Drugs in Shock

Drugs in Shock

1. Definition & overview of shock

• Shock is a clinical syndrome of inadequate tissue perfusion — an immediately life-threatening impairment of delivery of O₂ and nutrients to the organs — usually associated with hypotension and ultimately failure of organ systems (G&G 14e Ch.14, p.266).
• Clinically, shock is usually accompanied by hypotension, an altered mental state, oliguria, and metabolic acidosis; if untreated it progresses to a refractory, deteriorating state and death (Katzung 16e Ch.9, p.156).
• It is a medical emergency: urgent measures are directed to restoring and maintaining blood pressure and perfusion of vital organs (KDT 8e Ch.9, p.150).
• Causes / classification by mechanism (G&G 14e Ch.14, p.266; KDT 8e Ch.9, p.150):
  • Hypovolaemic — haemorrhage; volume depletion (severe diarrhoea, vomiting, burns) (KDT 8e Ch.9, p.150).
  • Cardiogenic — cardiac (pump) failure, e.g. myocardial infarction, arrhythmias (G&G 14e Ch.14, p.266; KDT 8e Ch.9, p.150).
  • Obstructive — obstruction to cardiac output due to pulmonary embolism, pericardial tamponade, or aortic dissection (G&G 14e Ch.14, p.266).
  • Distributive (peripheral circulatory dysfunction) — sepsis or anaphylaxis; KDT additionally lists neurogenic shock (trauma, drug overdose) within this peripheral-vasodilatory group (G&G 14e Ch.14, p.266; KDT 8e Ch.9, p.150).
• Katzung names the three major forms for the vasopressor-decision framework as septic, cardiogenic, and hypovolaemic (Katzung 16e Ch.9, p.156).
• Compensatory physiology: the fall in blood pressure produces marked activation of the sympathetic nervous system → peripheral vasoconstriction + increased rate and force of cardiac contraction. In early shock these mechanisms may maintain BP and cerebral blood flow, but blood flow to kidneys, skin, and other organs falls, causing impaired urine production and metabolic acidosis (G&G 14e Ch.14, p.266).