Photonic monitoring of treatment during infection and sepsis: development of new detection strategies and potential clinical applications

Despite the strong decline in the infection-associated mortality since the development of the first antibiotics, infectious diseases are still a major cause of death in the world. With the rising number of antibiotic-resistant pathogens, the incidence of deaths caused by infections may increase strongly in the future. Survival rates in sepsis, which occurs when body response to infections becomes uncontrolled, are still very poor if an adequate therapy is not initiated immediately. Therefore, approaches to monitor the treatment efficacy are crucially needed to adapt therapeutic strategies according to the patient's response. An increasing number of photonic technologies are being considered for diagnostic purpose and monitoring of therapeutic response; however many of these strategies have not been introduced into clinical routine, yet. Here, we review photonic strategies to monitor response to treatment in patients with infectious disease, sepsis, and septic shock. We also include some selected approaches for the development of new drugs in animal models as well as new monitoring strategies which might be applicable to evaluate treatment response in humans in the future. Figure Label-free probing of blood properties using photonics.

Characteristics of a Pseudomonas aeruginosa induced porcine sepsis model for multi-organ metabolic flux measurements

Survival of sepsis is related to loss of muscle mass. Therefore, it is imperative to further define and understand the basic alterations in nutrient metabolism in order to improve targeted sepsis nutritional therapies. We developed and evaluated a controlled hyperdynamic severe sepsis pig model that can be used for in vivo multi-organ metabolic studies in a conscious state. In this catheterized pig model, bacteremia was induced intravenously with 109 CFU/h Pseudomonas aeruginosa (PA) in 13 pigs for 18 h. Both the PA and control (nine) animals received fluid resuscitation and were continuously monitored. We examined in detail their hemodynamics, blood gases, clinical chemistry, inflammation, histopathology and organ plasma flows. The systemic inflammatory response (SIRS) diagnostic scoring system was used to determine the clinical septic state. Within 6 h from the start of PA infusion, a septic state developed, as was reflected by hyperthermia and cardiovascular changes. After 12 h of PA infusion, severe sepsis was diagnosed. Disturbed cardiovascular function, decreased portal drained viscera plasma flow (control: 37.6 ± 4.6 mL/kg body weight (bw)/min; PA 20.3 ± 2.6 mL/kg bw/min, P < 0.001), as well as moderate villous injury in the small intestines were observed. No lung, kidney or liver failure was observed. Acute phase C-reactive protein (CRP) and interleukin-6 (IL-6) levels did not change in the PA group. However, significant metabolic changes such as enhanced protein breakdown, hypocalcemia and hypocholesterolemia were found. In conclusion, PA-induced bacteremia in a catheterized pig is a clinically relevant model for acute severe sepsis and enables the study of complex multi-organ metabolisms.

The differential effects of recombinant brain natriuretic peptide, nitroglycerine and dihydralazine on systemic oxygen delivery and gastric mucosal microvascular oxygenation in dogs

Brain natriuretic peptide has vasodilatory properties and may thus increase splanchnic perfusion and oxygenation. We compared the effects of recombinant brain natriuretic peptide on gastric mucosal microvascular haemoglobin oxygenation (reflectance spectrophotometry) and systemic variables with those of equi-hypotensive doses of two other vasodilators (nitroglycerine and dihydralazine). Chronically instrumented, healthy dogs were randomly allocated to receive on different days, one of the three drugs (nitroglycerine and dihydralazine doses titrated to reduce mean arterial pressure by ∼20%). Brain natriuretic peptide significantly increased gastric mucosal microvascular haemoglobin oxygenation selectively, i.e. without concomitant haemodynamic effects. In contrast, the other vasodilators either did not increase gastric mucosal microvascular haemoglobin oxygenation at all (nitroglycerine), or did so only with marked increases in other systemic haemodynamic variables (dihydralazine). Our data suggest a potential role of recombinant brain natriuretic peptide selectively for increasing microvascular mucosal oxygenation. Studies are required to extend these findings to the clinical setting.

Magnesium sulfate mitigates acute lung injury in endotoxemia rats

BACKGROUND

Magnesium sulfate (MgSO4) possesses potent anti-inflammation capacity. We sought to elucidate the effects of MgSO4 on mitigating acute lung injury induced by endotoxemia. MgSO4 is an antagonist of the L-type calcium channels and the N-methyl-D-aspartate (NMDA) receptor. The roles of the L-type calcium channels and NMDA receptor in this regard were also elucidated.

METHODS

Ninety-six adult male rats were randomized to receive normal saline, MgSO4 (100 mg/kg), lipopolysaccharide (LPS), LPS plus MgSO4 (10, 50, or 100 mg/kg), LPS plus MgSO4 (100 mg/kg) plus the L-type calcium channel activator BAY-K8644, or LPS plus MgSO4 (100 mg/kg) plus exogenous NMDA (n=12 in each group). Between-group differences in lung injury were evaluated.

RESULTS

Histologic findings, in concert with assays of leukocyte infiltration (polymorphonuclear leukocytes/alveoli ratio and myeloperoxidase activity) and lung water content (wet/dry weight ratio), confirmed that LPS induced acute lung injury. LPS also caused significant inflammatory response (increases in chemokine, cytokine, and prostaglandin E2 concentrations) and imposed significant oxidative stress (increases in nitric oxide and malondialdehyde concentrations) in rat lungs. MgSO4 at the dosages of 50 mg/kg and 100 mg/kg, but not at 10 mg/kg, significantly mitigated the acute lung injury, lung inflammatory response, and oxidative stress caused by endotoxemia. Moreover, the protective effects of MgSO4 were counteracted by BAY-K8644 and exogenous NMDA.

CONCLUSIONS

MgSO4 mitigates lung inflammatory response, oxidative stress, and acute lung injury in endotoxemia rats in a dose-dependent manner. The mechanisms may involve antagonizing the L-type calcium channels and the NMDA receptor.

Endothelin-mediated gut microcirculatory dysfunction during porcine endotoxaemia

BACKGROUND

The potent vasoconstrictor endothelin-1 has been implicated in the pathogenesis of the microcirculatory dysfunction seen in sepsis. The mixed endothelin receptor antagonist tezosentan and the selective endothelin A-receptor antagonist TBC3711 were used to investigate the importance of the different endothelin receptors in modulating splanchnic regional blood flow and microvascular blood flow in endotoxaemia.

METHODS

Eighteen anaesthetized pigs were i.v. infused with endotoxin (Escherichia coli lipopolysaccharide, serotype 0111:b4) for 300 min. After 120 min, six animals received tezosentan and six animals received TBC3711. Six animals served as endotoxin-treated controls. Laser Doppler flowmetry was used to measure microcirculatory blood flow in the liver and ileum. Superior mesenteric artery flow (SMA(FI)) and portal vein flow (PV(FI)) were measured with ultrasonic flow probes, and air tonometry was used to measure Pco₂ in the ileal mucosa.

RESULTS

TBC3711 did not improve splanchnic regional blood flow or splanchnic microvascular blood flow compared with endotoxin-treated controls. Tezosentan increased PV(FI) (P<0.05), but SMA(FI) was not improved compared with the other groups. In the tezosentan group, microvascular blood flow in the ileal mucosa (MCQ(muc)) improved and mucosal-arterial Pco₂ gap decreased (P<0.05 for both) compared with endotoxin-treated controls and the TBC3711 group.

CONCLUSIONS

Tezosentan improved MCQ(muc) without any concomitant increase in SMA(FI), implying a direct positive effect on the microcirculation. TBC3711 was not effective in improving regional splanchnic blood flow or splanchnic microvascular blood flow. Dual endothelin receptor antagonism was necessary to improve MCQ(muc), indicating a role for the endothelin B-receptor in mediating the microcirculatory failure in the ileal mucosa.

Mechanisms, detection, and potential management of microcirculatory disturbances in sepsis

Despite improvements in resuscitation and treatment of sepsis, the morbidity and mortality remain unacceptably high. Microvascular dysfunction has been shown to play a significant role in the pathogenesis of sepsis and is a potential new target in the management of sepsis. Clinical studies, aided by new techniques that allow for real-time assessment of the microcirculation, have shown that disturbances in microcirculatory flow are common in sepsis and correlate with worse outcomes. Bedside measurement of microcirculatory perfusion has become simpler and more accessible, and may provide key insights into prognosis in sepsis and guide future therapeutics, much like mean arterial pressure (MAP), lactate, and mixed central oxygen saturation (SvO(2)) do now. The authors review here the role of microcirculatory dysfunction in sepsis and its potential role as a therapeutic target in sepsis.

Applying gases for microcirculatory and cellular oxygenation in sepsis: effects of nitric oxide, carbon monoxide, and hydrogen sulfide

PURPOSE OF REVIEW

Nitric oxide, carbon monoxide, and hydrogen sulfide (H2S) are gases that have received attention as signaling molecules regulating many biological processes. All of them were reported to have beneficial effects in inflammatory states, in particular for microcirculatory perfusion and tissue energy balance. Thus, this review will highlight the most important results with a focus on resuscitated, clinically relevant experimental models and, if available, human studies.

RECENT FINDINGS

There is ample evidence that nitric oxide, carbon monoxide, and H2S may exert cytoprotective effects in shock states due to their vasomotor, antioxidant, and anti-inflammatory properties as well as their potential to induce a hibernation-like metabolic state called 'suspended animation' resulting from inhibition of cytochrome-c-oxidase. It must be emphasized, however, that the three molecules may also be cytotoxic, not only because of their inhibition of cellular respiration but also because of their marked pro-inflammatory effects.

SUMMARY

It is still a matter of debate whether manipulating nitric oxide, carbon monoxide, or H2S tissue concentrations, either by using the inhaled gas itself or by administering donor molecules or inhibitors of their endogenous production, is a useful therapeutic approach to improve microcirculatory blood flow, tissue oxygenation, and cellular respiration. This is mainly due to their 'friend and foe character' documented in various experimental models, but also to the paucity of data from long-term, resuscitated large animal experiments that fulfil the criteria of clinically relevant models.

The microcirculation as a diagnostic and therapeutic target in sepsis

The microcirculation is defined as the smallest vessels where gas and nutrient exchange with tissues takes place. One of its primary functions is to ensure adequate oxygen delivery to meet the oxygen demands of tissue cells. Previous data from clinical and experimental studies and the recent development of new imaging modalities, such as Orthogonal Polarization Spectral videomicroscopy and Sidestream Dark Field imaging, have helped to identify the crucial role that microcirculation plays in sepsis. If not corrected, microcirculatory dysfunction can lead to respiratory distress in tissue cells and subsequent organ failure, even in the absence of global hemodynamic deficiency. In the present review, we will address past and recent developments regarding the role of the microcirculation as an important target in the pathogenesis of sepsis and its progression to multiple organ failure. Accordingly, we identify the microcirculation as an important diagnostic and therapeutic target for treatment in sepsis.

Bench-to-bedside review: nitric oxide in critical illness--update 2008

Nitric oxide (NO) is a unique and nearly ubiquitous molecule that is widely utilized as a signaling molecule in cells throughout the body. NO is highly diffusible, labile, and multiply reactive, suiting it well for its role as an important regulator of a number of diverse biologic processes, including vascular tone and permeability, platelet adhesion, neurotransmission, and mitochondrial respiration. NO can protect cells against antioxidant injury, can inhibit leukocyte adhesion, and can participate in antimicrobial defense, but can also have deleterious effects, including inhibition of enzyme function, promotion of DNA damage, and activation of inflammatory processes. This molecule's chemistry dictates its biologic activity, which can be both direct and indirect. In addition, NO has bimodal effects in a number of cells, maintaining homeostasis at low doses, and participating in pathophysiology in others. Perturbation of NO regulation is involved in the most important and prevalent disease processes in critical care units, including sepsis, acute lung injury, and multiple organ failure. Given that NO is ubiquitous, highly diffusible, and promiscuously reactive, its regulation is complex. The NO concentration, kinetics, and localization, both inside and outside the cell, are clearly crucial factors. In the present update we review a selection of studies that have yielded important information on these complex but important issues. Interpretation of these and other studies aimed at elucidating physiologic and pathophysiologic roles of NO must take this complexity into account. A full review of the role of NO in these diseases is beyond the scope of the current manuscript; the present article will focus on recent advances in understanding the complex role of NO in health and disease.

Epoprostenol improves mucosal tissue oxygen tension in an acute endotoxemic pig model

The objective of the present study was to determine the effects of increasing dosages of continuously infused epoprostenol (PGI), a prostacyclin analog, on intestinal oxygen supply and jejunal mucosal tissue oxygen tension in an acute endotoxic pig model. Jejunal mucosal tissue PO2, oxygen saturation of jejunal microvascular hemoglobin, and gut microvascular blood flow were investigated. Systemic hemodynamic variables, mesenteric-venous and systemic acid base and blood gas variables, and lactate measurements were recorded. Measurements were performed at baseline, after Escherichia coli LPS administration, and at 20-min intervals during incremental PGI infusion (n = 8; 25, 50, 100, and 200microg x kg x h, respectively); or infusion of an equal amount of isotonic sodium chloride solution (n = 7). LPS infusion led to a significant decrease in mucosal tissue oxygen tension and microvascular hemoglobin oxygen saturation. Epoprostenol infusion led to a significant, dose-dependent increase in cardiac index and systemic oxygen delivery. Mucosal tissue oxygen tension and microvascular hemoglobin oxygen saturation increased after PGI administration and even returned to more-than-baseline values. Continuously infused PGI increased intestinal hemoglobin oxygen saturation and mucosal tissue oxygen tension in a dose-dependent manner mainly due to an increase in villus blood flow in this acute endotoxic pig model.

Systematic evaluation of nitric oxide, tetrahydrobiopterin, and anandamide levels in a porcine model of endotoxemia

PURPOSE

Using a lipopolysaccharide (LPS)-treated porcine model, we examined: (1) whether nitric oxide (NO), anandamide, and tetrahydrobiopterin (BH4) increased or not in early endotoxic shock; and (2) the location of the major site of production of these molecules, by comparing their concentrations in arteries and the portal and hepatic veins.

METHODS

Ten pigs received an infusion of LPS at 1.7 microg x kg(-1)x h(-1) via the portal vein for 240 min. Consecutive changes in systemic hemodynamics, hepatosplanchnic circulation, and oxygen delivery were measured. Furthermore, the variable changes in the concentrations of nitrite and nitrate (NOx), anandamide, and BH4 were measured. To access the effects of surgery, anesthesia, and fluid management on BH4, an experiment without LPS infusion was performed in two other animals.

RESULTS

Mean arterial pressure and cardiac index started to decrease at 60 min after LPS infusion. However, systemic vascular resistance remained unchanged. Total hepatic blood flow and hepatic oxygen delivery also decreased significantly. NOx and anandamide did not change during LPS infusion. BH4 values did not change without LPS infusion. However, BH4 values increased significantly in the arterial, portal, and hepatic circulation during LPS infusion, especially in the hepatic vein (from 136.8 +/- 27.5 to 281.3 +/- 123.2 mol/ml; P < 0.01).

CONCLUSION

Our data suggest that the BH4 values were significantly increased in several organs, especially in the liver during endotoxic shock. Impaired cardiac output and decreased blood pressure appeared in the early phase of porcine endotoxemia. Longer-term observation of these parameters after LPS treatment should be performed as the next step in future studies.