52 AJTCCM VOL. 29 NO. 2 2023
Background. Shock is a state of circulatory insuciency that creates an imbalance between tissue oxygen supply and demand, resulting
in end-organ dysfunction and hypodynamic circulatory failure. Most patients with infectious and trauma-related illnesses present to the
emergency department (ED) in shock.
Objectives. To study the usefulness of the shock index (SI) and modied shock index (MSI) in identifying and triaging patients in shock
presenting to the ED.
Methods. is was a year-long observational, cross-sectional study of 290 patients presenting to the ED of a tertiary hospital in compensated
or overt shock. e SI and MSI were calculated at the time of rst contact, and then hourly for the initial 3 hours. Relevant background
investigations targeting the cause of shock and prognostic markers were done. e outcome measures of mortality and intensive care unit
admission were documented for each participant.
Results. e mean age of the participants was 49 years, and 67% of them were men. In consensus with local and national data, the major
medical comorbidities were hypertension (20%) and diabetes mellitus (16%). An SI ≥0.9 and an MSI ≥1.3 predicted in-hospital mortality
(p<0.05) and ICU admission (p<0.05) with no signicant superiority of the MSI over the SI in terms of mortality, although the MSI was a
better surrogate marker for critical care admission.
Conclusion. e study showed the complementary value of the SI and MSI in triage in a busy tertiary hospital ED, surpassing their
components such as blood pressure, heart rate and pulse pressure. We determined useful cut-os for these tools for early risk assessment in
the ED, and larger multicentre studies are needed to support our ndings.
Keywords. Shock, shock index, modied shock index, triage.
Afr J Thoracic Crit Care Med 2023;29(2):e286. https://doi.org/10.7196/AJTCCM.2023.v29i2.286
Complementary value of the Shock Index v. the Modied Shock
Index in the prediction of in-hospital intensive care unit admission
and mortality: A single-centre experience
S Surendhar,1 MD (Emerg Med); S Jagadeesan,2 MD (Int Med), MRCP ; A B Jagtap,3 MBBS
1 Senior Resident in Emergency Medicine, Jawaharlal Institute of Postgraduate Medical Education and research, Puducherry, India
2 Senior Resident in Internal Medicine, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
3 Postgraduate Resident in Internal Medicine, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India
Corresponding author: S Jagadeesan (drjagadeesans@gmail.com)
Study synopsis
What the study adds. e study highlights the usefulness of clinical bedside tools such as the shock index (SI) and modied shock index
(MSI) in triaging patients in the emergency department, and their role in predicting morbidity and mortality.
Implications of the ndings. Compared with systolic blood pressure, diastolic blood pressure and mean arterial pressure, alone or in
combination, the SI and MSI had higher sensitivity and specicity in terms of outcome prediction. While both an elevated SI and an elevated
MSI predicted in-hospital mortality, the MSI was a better surrogate marker for ICU admission.
Haemodynamic instability is a common nding in patients presenting
to the emergency department (ED) of any healthcare facility.
Appropriate triaging and timely intervention based on the severity
of the patient’s condition are benecial to the patient and enable
ecient use of resources. Shock is a state of circulatory insuciency
that creates an imbalance between tissue oxygen supply and demand,
resulting in end-organ dysfunction.[1] Pathophysiologically, shock
can be classied as distributive (33 - 50%), hypovolaemic (31 - 36%),
cardiogenic (14 - 29%) or obstructive (1%). e major regulators of
blood pressure are baroreceptors, which are further controlled by the
sympathetic and vagal activity of the medulla. Other factors aecting
blood pressure and heart rate are chemoreceptors and the renin-
angiotensin-aldosterone system.[2]
The shock index (SI) provides information on the patient’s
haemodynamic status and is calculated as the ratio of heart rate (HR) to
systolic blood pressure (SBP). It appears to be a reliable predictor of early
shock in situations such as trauma, infection and pulmonary embolism,
in which 0.9 is usually considered the threshold for comprehensive
evaluation. It is considered sensitive in reecting the pre-shock state,
as tachycardia precedes hypotension in early/compensated shock
ORIGINAL RESEARCH: ARTICLES
AJTCCM VOL. 29 NO. 2 2023 53
states. A considerable amount of research has
shown that a high SI predicts poor outcomes
in terms of mortality aer trauma. e SI is
increasingly used to predict the duration
and outcome of critical care admission,
including patients on mechanical ventilation.
In contrast, blood pressure (BP) or HR on
their own are not as sensitive in predicting the
severity of haemodynamic compromise.[3,4]
The modified shock index (MSI) is
calculated as the ratio of HR to mean
arterial pressure (MAP), which is the sum
of diastolic blood pressure (DBP) and one-
third of pulse pressure. The MSI indicates
the diastolic rather than the systolic function
of the heart and is therefore a near-ideal
surrogate marker for cardiac compromise, as
coronary perfusion is reliant on the diastolic
function/duration. A high MSI can therefore
be regarded as an ominous sign of low cardiac
output and systemic vascular resistance,
culminating in hypodynamic circulation.[5,6]
Although research has proved the
sensitivity of the SI and MSI in investigating
hypodynamic states, their actual predictive
capability in terms of in-hospital mortality
and duration of ICU admission in patients
from the ED is not as well known.
Methods
This was a year-long observational, cross-
sectional study of 290 patients who presented
to the ED of a tertiary hospital in compensated
or overt shock. All adult patients aged >18
years with predetermined threshold values
for vital signs (BP <90/60 mmHg, MAP <65
mmHg, capillary relling time >3 seconds,
or other signs of haemodynamic collapse)
were enrolled aer written informed consent
had been obtained from the patient or an
accompanying family member. Any adult
patient with decompensated shock due to any
underlying cause, including but not limited to
trauma or sepsis, was included. Patients who
were on heart rate-regulating drugs or had
atrioventricular block, cardiac arrhythmia,
spinal cord injury or cardiorespiratory arrest,
those who had received initial care out of
the hospital, and those with incomplete data
were excluded from the study. e parameters
that were necessary for calculation of the SI
and MSI were recorded at presentation and
on an hourly basis for the initial 3 hours of
hospitalisation. To obtain gures that could
be analysed, we determined threshold values
for the SI as 0.5 - 0.9 and those for the MSI
as 0.7 - 1.3, in accordance with the ndings
of earlier research.[7] Any value over the cut-
o limit at early monitoring was recorded
for evaluation. e primary objective of the
study was to measure in-hospital mortality
in patients with a raised index, while the
secondary objective was to determine the
rate of ICU admission. The details were
recorded on standard case record forms,
and all data were entered into an Excel
2019 spreadsheet (Microsoft Inc., USA).
Statistical analysis was done using Stata
soware, version 17, 2021 (StataCorp Inc.,
USA) e χ2 test was used to calculate the
p-value, with p<0.05 indicating signicance.
Appropriate approval was received from
the institutional ethics committee of the
hospital before the initiation of the study (ref.
no. BJMC/152/19).
Results
e mean age of the participants was 49 years,
and 67% of them were men. In consensus with
local and national data, the major medical
comorbidities were hypertension (20%) and
diabetes mellitus (16%). Sepsis and acute
cardiac failure (decompensated) were the most
common nal diagnoses, and were invariably
associated with increased mortality (Fig.1).
Among the non-traumatic surgical
emergencies, hollow viscus perforation (31%)
and acute pancreatitis (17%) were frequent.
Anotable nding was that with an increase in
the SI from 0.9 to 1.8, mortality rates showed
a considerable increase from 19% to 90%
(χ2=57.0095 (p<0.05)) ( 1).
As with the SI, an MSI >1.7 was associated
with an increased mortality rate, as shown in
Table2 (χ2=67.813 (p<0.05)).
e sensitivity and specicity of the SI in
predicting mortality were almost 100% and
23%, respectively (Table3). An MSI of 1.5 -
2.1 was highly suggestive of relatively higher
rates of ICU admission (p<0.05). As shown in
Table4, the sensitivity of the MSI in predicting
mortality was 98% with a specicity of 23%,
while the negative predictive value was 98%.
On analysis of individual parameters, an
MAP <65 mmHg was found to be a predictor
of mortality, with a sensitivity of 27% and a
specicity of 97%. A DBP <60 mmHg was also
statistically signicant in predicting mortality,
with a sensitivity of 75% and a specicity of
66%.
Patients, n
0 5 10 15 20 25 30 35 40 45 50
Final diagnosis
Death Discharge
18
Viral fever
120
Trauma
1
1
Tuberculosis
630
Sepsis
12
Pulmonary embolism
630
Polytrauma
5
3
Poisoning
614
Myocardial infarction
26
Heart failure
5
Enteric fever
11
Diabetic ketoacidosis
20
Community-acquired
pneumonia 915
Chronic liver disease
1
Cardiac tamponade
4
2
Acute kidney injury
513
Acute heart failure
11
Acute gastroenteritis
645
Abdominal pathology
Fig.1. Mortality in relation to nal diagnoses.
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54 AJTCCM VOL. 29 NO. 2 2023
Table1. SI distribution and mortality
SI Discharge, n (%)* Death, n (%)* Total, n (%)*
<0.9 5 (2.1) 0 5 (1.7)
0.9 - 1.1 152 (64.4) 10 (18.5) 162 (55.8)
1.2 - 1.4 68 (28.8) 28 (51.8) 96 (33.1)
1.5 - 1.7 10 (4.2) 11 (20.3) 21 (7.2)
1.8 - 2.0 1 (2.1) 4 (7.4) 5 (1.7)
≥2.1 0 1 (1.8) 1 (0.3)
Total, N 236 54 290
SI = shock index.
*Except where otherwise indicated.
Table2. MSI distribution and mortality
MSI Discharge, n (%)* Death, n (%)* Total, n (%)*
<1.1 1 (0.4) 0 1 (0.3)
1.1 - 1.2 62 (26.2) 1 (1.8) 63 (21.7)
1.3 - 1.4 63 (26.6) 6 (10.7) 69 (23.7)
1.5 - 1.6 56 (23.7) 8 (14.2) 64 (22.1)
1.7 - 1.8 29 (12.2) 17 (30.3) 46 (15.8)
1.9 - 2.0 16 (6.7) 9 (16.7) 25 (8.6)
2.1 - 2.2 8 (3.3) 6 (10.7) 14 (4.8)
≥2.3 1 (0.4) 7 (12.5) 8 (2.7)
Total 236 54 290
MSI = modied shock index.
*Except where otherwise indicated.
Table3. Sensitivity and specicity of the SI
SI Death, nDischarge, nTotal, N
≥0.9 54 231 285
<0.9 0 5 5
Total 54 236 290
Sensitivity, % Specicity, % PPV, % NPV, %
100 23 19 100
SI = shock index; PPV = positive predictive value; NPV = negative predictive value.
Table4. Sensitivity and specicity of the MSI
MSI Death, nDischarge, nTotal, N
≥1.3 53 173 226
<1.3 1 63 64
Total 54 236 290
Sensitivity, % Specicity, % PPV, % NPV, %
98 23 23 98
MSI = modied shock index; PPV = positive predictive value; NPV = negative predictive value.
Table5. Comparison of the SI and MSI for prediction of mortality
Death, nDischarge, nTotal, NSignicance
MSI ≥1.3 53 173 226 χ2=1.544
(p=0.213)
SI ≥0.9 54 231 285
Total 107 404 511
SI = shock index; MSI = modied shock index.
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AJTCCM VOL. 29 NO. 2 2023 55
In a head-to-head comparison of the SI and MSI, it was firmly
established that the MSI is not better than the SI in terms of predicting
mortality, although the MSI was more useful in predicting ICU
admission from the ED (Tables 5 and 6).
Discussion
e SI was rst proposed in the 1960s to identify apparently stable yet
critically ill trauma patients in the ED. It has since been shown to be a
simple, non-invasive risk stratication tool useful for detecting changes
in cardiovascular performance before the onset of systemic hypotension
and cardiorespiratory collapse, especially in patients with cardiogenic
shock, sepsis, ectopic pregnancy, gastrointestinal haemorrhage and
acute pulmonary embolism.[8] In the present study, in consensus with
Patients, n
0
MSI distribution
ICU admission Ward admission
1
1
4
2
12
2
25
39
7
41
23
17 52
162
1
10 20 30 40 50 60 70
≥2.9
2.7 - 2.8
2.5 - 2.6
2.3 - 2.4
2.1 - 2.2
1.9 - 2.0
1.7 - 1.8
1.5 - 1.6
1.3 - 1.4
1.1 - 1.2
<1.1
Fig.3. MSI and ICU admission. (MSI = modied shock index; ICU =
intensive care unit.)
Patients, n
0
SI distribution
ICU admission Ward admission
1
5
20
1
77
19
40 122
5
20 40 60 80 100 120 140
≥2.1
1.8 - 2.0
1.5 - 1.7
1.2 - 1.4
0.9 - 1.1
<0.9
Fig.2. SI and ICU admission. (SI = shock index; ICU = intensive care unit.)
SI distribution
Patients, n
70
0.99 -
1.10
58
1.1 -
1.22
0.87 -
0.98
47
1.23 -
1.34
28
1.35 -
1.47
14
1.47 -
1.58
8
1.59 -
1.70
5
1.71 -
1.82
3
1.83 -
1.94
1
1.95 -
2.07
80
70
60
50
40
30
20
10
0
Mortality, %
100
90
80
70
60
50
40
30
20
10
0
50
Fig.4. SI mortality trend (red curve). (SI = shock index.)
Patients, n
79
1.26 -
1.42
1.43 -
1.59
1.60 -
1.76
37
1.09 -
1.25
30
1.77 -
1.93
22
1.94 -
2.10
12
2.11 -
2.27
3
2.28 -
2.44
3
2.45 -
2.61
2
2.79 -
2.95
1
2.62 -
2.78
90
80
70
60
50
40
30
20
10
0
Mortality, %
100
90
80
70
60
50
40
30
20
10
0
MSI distribution
51 50
Fig.5. MSI mortality trend (red curve). (MSI = modied shock index.)
Table6. Comparison of the SI and MSI for prediction of ICU
admission
ICU
admission,
n
Ward
admission,
nTotal, NSignicance
MSI ≥1.3 142 84 226 χ2 = 8.185
(p = 0.004)
SI ≥0.9 143 142 285
Total 285 226 511
SI = shock index; MSI = modied shock index; ICU = intensive care unit.
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56 AJTCCM VOL. 29 NO. 2 2023
previous research on 2 500 patients by Berger etal.,[9] an SA ≥0.9 at
presentation had a clinically signicant association with in-hospital
mortality. Berger etal.[9] found that an SI >1 was the most specic
predictor of both hyperlactataemia and 28-day mortality in their study,
while a score of ≥0.85 predicted ICU admission in a retrospective
analysis at a single centre by Keller etal.[10] Analogous application of
the SI in patients with acute coronary syndrome and community-
acquired pneumonia proved benecial in other studies.[11,12] An MSI
≥1.3 predicted mortality with a high sensitivity of 98% and a specicity
of 23%, and a logarithmic increase in MSI was associated with increased
mortality. e same cut-o of 1.3 was found to be convincingly useful
in studies of patients with non-cause-specic reasons for shock.[5,13]
With sensitivity analysis (Figs2 - 5), an SI ≥0.9 and an MSI ≥1.3 at
initial assessment in the ED predicted in-hospital mortality and ICU
admission rates with no signicant superiority of the MSI over the SI in
terms of mortality, although the MSI was a better surrogate marker for
critical care admission.
ere were certain limitations to our study, such as the relatively
small sample size and lack of a uniform denition of an abnormal SI,
which was given in the range of 0.7 - 1.0. e study was done in only
one centre, and to extrapolate the ndings to a general population,
multicentre studies may be necessary.
Conclusion
e study showed that an SI ≥0.9 and an MSI ≥1.3 at rst ED contact
predict in-hospital mortality and ICU admission. As shock indices can
be measured at the bedside, they are useful in predicting a patient’s
clinical course and survival probability. Further larger and multicentre
studies are needed to support our ndings and shed more light into
the tunnel of ED triaging of sick patients, especially in resource-
limited countries.
Declaration. e research for this study was done in partial fullment of
the requirements for SS’s MD (Emerg Med) degree at Gujarat University,
India.
Acknowledgements. We thank the faculty and sta of the Department of
Emergency Medicine, B J Medical College and Civil Hospital, Ahmedabad,
for assisting with the study.
Author contributions. SS: conceptualised the study, draed the protocol
and collected the data. SJ: performed the statistical analysis and wrote the
manuscript. ABJ: assisted with protocol development and reviewed the
manuscript. All authors approved the nal document for publication.
Funding.None.
Conicts of interest.None.
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Submitted 12 September 2022. Accepted 3 May 2023. Published July 2023.
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