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Emergency Medicine Australasia (2014) 26, 223–228
doi: 10.1111/1742-6723.12232
REVIEW ARTICLE
Review article: Shock Index for prediction of critical bleeding post-trauma: A systematic review Alexander OLAUSSEN,1,2 Todd BLACKBURN,3 Biswadev MITRA4,5,6 and Mark FITZGERALD2,6 1 Department of Community Emergency Health and Paramedic Practice, Monash University, Melbourne, Victoria, Australia, 2Trauma Service, The Alfred Hospital, Melbourne, Victoria, Australia, 3Ambulance Victoria, Melbourne, Victoria, Australia, 4Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia, 5Emergency and Trauma Centre, The Alfred Hospital, Melbourne, Victoria, Australia, and 6National Trauma Research Institute, Melbourne, Victoria, Australia
Abstract Early diagnosis of haemorrhagic shock (HS) might be difficult because of compensatory mechanisms. Clinical scoring systems aimed at predicting transfusion needs might assist in early identification of patients with HS. The Shock Index (SI) – defined as heart rate divided by systolic BP – has been proposed as a simple tool to identify patients with HS. This systematic review discusses the SI’s utility post-trauma in predicting critical bleeding (CB). We searched the databases MEDLINE, Embase, CINAHL, Cochrane Library, Scopus and PubMed from their commencement to 1 September 2013. Studies that described an association with SI and CB, defined as at least 4 units of packed red blood cells (pRBC) or whole blood within 24 h, were included. Of the 351 located articles identified by the initial search strategy, five met inclusion criteria. One study pertained to the pre-hospital setting, one to the military, two to the in-hospital setting, and one included analysis of both pre-hospital and inhospital values. The majority of papers assessed predictive properties of the SI in ≥10 units pRBC in the first 24 h. The most frequently suggested optimal SI cut-off was ≥0.9. An association between higher SI and bleeding was
demonstrated in all studies. The SI is a readily available tool and may be useful in predicting CB on arrival to hospital. The evaluation of improved utility of the SI by performing and recording at earlier time-points, including the pre-hospital phase, is indicated. Key words: blood transfusion, haemorrhage, haemorrhagic, shock index, shock, wounds and injuries.
Background Haemorrhagic shock (HS) is the leading cause of preventable deaths following trauma,1 associated with most productive life years lost.2 Despite such epidemic proportions, early identification of HS might be challenging, especially in the pre-hospital environment, both because of varied pathophysiological manifestations3 and physiological compensation.4 It is now recognised that the traditional beliefs surrounding patient presentation in HS (hypotension and tachycardia) do not necessarily present early.5–7 HS has been noted to be both underrecognised8 and delayed in its diagnosis.9 This might lead to undertriage and inappropriate transfers.10,11 Early diagnosis of haemorrhage has been described as the sine qua non for improved outcomes post-injury. 12
Correspondence: Dr Alexander Olaussen, Department of Community Emergency Health and Paramedic Practice, Monash University, McMahons Road, Frankston, Melbourne, VIC 3199, Australia. Email: [email protected] Alexander Olaussen, BEmergHlth, BMedSc (Hons), Research Fellow; Todd Blackburn, BEmergHlth, Research Fellow; Biswadev Mitra, MBBS, MHSM, PhD, FACEM, Associate Professor; Mark Fitzgerald, MBBS, FACEM, Professor, Director. Accepted 5 February 2014
Key findings • The Shock Index is defined as heart rate divided by systolic blood pressure, and consistently elevates in critically bleeding trauma patients. • A Shock Index ≥0.9 following injury can identify patients with massive haemorrhage. • A cut-off of ≥1.0 is simpler to calculate and easily repeatable, both pre- and in-hospital.
Because most patients spend the majority of the ‘golden hour’ prehospital, 13 early detection and management of bleeding are crucial. Accurate early prediction offers opportunities for timely preparation of blood products and forewarning to hospital staff. However, when compared with the in-hospital setting, the pre-hospital setting has less assessment tools, less staff and more external stressors. Therefore, clinical tools in this setting need to be simple and user friendly. Blood loss estimation is notoriously challenging, and consistently reported as unreliable.14,15 When using simulated scenarios, the general error lies in smaller volumes tending to be overestimated and larger volumes tending to be underestimated. 16,17 The inaccuracies persist across the different occupations and level of experience, with no detectable outperformance of emergency physicians versus paramedics,16 or number of years of clinical experience.15,16 Interestingly, when providing the operator with haemodynamic unstable
© 2014 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine
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parameters, the estimates are driven upwards.16 One proposed method for improving the accuracy is the MAR method, which involves the use of the anterior surface of a clenched fist to equate to 20 mL.18 Although this improved the accuracy, blood loss estimates still remain vastly inaccurate, and therefore potentially useless. Early prediction of the need for large volumes of transfusion might help preparation for trauma reception and resuscitation. It has been generally accepted that a transfusion requirement of over 4 units of packed red blood cells, or half of an average person’s blood volume, is a clinically important threshold. Tools to predict such amounts of transfusion requirement have generally used a measure of massive transfusion (MT) as the outcome. 19 Many of these scoring systems are complicated and involve results from pathology tests and imaging. They are therefore often too time consuming for calculation inhospital and not practical for use in the pre-hospital phase. At the other spectrum, the use of BP and heart rate (HR) alone are simple, but their predictive values when used alone are often inaccurate.7 The Shock Index (SI), defined as HR divided by systolic BP (SBP) was first presented by Allgöwer and Burri20 in 1967 and in healthy adults, ranging from 0.5 to 0.7.21 Although the SI was popular in the 1980s, its use was reduced because of improved rescue times.22 However, its simplicity has attracted recent attention.23 Further described attractive features of the SI are its use in polytrauma,22 potentially great inter-observer reliability23 and ability to assess the haemodynamic status unaffected by compensation.24,25 A recent systematic review found the SI to be the only clinical sign consistently associated with blood loss, when compared with any of the traditional vital signs.6 Following injury, a higher SI has been associated with higher mortality,26–28 and injury severity,27,29 predicting which organ system is likely to fail22 and for specific injuries (e.g. isolated ballistic battlefield torso trauma).30 The SI has also been used as a predictor for length of hospital stay,28,31 number of ventilator days,31 left ventricular perfor-
mance 32 and likelihood of ICU admission.33 Additionally, numerous reports on the SI and any amount of blood transfused or the need for haemostatic interventions exist. 27,30,34 However, less is known about the SI’s ability to predict CB. The aims of this review were to: (i) review the available evidence on the SI’s utility in predicting CB posttrauma; and (ii) discuss the cut-off at which the SI could be considered abnormal both in the pre-hospital and the in-hospital setting.
Methods Information sources We searched six databases (Embase, MEDLINE, CINAHL, Scopus, PubMed and the Cochrane Library) from their commencement to the start of September 2013. We pooled the terms for haemorrhage (‘haemorrhage’ OR ‘hemorrhage’ OR ‘haemorrhagic shock’ OR ‘hemorrhagic shock’) combined with trauma (OR injuries OR wounds). ‘Shock Index’ and ‘SI’ had to be treated as text words. Last, we combined the search with ‘transfusion’ (transfusion, OR blood transfusion OR massive transfusion). We subsequently checked related reference lists. All studies detailing transfusion post-injury with data on the SI were included. Two blinded authors (AO and TB) extracted relevant articles.
Patients Adult trauma patients (age ≥16 years) in the resuscitation phase.
Exposure Determination of the SI.
Outcome Critical bleeding (CB), defined in our review as at least 4 units of either packed red blood cells or whole blood within a maximum of 24 h (≥4/24 h).
Data collection We extracted descriptive data about study size, number and demographics of patients in each study, arm and transfusion practice. Values of SI re-
ported and their association with CB were extracted.
Results The search yielded 351 articles, of which five met the inclusion criteria (Fig. 1). All studies, except Hagiwara et al.’s8 were retrospective in nature (Table 1). There were two studies that analysed the value of a pre-hospital SI for predicting CB. Mitra et al.23 reported a pre-hospital SI ≥1.0 after at least 1 L of fluid to have a specificity and sensitivity of 90.5% and 47.9%, respectively, for predicting ≥5/4 h. Vandromme et al.35 grouped their cohort into six categories based on SI. A SI >0.9– 1.1 had an estimated risk ratio (RR) of 1.61 (95% CI 1.13–2.31) for MT (≥10/24 h). When the cut-off was elevated to >1.1–1.3, the RR increased to 5.57 (95% CI 3.74–8.30). Vandromme et al.35 also investigated the SI at arrival to their ED. Within the same groups as above, the RR was higher for prediction of MT (≥10/ 24 h) when the SI was measured inhospital; for SI >0.9–1.1, the RR for MT was 3.49 (95% CI 2.34–5.20), and for SI >1.1–1.3, the RR for MT was 9.67 (95% CI 6.09–15.36). Mutschler et al.37 proposed four new groups of shock on arrival to hospital, depending on the SI: 0.9–1.1: RR (95% CI) = 1.61 (1.13–2.31) >1.1–1.3: RR (95% CI) = 5.57 (3.74–8.30) MT: SI 1.1 ± 0.4 No MT: SI 0.9 ± 0.5 SI ≥ 1.0–1.4: 31% MT SI ≥ 1.4: 57% MT >0.9–1.1: RR (95% CI) = 3.49 (2.34–5.20) >1.1–1.3: RR (95% CI) = 9.67 (6.09–15.36) MT: mean SI 1.05 ± 0.58 No MT: mean SI 0.64 ± 0.21 MT: SI at 1 L: 1.1 ± 0.6 No MT: SI at 1 L: 0.7 ± 0.2 4.3 NA‡ 13.2 3.4 ≥5Ø in 4 h ≥10Ø in 24 h Australia USA Mitra et al.23 Vandromme et al.35 Pre-hospital
1419 8111
MT % Country Author Setting
TABLE 1.
Descriptions of the included studies
Sample size
Critical bleeding definition
Penetrating injury %
Shock Index
A OLAUSSEN ET AL.
mines43 and more peripheral vascular disease compared with their younger counterparts.21 Additionally, hypertension – which affects 21.5% of Australians44 – deems a drop in SBP (e.g. ≥30 mmHg) more clinically relevant than a specific cut-off.45 Lastly, coronary interventions, such as betablockade, pacemakers and heart transplants, impede compensation and will skew the presentation towards less shocked.46 Athletes have a lower normal resting HR. Therefore values above 90/min or even 80/min47 have been suggested to equal tachycardia. Furthermore, top athletes have an increase in their blood volume, cardiac output and stroke volume, which should be remembered when assessing the circulation.43 Other groups to be aware of are the pregnant and those under influence of substances. The present study was limited in including primary retrospective analyses and in its inability to perform a meta-analysis given the heterogeneity among the definitions of SI and CB. We acknowledged that an unwise meta-analysis could lead to highly misleading conclusions. The lack of a universal definition for clinically important haemorrhage was highlighted with the commonest definition being (≥10/ 24 h). However, this definition has been argued to be inappropriate because it: (i) potentially introduce survival bias by missing early deaths; and (ii) include patients that are not in acute need of transfusion.48 A recent multicentre review of three Australian hospitals concluded that ≥5/4 h was the most sensitive definition for CB, but that ≥10/24 h also captured an important cohort.49 Our inclusion criteria of ≥4 units in the first 24 h was therefore potentially overly inclusive. However, this kind of sensitivity is desirable in disease identification, especially when using a tool as simple as the SI. This review was based on single SI recordings, which is a limitation given the extreme and potentially sinusoidal behaviour of vital signs immediately post-injury.
Conclusions The SI being simple and repeatable, appears to be useful in predicting CB.
© 2014 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine
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SHOCK INDEX FOR CRITICAL BLEEDING
Recommendations for the ideal cutoff were varied, with most studies using a cut-off of ≥0.9. However, the cut-off of ≥1.0 was observed to have higher specificity and might be simpler to calculate, in particular, for prehospital personnel. Prospective validation of the SI in the pre-hospital phase to predict CB, using appropriate definitions, is required.
8.
9.
Author contributions All authors have contributed to the conception and design, article drafting and revision for intellectual input. All authors have approved the final version submitted herein.
10.
11.
Competing interests None declared.
References 1. Gruen RL, Brohi K, Schreiber M et al. Haemorrhage control in severely injured patients. Lancet 2012; 380: 1099–108. 2. Kauvar DS, Lefering R, Wade CE. Impact of hemorrhage on trauma outcome: an overview of epidemiology, clinical presentations, and therapeutic considerations. J. Trauma 2006; 60: S3–11. 3. Harbrecht B, Forsythe R, Peitzman A. Management of shock. In: Feliciano D, Mattox K, Moore E, eds. Trauma, 6th edn. New York: McGraw-Hill Medical, 2008; 213– 34. 4. Dunjey S. Shock. In: Fulde GWO, ed. Emergency Medicine: The Principles of Practice, 5th edn. Sydney: Elsevier Churchill Livingstone, 2009; 158–66. 5. Parks JK, Elliott AC, Gentilello LM, Shafi S. Systemic hypotension is a late marker of shock after trauma: a validation study of Advanced Trauma Life Support principles in a large national sample. Am. J. Surg. 2006; 192: 727–31. 6. Pacagnella R, Souza J, Durocher J et al. A systematic review of the relationship between blood loss and clinical signs. PLoS ONE 2013; 8: e57594. 7. Guly HR, Bouamra O, Spiers M et al. Vital signs and estimated blood loss
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in patients with major trauma: testing the validity of the ATLS classification of hypovolaemic shock. Resuscitation 2011; 82: 556–9. Hagiwara A, Kimura A, Kato H et al. Hemodynamic reactions in patients with hemorrhagic shock from blunt trauma after initial fluid therapy. J. Trauma 2010; 69: 1161–8. Mackersie RC, Dicker RA. Pitfalls in the evaluation and management of the trauma patient. Curr. Probl. Surg. 2007; 44: 778–833. Haas B, Gomez D, Zagorski B, Stukel TA, Rubenfeld GD, Nathens AB. Survival of the fittest: the hidden cost of undertriage of major trauma. J. Am. Coll. Surg. 2010; 211: 804–11. Sampalis JS, Denis R, Frechette P, Brown R, Fleiszer D, Mulder D. Direct transport to tertiary trauma centers versus transfer from lower level facilities: impact on mortality and morbidity among patients with major trauma. J. Trauma 1997; 43: 288–96. Larson CR, White CE, Spinella PC et al. Association of shock, coagulopathy, and initial vital signs with massive transfusion in combat casualties. J. Trauma 2010; 69: S26– 32. Evans JA, van Wessem KJ, McDougall D, Lee KA, Lyons T, Balogh ZJ. Epidemiology of traumatic deaths: comprehensive population-based assessment. World J. Surg. 2010; 34: 158–63. Ashburn JC, Harrison T, Ham JJ, Strote J. Emergency physician estimation of blood loss. West. J. Med. 2012; 13: 376–9. Patton K, Funk D, McErlean M, Bartfield J. Accuracy of estimation of external blood loss by EMS personnel. J. Trauma 2001; 50: 914– 6. Frank M, Schmucker U, Stengel D et al. Proper estimation of blood loss on scene of trauma: tool or tale? J. Trauma 2010; 69: 1191–5. Williams B, Boyle M. Estimation of external blood loss by paramedics: is there any point? Prehosp. Disaster Med. 2007; 22: 502–6. Merlin MA, Alter SM, Raffel B, Pryor PW 2nd. External blood loss estimation using the MAR method. Am. J. Emerg. Med. 2009; 27: 1085– 90.
19. Burman S, Cotton BA. Trauma patients at risk for massive transfusion: the role of scoring systems and the impact of early identification on patient outcomes. Expert Rev. Hematol. 2012; 5: 211–8. 20. Allgöwer M, Burri C. Shock index. Dtsch. Med. Wochenschr. 1967; 92: 1947–50. 21. Otero R, Bryant Nguyen H, Rivers E. approach to the patient in shock. In: Tintinalli J, Cline D, eds. Tintinalli’s Emergency Medicine Manual, 7th edn. New York: McGraw-Hill Medical, 2012; 165– 72. 22. Grimme K, Pape HC, Probst C et al. Calculation of different triage scores based on the German trauma registry. Eur. J. Trauma 2005; 31: 480– 7. 23. Mitra B, Fitzgerald M, Chan J. The utility of a shock index ≥1 as an indication for pre-hospital oxygen carrier administration in major trauma. Injury 2013; 45: 61–5. 24. Birkhahn RH, Gaeta TJ, Terry D, Bove JJ, Tloczkowski J. Shock index in diagnosing early acute hypovolemia. Am. J. Emerg. Med. 2005; 23: 323–6. 25. Rady M, Smithline H, Blake H, Nowak R. A comparison of the shock index and conventional vital signs to identify acute, critical illness in the emergency department. Ann. Emerg. Med. 1994; 24: 685–90. 26. Cannon CM, Braxton CC, Kling-Smith M, Mahnken JD, Carlton E, Moncure M. Utility of the shock index in predicting mortality in traumatically injured patients. J. Trauma 2009; 67: 1426–30. 27. King R, Plewa M, Fenn N, Knotts F. Shock index as a marker for significant injury in trauma patients. Acad. Emerg. Med. 1996; 3: 1041–5. 28. Newgard CD, Rudser K, Hedges JR et al. A critical assessment of the outof-hospital trauma triage guidelines for physiologic abnormality. J. Trauma 2010; 68: 452–62. 29. Paladino L, Subramanian RA, Nabors S, Sinert R. The utility of shock index in differentiating major from minor injury. Eur. J. Emerg. Med. 2011; 18: 94–8. 30. Morrison JJ, Dickson EJ, Jansen JO, Midwinter MJ. Utility of admission physiology in the surgical triage of
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isolated ballistic battlefield torso trauma. J. Emerg. Trauma Shock 2012; 5: 233–7. McNab A, Burns B, Bhullar I, Chesire D, Kerwin A. A prehospital shock index for trauma correlates with measures of hospital resource use and mortality. Surgery 2012; 152: 473– 6. Rady MY, Nightingale P, Little RA, Edwards D. Shock index: a reevaluation in acute circulatory failure. Resuscitation 1992; 23: 227–34. 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: 460– 5. Demuro JP, Simmons S, Jax J, Gianelli SM. Application of the shock index to the prediction of need for hemostasis intervention. Am. J. Emerg. Med. 2013; 31: 1260–3. Vandromme MJ, Griffin RL, Kerby JD, McGwin G Jr, Rue LW 3rd, Weinberg JA. Identifying risk for massive transfusion in the relatively normotensive patient: utility of the prehospital shock index. J. Trauma 2011; 70: 384–90. Cancio LC, Wade CE, West SA, Holcomb JB. Prediction of mortality and of the need for massive transfusion in casualties arriving at combat support hospitals in Iraq. J. Trauma 2008; 64: S51–5.
37. Mutschler M, Nienaber U, Munzberg M et al. The shock index revisited – a fast guide to transfusion requirement? A retrospective analysis on 21,853 patients derived from the TraumaRegister DGU®. Crit. Care 2013; 17: R172. 38. Davis JW, Davis IC, Bennink LD, Bilello JF, Kaups KL, Parks SN. Are automated blood pressure measurements accurate in trauma patients? J. Trauma 2003; 55: 860–3. 39. Chen L, Reisner AT, Gribok A, Reifman J. Exploration of prehospital vital sign trends for the prediction of trauma outcomes. Prehosp. Emerg. Care 2009; 13: 286–94. 40. McNab A, Burns B, Bhullar I, Chesire D, Kerwin A. An analysis of shock index as a correlate for outcomes in trauma by age group. Surgery 2013; 154: 384–7. 41. Zarzaur BL, Croce MA, Fischer PE, Magnotti LJ, Fabian TC. New vitals after injury: shock index for the young and age × shock index for the old. J. Surg. Res. 2008; 147: 229– 36. 42. Salotollo K, Mains CW, Offner PJ, Bourg PW, Bar-Or D. A retrospective analysis of geriatric trauma patients: venous lactate is a better predictor of mortality than traditional vital signs. Scand. J. Trauma Resusc. Emerg. Med. 2013; 21: 7. 43. American College of Surgeons, Committee on Trauma. ATLS, Advanced
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Trauma Life Support for Doctors, 8th edn. Chicago: American College of Surgeons, 2008. Australian Bureau of Statistics. National health survey: first results, 2011-12 (4364.0). October 2012. Garrett P. Shock overview. In: Cameron P, Jelinek G, Kelly A, Murray L, Brown A, eds. Textbook of Adult Emergency Medicine, 3rd edn. Edinburgh and New York: Churchill Livingstone Elsevier, 2009; 45–56. Neideen T, Lam M, Brasel KJ. Preinjury beta blockers are associated with increased mortality in geriatric trauma patients. J. Trauma 2008; 65: 1016–20. Walker G. Resuscitation/shock/fluids. In: Shah K, Egan D, Quaas J, eds. Essential Emergency Trauma. Philadelphia: Wolters Kluwer Health, 2011; 8–12. Mitra B, Cameron PA, Gruen RL, Mori A, Fitzgerald M, Street A. The definition of massive transfusion in trauma: a critical variable in examining evidence for resuscitation. Eur. J. Emerg. Med. 2011; 18: 137–42. Zatta AJ, McQuilten ZK, Mitra B et al. Impact of massive transfusion definitions on critical bleeding event capture and outcomes. Vox Sang. 2012; 103: 29.
© 2014 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine
Emergency Medicine Australasia (2014) 26, 223–228
doi: 10.1111/1742-6723.12232
REVIEW ARTICLE
Review article: Shock Index for prediction of critical bleeding post-trauma: A systematic review Alexander OLAUSSEN,1,2 Todd BLACKBURN,3 Biswadev MITRA4,5,6 and Mark FITZGERALD2,6 1 Department of Community Emergency Health and Paramedic Practice, Monash University, Melbourne, Victoria, Australia, 2Trauma Service, The Alfred Hospital, Melbourne, Victoria, Australia, 3Ambulance Victoria, Melbourne, Victoria, Australia, 4Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia, 5Emergency and Trauma Centre, The Alfred Hospital, Melbourne, Victoria, Australia, and 6National Trauma Research Institute, Melbourne, Victoria, Australia
Abstract Early diagnosis of haemorrhagic shock (HS) might be difficult because of compensatory mechanisms. Clinical scoring systems aimed at predicting transfusion needs might assist in early identification of patients with HS. The Shock Index (SI) – defined as heart rate divided by systolic BP – has been proposed as a simple tool to identify patients with HS. This systematic review discusses the SI’s utility post-trauma in predicting critical bleeding (CB). We searched the databases MEDLINE, Embase, CINAHL, Cochrane Library, Scopus and PubMed from their commencement to 1 September 2013. Studies that described an association with SI and CB, defined as at least 4 units of packed red blood cells (pRBC) or whole blood within 24 h, were included. Of the 351 located articles identified by the initial search strategy, five met inclusion criteria. One study pertained to the pre-hospital setting, one to the military, two to the in-hospital setting, and one included analysis of both pre-hospital and inhospital values. The majority of papers assessed predictive properties of the SI in ≥10 units pRBC in the first 24 h. The most frequently suggested optimal SI cut-off was ≥0.9. An association between higher SI and bleeding was
demonstrated in all studies. The SI is a readily available tool and may be useful in predicting CB on arrival to hospital. The evaluation of improved utility of the SI by performing and recording at earlier time-points, including the pre-hospital phase, is indicated. Key words: blood transfusion, haemorrhage, haemorrhagic, shock index, shock, wounds and injuries.
Background Haemorrhagic shock (HS) is the leading cause of preventable deaths following trauma,1 associated with most productive life years lost.2 Despite such epidemic proportions, early identification of HS might be challenging, especially in the pre-hospital environment, both because of varied pathophysiological manifestations3 and physiological compensation.4 It is now recognised that the traditional beliefs surrounding patient presentation in HS (hypotension and tachycardia) do not necessarily present early.5–7 HS has been noted to be both underrecognised8 and delayed in its diagnosis.9 This might lead to undertriage and inappropriate transfers.10,11 Early diagnosis of haemorrhage has been described as the sine qua non for improved outcomes post-injury. 12
Correspondence: Dr Alexander Olaussen, Department of Community Emergency Health and Paramedic Practice, Monash University, McMahons Road, Frankston, Melbourne, VIC 3199, Australia. Email: [email protected] Alexander Olaussen, BEmergHlth, BMedSc (Hons), Research Fellow; Todd Blackburn, BEmergHlth, Research Fellow; Biswadev Mitra, MBBS, MHSM, PhD, FACEM, Associate Professor; Mark Fitzgerald, MBBS, FACEM, Professor, Director. Accepted 5 February 2014
Key findings • The Shock Index is defined as heart rate divided by systolic blood pressure, and consistently elevates in critically bleeding trauma patients. • A Shock Index ≥0.9 following injury can identify patients with massive haemorrhage. • A cut-off of ≥1.0 is simpler to calculate and easily repeatable, both pre- and in-hospital.
Because most patients spend the majority of the ‘golden hour’ prehospital, 13 early detection and management of bleeding are crucial. Accurate early prediction offers opportunities for timely preparation of blood products and forewarning to hospital staff. However, when compared with the in-hospital setting, the pre-hospital setting has less assessment tools, less staff and more external stressors. Therefore, clinical tools in this setting need to be simple and user friendly. Blood loss estimation is notoriously challenging, and consistently reported as unreliable.14,15 When using simulated scenarios, the general error lies in smaller volumes tending to be overestimated and larger volumes tending to be underestimated. 16,17 The inaccuracies persist across the different occupations and level of experience, with no detectable outperformance of emergency physicians versus paramedics,16 or number of years of clinical experience.15,16 Interestingly, when providing the operator with haemodynamic unstable
© 2014 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine
224
A OLAUSSEN ET AL.
parameters, the estimates are driven upwards.16 One proposed method for improving the accuracy is the MAR method, which involves the use of the anterior surface of a clenched fist to equate to 20 mL.18 Although this improved the accuracy, blood loss estimates still remain vastly inaccurate, and therefore potentially useless. Early prediction of the need for large volumes of transfusion might help preparation for trauma reception and resuscitation. It has been generally accepted that a transfusion requirement of over 4 units of packed red blood cells, or half of an average person’s blood volume, is a clinically important threshold. Tools to predict such amounts of transfusion requirement have generally used a measure of massive transfusion (MT) as the outcome. 19 Many of these scoring systems are complicated and involve results from pathology tests and imaging. They are therefore often too time consuming for calculation inhospital and not practical for use in the pre-hospital phase. At the other spectrum, the use of BP and heart rate (HR) alone are simple, but their predictive values when used alone are often inaccurate.7 The Shock Index (SI), defined as HR divided by systolic BP (SBP) was first presented by Allgöwer and Burri20 in 1967 and in healthy adults, ranging from 0.5 to 0.7.21 Although the SI was popular in the 1980s, its use was reduced because of improved rescue times.22 However, its simplicity has attracted recent attention.23 Further described attractive features of the SI are its use in polytrauma,22 potentially great inter-observer reliability23 and ability to assess the haemodynamic status unaffected by compensation.24,25 A recent systematic review found the SI to be the only clinical sign consistently associated with blood loss, when compared with any of the traditional vital signs.6 Following injury, a higher SI has been associated with higher mortality,26–28 and injury severity,27,29 predicting which organ system is likely to fail22 and for specific injuries (e.g. isolated ballistic battlefield torso trauma).30 The SI has also been used as a predictor for length of hospital stay,28,31 number of ventilator days,31 left ventricular perfor-
mance 32 and likelihood of ICU admission.33 Additionally, numerous reports on the SI and any amount of blood transfused or the need for haemostatic interventions exist. 27,30,34 However, less is known about the SI’s ability to predict CB. The aims of this review were to: (i) review the available evidence on the SI’s utility in predicting CB posttrauma; and (ii) discuss the cut-off at which the SI could be considered abnormal both in the pre-hospital and the in-hospital setting.
Methods Information sources We searched six databases (Embase, MEDLINE, CINAHL, Scopus, PubMed and the Cochrane Library) from their commencement to the start of September 2013. We pooled the terms for haemorrhage (‘haemorrhage’ OR ‘hemorrhage’ OR ‘haemorrhagic shock’ OR ‘hemorrhagic shock’) combined with trauma (OR injuries OR wounds). ‘Shock Index’ and ‘SI’ had to be treated as text words. Last, we combined the search with ‘transfusion’ (transfusion, OR blood transfusion OR massive transfusion). We subsequently checked related reference lists. All studies detailing transfusion post-injury with data on the SI were included. Two blinded authors (AO and TB) extracted relevant articles.
Patients Adult trauma patients (age ≥16 years) in the resuscitation phase.
Exposure Determination of the SI.
Outcome Critical bleeding (CB), defined in our review as at least 4 units of either packed red blood cells or whole blood within a maximum of 24 h (≥4/24 h).
Data collection We extracted descriptive data about study size, number and demographics of patients in each study, arm and transfusion practice. Values of SI re-
ported and their association with CB were extracted.
Results The search yielded 351 articles, of which five met the inclusion criteria (Fig. 1). All studies, except Hagiwara et al.’s8 were retrospective in nature (Table 1). There were two studies that analysed the value of a pre-hospital SI for predicting CB. Mitra et al.23 reported a pre-hospital SI ≥1.0 after at least 1 L of fluid to have a specificity and sensitivity of 90.5% and 47.9%, respectively, for predicting ≥5/4 h. Vandromme et al.35 grouped their cohort into six categories based on SI. A SI >0.9– 1.1 had an estimated risk ratio (RR) of 1.61 (95% CI 1.13–2.31) for MT (≥10/24 h). When the cut-off was elevated to >1.1–1.3, the RR increased to 5.57 (95% CI 3.74–8.30). Vandromme et al.35 also investigated the SI at arrival to their ED. Within the same groups as above, the RR was higher for prediction of MT (≥10/ 24 h) when the SI was measured inhospital; for SI >0.9–1.1, the RR for MT was 3.49 (95% CI 2.34–5.20), and for SI >1.1–1.3, the RR for MT was 9.67 (95% CI 6.09–15.36). Mutschler et al.37 proposed four new groups of shock on arrival to hospital, depending on the SI: 0.9–1.1: RR (95% CI) = 1.61 (1.13–2.31) >1.1–1.3: RR (95% CI) = 5.57 (3.74–8.30) MT: SI 1.1 ± 0.4 No MT: SI 0.9 ± 0.5 SI ≥ 1.0–1.4: 31% MT SI ≥ 1.4: 57% MT >0.9–1.1: RR (95% CI) = 3.49 (2.34–5.20) >1.1–1.3: RR (95% CI) = 9.67 (6.09–15.36) MT: mean SI 1.05 ± 0.58 No MT: mean SI 0.64 ± 0.21 MT: SI at 1 L: 1.1 ± 0.6 No MT: SI at 1 L: 0.7 ± 0.2 4.3 NA‡ 13.2 3.4 ≥5Ø in 4 h ≥10Ø in 24 h Australia USA Mitra et al.23 Vandromme et al.35 Pre-hospital
1419 8111
MT % Country Author Setting
TABLE 1.
Descriptions of the included studies
Sample size
Critical bleeding definition
Penetrating injury %
Shock Index
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mines43 and more peripheral vascular disease compared with their younger counterparts.21 Additionally, hypertension – which affects 21.5% of Australians44 – deems a drop in SBP (e.g. ≥30 mmHg) more clinically relevant than a specific cut-off.45 Lastly, coronary interventions, such as betablockade, pacemakers and heart transplants, impede compensation and will skew the presentation towards less shocked.46 Athletes have a lower normal resting HR. Therefore values above 90/min or even 80/min47 have been suggested to equal tachycardia. Furthermore, top athletes have an increase in their blood volume, cardiac output and stroke volume, which should be remembered when assessing the circulation.43 Other groups to be aware of are the pregnant and those under influence of substances. The present study was limited in including primary retrospective analyses and in its inability to perform a meta-analysis given the heterogeneity among the definitions of SI and CB. We acknowledged that an unwise meta-analysis could lead to highly misleading conclusions. The lack of a universal definition for clinically important haemorrhage was highlighted with the commonest definition being (≥10/ 24 h). However, this definition has been argued to be inappropriate because it: (i) potentially introduce survival bias by missing early deaths; and (ii) include patients that are not in acute need of transfusion.48 A recent multicentre review of three Australian hospitals concluded that ≥5/4 h was the most sensitive definition for CB, but that ≥10/24 h also captured an important cohort.49 Our inclusion criteria of ≥4 units in the first 24 h was therefore potentially overly inclusive. However, this kind of sensitivity is desirable in disease identification, especially when using a tool as simple as the SI. This review was based on single SI recordings, which is a limitation given the extreme and potentially sinusoidal behaviour of vital signs immediately post-injury.
Conclusions The SI being simple and repeatable, appears to be useful in predicting CB.
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Recommendations for the ideal cutoff were varied, with most studies using a cut-off of ≥0.9. However, the cut-off of ≥1.0 was observed to have higher specificity and might be simpler to calculate, in particular, for prehospital personnel. Prospective validation of the SI in the pre-hospital phase to predict CB, using appropriate definitions, is required.
8.
9.
Author contributions All authors have contributed to the conception and design, article drafting and revision for intellectual input. All authors have approved the final version submitted herein.
10.
11.
Competing interests None declared.
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