Drugs in Shock

Introduction — shock and its classification

• Shock — a clinical syndrome of inadequate tissue perfusion — an immediately life-threatening impairment of O₂ and nutrient delivery to organs — usually accompanied by hypotension, altered mental state, oliguria and metabolic acidosis; untreated it becomes refractory and fatal.
• A medical emergency — urgent measures are directed to restoring and maintaining blood pressure and perfusion of vital organs (brain, heart, kidney).
• Classification by mechanism — Hypovolaemic (haemorrhage, burns, severe vomiting/diarrhoea); Cardiogenic (pump failure — MI, arrhythmia); Obstructive (pulmonary embolism, tamponade, aortic dissection); Distributive (peripheral circulatory dysfunction — septic, anaphylactic, neurogenic). Katzung frames the three major vasopressor-decision forms as septic, cardiogenic and hypovolaemic.
• Compensatory physiology — the fall in BP drives sympathetic activation → peripheral vasoconstriction + ↑ rate and force of cardiac contraction; early on this may preserve BP and cerebral flow, but renal/skin/splanchnic flow falls → impaired urine output and metabolic acidosis.