Systemic inflammatory responses, coagulation/fibrinolytic system disorders and immune dysfunction are among the pathophysiological features common during sepsis (1). A previous study (1) has shown that the severity and prognosis of sepsis are closely associated with blood coagulation disorders or disseminated intravascular coagulation (DIC). Multiple organ dysfunction syndrome (MODS), which is a severe consequence of DIC, results in high mortality of septic patients. Early manifestation of DIC is not well diagnosed. The hypercoagulable state of early DIC has recently been named pre-DIC, characterized by a predisposing factor for DIC and fibrinolytic coagulation abnormalities, but with insufficient criteria for diagnosing DIC. Successful diagnosis of pre-DIC may prevent DIC, as underlying diseases and hematological abnormalities may be managed.

Three large-scale multi-center clinical trials were performed to investigate the efficacy of coagulation inhibitors as treatments for sepsis. In phase III clinical trials, recombinant human activated protein C (APC) was found to significantly reduce the 28-day mortality rate (2,3). Application of APC was strongly recommended by the Society of Critical Care Medicine (SCCM) for the treatment of severe septic patients, who had an acute physiology and chronic health evaluation (APACHE)-II score of >25 points (4). However, the cost of this treatment is >6,000 US dollars for each course, which makes it extremely expensive to apply for the majority of patients. Heparin, as an anticoagulant, which, not only inhibits the activation of the coagulation system, but is also an anti-inflammatory and immunomodulatory agent, has been widely used during DIC treatment and in the prevention and treatment of thrombotic diseases. It is easy to obtain and inexpensive. Several non-randomized clinical studies indicated that heparin partially inhibits sepsis by activating the coagulation system (5). However, there is a lack of randomized controlled prospective clinical studies. Therefore, the aim of present study was to investigate the effects of low-dose heparin treatment in patients with sepsis and pre-DIC to determine whether this treatment improves the coagulation status, MODS and/or the prognosis of patients.

Results of an epidemiological study in the USA found sepsis to have a high incidence of ~0.3%, which is on the increase at a rate of 1.5% annually (7). Financial issues are involved in the treatment of sepsis, with the annual cost being 17.4 billion US dollars. In addition, the mortality rate of sepsis is high, with findings of a previous study indicating that despite intensive care, mortality remains at 30–50% (8). More than half of the patients with sepsis present with coagulation factor abnormalities and the incidence of DIC is >20%. In cases of DIC incidence, the mortality rate is almost 63% (9). It has been confirmed that DIC leads to ischemic injury of vital organs (10) and eventually to MODS (11). Therefore, treating the coagulopathy state is necessary to improve multiple organ function, which may also be a promising approach for treating sepsis.

Sepsis involves the production of endotoxin by Gram-positive bacteria, a key mediator of the inflammatory response during septic shock. In the current study, 56% of the cases detected pathogens, 23% of which were gram-positive bacteria (Staphylococcus aureus being the most common).

Coagulation activation is an important feature in the pathogenesis of sepsis (9). Thrombin generation is a key step in an activated coagulation system. Due to the extremely short half-life of thrombin, it is difficult to determine activated thrombin levels in blood. Therefore, other molecular markers were used to confirm thrombin generation. In the present study, four molecular markers were selected to detect the early stages of coagulation. The markers are produced at various stages and appear earlier than PT, APTT and platelet abnormalities. In addition, the markers were selected to help diagnose the emergence of pre-DIC. These early indicators included F1+2, TAT, fibrinopeptide A and soluble fibrin monomer complex. F1+2 directly reflects the amount of generated thrombin, while the remaining three markers only partially reflect thrombin generation. Therefore, F1+2 is considered the most sensitive indicator of thrombin generation (12).

Heparin is a sulfated polysaccharide with a heterogeneous structure and complex polymerization (MW, 3–57 kDa). Heparin binds to AT-III, causing a conformational change that increases the flexibility of the reactive site loop, activating AT-III. The activated AT-III then inactivates thrombin and other proteases, including factor Xa. Heparin also binds platelets to induce platelet aggregation, resulting in a strong anticoagulant effect (13). In the present study, the subjects were in an early stage of DIC, during which blood is hypercoagulable, platelets are activated and activation of coagulation has already been initiated. In addition, during the pre-DIC period, there is no extensive micro-thrombosis, fibrinolysis, consumption or degradation of platelets and clotting factors. During low-dose heparin therapy, F1+2 showed a gradual increase, followed by a decrease over the first 24 h. At 72 h and 7 days, it was found to be present in significantly lower amounts (P<0.05). Similarly, TAT was initially increased, but subsequently decreased and eventually was reduced to only half the initial level at day 7, following initiation of low-dose heparin therapy (P<0.05). This was consistent with the observation that therapy led to the activation of coagulation (12). Heparin is not only involved with the coagulation factor Xa, but also collaborates with AT to inhibit thrombin. The heparin dose used to inhibit factor Xa was much lower than that required to inactivate thrombin, thus it is likely that the effectiveness of low-dose heparin is dependent on this mechanism to prevent thrombosis. Formation of thrombin is reduced by inhibiting factor Xa and F1+2, which explains the decrease in thrombin levels following a reduction in factor Xa. As a result, TAT decreases, which is consistent with the observations in the present study of decreased F1+2 and TAT levels.

AT-III is a member of the serine protease inhibitor family, which is the most important plasma inhibitor of the coagulation system. It is capable of inhibiting all serine proteases at a low speed, particularly factor Xa and thrombin. In the presence of heparin, inhibition speed increases significantly. AT is also known as a heparin cofactor. However, activity of AT is affected by the pH of the body, which means that loss of the inhibitor increases during acidosis. If acidosis is enhanced, AT activity significantly improves (14). During sepsis, elastase released from activated neutrophils inactivates AT. Clearance of TAT complexes, a process that occurs rapidly, results in the clearance of AT. Heparin may significantly increase AT activity. In the current study, following the administration of low doses of heparin to the patients, AT levels increased gradually. However, the patients were undergoing sepsis, which is usually associated with disturbances in oxygen supply and demand, an acid-base imbalance and high blood lactate (15). AT-III is therefore in a low state of activity. Moreover, with patients in a hypercoagulable state, when AT consumption and degradation are increased, AT-III recovery and improvement of oxygen metabolism are expected. This may be the reason for the recovery of AT-III not being observed following treatment.

PAI-1 is mainly synthesized by endothelial cells and secreted in the subendothelial space. It is the most important factor of a variety of PAIs and functions as an inhibitor of tissue plasminogen activator and urokinase. In the present study, PAI-1 levels of heparin-treated patients did not decrease significantly following heparin administration. This finding indicates that the concentration of plasma PAI-1 is important in the maintenance of patients with sepsis and DIC (16).

The current study has demonstrated that APACHE-II scores of the two treatment groups significantly decreased, while low-dose heparin intervention improved the scores more significantly. Low-dose heparin shortened the normal coagulation time by preventing clotting. Thus, heparin treatment not only improved blood circulation and oxygen supply, but also lowered the necessity of mechanical ventilation significantly (P=0.048). Altogether, this resulted in a shorter duration of stay at the hospital. Improvements in microcirculation not only blocked the development of DIC, but also decreased MODS.

A limitation of this study is the small number of patients enrolled in the present study. In addition, a few patients exited the study prematurely, not allowing time for follow-up. However, the study was conducted as a prospective clinical trial, which is uncommon and allows for several conclusions. No significant differences were observed between the two treatment groups, which confirms the results of an international clinical study aiming to determine the effects of low-dose heparin treatment during sepsis (17,18). The clinical results obtained indicate that shortening the stay in the ICU and decreasing the need for mechanical ventilation reduces the treatment costs of sepsis patients. In addition, the application of low-dose heparin is relatively inexpensive and safe, indicating the suitability for the early treatment of sepsis.