Highlights
- •Prehospital prediction of massive transfusion reduces delays in resuscitation.
- •Many factors reported to predict a massive transfusion protocol (MTP) are not available during flight transport.
- •In this study, whole blood, systolic blood pressure, and Glasgow Coma Scale score accurately predicted MTP in trauma patients.
- •Three factors available during flight are of clinical utility in MTP prediction.
Abstract
Objective
Early identification of the subset of trauma patients with acute hemorrhage who require resuscitation via massive transfusion protocol (MTP) initiation is vital because such identification can ensure the availability of resuscitation products immediately upon hospital arrival and result in improved clinical outcomes, including reduced mortality. However, there are currently few studies on the predictors of MTP in the unique setting of flight transport.
Methods
This was a retrospective study of adult trauma patients transported from the scene via flight to 6 trauma centers between March 1, 2019, and January 21, 2021. Patients were included if they had emergency medical service vitals documented. The variables collected included demographics, comorbidities, cause of injury, body regions injured, in-flight treatments, and transport vitals. The primary outcome was MTP initiated by the receiving hospital.
Results
A total of 212 patients were included, of whom 16 (8%) had MTP initiated. During flight transport, 24 (11%) received whole blood, 9 (4%) received packed red blood cells, 11 (5%) had a tourniquet placed, and 5 (2%) received tranexamic acid. In adjusted analyses, receiving whole blood during transport (odds ratio [OR] = 8.52, P < .01), systolic blood pressure ≤ 90 mm Hg (OR = 8.07, P < .01), and a Glasgow Coma Scale score < 13 (OR = 8.38, P < .01) were independently associated with MTP.
Conclusions
This retrospective cohort study showed that 3 factors readily available in the flight setting—receipt of whole blood, systolic blood pressure, and Glasgow Coma Scale score—are strong predictors of MTP at the receiving facility, particularly when considered in aggregate.
In trauma patients with acute blood loss, immediate resuscitation with blood products is vital to reduce mortality because uncontrolled hemorrhage is the underlying cause of up to 50% of deaths in the 24 hours after traumatic injury.
1
Additionally, delays of as little as 10 minutes in blood product administration have been found to increase the odds of mortality by 27% during the first hour after hospital arrival.American College of Surgeons. ACS TQIP massive transfusion in trauma guidelines. Available at: https://www.facs.org/-/media/files/quality-programs/trauma/tqip/transfusion_guildelines.ashx. Accessed April 13, 2022.
2
To facilitate the rapid availability of blood products, trauma centers have adopted massive transfusion protocols (MTPs) or standardized criteria that dictate when large amounts of blood products should be rapidly provided for incoming patients.3
Because timely resuscitation is key, previous studies have examined the use of various indexes measured before hospital arrival to predict which patients may require MTP initiation, thereby allowing more advance notice for quicker mobilization of blood products before the patient's arrival.
4
, 5
, 6
, 7
, 8
These previous studies have focused primarily on the shock index (heart rate over systolic blood pressure) and the Assessment of Blood Consumption (ABC) score.4
, 5
, 6
, 7
, 8
However, a 2019 systematic review of scoring systems used to predict MTP identified 24 scores, 18 in civilian and 6 in military populations, reported in the literature between 1998 and 2018.9
Although the ABC score is the most widely used to predict MTP, the systematic review found little consensus as to which score or index best predicts MTP without overestimation9
because blood products tend to be in short supply, and MTPs can account for up to 70% of all blood product administration at a trauma center.1
,American College of Surgeons. ACS TQIP massive transfusion in trauma guidelines. Available at: https://www.facs.org/-/media/files/quality-programs/trauma/tqip/transfusion_guildelines.ashx. Accessed April 13, 2022.
10
Many studies have attempted to increase the accuracy of prehospital MTP prediction by starting with standardized indexes and adding additional measures (eg, combining the ABC score with lactate measures
11
,12
or the shock index with the Glasgow Coma Scale [GCS] score).13
Although transport via helicopter compared with ground emergency medical services (EMS) has been shown to improve survival in severely injured trauma patients because of a shortened time to hospital arrival and access to remote regions,14
, 15
, 16
, 17
the prediction of MTP in patients transported via flight is challenging given the limited equipment in helicopters. Focused Assessment of Sonography in Trauma (FAST) scores, a component of the ABC score, and additional laboratory values such as lactate are generally not available. Therefore, this study aimed to identify factors available to EMS during flight transport that accurately predict MTP initiation among trauma patients.Methods
This was a retrospective study of adult (age ≥ 18 years) trauma patients transported directly from the scene via flight EMS to 1 of 6 trauma centers (2 American College of Surgeons–verified level 1, 1 level 2, and 3 level 3) between March 1, 2019, and January 31, 2021. Patients were included if they had the following flight transport variables documented: heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), saturated O2 (SO2), and GCS score. The following variables used in these analyses were those available to flight EMS personnel during transport: demographics (age and sex), comorbidities, cause of injury (motor vehicle–related injury, fall, cut/pierce, firearm, environmental, or other/unknown), body regions injured, receiving facility trauma level, transit time, in-flight treatments (blood products, tranexamic acid [TXA], tourniquet, and resuscitative endovascular balloon occlusion of the aorta (REBOA)), and transport vital signs. Variables that may be associated with MTP but that are not available during flight transport (eg, Injury Severity Score) were not considered in this analysis. However, 3 potentially predictive scores were considered: the unweighted and weighted Revised Trauma Score (RTS) calculated using GCS, SBP, and RR
18
and the shock index calculated using HR and SBP. Vital signs were categorized as abnormal as follows: HR ≤ 60 or ≥ 120, RR ≤ 12 or ≥ 20, SBP ≤ 90, SO2 ≤ 90, GCS < 13, and a shock index ≥ 0.90. Previous studies have proposed thresholds of the unweighted RTS < 1119
and the weighted RTS < 7.220
in defining severe trauma status and predicting mortality for triage purposes in trauma patients. Both of these thresholds were considered here. Data were collected from the hospital system–wide trauma registry and patient electronic medical records. The study was approved by the relevant hospital system institutional review board and was granted a waiver of the Health Insurance Portability and Accountability Act and consent.The primary outcome was the initiation of MTP after hospital arrival. All patient variables listed previously were examined for associations with MTP. Chi-square, Fisher exact, and Mann-Whitney U tests and unadjusted logistic regression were used to describe the patient population and investigate univariate associations with MTP. In adjusted logistic regression analyses, multiple models were used to determine whether calculated scoring systems or individual components of the scoring systems better predicted MTP. Therefore, all adjusted models considered variables significant at P < .25 in unadjusted regression analyses; the variables available for inclusion were abnormal GCS, SBP, HR, and RR individually (model 1); abnormal shock index, GCS, and RR (model 2); abnormal unweighted RTS at < 11 and HR (model 3); and abnormal weighted RTS at < 7.2 and HR (model 4). Therefore, each adjusted model contained only the composite score using a vital sign or the individual vital sign but not both. Area under the receiving operator curve (AUROC) analyses were used to measure the accuracy of each of the 4 adjusted models in predicting the outcome of MTP. Adjusted regression models used stepwise selection with an entry significance threshold of P < .25 and a stay threshold of P < .05 to determine the variables remaining in the final model. SAS 9.4 (SAS Institute) was used for all statistical analyses, and a significance threshold of P ≤ .05 was used.
Results
A total of 212 patients were included in the study (Table 1). Of all patients transported via flight EMS from the scene during the study period (N = 245), 13% (n = 33) were missing documentation of all vital signs and were excluded. Sixteen patients (8%) had MTP initiated on hospital arrival. The median age was 44 years, and a majority (n = 6158, 74%) were male. The most common comorbidities were hypertension (n = 31, 15%) and current smoker (n = 32, 15%). The most common cause of injury was a motor vehicle–related injury (n = 139, 66%), followed by a fall (n = 49, 23%). Fifty-six percent (n = 118) of patients had an extremity injury, 52% (n = 111) had a head injury, 51% (n = 108) had a chest injury, and 26% (n = 56) had an abdominal injury. Most patients were transported to an American College of Surgeons–verified level 1 trauma center (n = 185, 87%). During flight transport, 11% (n = 24) of patients received whole blood, 4% (n = 9) received packed red blood cells (PRBCs), 5% (n = 11) had a tourniquet placed, 2% (n = 5) received TXA, and 1 patient (1%) had a resuscitative endovascular balloon occlusion of the aorta (REBOA) sheath inserted.
Table 1Patient Characteristics and Factors Univariately Associated With a Massive Transfusion Protocol (MTP) in Trauma Patients Transported From the Scene Via Flight Service
| MTP | P Value | |||
|---|---|---|---|---|
| All | Yes | No | ||
| N = 212 | n = 16 (8%) | n = 196 (93%) | ||
| Demographics | ||||
| Age, median (IQR) | 44 (30-59) | 43 (29-53) | 44 (30-59) | .66 |
| Sex, n (% female) | 54 (26) | 4 (25) | 50 (26) | 1.00 |
| Comorbidities, n (%) | ||||
| Anticoagulants | 9 (4) | 1 (6) | 8 (4) | .51 |
| Hypertension | 31 (15) | 0 (0) | 31 (16) | .14 |
| Smoker | 32 (15) | 0 (0) | 32 (16) | .14 |
| Alcohol abuse | 4 (2) | 1 (6) | 3 (2) | .27 |
| Advance directive | 5 (2) | 2 (13) | 3 (2) | .05 |
| Diabetes | 9 (4) | 0 (0) | 9 (5) | 1.00 |
| COPD | 6 (3) | 0 (0) | 6 (3) | 1.00 |
| Stroke | 2 (1) | 0 (0) | 2 (1) | 1.00 |
| Cause of injury, n (%) | .05 | |||
| Vehicle-related injury | 139 (66) | 9 (60) | 130 (66) | |
| Fall | 49 (23) | 2 (13) | 47 (24) | |
| Cut/pierce | 4 (2) | 2 (13) | 2 (1) | |
| Firearm | 5 (2) | 1 (7) | 4 (2) | |
| Environmental | 5 (2) | 0 (0) | 5 (3) | |
| Other/unknown | 9 (4) | 1 (7) | 8 (4) | |
| Injury characteristics, n (%) | ||||
| Head injury | 111 (52) | 10 (63) | 101 (52) | .40 |
| Chest injury | 108 (51) | 12 (75) | 96 (49) | .07 |
| Abdominal injury | 56 (26) | 6 (38) | 50 (26) | .38 |
| Extremity injury | 118 (56) | 11 (69) | 107 (55) | .27 |
| Total injured regions, median (IQR) | 3 (2-4) | 4 (2-5) | 3 (2-3) | .18 |
| Transport details | ||||
| Receiving facility trauma level | .74 | |||
| Level 1 | 185 (87) | 15 (94) | 170 (87) | |
| Level 2 | 2 (1) | 0 (0) | 2 (1) | |
| Level 3 | 25 (12) | 1 (6) | 24 (12) | |
| Transit time in minutes, median (IQR) | 19 (13-27) | 16 (10-26) | 19 (13-28) | .21 |
| Transport treatments administered and vital signs | ||||
| Transport blood products/treatments, n (%) | ||||
| Prehospital whole blood | 24 (11) | 9 (56) | 15 (8) | < .01 |
| Prehospital PRBCs | 9 (4) | 3 (19) | 6 (3) | .02 |
| Prehospital TXA | 5 (2) | 2 (13) | 3 (2) | .05 |
| Prehospital tourniquet | 11 (5) | 2 (13) | 9 (5) | .20 |
| REBOA inserted | 1 (1) | 1 (6) | 0 (0) | .08 |
| EMS vitals | ||||
| Heart rate, median (IQR) | 90 (76-104) | 110 (78-126) | 90 (76-102) | .05 |
| HR ≤ 60 or ≥ 120, n (%) | 43 (20) | 8 (50) | 35 (18) | < .01 |
| Respiration rate, median (IQR) | 20 (16-22) | 21 (16-25) | 20 (16-22) | .21 |
| Respiration rate ≤ 12 or ≥ 20, n (%) | 114 (54) | 11 (69) | 103 (53) | .21 |
| SBP, median (IQR) | 126 (110-142) | 88 (77-120) | 127 (112-143) | <.01 |
| SBP ≤ 90, n (%) | 25 (12%) | 9 (56%) | 16 (8%) | <.01 |
| Saturated O2, median (IQR) | 94 (91-97) | 94 (87-97) | 94 (91-97) | .52 |
| Saturated O2 ≤ 90, n (%) | 41 (19) | 4 (25) | 37 (19) | .52 |
| GCS, median (IQR) | 15 (14-15) | 11 (8-15) | 15 (14-15) | <.01 |
| GCS < 13, n (%) | 37 (17) | 8 (50) | 29 (15) | <.01 |
| Shock index, median (IQR) | 0.70 (0.59-0.87) | 1.06 (0.71-1.45) | 0.69 (0.59-0.85) | <.01 |
| Shock index ≥ 0.9, n (%) | 50 (24) | 11 (69) | 39 (20) | <.01 |
| Unweighted revised trauma score, median (IQR) | 12.0 (11.0-12.0) | 10.5 (8.0-11.0) | 12.0 (11.0-12.0) | <.01 |
| Unweighted revised trauma score < 11, n (%) | 43 (20) | 8 (50) | 35 (18) | <.01 |
| Weighted revised trauma score, median (IQR) | 7.84 (7.55-7.84) | 6.90 (5.23-7.11) | 7.84 (7.84-7.84) | <.01 |
| Weighted revised trauma score < 7.2, n (%) | 46 (23) | 11 (79) | 35 (19) | <.01 |
COPD = chronic obstructive pulmonary disease; EMS = emergency medical services; GCS = Glasgow Coma Scale; HR = heart rate; IQR = interquartile range; PRBCs = packed red blood cells; REBOA = resuscitative endovascular balloon occlusion of the aorta; SBP = systolic blood pressure; TXA = tranexamic acid. Bold P values indicate statistical significance at P ≤ 0.05.
In univariate analyses, a cut/pierce cause of injury (odds ratio [OR] = 19.00, P = 0.05); receipt of prehospital whole blood (OR = 15.51, P < .01), PRBCs (OR = 7.31, P < .01), or TXA (OR = 9.19, P = .02); abnormal HR (OR = 4.60, P < .01); abnormal SBP (OR = 14.46, P < .01); abnormal GCS (OR = 5.76, P < .01); and abnormal shock index (OR = 8.86; P < .01) were significantly associated with MTP (Table 2; of note, only variables showing significance in unadjusted logistic regression analyses are shown in this table). The RTS was univariately associated with MTP at both thresholds used (ie, unweighted RTS < 11 [OR = 4.60, P < .01] and weighted RTS < 7.2 [OR = 15.40, P < .01]).
Table 2Unadjusted and Adjusted Associations With a Massive Transfusion Protocol (MTP) in Trauma Patients Transported From the Scene Via Flight Service
| Univariate Analysesa | Model 1: Considering Score Components Individually | Model 2: Considering Shock Index | Model 3: Considering Unweighted RTS | Model 4: Considering Weighted RTS | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | P Value | OR (95% CI) | P Value | OR (95% CI) | P Value | OR (95% CI) | P Value | OR (95% CI) | P Value | |
| Unadjusted | Adjusted | Adjusted | Adjusted | Adjusted | ||||||
| Cause of injury | ||||||||||
| Vehicle-related injury | 1.38 (0.33-5.87) | .10 | ||||||||
| Fall | Ref | — | ||||||||
| Cut/pierce | 19.00 (1.82-197.89) | .05 | ||||||||
| Firearm | 6.33 (0.58-69.64) | .46 | ||||||||
| Environmental | 1.73 (0.06-52.89) | .67 | ||||||||
| Other/unknown | 3.35 (0.36-31.36) | .94 | ||||||||
| Transport variables | ||||||||||
| Prehospital whole blood | 15.51 (5.07-47.52) | <.01 | 8.52 (5.24-32.43) | <.01 | 10.51 (2.89-38.29) | <.01 | 15.89 (4.95-50.96) | <.01 | 11.43 (3.03-43.11) | <.01 |
| Prehospital PRBCs | 7.31 (1.64-32.60) | <.01 | 7.85 (1.34-45.92) | .02 | ||||||
| Prehospital TXA | 9.19 (1.42-59.62) | .02 | ||||||||
| Transport vitals | ||||||||||
| HR ≤ 60 or ≥ 120 | 4.60 (1.62-13.09) | <.01 | — | |||||||
| SBP ≤ 90 | 14.46 (4.76-43.99) | <.01 | 8.07 (2.11-30.79) | <.01 | — | |||||
| GCS < 13 | 5.76 (2.00-16.56) | <.01 | 8.38 (2.23-31.49) | <.01 | 6.17 (1.74-21.83) | <.01 | ||||
| Shock index ≥ 0.9 | 8.86 (2.90-26.98) | <.01 | — | 4.45 (1.27-15.62) | .02 | |||||
| Unweighted RTS < 11 | 4.60 (1.62-13.09) | <.01 | — | — | ||||||
| Weighted RTS < 7.2 | 15.40 (4.08-58.15) | <.01 | — | — | 11.00 (2.70-44.72) | <.01 | ||||
| Model fit (AUROC) | — | .919 | .889 | .770 | .918 | |||||
AUROC = area under the receiving operator curve; CI = confidence interval; GCS = Glasgow Coma Scale; HR = heart rate; IQR = interquartile range; OR = odds ratio; PRBCs = packed red blood cells; REBOA = resuscitative endovascular balloon occlusion of the aorta; RTS = Revised Trauma Score; SBP = systolic blood pressure; TXA = tranexamic acid.
aAll variables with significance of P < .25 in unadjusted (univariate) logistic regression were considered for inclusion in the adjusted model. Stepwise selection with an entry significance threshold of P < .25 and a stay threshold of P < .05 was used to determine the final adjusted model. Bold text in the tables indicates statistically signifcant results at a threshold of P≤0.05.
In adjusted analyses, model 1, which considered the individual vital signs HR, RR, SBP, and GCS and no composite scores or scoring systems, showed significant independent associations between MTP and prehospital whole blood (OR = 8.52, P < .01), abnormal SBP (OR = 8.07, P < .01), and abnormal GCS (OR = 8.38, P < .01). In model 2, which considered the shock index but not SBP or HR individually, MTP was associated with prehospital whole blood (OR = 10.51, P < .01), abnormal GCS (OR = 6.17, P < .01), and abnormal shock index (OR = 4.45, P = .02). In model 3, which considered the unweighted RTS at a threshold of 11 but not GCS, SBP, or RR individually, MTP was associated with prehospital whole blood (OR = 15.89, P < .01) and prehospital PRBCs (OR = 7.85, P < .01). In model 4, which considered the weighted RTS at a threshold of 7.2 but not GCS, SBP, or RR individually, MTP was associated with prehospital whole blood (OR = 11.43, P < .01) and the weighted RTS < 7.2 (OR = 11.00, P < .01). The AUROC values for the adjusted models were 0.919 (model 1), 0.889 (model 2), 0.770 (model 3), and 0.918 (model 4).
Discussion
This study aimed to identify factors available to flight EMS personnel to aid in the prediction of MTP initiation upon hospital arrival given that immediate resuscitation with blood products is vital to reducing mortality in trauma patients with large volumes of blood loss. The prediction of MTP during flight transport is challenging because helicopters may lack equipment and laboratory testing abilities that are available in ground ambulances.
14
, 15
, 16
, 17
FAST scores, a component of 1 of the most widely recognized predictors of MTP (ie, the ABC score), are typically not performed or available during flight.4
,6
,7
Additionally, in an attempt to improve the predictive power of scoring systems, previous studies have built on existing scoring systems with additional factors also generally not available during flight transport, such as lactate measures.11
,12
Therefore, this study aimed to develop a method of predicting MTP with clinical utility to air transport personnel.The adjusted regression models used in this study showed the importance of 3 predictors of MTP, either considered individually or as part of composite scoring systems: receipt of whole blood during flight transport, SBP, and GCS. The 2 adjusted models with the highest AUROC scores were those that included SBP and GCS as individual measures (model 1) and the weighted RTS at a threshold of 7.2 (model 3). Although RR is a component of the RTS, this vital sign was not significantly associated with MTP when considered individually. Additionally, the unweighted RTS, which weighs GCS, SBP, and RR equally, was not significantly associated with MTP, whereas the weighted RTS, which weighs GCS and SBP more heavily than RR (weighted RTS = 0.9368 GCS + 0.7326 SBP + 0.2908 RR),
18
was, suggesting that GCS and SBP were the driving factors of the association with the weighted RTS. Because simplicity and speed are key factors in patient evaluation during transport, the results suggest that considering SBP and GCS individually rather than as part of the RTS may be of the greatest utility in predicting MTP, especially in the challenging flight transport setting.These findings are in keeping with a previous study that identified the combination of reverse shock index, of which SBP is a component, and GCS as important predictors of MTP in trauma patients.
13
In that study, the authors’ scoring system of reverse shock index multiplied by GCS had an AUROC value of 0.8413
; our adjusted regression model here that included prehospital whole blood, SBP ≤ 90, and GCS < 13 had an improved AUROC value of 0.919. Additionally, the previous study that developed the reverse shock index multiplied by GCS measure as well as the wealth of existing literature investigating factors associated with MTP have focused on the overall trauma patient population,4
, 5
, 6
, 7
, 8
, 9
, 10
, 11
, 12
, 13
and there is currently a lack of data on predictors of MTP in the unique setting of flight EMS transport.One limitation of this study was the relative rarity of the outcome; only 8% (n = 16) of patients had MTP initiated. However, the findings of this study may be useful in guiding prospective studies examining factors associated with MTP during flight transport (eg, future studies may benefit from increased focus on the documentation of all vital signs during transport). Additionally, although GCS showed an association with MTP both in this study and previous studies,
13
it is likely that GCS is a proxy measure for another patient factor, such as overall injury burden, because isolated traumatic brain injury is unlikely to cause the volume of blood loss that would necessitate MTP. However, because GCS is a readily available measure during flight transport, it has clinical utility in predicting MTP even if the mechanism behind this association is unknown. An additional limitation was the high rate of missing documented vital information during flight transport; 33 (13%) patients did not have documented vital signs to a degree sufficient for inclusion in the analyses. Upon examination of differences between patients with recorded versus missing vitals, those with missing vitals tended to be less severely injured; these patients had a lower median Injury Severity Score (10 compared with 13 among those with nonmissing vitals) and had fewer body regions with severe injuries (Abbreviated Injury Scale ≥ 4). It is likely that more complete documentation took place among more severely injured or less stable patients because precise vitals were necessary for the guidance of care, thus biasing the patient population toward those who were more severely injured. Better air transport documentation of vital signs may allow for a more complete patient population to be assessed in future studies.Conclusions
Our findings offer a valuable tool composed of a set of 3 factors (ie, prehospital whole blood, abnormal SBP, and abnormal GCS) that are able to accurately predict MTP and are readily available to EMS personnel during flight transport of trauma patients. These findings are unique because there is currently no scoring system or set of factors to predict MTP designed specifically for the setting of flight EMS transport of trauma patients, and they may help reduce delays in the availability of blood products upon hospital arrival among this patient population.
References
American College of Surgeons. ACS TQIP massive transfusion in trauma guidelines. Available at: https://www.facs.org/-/media/files/quality-programs/trauma/tqip/transfusion_guildelines.ashx. Accessed April 13, 2022.
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- A comparison between the ability of Revised Trauma Score and Kampala Trauma Score in predicting mortality; a meta-analysis.Arch Acad Emerg Med. 2019; 7: e6
- Revised trauma score: a triage tool in the accident and emergency department.Injury. 1991; 22: 35-37
- Revised trauma scoring system to predict in-hospital mortality in the emergency department: Glasgow Coma Scale, age, and systolic blood pressure score.Crit Care. 2011; 15: R191
Article info
Publication history
Published online: December 22, 2022
Identification
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© 2022 Air Medical Journal Associates. Published by Elsevier Inc. All rights reserved.
