Inotropy Index accurately predicts fluid responsiveness in volume resuscitation. Brendan E. Smith and Veronica M. Madigan School of Biomedical Science, Charles Sturt University, Bathurst, NSW, Australia. Specialist in Anaesthesia and Intensive Care, Bathurst Base Hospital, Bathurst, NSW, Australia.

1. Inotropy Index accurately predictsInotropy Index accurately predicts
fluid responsiveness in volumefluid responsiveness in volume
resuscitation.resuscitation.
Brendan E. SmithBrendan E. Smith1,21,2
and Veronica M. Madiganand Veronica M. Madigan11
11
School of Biomedical Science,School of Biomedical Science,
Charles Sturt University, Bathurst, NSW, Australia.Charles Sturt University, Bathurst, NSW, Australia.
22
Specialist in Anaesthesia and Intensive Care,Specialist in Anaesthesia and Intensive Care,
Bathurst Base Hospital, Bathurst, NSW, Australia.Bathurst Base Hospital, Bathurst, NSW, Australia.

2. Introduction.Introduction.
Inotropy (myocardial contractility) as aInotropy (myocardial contractility) as a conceptconcept is wellis well
known to all clinicians but not as aknown to all clinicians but not as a discrete quantitydiscrete quantity..
Depressed inotropy is an important feature of many EDDepressed inotropy is an important feature of many ED
presentations –presentations –
11oo
Cardiac Conditions – AMI, LVF, CardiomyopathyCardiac Conditions – AMI, LVF, Cardiomyopathy
22oo
Myocardial Depression – Septicaemia, Pancreatitis,Myocardial Depression – Septicaemia, Pancreatitis,
Pneumonia, DKA, Burns, Hypoxia, Crush Injury,Pneumonia, DKA, Burns, Hypoxia, Crush Injury,
Hypovolaemia, Anaemia, Thyroid Disorders,Hypovolaemia, Anaemia, Thyroid Disorders,
Hyper + Hypothermia, Poisoning,Hyper + Hypothermia, Poisoning, Evenomation,Evenomation,
Iatrogenic e.g. Antihypertensives, Chemotherapy,Iatrogenic e.g. Antihypertensives, Chemotherapy,
Electrolyte Disorders, Steroids, ……Electrolyte Disorders, Steroids, ……

3. Volume ResuscitationVolume Resuscitation
Is practiced every day in every ED in the worldIs practiced every day in every ED in the world
in a wide range of conditions!in a wide range of conditions!
What they all have in common is that whatWhat they all have in common is that what
we are trying to do is either :-we are trying to do is either :-
1)1) Increase Blood PressureIncrease Blood Pressure
2) Increase Cardiac Output2) Increase Cardiac Output
i.e. increase Blood Flowi.e. increase Blood Flow

4. Preload Inotropy AfterloadPreload Inotropy Afterload
Why is inotropy so important?Why is inotropy so important?
BP = SVR x HR x SV : SV x HR = COBP = SVR x HR x SV : SV x HR = CO
Fluid loadingFluid loading

5. Initially, a fall in SVR or in CO can be compensated by anInitially, a fall in SVR or in CO can be compensated by an
increased Cardiac Output or SVR which maintains BP,increased Cardiac Output or SVR which maintains BP,
thethe compensated phasecompensated phase..
But this process cannot go on forever! Eventually, the heartBut this process cannot go on forever! Eventually, the heart
cannot increase CO further or the circulation cannot increasecannot increase CO further or the circulation cannot increase
SVR further and BP will fall.SVR further and BP will fall.
This is theThis is the decompensated phasedecompensated phase..
The point at which this occurs depends on theThe point at which this occurs depends on the cardiaccardiac
reservereserve, which in turn depends on, which in turn depends on preloadpreload availability and onavailability and on
inotropyinotropy..

6. Total Inotropy = PE + KE
( = blood pressure + blood flow)
Inotropy = BPm x SV x 10Inotropy = BPm x SV x 10-3-3
++ 1 x SV x 101 x SV x 10-6-6
xx ρρ x Vx V22
7.5 x FT7.5 x FT 2 x FT2 x FT
(The Smith-Madigan Formula)(The Smith-Madigan Formula)
The SI unit of inotropy is the WattThe SI unit of inotropy is the Watt

7. Inotropy IndexInotropy Index
But how do we judge inotropy in patients of varying size,But how do we judge inotropy in patients of varying size,
e.g. large and small adults, children, infants?e.g. large and small adults, children, infants?
By analogy to cardiac index which is –By analogy to cardiac index which is –
Cardiac Index = Cardiac OutputCardiac Index = Cardiac Output
Body Surface AreaBody Surface Area
Smith-Madigan Inotropy Index = InotropySmith-Madigan Inotropy Index = Inotropy
BSABSA
The SI unit of SMII is therefore W/mThe SI unit of SMII is therefore W/m22

8. Clinical ObservationClinical Observation
The response of patients to volume loading isThe response of patients to volume loading is
variable, from a good response to littlevariable, from a good response to little
or even no response at all.or even no response at all.
Why is this so?Why is this so?
Could it be due to variations in inotropy indexCould it be due to variations in inotropy index
affecting volume responsiveness?affecting volume responsiveness?

9. Starling Curves and Inotropy IndexStarling Curves and Inotropy Index
Left ventricular end diastolic volumeLeft ventricular end diastolic volume
StrokeStroke
VolumeVolume
ΔΔSVSV
inotropyinotropy
SMII = 0.8SMII = 0.8

10. Patient Selection.Patient Selection.
Convenience sample of 41 adult patientsConvenience sample of 41 adult patients
admitted to ED with diagnosis of non-admitted to ED with diagnosis of non-
cardiogenic shock where volume expansioncardiogenic shock where volume expansion
was to be used.was to be used.

11. Shock Criteria – any 3 ofShock Criteria – any 3 of
HypotensionHypotension
TachycardiaTachycardia
Impaired Cerebral FunctionImpaired Cerebral Function
Poor Peripheral PerfusionPoor Peripheral Perfusion
Cold and Clammy SkinCold and Clammy Skin

12. ObserverObserver
Observer was not involved in clinicalObserver was not involved in clinical
decision making – collected data only.decision making – collected data only.

13. Data collectedData collected
1) Blood pressure1) Blood pressure
- prior to any iv fluid then at 15 minute intervals using- prior to any iv fluid then at 15 minute intervals using
automated oscillotonometry or arterial line when presentautomated oscillotonometry or arterial line when present
2) Heart Rate2) Heart Rate
- prior to any iv fluid then at 15 minute intervals from ECG- prior to any iv fluid then at 15 minute intervals from ECG

14. 3) Cardiac Output3) Cardiac Output
- measured by observer using ultrasonic cardiac- measured by observer using ultrasonic cardiac
output monitor (USCOM) from suprasternal notchoutput monitor (USCOM) from suprasternal notch
prior to iv fluid and then every 15 minutesprior to iv fluid and then every 15 minutes
4) Cerebral Function - On four point scale4) Cerebral Function - On four point scale
a) Normal (A = “alert”)a) Normal (A = “alert”)
b) Slightly impaired (B = “blunted”)b) Slightly impaired (B = “blunted”)
c) Confused (C = “confused”)c) Confused (C = “confused”)
d) Insensible (D = “doolally”)d) Insensible (D = “doolally”)

15. 5) SM Inotropy Index5) SM Inotropy Index
- Retrospectively calculated from the USCOM- Retrospectively calculated from the USCOM
readings, BP and Hb from the Smith-Madigan Formulareadings, BP and Hb from the Smith-Madigan Formula
for each 15 minute observation.for each 15 minute observation.

16. Exit Criteria.Exit Criteria.
Data collection ceased when patient judged toData collection ceased when patient judged to
be adequately resuscitated by ED staff orbe adequately resuscitated by ED staff or
when transferred to ICU or other facility.when transferred to ICU or other facility.

17. Data AnalysisData Analysis
The dataThe data were analysed using SPSS v16 softwarewere analysed using SPSS v16 software
using Analysis of Variance, Chi square, Fisher’s exactusing Analysis of Variance, Chi square, Fisher’s exact
test, Regression Analysis and Pearson and Spearmantest, Regression Analysis and Pearson and Spearman
Correlations.Correlations.

18. HypovolaemiaHypovolaemia
21 Patients were judged to have absolute hypovolaemia.21 Patients were judged to have absolute hypovolaemia.
6 due to whole blood loss6 due to whole blood loss
15 due to fluid loss / dehydration15 due to fluid loss / dehydration
12 Patients had relative hypovolaemia due to septicaemia.12 Patients had relative hypovolaemia due to septicaemia.
8 Patients had a mixed pattern of hypovolaemia.8 Patients had a mixed pattern of hypovolaemia.

19. Successful Outcome.Successful Outcome.
Positive response to volume resuscitationPositive response to volume resuscitation
was taken as an increase in mean arterialwas taken as an increase in mean arterial
pressure or cardiac output of 10% or morepressure or cardiac output of 10% or more
following =>20ml/kg of fluid.following =>20ml/kg of fluid.

20. Hypovolaemia (n = 21)Hypovolaemia (n = 21)
+ve response+ve response -ve response-ve response
Blood lossBlood loss 66 00
Fluid loss /Fluid loss / 99 66
DehydrationDehydration
Mean SMIIMean SMII 1.481.48 0.840.84
RangeRange (1.28 – 1.72)(1.28 – 1.72) (0.68 – 1.15)(0.68 – 1.15)
p =p = 0.0020.002

21. Septicaemia (n = 12)Septicaemia (n = 12)
+ve response+ve response -ve response-ve response
N =N = 44 88
Mean SMIIMean SMII 1.361.36 0.970.97
RangeRange (1.21 – 1.49)(1.21 – 1.49) (0.63 –(0.63 –
1.04)1.04)
p =p = 0.020.02

22. Mixed Pattern (n = 8)Mixed Pattern (n = 8)
+ve response+ve response -ve response-ve response
N =N = 44 44
Mean SMIIMean SMII 1.311.31 0.910.91
RangeRange (1.07 – 1.52)(1.07 – 1.52) (0.73 –(0.73 –
1.15)1.15)
p =p = 0.0650.065

23. All Patients (n = 41)All Patients (n = 41)
n =n = +ve+ve -ve-ve
SMII > 1.1SMII > 1.1 2424 2222 22
SMII <1.1SMII <1.1 1717 11 1616
p =p = <0.001<0.001

24. First SMIIFirst SMII
%%ΔΔ
COCO

25. ConclusionsConclusions
Initial SMII measurement accurately predicts patientInitial SMII measurement accurately predicts patient
responsiveness in volume resuscitation.responsiveness in volume resuscitation.
Initial SMII values below 1.1 W/mInitial SMII values below 1.1 W/m22
are associated withare associated with
a poor response to iv fluid in 94% of cases.a poor response to iv fluid in 94% of cases.
Initial SMII values below 1.1 W/mInitial SMII values below 1.1 W/m22
may indicate themay indicate the
early use of inotropes in volume resuscitation.early use of inotropes in volume resuscitation.