Etiology and Risk Groups
Inflammation by its very nature is always a systemic response of the body to a damaging (phlogistic) agent, but it is in SIRS that this principle is manifested to the maximum extent. The syndrome rarely occurs in isolation; most often it becomes a complication of severe pathological conditions.
High-risk groups include patients with the following diagnoses:
- Sepsis.
- Generalized peritonitis.
- Intestinal obstruction.
- Renal or hepatic failure.
- States following post-ischemic organ reperfusion or large tissue masses.
Pathogenesis and Mechanisms of Intoxication
SIRS is based on acute and severe endotoxemia. The initiating link in pathogenesis is the failure of natural detoxification systems (liver, kidneys, lungs, skin, gastrointestinal tract) and the immune-biological surveillance system (IBS). An additional source of intoxication is toxic substances from the gastrointestinal tract (skatoles, indoles, phenols), which massively enter the bloodstream due to increased permeability of the intestinal wall.
Biologically active substances (BAS) rapidly accumulate in the body's fluids. By origin, they are divided into four groups:
- Inflammatory mediators: cytokines, biogenic amines, lipoperoxides, prostaglandins, leukotrienes, acute-phase proteins, and enzymes.
- Products of normal metabolism: urea, creatinine, bilirubin glucuronide. They accumulate due to impaired excretion against the background of renal and hepatic failure.
- Products of impaired metabolism: ammonia (in liver failure) or ketone bodies (in concomitant diabetes mellitus).
- Products of tissue destruction: compounds formed during cell breakdown directly at the primary site of inflammation.
An excess of these substances impacts microcirculation, provokes DIC syndrome (disseminated intravascular coagulation with widespread microthrombosis), and leads to multiple organ dysfunction syndrome (MODS). In addition, many BAS possess antigenic activity, causing allergic reactions, immunodeficiencies, pathological tolerance, and autoimmune aggression reactions.
Stages of SIRS Development
The generalization process of inflammation proceeds in three sequential stages:
- Stage of compensation (adaptation). The body tries to cope with the avalanche of toxins from the inflammation focus by maximally activating detoxification systems. Simultaneously, CARS (Compensatory Anti-inflammatory Response Syndrome) is initiated.
- Stage of generalization. The body's reserves are depleted, and adaptation mechanisms work at their limit.
- Stage of decompensation (deadaptation). Cleansing mechanisms finally fail. Multiple organ dysfunction rapidly progresses. While failure of 1–2 organs is still amenable to medical correction, the failure of three vital organs turns the condition into a critical one requiring specialized organ-replacement procedures.
Diagnostic Criteria
A diagnosis of SIRS is valid if a patient exhibits at least two of the four clinical and laboratory signs:
- Body temperature: fever above 38 °C or hypothermia below 36 °C (the latter is characteristic of the decompensation stage).
- Tachycardia: heart rate exceeds 90 beats per minute.
- Tachypnea: respiratory rate greater than 20 breaths per minute, accompanied by hypocapnia (decrease in PaCO₂ below 32 mmHg).
- Changes in the complete blood count (leukogram): marked leukocytosis (> 12×10⁹/L), leukopenia (< 4×10⁹/L in the decompensation stage), or a left shift (the proportion of band neutrophils exceeds 10%).
Principles of Treatment
Therapy for systemic inflammatory response is based on three fundamental principles:
- Etiotropic principle: aims to eliminate or reduce the strength of the phlogistic factor. A classic example is the use of antibiotics or sulfonamides to destroy infectious agents.
- Pathogenetic principle: the goal is to disrupt key links in the inflammatory mechanism. Action is directed at blocking the processes of alteration (damage) and exudation (for example, using antihistamines). Simultaneously, general and local adaptation mechanisms are stimulated: compensation, regeneration, protection, and tissue restoration.
- Symptomatic therapy: necessary to prevent or eliminate distressing symptoms that worsen the patient's condition. Painkillers, tranquilizers, anti-stress drugs, and agents helping to normalize physiological systems are used.