Cardiac Output

CARDIAC OUTPUT

Definition: Volume of blood pumped by the heart per min

CO = SV x HR

Norm ~ 5 l/min

Cardiac index – correcte d for body surface area

Affected by :

Met. Rate – pregn ancy, hyperthyroid, septic

Preload / contractility / afterload

Clinical indicators of CO imp recise

Affected by anaesthetic agents used in everyday practice

Provides estimate of:

·            whole body perfusion

·            oxygen deli very 

·              left ventricular function Persistently low CO associated with poor outcome

Methods: Fick method

Dilution techniques – dye / thermal / lithium

Pulse contour analysis- LiDCO & PiCCO

Oesophageal doppler

TOE

Transthoracic impedance plethysmography

Inert gas through flow

Non-invasive cardiac output measurement

Fick Principle: Measure volume displacement 1st proposed 1870 ―the total uptake or release of a substance by an organ is the product of the blood flow through that organ and the arteriovenous concentration difference of the substance. Limited by cumbersome equipment, sampling errors need for invasive monitoring and steady-state haemodynamic and metabolic conditions

Indicator dilution techniques

An indicator mixed into a unit volume of constantly flowing blood can be used to identify that volume of blood in time, provided the indicator remains in the system between injection and measurement and mixes completely in the blood.

Dye dilution

·        Inert dye – indocyanin green

·   Injected into pulmonary artery and arterial conc. measured using a calibrated cuvette densitometer 

·        Plot indicator dilution curve (see diagram) CO derived from area under curve.

Indicator Dilution Curve

Cardiac Output Measurement