AJTCCM VOL. 29 NO. 2 2023 43
EDITORIAL
In this issue of AJTCCM, Surendhar etal.[1] present their ndings
validating the complementary value of using a triage tool to determine
the state of circulatory failure in patients seen at a busy tertiary
emergency department (ED) in India. Circulatory failure is crudely
dened as the inability of the body to maintain cellular oxygenation
– a syndrome dened as ‘shock’.[2] It is a common condition, with
approximately one-third of patients presenting to an ED with this
syndrome requiring admission to a high-dependency unit or an
intensive care unit (ICU) for supportive care.[3]
Shock is defined physiologically by the equation: Delivery of
oxygen = cardiac output × arterial oxygen content.[4] Decreased
oxygen delivery is termed hypoxia, as opposed to a decrease in oxygen
saturation alone, which is termed hypoxaemia. ere are a multitude
of different pathologies that result in a state of shock or tissue
hypoxia. ese are crudely dened by pathophysiological aetiology
into the hypovolaemic form, in which there is internal or external
uid loss, cardiogenic, arising from cardiac pump failure, obstructive,
arising from impaired venous return, and distributive, caused by a
loss of vascular tone with vasodilation.[3] However, in most patients
presenting to an ED, several of these mechanisms may overlap even
if there is a single underlying disease process, making the distinction
between them dicult.[5]
The primary physiological manifestations of the shock state are
hypotension and tachycardia, and these are accompanied by secondary
features of tissue hypoperfusion, which include cold and clammy skin
with decreased capillary blood ow, reduced urinary output due to renal
hypoxia, and altered mentation due to cerebral hypoxia. e easiest and
most objective way to measure this physiological state is with the blood
pressure and heart rate. A systolic arterial pressure <90 mmHg or a
mean arterial pressure (MAP) <70 mmHg with associated tachycardia
defines a low cardiac output state.[3] This pathological state with a
decreased cardiac output and the associated compensatory response
with tachycardia are the two main constituents of the shock index (SI)
used by Surendhar etal.[1] as a triage tool.[6] A modied version of the
shock index (MSI), using the ratio of the heart rate to the MAP, was also
used in this study to ascertain whether either had a better predictive
value when used in the ED to predict in-hospital outcomes.[7]
e major nding reported was that an SI ≥0.9 and an MSI ≥1.3
predicted in-hospital mortality (p<0.05) and ICU admission (p<0.05).
There was no significant superiority of the MSI over the SI in
predicting mortality, although the MSI was a better surrogate marker
for ICU admission. However, the study did exclude patients who were
on heart rate-regulating drugs and those who had atrioventricular
block, cardiac arrhythmia or spinal cord injury, which is a major
limitation of the universal applicability of the SI or the MSI as triage
tools. Many patients who present to the ED are on medication that
affects the physiological response of the heart, and the different
pathophysiological mechanisms causing shock are oen associated
with some form of cardiac dysrhythmia.
Furthermore, the study reported sensitivity and specicity of the SI
of 100% and 23%, respectively, in predicting mortality, whereas the
MSI was reported to have sensitivity and specicity of 98% and 23%,
respectively, in predicting mortality. e poor specicity of the SI and
the MSI, with very low negative predictive values, while superior to
blood pressure and heart rate individually, mean that they oer little
additional benet as screening or triage tools. e main reason for
these ndings is the heterogeneous nature of the illnesses in patients
presenting to the ED, as well as the unpredictable physiological
response in critical illness.
ese ndings have been corroborated in a comprehensive literature
review by Koch etal.[8] on the SI, concluding that the SI should never
be used in isolation to diagnose or rule out critical illness. Rather, it
could be part of a triage bundle in clinical decision-making in the
ED around the need for admission and the likelihood of mortality.[8]
Ismail S Kalla, MB BCh, PhD, FCP (SA), FCCP (USA), Cert
Pulmonology (SA), Cert Critical Care (SA)
Associate Professor and Academic Head of Department – Internal
Medicine, Faculty of Health Sciences, University of the Witwatersrand,
Johannesburg, South Africa
iskalla786@gmail.com
Guy A Richards, MB BCh, PhD, FCP (SA), FRCP, MASSAf
Emeritus Professor of Critical Care, Faculty of Health Sciences,
University of the Witwatersrand, Johannesburg, South Africa
1. Surendhar S, Jagtap AB, Jagadeesan S. Complementary value of the shock index
v. the modified shock index in the prediction of in-hospital intensive care unit
admission and mortality: A single-centre experience. Afr J oracic Crit Care Med
2023;29(2):e286. https://doi.org/10.7196/AJTCCM.2023.v29i2.286
2. Sakr Y, Reinhart K, Vincent J-L, etal. Does dopamine administration in shock inuence
outcome? Results of the Sepsis Occurrence in Acutely Ill Patients (SOAP) Study. Crit
Care Med 2006;34(3):589-597. https://doi.org/10.1097/01.CCM.0000201896.45809.E3
3. Vincent JL, de Backer D. Circulatory shock. N Engl J Med 2013;369(18):1726-1734.
https://doi.org/10.1056/NEJMra1208943
4. Nelson DP, Beyer C, Samsel RW, Wood LD, Schumacker PT. Pathological supply
dependence of O2 uptake during bacteremia in dogs. J Appl Physiol 1987;63(4):1487-
1492. https://doi.org/10.1152/jappl.1987.63.4.1487
5. Vincent J-L, Ince C, Bakker J. Clinical review: Circulatory shock – an update: A tribute
to Professor Max Harry Weil. Crit Care 2012;16(6):239.
6. Keller AS, Kirkland LL, Rajasekaran SY, Cha S, Rady MY, Huddleston JM. Unplanned
transfers to the intensive care unit: The role of the shock index. J Hosp Med
2010;5(8):460-465. https://doi.org/10.1002/jhm.779
7. Liu Y-C, Liu J-H, Fang ZA, etal. Modified shock index and mortality rate of
emergency patients. World J Emerg Med 2012;3(2):114-117. https://doi.org/10.5847/
wjem.j.issn.1920-8642.2012.02.006
8. Koch E, Lovett S, Nghiem T, Riggs R, Rech MA. Shock index in the emergency
department: Utility and limitations. Open Access Emerg Med 2019;11:179-199.
https://doi.org/10.2147/OAEM.S178358
Afr J Thoracic Crit Care Med 2023;29(2):e1230. https://doi.
org/10.7196/AJTCCM.2023.v29i2.1230
e usefulness of the shock index and the modied shock index in
predicting patient outcomes in a tertiary emergency department
inIndia
