Emergency Medicine · Sepsis and Shock
The facts most likely to be tested
SIRS is defined by the presence of at least two of four criteria: temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >20 bpm or PaCO2 <32 mmHg, and white blood cell count >12,000/mm³ or <4,000/mm³.
SIRS is a non-specific clinical response that can be triggered by both infectious (sepsis) and non-infectious (pancreatitis, burns, trauma) insults.
Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, now clinically identified by a qSOFA score of 2 or more.
The qSOFA score utilizes three clinical variables: respiratory rate ≥22/min, altered mentation, and systolic blood pressure ≤100 mmHg.
Septic shock is a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are profound enough to substantially increase mortality, requiring vasopressors to maintain a mean arterial pressure (MAP) ≥65 mmHg despite adequate fluid resuscitation.
Lactate levels >2 mmol/L in the setting of suspected infection are a critical marker of tissue hypoperfusion and correlate with increased mortality risk.
Initial management of patients meeting SIRS criteria with suspected infection requires early goal-directed therapy, including broad-spectrum antibiotics and 30 mL/kg intravenous crystalloid fluid bolus.
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A 54-year-old male is brought to the emergency department after a motor vehicle accident. He is found to have a heart rate of 105 bpm, a respiratory rate of 24 breaths/min, and a temperature of 38.5°C. His white blood cell count is 14,000/mm³ with a left shift. He has no evidence of infection on physical exam or imaging. His blood pressure is 110/70 mmHg and he is alert and oriented.
Which of the following is the most accurate classification for this patient's clinical presentation?
Systemic Inflammatory Response Syndrome (SIRS)
The patient meets three of the four SIRS criteria (tachycardia, tachypnea, and hyperthermia/leukocytosis) in the absence of an infectious source, confirming a non-infectious SIRS response to trauma.
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Etiology / Epidemiology
SIRS is a non-specific inflammatory response to infection, trauma, burns, or pancreatitis. It represents a systemic dysregulation of the host immune response.
Clinical Manifestations
Defined by meeting ≥2 of 4 criteria: Tachycardia, Tachypnea, Temp >38°C or <36°C, and WBC >12k or <4k.
Diagnosis
Clinical diagnosis based on SIRS criteria. Blood cultures and lactate are mandatory to rule out sepsis.
Treatment
Identify and treat the underlying trigger. IV fluid resuscitation is the first-line intervention for hemodynamic stability.
Prognosis
Progression to septic shock carries a >40% mortality rate. Early recognition is the primary determinant of survival.
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Epidemiology & Etiology
SIRS is triggered by both infectious (sepsis) and non-infectious insults. Common non-infectious triggers include acute pancreatitis, major trauma, and extensive burns. It is a common clinical state in the ICU setting requiring rapid differentiation between infectious and sterile inflammation.
Pertinent Anatomy
Systemic involvement affects the cardiovascular system (vasodilation), respiratory system (alveolar-capillary leak), and renal system (hypoperfusion). These anatomical shifts drive the clinical presentation of shock and organ failure.
Pathophysiology
The process begins with a massive release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6). This leads to widespread endothelial dysfunction, increased vascular permeability, and a pro-coagulant state. If unchecked, this results in capillary leak, tissue hypoxia, and eventual multi-organ dysfunction syndrome (MODS).
Clinical Manifestations
Patients present with tachycardia (>90 bpm), tachypnea (>20 bpm or PaCO2 <32 mmHg), and temperature extremes. Altered mental status is a critical red flag indicating end-organ hypoperfusion. Look for leukocytosis or leukopenia on the CBC as a hallmark of systemic immune activation.
Diagnosis
Diagnosis is strictly clinical using the SIRS criteria. Serum lactate is the gold standard for assessing tissue perfusion and prognosis. Blood cultures must be obtained prior to antibiotic administration to distinguish SIRS from sepsis.
Treatment
Management focuses on the underlying insult. IV crystalloids (e.g., 30mL/kg) are the first-line therapy for hypotension. Avoid vasopressors until adequate fluid resuscitation is achieved. If infection is suspected, initiate broad-spectrum antibiotics within one hour.
Prognosis
The primary complication is septic shock and MODS. Patients require continuous monitoring of urine output and mean arterial pressure (MAP) to prevent irreversible organ damage.
Differential Diagnosis
Sepsis: SIRS criteria plus a confirmed or suspected source of infection
Anaphylaxis: SIRS criteria plus urticaria, angioedema, or respiratory distress
Adrenal Crisis: SIRS criteria plus refractory hypotension despite fluids
Thyroid Storm: SIRS criteria plus hyperpyrexia and altered mental status
Pulmonary Embolism: SIRS criteria plus hypoxia and clear lung fields