CirculationDiklit IRD RSSA Rev Edition Jan 2006

What is needed to maintain perfusion?PumpPipesFluid HeartBlood VesselsBlood

Flow = PerfusionAdequate Flow = Adequate PerfusionInadequate Flow = InAdequate Perfusion (Hypoperfusion)Hypoperfusion = Shock

How can perfusion fail?Pump FailurePipe FailureLoss of Volume

Pre load : ventricular volume at the end of distole ContractilityAfter load : left ventricular wall tension required to over come the impedance to the ejection of blood from ventricle during systole. Stroke volume : amount of blood secretes during systolic / secondCardiac Out Put : stroke volume x heart beat per minute

Afterload = determined by: - The total peripheral resistance (which is determined by the sympathetic tone, baroreceptor activity, the renin-angiotensin-aldosterone axis, and the tissue oncotic pressure), and - The systolic wall tension (which follows the: law of Laplace = TMP x r / 2 h [transmural pressure x radius / 2 x wall thickness]).

ContractilityThe Starling Concept equates preload with stroke volume.

Stroke volume = EDV-ESV

Ejection fraction = EDV ESV x 100% / EDV

Contractility Ventricular stroke volume (SV) is the difference between the ventricular end-diastolic volume (EDV) and the end-systolic volume (ESV).

EDV is about 120 ml of blood and the ESV about 50 ml of blood. The difference in these two volumes, 70 ml, represents the SV

Determining Factors

ContactilityIncreased by inotropic agents: Adrenaline / Nor adrenaline Dobutamine / Dopamine CalciumDecreased by: Acidosis Hypoxia Hypocalcaemia

Arterial Pulse Pressure The maximal change in aortic pressure during systole (from the time the aortic valve opens until the peak aortic pressure is attained represents the aortic pulse pressure

Pulse Pressure = Systolic Pressure Diastolic Pressure

Pulse Pressurevalue is determined by the compliance of the aorta as well as the ventricular stroke volume. If the aorta were a rigid tube, the pulse pressure would be very high.

The more compliant the aorta, the smaller the pressure change during ventricular ejection (i.e., smaller pulse pressure)

Therefore, aortic compliance is a major determinant, along with stroke volume, of the pulse pressure

Mean Arterial PressureDetermined by the cardiac output (CO), systemic vascular resistance (SVR), and central venous pressure (CVP)

is based upon the relationship between flow, pressure and resistance

flow, pressure and resistance

MAP = (CO SVR) + CVP

MAP = CO SVR

Signs of Pumping Failure Gallops rhythmBasilar ronchiJugular venous distensionDecreasing M A P

How to treat Circulatory Failure. Fluids Inotropes Vasoconstrictors Vasodilators

QUESTION ?

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