Haemodynamic drugs

Catecholamines

• Drugs that promote blood flow and BP, by stimulating adrenergic receptors
• Used to improve cardiac output, especially in sepsis or trauma
• No individual drug has been shown to be superior to the others for clinical outcomes

• Dobutamine
  • 'Inodilator': improves cardiac contractility as well as reducing systemic and pulmonary vascular resistance, so doesn't change the BP much overall
  • Minimal change in heart rate
  • Improves coronary flow and myocardial perfusion, but at the expense of an increase in myocardial oxygen consumption - sometimes worsening the picture
  • Best use for myocardial depression in septic shock, in conjunction with a vasoconstrictor to raise the BP
  • Sometimes used augment cardiac output in decompensated heart failure, but not so much any more
• Dopamine
  • Precursor for noradrenaline
  • Activates alpha and beta receptors at different doses
  • Renal, mesenteric, coronary and cerebral vasodilation
  • Low dose - particularly evident renal artery vasodilation
  • High dose - activates alpha receptors, acting as vasopressor
  • Not used as much any more, but sometimes used in cardiogenic shock or septic shock
  • Also may be useful in intestinal ischaemia at low doses
• Adrenaline
  • Most potent natural beta-agonist
  • Stimulates both alpha and beta receptors, increasing heart rate, stroke volume and BP
  • Resuscitation of cardiac arrest, anaphylactic shock
• Noradrenaline
  • Noradrenaline = meteraminol = aramine
  • Both alpha and beta. Potent activity as a vasopressor.
  • Vasoconstrictive effects = increased MAP, minimal change in HR
  • Used for profound hypotension with adequate volume
    • Septic shock - just because it has fewer adverse effects than other catecholamines
    • Severe neurologic events
  • If max noradrenaline can't reach MAP of 65, dopamine or vasopressin will be added, but there is no evidence that that improves outcomes

Vasodilators

• Reduces both preload and afterload - reduces metabolic demands of myocardium
• Useful with poorly controlled HTN immediately post-op
• Nitroprusside
  • Effective vasodilator on artery and veins
  • Rapid onset and offset
  • 0.5microg/kg/min then titrate up
  • Favoured in hypertensive emergencies
  • Risk of cyanide intoxication
• Nitroglycerin
  • Predominately venodilation, but also arteries
  • Dilates coronary arteries - preferable in CAD
  • Used to augment cardiac output in decompensated heart failure and to relieve chest pain in patients with stable angina

Adjuncts

• Septic/neurogenic shock whose blood pressure fails to respond to volume resus
• Useful in maintenance of BP that has been lowered by GA or regional anaesthetic
• Vasopressin
  • "ADH" - antidiuretic hormone
  • Produces vasoconstriction by actions on vascular smooth muscle
  • Often added to noradrenaline in severe septic shock - no survival benefit
  • Promotes splanchnic vasoconstriction in variceal bleeding
• Phenylephrine
  • Pure alpha agonist
  • Useful in maintaining BP in patients with epidurals, but somewhat questionable in this circumstance
  • Bradycardia, low cardiac output, renal hypoperfusion