Does tissue acidosis in sepsis indicate tissue hypoperfusion?

The interface between monitoring and physiology at the bedside

Hemodynamic instability as a clinical state represents either a perfusion failure with clinical manifestations of circulatory shock or heart failure or 1 or more out-of-threshold hemodynamic monitoring values, which may not necessarily be pathologic. Different types of causes of circulatory shock require different types of treatment modalities, making these distinctions important. Diagnostic approaches or therapies based on data derived from hemodynamic monitoring assume that specific patterns of derangements reflect specific disease processes, which respond to appropriate interventions. Hemodynamic monitoring at the bedside improves patient outcomes when used to make treatment decisions at the right time for patients experiencing hemodynamic instability.

[Blood concentrations of lactate, C-reactive protein, and creatinine as early indicators of severity and outcome of sepsis]

INTRODUCTION

Since the outcome in septic patients can significantly be improved if the appropriate therapy is introduced timely early, the early diagnosis of sepsis and its complications is essential. The aim of this study was to compare mean values of the initial blood concentrations of lactate, C-reactive protein and creatinine and the severity of illness and the outcome of sepsis.

MATERIALS AND METHODS

A total of 30 septic patients were included in the study. The diagnosis of sepsis and its complications was made according to consensus criteria. The severity of illness was scored by an acute physiology, age and chronic health evaluation septic score. The patients were subdivided into different groups, those with sepsis, severe sepsis or septic shock, those with or without multiple organ dysfunction syndrome, and survivors and nonsurvivors.

RESULTS

The differences in mean values of lactate levels among all studied groups were significantly high, whereas the level of C-reactive protein were significantly higher only in the non-survivors compared to the survivors (p < 0.05). The concentrations of creatinine were significantly higher in the patients with septic shock compared to the patients with sepsis, and in the patients with multiple organ dysfunction syndrome and the non-survivors compared to the corresponding groups (p < 0.05). The septic score clearly discriminated patients with different severity of sepsis, development of multiple organ dysfunction syndrome and survival and positively correlated with the concentrations of lactate, C-reactive protein and creatinine (the best correlation ranks were with lactate levels, p < 0.001).

DISCUSSION AND CONCLUSION

Our results suggest that lactate level is a better parameter of illness severity and outcome of sepsis than levels of C-reactive protein and creatinine. When compared to the above parameters, the septic score determined on the day of admission to hospital is a much better criterion to classify patients into groups with different severity of sepsis, with and without multiple organ dysfunction syndrome and into survivors and non-survivors.

Association between outcome and changes in plasma lactate concentration during presurgical treatment in dogs with gastric dilatation-volvulus: 64 cases (2002-2008)

OBJECTIVE

To determine whether changes in presurgical plasma lactate concentration (before and after initial fluid resuscitation and gastric decompression) were associated with short-term outcome for dogs with gastric dilatation-volvulus (GDV).

DESIGN

Retrospective case series.

ANIMALS

64 dogs.

PROCEDURES

Medical records were reviewed, and signalment, history, resuscitative treatments, serial presurgical lactate concentrations, surgical findings, and short-term outcome were obtained for dogs with confirmed GDV.

RESULTS

36 of 40 (90%) dogs with an initial lactate concentration <or= 9.0 mmol/L survived, compared with only 13 of 24 (54%) dogs with a high initial lactate (HIL) concentration (> 9.0 mmol/L). Within HIL dogs, there was no difference in mean +/- SD initial lactate concentration between survivors and nonsurvivors (10.6 +/- 2.3 mmol/L vs 11.2 +/- 2.3 mmol/L, respectively); however, there were significant differences in post-treatment lactate concentration, absolute change in lactate concentration, and percentage change in lactate concentration following resuscitative treatment. By use of optimal cutoff values within HIL dogs, survival rates for dogs with final lactate concentration > 6.4 mmol/L (23%), absolute change in lactate concentration <or= 4 mmol/L (10%), or percentage change in lactate concentration <or= 42.5% (15%) were significantly lower than survival rates for dogs with a final lactate concentration <or= 6.4 mmol/L (91%), absolute change in lactate concentration > 4 mmol/L (86%), or percentage change in lactate concentration > 42.5% (100%).

CONCLUSIONS AND CLINICAL RELEVANCE

Calculating changes in plasma lactate concentration following initial treatment in dogs with GDV may assist in determining prognosis and identifying patients that require more aggressive treatment.

Early serum procalcitonin, interleukin-6, and 24-hour lactate clearance: useful indicators of septic infections in severely traumatized patients

BACKGROUND

Elevated lactate and interleukin-6 (IL-6) levels were shown to correlate with mortality and multiple organ dysfunction in severely traumatized patients. The purpose of this study was to test whether an association exists between 24-hour lactate clearance, IL-6 and procalcitonin (PCT) levels, and the development of infectious complications in trauma patients.

METHODS

A total of 1757 consecutive trauma patients with an Injury Severity Score (ISS) > 16 admitted over a 10-year period were retrospectively analyzed over a 21-day period. Exclusion criteria included death within 72 h of admission (24.5%), late admission > 12 h after injury (16%), and age < 16 years (0.5%). Data are stated as the median (range).

RESULTS

Altogether, 1032 trauma patients (76.2% male) with an average age of 38 years, a median ISS of 29 (16-75), and an Acute Physiology, Age, and Chronic Health Evaluation (APACHE) II score of 14 (0-40) were evaluated. The in-hospital mortality (>3 days) was 10%. Patients with insufficient 24-hour lactate clearance had a high rate of overall mortality and infections. Elevated early serum procalcitonin on days 1 to 5 after trauma was strongly associated with the subsequent development of sepsis (p < 0.01) but not with nonseptic infections. The kinetics of IL-6 were similar to those of PCT but did differentiate between infected and noninfected patients after day 5.

CONCLUSIONS

This study demonstrates that elevated early procalcitonin and IL-6 levels and inadequate 24-hour lactate clearance help identify trauma patients who develop septic and nonseptic infectious complications. Definition of specific cutoff values and early monitoring of these parameters may help direct early surgical and antibiotic therapy and reduce infectious mortality.

The molecular basis of paediatric malarial disease

Severe falciparum malaria is an acute systemic disease that can affect multiple organs, including those in which few parasites are found. The acute disease bears many similarities both clinically and, potentially, mechanistically, to the systemic diseases caused by bacteria, rickettsia, and viruses. Traditionally the morbidity and mortality associated with severe malarial disease has been explained in terms of mechanical obstruction to vascular flow by adherence to endothelium (termed sequestration) of erythrocytes containing mature-stage parasites. However, over the past few decades an alternative ‘cytokine theory of disease’ has also evolved, where malarial pathology is explained in terms of a balance between the pro- and anti-inflammatory cytokines. The final common pathway for this pro-inflammatory imbalance is believed to be a limitation in the supply and mitochondrial utilisation of energy to cells. Different patterns of ensuing energy depletion (both temporal and spatial) throughout the cells in the body present as different clinical syndromes. This chapter draws attention to the over-arching position that inflammatory cytokines are beginning to occupy in the pathogenesis of acute malaria and other acute infections. The influence of inflammatory cytokines on cellular function offers a molecular framework to explain the multiple clinical syndromes that are observed during acute malarial illness, and provides a fresh avenue of investigation for adjunct therapies to ameliorate the malarial disease process.

Lactate versus non-lactate metabolic acidosis: a retrospective outcome evaluation of critically ill patients

Introduction

Acid–base abnormalities are common in the intensive care unit (ICU). Differences in outcome exist between respiratory and metabolic acidosis in similar pH ranges. Some forms of metabolic acidosis (for example, lactate) seem to have worse outcomes than others (for example, chloride). The relative incidence of each type of disorder is unknown. We therefore designed this study to determine the nature and clinical significance of metabolic acidosis in critically ill patients.

Methods

An observational, cohort study of critically ill patients was performed in a tertiary care hospital. Critically ill patients were selected on the clinical suspicion of the presence of lactic acidosis. The inpatient mortality of the entire group was 14%, with a length of stay in hospital of 12 days and a length of stay in the ICU of 5.8 days.

Results

We reviewed records of 9,799 patients admitted to the ICUs at our institution between 1 January 2001 and 30 June 2002. We selected a cohort in which clinicians caring for patients ordered a measurement of arterial lactate level. We excluded patients in which any necessary variable required to characterize an acid–base disorder was absent. A total of 851 patients (9% of ICU admissions) met our criteria. Of these, 548 patients (64%) had a metabolic acidosis (standard base excess < -2 mEq/l) and these patients had a 45% mortality, compared with 25% for those with no metabolic acidosis (p < 0.001). We then subclassified metabolic acidosis cases on the basis of the predominant anion present (lactate, chloride, or all other anions). The mortality rate was highest for lactic acidosis (56%); for strong ion gap (SIG) acidosis it was 39% and for hyperchloremic acidosis 29% (p < 0.001). A stepwise logistic regression model identified serum lactate, SIG, phosphate, and age as independent predictors of mortality.

Conclusion

In critically ill patients in which a measurement of lactate level was ordered, lactate and SIG were strong independent predictors of mortality when they were the major source of metabolic acidosis. Overall, patients with metabolic acidosis were nearly twice as likely to die as patients without metabolic acidosis.

Efficiency of triiodothyronine treatment on organ donor hemodynamic management and adenine nucleotide concentration

OBJECTIVE

We compared hemodynamic values, oxygen utilization, and adenine nucleotide concentration in the extracted organs of brain-dead donors treated with triiodothyronine vs. standard support treatment.

DESIGN

Prospective, randomized, double-blind controlled study.

PATIENTS

We recruited 52 consecutive adult cadaveric organ donors. Inclusion criteria were diagnosis of brain-death, transplantation suitability, and family consent for donation; exclusion criterion was preexisting thyroid disease.

INTERVENTIONS

The treatment group (n=29) received an intravenous bolus of 1 microg/kg triiodothyronine followed by continuous perfusion at 0.06 microg/kg per hour, and controls (n=23) received 0.9% ClNa delivered over 270 min. Hemodynamics, tonometry, thyroid hormones, and serum lactate were measured every 90 min from brain death to extraction procedure. Biopsies were processed to determine adenine nucleotides concentration.

RESULTS

Hemodynamic measurements did not differ significantly in the two groups, and the inotrope dose could not be diminished after treatment. Thyrotropin levels increased from brain death to extraction procedure in controls. Thyrotropin measured 90 and 180 min after the beginning of the perfusion was significantly lower in the treatment group than controls. The Pco2 gap increased in both groups from brain death to the extraction procedure. The lactate level of the treatment group was lower than in controls. Biopsy specimens were obtained in 19 controls and in 20 donors of the treatment group; the adenine nucleotides concentration did not show any significant difference.

CONCLUSIONS

Triiodothyronine did not add any benefit over the standard management of the organ donor nor did it affect the adenine nucleotides concentration of any biopsied organs.

Early lactate clearance is associated with improved outcome in severe sepsis and septic shock

OBJECTIVE

Serial lactate concentrations can be used to examine disease severity in the intensive care unit. This study examines the clinical utility of the lactate clearance before intensive care unit admission (during the most proximal period of disease presentation) as an indicator of outcome in severe sepsis and septic shock. We hypothesize that a high lactate clearance in 6 hrs is associated with decreased mortality rate.

DESIGN

Prospective observational study.

SETTING

An urban emergency department and intensive care unit over a 1-yr period.

PATIENTS

A convenience cohort of patients with severe sepsis or septic shock.

INTERVENTIONS

Therapy was initiated in the emergency department and continued in the intensive care unit, including central venous and arterial catheterization, antibiotics, fluid resuscitation, mechanical ventilation, vasopressors, and inotropes when appropriate.

MEASUREMENTS AND MAIN RESULTS

Vital signs, laboratory values, and Acute Physiology and Chronic Health Evaluation (APACHE) II score were obtained at hour 0 (emergency department presentation), hour 6, and over the first 72 hrs of hospitalization. Therapy given in the emergency department and intensive care unit was recorded. Lactate clearance was defined as the percent decrease in lactate from emergency department presentation to hour 6. Logistic regression analysis was performed to determine independent variables associated with mortality. One hundred and eleven patients were enrolled with mean age 64.9 +/- 16.7 yrs, emergency department length of stay 6.3 +/- 3.2 hrs, and overall in-hospital mortality rate 42.3%. Baseline APACHE II score was 20.2 +/- 6.8 and lactate 6.9 +/- 4.6 mmol/L. Survivors compared with nonsurvivors had a lactate clearance of 38.1 +/- 34.6 vs. 12.0 +/- 51.6%, respectively (p =.005). Multivariate logistic regression analysis of statistically significant univariate variables showed lactate clearance to have a significant inverse relationship with mortality (p =.04). There was an approximately 11% decrease likelihood of mortality for each 10% increase in lactate clearance. Patients with a lactate clearance> or =10%, relative to patients with a lactate clearance <10%, had a greater decrease in APACHE II score over the 72-hr study period and a lower 60-day mortality rate (p =.007).

CONCLUSIONS

Lactate clearance early in the hospital course may indicate a resolution of global tissue hypoxia and is associated with decreased mortality rate. Patients with higher lactate clearance after 6 hrs of emergency department intervention have improved outcome compared with those with lower lactate clearance.

The pathophysiology of falciparum malaria

Falciparum malaria is a complex disease with no simple explanation, affecting organs where the parasite is rare as well as those organs where it is more common. We continue to argue that it can best be understood in terms of excessive stimulation of normally useful pathways mediated by inflammatory cytokines, the prototype being tumor necrosis factor (TNF). These pathways involve downstream mediators, such as nitric oxide (NO) that the host normally uses to control parasites, but which, when uncontrolled, have bioenergetic failure of patient tissues as their predictable end point. Falciparum malaria is no different from many other infectious diseases that are clinically confused with it. The sequestration of parasitized red blood cells, prominent in some tissues but absent in others with equal functional loss, exacerbates, but does not change, these overriding principles. Recent opportunities to stain a wide range of tissues from African pediatric cases of falciparum malaria and sepsis for the inducible NO synthase (iNOS) and migration inhibitory factor (MIF) have strengthened these arguments considerably. The recent demonstration of bioenergetic failure in tissue removed from sepsis patients being able to predict a fatal outcome fulfils a prediction of these principles, and it is plausible that this will be demonstrable in severe falciparum malaria. Understanding the disease caused by falciparum malaria at a molecular level requires an appreciation of the universality of poly(ADP-ribose) polymerase-1 (PARP-1) and Na(+)/K(+)-ATPase and the protean effects of activation by inflammation of the former that include inactivation of the latter.

Ileus in critical illness: mechanisms and management

Nonobstructive ileus, signifying the impairment of coordinated propulsive intestinal motility, remains a frequently documented and almost inevitable consequence of open abdominal surgery and sepsis. Despite the frequency and major impact of ileus on morbidity and mortality, the exact underlying molecular and cellular mechanisms of this important clinical conundrum are still ill defined. Animal models suggest that both neuronal and local inflammatory responses within the intestinal muscularis mechanistically contribute to intestinal ileus. The neuronal mechanism appears to involve the enhanced release of nitric oxide from inhibitory motor neurons. Likewise, nitric oxide and prostaglandins are released from inflammatory cells (macrophages and monocytes) via the induction of nitric oxide synthase (iNOS) and cyclooxygenase-2. Recently, preliminary data have confirmed the existence of an intraoperative local muscularis inflammatory response during surgery in human patients.

Anions and the anaesthetist

Anions are the negative components of most chemical structures and play many important physiological and pharmacological roles that are of interest to the anaesthetist. Their relevance is reviewed with a particular emphasis on the inorganic anions (halides, bicarbonate, phosphate and sulphate) and the significance and limitations of the anion gap. Organic anions (albumin, lactate) are also discussed, albeit briefly. The suitability of anions for their role in neurotransmission and acid-base balance is outlined.

MCP-1 causes leukocyte recruitment and subsequently endotoxemic ileus in rat

Endotoxemia causes an inflammatory response within the intestinal muscularis and gastrointestinal dysmotility. We hypothesize that the resident macrophage-derived chemokine monocyte chemoattractant protein-1 (MCP-1) plays a significant role in the recruitment of leukocytes into the lipopolysaccharide (LPS)-stimulated rat intestinal muscularis. MCP-1 mRNA expression was investigated by RT-PCR. Leukocyte extravasation and MCP-1 protein localization were determined by immunohistochemistry. Contractile activity was assessed by using a standard organ bath in rats that were treated with saline, recombinant MCP-1, LPS, LPS + nonspecific antibody, or LPS + MCP-1 antibody. Endotoxemia caused a significant 280-fold increase in MCP-1 mRNA expression in the muscularis, peaking at 3 h. MCP-1 protein was immunohistochemically located to muscularis macrophages. LPS application caused significant leukocyte recruitment into the muscularis and a 51% decrease in muscle contractility. MCP-1 antibody treatment significantly averted leukocyte recruitment and significantly prevented muscle dysfunction. These parameters were not significantly altered by the nonspecific antibody. Results show that resident muscularis macrophage-derived MCP-1 plays a major role in the recruitment of monocytes during endotoxemia, which then subsequently secrete kinetically active substances that cause ileus.

Debate: Transfusing to normal hemoglobin levels improves outcome

Red cells are uniquely designed to transport oxygen and facilitate oxygen uptake by systemic tissues. Blood transfusions are thus logical therapeutic choices in patients who exhibit signs of oxygen debt. A small number of studies that have addressed patients with metabolic or physiologic signs of oxygen debt or regional ischaemia suggest that liberal blood transfusion strategies improve outcome. Therefore, armed with an understanding of the variety of clinical presentations characterising oxygen debt, as well as an appreciation of the risks involved, blood transfusions should be considered in all critically ill patients. This includes the consideration of liberalized hemoglobin triggers and hemoglobin thresholds in normal ranges.

Understanding gastrointestinal perfusion in critical care: so near, and yet so far

An association between abnormal gastrointestinal perfusion and critical illness has been suggested for a number of years. Much of the data to support this idea comes from studies using gastric tonometry. Although an attractive technology, the interpretation of tonometry data is complex. Furthermore, current understanding of the physiology of gastrointestinal perfusion in health and disease is incomplete. This review considers critically the striking clinical data and basic physiological investigations that support a key role for gastrointestinal hypoperfusion in initiating and/or perpetuating critical disease.

Abnormal tissue oxygenation and cardiovascular changes in endotoxemia

Experimental sepsis induces disturbances in microcirculatory flow and nutrient exchange that may result in impaired tissue oxygenation. Volume resuscitation is a principal clinical intervention in patients with sepsis. Nitric oxide (NO) has been implicated in the pathophysiology of endotoxemia, but few data exist concerning the effects of either NO synthase inhibition (NOSi) or volume resuscitation on microvascular regulation and tissue oxygenation. Amperometric measurements were made of skeletal muscle (tissue) oxygen tension (PtO2) and its response to changes in fraction of inspired oxygen (FIO2) in rats rendered endotoxemic. Simultaneous measurements were made of systemic hemodynamic indices and arterial blood gas tensions. At normal PaO2, PtO2 in endotoxemic animals was significantly lower than in control animals, with marked attenuation of the response to increasing FIO2. These changes were associated with significant metabolic acidemia. In volume-resuscitated endotoxemic rats, PtO2 and blood pH were unchanged. A significant reduction in the PtO2 response to hyperoxia was observed in animals treated with the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), an effect not reversed by fluid resuscitation. These data suggest that significant tissue hypoxia and abnormal microvascular control occur in endotoxemia. Volume resuscitation can reverse the changes in PtO2, whereas nitric oxide synthase (NOS) inhibition has deleterious effects on muscle PtO2 in both control and endotoxemic animals.

Hepatic oxygen metabolism in porcine endotoxemia: the effect of nitric oxide synthase inhibition

The role of endotoxin (lipopolysaccharide, LPS) and nitric oxide in hepatic oxygen metabolism was investigated in 36 pigs receiving 1) LPS (1.7 microgram. kg-1. h-1) for 7 h and NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg) after 3 h, 2) LPS, 3) NaCl and L-NAME, and 4) NaCl. Infusion of LPS reduced hepatic oxygen delivery (DO2H) from 60 +/- 4 to 30 +/- 5 ml/min (P < 0.05) and increased the oxygen extraction ratio from 0.29 +/- 0.07 to 0.68 +/- 0.04 after 3 h (P < 0.05). Hepatic oxygen consumption (VO2H) was maintained (18 +/- 4 and 21 +/- 4 ml/min, change not significant), but acidosis developed. Administration of L-NAME during endotoxemia caused further reduction of DO2H from 30 +/- 3 to 13 +/- 2 ml/min (P < 0.05) and increased hepatic oxygen extraction ratio from 0.46 +/- 0.04 to 0.80 +/- 0.03 (P < 0.05). There was a decrease in VO2H from 13 +/- 2 to 9 +/- 2 ml/min that did not reach statistical significance, probably representing a type II error. Acidosis was aggravated. Administration of L-NAME in the absence of endotoxin also increased the hepatic oxygen extraction ratio, but no acidosis developed. In a different experiment, liver blood flow was mechanically reduced in the presence and absence of endotoxin, comparable to the flow reductions caused by L-NAME. The increase in hepatic oxygen extraction ratio (0.34) and maximum hepatic oxygen extraction ratio (approximately 0.90) was similar whether DO2H was reduced by occlusion or by L-NAME. We concluded that L-NAME has detrimental circulatory effects in this model. However, neither endotoxin nor L-NAME seemed to prevent the ability of the still circulated parts of the liver to increase hepatic oxygen extraction ratio to almost maximum when oxygen delivery was reduced. The effect of L-NAME on oxygen transport thus seems to be caused by a reduction in DO2H rather than by alterations in oxygen extraction capabilities.

Effects of vasoactive drugs on gastric intramucosal pH

OBJECTIVE

To review current knowledge about the effects of vasoactive agents on gastric intramucosal pH (pHi).

DATA SOURCES

All studies involving pHi and vasoactive agents were retrieved from a computerized MEDLINE search from 1980 to 1997. We also reviewed the reference lists of all available review articles and primary studies to identify references not found in the computerized searches.

STUDY SELECTION

Clinical and experimental studies using dopamine, dopexamine, dobutamine, norepinephrine, epinephrine, nitric oxide, N-acetylcysteine, prostaglandins, or pentoxifylline were considered if splanchnic perfusion and/or pHi measurements were utilized.

DATA EXTRACTION

From the selected studies, information was obtained regarding patient population, dosing regimen, duration of study, and effects on splanchnic blood flow (SBF), splanchnic oxygenation, and pHi.

DATA SYNTHESIS

Although dopaminergic effects increase SBF, dopamine does not generally increase pHi. Data on the effects of dopexamine on pHi are scarce and inconsistent. Dobutamine can significantly increase SBF and usually increases pHi. In septic patients, norepinephrine seems to increase pHi. Epinephrine may have detrimental effects on gastric perfusion. Prostacyclin seems to increase pHi but data are limited. Insufficient evidence exists to support the beneficial effects of nitric oxide donors or blockers, pentoxifylline, or N-acetylcysteine on pHi.

CONCLUSIONS

Overall, the effects of vasoactive agents on pHi are unpredictable. Among the catecholamines, dopamine is the least likely, and dobutamine the most likely, to increase pHi.

Comparison of air tonometry with gastric tonometry using saline and other equilibrating fluids: an in vivo and in vitro study

OBJECTIVE

1) To compare saline gastric tonometry monitoring with air tonometry (Tonocap) in a group of general ICU patients. 2) An in vitro investigation of the performance of other fluids used in gastric tonometry and to assess the effects of variation of temperature and carbon dioxide concentration within the range encountered in clinical use.

DESIGN

a) A prospective, observational study in ICU patients b) A comparative laboratory study.

SETTING

The general Intensive Care Unit (ICU) and the laboratory at Leeds General Infirmary.

PATIENTS AND PARTICIPANTS

Nine patients in the general ICU with severe sepsis or septic shock.

MEASUREMENTS AND RESULTS

In vivo comparison of saline and air tonometry demonstrated a difference between the two techniques. Bland & Altman analysis showed a mean bias in the measurement of gastric PCO2 of 1.88 kPa with a precision of 1.22 kPa, with saline giving the lower result. In vitro, saline, air (Tonocap), gelatin and heparinised blood were used, at temperatures of 33-42 degrees C and at carbon dioxide concentrations of 4-8 kPa. While gelatin and blood gave unpredictable results, dependent on temperature and carbon dioxide concentration, air tonometry gave highly reproducible results. A consistent bias between the results with saline and air tonometry was seen over the range of temperatures and carbon dioxide (CO2) concentrations studied. The mean bias was 0.85 kPa with a precision of 0.40 kPa, saline consistently giving lower results.

CONCLUSIONS

There are clinically significant differences in values for gastric mucosal PCO2 measured by air tonometry and saline tonometry both in vivo and in vitro.

Nitric oxide and the haemodynamic profile of endotoxin shock in the conscious mouse

1. The release of cytokines following administration of endotoxin and the contribution of nitric oxide (NO) to the subsequent haemodynamic profile were investigated in the conscious mouse. 2. Administration of endotoxin (E. Coli, 026:B6, 12.5 mg kg(-1), i.v.) elevated the concentration of tumour necrosis factor-alpha (TNF-alpha) in the plasma within 0.5 h, reaching a maximum at 2 h and returning to control concentrations by 4 h. In addition, the concentration of interleukin-6 (IL-6) in the plasma was also elevated within 1 h, reaching a maximum at 3 h and remaining elevated throughout the 12 h of study. 3. Endotoxin (12.5 mg kg(-1), i.v.) induced the expression of a Ca2+-independent (inducible) NO synthase in the mouse heart and elevated the concentrations of nitrite and nitrate in the plasma within 4 h, reaching a maximum at 12 h. This was accompanied by a progressive fall in blood pressure over the same period. 4. The vasopressor effect of noradrenaline (0.5-4 microg kg(-1) min(-1), i.v.) administered as a continuous infusion was significantly attenuated 7 h after endotoxin (12.5 mg kg(-1), i.v). 5. The NO synthase inhibitor NG-monomethyl-L-arginine HCl (L-NMMA; 1-10 mg kg(-1), i.v. bolus) reversed the fall in blood pressure when administered 7 h after endotoxin (12.5 mg kg(-1), i.v.). 6. In an attempt to maintain a constant blood concentration, L-NMMA was administered as a continuous infusion (10 mg kg(-1) h(-1), i.v.), beginning 4 h after a lower dose of endotoxin (6 mg kg(-1), i.v.). Such treatment prevented the fall in blood pressure and the elevation of nitrite and nitrate in the plasma throughout the 18 h of observation. 7. The fall in blood pressure following endotoxin (3 mg kg(-1), i.v.) was significantly reduced throughout the 18 h of observation in homozygous mutant mice lacking the inducible NO synthase. 8. In summary, we have developed a model of endotoxin shock in the conscious mouse in which an overproduction of NO by the inducible NO synthase is associated with the haemodynamic disturbances. This model, which exhibits many of the characteristics of septic shock in man, will enable the study of the pathology of this condition in more detail and aid the investigation of potential therapeutic agents both as prophylactics and, more importantly, as treatments.