Nutrient modulation of inflammatory and immune function

Enteral nutrition in the critically ill patient

Timing and route of nutrition provided to critically ill patients can affect their outcome. Early enteral nutrition has been shown to decrease specifically infectious morbidity in the critically ill patient. There is a small group of patients who are malnourished on arrival to the intensive care unit and in these patients parenteral nutrition is beneficial.

PROUD: effects of preoperative long-term immunonutrition in patients listed for liver transplantation

Background

Patients with end stage liver disease are characteristically malnourished which is associated with poor outcome. Formulas enriched with arginine, ω-3 fatty acids, and nucleotides, "immunonutrients", potentially improve their nutritional status. This study is designed to evaluate the clinical outcome of long-term "immunonutrition" of patients with end-stage liver disease while on the waiting list for liver transplantation.

Methods/design

A randomized controlled double blind multi-center clinical trial with two parallel groups comprising a total of 142 newly registered patients for primary liver transplantation has been designed to assess the safety and efficacy of the long-term administration of ORAL IMPACT^®, an "immunonutrient" formula, while waiting for a graft. Patients will be enrolled the day of registration on the waiting list for liver transplantation. Study ends on the day of transplantation. Primary endpoints include improved patients' nutritional and physiological status, as measured by mid-arm muscle area, triceps skin fold thickness, grip strength, and fatigue score, as well as patients' health related quality of life. Furthermore, patients will be followed for 12 postoperative weeks to evaluate anabolic recovery after transplantation as shown by reduced post-transplant mechanical ventilation, hospital stay, wound healing, infectious morbidities (pneumonia, intraabdominal abscess, sepsis, line sepsis, wound infection, and urinary tract infection), acute and chronic rejection, and mortality.

Discussion

Formulas enriched with arginine, ω-3 fatty acids, and nucleotides have been proven to be beneficial in reducing postoperative infectious complications and length of hospital stay among the patients undergoing elective gastrointestinal surgery. Possible mechanisms include downregulation of the inflammatory responses to surgery and immune modulation rather than a sole nutritional effect.

Trial registration

ClinicalTrials.gov NCT00495859

Arginine Immunonutrition in Critically Ill Patients: A Clinical Dilemma

Commercial enteral nutritional formulas for enhancement of the immune system are widely used in critical care. Immunonutrition with arginine can enhance inflammatory and immunologic responses in animal models and in humans. Although clinical improvements in surgical patients have been reported, benefits in critically ill patients with systemic inflammatory response syndrome, sepsis, or organ failure are less clear. Recent meta-analyses on the use of immunonutrition with arginine in critically ill and surgical patients revealed methodological weaknesses in most published studies. Specifically, a meta-analysis indicated that critically ill patients with preexisting severe sepsis may have an increased mortality rate when fed an immunonutritional enteral formula that contains arginine. These findings brought about confusion and controversy over the use of immunonutritional formulas in subsets of critically ill patients. A review of the literature on the function of arginine, its effect on the immune system, its roles in immunonutrition and in the clinical outcomes of critically ill patients, and the implications for nursing practice indicated that the benefits of immunonutrition with arginine in critically ill patients are unproven and warrant further study. Until more information is available, nutritional support should focus primarily on preventing nutritional deficiencies rather than on immunomodulation.

Nutrient involvement in preeclampsia

Preeclampsia is a pregnancy-specific condition that increases maternal and infant mortality and morbidity. It is diagnosed by new-onset increased blood pressure and proteinuria during gestation; for many years these markers were the sole targets for study. More recently, increased attention to the multisystemic nature of the syndrome with involvement of almost all organs, activation of coagulation and increased sensitivity to pressor agents has expanded understanding of the disorder. The epidemiology of preeclampsia, being more common in poor women, long ago suggested that nutrients might be involved in the disorder. Numerous conflicting hypotheses were advanced but the testing of these hypotheses has either been done poorly or not at all. Review of the available data indicates very few studies that provide useful insights. In many studies the syndrome is poorly defined and in most studies nutritional data (questionnaires or biomarkers) are obtained on women with the clinical syndrome. In overtly preeclamptic women it is impossible to decipher cause from effect. Nonetheless, current concepts of the genesis of preeclampsia that include endothelial dysfunction, inflammatory activation, oxidative stress and predisposing maternal factors provide targets for well-designed nutritional investigation. In this review the current concepts of the pathogenesis of preeclampsia are reviewed and available data are assessed in light of these concepts. Targets for nutritional investigation based on the current knowledge of pathophysiology are suggested.

Immune-enhancing enteral diet increases blood flow and proinflammatory cytokines in the rat ileum

BACKGROUND

Enteral feeding improves outcome following surgery. Benefits depend on timing, route (enteral vs parenteral), and nutrient composition (standard vs immune-enhancing diets; IED). IED augments intestinal immunity and stimulates gut blood flow during absorption in a nutrient-specific manner. We hypothesize that a mechanism for the gut protective effect of IED is augmentation of blood flow to the gut-associated lymphoid tissue (GALT) in the terminal ileum.

METHODS

Male Sprague-Dawley rats (200-230 g) were fed for 5 days either an IED (Impact, Novartis) or an isocaloric, isonitrogenous control diet (CD, Boost, Mead-Johnson) matched to the daily caloric intake (rat chow). Rats were then anesthetized and cannulated for microsphere determination of whole organ blood flow. Blood glucose levels and blood flow to abdominal organs were determined at baseline and 30, 60, 90, and 120 min after gastric gavage (2 ml) with IED or CD. Intestinal tissues were harvested for cytokine levels (ELISA: IL-4, IL-10, IFN-gamma, and IgA).

RESULTS

Chronic IED increased baseline blood flow in the distal third of the small intestine compared to chow-fed and CD. Baseline blood flow was comparable between IED and CD in all other organs. CD and IED produced different blood flow patterns after gavage. CD increased blood flow compared to baseline and IED in antrum, duodenum, and jejunum. Ileal blood flow remained elevated in IED rats for 2 h, perhaps suggesting maximal blood flow. IED increased blood glucose compared to CD. Chronic IED increased IL-4 and decreased IL-10 in the terminal ileum.

CONCLUSIONS

Chronic IED exposure increases and sustains ileal blood flow compared to CD with altered proinflammatory cytokine expression. Our data suggest that a mechanism for the IED effect involves the selective perfusion of the terminal ileum and contiguous GALT during IED nutrient absorption.

Omega-3 fatty acids in immune-enhancing enteral diets selectively increase blood flow to the ileum by a bile acid dependent mechanism

BACKGROUND

The immune-enhancing diet (IED) (Impact, Novartis Corp, Minneapolis, Minn) initiates a delayed and sustained increase in blood flow to the ileum and gut-associated lymphoid tissue. The immune-enhancing benefits of Impact (Novartis Corp) are attributed to the addition of L-arginine, fish oil (FO), and RNA fragments to a standard enteral diet. The sustained increase in blood flow to the gut-associated lymphoid tissue during IED exposure might account for these immune effects. We hypothesized that the increase in ileal blood flow with IED might be a result of ileal omega-3 fatty acid absorption in the ileum by a bile-dependent mechanism.

METHODS

Male Sprague-Dawley rats (200 g-230 g) were anesthetized and cannulated for microsphere measurement of whole organ blood flow. Rats received gastric gavage (2 mL) with either IED, an isocaloric, isonitrogenous control diet (CD) (Boost, Mead-Johnson, Evansville, Ind), CD plus menhaden FO (CD+FO), or CD+FO plus bile duct ligation (BDL). Blood flow was determined at baseline and 30, 60, and 120 minutes after short-term gavage.

RESULTS

Baseline blood flow and central hemodynamics were comparable in all groups. In the ileum, at 120 minutes postgavage, blood flow was increased by IED and CD+FO compared with baseline and CD. BDL prevented the increase in blood flow in the CD+FO+BDL rats. All groups exhibited differences in splanchnic blood flow distribution after gavage: CD and CD+FO+BDL increased blood flow compared with baseline early in the proximal gut and spleen. IED and CD+FO produced a delayed, sustained hyperemia to the distal gut.

CONCLUSIONS

Gastrointestinal blood flow distribution after feeding is dependent on nutrient composition. These findings suggest that omega-3 fatty acids are the components of the enteral IED, Impact (Novartis Corp), which produce the increased blood flow to the terminal ileum and its contiguous gut-associated lymphoid tissue. Our data suggests that an intact enterohepatic bile pathway is needed for the IED blood flow effect.

Alterations in lymphocyte function and relation to phospholipid composition after burn injury in humans

OBJECTIVE

Lymphocyte functions are dependent on fatty acid composition of membranes, and impaired functions can predispose patients to infection after burn injury. The current study was designed to describe changes in lymphocyte-phospholipid composition and lymphocyte-related immune functions from early to late recovery time points after burn injury.

DESIGN

Prospective observational.

SETTING

Firefighter's Burn Treatment Center, University of Alberta Hospital, Edmonton, Alberta, Canada.

PATIENTS

Subjects (n = 10) with >10% total body surface burn area.

MEASUREMENTS AND MAIN RESULTS

Blood was drawn from subjects at specific time points (0 days to >50 days) after burn injury. Fatty acid composition of the major phospholipid classes of isolated lymphocytes was determined by using gas liquid chromatography. Lymphocyte phenotypes and proliferation ([(3)H]-thymidine uptake and interleukin-2 and interferon-gamma production) in response to mitogens were determined. Lymphocyte phospholipid 20:4n-6 content was 30% to 60% lower early compared with late postburn time points (p <.001). Interferon-gamma production by stimulated cells was found to negatively correlate with n-3 content (r =.7, p =.008). The expression of CD25 on antigen-mature CD8+ cells was associated with higher proliferative responses (r =.88, p <.004). Proportion of CD8+ cells was lower, and the proportion of activated monocytes was higher early compared with late postburn (p <.05). Natural killer cell cytotoxicity was low early after burn and increased with recovery.

CONCLUSIONS

The results of this preliminary study suggest that immune activation occurs between the second and third week after burn injury, which is associated with changes in 20:4n-6 and n-3 fatty acid content of lymphocyte phospholipid. This study suggests that there is release or impaired synthesis of 20:4n-6 early after burn injury that may be related to functional changes in immune cells.

Immune-enhancing enteral diet selectively augments ileal blood flow in the rat

BACKGROUND

Clinical studies show that immune-enhancing enteral diets (IED; with L-arginine, fish oil, and RNA fragments) decrease the rate of sepsis and shorten the length of hospital stay after the start of enteral feeding. These beneficial effects are dependent on the route of administration (enteral vs parenteral) and on the nutrient composition (IED vs standard diets). Gut exposure to an IED seems to preserve and/or augment intestinal mucosal immunity. However, nutrient absorption stimulates gut blood flow in a nutrient-specific manner (i.e., postprandial hyperemia). We hypothesized that an IED would initiate a different pattern of whole organ blood flow compared to a standard diet. This suggests that a mechanism for the protective effect of IED might be the preferential augmentation of gut blood flow to gut-associated lymphoid tissue (GALT) or mucosa-associated lymphoid tissue (MALT).

METHODS

Male Sprague-Dawley rats (200-225 g) were anesthetized and cannulated for colorimetric microsphere determination of blood flow distribution (with the phantom organ technique). Animals received gastric gavage (2 ml) of an IED (Impact; Novartis) or an isocaloric, isonitrogenous control diet (Boost; Mead-Johnson). Blood flow to the antrum, duodenum, jejunum, ileum, colon, liver, kidneys, and spleen was determined at baseline and 30, 60, 90, and 120 min after gavage.

RESULTS

Baseline blood flows to the left and right kidneys were within 10%, indicating the technical integrity of the microsphere technique and assay. Control diet augmented blood flow compared to IED in the antrum, duodenum, jejunum, and spleen. Conversely, IED gavage stimulated a delayed and sustained hyperemic response in the ileum. IED also increased hepatic blood flow early (30 min). IED increased blood glucose levels compared to control diet at 30, 60, and 90 min, suggesting enhanced nutrient absorption.

CONCLUSIONS

These data show that blood flow distribution depends on nutrient composition and that IED preferentially augments blood flow to the ileum. Since the terminal jejunum and ileum contain much of the GALT, our data suggest that a mechanism for enterally stimulated mucosal immunity involves selective perfusion of the terminal ileum during IED nutrient absorption.

Immune-modulatory actions of arginine in the critically ill

Current trials of immune-enhancing diets suggest several beneficial clinical effects. These products are associated with a reduction in infectious risk, ventilator days, ICU and hospital stay. However, methodological weaknesses limit the inferences we can make from these studies. Furthermore, improvements in outcomes were largely seen in surgical patients and in patients who tolerated critical amounts of formula. We propose that the beneficial findings cannot easily be extrapolated to other patient populations since there is suggestion from clinical trials that the sickest patients, especially those with severest appearances of sepsis, shock and organ failure may not benefit or may even be harmed. In these conditions we hypothesize that systemic inflammation might be undesirably intensified by immune-enhancing nutrients like arginine in critically ill patients. In this paper, we review the purported effects of arginine on the immune system and organ function to understand the scientific rationale for its inclusion into enteral feeding products. We conclude that patients with the most severe appearances of the systemic inflammatory response syndrome should not receive immune-enhancing substrates which may aggravate systemic inflammation and worsen clinical outcomes.

The importance of patients' nutritional status in wound healing

Good nutritional status is essential for wound healing to take place. Ignoring nutritional status may compromise the patient's ability to heal and subsequently prolong the stages of wound healing. Glucose provides the body with its power source for wound healing and this give energy for angiogenesis and the deposition of new tissue. Therefore, it is vital that the body receives adequate amounts of glucose to provide additional energy for wound healing. Fatty acids are essential for cell structure and have an important role in the inflammatory process. Wound healing is dependent on good nutrition and the presence of suitable polyunsaturated fatty acids in the diet. Protein deficiency has been demonstrated to contribute to poor healing rates with reduced collagen formation and wound dehiscence. High exudate loss can result in a deficit of as much as 100g of protein in one day. This subsequently needs to be replaced with a high protein diet. Vitamins are also important in wound healing. Vitamin C deficiency contributes to fragile granulation tissue. There is a correlation between low serum albumin and body mass index (BMI) and the development of pressure ulcers. Also, low serum albumin and high Waterlow score have a positive association. The body automatically renews tissue while we are asleep but this does not mean that protein synthesis does not take place during our wakeful hours. Holistic assessment of nutrition and early detection of malnutrition are essential to promote effective wound healing.

The scientific basis of immunonutrition

Substrates with immune-modulating actions have been identified among both macro- and micronutrients. Currently, the modes of action of individual immune-modulating substrates, and their effects on clinical outcomes, are being examined. At present, some enteral formulas are available for the clinical setting which are enriched with selected immune-modulating nutrients. The purpose of the present paper is to review the scientific rationale of enteral immunonutrition. The major aspects considered are mucosal barrier structure and function, cellular defence function and local or systemic inflammatory response. It is notable that in critical illness the mucosal barrier and cellular defence are impaired and a reinforcement with enteral immunonutrition is desirable, while local or systemic inflammatory response should be down regulated by nutritional interventions. The results available from clinical trials are conflicting. Meta-analyses of recent trials show improvements such as reduced risk of infection, fewer days on a ventilator, and reduced length of intensive care unit and hospital stay. Thus, a grade A recommendation was proclaimed for the clinical use of enteral immune-modulating diets. Improvement in outcome was only seen when critical amounts of the immune-modulating formula were tolerated in patients classified as being malnourished. However, in other patients with severe sepsis, shock and organ failure, no benefit or even disadvantages from immunonutrition were reported. In such severe conditions we hypothesize that systemic inflammation might be undesirably intensified by arginine and unsaturated fatty acids, directly affecting cellular defence and inflammatory response. We therefore recommend that in patients suffering from systemic inflammatory response syndrome great caution should be exercised when immune-enhancing substrates are involved which may aggravate systemic inflammation.

Effects of maximizing oxygen delivery on morbidity and mortality in high-risk surgical patients

OBJECTIVE

To evaluate the effects of maximizing the oxygen delivery on morbidity and mortality in patients >60 yrs of age and/or with chronic diseases of vital organs who underwent major elective surgery.

DESIGN

Prospective, randomized, controlled trial.

SETTING

A 24-bed general intensive care unit of a teaching hospital.

PATIENTS

Thirty-seven high-risk patients who underwent major surgery.

INTERVENTIONS

The hemodynamic and oxygen transport variables and outcomes in 18 patients (control group) treated to maintain normal values of oxygen delivery were compared with 19 patients (protocol group) treated to maintain "supranormal" values. Therapy in both groups consisted of volume expansion and, when necessary, dobutamine to reach target values, during the surgery and 24 hrs postoperatively.

MEASUREMENTS AND MAIN RESULTS

We interrupted the study because of a significant difference in the 60-day mortality rate. The mortality rate in the control group was significantly higher when compared with the protocol group (9/18 [50%] vs. 3/19 [15.7%], p < .05). The prevalence of clinical and infectious complications was higher in the control group than in the protocol group (67% and 31% respectively; relative risk, 0.47; 95% confidence interval, 0.226-0.991; p < .05) and there was a trend toward more severe organ dysfunction in nonachievers patients (17/24 [71%] vs. 6/13 [46%], relative risk, 0.65; 95% confidence interval, 0.343-1.237; NS).

CONCLUSION

Older patients with existing cardiorespiratory illness undergoing major surgery have a reduced morbidity and mortality when dobutamine is used to maximize oxygen transport.

Nutritional modulation of gut inflammation

Nutritional therapy is an important component of the management of gastrointestinal inflammation, which disrupts the gut mucosal barrier leading to sepsis, SIRS and MODS. Future studies will be needed to define the role of specific nutrients in enhancing mucosal barrier function and supporting general immune function, and how this affects morbidity and mortality of critically-ill patients.

Treatment of sepsis and septic shock: a review

Septic shock is one of the leading causes of death in intensive care units, and its incidence is increasing. Mortality rates as high as 95% are reported, with rates of 60% or more even when diagnosed and treated promptly. This review examines the definition of septic shock, its pathogenesis, and supportive therapy, with particular attention to intervention during the septic shock cascade.

Early enteral administration of a formula (Impact) supplemented with arginine, nucleotides, and fish oil in intensive care unit patients: results of a multicenter, prospective, randomized, clinical trial

OBJECTIVE

To determine if early enteral feeding, in an intensive care unit (ICU) patient population, using a formula supplemented with arginine, dietary nucleotides, and fish oil (Impact), results in a shorter hospital stay and a reduced frequency of infectious complications, when compared with feeding a common use enteral formula (Osmolite.HN).

DESIGN

A prospective, randomized, double-blind, multicenter trial.

SETTING

ICUs in eight different hospitals.

PATIENTS

Of 326 patients enrolled in the study, 296 patients were eligible for analysis. They were admitted to the ICU after an event such as trauma, surgery, or sepsis, and met a risk assessment screen (Acute Physiology and Chronic Health Evaluation II [APACHE II] score of > or = 10, or a Therapeutic Intervention Scoring System score of > or = 20) and study eligibility requirements. Patients were stratified by age (< 60 or > or = 60 yrs of age) and disease (septic or systemic inflammatory response syndrome).

INTERVENTIONS

Patients were enrolled and full-strength tube feedings were initiated within 48 hrs of the study entry event. Enteral feedings were advanced to a target volume of 60 mL/hr by 96 hrs of the event. One hundred sixty-eight patients were randomized to receive the experimental formula, and 158 patients were randomized to receive the common use control formula.

MEASUREMENTS AND MAIN RESULTS

Both groups tolerated early enteral feeding well, and the frequency of tube feeding-related complications was low. There were no significant differences in nitrogen balance between groups on study days 4 and 7. Patients receiving the experimental formula had a significant (p = .0001) increase in plasma arginine and ornithine concentrations by study day 7. Plasma fatty acid profiles demonstrated higher concentrations of linoleic acid (p < .01) in the patients receiving the common use formula and higher concentrations of eicosapentaenoic and docosahexaenoic acid (p < .01) in the patients receiving the experimental formula. The mortality rate was not different between the groups and was significantly (p < .001) lower than predicted by the admission severity scores in both feeding groups. In patients who received at least 821 mL/day of the experimental formula, the hospital median length of stay was reduced by 8 days (p < .05). In patients stratified as septic, the median length of hospital stay was reduced by 10 days (p < .05), along with a major reduction in the frequency of acquired infections (p < .01) in the patients who received the experimental formula. In the septic subgroup fed at least 821 mL/day, the median length of stay was reduced by 11.5 days, along with a major reduction in acquired infections (both p < .05) in the patients who received the experimental formula.

CONCLUSIONS

Early enteral feeding of the experimental formula was safe and well tolerated in ICU patients. In patients who received the experimental formula, particularly if they were septic on admission to the study, a substantial reduction in hospital length of stay was observed, along with a significant reduction in the frequency of acquired infections.

The modern version of adult respiratory distress syndrome

Adult respiratory distress syndrome (ARDS) remains a highly lethal complication of autodestructive inflammation. This syndrome originally referred to a single organ failure but is now considered a component, usually the first, of the multisystem organ failure syndrome (MOFS). Cytokines, neutrophils, and endothelial adherence molecules initiate the disease process, with cell injury caused by oxidants and proteases released from inflammatory cells. ARDS, if progressive, will result in pulmonary fibrosis. Improved ventilatory support techniques have not been shown to decrease mortality. Pharmacologic manipulation of the inflammatory response is a more promising method of controlling the disease process.

Indications for enteric tube feedings in oral and maxillofacial surgery

The catabolic effects of surgical trauma and sepsis have long been recognized. Oral and maxillofacial surgical patients represent a unique group in that their surgery and its effects on the stomatognathic system may adversely affect the ability to receive adequate nutrition. This article discusses some basic nutritional principles and describes the indications and guidelines for enteric tube feeding in this patient population.

Basic concepts of immunology and its application to clinical nutrition

In recent years, evidence has accumulated on the effects of nutrients on metabolic processes. The role of specific nutrients in modulating immune function has received much attention because of the significant role of the immune system in a variety of disease states. The immune system depends on the complex interactions of its various parts. In response to an "antigen" or foreign substance that penetrates the external protective barriers of the human body, nonspecific (phagocytes, complement) defense mechanisms and antigen-specific factors are activated. The antigen-specific immune system relies on both humoral (antibodies and B cells) and cellular (T cells and lymphokines) defenses. Malnutrition causes a decline in all aspects of host defense. Correction of malnutrition in hospitalized patients and restoration of immunocompetence has become a goal of nutrition support practitioners today. The application of current research findings to patient care requires a basic understanding of immunology.

Role of dietary supplements in nutritional support

Nursing staff play a key role in the multidisciplinary team in ensuring that nutritional support is provided where needed and that dietary supplements are used appropriately. This article reviews the wide range of feeds and supplements that are available and the indications for their use.

Perioperative care of the immunocompromised patient

Immunocompromised patients are increasingly common in modern surgical practice. Challenges related to their care include identifying the determinants of increased risk and selecting the appropriate therapy for individual patients. There are multiple and overlapping causes of immunosuppression in surgical patients that make the interpretation of clinical trials difficult. A clear understanding of these mechanisms guides the physician to choose the immunomodulatory agents that can be used for improving current rates of complication and mortality. The best practical approach to immunocompromised patients involves determining who is at risk, aggressive diagnosis, early therapy, and a high index of suspicion for infectious complications.

Multiple organ failure. Pathophysiology and potential future therapy

Multiple organ failure (MOF) has reached epidemic proportions in most intensive care units and is fast becoming the most common cause of death in the surgical intensive care unit. Furthermore, in spite of the development of successive generations of new and more powerful antibiotics and increasing sophisticated techniques of organ support, our ability to salvage patients once MOF has become established has not appreciably improved over the last two decades. Clearly, new therapeutic strategies aimed at preventing or limiting the development of the physiologic abnormalities that induce organ failure are needed to improve survival in these critically ill patients. Based on our rapidly increasing knowledge of the mechanisms of MOF and the fruits of molecular biology, a number of new therapeutic approaches are in various stages of development. To effectively use these new therapeutic options as they become available, it is necessary to have a clear understanding of the pathophysiology of MOF. Thus, the goals of this review are to integrate the vast amount of new information on the basic biology of MOF and to focus special attention on the potential therapeutic consequences of these recent advances in our understanding of this complex and perplexing syndrome.

Effects of anaesthesia and surgery on the immune response

Alterations have been found to occur in every component of immune response during anaesthesia and surgery. These alterations represent the body's general physiological responses and are mainly dependent on the extent of surgery, as well as other factors such as the patient's age and health status, medication and blood transfusion. Anaesthetic and operative complications have profound effects on these responses. Basically, the immune response to anaesthesia and surgery is a beneficial reaction, needed in local host defences and wound healing and in preventing the body from making autoantibodies against its own tissues. The responses may, however, contribute to the development of postoperative infections and spread of malignant disease. During uncomplicated conventional surgery, the immune response usually passes clinically unnoticed without any harmful effects. Absent responses and excessively high responses, on the other hand, harm the patient. Our understanding of immunological phenomena and our possibilities of controlling mediator activation are now lagging behind the technical advances made in operative treatment. If we want to decrease operative morbidity and mortality to below their present levels, more attention should be directed to immune responses to major surgery, injuries and operative complications with massive mediator release which place the surgical patient at risk. Experimental evidence suggests that results of treatment in injured and operated patients can in the future be improved by controlling immune responses and their mediator systems. Our current level of knowledge of immune responses is already helping us to avoid many immune-mediated complications. However, routine interference with these responses is not indicated.