mechanism of action. From animal models of shock, vasopressin has been shown to produce greater blood flow diversion from non-vital to vital organ beds (particularly the brain) than does adrenaline. Although vasopressin has similar direct actions to the catecholamines, it may uniquely also inhibit some of the pathologic vasodilator processes that occur in shock states. There is current interest in the use of vasopressin in the treatment of shock due to ventricular fibrillation, hypovolaemia, sepsis and cardiopulmonary bypass. This article reviews the physiology and pharmacology of vasopressin and all of the relevant animal and human clinical literature on its use in the treatment of shock following a MEDLINE (1966-2000) search.

Hemodynamic and metabolic effects of low-dose vasopressin infusions in vasodilatory septic shock

OBJECTIVE

To investigate the physiologic effects of exogenous vasopressin as a potential alternative to traditional high-dose catecholamine therapy for septic patients with vascular hyporeactivity to catecholamines.

DESIGN

Prospective, case-controlled study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Vasopressin was infused in 16 critically ill septic patients who remained persistently hypotensive despite infusions of pharmacologic doses of catecholamines.

INTERVENTION

Continuous intravenous infusion of vasopressin at 0.04 units/min for 16 hrs, in place of escalating the amount of catecholamines being infused.

MEASUREMENTS AND MAIN RESULTS

After administration of vasopressin, systemic vascular resistance and mean arterial pressure were immediately and significantly increased in comparison with the values obtained just before vasopressin. When the vasopressin infusions were discontinued, mean arterial pressure decreased immediately and dramatically. We did not detect any obvious adverse cardiac effects during the vasopressin infusions. Vasopressin had no effect on other hemodynamic parameters or any of the metabolic parameters studied, including measures of oxygenation, plasma glucose, or electrolytes. Urine output increased significantly during the administration of vasopressin, although this effect may be nonspecific. Lactate concentrations decreased, particularly in the survival group, but the decreases were not significant. Overall survival was 56%.

CONCLUSIONS

Low-dose vasopressin infusions increased mean arterial pressure, systemic vascular resistance, and urine output in patients with vasodilatory septic shock and hyporesponsiveness to catecholamines. The data indicate that low-dose vasopressin infusions may be useful in treating hypotension in these patients.

The effects of vasopressin on endotoxin-induced attenuation of contractile responses in human gastroepiploic arteries in vitro

We studied the effects of vasopressin on contraction in normal and endotoxin-treated human gastroepiploic arterial rings in vitro. In this tissue, vasopressin (50-500 pg/mL) produced concentration-dependent, endothelium-independent contractions. Vasopressin also potentiated the contraction elicited by 1.0 micromol/L norepinephrine (NE) in both the presence and absence of endothelium. Endotoxin (10 microg/mL) attenuated the 1.0 micromol/L NE-induced contractions, and this attenuation was reversed by 300 micromol/L N(G)-nitro-L-arginine-methyl ester (L-NAME) and by 300 micromol/L N(G)-nitro-L-arginine (L-NoArg). After 12 h endotoxin treatment, the vasopressin-induced contraction was attenuated, and the enhancing effect of vasopressin was diminished. However, both before and after endotoxin, the enhancement produced by vasopressin was larger than the vasopressin-contraction itself. An antagonist of the vasopressin V1 receptor, 1.0 micromol/L beta-mercapto-[beta,beta-cyclopentamethylenpropionyl1,O-MeTyr2+ ++,Arg8]-vasopressin, and an antagonist of V1 + V2 receptor receptor, 1.0 micromol/L des-Gly9-[beta-mercapto-beta,beta-cyclopentamethylenepropionyl1 ,O-Et-Tyr2,Val,Arg8]-vasopressin, each diminished the vasopressin-induced enhancement of the NE contraction.

IMPLICATIONS

The results of our study suggest that, in addition to its direct vasoconstrictor effect, vasopressin strongly enhances the responses to norepinephrine through V1-receptor stimulation and that vasopressin could find a role in the management of endotoxin-induced vasodilation.

Endogenous vasopressin increases acute endotoxin shock-provoked gastrointestinal mucosal injury in the rat

Administration of a low dose of endotoxin (from Escherichia coli, 3 mg kg(-1), i.v.), which does not affect vascular permeability or blood pressure over 1 h, leads to the release of endogenous vasopressin and damage to the mucosal microvasculature. Thus, endogenous vasopressin could be involved in septic shock. In the present study, we investigated the role of endogenous vasopressin in gastrointestinal mucosal injury induced by acute endotoxin shock, which was generated in rats by administering a high dose of E. coli endotoxin (50 mg kg(-1), i.v.). Tissues were removed 15 min after endotoxin. The vasopressin V1 receptor antagonist, d[CH2]5Tyr[Me]arginine-vasopressin (0.2-1 microg kg(-1), i.v.), was injected 10 min before endotoxin. Monastral blue (30 mg kg(-1), i.v.), which stains damaged vasculature, was injected 10 min before autopsy. Endotoxin reduced systemic arterial blood pressure (from 115+/-5 to 42+/-4 mmHg), generated macroscopic and microvascular injury, and elevated plasma vasopressin levels (from 3.4+/-0.2 to 178+/-16 pg ml(-1)). The vasopressin V1 receptor antagonist reduced this macroscopic injury, and in the vasopressin-deficient Brattleboro rat a similar reduction of gastrointestinal mucosal damage was found. Substantial decreases in endotoxin-induced microvascular damage were observed in each tissue, e.g., the gastric Monastral blue staining was reduced by 47+/-3% and 96+/-3% (P < 0.01) after vasopressin V1 receptor antagonist treatment and in Brattleboro rats, respectively. Vasopressin, acting through its V1 receptors, thus appears to be involved in acute endotoxin shock-provoked gastrointestinal injury.