Progressive decrease in constrictor reactivity of the non-absorbing intestine during chronic sepsis.

Chronic sepsis leads to an impaired intestinal microcirculation, which might reflect altered microvascular control. We hypothesized that intestinal microvascular sensitivity to norepinephrine (NE) is decreased during chronic sepsis. Chronic sepsis was induced by a polymicrobial inoculation of implanted subcutaneous sponges in rats. Septic rats were studied either 24 or 72 h after a single inoculation (1-hit) of bacteria. Other rats received a second inoculation (2-hit) of bacteria 48 h later and were studied at 24 h after the second inoculation. NE (0.01-1.0 microM) responses in the non-absorbing terminal ileal arterioles (inflow A1, proximal-p and distal-d premucosal A3) were measured by video microscopy. NE threshold sensitivity (pD(T20) = -log of 20% response dose) was analyzed. pD(T20) was significantly decreased in A1, pA3, and dA3 of 1-hit 24-h septic rats (P < 0.05), and was further decreased in all vessels of 2-hit 72-h septic rats (P < 0.05). In contrast, the pDT(T20) of all three vessels significantly returned toward normal values after 72 h in rats that had only 1 bacteria inoculation. We conclude that an initial bacterial challenge decreases vasoconstrictor reactivity of the intestinal microcirculation and that subsequent repeated bacterial challenge exacerbates this defect in vasoconstrictor control in the non-absorbing intestine.

Sepsis increases NOS-2 activity and decreases non-NOS-mediated acetylcholine-induced dilation in rat aorta.

INTRODUCTION: Acetylcholine (Ach) is frequently used to assess endothelium-dependent vasodilation during sepsis. However, the effects of sepsis on constitutive nitric oxide synthase activity (NOS-1 and -3) and other non-NOS effects of Ach are unclear. METHODS: Sepsis was induced in rats by inoculation of an implanted sponge with Escherichia coli and Bacteroides fragilis (10(9) CFU each). Thoracic aortic rings (2 mm) were harvested at 24 h from septic (N = 9) and control (N = 9) rats and were suspended in physiological salt solution (PSS), PSS + l-N(6)-(1-iminoethyl)lysine (l-NIL: NOS-2 inhibitor, 10 microM), or PSS + l-N(G)-monomethylarginine (l-NMMA: NOS-1, -2, and -3 inhibitor, 60 microM). Rings were set at 1-g preload and precontracted with phenlyephrine (10(-8) M). Relaxation dose-response curves were generated with six doses of Ach (3 x 10(-8) to 10(-5) M). RESULTS: Sepsis increased the maximal relaxation to Ach under basal conditions. NOS 2 inhibition with l-NIL decreased Ach-induced relaxation in controls (66% vs 84%, P < 0.05, two-way ANOVA) and more so in septic rats (44% vs 93%, P < 0.05). Total NOS inhibition with l-NMMA decreased Ach-induced relaxation to 45% (P < 0.05) in controls and to 30% (P < 0.05) in septic animals. CONCLUSIONS: Inhibition of NOS-1, -2, and -3 failed to abolish Ach-induced relaxation, suggesting the presence of other Ach-induced vasodilator mechanisms. NOS-2 inhibition reduced Ach-induced relaxation by 20-25% in the normal thoracic aorta, but by 50% in septic animals. The remaining Ach-induced non-NOS vasodilation (after inhibition of NOS-1 + NOS-2 + NOS-3) was reduced from 45% in normals to 30% in septic animals. Vascular dysregulation in sepsis is a complex event involving increased NOS-2, decreased NOS-1 + NOS-3, and decreased Ach-induced non-NOS vasodilator mechanisms.

PAF increases vascular permeability without increasing pulmonary arterial pressure in the rat.

In vivo pulmonary arterial catheterization was used to determine the mechanism by which platelet-activating factor (PAF) produces pulmonary edema in rats. PAF induces pulmonary edema by increasing pulmonary microvascular permeability (PMP) without changing the pulmonary pressure gradient. Rats were cannulated for measurement of pulmonary arterial pressure (Ppa) and mean arterial pressure. PMP was determined by using either in vivo fluorescent videomicroscopy or the ex vivo Evans blue dye technique. WEB 2086 was administered intravenously (IV) to antagonize specific PAF effects. Three experiments were performed: 1) IV PAF, 2) topical PAF, and 3) Escherichia coli bacteremia. IV PAF induced systemic hypotension with a decrease in Ppa. PMP increased after IV PAF in a dose-related manner. Topical PAF increased PMP but decreased Ppa only at high doses. Both PMP (88 +/- 5%) and Ppa (50 +/- 3%) increased during E. coli bacteremia. PAF-receptor blockade prevents changes in Ppa and PMP after both topical PAF and E. coli bacteremia. PAF, which has been shown to mediate pulmonary edema in prior studies, appears to act in the lung by primarily increasing microvascular permeability. The presence of PAF might be prerequisite for pulmonary vascular constriction during gram-negative bacteremia.

Sustained infection induces 2 distinct microvascular mechanisms in the splanchnic circulation.

BACKGROUND: Altered intestinal blood flow during systemic inflammation leads to organ dysfunction. Mucosal ischemia occurs during sepsis despite an increase in portal blood flow. We hypothesized that separate mechanisms are active in the large resistance and small mucosal microvessels to account for this dichotomy. METHODS: Chronic infection was induced in rats by bacterial inoculation (Escherichia coli and Bacteroides fragilis) of an implanted subcutaneous sponge. Separate groups were studied at 24 and 72 hours after a single inoculation of bacterium or 24 hours after a second inoculation (ie, 72 hours of sepsis). Time-matched controls were used for each group. Intravital microscopy of the terminal ileum was used to assess endothelial-dependent vasodilation to acetylcholine (10(-9) to 10(-5) mol/L) in resistance (A(1)) and premucosal (A(3)) arterioles. Threshold sensitivity (-log of 20% response dose) was calculated from dose response curves for each animal. RESULTS: Vasodilator sensitivity to acetylcholine in A(1) arterioles was significantly decreased at 24 hours, and these changes persisted up to 72 hours after a single bacterial inoculation. There was no change in the dilator sensitivity of A(3) arterioles after a single inoculation. When there was a challenge with a second bacterial inoculation, there was a reversal of the A(1) dilator response and an increase in A(3) sensitivity. CONCLUSIONS: An initial septic event results in a decrease in dilator reactivity in the resistance A1 arterioles that persists for at least 72 hours. A sustained septic challenge results in increased dilator reactivity in both A(1) and A(3) vessels. This enhanced sensitivity during sepsis suggests that more than 1 therapeutic approach to preservation of intestinal blood flow will be necessary.

Lazaroid and pentoxifylline suppress sepsis-induced increases in renal vascular resistance via altered arachidonic acid metabolism.

Early sepsis leads to renal hypoperfusion, despite a hyperdynamic systemic circulation. It is thought that failure of local control of the renal microcirculation leads to hypoperfusion and organ dysfunction. Of the many mediators implicated in the pathogenesis of microvascular vasoconstriction, arachidonic acid metabolites are thought to be important. Vasoconstriction may be due to excess production of vasoconstrictors or loss of vasodilators. Using the isolated perfused kidney model, we describe a sepsis-induced rise in renal vascular resistance and increased production of key arachidonic acid metabolites, both vasoconstrictors and vasodilators, suggesting excessive production of vasoconstrictors as a cause for microcirculatory hypoperfusion. There is evidence of increased enzymatic production of arachidonic acid metabolites as well as nonenzymatic, free radical, catalyzed conversion of arachidonic acid. Pentoxifylline (a phosphodiesterase inhibitor) and U74389G (an antioxidant) both have a protective effect on the renal microcirculation during sepsis. Both drugs appear to alter the renal microvascular response to sepsis by altering renal arachidonic acid metabolism. This study demonstrates that sepsis leads to increased renal vascular resistance. This response is in part mediated by metabolites produced by metabolism of arachidonic acid within the kidney. The ability of drugs to modulate arachidonic acid metabolism and so alter the renal response to sepsis suggests a possible role for these agents in protecting the renal microcirculation during sepsis.

Regulation of intestinal blood flow.

The gastrointestinal system anatomically is positioned to perform two distinct functions: to digest and absorb ingested nutrients and to sustain barrier function to prevent transepithelial migration of bacteria and antigens. Alterations in these basic functions contribute to a variety of clinical scenarios. These primary functions intrinsically require splanchnic blood flow at both the macrovascular and microvascular levels of perfusion. Therefore, a greater understanding of the mechanisms that regulate intestinal vascular perfusion in the normal state and during pathophysiological conditions would be beneficial. The purpose of this review is to summarize the current understanding regarding the regulatory mechanisms of intestinal blood flow in fasted and fed conditions and during pathological stress.

Platelet-activating factor and bacteremia-induced pulmonary hypertension.

BACKGROUND: Acute lung injury is a common complication of gram-negative sepsis. Pulmonary hypertension and increased lung vascular permeability are central features of lung injury following experimental bacteremia. Platelet-activating factor is a prominent proinflammatory mediator during bacterial sepsis. Our previous studies have demonstrated that exogenous administration of platelet-activating factor (PAF) induces pulmonary edema without causing pulmonary hypertension. Interestingly, inhibition of PAF activity during Escherichia coli bacteremia prevents the development of both pulmonary hypertension and pulmonary edema. These data suggest that PAF contributes to pulmonary hypertension during sepsis, but that this is unlikely to be a direct vascular effect of PAF. The goal of the present study was to investigate the mechanism by which acute E. coli bacteremia induces pulmonary injury and to define the role that PAF plays in this injury. We hypothesized that the effects of PAF on pulmonary hypertension during bacteremia are due to the effects of PAF on other vascular mediators. Several studies suggest that PAF induces the expression of endothelin-1 (ET), a potent peptide vasoconstrictor. Further, our previous studies have implicated ET as a central mediator of systemic vasoconstriction during bacteremia. We therefore sought to assess whether ET is modulated by PAF. E. coli has also been demonstrated to increase endothelial production of nitric oxide (NO), which contributes to maintenance of basal vascular tone in the pulmonary circulation. We hypothesized that PAF might increase pulmonary vascular resistance during bacteremia by activating neutrophils, increasing expression of ET, and decreasing the tonic release of NO. Furthermore, we hypothesized that hypoxic vasoconstriction did not contribute to pulmonary vasoconstriction during the first 120 min of E. coli bacteremia. METHODS: Pulmonary artery pressure (PAP), blood pressure (BP), heart rate (HR), and arterial blood gases (ABG) were measured in anesthetized spontaneously breathing adult male Sprague-Dawley rats. E. coli (10(9) CFU/100 g body wt) was injected at t = 0, and hemodynamic data were obtained at 10-min intervals and ABG data at 30-min intervals for a total of 120 min. Sham animals were treated equally but received normal saline in place of E. coli. In treatment groups, a 2.5 mg/kg dose of WEB 2086, a PAF receptor antagonist, was administered intravenously 15 min prior to the onset of sepsis or sham sepsis. The groups were (1) intravenous E. coli (n = 5); (2) intravenous WEB 2086 pretreatment + intravenous E. coli (n = 5); (3) intravenous WEB 2086 alone (n = 5); and (4) intravenous normal saline (n = 6). Nitric oxide metabolites (NOx) and ET concentrations were assayed from arterial serum samples obtained at the end of the protocol. Lung tissue was harvested for measurement of myeloperoxidase (MPO) activity and pulmonary histology. RESULTS: E. coli bacteremia increased HR, PAP, and respiratory rate early during sepsis (within 20 min), while hypoxemia, hypotension, and hemoconcentration were not manifest until the second hour. Pretreatment with WEB 2086 completely abrogated all of these changes. E. coli bacteremia increased the activity of serum ET, lung MPO, and neutrophil sequestration in the lung parenchyma via a PAF-dependent mechanism. However, the mechanism of increased production of NO appears to be PAF independent. CONCLUSIONS: These data support the hypothesis that E. coli bacteremia rapidly induces pulmonary hypertension stimulated by PAF and mediated at least in part by endothelin-1 and neutrophil activation and sequestration in the lung. Microvascular injury with leak is also mediated by PAF during E. coli bacteremia, but the time course of resultant hypoxemia and hemoconcentration is slower than that of pulmonary hypertension. The contribution of hypoxic vasoconstriction in exacerbating pulmonary hypertension in gram-negative sepsis is probably a late

Decreased alpha-adrenergic response in the intestinal microcirculation after "two-hit" hemorrhage/resuscitation and bacteremia.

BACKGROUND: The two-hit theory of multiple organ dysfunction syndrome proposes that an initial insult primes the host for an altered response to subsequent stimuli. We have previously documented enhanced dilator tone in the small intestine after a two-hit insult; however, the effects on vasoconstrictor function are unknown. We postulated that prior hemorrhage and resuscitation followed by bacteremia would alter microvascular responsiveness to alpha-adrenergic stimulation. METHODS: Male Sprague-Dawley rats underwent fixed-volume hemorrhage with resuscitation (H/R) or sham procedure (Sham). At 24 or 72 h, in vivo videomicroscopy of the small intestine was performed (inflow A1 and premucosal A3 arterioles). Constrictor function was assessed by topical application of norepinephrine (NE; 10(-8)-10(-6) M) before and 1 h after intravenous Escherichia coli or saline. RESULTS: Sham, 24 or 72 h H/R, and E. coli alone produced no significant changes in A1 or A3 response to NE. Sequential H/R + E. coli resulted in decreased constrictor response in both A1 (72 h H/R + E. coli-38% from baseline vs Sham - 54%, P < 0.05) and A3 arterioles (-8% vs -51%, P < 0.05) at high doses of NE (10(-6) M). CONCLUSIONS: Prior H/R primes the intestinal microvasculature for an altered response during a subsequent stress and these effects persist for up to 72 h following H/R. Sequential insults in this two-hit model caused marked hyporesponsiveness to NE. These alterations in control of microvascular tone might contribute to the hemodynamic compromise of sepsis, impair mucosal blood flow, and contribute to the development of MODS.

Glucose and glutamine gavage increase portal vein nitric oxide metabolite levels via adenosine A2b activation.

INTRODUCTION: Postprandial intestinal hyperemia is a complex vascular response during nutrient absorption. Many mediators have been studied including enteric reflexes, GI hormones, and absorption-stimulated metabolic mediators such as pH and adenosine. We have shown that nitric oxide (NO) mediates premucosal arteriolar dilation during glucose absorption and that glucose-induced portal vein NO metabolite production requires adenosine A2b receptor activation. We hypothesize that Na+-linked absorption of l-glutamine or l-glycine might also stimulate NO release in the enteroportal circulation via adenosine A2b receptors. METHODS: Male Sprague-Dawley rats (190-220 g) were anesthetized with urethane/alpha-chloralose and cannulated for hemodynamic monitoring and blood sampling. A right paramedian abdominal incision was made for access to both the stomach (gavage) and the portal vein (blood sampling). Animals received intragastric nutrient gavage (saline, d-glucose, l-glutamine, racemic glycine, or oleic acid) with and without adenosine A2b receptor blockade. NO metabolites (NOx) were measured by a fluorescent modified-Greiss assay at baseline and 30 min after nutrient gavage. RESULTS: Glucose and glutamine gavage increased portal NOx levels compared to baseline, while glycine and oleic acid gavage did not. Adenosine A2b antagonism returned NOx levels to baseline in both glucose and glutamine gavage animals, but did not alter portal NOx levels in glycine- or oleic acid-treated animals. CONCLUSIONS: These data suggest that nutrient-induced adenosine is involved in a signaling process from the intestinal epithelium to nitric oxide-producing cells elsewhere in the vasculature. Adenosine A2b receptors are required for NO production during Na+-linked glucose or glutamine absorption.

Subacute sepsis impairs vascular smooth muscle contractile machinery and alters vasoconstrictor and dilator mechanisms.

INTRODUCTION: Sepsis results in hyporesponsiveness to alpha-adrenergic stimulation. This is thought to be mediated by the release of vasoactive compounds from the septic endothelium or by the direct effect of sepsis on vascular smooth muscle (VSM) contractile mechanics and machinery. Previous studies have used lethal models of sepsis or endotoxemia to examine this phenomenon. The present study utilizes a clinically relevant, nonlethal model of soft tissue infection to determine the effects of sepsis on alpha-adrenergic mechanisms. We hypothesize that subacute sepsis causes impaired alpha-adrenergic vascular responsiveness by a combination of effects on adrenergic constrictor mechanisms, endogenous dilator tone, and VSM contractile function. METHODS: Male Sprague-Dawley rats underwent implantation of a 2 x 2-cm2 gauze sponge into a subcutaneous pocket created at the base of the tail. Five days after implantation, sepsis (S) was induced by inoculation of the sponge with 10(9) CFU Escherichia coli and Bacteroides fragilis. Controls (C) were inoculated with saline. Thoracic aortic harvest was performed 24 and 48 h after sponge inoculation for organ bath ring studies. Receptor-mediated (phenylephrine) and nonreceptor-mediated (KCl) maximum force of contraction (Fmax) was measured. Vessel sensitivity (pD2) to phenylephrine, acetylcholine, and KCl was calculated from dose-response curves. RESULTS: At 24 h, sepsis resulted in a lower Fmax to phenylephrine (1.15 for C vs 0.5 for S, P < 0.05 by ANOVA), despite an increase in vessel sensitivity (pD2) to alpha-adrenergic stimulation (6.70 for C vs 6.88 for S, P < 0.05 by ANOVA). Fmax to KCl was lower in septic animals at 24 h (3. 50 for C vs 2.77 for S, P < 0.05 by ANOVA) and sensitivity to acetylcholine (pD2) was markedly increased (6.56 for C vs 7.23 for S, P < 0.05 by ANOVA). At 48 h, the impairment in Fmax to alpha-adrenergic stimulation (2.29 for C vs 1.72 for S, P < 0.05 by ANOVA) and KCl (3.5 for C vs 3.08 for S. P < 0.05 vs 24 h C by ANOVA) persisted without any change in sensitivity to phenylephrine or acetylcholine. CONCLUSIONS: Subacute sepsis results in an early suppression of maximum contractile force despite an increase in adrenergic receptor sensitivity (pD2). This may be secondary to an elevation in dilator sensitivity combined with a direct effect of sepsis on VSM contractile mechanisms. Later in the septic process, however, alpha-adrenergic hyporesponsiveness ( downward arrow Fmax) is primarily due to changes in VSM contractile machinery.

Complement activation mediates intestinal injury after resuscitation from hemorrhagic shock.

BACKGROUND: Endothelial cell injury after hemorrhage and resuscitation (HEM/RES) might contribute to intestinal hypoperfusion and mucosal ischemia. Our recent work suggests that the injury might be the result of complement activation. We hypothesized that HEM/RES causes complement-mediated endothelial cell dysfunction in the small intestine. METHODS: Male Sprague-Dawley rats (195-230 g) were anesthetized and HEM to 50% of baseline mean arterial pressure for 60 minutes. Just before RES, animals received either soluble complement receptor-1 (sCR1, 15 mg/kg) to inhibit complement activation or saline vehicle. Resuscitation was with shed blood and an equal volume of saline. Two hours after RES, the small bowel was harvested to evaluate intestinal nitric oxide synthase activity (NOS), neutrophil influx, histology, and oxidant injury. RESULTS: HEM/RES induced tissue injury, increased neutrophil influx, and reduced NOS activity by 50% (vs. SHAM), all of which were completely prevented by sCR1 administration. There were no observed differences in oxidant injury between the groups. CONCLUSION: Histologic tissue injury, increased neutrophil influx, and impaired NOS activity after HEM/RES were all prevented by complement inhibition. Direct oxidant injury did not seem to be a major contributor to these alterations. Complement inhibition after HEM might ameliorate reperfusion injury in the small intestine by protecting the endothelial cell, reducing neutrophil influx and preserving NOS function.

Altered vasoconstrictor and dilator responses after a "two-hit" model of sequential hemorrhage and bacteremia.

BACKGROUND: The "two-hit" theory of multiple organ dysfunction (MOD) proposes that an initial insult, such as hemorrhage (HEM), primes the host for an abnormal response to a second stress such as infection. The immunologic/inflammatory component of this theory has been well examined; however, the effects on vascular responsiveness are poorly understood. We hypothesized that HEM primes the vasculature for an altered response to a second pathophysiologic stress. METHODS: Male Sprague-Dawley rats underwent a fixed-volume HEM with resuscitation (H/R) or sham procedure (Sham). At 48 h, animals were given iv E. coli or saline and followed for 1 h. Thoracic aortic rings were then placed in organ baths containing Krebs buffer aerated with 95% O2, 5% CO2. Cumulative dose-response curves to phenylephrine (PHE) and acetylcholine (ACH) were obtained. Maximum force of contraction (Fmax) was measured and pD2 values (receptor sensitivity) were derived. RESULTS: H/R alone resulted in heightened constrictor tone and blunted dilator tone. E. coli reduced Fmax in response to PHE by 50% in Sham vs 76% in H/R. Receptor sensitivity (pD2) to PHE was reduced to a greater degree in H/R (3-fold vs 2-fold). These animals also had a more pronounced enhancement of ACH receptor sensitivity (7-fold vs 2-fold). CONCLUSIONS: Hemorrhage primes the vasculature for an altered response to a subsequent stress. When infection is added as a "second hit," responsiveness to adrenergic agents is diminished and dilator tone is increased. These data may explain the cardiovascular derangements seen clinically in patients who develop MODS after major hemorrhage followed sequentially by infection.

E. Coli bacteremia-induced changes in the skeletal muscle microcirculation vary with anesthetics.

AIM: To test if anesthetic procedures change the hemodynamic pattern in animals with experimental septic shock. METHODS: The effect of two anesthetics on systemic hemodynamic and skeletal muscle microcirculatory responses in high cardiac output live E. coli bacteremia was studied in rats and compared to the effect of two other anesthetic procedures in previously published studies. RESULTS: Baseline blood pressures and cardiac outputs were similar in rats with decerebrate, ketamine/xylazine, pentobarbital or urethane/chloralose anesthesia. There was a relative baseline tachycardia in decerebrate rats. Ketamine/xylazine anesthetized rats had reduced blood pressure, cardiac output, and heart rate. In decerebrate, pentobarbital, and urethane/chloralose anesthesia, cardiac output increased initially during bacteremia but did not remain elevated in pentobarbital anesthesia. Blood pressure and heart rate remained constant in pentobarbital, decerebrate, and urethane/chloralose anesth esia. During bacteremia, cardiac output, blood pressure, and vascular resistance did not change with ketamine/xylazine, but the heart rate increased. Baseline diameters of cremaster muscle large (A1) arterioles were higher in decerebrate anesthesia. A1 arterioles constricted during high cardiac output bacteremia in decerebrate rats, and pentobarbital or urethane/chloralose-anesthetized rats. A4 arterioles in bacteremia dilated in decerebrate and pentobarbital anesthesia, but did not change under urethane/chloralose and ketamine/xylazine anesthesia. CONCLUSION: Anesthetics influence baseline systemic variables and the response of systemic hemodynamics of rats to E. coli bacteremia. During bacteremia, anesthetics primarily affect the reactivity of skeletal muscle small arterioles. Ketamine/xylazine anesthesia has the most pronounced effect on systemic and microcirculatory variables and seems to be an inappropriate choice in sepsis experiments in rats.

Microvascular endothelial cell control of peripheral vascular resistance during sepsis.

OBJECTIVE: To determine the endothelial-dependent control of decreased peripheral vascular resistance in skeletal muscle microvessels during evolving sepsis. MATERIALS AND INTERVENTIONS: Acute (4 hours, n=7), established (24 hours, n=7), or chronic (72 hours, n=8) infection was induced in Sprague-Dawley rats (150-175 g) by injecting Escherichia coli and Bacteroides fragilis (1 x 10(9) colony-forming units for both) into a subcutaneous sponge. Control animals were injected with an isotonic sodium chloride solution and analyzed at the same time points: (n=6-8 per group). Dilation in response to the topically applied endothelial-dependent agonist acetylcholine (ACH) (1 x 10(-9) to 1 x 10(-5) mol/L) was measured in inflow first-order (A1) and precapillary fourth-order (A4) arterioles in cremaster muscle in vivo with videomicroscopy. Acetylcholine dose-response curves were used to determine vascular reactivity by calculating the concentration of ACH necessary to elicit 50% of the maximal dilator response. MAIN OUTCOME MEASURES: In vivo reactivity of striated muscle microvessels to the dilation agonist ACH during acute, established, and chronic infection. RESULTS: A1 vessels were unresponsive to all doses of ACH at all time points. A4 vessels showed an increased dilator response during short-term treatment, which deteriorated over time to depressed dilation during chronic infection. CONCLUSIONS: Precapillary A4 vessels have increased dilator reactivity during early sepsis, which progresses to depressed levels with chronic infection. A1 microvessels remain dilated and are not substantially influenced by endothelial dilator mechanisms initiated by ACH. Maximum dilation of the large A1 vessels appears to contribute to the decrease in peripheral vascular resistance noted during systemic infection.

Small intestinal production of nitric oxide is decreased following resuscitated hemorrhage.

BACKGROUND: Small intestine microvascular vasoconstriction and hypoperfusion develop after resuscitation (RES) from hemorrhage (HEM), despite restoration of central hemodynamics. The responsible mechanisms are unclear. We hypothesized that the microvascular impairment following HEM/RES was due to decreased intestinal microvascular nitric oxide (NO) production. METHODS: Male Sprague-Dawley rats (195-230 g) were utilized and three experimental groups were studied: (1) SHAM (cannulated but no HEM), (2) HEM only, and (3) HEM/RES. HEM was to 50% of baseline mean arterial pressure for 60 min, and RES was with shed blood and an equivalent volume of saline. Ex vivo isolated intestinal perfusion and a fluorometric modification of the Greiss reaction were used to quantify production of NO metabolites (NOx). Perfusate von Willebrand factor (vWF) was used as an indirect marker of endothelial cell activation or injury. To assess the degree of NO scavenging by oxygen-derived free radicals, immunohistochemistry was used to detect nitrotyrosine formation in the intestine. RESULTS: Intestinal NOx decreased following HEM/RES (SHAM 1.35 +/- 0.2 mM vs HEM/RES 0.60 +/- 0.1 mM, P < 0.05), but not with HEM alone (1.09 +/- 0.3 mM). There were no differences in serum NOx levels between the three groups. Release of vWF was increased during the HEM period (SHAM 0.18 +/- 0.1 g/dl vs HEM 1.66 +/- 0.6 g/dl, P < 0.05). There was no detectable nitrotyrosine formation in any group. CONCLUSIONS: Intestinal NO metabolites decrease following HEM/RES. Elevated vWF levels during HEM and the lack of detectable nitrotyrosine suggest that this is due to decreased endothelial cell production of NO. HEM/RES-induced endothelial cell dysfunction may contribute to persistent small intestine post-RES hypoperfusion and vasoconstriction.

Complement inhibition prevents gut ischemia and endothelial cell dysfunction after hemorrhage/resuscitation.

BACKGROUND: Complement, a nonspecific immune response, is activated during hemorrhage/resuscitation (HEM/RES) and is involved in cellular damage. We hypothesized that activated complement injures endothelial cells (ETCs) and is responsible for intestinal microvascular hypoperfusion after HEM/RES. METHODS: Four groups of rats were studied by in vivo videomicroscopy of the intestine: SHAM, HEM/RES, HEM/RES + sCR1 (complement inhibitor, 15 mg/kg intravenously given before resuscitation), and SHAM + sCR1. Hemorrhage was to 50% of mean arterial pressure for 60 minutes followed by resuscitation with shed blood plus an equal volume of saline. ETC function was assessed by response to acetylcholine. RESULTS: Resuscitation restored central hemodynamics to baseline after hemorrhage. After resuscitation, inflow A1 and premucosal A3 arterioles progressively constricted (-24% and -29% change from baseline, respectively), mucosal blood flow was reduced, and ETC function was impaired. Complement inhibition prevented postresuscitation vasoconstriction and gut ischemia. This protective effect appeared to involve preservation of ETC function in the A3 vessels (SHAM 76% of maximal dilation, HEM/RES 61%, HEM/RES + sCR1 74%, P < .05). CONCLUSIONS: Complement inhibition preserved ETC function after HEM/RES and maintained gut perfusion. Inhibition of complement activation before resuscitation may be a useful adjunct in patients experiencing major hemorrhage and might prevent the sequelae of gut ischemia.

Microvascular changes explain the "two-hit" theory of multiple organ failure.

OBJECTIVE: The objective was to determine intestinal microvascular endothelial cell control after sequential hemorrhage and bacteremia. SUMMARY BACKGROUND DATA: Sepsis that follows severe hemorrhagic shock often results in multiple system organ failure (MSOF) and death. The sequential nature of this clinical scenario has led to the idea of a "two-hit" theory for the development of MSOF, the hallmark of which is peripheral vasodilation and acidosis. Acute bacteremia alone results in persistent intestinal vasoconstriction and mucosal hypoperfusion. Little experimental data exist to support the pathogenesis of vascular dysregulation during sequential physiologic insults. We postulate that hemorrhagic shock followed by bacteremia results in altered microvascular endothelial cell control of dilation and blood flow. METHODS: Rats underwent volume hemorrhage and resuscitation. A sham group underwent the vascular cannulation without hemorrhage and resuscitation, and controls had no surgical manipulation. After 24 and 72 hours, the small intestine microcirculation was visualized by in vivo videomicroscopy. Mean arterial pressure, heart rate, arteriolar diameters, and A1 flow by Doppler velocimetry were measured. Endothelial-dependent dilator function was determined by the topical application of acetylcholine (ACh). After 1 hour of Escherichia coil bacteremia, ACh dose responses were again measured. Topical nitroprusside was then applied to assess direct smooth muscle dilation (endothelial-independent dilator function) in all groups. Vascular reactivity to ACh was compared among the groups. RESULTS: Acute bacteremia, with or without prior hemorrhage, caused significant large-caliber A1 arteriolar constriction with a concomitant decrease in blood flow. This constriction was blunted at 24 hours after hemorrhage but was restored to control values by 72 hours. There was a reversal of the response to bacteremia in the premucosal A3 vessels, with a marked dilation both at 24 and 72 hours. The sequence of hemorrhage and E. coli resulted in a progressive enhanced reactivity to the endothelial-dependent stimulus of ACh in the A3 vessels at 24 and 72 hours. Reactivity to endothelial-independent smooth muscle relaxation and subsequent vessel dilation was similar for all groups. CONCLUSIONS: These data indicate that there is altered endothelial control of the intestinal microvasculature after hemorrhage in favor of enhanced dilator mechanisms in premucosal vessels with enhanced constrictor forces in inflow vessels. This enhanced dilator sensitivity is most evident in small premucosal vessels. This experimental finding supports the premise that an initial pathophysiologic stress alters the subsequent microvascular blood flow responses to systemic inflammation. These changes in the intestinal microcirculation are in concert with the "two-hit" theory for MSOF.

Multivariate analysis of factors associated with postoperative pulmonary complications following general elective surgery.

OBJECTIVE: To develop a predictive model identifying perioperative conditions associated with postoperative pulmonary complications (PPCs). DESIGN: A prospective survey of patients whose preoperative history and physical examination, spirometric, PaO2 and PaCO2 analysis, and operative results were recorded. These patients underwent postoperative cardiopulmonary examinations until they were discharged from the hospital; their medical records were also reviewed until they were discharged from the hospital. SETTING: The Louisville Veterans Administration Medical Center, Louisville, Ky. PATIENTS: A randomly chosen sample of patients aged 40 years or older who required elective, nonthoracic surgery under general or spinal anesthesia and who were hospitalized at least 24 hours postoperatively. MAIN OUTCOME MEASURE: An analysis of risk factors associated with the development of 1 or more of the following conditions: acute bronchitis, bronchospasm, atelectasis, pneumonia, adult respiratory distress syndrome, pleural effusion, pneumothorax, prolonged mechanical ventilation, or death secondary to acute respiratory failure. RESULTS: Postoperative pulmonary complications developed in 16 (11%) of 148 patients. The risk factors found to be higher among those with PPCs compared with those without PPCs were postoperative nasogastric intubation (81% vs 16%, P<.001), preoperative sputum production (56% vs 21%, P=.005), and longer anesthesia duration (480 vs 309 minutes, P<.001). Upper abdominal surgery was performed in 11 (69%) of the 16 patients with PPCs and in 20 (15%) of the 132 patients without PPCs (P<.001); this difference lost significance in multivariate analysis. The final linear logistic model included postoperative nasogastric intubation (odds ratio [OR], 21.8), preoperative sputum production (OR, 4.6), and longer anesthesia duration (OR exp[0.01x] for an increase in x minutes) (1 minute of additional anesthesia time increases the OR to 1.01), resulting in 92% accuracy in predicting PPCs. CONCLUSIONS: We identified 3 potentially modifiable risk factors for PPCs. If validated, our results may lead to modifications of perioperative care that will further reduce PPCs.