Cardiac output can be measured using invasive and non-invasive methods. Invasive methods include the Fick method, dye dilution, and thermodilution, which require a pulmonary artery catheter. Non-invasive methods include echocardiography, which uses ultrasound to visualize cardiac structures and Doppler to measure blood flow velocities, and pulse pressure analysis. Measurement of cardiac output is important for critically ill patients to optimize oxygen delivery and support circulation.

1. MEASUREMENT OF
CARDIAC OUTPUT
PRESENTOR-
Dr. K. AMUDHA LAKSHMI M.B.B.S.,D.O.,M.D

2. INTRODUCTION
HISTORY
METHODS OF MEASURING CARDIAC
OUTPUT
INVASIVE METHODS
NON INVASIVE METHODS
SUMMARY
REFERENCES

3. INTRODUCTION
• Cardiac output is the volume of blood pumped
into the aorta each minute by the ventricle
• It is the determinant of global oxygen transport
to the body
• It reflects the efficiency of cardiovascular
system

4. HISTORY
ADOLPH EUGEN
FICK(1829-1901)
1855 – Introduced Fick’s
law of diffusion
1870- was the first one to
develop a technique for
measuring cardiac output
i.e Direct Fick method.

5. DYE DILUTION METHOD
• Introduced by G.N.STEWART
in 1897
• Extended by W.F.HAMILTON
in 1932
G.N.STEWART

6. INGE EDLER -FATHER OF ECHOCARDIOGRAPHY
CARL HELMUTH HERTZ discovered
echocardiography in 1950
INGE EDLER CARL HELMUTH HERTZ

7. CHRISTIAN DOPPLER, an astronomer in 19th
century discovered the principles of Doppler

8. CARDIAC OUTPUT MEASUREMENT
AIM:
Hemodynamic monitoring
In Critically ill patients, to optimize oxygen
delivery to the tissues
Oxygen delivery is determined by cardiac
output
Assess the blood flow to the tissues & helps to
support a failing circulation

9. WHY SHOULD WE MEASURE?
In many critically ill patients ,low cardiac
output leads to significant morbidity &
mortality.
The clinical assessment of cardiac output is
unreliable / inaccurate

10. WHEN SHOULD WE MONITOR?
High risk critically ill surgical patients - large
fluid shifts, bleeding & hemodynamic
instability expected
Goal directed therapy (GDT) i.e To set
therapeutic endpoints thereby improving
patient care & outcome

11. FEATURES OF IDEAL CARDIAC OUTPUT
MONITOR
Safe & accurate
Quick & easy
Operator independent i.e the skill of the
operator doesn’t affect the information
collected
Provide continuous measurement
Reliable during various physiological states

12. METHODS OF MEASURING CARDIAC
OUTPUT
INVASIVE
Fick’s method
Dye Diltuion method
Thermodilution
Cineradiographic
technique
X ray method
NON – INVASIVE
Endotracheal cardiac output
monitor (ECOM)
TTE/Trans thoracic
echocardiography
TEE/Trans esophageal
echocardiography- Doppler
Pulse pressure method
Method employing inhalation
of Inert gases

13. FACTORS AFFECTING SELECTION OF
CARDIAC OUTPUT MONITORING
DEVICES
Institution
Type of institution
Availability of monitoring techniques
Level of standardization
Potential integration into existing monitor
systems
Level of experience

14. Devices
Invasiveness
Handling
Technical limitations
Validity ,accuracy & repeatability
Availability of additional hemodynamic
information

15. Patient
Severity of specific diseases
Heart rhythm
Contraindications
Type of intervention
Type of treatment protocol

16. METHODS OF MEASURING CARDIAC
OUTPUT
SIMPLE METHOD
CO(L/min)=HR(beats/min)x SV(L/beat)
SV :stroke volume- volume ejected during each
beat.
CO(cardiac output at rest)=5-6L/min
HR(Heart rate)=72 beats/min, SV=0.07
L/min(70ml)

17. INVASIVE METHODS

18. FICK’S PRINCIPLE
It states that the amount
of a substance taken up by
an organ (or by the whole
body) per unit of time is
equal to the arterial level of
the substance (A) minus the
venous level (V) times the
blood flow (F), i.e
Q=A-VxF
Or F=Q/A-V

19. This principle can be used only in situations in
which the arterial blood is the sole source of
the substance taken up.
The Fick’s principle can be used to measure
cardiac output by two methods:
Direct method
Indirect method.

20. FICK’S PRINCIPLE (DIRECT
METHOD)
Cardiac output = O2 taken
by the lungs
ml/min/AO2-VO2

21. Amount of O2 uptake/min - spirometer
Mixed venous blood(VO2)-The cardiac catheter
is inserted into brachial vein subclavian vein
right atrium right ventricle pulmonary
artery.
Systemic arterial blood(AO2)-brachial or
femoral artery

22. Cardiac output = O2 taken
by the lungs
ml/min/AO2-VO2
=200ml/min/200-160 ml
=200/40
=5 L/min

23. • Pulmonary blood
flow=amount of O2 taken
by the lungs/min/PVO2-
PAO2
• O2 uptake is 250 ml/min,
PVO2 is 19 ml/100 ml and
PAO2 is 14 ml/100 ml,
then
• Cardiac
output=250x100/19-14
=25000ml/min/5
=5000ml/min
=5L/min

24. ADVANTAGES
Result is accurate
No chemical is injected

25. DISADVANTAGES OF FICK’S PRINCIPLE (DIRECT
METHOD)
Catheterization should be done by expert
hands
Hospitalization is required
It is an invasive technique, so there are risks
of infection and haemorrhage.
The cardiac output estimated may be
somewhat higher than normal as the patient
becomes conscious of the whole technique.

26. Simultaneous measurement of oxygen
consumption makes the process difficult.
A fatal complication like ventricular
fibrillation may occur if the indwelling
catheter irritates the ventricular walls,
especially when the cardiac output is being
measured during heavy exercise.
Difficult to measure in ambulatory patients

27. FICK’S PRINCIPLE (INDIRECT METHOD)
In this method, arterial puncture and right
heart catheterization are avoided and CO2
excretion by the lungs is used instead of O2
uptake
CO2 excretion by the lungs - spirometry
Arterial CO2 (PACO2) is estimated from
alveolar air
Mixed venous blood CO2 (PVCO2) is
estimated by rebreathing into a closed bag.

28. With rebreathing, the CO2 in the bag will come
into equilibrium with the venous blood in lungs.
The breathing should be done in an
interrupted manner so that the blood level of
CO2 is not increased.
• According to Fick’s principle:
Cardiac output=CO2 output/min/PACO2-
PVCO2

29. INDICATOR OR DYE DILUTION
METHOD /HAMILTON’S DYE
DILUTION METHOD
Principle
Introduced by G. N.
Stewart in 1897 and
extended by W. F. Hamilton
in 1932, is a variation of the
Fick procedure.

30. The blood flow in l/min (F) is given by the
following formula:
F=Q/Ct
F = Blood flow in l/min
Q = Quantity of the dye injected
C = Mean concentration of dye
t = Time duration in seconds of the first passage
of dye through the artery.

31. Prerequisites for an Ideal indicator (Dye)
It should be nontoxic.
It must mix evenly in the blood.
It should be relatively easy to measure its
concentration.
It should not alter the cardiac output or
hemodynamics of blood flow.
Either it must not be changed by the body
during mixing period or the amount changed
must be known.
The dye commonly used is Evans blue (T-
1824) or radioactive isotopes or cardiogreen.

32. Procedure- Injection of dye
A few millilitre of venous blood is
withdrawn from the antecubital vein and it is
mixed with 5 mg Evans blue dye.
The blood containing dye is then injected
rapidly into the vein.

33. Estimation of duration of first passage of dye (t)
and mean concentration (C) of dye in arterial
blood.
Serial samples of arterial blood from the
brachial artery are taken every 2s and the dye
concentration is determined by photo
colorimetry
Dye concentration is plotted on a semi-log
paper

34. AG=C
AE=t

35. F=Q/Ct
Amount of dye injected (Q) is 5 mg
Time duration for first circulation is 40 s
Mean concentration of dye (C) = 15 mg/l, then
Cardiac output=Qx60/Cxt
=5x60/15x40
=300/60
=5L/min

36. • Investigating cardiac septal defects
• not used
ADVANTAGES
Accurate method
DISADVANTAGES
Procedure should not be repeated in short time

37. THERMODILUTION METHOD
Principle.
It is also an indicator dilution technique in
which instead of a dye, ‘cold saline’ is used as an
indicator.
The cardiac output is measured by
determining the resultant change in the blood
temperature in pulmonary artery.
The change in temperature is inversely
proportional to the amount of blood flowing
through the pulmonary artery.

38. PROCEDURE
In this technique, two
thermistors, one each in
the inferior vena cava and
pulmonary artery are
placed with the help of
cardiac catheter.

39. A known volume of sterile cold saline is then
injected into the inferior vena cava.
Temperature of the blood entering the heart
from inferior vena cava and that of the blood
leaving the heart via pulmonary artery is
determined by the thermistors.

40. F=V1x(TB-TI)/ ΔTB xt
F – blood flow in litre per second
VI – volume of the injectate
TB and TI – Temperature of blood and
injectate, respectively
ΔTB – mean change in the pulmonary artery
blood
t – duration of first passage of injectate in
seconds.

41. ADVANTAGES
Saline is harmless
Cold is dissipated, so recirculation is not a problem
Withdrawal of blood for sampling is not required
Can be repeated many times
Preferred for infants and small children in whom
the blood volume is limited & saline is non toxic
Useful in severely sick patients
DISADVANTAGES
Cardiac catheterization required

42. X-RAY METHOD
Radio-opaque dye is injected intravenously
Size of heart detected from serial x-rays in
systole & diastole
Cardiac output measured using computer
programmes.

43. CINERADIOGRAPHY
Diagnostic technique in
which a camera is used to
record images of internal
body structures produced
through radiography or
fluoroscopy
Takes high speed X-ray
motion pictures

44. ANGIOGRAPHY
Visualizes coronary
arteries, also measures
End diastolic & End
systolic volume
Cardiac output=(EDV-
ESV)xHR

45. NON INVASIVE METHODS

46. ENDOTRACHEAL CARDIAC OUTPUT
MONITOR(ECOM)/IMPEDENCE CARDIOGRAPHY
ECOM measures cardiac
output using impedance
plethysmography
Is based on the principle of
bio-impedance.
Current is passed through
electrodes attached to
endotracheal tube shaft &
cuff
Change in impedance
secondary to aortic blood
flow is detected by
electrode on the cuff.

47. An algorithm calculates stroke volume on
impedance changes & cardiac output can be
calculated
Impedance affected by aortic blood flow
LIMITATIONS
Electrocautery affects its accuracy
Coronary blood flow is not calculated
Is not validated in humans
Is costly & has not become very popular

48. ECHO ECHOCARDIOGRAPHY

49. DELIVERY ROUTES
TRANSTHORACIC WINDOW
Left parasternal
Apical
Subcostal
Right parasternal
Suprasternal
Posterior thoracic
TRANSESOPHAGEAL
INTRAVASCUAR
Intracardiac
Intracoronary
EPICARDIAL

50. TRANS THORACIC
ECHOCARDIOGRAPHY/
CARDIAC ULTRASOUND
Echocardiography
refers to ultrasonic evaluation
of cardiac functions.
It is a non-invasive
technique that does not
involve injections or insertion
of a catheter.
It involves B-scan
ultrasound at a frequency of
2.25 MHz using a transducer
which also acts as receiver of
the reflected waves.

51. The reflections are
recorded in a
photosensitive paper
using an oscilloscope.
The thickness &
movement of the
ventricular walls,
chambers, septum, and
valves during the cardiac
cycle.

52. When combined with Doppler techniques, can
be used to measure velocity and volume of
flow through the valves.
Also Evaluates end-diastolic volume (EDV),
end-systolic volume (ESV), cardiac output (CO)
and valvular defects.

53. ACOUSTIC WINDOWS
Para sternal-long axis &
short axis views
Apical-4 chamber & 2
chamber views
Sub costal- 4 chamber view
Suprasternal view

54. MODALATIES OF ECHO
CONVENTIONAL ECHO
Two dimensional echo (2-D echo)
Motion mode echo ( M- mode echo)
DOPPLER ECHO
Continuous wave (CW) doppler
Pulsed wave(PW) doppler
Colour flow(CF) doppler

56. TWO DIMENSIONAL ECHO M- MODE ECHO

57. ADVANTAGES
Non-invasive
Quick
Allows for measurement of
the ventricles,
visualization of the valves
,estimation of ejection
fraction
DISADVANTAGES
User dependent
Possible interference from
bone ,lung & soft
tissues

58. TRANS ESOPHAGEAL
ECHOCARDIOGRAPHY
(TEE)/DOPPLER
Provides information
on the velocity, direction,
and character of blood flow,
just as police radar
monitors traffic.
Information is
obtained with the beam
parallel to the flow of blood.
Can continuously
monitor the velocity of
flowing blood in a blood
vessel or part of the heart.

60. The strength of the
returning signal, which
depends on the number
of red blood cells moving
at that velocity.
Can distinguish the
character of flow: laminar
versus turbulent.

61. Blood moves through the
mitral valve and into the
left ventricle during
diastole. Because blood is
flowing toward the
transducer, its velocity is
encoded as red.
Blood moves out of the
ventricle and toward the
aortic valve during
systole. Because blood is
flowing away from the
transducer, its velocity is
encoded as blue.

62. A magnetic resonance scanner can also
be used in two-dimensional phase-contrast
mapping to yield quantitative measurements
of blood flow velocity.

63. ADVANTAGES
Minimally invasive
Minimal interference from
bone, lungs & soft
tissues
Quickly inserted & analyzed
Little training required
Very few complications
DISADVANTAGES
May require sedation
User dependent
Probe may detect other
vessels e.g intracardiac
,intrapulmonary vessels
Contraindicted in
esophageal surgeries
Depends on accurate
probe positioning

64. Ballistocardiography method
This method is not used
practically.
Refers to graphical record of the
pulsations created due to ballistic
recoil of the pumping heart.
The ballistic recoil occurs in
accordance with Newton’s third law
of motion, i.e. when heart pumps
blood into aorta and pulmonary
artery, recoil of the body occurs in
the opposite direction. This is similar
to that of ballistic recoil when a
bullet is fired from the rifle.

65. The ballistic recoil pulsations can be
recorded graphically by making the subject to
lie on a suspended bed movable in the long
axis of the body.
The cardiac output is determined by
analyzing the graph obtained.
Not an accurate one

66. PULSE PRESSURE METHOD
Pulse pressure -Difference between systolic
& diastolic pressures provides rough idea
about cardiac output

67. METHOD EMPLOYING INHALATION OF INERT
GASES
Also called foreign gas re-breathing
In this technique, an inert gas which dissolves
in plasma but does not combine with Hb or other
constituents of the blood is used as an indicator.
Gases- nitrous oxide,CO2 and acetylene
The pulmonary blood flow is determined by
The quantity of gas absorbed in the given time
The partial pressure of the gas in the alveolar
air
The solubility of the gas (a known factor).

68. SUMMARY
INVASIVE
Pulmonary artery catheter
(Fick’s method,
Dye, Thermodilution)
Cineradiographic
technique
X-ray method
NON – INVASIVE
Endotracheal cardiac output
monitor (ECOM)
TTE/Trans Thoracic
echocardiography
TEE/Trans esophageal
doppler
Pulse pressure method
Method employing
inhalation of Inert gases
METHODS OF MEASURING CARDIAC OUTPUT

69. REFERENCES
• GUYTON AND HALL- Text Book of Medical Physiology-
13th International edition.
• GANONG ‘S Review of Medical Physiology 26th edition.
• Text book of medical Physiology- INDHU KHURANA 2nd
edition
• Comprehensive Text Book of Medical Physiology- G.K.
PAL 2nd edition
• BERNE & LEVY-Text book of Medical Physiology 1st
edition
• BORON-Text book of Medical Physiology 3rd edition
• BRAUNWALD’S Text book of Heart Disease 11th
edition