17 Cardiac and noncardiac shock (circulatory failure)
Overview/pathophysiology
A shock state exists when tissue perfusion decreases to the point of cellular metabolic dysfunction. Shock is classified according to the causative event.
Hypovolemic shock:
Occurs when volume in the intravascular space is inadequate and cannot meet the metabolic needs of tissues, as with severe hemorrhage or dehydration.
Cardiogenic shock:
Occurs when cardiac failure results in decreased tissue perfusion, as in severe myocardial infarction (MI) in which more than 40% of heart muscle has been affected.
Distributive shock conditions:
Characterized by displacement of a significant amount of vascular volume. The three types are neurogenic shock, anaphylactic shock, and septic shock.
Neurogenic shock:
Occurs when a neurologic event (e.g., spinal cord injury) causes loss of sympathetic tone, resulting in massive vasodilation and decreased perfusion pressures.
Anaphylactic shock:
Caused by a severe systemic response to an allergen (foreign protein), resulting in massive vasodilation, increased capillary permeability, decreased perfusion, decreased venous return, and subsequent decreased cardiac output.
Septic shock:
Occurs when bacterial toxins cause an overwhelming systemic infection.
Regardless of the cause, shock results in cellular hypoxia secondary to decreased perfusion and ultimately in cellular, tissue, and organ dysfunction. A prolonged shock state can result in death; therefore, early recognition and intervention are essential.
Health care setting
Critical care unit (e.g., cardiogenic shock in coronary care unit; distributive shock in medical intensive care unit [ICU])
Assessment
Early signs and symptoms:
Cool, pale, and clammy skin; decreased pulse strength; dry and pale mucous membranes; restlessness; hyperventilation; anxiety; nausea; thirst; weakness.
Physical assessment:
Rapid heart rate (HR); decreased systolic blood pressure (SBP) and increased diastolic blood pressure (DBP) secondary to catecholamine (sympathetic nervous system [SNS]) response.
Late signs and symptoms:
Decreased urinary output, hypothermia, drowsiness, diaphoresis, confusion, and lethargy, all of which can progress to a comatose state.
Diagnostic tests
Diagnosis is usually based on presenting symptoms and clinical signs.
Arterial blood gas (ABG) values:
May reveal metabolic acidosis or respiratory alkalosis (bicarbonate [HCO3−] less than 22 mEq/L and pH less than 7.40) caused by anaerobic metabolism.
Serial measurement of urinary output:
Less than 30 mL/hr (0.5 mL/kg/hr) indicates decreased perfusion and decreased renal function.
For anaphylactic shock
WBC count:
Will reveal increased eosinophils, a type of granulocyte that appears in the presence of allergic reaction.
Nursing diagnoses:
Risk for electrolyte imbalance
related to decreased circulating blood volume occurring with shock
Desired Outcome: Within 1-2 hr of treatment, patient has adequate perfusion as evidenced by peripheral pulse amplitude more than 2+ on a 0-4+ scale; brisk capillary refill (less than 2 sec); SBP greater than 90 mm Hg; Sao2 greater than 92%; mean arterial pressure (MAP) 70-100 mm Hg; CVP at least 5 cm H2O; HR regular and 100 bpm or less; no significant change in mental status; orientation to person, place, and time; and urine output at least 30 mL/hr (0.5 mL/kg/hr).
