Septic Shock: Causes, Symptoms and Treatments

Second only to cardiogenic shock as the leading cause of shock death, septic shock (usually a result of bacterial infection) causes inadequate blood perfusion and circulatory collapse. It occurs most often among hospitalized patients, especially men over age 40 and women ages 25 to 45.

About 25% of patients who develop gram-negative bacteremia go into shock. Unless vigorous treatment begins promptly, preferably before symptoms fully develop, septic shock rapidly progresses to death (often within a few hours) in up to 80% of these patients.

Causes of Septic Shock:

In two-thirds of patients, septic shock results from infection with gram-negative bacteria: Escherichia coli, Klebsiella, Enterobacter, Proteus, Pseudomonas, and Bacteroides; in others, from gram­positive bacteria: Streptococcus pneumoniae, Streptococcus pyogenes, and Actinomyces. Infections with viruses, rickettsiae, chlamydiae, and protozoa may be complicated by shock.

These microbes produce septicemia in persons whose resistance is already compromised by an existing condition. Infection also results from translocation of bacteria from other areas of the body through surgery, I.V. therapy, and catheters.

Septic shock often occurs in patients hospitalized for primary infection of the genitourinary, biliary, GI, and gynecologic tracts. Other predisposing factors include immunodeficiency, advanced age, trauma, burns, diabetes mellitus, cirrhosis, and disseminated cancer.

Signs and symptoms of Septic Shock:

Indications of septic shock vary according to the stage of the shock, the microbe causing it, and the age of the patient.

1. Early stage: oliguria, sudden fever (over 101 F [38.3° C]), chills, nausea, vomiting, diarrhea, and prostration.

2. Late stage: restlessness, apprehension, irritability, thirst from decreased cerebral tissue perfusion, tachycardia, and tachypnea. Hypotension, altered level of consciousness, and hyperventilation may be the only signs among infants and elderly people.

Hypothermia and anuria are common late signs. Complications of septic shock include disseminated intravascular coagulation (DIC), renal failure, heart failure, GI ulcers, and abnormal hepatic function.

Diagnosis of Septic Shock:

Observation of one or more typical signs (fever, confusion, nausea, vomiting, hyperventilation) in a patient suspected of having an infection suggests septic shock and necessitates immediate treatment.

In the early stages, arterial blood gas (ABG) analysis indicates respiratory alkalosis (low partial pressure of carbon dioxide [PaC0 2 ], low or normal bicarbonate [HC0 3 -] level, and high pH). As shock progresses, metabolic acidosis develops, with hypoxemia indicated by decreasing Pco 2 (which may increase as respiratory failure ensues), as well as decreasing partial pressure of oxygen, HC0 3 -, and pH levels.

The following laboratory tests support the diagnosis and determine the treatment:

1. blood cultures to isolate the microbe

2. decreased platelet count and leukocytosis (15,000 to 30,000/ul)

3. increased blood urea nitrogen and creatinine levels and decreased creatinine clearance

4. abnormal prothrombin and partial thromboplastin time

5. simultaneous measurement of urine and plasma osmolalities for renal failure (urine osmolality below 400 milliosmoles, with a ratio of urine to plasma below 1.5)

6. decreased central venous pressure (CVP), pulmonary artery wedge pressure (PAWP), and cardiac output (in early septic shock, cardiac output increases)

7. electrocardiogram demonstrating ST­segment depression, inverted T waves, and arrhythmias resembling myocardial infarction.

Treatment of Septic Shock:

The first goal of treatment is to monitor and reverse shock through volume expansion. I.V. fluids are administered, and a pulmonary artery catheter is inserted to check pulmonary circulation and PAWP. Administration of whole blood or plasma can then raise the PAWP to a satisfactory level of 14 to 18 mm Hg. A ventilator may be necessary for proper ventilation to overcome hypoxia. A urinary catheter allows accurate measurement of hourly urine output.

Treatment also requires immediate administration of I.V. antibiotics to control the infection. Depending on the organism, the antibiotic combination usually includes an aminoglycoside, such as gentamicin or tobramycin for gram-negative bacteria, combined with a penicillin, such as piperacillin or ticarcillin.

Sometimes treatment includes a cephalosporin, such as cefazolin, and nafcillin for suspected staphylococcal infection instead of ticarcillin. Therapy may also include metronidazole for non sporulating anaerobes (Bacteroides), although it may cause bone marrow depression, and clindamycin, which may produce pseudomembranous enterocolitis.

Appropriate anti-infectives for other causes of septic shock depend on the suspected organism. Other measures to combat infections include surgery to drain and excise abscesses, and debridement.

If shock persists after fluid infusion, treatment with vasopressors, such as dopamine, maintains adequate blood perfusion in the brain, liver, GI tract, kidneys, and skin. Other treatment includes l.V. bicarbonate to correct acidosis and I.V. corticosteroids, which may improve blood perfusion and increase cardiac output.

Special considerations of Septic Shock:

1. Determine which of your patients are at high risk for developing septic shock. Know the signs of impending septic shock, but don't rely solely on technical aids to judge the patient's status. Consider any change in mental status and urine output as significant as a change in CVP.

2. Carefully maintain the pulmonary artery catheter. Check ABG values for adequate oxygenation or gas exchange, watching for any changes.

3. Keep accurate intake and output records. Maintain adequate urine output (0.5 to 1 ml/kg/hour) and systolic pressure. Be careful to avoid fluid overload.

4. Monitor serum gentamicin level, and administer drugs.

5. Watch closely for complications of septic shock: DIC (abnormal bleeding); renal failure (oliguria, increased specific gravity); heart failure (dyspnea, edema, tachycardia, distended neck veins); GI ulcers (hemalemesis, melena); and hepatic abnormalities (jaundice, hypoprothrombinemia, and hypoalbuminemia).