Original article
Are Shock Index and Adjusted Shock Index useful in predicting mortality and length of stay in community-acquired pneumonia?

https://doi.org/10.1016/j.ejim.2010.12.009Get rights and content

Abstract

Background

Community Acquired Pneumonia (CAP) is a common infection which is associated with a significant mortality. Shock index, heart rate divided by blood pressure, has been shown to predict mortality in several conditions including sepsis, acute myocardial infarction and traumatic injuries. Very little is known about the prognostic value of shock index in community acquired pneumonia (CAP).

Objective

To examine the usefulness of shock index (SI) and adjusted shock index (corrected to temperature) (ASI) in predicting mortality and hospital length of stay in patients admitted to hospital with CAP.

Methods

A prospective study was conducted in three hospitals in Norfolk & Suffolk, UK. We compared risk of mortality and longer length of stay for low (=<1.0, i.e. heart rate =< systolic BP) and high (> 1.0, i.e. heart rate > systolic BP) SI and ASI adjusting for age, sex and other parameters which have been shown to be associated with mortality in CAP.

Results

A total of 190 patients were included (males = 53%). The age range was 18–101 years (median = 76 years). Patients with SI & ASI > 1.0 had higher likelihood of dying within 6 weeks from admission. The adjusted odds ratio for 30 days mortality were 2.48 (1.04–5.92; p = 0.04) for SI and 3.16 (1.12–8.95; p = 0.03) for ASI. There was no evidence to suggest that they predict longer length of stay.

Conclusion

Both SI and ASI of > 1.0 predict 6 weeks mortality but not longer length of stay in CAP.

Introduction

Community acquired pneumonia (CAP) results in about 83,000 hospital admissions in UK every year [1], [2]. Among those patients who require hospitalisation, the average mortality rate is 12%. However, the mortality in CAP can be as high as 40% in patients who develop sepsis or require intensive care therapy [3].

Early and correct identification of patients at risk of death from CAP remains crucial and several indices have been developed. The CURB-65 score which scores 1 each for confusion, serum urea nitrogen level > 19.6 mg/dL [to convert to millimole per litre, multiply by 0.357 i.e. Urea > 7 mmol/L], respiratory rate  30/min, low blood pressure [< 90 mm Hg systolic or  60 mm Hg diastolic, and age  65 years) (severe pneumonia: ≥3 score) is recommended by the British Thoracic Society in the UK to identify patients at risk of dying from CAP. However, blood pressure is dependent on the cardiac output and the peripheral resistance. Using the blood pressure criterion in the severity assessment of CAP may lead to false negativity in the older people due to high prevalence of systolic hypertension with increasing age.

Shock Index (SI) is the ratio of heart rate to systolic blood pressure [4]. It is a sensitive indicator of left ventricular dysfunction [4]. Despite vital signs that may not appear strikingly abnormal, an elevated SI has been found to be useful in identifying patients requiring hospital admission and/or intensive care therapy [5]. Shock Index has been shown to be inversely related to left ventricular stroke volume in acute circulatory failure [6]. Shock index has also been studied as a marker for significant injury in trauma patients with hypovolaemic shock [7]. SI is a better predictor of 48 hour mortality in victims of blunt injury than either heart rate or systolic blood pressure alone [8].

Shock Index normally ranges from 0.5 to 0.7. In a study looking at healthy blood donors with uncompensated blood volume loss, SI was high after 5 min of giving blood [9]. In predicting rupture of ectopic pregnancy, high SI was found to be more useful than heart rate or blood pressure on its own [10]. In risk stratifying patients with acute pulmonary embolism, SI of ≥1.0, independent of echocardiographic findings, was found to be associated with increased in-hospital mortality [11].

To date, very little is known about Shock index and Adjusted Shock Index (corrected to temperature) (ASI) in predicting mortality in patients admitted to the hospital with CAP.

Our hypothesis is that admission SI and/or ASI may be useful in correctly identifying people with CAP who are at a high risk of dying within 6 weeks and may also be used to predict the length of hospital stay.

Section snippets

Methods

We compiled data of prospective audits of CAP from three UK hospitals: one University Hospital in Central Norfolk with a catchment population of ~ 750,000 (April–August 2008), one district general hospital in West Norfolk with a catchment population of ~ 250,000 (December 2006–Jan 2007), and one large district general hospital in Suffolk with a catchment population of ~ 500,000 (April 2007). We used the standardised definition of CAP, case ascertainment method, inclusion and exclusion criteria and

Results

190 patients with CAP admitted to three UK hospitals were included in the study. There were 100 males (53%). The age range was 18- 101 years (median = 76 years).

The sample characteristics presented in Table 1 compares men and women. The median age among the men was 73.2 years (95% CI: 72.9 to 79.9 years) and that for women was 78.7 years (95% CI: 74 to 83.8 years). The median body temperature was similar between men and women but women had a slightly higher median heart rate. Comparing men to women,

Discussion

We found that both high shock index (SI) and adjusted shock index (ASI) of > 1.0 predict death at 6 weeks with all deaths occurring within 30 days in this population with community acquired pneumonia. There was no evidence to suggest that they predict length of stay (defined as stay greater than median).

The number of patients included in the study is somewhat modest at 190 patients. However, the sample size is comparable with the original validation study of CURB-65 by Lim et al [14].

The clear

Learning points

  • Risk stratifying patients with community-acquired pneumonia is vital in acute care assessment.

  • Shock index and adjusted shock index are easy to derive and they predict 6 weeks mortality in community acquired pneumonia.

Funding

None.

Disclosure/competing interest statement

None.

Author contributions

PKM, SMT, AVK and DNS designed the audit pro-forma. DNS, HR, ACS, PP and PS collected the data. PKM, SMT and AVK verified the data. PM analysed the data. PS and PKM prepared the draft manuscript and all co-authors contributed in writing of the manuscript.

Acknowledgements

We thank the Clinical Audit Departments of Queen Elizabeth Hospital, King's Lynn; Ipswich Hospital, Ipswich; and Respiratory Medicine Department of Norfolk and Norwich University Hospital, Norwich for their help and assistance with the project.

References (22)

  • M.J. Fine et al.

    A prediction rule to identify low-risk patients with community-acquired pneumonia

    N Engl J Med

    (1997)
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