Hemodynamics & Pressors – Study Notes

Key Equations

• MAP equation:
  MAP = CO × SVR

• CO equation:
  CO = HR × Stroke Volume

Receptor Physiology

α-1 Receptors

• SVR: Increases

• Location: Arteriolar walls

• Effect: Vasoconstriction

• Presence in heart: Yes

β-1 Receptors

• HR: Increases

• Contractility: Increases

• CO: Increases

β-2 Receptors

• Vasodilation

• Smooth muscle relaxation

Dopaminergic Receptors

• CO: Increased

• Contractility: Increased

Dobutamine

• Receptors: β-1, β-2

• Dose: 2.5–40 mcg/kg/min

• Half-life: 2 min

• Effects:

  • Positive inotrope (↑ contractility)

  • ↑ HR

  • ↑ CO

  • Vasodilator

  • ↓ Afterload / SVR

• Brand name: Dobutrex

Milrinone

• Class: PDE-III inhibitor

• Effects:

  • Positive inotrope

  • Reduced afterload

  • Improved diastolic dysfunction

• Loading dose: 50 mcg/kg over 10 min

• Continuous infusion: 0.2–0.75 mcg/kg/min

• Half-life: 150 min

Dopamine

• Receptors/vascular sites: Renal, splanchnic, coronary, cerebral

• Dose: 5–20 mcg/kg/min

• Half-life: 2 min

• Brand name: None (just dopamine)

Norepinephrine

• Receptors: β-1, α-1

• Dose: 0.05–0.5 mcg/kg/min

• Half-life: 2–7 min

• Effects:

  • ↑ CO

  • Vesoconstriction

  • Arteriolar constriction

  • Less impairment of renal & splanchnic perfusion

• Brand name: Levophed

Vasopressin

• Dose: 0.01–0.04 units/min

• Half-life: 10–20 min

• Effects:

  • ↑ Vascular resistance

  • ↑ Vasoconstriction

  • ↑ BP

  • ↑ UOP

• Brand name: Pitressin

Key Trials

• Tsuneyoshi et al., 2001: Vasopressin + catecholamine ↑ MAP, SVR, UOP

• Dünser et al., 2003: NE + AVP more effective than NE alone, but ↑ new-onset tachyarrhythmias (8% vs 54%)

• VASST, 2008:

  • NE vs NE + AVP in septic shock

  • No reduction in 28-day mortality overall

  • Trend towards benefit in “less severe” septic shock

    • NE + AVP: 27% mortality

    • NE alone: 36% mortality (p=0.05)

Phenylephrine

• Receptor: α-1

• Dose: 0.5–9.1 mcg/kg/min

• Half-life: 2–3 hours

• Effects:

  • ↑ MAP

  • ↓ HR

  • ↓ Renal + splanchnic perfusion

  • ↓ CO

• Tachyarrhythmias: Least among pressors

• Brand name: Neosynephrine

Epinephrine

• Receptors: β-1, β-2, α-1

• Dose: 0.05–0.5 mcg/kg/min

• Half-life: 2 min

• Effects:

  • ↑ CO

  • ↓ SVR

  • Splanchnic vasoconstriction

• Brand name: Epinephrine (none specific)

Landmark Trial

• SOAP II (2010): Compared dopamine vs norepinephrine as first-line pressors in shock.

  • Overall 28-day mortality: no difference

  • Dopamine: more arrhythmias, worse outcomes in cardiogenic shock