Inotropes in Cardiac Surgery

Basics

Cardiac Cycle

• Phase 1 - Atrial Contraction

• Phase 2 - Isovolumetric Contraction

• Phase 3 - Rapid Ejection

• Phase 4 - Reduced Ejection

• Phase 5 - Isovolumetric Relaxation

• Phase 6 - Rapid Filling

• Phase 7 - Reduced Filling

Sympathetic / Parasympathetic  Sympathetic Parasympathetic

Heart    

Chronotropy (rate) + + + _ _ _

Inotropy (contractility) + + +   _

Dromotropy (conduction velocity)

+ + _ _ _

Vessels (Vasoconstriction)

   

Resistance (vasoconstriction)

+ + +   0

Capacitance (venous volume)

+ + + 0

Starlings Law

BEFORE INOTROPES

• Fluid – Bolus– Legs up

• Rhythm– ECG, SR, slow, fast, paced on ventricle, ST’s, ectopics

• Tamponade– CVP, BE, UO, temp, CXR, echo

• Bleeding– Drains, CXR, Hb

• Pneumothorax– CXR, examine, vent alarms

• Fight Ventilator– Paralyse, sedate or extubate

Which Inotrope

• Ohms Law

• V=I x R

• BP=CO x SVR

• Simple terms• Low or high cardiac output, what is the PA

pressure

Inotropes• Atropine• Ca2+

• Dopamine• Dopexamine• Dobutamine• Adrenaline• Noradrenaline• Isoprenaline• Enoximone• Aminophylline• Vasopressin• Methylene blue• NO

Receptors

Atropine

• Antimuscurinic ie causes tachycardia

• Some pateints have muscurinic receptors on ventricle as well ie inotropic

• Increases HR

• CO=SV x HR

Ca2+

• Inotrope and vasoconstrictor

• Short acting

• Beware radial artery patients

• Warn patient if awake

Dopamine

• Acts on dopamine receptors on heart and kidney

• Causes a tachycardia (CO=SV x HR)

• Increases urine output in some patients

• Less metabolic side effects compared with adrenaline

• Beware patients with tachycardia (give k+, Mg2+)

Dopexamine

• Tachycardia

• Increase splanchnic and renal blood flow

• VASODILATOR

• Beware

• Vasodilated patients

Dobutamine

• Like dopamine• Has less effect on

pulmonary artery pressure good for mitral valve patients

Adrenaline

• Excellent inotrope but dirty

• Increased heart rate and inotropy (ß1-adrenoceptor mediated)

• Vasoconstriction in most systemic arteries and veins (postjunctional a 1 and a 2 adrenoceptors)

• Vasodilation in muscle and liver vasculatures at low concentrations (b2-adrenoceptor); vasoconstriction at high concentrations (a1-adrenoceptor mediated)

Adrenaline

Noradrenaline

• Vasoconstrictor

• Increased heart rate and increased inotropy (ß1-adrenoceptor mediated)

• Vasoconstriction occurs in most systemic arteries and veins (postjunctional a 1 and a 2 adrenoceptors)

• Ask can I wake patient up to avoid Norad

• Must have a good cardiac output

Noradrenaline

Isoprenaline

• Causes tachycardia and vasodilatation

• Good in patients with high PA pressures

• Beware vasodilated patients

Enoximone

Phosphodiesterase Inhibitor

Good in patients with high PA pressure

“2nd line when adrenaline having no effect “receptor dissociation”

Aminophylline

• Phosphodiesterase inhibitor

• Main effect on lung compared to heart

• Good in patients who have hypoxic vasoconstriction “short fat little smoker with poor urine output”

Vassopresin

• 2nd line vasoconstrictor

• Most powerful available

• Associated with organ ischaemia

Methylene blue

• Whatever the mechanism the final step of vasodilatation is NO

• Methylene blue inhibits NO synthesis

Nitric Oxide

What else

• IABP

• LVAD

• RVAD

• BVAD