What is severe sepsis and septic shock ?

Severe sepsis refers to sepsis-induced tissue hypoperfusion or organ dysfunction with any of the following thought to be due to the infection.

• Sepsis-induced hypotension
• Serum Lactate levels above upper limits of laboratory normal
• Urine output < 0.5 mL/kg/hr for more than two hours inspite of adequate fluid resuscitation
• Acute lung injury with PaO 2 /FIO 2 < 250 in the absence of pneumonia as infection source
• Acute lung injury with PaO 2 /FIO 2 < 200 in the presence of pneumonia as infection source
• Creatinine > 2 mg/dL 
• Bilirubin > 2 mg/dL 
• Platelet count < 100,000 microL –1
• Coagulopathy (INR > 1.5)

Sepsis-induced hypotension is defined as a systolic blood pressure (SBP) < 90 mmHg or mean arterial pressure (MAP) < 70 mmHg or a SBP decrease > 40 mmHg or less than two standard deviations below normal for age in the absence of other causes of hypotension.

Components of Sepsis-induced tissue hypoperfusion are

1. Infection-induced hypotension
2. Elevated lactate
3. Oliguria.  

Septic shock - Septic shock is defined as sepsis-induced hypotension persisting despite adequate fluid resuscitation, which may be defined as infusion of 30 mL/kg of crystalloids Septic shock is due to marked reduction in systemic vascular resistance, this is often associated with an increase in cardiac output.

Major complications of sepsis(Cardiopulmonary,Renal,Coagulation,Neurologic)

Sepsis is usually associated with multiple target organ dysfunction.Major complications are seen in cardiac, respiratory, renal, neurological and coagulation system.

1) Cardiopulmonary complication in sepsis

Ventilation perfusion mismatch (V/Q – mismatch) produces a fall in arterial PO2 early in the course of illness.Progressive diffuse pulmonary infiltrates and arterial hypoxemia (PaO2/FIO2, <200) are  early indicators of the development of the acute respiratory distress syndrome (ARDS). 

ARDS develops in ~50% of patients with diagnosed with severe sepsis or septic shock.

Depression of myocardial function is common in sepsis

This is manifested as increased end-diastolic and systolic ventricular volumes with a decreased ejection fraction.Myocardial suppression develops within 24 hours in most patients admitted with severe sepsis.

2) Renal complications

ATN, acute cortical necrosis, interstitial, nephritis, or drug induced damage are the major renal complications in sepsis.Most cases renal failure is occur secondary to acute tubular necrosis (ATN) induced due to hypotension or capillary injury. Drug-induced renal damage may also complicate therapy, especially when hypotensive patients are treated with aminoglycoside antibiotics.Oliguria, azotemia, proteinuria, and nonspecific urinary casts are frequently found.

3) Coagulation abnormality

Thrombocytopenia is seen in 10–30% of patients, the underlying mechanisms are not clear.In patients with DIC the platelet counts are usually very low (<50,000/L) ,this low counts may be secondary to diffuse endothelial injury or due to microvascular thrombosis.

4 ) Neurologic complications  

Critical illness polyneuropathy is the most common neurologic complications.This is commonly seen when the septic illness lasts for weeks or months, problem due to "critical-illness" polyneuropathy is that it may prevent weaning from ventilatory support and patients experience distal motor weakness.Electrophysiologic studies are helpful to rule out other conditions such as GBS , metabolic disturbances, and toxin activity .