Multiple organ failure

Purpose: Cytokines have been associated with the development of sepsis and diffuse tissue injury following septic or endotoxic challenges in humans. Furthermore, relative organ-system dysfunction, not specific organ dysfunction, appears to predict outcome from critical illness. We hypothesized that persistence of inflammatory cytokines within the circulation, reflecting a generalized systemic inflammatory response, is associated with multiple-system organ failure (MSOF) and death from critical illness. In addition, since hepatic function is central to host-defense homeostasis, we further reasoned that critically ill patients with hepatic cirrhosis would have an increased incidence of MSOf and death following sepsis associated with a persistence of cytokines in the blood. Patients and Methods: We measured serum levels of tumor necrosis factor (TNF), interleukin (IL) I, IL-2, IL-6, and interferon gamma (IFG) serially for the first 48 h following the onset of hypotension (systolic blood pressure <90 mm Hg) thought likely to be due to sepsis in all patients presenting to one ICU. These data were correlated with initial severity of shock and retrospective determination of septic or nonseptic origin, preexistent hepatic cirrhosis, subsequent development of MSOF, and outcome. Results: Fifty-three specific episodes of shock in 52 patients were recorded (35 septic and 18 nonseptic episodes). Mortality was higher in septic patients (41 vs 17 percent, p<0.01), as was the development of MSOF (29 vs 6 percent, p<0.001), incidence of cirrhosis (21 vs 0 percent, p<0.01), and TNF levels over the study interval (p<0.01). Nonseptic patients also had an initial elevation in TNF over 48-h levels (p<0.05) that were higher than serum levels reported for normal subjects ([Chi.sup.2] p<0.05). There was no relation between peak TNF level and outcome. Sixty-seven percent of the cirrhotic patients had development of MSOF and died, while only 30 percent of the noncirrhotic patients had development of MSOF or died (p<0.05). The TNF and IL-6 levels in patients who had MSOF or who died were both elevated and did not decrease over time independent of presence or absence of sepsis (p<0.01). Similarly, IL-6 levels after 12 h were higher in cirrhotic patients than in noncirrhotic septic patients (p<0.05). No elevation in IL-1, IL-2, or IFG was seen in any patient subpopulation. Conclusions: TNF and IL-6 serum levels are higher in septic than in nonseptic shock, but the persistence of TNF and IL-6 in the serum rather than peak levels of cytokines predicts a poor outcome in patients with shock.

Septic shock continues to be a highly fatal disease process despite aggressive therapy and whether or not it occurs as an initial process or as a complication of preexistent organ system failure.[1-3] The persistently high mortality rate of patients in septic shock appears to be related to the development of multiple-system organ failure (MSOF). Cytokine-related systemic intravascular inflammation may represent a common pathogenic link between initial insult and MSOF in septic shock. Such cytokines as tumor necrosis factor (TNF) have been implicated in the development of the septic state and in diffuse tissue injury in animal models.[4,5] They are also produced following endotoxin challenge in humans.[6] TNF, together with other cytokines such as interleukin (IL) 1, IL-2, IL-6, and interferon gamma (IFG), appears both to form and to modulate the response to an inflammatory stimulus.[4,5,7-10] Numerous cytokines have also been implicated in the systemic response to sepsis.[11]

Factors other than the initial severity of circulatory shock may also determine outcome of sepsis. Knaus et al[12] suggested that outcome from critical illness was related more to the overall level of organ systems dysfunction over time than to dysfunction of a specific organ system. The etiology of organ system dysfunction during sepsis appears to be related to systemic activation of numerous effector cells and noncellular substances that may act on remote tissues.[4,7,8,13] We and others have previously hypothesized that persistence of intravascular inflammation, as can be characterized by continued elevation of inflammatory cytokines within the circulation, and not their initial levels following insult, determines which patients with septic shock have development of MSOF.[14,15] According to this hypothesis, patients who either produce excessive amounts of cytokines or cannot clear them from the circulation may be at increased risk of having MSOF develop and dying after an insult. In support of this hypothesis, Matuschak et al[16] have shown that patients with end-stage liver failure who have development of ARDS invariably die despite aggressive intensive care. Since liver function is central in host-defense homeostasis, the liver being a major organ involved in clearance and secretion of TNF into the circulation,[17] we reasoned that preexistent liver failure might place a patient in shock at increased risk for the development of MSOF and death owing to a persistence of inflammatory mediators within the circulation.[18,19]

Accordingly, we measured sequentially the levels of many inflammatory cytokines, including TNF and IL-6, in patients presumed to be in septic shock, in an attempt to define the relation between level of systemic inflammatory activation, sepsis, severity of shock, preexistent hepatic cirrhosis, subsequent development of MSOF, and outcome. Our data suggest that patients in septic shock have higher levels of TNF and IL-6 during the acute phase of their illness, but that persistence of these cytokines in the blood rather than initial peak levels is more characteristic of patients who ultimately have development of MSOF and die.

METHODS

Patients

With approval from the Institutional Review Board of Erasmus Hospital, we prospectively studied all patients in our ICU over a 6-month period presenting with undiagnosed hypotension (systolic arterial pressure <90 mm Hg), evidence of tissue hypoperfusion, and infection as a possible cause of circulatory shock. Serial measurements of TNF, IL-1, IL-2, IL-6, and IFG levels were taken from serum samples collected at presentation (t=0) and again 1, 2, 4, 12, 24 and 48 h later. We took care of avoid exogenous sources of endotoxin contamination (using endotoxin-free tubes, pipettes, and needles). We correlated serum cytokine levels with clinical status (sepsis vs nonsepsis, severity of shock), organ system function (preexistent hepatic cirrhosis, subsequent MSOF), and outcome (survival) as defined below. These data were obtained by retrospective chart review.

Definitions

1. Sepsis: The presence of a confirmed source of infection plus fever (temperature >38.5 [degrees] C) and leukocytosis (>12,000 WBCs per deciliter).

2. Shock Severity: Evidence of tissue hypoperfusion: urine output <30 ml/h, decreased sensorium, and diaphoresis. Level 0, hypotension or vascular instability rapidly reversible without specific therapy, and serum lactate level <2 mmol/L; level 1, hypotension rapidly reversible with intravascular fluid replacement associated with evidence of altered organ perfusion; level 2, hypotension requiring vasoactive pressor support; and level 3, hypotension not responsive to maximal resuscitative therapy for 2 h or more.

3. Preexistent Hepatic Cirrhosis: History of biopsy-proved hepatic cirrhosis and/or previous episodes of either recurrent jaundice, upper gastrointestinal hemorrhage associated with esophageal varices or ascites.

4. MSOF: Failure in three or more organ systems following entry into the study.

Pulmonary: Either (1) ARDS: acute respiratory failure with bilateral infiltrates on chest roentgenogram with a predisposing risk factor, such as sepsis, aspiration, or polytrauma, plus pulmonary artery occlusion pressure ([P.sub.pao])<18 mm Hg. [PaO.sub.2]/[FIO.sub.2]<150 or <200 on positive end-expiratory pressure, or (2) ventilator-dependent acute respiratory failure for more than 3 days.

Renal: Urine output <30 ml/h, serum urea nitrogen >60 mg/dl or creatinine >3.5 mg/dl.

Cardiovascular: 54> heart rate <140 beats per minute, mean arterial pressure <50 mm Hg, [P.sub.pao] >18 mm Hg, or requirement of inotropic agents for >12 h.

Central nervous system: Glasgow Coma Score <6.

Hematologic: White blood cells <1,000/[mm.sup.3] and/or platelet count <20,000/[mm.sup.3].

Hepatic: Encephalopathy with asterixis; prothrombin time >2.5 times normal, not correctable with vitamin K, and bilirubin >4 mg/ dl in a patient without prior hepatic cirrhosis.

Gastrointestinal: No bowel sounds and either gastric retention >500 ml/d or bloody diarrhea >500 ml/d.

Survival

Survival was defined as discharge from the hospital. Intraunit and hospital death, time on ventilator, and functional status at discharge were also recorded, although not used for statistical analysis.

Serum Assays

Serum lactate levels were measured in duplicate from arterial samples kept on ice before measurement (Automated Analyzer, Hitachi, Tokyo, Japan). Serum samples for subsequent measurement of cytokine levels were stored at - 20[degrees] C.

Serum concentrations of TNF were determined using an immunoradiometric assay (IRMA) with a sensitivity of 1 pg/ml (IRE-Medgenix, Fleurus, Belgium), as previously described.[20] Briefly, the IRMA is based on coated-tube separation and the oligoclonal system, in which several monoclonal antibodies directed against distinct epitopes of TNF are used. Standards of recombinant TNF were used at concentrations of 0 to 5,000 pg/ml. Standards contained 15.8 kBq ([+ or -] 0.4 [unkeyable]Ci) of [sup.125]I-TNF per milliliter. Standard and samples (0.20 ml) and [sup.125]I-labeled anti-TNF antibodies (0.05 ml) were mixed and incubated for 20 h at room temperature. The contents were aspirated, tubes washed with 2 ml of polysorbate 20 (Tween 20) and counted for 1 min in a gamma scintillation counter. Interassay variations were less than 10 percent.

Serum concentrations of IL-1 and IL-2 were measured by radioimmunoassay (RIA) (IRE, Medgenix). Standards consisting of recombinant IL-1 or IL-2 were used at concentrations of 0 to 10 ng/ ml. Standards and samples (0.1 ml) were mixed with rabbit antiserum (0.1 ml) and were incubated for 24 h at 4[degrees] C. After 0.1 ml of [sup.125]I-IL-1 or IL-2 was added, the tubes were incubated an additional 4 h. Antirabbit gamma globulin antiserum mixed with polyethylene glycol was added to precipitate the [sup.125]I-IL-1 or IL-2 antibody complex. After centrifugation, bound radioactivity was determined over 5 min in a gamma scintillation counter. Interassay variation was less than 15 percent.

Serum concentrations of IFG were also measured by both an IRMA and an RIA (IRE, Medgenix), as described above. Interassay variation was less than 10 percent.

Remeasurement of serum IL-1, or IL-2, and IFG was performed with the last 20 patients enrolled in the study using sandwich assay methods to minimize the effects of potential circulating inhibitors of the RIA.

Serum IL-6 activity was assayed using IL-6-dependent mouse hybridoma 7TD1, cultivated in flat-bottomed microtiter plates containing 2,000 cells per well in the presence of serial dilutions of the serum sample. After 4 days of culture, the number of surviving cells was determined by a colorimetric assay for hexosaminidase, as previously described.[21] Hybridoma growth factor/IL-6 activity was expressed in units per milliliter, defined as the dilution giving half-maximal proliferation of 7TD1 cells. One unit corresponds to approximately 5 pg/ml of IL-6. The 7D1 cells do not respond to TNF, IL-1 beta, IL-2, interferon alpha, interferon beta, IFG, or any of the known colony-stimulating factors other than IL-6.[21] The biologic activity of IL-6 samples was completely neutralized by adding monospecific rabbit polyclonal antirecombinant human IL-6 antibodies to the test samples. The interassay variability ([+ or -] 30 percent) was corrected by the use of an internal standard. Each sample was tested four times. Samples were heated at 56 [degrees] C for 30 min before the assay to eliminate inhibitory factors. The lower limit of detection of IL-6 activity in sera was also measured after addition of 100 U of recombinant IL-6.

Statistical Analysis

Fisher's exact test was used to test for differences between septic and nonseptic groups for incidence of hepatic cirrhosis, MSOF, and mortality. Two-way analysis of variance with repeated measures was used for cytokine levels over time. A Bonferoni post hoc comparison was used to determine differences in cytokine levels over time and between groups and subgroups. Comparisons between measured cytokine levels at specific times and published values were done by [Chi.sup.2] analysis. Comparison between peak and mean cytokine levels between specific subgroups was done by a Mann-Whitney U test. To assess the interaction between continuous variables and survival, we performed a multivariate Hotelling [T.sup.2] test using age and mean serum cytokine levels.

RESULTS

A total of 55 episodes of shock in 54 patients were studied. Data from two patients were excluded from analysis. One patient had HIV-positive disease and was believed to represent a novel immunologic response, and the other patient was admitted to the hospital in the terminal stages of glioblastoma, was not actively resuscitated, and died within the first hour. The reported analysis includes 53 episodes of shock in 52 patients. One patient had a repeated episode of shock occurring 3 weeks after resolution of the initial episode. He was studied twice because the two events were thought to be unrelated.

Of the 53 episodes of shock, 35 were defined as septic and 18 were defined as nonseptic. Only 16 nonseptic patients had sequential measurements of serum cytokine levels allowing further data analysis. Samples were not collected in the other three patients because their conditions improved rapidly and they were discharged from the ICU. All nonseptic patients had clearly defined noninfectious causes of hypotension. Ten septic patients had development of MSOF and died, six of whom also had hepatic cirrhosis. Four noncirrhotic septic patients died without having MSOF develop. Three nonseptic patients died, none of whom had hepatic cirrhosis or MSOF. One nonseptic patient had development of MSOF and survived after requiring ventilatory support for 48 days. No patient required the onset of gastrointestinal failure for development of MSOF although three patients with MSOF subsequently had development of gastrointestinal failure as well. Severity of shock within the first 2 h of its occurrence was higher in nonsurvivors than survivors but was not different between septic and nonseptic groups. There were no differences in patient age between survivors and nonsurvivors. Compared with nonseptic patients, septic patients had a higher incidence of hepatic cirrhosis (6/34 vs 0/18, p <0.05) and MSOF (10/34 vs 1/19, p<0.05). These differences persisted even when patients were stratified by severity of shock. Septic patients tended to have a higher mortality (14/34 vs 1/19, p = 0.0764), which was significant when compared only in patients with level 2 or 3 shock severity.

Serum Cytokine Levels

Serum cytokine levels over time in both septic and nonseptic groups are summarized in Table 1. Peak cytokine levels for these and other specific subgroups are listed in Table 2, and mean cytokine levels for these same groups appear in Table 3. Both TNF and IL-6 demonstrated marked interpatient variability over similar diagnoses and intrapatient variability over time. In contrast, TNF and IL-6 values from normal volunteers in our laboratory are both low and constant over time (TNF 3.1 [+ or -] 1.2 pg/ml and IL-6 <2 U/ml).[6,22] Marked variability in individual sample TNF and IL-6 levels characterized our study. However, individual serum samples gave consistent values for both TNF and IL-6 when measured in duplicate and when remeasured between assay kits. Despite the marked variability of TNF and IL-6 levels characterizing both septic and nonseptic patient subgroups (Fig 1), both peak and mean TNF levels at all times were higher in septic patients than in nonseptic patients (p<0.01) (Fig 1, Table 1). TNF levels decreased over time in septic patients (p<0.01). In nonseptic patients, however, mean TNF levels at 0 and 1 h were significantly higher than in normal subjects as reported by our laboratory (p<0.05).[6,22] TNF levels decreased to normal levels (<10 pg/ml) in all nonseptic patients by 12 h. IL-6 levels were higher in septic than in nonseptic patients (p<0.05), but the values varied widely over time and the degree of variability of peak IL-6 levels between subjects was great. Although the differences in TNF and IL-6 levels between septic and nonseptic patients were significant within the first hour after the onset of shock, they were not associated with severity of shock or outcome. Similarly, in most nonsurvivors, neither TNF nor IL-6 demonstrated preterminal increases. [TABULAR DATA OMITTED]

Neither IL-1, IL-2, nor IFG levels were elevated or demonstrated significant change over the study interval in septic and nonseptic patients combined, although a few patients had isolated elevations in one of these cytokines. Specifically, IFG serum levels >2 U/ml were seen in four patients: two with Gram-negative sepsis, one with fungal sepsis, and one with disseminated herpes simplex infection. Interestingly, IFG levels also tended to be lower in patients with hepatic cirrhosis. Serum IL-1 levels >1 ng/ml were seen in one patient with Gram-negative sepsis complicating the course of hairy-cell leukemia. Serum IL-2 levels >1 U/ml were seen in 12 patients. Remeasurement of serum IL-1, IL-2, and IFG using sandwich assay methods of the RIA did not yield increased cytokine values. These cytokine levels, on the average, are similar to those from normal volunteers as measured in our laboratory (IL-1 [is less than or equal to]0.2 ng/ml, IL-2 [is less than or equal to]0.2 U/ml, and IFG [is less than or equal to]0.2 U/ml). There was no relation between levels of IL-1, IL-2, or IFG and sepsis, outcome, TNF levels, or IL-6 levels. In 23 subjects (5 nonseptic and 18 septic), peak serum TNF levels occurred between 1 and 4 h following entry into the study. In none of these patients were IFG, IL-1, or IL-2 levels elevated in the serum samples taken prior to these times of peak TNF activity.

Relation of Serum Cytokines to Infectious Organism

Of the 35 episodes of septic shock, 10 were due to Gram-positive organisms, 18 were Gram-negative or mixed infections, 4 were culture negative, 2 were viral (disseminated herpes simplex infection and cytomegalovirus pneumonia), and 1 was fungal in origin (Candida species). There was no specific pattern in TNF or IL-6 peak serum levels between these subgroups; however, the number of subjects in each group was small (Fig 2). Of the four patients who had culture-negative sepsis, three had pneumonitis with purulent sputum but were receiving parenteral antibiotics at the time cultures were taken, and one had multiple localized peritoneal abscesses following bowel perforation.

Relation of Serum Cytokines to Survival

Although septic patients had a higher mortality rate than nonseptic patients did, other factors were independently related to survival. Severity of shock was lower within the first 2 h in survivors (1.1 vs 2.4, survivor vs nonsurvivor, p<0.0001). However, TNF or IL-6 peak serum levels did not correlate with shock severity (Fig 3) or survival (Fig 4). Mean TNF levels over the entire course were lower in survivors (84[+ or -]302 vs 120[+ or -]234 pg/ml, survivors vs nonsurvivors, p<0.0001), but were similar between groups during the first 2 h (155[+ or -]503 vs 177[+ or -]340 pg/ml) (Fig 5). Survivors had lower TNF levels at 48 h than did nonsurvivors (12[+ or -]14 vs 35[+ or -]36 pg/ml, p<0.01). Both preexistent hepatic cirrhosis and the development of MSOF were associated with higher mortality than occurred in patients without these conditions (p<0.001). Using a multivariate Hotelling [T.sup.2] test for age and mean serum cytokine levels, we found no difference between survivors and nonsurvivors (approximate [F.sub.6,46] = 0.89, p = 0.514).

Relation of Serum Cytokines to MSOF

The development of MSOF portends a grave prognosis. All septic patients with MSOF died, and the one nonseptic patient with MSOF who lived had a prolonged period of intensive care (62-day ICU stay, 48 days receiving artificial ventilation). Patients who subsequently had development of MSOF had higher TNF levels at the onset of shock, although peak levels were higher in some patients who did not have development of MOSF. However, persistence of elevated TNF levels was characteristic of all patients who had development of MSOF, independent of sepsis (p<0.005), and this difference persisted even when septic patients with MSOF were compared with only septic patients without MSOF (Fig 6). When lowest TNF values during the 48-h study period were compared, patients who did not have development of MSOF (n = 42) had a lower level than patients who did (n = 11) (13[+ or -]17 vs 43[+ or -]41 pg/ml, p<0.01).

Relation of Serum Cytokines to Hepatic Cirrhosis

All patients with hepatic cirrhosis who presented with hypotensive shock had sepsis confirmed as the cause of shock. Of the six cirrhotic patients in this study, five had development of MSOF and died, and one survived. Cirrhotic patients had a significantly greater likelihood of developing MSOF and dying than did noncirrhotic septic patients (p<0.05). The levels of TNF in cirrhotic patients were significantly greater than those in nonseptic patients (p<0.01), but they were similar to those in noncirrhotic septic patients. However, in contrast to the values in noncirrhotic septic patients, the serum levels of TNF and IL-6 did not decrease over time in cirrhotic patients; this difference was significant for IL-6 levels at 12 h (p<0.05). The profile of IL-6 values over time for the subset of patients with hepatic cirrhosis and MSOF was similar to that for cirrhotic patients.

DISCUSSION

Septic shock is a highly lethal disease process.[1,3] Previous studies have shown that mortality rates correlate with initial severity of shock,[23] duration of organ failure,[12] combined nonspecific sepsis and MSOF,[1] and preexistent liver failure.[16,19] Our data agree with all these findings and extend our understanding of the processes involved in tissue dysfunction in shock, by the simultaneous measurement of serum cytokines. Although serum levels of TNF and IL-6 decreased in all patients following the initial event, persistence of elevated levels of TNF and IL-6 in critically ill patients is associated with the preexistence of hepatic cirrhosis, the subsequent development of MSOF, and mortality. However, neither peak serum levels of TNF or IL-6, nor serum levels of IL-1, IL-2 or IFG were associated with clinical course, and individual patient serum TNF and IL-6 were highly variable, consistent with the complex nature of the inflammatory process associated with shock states. These findings, although agreeing with our bias, may reflect patients' heterogeneity of response to the insult, variable entry times of patients into the study relative to the insult, differences in severity of the insult, or epiphenomena of the systemic expression of MSOF.

Inflammatory Cytokines in Septic Shock

Waage et al[24] demonstrated that serum TNF levels correlated with mortality in meningococcal septic shock. Subsequent studies from their group showed that IL-6 levels were also elevated in these patients, carrying a similar relation to mortality, while IL-1 levels were variable, but if elevated were also associated with a fatal outcome.[4] Helfgott et al[25] studied seven patients with acute bacterial infection and demonstrated multiple forms of IL-6 in serum and cerebrospinal fluid. Hack et al[26] measured serial IL-6 levels in 37 patients with sepsis or septic shock. Increased levels of IL-6 were found in 32 or 37 patients. Serum IL-6 levels correlated with severity of shock and C3a and C4a levels, and correlated inversely with C1 inhibitor. These investigators, however, did not measure serum levels of other cytokines or note the development of MSOF or the coexistence of hepatic dysfunction. Marks et al,[27] using a relatively insensitive enzyme-linked immunosorbent assay method, found that serum TNF levels are elevated initially in many septic patients but decrease over the first 24 h. Furthermore, Calandra et al[14] measured TNF, IL-1, and IFG prospectively in 70 patients with septic shock. They demonstrated that absolute levels of TNF over time correlated inversely with survival. In a follow-up report on this same group of patients, Calandra et al[15] demonstrated that IL-6 levels were also elevated in patients with Gram-negative bacteremia. Others have also documented elevated but variable serum TNF levels in patients in septic shock.[28,30] Collectively, these studies suggest that elaboration of the inflammatory cytokines TNF and IL-6 plays a pivotal role in the systemic response of the host to sepsis and to outcome. These studies, however, are limited by their lack of nonseptic control patients as well as, in the first group of studies cited, by the use of specific inflammatory agents in otherwise healthy subjects. Our data support and extend these preliminary observations by demonstrating relations between cause of shock, circulatory serum cytokine levels, development of MSOF, and outcome and by the simultaneous measurement of serum TNF and IL-6 levels. Septic patients had greater increases in TNF and IL-6 levels than did nonseptic shock patients. Patients with sepsis and preexistent hepatic cirrhosis, those who went on to have development of MSOF, and nonsurvivors had persistently higher mean TNF levels, suggesting that TNF is either excessively produced, inadequately cleared, or both in these conditions.

Inflammatory Cytokines in Nonseptic Shock

Although nonseptic patients had lower serum TNF levels than did septic patients, some nonseptic patients had higher initial serum TNF levels than some septic patients (Fig 1), and mean serum TNF levels in nonseptic patients were elevated over normal, unstimulated serum levels.[6,22] Similarly, serum IL-6 levels did not differ between septic and nonseptic groups and, unlike Hack et al,[26] we saw no correlation between serum IL-6 level and mortality. The persistence of IL-6 in the serum of nonseptic patients may reflect the long half-life of the cytokine.[26] Similarly, as markers of inflammation, peak levels of TNF and IL-6 did not correlate with severity of shock or outcome. Thus, the detection of elevated levels of TNF and/or IL-6 in the serum of patients in shock is not specific for a septic cause. Furthermore, since septic and nonseptic patients had similar levels of shock severity, it appears that neither peak nor mean TNF levels are a major determinant of the hemodynamic response of the host to these septic and nonseptic insults. Given the central initiating position of these cytokines in the expression of the inflammatory process, these data are consistent with the hypothesis that increased TNF and IL-6 levels in the sera reflect a nonspecific host response to overwhelming stress as manifested by the shock state.

MSOF, Hepatic Cirrhosis, and Serum Cytokines

Interestingly, in the patients who had development of MSOF, serum TNF levels were increased and remained elevated while in all other patients they rapidly decreased over 12 h. These data are consistent with the hypothesis that persistence of a systemic inflammatory response is more important in determining remote organ dysfunction than is the magnitude of the initial response.[18] Our data from patients with hepatic cirrhosis support these findings. Not surprisingly, patients with preexistent hepatic cirrhosis who had development of hypotensive shock had a greater likelihood of developing MSOF and dying than did patients without cirrhosis. These data agree with the previous findings of Matuschak et al,[16] who demonstrated that patients with end-stage liver failure had an increased likelihood of developing acute respiratory failure and dying if they presented initially with hemodynamic instability. Similarly, Deviere et al,[31] using similar TNF but different IL-6 analysis methods, demonstrated that in the absence of infection, patients with hepatic cirrhosis had increased serum TNF and IL-6 levels as compared with a noncirrhotic outpatient population (TNF 12.0[+ or -]1.2 vs 3.1[+ or -]1.2 pg/ml, and IL-6 6 1,584[+ or -]562 vs 259[+ or -]114 U/ml). These data are consistent with increased production and/or decreased clearance of TNF in patients with hepatic dysfunction. These increased cytokine levels were associated with an excessive lipopolysaccharide (LPS)-induced production in vitro of the cytokines IL-1, IL-6, and TNF. Cytokine production was reversible by preincubation with normal serum.[32] These data suggest that in liver failure states, a high degree of monocyte priming occurs and may result in excess production of inflammatory mediators in response to the normal inflammatory stimulator load placed on the liver. In further support for an altered inflammatory response in hepatic cirrhosis, Matuschak et al[33] demonstrated increased eicosanoid production and mortality in rats with impaired hepatocytic function. In that study, mortality rate could be reduced and abnormal eicosanoid metabolism reversed by inhibition of the lipoxygenase pathway.

Our patients with hepatic cirrhosis did not manifest an initial peak TNF response to septic shock. This lack of response to a septic challenge is consistent with tissue culture studies demonstrating that monocytes from patients with cirrhosis elaborate less TNF in response to LPS than do monocytes from normal volunteers.[32] Thus, patients with hepatic cirrhosis may represent a unique population in their response to septic challenges owing to both an abnormal basal state of immune cell activation and altered immune response to proinflammatory stimuli. These studies collectively suggest that the development of MSOF is associated with a continual elevation of proinflammatory cytokines in the blood, due either to continual stimulation of the afferent limb of the immune response or to failure to clear performed inflammatory mediators.

We saw no elevation in IL-1, IL-2, or IFG levels in any subgroup. Previous studies suggest that IL-1 appears in the circulation early after endotoxin challenge, with other systemic responses following it by approximately 30 min.[7] Since entry into our study was heralded by an acute hypotensive response, early transient elevations in serum IL-1 levels could have been missed. However, our IL-1 data are similar to those of Damas et al[30] who reported that serum IL-1 levels demonstrated no time-dependent or outcome-determining differences in patients with severe sepsis. However, serum levels of neither IL-1, IL-2, nor IFG were related to cause, severity, or outcome of shock. Since our assay detected low levels of these mediators in renal transplantation patients given OKT3[34], it seems unlikely that the assays were not accurate enough to detect elevations of these cytokines. Also, three patients were initially entered into the study because of clearly nonseptic etiologies, only to become septic within 24 h of a nonrelated event (aspiration pneumonia in two, and colonic perforation in one). None of these patients demonstrated any preseptic episode elevations in any of the measured cytokines. Finally, in 23 patients peak serum TNF levels occurred after entry into the study. In these patients no prior elevations in IL-1, IL-2, or IFG were observed. However, since such early elevations in the serum levels of these cytokines may be brief, it is possible that we missed the event.

As in other studies,[6,7,14,15,20,21,24,26,28-30,33] the range of TNF and/or IL-6 levels in our patients was great. Such interpatient and intrapatient variability reduced the statistical strength of most comparisons. The causes of this variability are unclear. Septic patients demonstrated a progressive decrease in serum TNF levels over time, independent of initial level. Like Hack et al,[26] who measured IL-6 levels in septic patients, we saw no correlation between serum TNF and IL-6 levels and cause of shock, infecting organism (septic patients only), coincident renal function, or age. Peak serum levels of TNF and IL-6 may reflect an interplay between affector cell receptivity and intensity of initial inflammatory stimulus. However, we saw no correlation between peak serum TNF levels and either severity or outcome of shock. Monocytes once stimulated to produce and release cytokines tend to be less responsive to subsequent stimulation. However, if this were the cause of the fall in TNF and IL-6 serum levels, owing to constant uptake by the tissues, then no differences in late (>6 h) serum cytokine levels should have been seen in any subgroup. The universal finding, however, of a persistently elevated serum TNF level after 12 h in patients who go on to have development of MSOF and die suggests that factors other than peak intensity of response, monocyte inhibition, and cytokine uptake by the periphery, determine survival. The persistence of elevated levels of TNF in the serum of patients who progress to MSOF suggests a relationship between processes that maintain elevated serum TNF levels and remote organ dysfunction in critically ill patients.

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