Systemic inflammatory response syndrome

Overview

Systemic Inflammatory Response Syndrome (SIRS) is a clinical condition characterized by a widespread inflammatory response throughout the body. It can be triggered by a variety of insults, including infection, trauma, burns, pancreatitis, or other inflammatory states. SIRS represents a systemic activation of the immune system that can lead to organ dysfunction and, if severe and untreated, progress to sepsis, septic shock, or multiple organ failure.

Recognizing and managing SIRS early is crucial to prevent serious complications and improve patient outcomes.

Causes

SIRS can be caused by both infectious and non-infectious factors:

• Infectious causes: Bacterial, viral, fungal, or parasitic infections leading to sepsis.

• Non-infectious causes: Major trauma, burns, pancreatitis, ischemia-reperfusion injury, surgery, and autoimmune diseases.

• Other triggers: Transfusion reactions, drug reactions, and malignancies.

Symptoms

The clinical features of SIRS reflect the systemic inflammatory response and may include:

• Fever or hypothermia (body temperature >38°C or <36°C)

• Tachycardia (heart rate >90 beats per minute)

• Tachypnea (respiratory rate >20 breaths per minute) or arterial carbon dioxide tension (PaCO₂) <32 mm Hg

• Abnormal white blood cell count (leukocytosis >12,000/mm³, leukopenia <4,000/mm³, or >10% immature neutrophils)

• Signs of organ dysfunction such as altered mental status, decreased urine output, or hypotension in severe cases

Diagnosis

Diagnosis of SIRS is clinical and based on the presence of at least two of the following criteria:

• Body temperature >38°C or <36°C

• Heart rate >90 beats per minute

• Respiratory rate >20 breaths per minute or PaCO₂ <32 mm Hg

• White blood cell count >12,000/mm³, <4,000/mm³, or >10% immature forms (bands)

Additional laboratory and imaging tests are used to identify underlying causes and assess organ function:

• Blood cultures and microbiological studies to detect infection

• Complete blood count, renal and liver function tests

• Arterial blood gases

• Imaging studies such as chest X-ray or ultrasound

Treatment

Treatment of SIRS involves addressing the underlying cause and supportive care to manage the systemic inflammatory response:

• Infection control: Prompt administration of appropriate antibiotics or antiviral therapy if infection is suspected or confirmed.

• Supportive care: Fluid resuscitation, oxygen therapy, and hemodynamic support.

• Organ support: Mechanical ventilation, renal replacement therapy, or vasopressors in cases of organ failure.

• Anti-inflammatory therapy: Use of corticosteroids or other immunomodulatory agents may be considered in selected cases.

• Monitoring: Continuous evaluation of vital signs, laboratory markers, and organ function.

Prognosis

The prognosis of SIRS varies depending on the severity, underlying cause, and timeliness of treatment. Mild cases resolve with supportive care and treatment of the precipitating factor.

However, if SIRS progresses to sepsis or septic shock, mortality rates increase significantly. Early recognition, aggressive management, and multidisciplinary care improve survival and reduce complications.