Shock index in diagnosing early acute hypovolemia

Automated prediction of early blood transfusion and mortality in trauma patients

BACKGROUND

Prediction of blood transfusion needs and mortality for trauma patients in near real time is an unrealized goal. We hypothesized that analysis of pulse oximeter signals could predict blood transfusion and mortality as accurately as conventional vital signs (VSs).

METHODS

Continuous VS data were recorded for direct admission trauma patients with abnormal prehospital shock index (SI = heart rate [HR] / systolic blood pressure) greater than 0.62. Predictions of transfusion during the first 24 hours and in-hospital mortality using logistical regression models were compared with DeLong's method for areas under receiver operating characteristic curves (AUROCs) to determine the optimal combinations of prehospital SI and HR, continuous photoplethysmographic (PPG), oxygen saturation (SpO2), and HR-related features.

RESULTS

We enrolled 556 patients; 37 received blood within 24 hours; 7 received more than 4 U of red blood cells in less than 4 hours or "massive transfusion" (MT); and 9 died. The first 15 minutes of VS signals, including prehospital HR plus continuous PPG, and SpO2 HR signal analysis best predicted transfusion at 1 hour to 3 hours, MT, and mortality (AUROC, 0.83; p < 0.03) and no differently (p = 0.32) from a model including blood pressure. Predictions of transfusion based on the first 15 minutes of data were no different using 30 minutes to 60 minutes of data collection. SI plus PPG and SpO2 signal analysis (AUROC, 0.82) predicted 1-hour to 3-hour transfusion, MT, and mortality no differently from pulse oximeter signals alone.

CONCLUSION

Pulse oximeter features collected in the first 15 minutes of our trauma patient resuscitation cohort, without user input, predicted early MT and mortality in the critical first hours of care better than the currently used VS such as combinations of HR and systolic blood pressure or prehospital SI alone.

LEVEL OF EVIDENCE

Therapeutic/prognostic study, level II.

Haemostasis. Part 1: The management of post-extraction haemorrhage

The management of bleeding complications following a dental extraction is an essential skill for the dental practitioner. Extractions are often carried out on patients with complex medical histories and a long list of medications. This paper aims to help the clinician manage post-extraction haemorrhage. A review of the management of patients on anti-thrombotic medications will be covered in a subsequent paper.

CLINICAL RELEVANCE

This article reviews the management of haemorrhage following tooth extraction; from the risk assessment of any underlying medical conditions and medications, to the clinical techniques used to control bleeding following an extraction.

Shock index predicts mortality in geriatric trauma patients: an analysis of the National Trauma Data Bank

BACKGROUND

Heart rate and systolic blood pressure are unreliable in geriatric trauma patients. Shock index (SI) (heart rate/systolic blood pressure) is a simple marker of worse outcomes after injury. The aim of this study was to assess the utility of SI in predicting outcomes. We hypothesized that SI predicts mortality in geriatric trauma patients.

METHODS

We performed a 4-year (2007-2010) retrospective analysis using the National Trauma Data Bank. Patients 65 years or older were included. Transferred patients, patients dead on arrival, missing vitals on presentation, and patients with burns and traumatic brain injury were excluded. A cutoff value of SI greater than or equal to 1 (sensitivity, 81%; specificity, 79%) was used to define hemodynamic instability. The primary outcome measure was mortality. Secondary outcome measures were need for blood transfusion, need for exploratory laparotomy, and development of in-hospital complications. Multiple logistic regressions were performed.

RESULTS

A total of 485,595 geriatric patients were reviewed, of whom 217,190 were included. The mean (SD) age was 77.7 (7.1) years, 60% were males, median Glasgow Coma Scale (GCS) score was 14 (range, 3-15), median Injury Severity Score (ISS) was 9 (range, 4-18), and mean (SD) SI was 0.58 (0.18). Three percent (n = 6,585) had an SI greater than or equal to 1. Patients with SI greater than or equal to 1 were more likely to require blood product requirement (p = 0.001), require an exploratory laparotomy (p = 0.01), and have in-hospital complications (p = 0.02). The overall mortality rate was 4.1% (n = 8,952). SI greater than or equal to 1 was the strongest predictor for mortality (odds ratio, 3.1; 95% confidence interval, 2.6-3.3; p = 0.001) in geriatric trauma patients. Systolic blood pressure (p = 0.09) and heart rate (p = 0.2) were not predictive of mortality.

CONCLUSION

SI is an accurate and specific predictor of morbidity and mortality in geriatric trauma patients. SI is superior to heart rate and systolic blood pressure for predicting mortality in geriatric trauma patients. Geriatric trauma patients with SI greater than or equal to 1 should be transferred to a Level 1 trauma center.

LEVEL OF EVIDENCE

Prognostic/epidemiologic study, level III.

Rapid Emergency Medicine Score (REMS) in the trauma population: a retrospective study

OBJECTIVE

Rapid Emergency Medicine Score (REMS) is an attenuated version of the Acute Physiology and Chronic Health Evaluation (APACHE) II score and has utility in predicting mortality in non-surgical patients, but has yet to be tested among the trauma population. The objective was to evaluate REMS as a risk stratification tool for predicting in-hospital mortality in traumatically injured patients and to compare REMS accuracy in predicting mortality to existing trauma scores, including the Revised Trauma Score (RTS), Injury Severity Score (ISS) and Shock Index (SI).

DESIGN AND SETTING

Retrospective chart review of the trauma registry from an urban academic American College of Surgeons (ACS) level 1 trauma centre.

PARTICIPANTS

3680 patients with trauma aged 14 years and older admitted to the hospital over a 4-year period. Patients transferred from other hospitals were excluded from the study as were those who suffered from burn or drowning-related injuries. Patients with vital sign documentation insufficient to calculate an REMS score were also excluded.

PRIMARY OUTCOME MEASURES

The predictive ability of REMS was evaluated using ORs for in-hospital mortality. The discriminate power of REMS, RTS, ISS and SI was compared using the area under the receiver operating characteristic curve.

RESULTS

Higher REMS was associated with increased mortality (p<0.0001). An increase of 1 point in the 26-point REMS scale was associated with an OR of 1.51 for in-hospital death (95% CI 1.45 to 1.58). REMS (area under the curve (AUC) 0.91±0.02) was found to be similar to RTS (AUC 0.89±0.04) and superior to ISS (AUC 0.87±0.01) and SI (AUC 0.55±0.31) in predicting in-hospital mortality.

CONCLUSIONS

In the trauma population, REMS appears to be a simple, accurate predictor of in-hospital mortality. While REMS performed similarly to RTS in predicting mortality, it did outperform other traditionally used trauma scoring systems, specifically ISS and SI.

Recent advances of hemorrhage management in severe trauma

Trauma is one of the most common causes of mortality worldwide with a substantial percentage of deaths resulting secondary to haemorrhages, which are preventable and treatable when adequately managed. This paper offers a review of the current literature on how to successfully resuscitate patients with major haemorrhage.

Improvements in the hemodynamic stability of combat casualties during en route care

Three Forward Aeromedical Evacuation platforms operate in Southern Afghanistan: UK Medical Emergency Response Team (MERT), US Air Force Expeditionary Rescue Squadron (PEDRO), and US Army Medical Evacuation Squadrons (DUSTOFF), each with a different clinical capability. Recent evidence suggests that retrieval by a platform with a greater clinical capability (MERT) is associated with improved mortality in critical patients when compared with platforms with less clinical capability (PEDRO and DUSTOFF). It is unclear whether this is due to en route resuscitation or the dispatch procedure. The aim of this study was to compare prehospital Shock Index (SI = heart rate / systolic blood pressure) with admission values as a measure of resuscitation, across these platforms. Patients were identified from the Department of Defense Trauma Registry, who were evacuated between June 2009 and June 2011 in Southern Afghanistan. Data on platform type, physiology, and injury severity was extracted. Overall, 865 patients were identified: 478 MERT, 291 PEDRO, and 96 DUSTOFF patients and groups were compared across three injury severity scoring (ISS) bins: 1 to 9, 10 to 25, and 26 or greater. An improvement in the admission SI was observed across all platforms in the lowest ISS bin. Within the middle bin, both the MERT and PEDRO groups saw improved SI on admission, but not the DUSTOFF group. This trend was continued only in the MERT group for the highest ISS bin (1.39 ± 0.62 vs. 1.09 ± 0.42; P = 0.001), whereas a deterioration was identified in the PEDRO group (0.88 ± 0.37 vs. 1.02 ± 0.43; P = 0.440). The use of a Forward Aeromedical Evacuation platform with a greater clinical capability is associated with an improved hemodynamic status in critical casualties. The ideal prehospital triage should endeavor to match patient need with clinical capability.

The utility of a shock index ≥ 1 as an indication for pre-hospital oxygen carrier administration in major trauma

INTRODUCTION AND AIMS

The use of intravenous oxygen carriers (packed red blood cells (PRBC), whole blood and synthetic haemoglobins (HBOCs) for selected pre-hospital trauma resuscitation cases has been reported, despite a lack of validated clinical indications. The aim of this study was to retrospectively identify a sub-group of adult major trauma patients most likely to benefit from pre-hospital oxygen carrier administration and determine the predictive relationship between pre-hospital shock index (SI) [pulse rate/systolic blood pressure] and haemorrhagic shock, blood transfusion and mortality.

METHODS

A retrospective review of adult major trauma patients recorded in The Alfred Trauma Registry was conducted. Patients were included if they received at least 1L of pre-hospital crystalloid and spent over 30 min in transit. The association of shock index and transfusion was determined. Patients were further sub-grouped by mode of transport to determine the population of trauma patients who could be included into prospective studies of intravenous oxygen carriers.

RESULTS

There were 1149 patients included of whom 311 (21.9%) received an acute blood transfusion. The SI correlated well with transfusion practice. A SI ≥ 1.0, calculated after at least 1L of crystalloid transfusion, identified patients with a high specificity (93.5%; 95% CI: 91.8-94.8) for receiving a blood transfusion within 4h of hospital arrival. While patients transported by helicopter had higher injury severity and blood transfusion requirement, there were no difference in physiological variables and outcomes when compared to patients transported by road car.

CONCLUSIONS

A shock index ≥ 1.0 is an easily calculated variable that may identify patients for inclusion into trials for pre-hospital oxygen carriers. Shocked patients have high mortality rates whether transported by road car or by helicopter. The efficacy of pre-hospital intravenous oxygen carriers should be trialled using a shock index ≥ 1.0 despite fluid resuscitation as the clinical trigger for administration.

Prognostic value of shock index in children with septic shock

OBJECTIVES

Septic shock is frequent in children and is associated with high mortality and morbidity rates. Early recognition of severe sepsis improve outcome. Shock index (SI), ratio of heart rate (HR) and systolic blood pressure (SBP), may be a good noninvasive measure of hemodynamic instability that has been poorly studied in children. The aim of the study was to explore the usefulness of SI as an early index of prognosis for septic shock in children.

METHODS

The study was retrospective and performed in 1 pediatric intensive care unit at a university hospital. The following specific data were collected at 0, 1, 2, 4, and 6 hours after admission: HR and SBP for SI calculation and lactate concentration. Patients were divided into 2 groups according to their outcome (death/survival).

RESULTS

A total of 146 children admitted with septic shock between January 2000 and April 2010 were included. Shock index was significantly different between survivors and nonsurvivors at 0, 4, and 6 hours after admission (P = 0.02, P = 0.03, and P = 0.008, respectively). Age-adjusted SIs were different between survivors and nonsurvivors at 0 and 6 hours, with a relative risk of death at these time points of 1.85 (1.04-3.26) (P = 0.03) and 2.17 (1.18-3.96) (P = 0.01), respectively. Moreover, an abnormal SI both at admission and at 6 hours was predictive of death with relative risk of 1.36 (1.05-1.76).

CONCLUSIONS

In our population of children with septic shock, SI was a clinically relevant and easily calculated predictor of mortality. It could be a better measure of hemodynamic status than HR and SBP alone, allowing for the early recognition of severe sepsis.

Assessment of shock index in healthy dogs and dogs in hemorrhagic shock

OBJECTIVE

To compare the shock index (SI) in a population of healthy dogs to a population of dogs with confirmed hemorrhagic shock.

DESIGN

Retrospective analysis of data collected prospectively from 2 previous studies.

SETTING

University teaching hospital.

ANIMALS

Seventy-eight healthy control dogs enrolled in a study to establish a reference interval for a tissue oxygen monitor; 38 dogs with confirmed hemorrhagic shock enrolled in a study to evaluate the tissue oxygen monitor in hemorrhagic shock. The heart rate and systolic blood pressure obtained during the respective studies were used to calculate the SI.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Shock index was significantly higher in the hemorrhage group (median 1.37, range 0.78-4.35) than the control group (median 0.91, range 0.57-1.53); 92% of the dogs in hemorrhagic shock had an SI of >0.91. Compared with controls, dogs in hemorrhagic shock had significantly lower body temperatures (median 38.3°C, range 35.6-39.9°C versus median 38.7°C, range 37.5-39.9°C), higher heart rates (median 150/min, range 120-220/min versus median 110/min range 80-150/min), lower systolic blood pressures (mean 112 mm Hg, SD ±35.8 mm Hg versus mean 125 mm Hg, SD ±21.5 mm Hg), higher lactate concentrations (median 0.51 mmol/L, range 0.078-1.41 mmol/L versus median 0.11 mmol/L, range 0.033-0.33 mmol/L), and lower hemoglobin concentrations (median 81 g/L, range 56-183 g/L versus median 162.5 g/L, range 133-198 g/L).

CONCLUSIONS

Shock index is a simple and easy calculation that can be used as an additional triage tool and should prompt further investigation for hemorrhage if the values are >0.9.

The Shock Index revisited - a fast guide to transfusion requirement? A retrospective analysis on 21,853 patients derived from the TraumaRegister DGU

INTRODUCTION

Isolated vital signs (for example, heart rate or systolic blood pressure) have been shown unreliable in the assessment of hypovolemic shock. In contrast, the Shock Index (SI), defined by the ratio of heart rate to systolic blood pressure, has been advocated to better risk-stratify patients for increased transfusion requirements and early mortality. Recently, our group has developed a novel and clinical reliable classification of hypovolemic shock based upon four classes of worsening base deficit (BD). The objective of this study was to correlate this classification to corresponding strata of SI for the rapid assessment of trauma patients in the absence of laboratory parameters.

METHODS

Between 2002 and 2011, data for 21,853 adult trauma patients were retrieved from the TraumaRegister DGU database and divided into four strata of worsening SI at emergency department arrival (group I, SI <0.6; group II, SI ≥0.6 to <1.0; group III, SI ≥1.0 to <1.4; and group IV, SI ≥1.4) and were assessed for demographics, injury characteristics, transfusion requirements, fluid resuscitation and outcomes. The four strata of worsening SI were compared with our recently suggested BD-based classification of hypovolemic shock.

RESULTS

Worsening of SI was associated with increasing injury severity scores from 19.3 (± 12) in group I to 37.3 (± 16.8) in group IV, while mortality increased from 10.9% to 39.8%. Increments in SI paralleled increasing fluid resuscitation, vasopressor use and decreasing hemoglobin, platelet counts and Quick's values. The number of blood units transfused increased from 1.0 (± 4.8) in group I to 21.4 (± 26.2) in group IV patients. Of patients, 31% in group III and 57% in group IV required ≥10 blood units until ICU admission. The four strata of SI discriminated transfusion requirements and massive transfusion rates equally with our recently introduced BD-based classification of hypovolemic shock.

CONCLUSION

SI upon emergency department arrival may be considered a clinical indicator of hypovolemic shock in respect to transfusion requirements, hemostatic resuscitation and mortality. The four SI groups have been shown to equal our recently suggested BD-based classification. In daily clinical practice, SI may be used to assess the presence of hypovolemic shock if point-of-care testing technology is not available.

The pulse pressure/heart rate ratio as a marker of stroke volume changes during hemorrhagic shock and resuscitation in anesthetized swine

BACKGROUND

Emergency physicians and anesthesiologists need accurate estimates of stroke volume when massive unexpected hemorrhage occurs. Using an animal model of hemorrhagic shock under general anesthesia, we hypothesized that the pulse pressure-heart rate ratio (PP/HR) would be an accurate marker of stroke volume changes during hemorrhage and resuscitation.

METHODS

In 16 swine under bispectral index-controlled, intravenous propofol-remifentanil anesthesia, pressure-controlled hemorrhagic shock was induced to achieve 30 mm Hg of mean arterial pressure, after which treatment was randomized to fluid (HES, n = 4), norepinephrine (NE, n = 4), both (HES + NE, n = 4), or neither (control, n = 4). Pulmonary artery thermodilution continuous cardiac output, stroke volume, and central arterial pressures were recorded at baseline (T0), after 30 minutes (T30) and 60 (T60) minutes of hemorrhage, during treatment (T90 and T120) and after blood retransfusion (T180).

RESULTS

At T60, blood withdrawal was 995 (301) mL (38 [8] mL/kg), resulting in a 70% decrease in stroke volume and a 3.3-fold decrease in PP/HR (each p < 0.01). When stroke volume data pointed at T0, T30 and T60 were plotted against the various hemodynamic variables under study, the PP/HR ratio exhibited the strongest relationship to stroke volume (r = 0.72). The area under the receiver operating characteristic curve set to detect a 15% stroke volume decrease was larger for PP/HR (0.95 [0.94-0.97]) than for mean arterial pressure (0.91 [0.89-0.93]) (p < 0.013). During resuscitation in the HES and NE groups, correlation coefficients were significantly higher between stroke volume and PP/HR (0.75 [0.63-0.84] and 0.79 [0.67-0.86]) than between stroke volume and mean arterial pressure (0.52 [0.32-0.67], p = 0.042, and 0.49 [0.28-0.65], p = 0.0018, respectively).

CONCLUSION

The PP/HR ratio was strongly related to stroke volume during hemorrhagic shock and resuscitation in anesthetized swine.

Evaluation of the shock index in dogs presenting as emergencies

OBJECTIVES

To (1) determine a reference interval for shock index (SI) [defined as heart rate (HR)/systolic blood pressure (SBP)], in a group of healthy dogs, and (2) compare SI in healthy dogs with dogs presenting to the emergency room (ER) deemed to be in or not in a state of shock.

DESIGN

Prospective study.

ANIMALS

Sixty-eight clinically normal dogs, 18 dogs that were presented to the ER deemed to be in shock and 19 dogs presenting to the ER not deemed to be in shock.

SETTING

University teaching hospital.

INTERVENTIONS

Peripheral or central venous blood sampling.

MEASUREMENTS AND MAIN RESULTS

Heart rate and SBP were recorded on simulated presentation (healthy dogs), and emergency presentations for both dogs deemed to be in shock and dogs not deemed in shock. Dogs in shock had a median SI of 1.37 (0.87-3.13), which was significantly higher than both other groups; dogs not deemed in shock had median SI 0.73 (0.56-1.20), P < 0.0001 and healthy dogs had median SI 0.78 (0.37-1.30) P < 0.0001), respectively. Receiver operator characteristic curve analysis suggested a SI cut-off of 1.0, yielding an area under the receiver operator characteristic (AUROC) of 0.89 (Specificity (Sp) 89, Sensitivity (Sn) 90) when comparing dogs deemed in shock with healthy dogs, and 0.92 (Sp 95, Sn 89) when comparing dogs in shock with to dogs not deemed in shock.

CONCLUSIONS

The SI is an easy and noninvasive patient parameter that is higher in dogs that are deemed to be in shock than both healthy dogs and dogs presented as emergencies but not deemed to be in a state of shock. The measurement of SI may have some benefit in clinical assessment of emergency patients.

A new severity predicting index for hemorrhagic shock using lactate concentration and peripheral perfusion in a rat model

Forty percent of trauma deaths are due to hemorrhage, with 33% to 56% occurring in the prehospital environment. This study proposes a new index (NI) based on the ratio of serum lactate concentration (LC) to peripheral perfusion (PP) as an indicator of hemorrhage-induced mortality during the prehospital stage. Thirty-six anesthetized rats were randomized into three groups according to volume of controlled blood loss. We measured heart rate (HR), systolic and diastolic blood pressures (SBP and DBP), mean arterial pressure (MAP), pulse pressure (PPR), respiration rate (RR), temperature (TEMP), LC, PP, shock index (SI = HR/SBP), and proposed the new hemorrhage-induced mortality index (NI = LC/PP). Peripheral perfusion, defined as peripheral tissue perfusion and skin microcirculation, was continuously monitored by laser Doppler flowmetry. All parameters were analyzed for changes between prehemorrhage and posthemorrhage to investigate the effects of hemorrhage on mortality. Areas under a receiver operating characteristic curve (AUCs) in descending order for NI, SI, PP, SBP, MAP, PPR, DBP, TEMP, LC, RR, and HR were 0.975, 0.941, 0.922, 0.919, 0.903, 0.884, 0.847, 0.816, 0.783, 0.744, and 0.672, respectively. The correlation coefficients with mortality for NI, SI, PP, SBP, MAP, PPR, DBP, TEMP, LC, RR, and HR were -0.818, -0.759, 0.726, 0.721, 0.694, 0.662, 0.597, 0.544, -0.487, 0.420, and -0.296, respectively, with the same order as the AUC. NI was shown to be an optimal independent mortality predictor on multivariable logistic regression analysis. In conclusion, the newly proposed hemorrhage-induced mortality index, based on blood lactate/PP ratio, was a better marker for predicting mortality in rats undergoing acute hemorrhage in comparison to the other parameters evaluated in this study.

Age- and sex-specific normal values for shock index in National Health and Nutrition Examination Survey 1999-2008 for ages 8 years and older

PURPOSE

Shock index (SI), the ratio of heart rate to systolic blood pressure, has found to outperform conventional vital signs as a predictor of shock. Although age-specific vital sign norms are recommended in screening for shock, there are no reported age- or sex-specific norms for SI. Our primary goal was to report age- and sex-specific SI normal values for a nationally representative population 10 years and older by 5-year age groups. A secondary goal was to report SI normal values for children ages 8 to 19 years by 1-year age groups.

BASIC PROCEDURES

Weighted data from the National Health and Nutrition Examination Survey 1999-2008 data sets were used to generate age- and sex-specific percentile curves of SI for subjects 8 years and older.

MAIN FINDINGS

The primary analysis included 33906 subjects (101837 weighted) 10 years and older. The secondary analysis included 13393 subjects (37983 weighted) 8 to 19 years old. Normalized SI values for each percentile decreased with increasing age and were higher for females across all ages. The most commonly cited SI threshold of 0.9 exceeded the 97th percentile for males younger than 25 years and for females younger than 40 years.

CONCLUSIONS

This first report of age- and sex-specific normal values for SI indicates that SI norms vary by age and sex. Just as age-specific vital sign norms are recommended in screening for shock, our findings suggest that age- and sex-specific SI norms may be more effective in screening for shock than a single-value threshold.

A systematic review of the relationship between blood loss and clinical signs

INTRODUCTION

This systematic review examines the relationship between blood loss and clinical signs and explores its use to trigger clinical interventions in the management of obstetric haemorrhage.

METHODS

A systematic review of the literature was carried out using a comprehensive search strategy to identify studies presenting data on the relationship of clinical signs & symptoms and blood loss. Methodological quality was assessed using the STROBE checklist and the general guidelines of MOOSE.

RESULTS

30 studies were included and five were performed in women with pregnancy-related haemorrhage (other studies were carried in non-obstetric populations). Heart rate (HR), systolic blood pressure (SBP) and shock index were the parameters most frequently studied. An association between blood loss and HR changes was observed in 22 out of 24 studies, and between blood loss and SBP was observed in 17 out of 23 studies. An association was found in all papers reporting on the relationship of shock index and blood loss. Seven studies have used Receiver Operating Characteristic Curves to determine the accuracy of clinical signs in predicting blood loss. In those studies the AUC ranged from 0.56 to 0.74 for HR, from 0.56 to 0.79 for SBP and from 0.77 to 0.84 for shock index. In some studies, HR, SBP and shock index were associated with increased mortality.

CONCLUSION

We found a substantial variability in the relationship between blood loss and clinical signs, making it difficult to establish specific cut-off points for clinical signs that could be used as triggers for clinical interventions. However, the shock index can be an accurate indicator of compensatory changes in the cardiovascular system due to blood loss. Considering that most of the evidence included in this systematic review is derived from studies in non-obstetric populations, further research on the use of the shock index in obstetric populations is needed.

Hypotension during gradual blood loss: waveform variables response and absence of tachycardia

BACKGROUND

Variation in arterial pressure and plethysmographic waveforms has been shown to be predictors of cardiac output response to fluid challenge. The objective of this study was to evaluate the ability of arterial and plethysmographic waveform variables to predict hypotension during blood loss.

METHODS

Patients undergoing autologous haemodilution were studied. After anaesthesia induction, blood was withdrawn in steps of 2% of estimated circulating blood volume (ECBV). Arterial and plethysmographic waveforms were recorded and analysed offline at each step of blood withdrawal.

RESULTS

Thirty-four (29%) out of 118 studied patients tolerated 20% ECBV withdrawal without hypotension. Patients who tolerated 20% ECBV withdrawal were younger than those who did not [mean (sd): 53.8 (11.1) vs 62.7 (10.7); P<0.0001]. Patients with hypertension developed hypotension earlier than healthier patients did. There were no differences at the baseline in arterial and plethysmographic waveform variables between those who did and those who did not tolerate 20% of ECBV withdrawal. All values of variables increased significantly from the baseline after the withdrawal of 4% of ECBV (P<0.005). There were no changes in heart rate (HR), 73 (12) at the baseline and 76 (13) after 20% of ECBV withdrawal (P=0.4).

CONCLUSIONS

Arterial and plethysmographic waveform variables were augmented with increasing blood loss in all patients. Older patients, patients who received anti-hypertensive drugs, or both developed hypotension earlier than others. Baseline values were weak predictors of hypotension during stepwise blood withdrawal. No clinically significant increase in HR was observed, regardless of tolerance of arterial pressure to blood withdrawal.

Safety of prehospital intravenous fentanyl for adult trauma patients

BACKGROUND

Little is known about the safety of intravenous fentanyl for adult trauma patients in the prehospital setting. Our objective was to study the hemodynamic effect of prehospital intravenous fentanyl in initially normotensive adult trauma patients.

METHODS

A quasi-experimental design was used to compare adult trauma patients who received intravenous fentanyl and those who did not receive fentanyl in a large regional prehospital system and its affiliated Level I trauma center. Emergent adult trauma patients were included with an initial prehospital Glasgow Coma Scale score of ≥13 and systolic blood pressure >90 mm Hg. Patients were stratified into two groups, those who received a single dose of intravenous fentanyl (100 μg) and those who did not. The outcome was initial emergency department (ED) shock index (heart rate divided by systolic blood pressure). Multivariable linear regression was used to estimate the effect of fentanyl on ED shock index while adjusting for prehospital shock index, age, gender, Trauma Injury Severity Score, and the propensity for receiving fentanyl.

RESULTS

Seven hundred sixty-three patients were included, of whom 217 (28%) received fentanyl. The groups had comparable demographics (age, gender, and race/ethnicity) but different clinical characteristics (ED vital signs, Injury Severity Score, mechanism, and ED disposition). The adjusted ED shock index of fentanyl patients improved (-0.03; 95% confidence interval: -0.05 to 0.00; p = 0.02) compared with no fentanyl.

CONCLUSION

Prehospital intravenous fentanyl did not adversely affect the initial ED shock index in adult trauma patients. Additional research should be performed to confirm and extend our findings.

LEVEL OF EVIDENCE

III.

The importance of vital signs in the triage of injured patients

BACKGROUND

Vital signs are indicators of a patient presenting to an emergency department (ED). Abnormal vital signs have been associated with an increased likelihood of admission to the hospital. Physicians have long recognized the importance of vital sign observations, and vital sign measurement has proven to be useful for detecting serious diseases during triage in EDs.

METHODS

The study included all patients with injuries presented to the ED of a general hospital in Greece. For these patients, sex, age, cause of injury, vital signs at the time of admission to ED (systolic blood pressure, diastolic blood pressure, mean blood pressure, heart rate, and oxygen saturation), and the course of the patient (admission to hospital, discharge from ED) were recorded. The statistical analysis of data was done by the statistical package SPSS 15. It was performed using univariate regression and Spearman correlation coefficient.

RESULTS

A total of 2703 patients were registered, of which 71% were men aged 31.9 ± 0.38 years and 29% were women aged 45.7 ± 0.79 years. The main causes of injury were car accident, motor accident, pedestrian accident, fall from a height, and assault. By logistic regression, the correlation was found between mean blood pressure, systolic blood pressure, oxygen saturation, and hospitalization or discharge of the patients.

CONCLUSIONS

The measurement of mean blood pressure, systolic blood pressure, and oxygen saturation of the injured patients during the admission to the ED can predict the disease course of patients.

Time series analysis as input for clinical predictive modeling: modeling cardiac arrest in a pediatric ICU

Background

Thousands of children experience cardiac arrest events every year in pediatric intensive care units. Most of these children die. Cardiac arrest prediction tools are used as part of medical emergency team evaluations to identify patients in standard hospital beds that are at high risk for cardiac arrest. There are no models to predict cardiac arrest in pediatric intensive care units though, where the risk of an arrest is 10 times higher than for standard hospital beds. Current tools are based on a multivariable approach that does not characterize deterioration, which often precedes cardiac arrests. Characterizing deterioration requires a time series approach. The purpose of this study is to propose a method that will allow for time series data to be used in clinical prediction models. Successful implementation of these methods has the potential to bring arrest prediction to the pediatric intensive care environment, possibly allowing for interventions that can save lives and prevent disabilities.

Methods

We reviewed prediction models from nonclinical domains that employ time series data, and identified the steps that are necessary for building predictive models using time series clinical data. We illustrate the method by applying it to the specific case of building a predictive model for cardiac arrest in a pediatric intensive care unit.

Results

Time course analysis studies from genomic analysis provided a modeling template that was compatible with the steps required to develop a model from clinical time series data. The steps include: 1) selecting candidate variables; 2) specifying measurement parameters; 3) defining data format; 4) defining time window duration and resolution; 5) calculating latent variables for candidate variables not directly measured; 6) calculating time series features as latent variables; 7) creating data subsets to measure model performance effects attributable to various classes of candidate variables; 8) reducing the number of candidate features; 9) training models for various data subsets; and 10) measuring model performance characteristics in unseen data to estimate their external validity.

Conclusions

We have proposed a ten step process that results in data sets that contain time series features and are suitable for predictive modeling by a number of methods. We illustrated the process through an example of cardiac arrest prediction in a pediatric intensive care setting.

Are shock index and adjusted shock index useful in predicting mortality and length of stay in community-acquired pneumonia?

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.

Hemodynamic reactions in patients with hemorrhagic shock from blunt trauma after initial fluid therapy

OBJECT

This study sought to define hemorrhagic shock from blood pressure and heart rate and then to provide a treatment policy based on response to initial fluid therapy.

MATERIALS

This was a prospective clinical observational study conducted in eight hospitals. Subjects were consecutive patients with trauma who met any of the field triage conditions proposed by the Committee on Trauma of the American College of Surgeons. Initial fluid therapy was performed in patients with suspected hemorrhagic shock. Patients who required blood transfusion ≥ 4 U within 24 hours or interventions for active bleeding within 24 hours were classified into a "bleeding group" (B). A "nonbleeding group" (non-B) comprised patients who did not require blood transfusion ≥ 4 U or other interventions within 24 hours. Our committee maintained the database of survey items. Four of the hospitals were selected at random to provide training data and that was used in a recursive partitioning analysis to predict the B group. Data on patients in the other four facilities were used for validation.

RESULTS

There were a total of 400 patients studied. The training set consisted of 261 patients, 50 of whom were classified into the B group. A total of 94% patients with hemorrhagic shock suspected clinically, shock index at admission (first SI) ≥ 0.8, and SI at 1 L of fluid resuscitation (second SI) ≥ 1.0 were assigned to the B group. The non-B group (92%) were patients those whose first SI was < 0.8 and base deficits at admission ≥ -1.0. Validation data consisted of 139 patients. The sensitivity, specificity, and accuracy of these data to predict the B group were 71%, 93%, and 89%, respectively.

CONCLUSIONS

Patients whose first SI was ≥ 0.8 and second SI ≥ 1.0 would be diagnosed as "nonresponders" by American College of Surgeons. Patients with first SI < 0.8 and base deficits ≥ -1.0 will not be candidates for the B group.

Unplanned transfers to the intensive care unit: the role of the shock index

BACKGROUND

Unplanned (unexpected) transfers to the intensive care unit (ICU) are typically preceded by physiologic instability. However, trends toward instability may be subtle and not accurately reflected by changes in vital signs. The shock index (SI) (heart rate/systolic blood pressure as an indicator of left ventricular function, reference value of 0.54) may be a simple alternative means to predict clinical deterioration.

OBJECTIVE

To assess the association of the SI with unplanned ICU transfers.

DESIGN

Retrospective case-control study.

SETTING

Academic medical center.

PATIENTS

Fifty consecutive general medical patients with unplanned ICU transfers between 2003 and 2004 and 50 matched controls admitted to the same general medical unit between 2002 and 2004.

MEASUREMENTS

Demographic data and vital signs abstracted from chart review.

RESULTS

The SI was associated with unplanned ICU transfer at values of 0.85 or greater (P < 0.02; odds ratio, 3.0) and there was a significant difference between the median of worst shock indices of cases and controls (0.87 vs. 0.72; P < 0.005). There was no significant difference in age, race, admission ward, or Charlson Comorbidity Index, but hospital stay for cases was significantly longer (mean [standard deviation, SD], 14.8 [9.7] days vs. 5.7 [6.3] days; P < 0.001).

CONCLUSIONS

SI is associated with unplanned transfers to the ICU from general medical units at values of 0.85 or greater. Future studies will determine whether SI is more accurate than simple vital signs as an indicator of clinical decline. If so, it may be a useful trigger to activate medical emergency or rapid response teams (RRTs).

Identifying life-threatening shock in the older injured patient: an analysis of the National Trauma Data Bank

OBJECTIVE

Reliance on traditional vital signs (TVS), particularly in older patients, to identify life-threatening shock after injury may be unreliable. Shock index (SI), defined as heart rate divided by systolic blood pressure (SBP), may be a better indicator of early shock after injury than TVS. Multiplying age by SI (age x SI) may be better in older injured patients. We hypothesized that age x SI would be a better predictor of 48-hour mortality in old patients (age, >55 years) compared with TVS, whereas for young patients (age, <or=55 years), SI would be a better predictor than TVS.

METHODS

Version 8.1 of the National Trauma Data Bank was queried for incidents of blunt, non-neurologic injury occurring during 2007, to patients aged 18 to 81 years. Areas under the receiver operating characteristic curves (AUC) were compared for TVS, SI, and age x SI in young and old patients for predicting 48-hour mortality.

RESULTS

A total of 189,574 incidents were identified. Overall 48-hour mortality was 1.18%. For young patients, there was no difference between SBP (AUC, 0.654) and SI (AUC, 0.655) for predicting 48-hour mortality. For old patients, age x SI (AUC, 0.693) was a better predictor of 48-hour mortality compared with heart rate (AUC, 0.626; p < 0.0001), SBP (AUC, 0.657; p < 0.0002), or SI (AUC, 0.684; p < 0.008).

CONCLUSION

TVS are inadequate predictors of shock after non-neurologic blunt injury. Using SI in the young and age x SI in old to identify patients at risk for early mortality after blunt injury could result in earlier definitive treatment.

A keratin biomaterial gel hemostat derived from human hair: evaluation in a rabbit model of lethal liver injury

Effective hemostatic dressings that are compatible with tissues are needed. Keratins are a class of biomaterials that can be derived by extraction of proteins from human hair. We have recently discovered that keratin biomaterials have hemostatic characteristics and hypothesize that a keratin hydrogel having the ability to absorb fluid and bind cells may be an effective hemostat. The goal of this study was to test a keratin hydrogel and evaluate it compared to current hemostats. Thirty-two New Zealand white rabbits received a lethal liver injury. Eight animals each were assigned to negative control, QuickClot, HemCon bandage, and keratin treatment groups. Vital stats and other data were recorded during surgery and all surviving animals were sacrificed after 72 h. Histology was conducted on all surviving animals. Twenty-four-hour survival rates were 0%, 62.5%, 62.5%, and 75% for the negative control, QuickClot, HemCon, and keratin groups, respectively. Other outcomes included blood loss, mean arterial pressure, heart rate, shock index, and liver histology. All of the hemostats were statistically better than the negative control group at late operative time points. The keratin group consistently performed as well as, or better than, the commercial hemostats. Histology showed an interesting healing response at the hemostat-liver interface in the keratin group.

Exploration of prehospital vital sign trends for the prediction of trauma outcomes

OBJECTIVES

We explored whether there are diagnostically useful temporal trends in prehospital vital signs of trauma patients.

METHODS

Vital signs were monitored during transport to a level I trauma center and electronically archived. Retrospectively, we identified reliable vital signs recorded from the 0- to 7-minute interval and from the 14- to 21-minute interval during transport, and, for each subject, we computed the temporal differences between the two intervals' vital signs, the intrasubject 95% data ranges, the values during the initial 2 minutes, and the 21-minute overall means. We tested for differences between subjects with major hemorrhage versus control subjects, and computed receiver-operating characteristic (ROC) curves. We conducted sensitivity analyses, exploring alternative clinical outcomes, temporal windows, and methods of identifying reliable data.

RESULTS

Comparing major hemorrhage cases versus controls, there were no discriminatory differences in temporal vital sign trends. Hemorrhage cases had significantly wider intrasubject data ranges for systolic blood pressure (SBP), respiratory rate (RR), and shock index (SI) versus controls. All results were consistent in several sensitivity analyses.

CONCLUSIONS

Our findings add to a growing body of evidence that prehospital vital sign trends over 21 minutes or less are unlikely to be diagnostically useful because of substantial nondirectional fluctuations in vital signs that would obscure any subtle, progressive temporal trends. SBP, RR, and SI values were significantly different for high-acuity patients, and had more variability. Taken together, these findings suggest that higher-acuity patients experience episodes of instability rather than gradual, steady decline. Measures that account for data variability, such as taking the average of multiple measurements, may improve the diagnostic utility of prehospital vital signs.

Can we improve the clinical utility of respiratory rate as a monitored vital sign?

Respiratory rate (RR) is a basic vital sign, measured and monitored throughout a wide spectrum of health care settings, although RR is historically difficult to measure in a reliable fashion. We explore an automated method that computes RR only during intervals of clean, regular, and consistent respiration and investigate its diagnostic use in a retrospective analysis of prehospital trauma casualties. At least 5 s of basic vital signs, including heart rate, RR, and systolic, diastolic, and mean arterial blood pressures, were continuously collected from 326 spontaneously breathing trauma casualties during helicopter transport to a level I trauma center. "Reliable" RR data were identified retrospectively using automated algorithms. The diagnostic performances of reliable versus standard RR were evaluated by calculation of the receiver operating characteristic curves using the maximum-likelihood method and comparison of the summary areas under the receiver operating characteristic curves (AUCs). Respiratory rate shows significant data-reliability differences. For identifying prehospital casualties who subsequently receive a respiratory intervention (hospital intubation or tube thoracotomy), standard RR yields an AUC of 0.59 (95% confidence interval, 0.48-0.69), whereas reliable RR yields an AUC of 0.67 (0.57-0.77), P < 0.05. For identifying casualties subsequently diagnosed with a major hemorrhagic injury and requiring blood transfusion, standard RR yields an AUC of 0.60 (0.49-0.70), whereas reliable RR yields 0.77 (0.67-0.85), P < 0.001. Reliable RR, as determined by an automated algorithm, is a useful parameter for the diagnosis of respiratory pathology and major hemorrhage in a trauma population. It may be a useful input to a wide variety of clinical scores and automated decision-support algorithms.

Mortality and functional morbidity after use of PALS/APLS by community physicians

OBJECTIVES

To test the hypothesis that pediatric shock is a common cause of death and functional morbidity and that pediatric advanced life support (PALS)/advanced pediatric life support (APLS) resuscitation in the community hospital setting improves child health outcomes.

METHODS

This study included all children consecutively transported to 5 regional, tertiary care children's hospitals over 4 years, and is a prospective cohort study comparing outcomes in children who did or did not receive PALS/APLS resuscitation in the community hospital.

RESULTS

Shock occurred in 37% of the patients transferred to the tertiary centers. Regardless of trauma status, children with shock had an increased mortality rate compared with those without shock (all patients: 11.4% vs 2.6%), trauma patients (28.3% vs 1.2%), and nontrauma patients (10.5% vs 2.8%). Early shock reversal was associated with reduced mortality (5.06% vs 16.37%) and functional morbidity (1.56% vs 4.11%) rates. Early use of PALS/APLS-recommended interventions was associated with reduced mortality (8.69% vs 15.01%) and functional morbidity (1.24% vs 4.23%) rates. After controlling for center, severity of illness, and trauma status, early reversal of shock and use of PALS/APLS-recommended interventions remained associated with reduced morbidity and mortality rates.

CONCLUSIONS

Shock is common in children who are transferred for tertiary care. Pediatric shock recognition and resuscitation in the community hospital improves survival and functional outcome regardless of diagnostic category. The development of shock/trauma systems for children with and without trauma seems prudent.

Clinical significance of plasma ammonia in patients with traumatic hemorrhage

BACKGROUND

Hemorrhagic shock has been reported to elevate the concentration of ammonia in the blood of animals. However, only one clinical study, of a few surgical patients, found a similar effect. This investigation sought to determine whether ammonia is elevated in the plasma of trauma patients with hemorrhage and whether it could be used to predict serious hemorrhage.

METHODS

Subjects were consecutive trauma patients admitted to our Level I trauma center between November 2006 and April 2008 who met the inclusion criteria to determine plasma ammonia. Their blood was sampled at admission. Patients who required blood transfusion > or = 2 U or intervention for bleeding within 24 hours were classified into a bleeding group. Patients who did not require a transfusion or interventions were classified as controls. In addition to routine hemodynamic measurements, we recorded the hourly infused volume of Ringer's lactate solution (infusion volume) during emergency room treatment and total transfused blood volume within the first 24 hours.

RESULTS

The subjects were 282 trauma patients. Their mean age was 44.0 +/- 20.4 years old, and their mean injury severity score was 15.8 +/- 13.1. Ammonia was significantly correlated with systolic blood pressure, shock index at admission, infusion volume, base deficit, and injury severity score. Forty-one patients required blood transfusion and 31 needed intervention for arterial bleeding. Because some patients required both therapies, the bleeding group consisted of 46 patients. The control group consisted of 236 patients who needed neither blood transfusion nor intervention. The plasma ammonia concentration in the bleeding group (113 +/- 52.2 microg/dL) was significantly higher than in the control group (55.4 +/- 20.8 microg/dL). In the bleeding group, the ammonia concentration of patients who died from bleeding (170 +/- 68.7 microg/dL) was significantly higher than in survivors (102 +/- 40.7 microg/dL). The best ammonia concentration cutoff value that maximized sensitivity and specificity to select for the bleeding group was > or = 77 microg/dL (sensitivity, 82%; specificity, 89%).

CONCLUSIONS

Elevated plasma ammonia concentration at admission can be a clinically significant indicator for traumatic hemorrhage that requires treatment.