4.2. Measurements
            4.2.6. Blood flow measurement
4.2.6.1. Cardic output measurement

Total cardiac output

Methods

A. Flowmeters

B. Fick principle

C. Imaging techniques

D. From arterial pressure

Direct Fick method

Based on Fick principle

i.e. Blood flow
= uptake / a-V concentration difference

Will require:

Therefore,

Cardiac output
= O2 consumption / CaO2-CvO2
= 250(mL/min) / [200 (mLO2/L) -150 (mLO2/L)]
= 250/50
= 5 Lmin

Thermodilution method

Application of Stewart-Hamilton indicator dilution technique
* (modification of Fick principle)

Method

A double-lumen pulmonary artery catheter put in through peripheral vein

--> Advance the tip into the pulmonary artery

At this position,

The cathether opening would be a few inches proximal to the tip, in the right atrium.

Then,

Cold saline of known volume injected

--> Cold saline mixes with blood and temperature change is detected downstream by the thermistor at the catheter tip.

Calculation when dye is used

Quantity of dye used (n)
= mean concentration (c) x Q (t1-t2)

i.e. n = cQ(t1-t2)

Also, mean concentration
= area under curve/t2-t1

Therefore,

Q = n / area under curve

Need to correct for

Advantage

Disadvantage



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