Validating a pragmatic definition of shock in adult patients presenting to the ED

American Journal of Emergency Medicine 32 (2014) 1345–1350 Contents lists available at ScienceDirect American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem Original Contribution Validating a pragmatic definition of shock in adult patients presenting to the ED☆,☆☆ Yan-ling Li, MS a, b, Cangel Pui-yee Chan, PhD a, King-keung Sin, PhD c, Stewart S.W. Chan, MBBS(Syd.) a, Pei-yi Lin, BM b, Xiao-hui Chen, BM b, Brendan E. Smith, MB, ChB d, e, Gavin M. Joynt, BMed f, Colin A. Graham, MD a, Timothy H. Rainer, MD a,⁎ a Accident and Emergency Medicine Academic Unit, The Chinese University of Hong Kong, Hong Kong, China Emergency Department, The Second Affiliated Hospital of Guangzhou Medical University, China c Department of Chemistry, The Hong Kong University of Science and Technology, Hong Kong, China d School of Biomedical Science, Charles Sturt University, Bathurst, New South Wales, Australia e Intensive Care Unit, Bathurst Base Hospital, Bathurst, New South Wales, Australia f Anesthesia and Intensive Care, The Chinese University of Hong Kong, Hong Kong, China b a r t i c l e i n f o Article history: Received 20 June 2014 Accepted 12 August 2014 a b s t r a c t Objective: The importance of the early recognition of shock in patients presenting to emergency departments is well recognized, but at present, there is no agreed practical definition for undifferentiated shock. The main aim of this study was to validate an a priori clinical definition of shock against 28-day mortality. Design, setting and subjects: This prospective, observational, cross-sectional, single-center study was conducted in Hong Kong, China. Data were collected between July 1, 2012, and January 31, 2013. An a priori definition of shock was designed, whereby patients admitted to the resuscitation room or high dependency area of the emergency department were divided into 1 of 3 groups—no shock, possible shock, and shock. The primary outcome was 28-day mortality. Secondary outcomes were in-hospital mortality or admission to the intensive or coronary care unit. Measurements and main results: A total of 111 patients (mean age, 67.2 ± 17.1 years; male = 69 [62%]) were recruited, of which 22 were classified as no shock, 54 as possible shock, and 35 as shock. Systolic blood pressure, mean arterial pressure, lactate, and base deficit correlated well with shock classifications (P b .05). Patients who had 3 or more positively defined shock variables had a 100% poor composite outcome rate (5 of 5). Patients with 2 shock variables had a 66.7% (4 of 6) poor composite outcome rate. Conclusions: A simple, practical definition of undifferentiated shock has been proposed and validated in a group of patients presenting to an emergency department in Hong Kong. This definition needs further validation in a larger population and other settings. © 2014 Elsevier Inc. All rights reserved. 1. Introduction Patients frequently present to emergency departments with critical illness and injury [1]. Shock is a life-threatening emergency that requires urgent and rapid assessment, diagnosis, and treatment [2]. ☆ Funding: None. ☆☆ The name of organization and date of assembly if the article has been presented: The article has been presented in the 2014 International Conference on Emergency Medicine(ICEM) on June 12th. ⁎ Corresponding author. Accident and Emergency Medicine Academic Unit, Chinese University of Hong Kong, Rooms 02C44, Main Clinical Block and Trauma Centre, Prince of Wales Hospital, Shatin, New Territories, Hong Kong. Tel.: +852 2632 1033; fax: +852 2648 1469. E-mail addresses: lylgyey@126.com (Y. Li), cangelchancc@gmail.com (C.P. Chan), willissin@gmail.com (K. Sin), stewart_chan@hotmail.com (S.S.W. Chan), linpeiyi@163.com (P. Lin), cxhgz168@126.com (X. Chen), brendanprivate@hotmail.com (B.E. Smith), gavinmjoynt@cuhk.edu.hk (G.M. Joynt), cagraham@cuhk.edu.hk (C.A. Graham), thrainer@cuhk.edu.hk (T.H. Rainer). http://dx.doi.org/10.1016/j.ajem.2014.08.029 0735-6757/© 2014 Elsevier Inc. All rights reserved. Protocol-driven therapy has the potential to reduce in-hospital mortality for septic shock and other forms of shock from as much as 50% to 10% when compared with standard therapy [3–5]. However, the rapid evaluation, diagnosis of type, and severity categorization of shock in critically ill patients in the emergency department (ED) is at best moderate and often difficult [6,7]. The conceptual qualitative definition of shock is well known, namely, a global insufficiency of tissue perfusion leading to inadequate delivery of oxygen and nutrients to meet the needs of the tissues [8]. However, producing a single, practical, and quantitative definition of shock is not so easy. The absence of a consistent quantitative definition of shock means that emergency patients may often be poorly diagnosed and consequently undertreated. The ability to interpret research findings is also compromised because definitions of shock may vary widely from study to study. Notwithstanding the lack of a single accepted definition, many factors have been shown to correlate with the likelihood and severity of shock, and also with 1346 Y. Li et al. / American Journal of Emergency Medicine 32 (2014) 1345–1350 clinical outcomes such as intensive care unit (ICU) admission and mortality [7,9]. Hypotension, elevated lactate [10], base deficit [11], acidosis [12], and oxygen delivery [13] all correlate with shock. Septic shock has been well studied and is well defined [14,15]. The definitions of sepsis categories into sepsis, severe sepsis and septic shock, were developed on the basis of a number of factors, namely, practicality, knowledge of previously published work, conventional wisdom, and experience. Patients categorized into these defined groups were expected to show differences in outcome, and this was confirmed by progressive increases in mortality rates. The mortality rate from septic shock alone in adults may vary from 10% to 46% in some studies [3,4,16,17]. This practical method of developing definitions could possibly be adapted to develop a more generic quantitative definition of shock. A clear working definition of shock that encompasses all modalities could guide clinical monitoring and treatment in a similar way to those used for sepsis and septic shock and perhaps facilitate more effective research. In this study, a pragmatic, quantitative a priori definition of shock has been proposed. This definition is also based on practicality, previously published work, and the opinion of experienced clinicians. It uses clinical and point-of-care investigations, which are readily available in modern EDs [10,11,18,19]. The primary aim of this study was to validate the a priori definition of shock against 28-day mortality. In addition, we sought to identify other variables that might be useful for diagnosing and assessing shock. 2. Methods Ethical approval was obtained from the Clinical Research Ethics Committee of The Chinese University of Hong Kong to conduct a prospective, single-center study in the ED of the Prince of Wales Hospital, Hong Kong, China. Adult patients older than 18 years, admitted to the resuscitation rooms or emergency high dependency unit on week days between 9:00 AM and 4:00 PM were recruited. This corresponds with patients in ED triage categories 1 (critical), 2 (emergency), or 3 (urgent) out of a 5-point scale, where 1 is the most serious and 5 is the least serious. Our local target is for category 1 cases to be seen by a doctor immediately in the resuscitation room, category 2 to be seen within 15 minutes, and 90% of category 3 cases to be seen within 30 minutes. Written consent was obtained either from the patient or a relative wherever possible. A waiver of consent was applied to patients who, because of confusion or unconsciousness, were unable to give consent, and when a relative was not present. In these cases, consent was sought from the patient or a relative as soon as practically possible. Patients were excluded if they were known to be or suspected of being pregnant, were breastfeeding, or had presentations that were considered to be postseizure, or post-exercise. 2.1. Measurements Patient demographic data included sex, age, ethnicity, height, weight, and comorbidity. Clinical data included respiratory rate, heart rate, systolic and diastolic blood pressure (SBP and DBP), and the presence or absence of a radial pulse and, if present, whether the pulse was bounding, normal, or weak. We also assessed capillary return, peripheral skin temperature, skin color, oxygen saturation, and Glasgow Coma Score. Arterial pressure was measured with an appropriately sized cuff using an oscillometric device (Omron HEM7200 Automatic Blood Pressure Monitor, Omron Healthcare Co, Ltd, Japan). Pulse pressure (SBP-DBP) was calculated from measured variables. Investigations included full blood count, serum creatinine, urea and electrolytes, venous blood gases, blood glucose, electrocardiographs, and chest X-ray. 2.2. Sample size The method we were using has no previous data from which to formulate a sample size calculation, but the information in our study may be useful for future studies and their sample size calculations. 2.3. Definitions Group definitions for shock were derived after literature review and by consensus opinion among those authors (THR, GMJ, BES, SSWC, CAG, and YLL) who are all experienced acute care clinicians. After all patients were recruited, data were divided into 1 of 3 groups based on a priori shock definitions—shock, possible shock, and no shock. Table 1 shows a summary of the definitions of shock, possible shock, and no shock groups. Patients were classified as “no shock” if all of the following criteria were present. 1. There was sign of normal tissue perfusion, that is, normal skin (not mottled); 2. Blood pressure was “normal,” defined as both SBP ≥90 mm Hg, and mean arterial pressure (MAP) ≥ 65 mm Hg [3,20]; and 3. Acid-base status was normal, defined as a lactate level less than 1.5 mmol/L, and a pH N 7.3, and a base deficit of 0 to N−3 mEq/L. Patients were classified as “possible shock” if there was sign of normal tissue perfusion, as defined above, normal blood pressure defined as both SBP ≥90 mm Hg and MAP ≥65 mm Hg, but some degree of abnormal acid-base status defined as either a lactate level of 1.5 to 4.0 mmol/L, or a pH of 7.1 to 7.3, or a base deficit of −3 to −5 mEq/L. Patients were classified as “shock” if any one of the following were present: 1. Evidence of overt sign of tissue hypoperfusion such as mottled skin; or 2. Evidence of an abnormal blood pressure defined as either SBP b 90 mm Hg or MAP b 65 mm Hg; or 3. Evidence of grossly abnormal acid-base status defined as a lactate level ≥4.0 mmol/L, or a pH ≤7.1, or a base deficit of ≤−5 mEq/L. Urine output was not considered as a criterion for the definition of shock in this study because patient stay in the ED was intended to be short. Table 1 A priori definition of shock, possible shock, and no shock Variable Shock Possible shock No shock Shock is present if any ONE of the following are found Shock is possible if ALL of (A + B) are present and any one of C is found Shock is NOT present if ALL of the following are present A. Tissue perfusion Skin Yes No No mottling B. Blood pressure SBP b90 ≥90 ≥90 MAP b65 ≥65 ≥65 C. Acid-base status Lactate ≥4.0 1.5 to b4.0 b1.5 pH ≤7.1 7.1 to 7.3 N7.3 Base ≤−5.0 −3.0 to −5.0 N−3.0 deficit D. Skin temperature When present, shock was further classified according to skin temperature into 1 of 3 groups: • Cold • Warm • Hot 1347 Y. Li et al. / American Journal of Emergency Medicine 32 (2014) 1345–1350 Hypotension is not necessary for the diagnosis of shock, and acidosis can be variable. However, for the purposes of this article, hypotension was defined as either SBP b90 mm Hg or MAP b 65 mm Hg. Metabolic acidosis was defined as either a lactate ≥ 4 mmol/L or a base deficit ≤−5 mmol/L [19–21]. We have used the term cryptic shock for those cases with probable global tissue hypoperfusion but with a SBP ≥ 90 mm Hg. For the purpose of this study, cryptic shock was, thus, defined as a metabolic acidosis in the presence of a normal blood pressure [21], in the absence of genetic, pharmacological, or renal causes for the acidosis. Systemic inflammatory response syndrome (SIRS) was defined as being present when 2 or more of the following 4 standard criteria for SIRS were present: temperature N 38°C or b 36°C; heart rate N90 beat/min; respiratory rate N20 breath/min or PaCO2 b 32 mm Hg (b4.3 kPa); and white blood cell count N12 × 10 9/L, b4 × 10 9/L, or N10% immature forms [22]. 2.4. Outcome measures The primary outcome in this study was 28-day mortality. Secondary outcomes were in-hospital mortality, admission to intensive or coronary care unit (ICCU), or a composite of ICCU admission and 28-day mortality. 2.5. Statistical analysis The data were analyzed using StatView v5.0 (SAS Institute Inc 1998) to calculate medians and interquartile ranges, as well as means and standard deviations. χ 2 tests were used for categorical variables, whereas Kruskal-Wallis tests were used to compare continuous variables. A P ≤ .05 was considered to be significant. 3. Results Between July 1, 2012, and January 31, 2013, 111 cases were recruited. Table 2 shows the baseline characteristics of the study patients categorized by the a priori definition of shock. There were significant differences between groups with regard to mean, SBP and DBP, pulse pressure; presence of SIRS; serum concentrations of creatinine, urea, lactate, and albumin; and base deficit and hemoglobin concentration. Three patients required mechanical ventilation (acute exacerbation of chronic obstructive pulmonary disease, n = 1; motor neurone disease, n = 1; subdural hemorrhage, n = 1), but this was performed after all variables for the a priori definition were collected. Table 3 shows the analysis of shock variables used in the shock definition and shock category. All the categories of the definition criteria correlated significantly with shock category, with the exception of mottled skin and pH. A clinical assessment of the patients’ peripheral temperature, judged by whether it was warm or cold to touch by the ED doctor, was also significantly different across groups. Table 4 shows the criteria for the allocation of each patient to the shock group. Only 12 (34%) of 35 of patients had hypotension (SBP b90 mm Hg and/or MAP b 65 mm Hg). Of these 12, only 4 (33%) were classified as having shock on the basis of acid-base status (lactate ≥ 4 mmol/L and/or base deficit ≤ −5 mEq/L). Of 35 patients, 27 (77%) had lactate ≥4 mmol/L (n = 17) or a base deficit ≤−5 mM/L (n = 16), or a pH ≤ 7.1 (n = 1). Of 35 patients, 23 (66%) had cryptic shock. Table 2 Baseline characteristics (N = 111) by a priori shock definition Variable Age, years, median (IQR) Male sex, no. (%) BMI, kg/m2, median (IQR) Past medical history/comorbidity Hypertension, no. (%) Diabetes mellitus, no. (%) Cancer, no. (%) Hyperlipidemia, no. (%) Observations SBP, mm Hg, median (IQR) DBP, mm Hg, median (IQR) MAP, mm Hg, median (IQR) Pulse pressure, mm Hg, median (IQR) Heart rate, beat/min, median (IQR) Respiratory rate, beat/min, median (IQR) Temperature, °C, median (IQR) Glasgow Coma Score, median (IQR) Clinical findings Capillary return N2 s, no. (%) Abnormal skin color, no. (%)O SIRS present, no. (%) Investigations Creatinine, umol/L, median (IQR) Urea, mmol/L, median (IQR) Lactate, mmol/L, median (IQR) Serum albumin, g/L, median (IQR) Serum glucose, mmol/L, median (IQR) Base deficit, mmol/L, median (IQR) Hemoglobin, g/dL, median (IQR) Interventions Oxygen saturation, SaO2, % a No shock n = 22 73.0 (56.0 to 85.0) 10 (45.5) 21.9 (19.5 to 23.3) 13 (59.1) 5 (22.7) 5 (22.7) 5 (22.7) 146.5 73.0 97.5 64.5 85.5 18.0 36.8 15.0 (119.0 to 168.0) (62.0 to 85.0) (86.3 to 108.7) (57.0 to 104.0) (68.0 to 96.0) (18.0 to 22.0) (36.4 to 37.1) (15.0 to 15.0) 1 (4.6) 2 (9.1) 3 (13.6) Possible shock n =54 70.5 (57.0 to 81.0) 38 (70.4) 23.0 (19.7 to 25.7) 31 (57.4) 13 (24.1) 8 (14.8) 20 (37.0) 137.5 73.0 95.0 61.0 85.0 18.0 36.5 15.0 (120.0 to 159.0) (63.0 to 90.0) (83.3 to 111.7) (49.0 to 79.0) (74.0 to 101.0) (16.0 to 24.0) (36.1 to 37.0) (15.0 to 15.0) 6 (11.2) 5 (10.2) 18 (33.3) 82.0 (63.3 to 103.3) 5.6 (5.3 to 8.4) 1.2 (1.0 to 1.3) 40.0 (34.0 to 44.0) 5.9 (5.4 to 6.9) 0 (−1.0 to 3.0) 12.3 (11.0 to 13.4) 85.0 (71.8 to 117.3) 5.9 (4.2 to 7.8) 2.0 (1.7 to 2.3)c 41.0 (35.5 to 44.5) 7.2 (6.1 to 9.0)c 0 (−2.0 to 1.8) 12.9 (11.0 to 14.7) 99.0 (98.0 to 100.0) 98.0 (97.0 to 99.0) Comparison between no shock and shock groups, P b .05. b Comparison between possible shock and shock groups, P b .05. c Comparison between no shock and possible shock groups, P b .05. ⁎ Statistically significant. O This symbol represents for pale, cyanosed, mottled, red or black skin colour. † Chi-squared test. P† Shock n = 35 66.0 (54.3 to 75.8) 21 (60.0) 22.0 (18.7 to 25.9) 22 11 10 11 125.0 60.0 81.667 59.0 94.0 20.0 36.0 15.0 (62.9) (31.4) (28.6) (31.4) (88.0 (54.0 (65.9 (35.8 (71.3 (16.0 (36.0 (14.2 to to to to to to to to .8767 .6841 .2846 .4761 141.0)ab 70.8)ab 93.6)ab 71.5)a 110.8) 24.0) 37.4) 15.0) 8 (22.9) 8 (22.9) 20 (57.1) 123.0 11.2 3.8 33.0 7.2 −4.5 10.6 .6171 .1208 .4691 (93.3 to 222.5)ab (5.7 to 21.1)ab (1.7 to 4.6)ab (29.0 to 41.8)b (5.3 to 10.4)a (−6.0 to 0.5)ab (9.2 to 12.7)b 98.0 (95.3 to 99.0) .0048⁎ .0006⁎ .0007⁎ .0205⁎ .7574 .9895 .2986 .1674 .1111 .1482 .0031⁎ .0017⁎ .0045⁎ b.0001⁎ .0284⁎ .0542 .0003⁎ .0040 .1049 1348 Y. Li et al. / American Journal of Emergency Medicine 32 (2014) 1345–1350 Table 3 Analysis of shock variables used in the a priori definition and shock category (N = 111) Variables No shock n = 22 Possible shock n =54 Shock n = 35 Pa Mottled skin SBP b90 mm Hg ≥90 mm Hg MAP b65 mm Hg ≥65 mm Hg Lactate ≥4.0 mmol/L 1.5-3.9 mmol/L b1.5 mmol/L pH ≤7.1 7.1-7.3 N7.3 Base deficit ≤−5 mEq/L N−5 to −3 mEq/L N−3 mEq/L Peripheral temperature Normal Cold Warm 0 0 2 .1096 b.0001⁎ 0 22 0 54 10 25 0 22 0 54 8 27 0 0 22 0 54 0 17 10 8 0 0 22 0 1 51 1 3 28 0 0 22 0 10 42 16 2 14 17 5 0 26 27 1 11 19 5 .0001⁎ b.0001⁎ Of 5 shock variables considered for the shock category (SBP b 90 mm Hg, MAP b 65 mm Hg, lactate ≥4 mmol/L, pH ≤ 7.1, base deficit ≤−5 mM/L), 24 (68.6%) patients had only 1 positive shock variable, 6 (17.1%) patients had 2 positive shock variables, 4 (11.4%) patients had 3 positive shock variables, and 1 (2.9%) patient had 4 positive shock variables. Patients who had 3 or more shock variables had a 100% poor composite outcome rate (5 of 5). Those who had 2 shock variables had a 66.7% poor composite outcome rate (4 of 6). Table 5 shows the relationship between shock classification groups, mortality, and ICCU admission. There is an increase in the rate of 28-day mortality, in hospital mortality, ICCU admission, and a composite of ICCU admission and mortality across the shock classification groups no shock to possible shock and to shock. .1603 4. Discussion b.0001⁎ .0022⁎ a χ2 test. ⁎ Statistically significant. This study confirms that in a heterogenous group of 111 urgent and critical patients admitted to the resuscitation room or high dependency unit of an ED, an a priori definition of shock is able to identify patients at higher risk of poor outcomes. The classification and definition are practical, quick, and easy to determine using tests available at the point of care. It has been validated by the greater percentage of cases with poor composite outcome across the shock classification groups, and also by the greater percentage of cases with poor prognosis for ICU admission alone, CCU admission alone, and mortality alone. The a priori definition of shock was derived by a group of senior emergency physicians and intensivists who were familiar with acute critical illness and emergency medicine. Validation was sought firstly by demonstrating a significant relationship between classification Table 4 Individualized patient classification in the shock group (n = 35) Study no. SBP b90 mm Hg MAP b65 mm Hg Lactate ≥4 mmol/L 15 140 141 98 126 145 108 31 49 65 17 130 104 70 79 110 37 75 85 92 95 116 132 133 152 53 72 84 91 97 131 134 146 154 157 Summary total Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y pH ≤7.1 Y Base deficit ≤−5mmol/L Peripheral temperature Composite outcome present Y Hot Cold Warm Cold Hot Cold Cold Cold Cold Warm Warm Cold Cold Cold Hot Warm Hot Cold Warm Cold Warm Cold Cold Hot Warm Cold Warm Cold Cold Warm Cold Warm Cold Cold Warm Hot = 5 Warm = 11 Cold = 19 Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y = 10 n = 25 Y=8 n = 27 Y = 17 n = 18 Y Y=1 n = 34 Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y = 16 n = 19 Y Y Y Y Y Y Y Y Y Y Y Y Y Y = 16 N = 19 1349 Y. Li et al. / American Journal of Emergency Medicine 32 (2014) 1345–1350 groups and individual variables, and secondly, by demonstrating a “dose-response” relationship between the severity of shock according to the classification and the final outcomes, which provides face validity to the proposed a priori definition. Two variables that were included in the classification did not show significant associations with outcome. These were mottled skin and pH. These variables may be a feature of late shock, and such cases may not have been present in this study. For example, the lack of significance of pH in this study may result from an absence of critically ill respiratory cases. Those patients who are most severely ill may not be able to provide a respiratory compensation in response to metabolic acidosis, whereas those patients who are not so ill may be able to increase their minute ventilation, reduce their arterial carbon dioxide tension, and thereby correct their pH back toward normal. Although the results of this study would suggest that it is possible to simplify the definition by removing these 2 variables, we are reluctant to do so at this stage until larger scale studies confirm their irrelevance. Several other factors regarding the population characteristics in this study may be of relevance. This study contained a large proportion of patients with cancer and a low number of respiratory or cardiovascular cases than in other EDs. The high proportion of cancer cases may reflect that fact that until recently, cancer has been the leading cause of death in Hong Kong. Secondly, our hospital is a tertiary referral cancer center, and there is a chronic shortage of cancer beds for early admission of cancer cases in our hospital. The greater degree of anemia in patients with shock was also noted. Hemoglobin is a crucial factor in tissue oxygen delivery and an essential contributing variable in the DO2 equation (DO2 = 1.34 × Hb [g/L] × CO [L/min] × SpO2 [%]). It may have a role in future definitions of shock or as a predictor of outcome. This table raises 2 other important considerations. Both oxygen saturation and cardiac output are vital components of the DO2 equation, which suggests that they should be tested clinically with a view to being included in future definitions of shock. In this study, however, oxygen saturation was not significantly associated with shock. Further studies will be required to evaluate the possible inclusion of cardiac output in an a priori definition of shock, but its role is important and may require further consideration. Emergency physicians in busy departments may be reluctant to measure cardiac output using central, invasive catheters. However, the measurement of cardiac output is important in EDs and should be considered in future studies on shock. Novel, noninvasive, accurate techniques for its assessment may render this more practical [23–25]. Few studies have addressed the definition of shock, especially undifferentiated shock in the emergency setting. Although MAP is frequently used in ICUs for assessing blood pressure [10], in EDs, SBP has been the most popular single variable used by clinicians [7,8,11]. However, there is no agreed criterion for the diagnosis of shock based on SBP, which varies from less than 90 mm Hg to less than 110 mm Hg in published series [18,26,27]. This definition inevitably excludes some patients with occult or nonhypotensive shock where there is significant evidence of tissue hypoperfusion. Both the clinical and research implications for missing the diagnosis of shock are obvious. Shock was diagnosed in most cases based on SBP, MAP, lactate, or base deficit. The higher the number of positive shock criteria, the greater the probability of a poor outcome. Two thirds of patients with 2 variables were ultimately admitted to ICU/CCU or died, whereas those patients with 3 or more variables had a 100% incidence of a poor outcome. It is interesting to note that a single variable such as lactate or base deficit performed better than SBP as a predictor of poor outcome, as SBP is an indirect and unreliable indicator of cardiac output and global perfusion, being affected by chronic drug therapy and other factors [28]. The 28-day mortality correlated well with the shock classification. This study has a number of limitations. First, it is a pragmatic study as there is no “gold standard” for shock with which we can compare our definition. However, this is a study performed in a real-life setting with definitions that correlate well with relevant outcomes. Second, Table 5 Relationship between shock classification groups, mortality, and ICCU admission (N = 111) Outcomes 28-Day mortality No Yes In-hospital mortality No Yes ICCU admission No Yes ICCU or in-hospital mortality No Yes Number No shock n = 22 Possible shock n = 54 Shock n = 35 P† 98 13 22 0 (0%) 50 4 (7.4%) 26 9 (25.7%) .0052⁎ 96 15 21 1 (4.5%) 49 5 (9.3%) 26 9 (25.7%) .0332⁎ 98 15 20 2 (9.1%) 50 4 (7.4%) 26 9 (25.7%) .0378⁎ 83 28 19 3 (13.6%) 46 8 (16.7%) 19 16 (45.7%) .0033⁎ ⁎ Statistically significant. this was a preliminary study, and the sample size was only moderate. Nevertheless, there was a good distribution of cases that would broadly represent the spectrum of severity of diseases in patients presenting to EDs. Third, this was a single-center study and the generalizability of the data cannot be assured. Finally, our lactate levels were venous and may differ from arterial values, although this difference has been measured in the ED and has been shown to be small (average bias, − 0.1 mmol/L; 95% confidence interval, − 0.01 to − 0.37 mmol/L) [29]. A cutoff value of venous lactate of 4 mmol/L was significant and would be useful in clinical practice. Future studies are required to further validate and refine the definitions and to test them in broader ED populations. Testing against other potential standards of tissue perfusion such as oxygen delivery and extraction would also provide further possible factors for inclusion in the shock definition. Invasive and noninvasive hemodynamic methods may help to confirm the definitions and refine assessment in less clear cases. Other strategies might include adding parameters such as DBP, pulse pressure, hemoglobin, serum albumin, urea, creatinine, and glucose. In this study, both DBP and pulse pressure were significantly associated with shock classification and may be worth consideration in future studies. Because the SIRS score is a crude indication of the degree of inflammation, the high proportion of patients with SIRS implies that our population of shocked patients was associated with inflammatory rather than noninflammatory cause and responses, and the relationship between the combination of SIRS, elevated lactate, and poor outcome may require further study. 5. Conclusion A simple, practical definition of undifferentiated shock has been proposed and validated in a group of patients presenting to an ED in Hong Kong. This objective definition of shock has potential to form the basis for clinical decision making and may be particularly useful to provide a similarly objective benchmark for risk stratification in shock-related clinical research. The definition needs further validation in a larger population and other settings. References [1] Hodkinson PW, Wallis LA. Cross-sectional survey of patients presenting to a South African urban emergency centre. Emerg Med J 2009;26(9):635–40. [2] Moranville MP, Mieure KD, Santayana EM. Evaluation and management of shock states: hypovolemic, distributive, and cardiogenic shock. J Pharm Pract 2011;24 (1):44–60. [3] Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B, et al. Early goaldirected therapy in the treatment of severe sepsis and septic shock. N Engl J Med 2001;346:1368–77. 1350 Y. Li et al. / American Journal of Emergency Medicine 32 (2014) 1345–1350 [4] Sebat F, Musthafa AA, Johnson D, Kramer AA, Shoffner D, Eliason M, et al. Effect of a rapid response system for patients in shock on time to treatment and mortality during 5 years. Crit Care Med 2007;35(11):2568–75. [5] Sivayoham N, Rhodes A, Jaiganesh T, van Zyl Smit N, Elkhodhair S, Krishnanandan S. Outcomes from implementing early goal-directed therapy for severe sepsis and septic shock: a 4-year observational cohort study. Eur J Emerg Med 2012;19(4):235–40. [6] van der Vegt AE, Holman M, ter Maaten JC. The value of the clinical impression in recognizing and treating sepsis patients in the emergency department. Eur J Emerg Med 2012;19(6):373–8. [7] Strehlow MC. Early identification of shock in critically ill patients. Emerg Med Clin North Am 2010;28(1):57–66. [8] Graham CA, Parke TR. Critical care in the emergency department: shock and circulatory support. Emerg Med J 2005;22(1):17–21. [9] Thiel SW, Rosini JM, Shannon W, Doherty JA, Micek ST, Kollef MH. Early prediction of septic shock in hospital patients. J Hosp Med 2010;5(1):19–25. [10] Bernardin G, Pradier C, Tiger F, Deloffre P, Mattei M. Blood pressure and arterial lactate level are early indicators of short-term survival in human septic shock. Intensive Care Med 1996;22(1):17–25. [11] Mutschler M, Nienaber U, Brockamp T, Wafaisade A, Fabian T, Paffrath T, et al. Renaissance of base deficit for the initial assessment of trauma patients: a base deficit-based classification for hypovolemic shock developed on data from 16,305 patients derived from the Trauma Register DGU®. Crit Care 2013;17(2):R42. [12] Theerawit P, Kiastboonsri S, Ingsathit A, Tanwanttanathavorn K. Prognostic indicators related to risk of death in shock patients: a new simplified score. Singapore Med J 2011;52(2):81–5. [13] Cohn SM, Nathens AB, Moore FA, Rhee P, Puyana JC, Moore EE, et al. Tissue oxygen saturation predicts the development of organ dysfunction during traumatic shock resuscitation. J Trauma 2007;62(1):44–54. [14] Nguyen HB, Rivers EP, Abrahamian FM, Moran GJ, Abraham E, Trzeciak S, et al. Severe sepsis and septic shock: review of the literature and emergency department management guidelines. Ann Emerg Med 2006;48(1):28–54. [15] Vincent JL. Clinical sepsis and septic shock—Definition, diagnosis and management principles. Langenbecks Arch Surg 2008;393(6):817–24. [16] Riché FC, Dray X, Laisné MJ, Matéo J, Raskine L, Sanson-Le Pors MJ, et al. Factors associated with septic shock and mortality in generalized peritonitis: comparison between community-acquired and postoperative peritonitis. Crit Care 2009;13 (3):R99. [17] Rodríguez F, Barrera L, De La Rosa G, Dennis R, Dueñas C, Granados M, et al. The epidemiology of sepsis in Colombia: a prospective multicenter cohort study in ten university hospitals. Crit Care Med 2011;39(7):1675–82. [18] Westaby S, Kharbanda R, Banning AP. Cardiogenic shock in ACS. Part 1: prediction, presentation and medical therapy. Nat Rev Cardiol 2011;9(3):158–71. [19] Manji RA, Wood KE, Kumar A. The history and evolution of circulatory shock. Crit Care Clin 2009;25:1–29. [20] Dellinger RP, Carlet JM, Masur H, Gerlach H, Calandra T, Cohen J, et al. Surviving Sepsis Campaign guidelines for management of severe sepsis and septic shock. Intensive Care Med 2004;30(4):536–55. [21] Puskarich MA, Trzeciak S, Shapiro NI, Heffner AC, Kline JA, Jones AE, et al. Outcomes of patients undergoing early sepsis resuscitation for cryptic shock compared with overt shock. Resuscitation 2011;82(10):1289–93. [22] Bone RC, Balk RA, Cerra FB, Dellinger RP, Fein AM, Knaus WA, et al. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. The ACCP/SCCM Consensus Conference Committee American College of Chest Physicians/Society of Critical Care Medicine. Chest 1992;101(6):1644–55. [23] Nguyen HB, Banta DP, Stewart G, Kim T, Bansal R, Anholm J. Cardiac index measurements by transcutaneous doppler ultrasound and transthoracic echocardiography in adult and pediatric emergency patients. J Clin Monit Comput 2010;24(3):237–47. [24] Dey I, Sprivulis P. Emergency physicians can reliably assess emergency department patient cardiac output using the USCOM continuous wave Doppler cardiac output monitor. Emerg Med Australas 2005;17(3):193–9. [25] Cattermole GN, Leung PY, Mak PS, Chan SS, Graham CA, Rainer TH. The normal ranges of cardiovascular parameters in children measured using the ultrasonic cardiac output monitor. Crit Care Med 2010;38(9):1875–81. [26] Van Biesen W, Vanholder R, Lameire N. Defining acute renal failure: RIFLE and beyond. Clin J Am Soc Nephrol 2006;1:1314–9. [27] Agrawal A, Gupta A, Consul S, Shastri P. Comparative study of dopamine and norepinephrine in the management of septic shock. Saudi J Anaesth 2011;5(2): 162–6. [28] Callaway DW, Shapiro NI, Donnino MW, Baker C, Rosen CL. Serum lactate and base deficit as predictors of mortality in normotensive elderly blunt trauma patients. J Trauma 2009;66:1040–4. [29] Younger JG, Falk JL, Rothrock SG, Rothrock SG. Relationship between arterial and periperhal venous lactate levels. Acad Emerg Med 1996;3(7):730–3.