Pre-hospital blood product transfusion and calcium management in the United Kingdom: a multicentre service evaluation

Abstract

Background

Hypocalcaemia and hypercalcaemia are associated with increased morbidity and mortality in trauma patients. Although in-hospital calcium replacement protocols target normocalcaemia, UK pre-hospital services lack standardised calcium monitoring capabilities and demonstrate significant variation in calcium supplementation. No evidence-based guidelines exist for pre- and early in-hospital calcium administration in patients receiving blood product transfusion. This study characterises current UK pre-hospital calcium management in patients requiring blood transfusion prior to ionised calcium (iCa) measurement.

Methods

A multicentre pre-hospital service evaluation across five UK Helicopter Emergency Medicine Services (HEMS) from February to April 2024, including all adult trauma patients receiving pre-hospital blood transfusions. Data collected included baseline demographics, pre- and in-hospital blood products transfused, calcium dose and calcium measurement in the Emergency Department. The primary outcome was iCa on initial blood gas measurement.

Results

Fifty-eight patients were included, stratified by calcium levels on hospital arrival: 25 (43.1%) hypocalcaemic, 20 (34.5%) normocalcaemic, and 13 (22.4%) were hypercalcaemic. Most patients were male (84%) sustained blunt trauma (76%) and the overall median iCa was 1.14 mmol/L on first blood gas analysis. Pre-hospital calcium was given to 57%, with hypercalcaemic patients more likely to receive replacement. Normocalcaemic patients received fewer blood products overall. Increasing blood product administration was associated with lower calcium levels, especially in those not receiving pre-hospital calcium.

Conclusion

Hypocalcaemia and hypercalcaemia were common. Calcium replacement protocols may under- or overtreat due to diverse injury patterns and baseline patient factors. Pre-hospital point-of-care testing (POCT) for iCa could help tailor treatment, especially in cases with longer times between injury and arrival at hospital. We demonstrate the feasibility of collecting comprehensive pre- and in-hospital data across multiple HEMS services to better inform future guidelines in patients with traumatic haemorrhage.

Background

Hypocalcaemia is associated with worse outcomes compared to a normal ionised calcium (iCa) level in patients who suffer major trauma [1, 2, 3–4]. The aetiology of hypo- and hypercalcaemia in this context is unclear, but a significant proportion of major trauma patients are hypocalcaemic at hospital admission prior to receiving any blood products [5, 6]. More recent work has highlighted that patients who are hypercalcaemic also have worse outcomes than those with a normal calcium level. This has been described as the bimodal calcium variation with both hypo- and hypercalcaemia being associated with poor outcomes in trauma patients [7, 8–9].

Administration of citrated blood products can cause hypocalcaemia due to calcium chelation, a process where calcium ions are bound by a chelating agent. These chelating agents, like vitamin-K-activated proteins, form bonds with calcium, effectively lowering its levels in the body. In hospital, calcium replacement aims to achieve normal calcium levels guided by point-of-care testing (POCT) [10]. Whilst there are existing international recommendations for calcium replacement for in-hospital patients such as the Joint Trauma System Damage Control Resuscitation (JTS-DCR) Guidance [11, 12], there is currently no universally accepted prehospital protocol. Less than a third of UK Helicopter Emergency Medicine Services (HEMS) services carry POCT and none routinely measures calcium levels on consecutive patients receiving prehospital blood products. Instead, clinical teams empirically administer calcium replacement according to their local Standard Operating Procedure (SOP), after a specified number of units, or based on individual clinicians’ judgement [13, 14]. It is unclear if this achieves normal calcium levels. Moreover, a recent survey identified significant variation in the timing, preparation and dose of calcium administered by the 25 pre- hospital care organisations in the UK that currently carry blood products, with one service not giving calcium at all, concluding that there is no clear evidence to guide the optimal prehospital supplementation of calcium [14]. Another survey of UK HEMS, all of whom carry prehospital blood, showed wide variation in the type and volume of blood products carried [13]. It also demonstrated a wide range of clinician opinions on the definition and measurement of ionised hypocalcaemia, and the way in which it should be empirically treated in the pre-hospital setting [13].

This study aimed to establish the current practice of calcium administration and in-hospital iCa for patients requiring prehospital blood transfusion in UK HEMS. Further, the study aimed to identify trends and variations in iCa based on the type and frequency of prehospital blood components transfused.

Methods

Study setting and design

A prospective multicentre service evaluation across a cohort of five UK HEMS organisations in the United Kingdom, between 1 February 2024 and 25 April 2024. HEMS included: Air Ambulance Charity Kent Surrey Sussex (KSS), The Air Ambulance Service (TAAS), Essex and Hertfordshire Air Ambulance (EHAAT), Lincolnshire and Nottingham Air Ambulance (LNAA) and Hampshire and Isle of White Air Ambulance (HIOWAA). These services respond alongside the regional Emergency Medical Services (EMS) to provide doctor-critical care paramedic/paramedic care either by helicopter or rapid response vehicle over diverse urban and rural areas and populations. The participating services are all publicly funded and respond to a wide range of trauma cases in their respective regions. At the time of data collection, none of the services involved were using POCT to guide calcium replacement. The blood products and calcium replacement protocols differed for each service and can be viewed in Supplementary Table 1.

Patient selection

Patients eligible for inclusion were consecutive adult trauma patients (aged 16 years or older) who received a pre-hospital blood transfusion and were transported to hospital during the study period, and an iCa measurement was taken as part of routine care during the hospital admission process. Exclusion criteria include paediatric patients (< 16 years), patients who did not survive to hospital admission, patients not receiving blood products prior to emergency department (ED) arrival, and patients receiving blood products or calcium for atraumatic haemorrhage.

Pre-hospital blood products and calcium transfusion

Data on the type and amount of pre-hospital blood products administered to eligible patients were collected from each study site along with the calcium preparation and dose administered in the pre-hospital setting. Pre-hospital blood products included packed red blood cells (PRBC), lyophilised plasma (FDP), fresh frozen plasma (FFP), whole blood (WB) as part of the Study of Whole Blood in Frontline Trauma Trial [15], fibrinogen, or prothrombin complex concentrate (PCC). Calcium levels were measured at the first point-of-care sample (venous or arterial blood gas) upon arrival at ED. Time from emergency call (999) to first recorded iCa on in-hospital blood gas was recorded. Where applicable, blood products and calcium administered in-hospital but prior to first point of care sample being taken were also recorded. Normal ranges for iCa were collected from the blood gas machine operated as part of the data collected for each patient, allowing for subsequent classification and stratification of patients into hypo-, normo- or hypercalcaemic groups.

Primary and secondary outcomes

The primary outcome was iCa on the first in-hospital blood gas.

Secondary outcome(s) included:

1. Time to iCa measurement.

2. 30-day all-cause mortality.

3. Feasibility of gathering key data points including details of blood products and calcium given in hospital prior to POCT*.

*Currently this data is not available through UK National Databases as the specifics of when in-hospital blood products and calcium are administered in relation to blood gases are not recorded.

Data collection

Five UK HEMS services, with a mixed urban and rural population, and clinician representation on the Pre-Hospital Trainee Operated Research Network (PHOTON) were included in the study. Patient records were screened for eligibility and data was collected from eligible patient records through the designated electronic patient record system (EPCR) of the participating HEMS sites. In-hospital and 30-day survival data is routinely collected from hospital records in accordance with each services’ local data sharing agreements for the purpose of clinical audit and service evaluation. Data was collected by individual local area investigators, namely a respective PHOTON committee member, at each service. Study data was subsequently secured anonymously within the Research and Data Capture (REDCap) Data Management System hosted at KSS. REDCap is a secure, web-based application designed to support data capture for research studies, which has the required safeguards for research data security and privacy.

Ethical considerations and data governance

Data was routinely collected and met Health Research Authority (HRA, UK) criteria for service evaluation and ethical approval was not required. The multicentre service evaluation was approved through each participating services Research and Data Governance Departments with a signed shared data sharing agreement. Patient data points were fully anonymised through data entry and analysis in accordance with local and national data protection guidelines. Study conduct was in accordance with Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) [16].

Statistical analysis

Descriptive statistics were used to summarise the characteristics of the study population. Frequencies and percentages were used for categorical variables. Medians with interquartile ranges (IQR) were reported for continuous variables due to non-normal distributions. Chi square (X²) test was used to compare categorical variables between calcium status groups (hypocalcaemia, normocalcaemia, and hypercalcaemia). Kruskal-Wallis rank sum test was applied to compare continuous variables (iCa levels and time to measurement) across the three calcium groups, as data did not meet assumptions for parametric testing. For blood product administration analysis patients were stratified by calcium treatment status (with and without calcium administration). Comparisons between groups used Chi square (X²) test for categorical outcomes and Kruskal-Wallis test for continuous variables. Time-to-event analysis for calcium measurement was performed using median time intervals from emergency call (999) to ionised calcium measurement, with comparisons across calcium status groups using Kruskal-Wallis testing. All statistical analyses were performed using R version 4.3.3 (R Core Team, 2023). R packages included: tidyverse for data manipulation, gtsummary for summary statistics and hypothesis testing, ggplot2 for visualisation, flextable for table formatting, and base R stats package for statistical computations. Statistical significance was predetermined at p < 0.05, with exact p-values.

Results

Baseline demographics, patient characteristics and calcium administration

Seventy-four patients met inclusion criteria across the five HEMS sites during the study period. This equates to an average of just over 1 patient per service per week. Of these, 58 patients (78%) had a recorded first iCa level measured and were included in the study. 25 patients (43.1%) were hypocalcaemic on arrival, 20 (34.5%) normocalcaemic, and 13 (22.4%) hypercalcaemic (Fig. 1). Of the included patients, 49 (84%) were male, blunt trauma was the predominant mechanism of injury (76%), and the median iCa measurement at ED arrival was 1.14 mmol/L (IQR 1.07–1.30). Baseline demographics, patient characteristics and calcium administration are depicted in Table 1.

[See PDF for image]

Fig. 1

Flow diagram of study population stratified between hypocalcaemia, normocalcaemia and hypercalcaemic. PH, pre- hospital. iCa, ionised calcium. ED, Emergency Department

Table 1. Baseline demographics, patient characteristics and calcium administration stratified by hypocalcaemia, normocalcaemia and hypercalcaemia

Characteristic	Overall, n = 58	Hypocalcaemia, n = 25	Normocalcaemia, n = 20	Hypercalcaemia, n = 13	p-value1
Sex
Male (n, %)	49 (84)	21 (84)	17 (85)	11 (85)	> 0.999
Female (n, %)	9 (16)	4 (16)	3 (15)	2 (15)
Age category
16–30 years (n, %)	15 (26)	6 (24)	5 (25)	4 (31)	0.668
31–50 years (n, %)	20 (34)	11 (44)	5 (25)	4 (31)
51–70 years (n, %)	16 (28)	7 (28)	6 (30)	3 (23)
> 70 years (n, %)	7 (12)	1 (4.0)	4 (20)	2 (15)
Injury mechanism
Blunt (n, %)	44 (76)	19 (76)	14 (70)	11 (85)	0.623
Penetrating (n, %)	14 (24)	6 (24)	6 (30)	2 (15)
Pre-hospital calcium
0 ml (n, %)	26 (45)	15 (60)	10 (50)	1 (7.7)	0.004
10 ml (n, %)	29 (50)	10 (40)	9 (45)	10 (77)
20 ml (n, %)	2 (3.4)	0 (0)	0 (0)	2 (15)
5 ml (n, %)	1 (1.7)	0 (0)	1 (5.0)	0 (0)
Pre-hospital blood products
PRBC (n, %)	48 (83)	23 (92)	15 (75)	10 (77)	> 0.999
FFP (n, %)	49 (84)	22 (88)	17 (85)	10 (77)
FDP (n, %)	4 (6.9)	0 (0)	1 (5.0)	3 (23)
Whole blood (n, %)	8 (14)	1 (4.0)	4 (20)	3 (23)
In-hospital calcium
10 ml (n, %)	6 (10)	3 (12)	2 (10)	1 (7.7)	> 0.999
In-hospital blood products (units)
PRBC (n, %)	9 (16)	5 (20)	3 (15)	1 (7.7)	0.739
FFP (n, %)	7 (12)	4 (16)	2 (10)	1 (7.7)
FDP (n, %)	1 (1.7)	0 (0)	1 (5.0)	0 (0)
30-day mortality
Alive (n, %)	31 (61)	14 (58)	10 (63)	7 (64)	> 0.999
Dead (n, %)	20 (39)	10 (42)	6 (38)	4 (36)
Missing (n)	7	1	4	2

IQR, Interquartile range; PRBC, Packed red blood cells; FFP, Fresh frozen plasma; FDP, Freeze- dried plasma; iCa, Ionised calcium. ¹Fisher’s Exact test, Kruskal-Wallis rank sum test as appropriate

Blood product transfusion volumes in relation to calcium status

Pre-hospital blood product administration included packed red blood cells (median 1 unit [IQR 1–2]), FFP (median 1 unit [IQR 0–2]), FDP (median 0 units [IQR 0–0], 6.9% of patients) and whole blood (median 0 units [IQR 0–0], 14% of patients) (Fig. 2).

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Fig. 2

Blood component administration by calcium status (with and without calcium). PRBC, packed red blood cells; FFP, fresh frozen plasma; FDP, freeze-dried plasma. Note: Plot depicts those who received calcium at any point, either pre- hospital or in-hospital. Error bars show standard error from the mean

Pre-hospital calcium administration

Pre-hospital calcium was administered to 32 (55%) patients with significant variation by calcium status (p = 0.004) (Table 2). Hypercalcaemic patients were most likely to receive calcium treatment, with 77% (n = 10) receiving 10 ml and 15% (n = 2) receiving 20 ml, while only 8% (n = 1) received no calcium. In contrast, 60% (n = 15) of hypocalcaemic patients and 50% (n = 10) of normocalcaemic patients received no pre-hospital calcium. Among treated patients 36% (n = 9) of hypocalcaemic and 45% (n = 9) of normocalcaemic patients received 10 ml doses.

Pre-hospital blood product administration was extensive across all groups (p > 0.999). PRBC was given to 92% of hypocalcaemic, 75% of normocalcaemic, and 77% of hypercalcaemic patients. FFP administration was similarly high (88%, 85%, and 77% respectively). Notable differences emerged in FDP usage, with hypercalcaemic patients receiving substantially more FDP (23%) compared to hypocalcaemic (0%) and normocalcaemic patients (5%). Whole blood administration was highest in hypercalcaemic patients (23%) compared to hypocalcaemic (4%) and normocalcaemic groups (20%). However, we note the small cohort number of patients given whole blood units across the study.

Patients with normocalcaemia (1.1-1.3mmol/L) received fewer blood products overall (mean total 2.5 units) showing an 18.8% reduction compared to the hypocalcaemic group (mean total 3.08 units). The normocalcaemic group showed a more balanced transfusion profile with increased relative usage of whole blood (median 0.3 units) despite similar percentages receiving PRBC (75% versus 92%) and FFP (85% vs. 88%).

Hypercalcaemic patients (> 1.3mmol/L) demonstrated a similar overall transfusion volume (median 3.31 units) to the hypocalcaemic group (median 3.08 units). This hypercalcaemic group received a notably different distribution of blood products, with substantial usage of FDP (0.54 units, 23.1% of patients) and whole blood (0.38 units, 23.1% of patients) compared to other groups, alongside FFP (1.23 units, 76.9% of patients) and PRBC (1.15 units, 76.9% of patients).

Table 2. Baseline characteristics and descriptors for patients who received pre-hospital calcium (n = 32)

Characteristic	Value
Total patients who received pre-hospital calcium	32
Sex distribution
Male (n, %)	4 (12.1)
Female (n, %)	28 (87.9)
Age < 50 years	24 (72.7)
Blunt injury mechanism (n, %)	25 (75.8)
Calcium dosage received (10% Calcium Chloride)
5 ml (n, %)	2 (3)
10 ml (n, %)	28 (90)
20 ml (n, %)	2 (6)
iCa level (mmol/L), median (IQR)
Overall	1.25 (1.06–1.36)
5 ml	1.13 (1.13–1.13)
10 ml	1.21 (1.04–1.35)
20 ml	1.5 (1.49–1.51)
30-day mortality
Alive (n, %)	17 (58.6)
Dead (n, %)	11 (37.9)
Missing (n, %)	4 (13.7)

iCa, ionised calcium measurement; IQR, interquartile range

Time to ionised calcium measurement

Table 3 demonstrates time intervals from emergency call to iCa measurement across stratified groups. Although not statistically significant, measurement timing varied by calcium status (Kruskal-Wallis p = 0.061). Hypocalcaemic patients had the shortest median time to measurement (02:41, IQR 02:11 − 03:27), while normocalcaemic (03:25, IQR 02:42 − 03:42) and hypercalcaemic patients (03:16, IQR 02:58 − 03:42) showed prolonged intervals. These temporal differences may reflect variation in trauma severity, haemostatic dysfunction, or clinical presentations that influence triage priorities. The observed patterns suggest potential opportunities for optimising point-of-care calcium assessment protocols in trauma patients, particularly given the clinical significance of early calcium status identification in managing coagulopathy and resuscitation outcomes.

Table 3. Median time from 999 emergency call to measurement of iCa in hospital

Calcium Status	n	Median Time to iCa (hh: mm) Median (IQR)	p-value
Hypocalcaemia	25	02:41 (02:11 − 03:27)	0.061
Normocalcaemia	20	03:25 (02:42 − 03:42)
Hypercalcaemia	13	03:16 (02:58 − 03:42)
Overall	58	03:07 (02:26 − 03:32)

iCa, Ionised calcium; IQR, Interquartile Range. ¹p-value from Kruskal-Wallis test comparing time to iCa across calcium status groups

Relationship between ionised calcium and blood products transfused

In the analysis of blood product administration and iCa distinct patterns emerged based on pre-hospital calcium administration status (Fig. 3). Among patients who received pre-hospital calcium (Fig. 3a), whole blood and lyophilised plasma demonstrated positive correlations with ionised calcium levels, with increasing units associated with higher calcium concentrations. Conversely, both FFP and PRBC exhibited negative correlations in all patients, regardless of pre-hospital or in-hospital calcium administration, suggesting these products may contribute to decreasing calcium levels as transfusion volume increases. The effect appears more pronounced in patients who did not receive pre-hospital calcium (Fig. 3b) particularly for PRBC, indicating potential clinical significance for transfusion strategies in trauma patients at risk for hypocalcaemia.

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Fig. 3

a) Mean ionised calcium level and 95% CI in relation to any blood components received (with calcium), b) mean ionised calcium and 95% CI in relation to blood product received (without calcium). CI, Confidence Interval. FDP, Freeze-dried Plasma; FFP, Fresh Frozen Plasma; PRBCs, Packed Red Blood Cells. Note. Grey shading reflects the Confidence Interval for unit numbers

Discussion

This study, looking at patients treated by five UK HEMS services, demonstrated that trauma patients who are administered pre-hospital blood products receive a wide range of different blood products and volumes as well as highly varied strategies of calcium replacement. It also showed that at the time of first hospital blood sampling there was a wide range of iCa levels, with only 34% [20] of patients having an iCa within the normal range.

At the point of blood gas analysis all patients had received empirical dosing of calcium to counteract ethylenediaminetetraacetic acid (EDTA) chelation both pre- and in-hospital. Before point-of-care directed treatment there is a potential risk of harm if patients with hypercalcaemia have further calcium administered or if calcium replacement is inadequate in hypocalcaemic patients. The relationship between hypercalcaemia and poor outcomes reported in other studies is an association which may relate to injury severity [7] where it is postulated that hypercalcaemia originates from muscle damage and orthopaedic injuries with proposed mechanisms of harm in hypercalcaemia including disruption of cell signalling pathways, ultimately leading to cell death and cardiac dysfunction [9].

Hypocalcaemia is noted to be a common finding in critically ill patients regardless of their underlying pathology [17]. A recent study has also identified an association between hypocalcaemia and poor outcomes in traumatic brain injury [18]. Even prior to blood transfusion, trauma patients have been shown to have disordered calcium homeostasis. A recent meta-analysis showed that prior to blood transfusion, 56% of patients with major traumatic injuries were hypocalcaemic [18].

The association between traumatic haemorrhage, abnormal ionised calcium levels and poor outcomes has been widely reported [1, 2, 3–4], however no causal link has been identified. It is not clear if abnormal calcium levels are a marker of disease severity or whether the abnormal calcium levels themselves lead to poor outcomes [6]. This absence of clarity could be explained, in part, because bleeding patients are a heterogenous population in terms of their mechanism of injury, pre-existing co morbidities and their calcium levels at first measurement. For example, those with ‘blunt’ mechanism of injury represent a wide variety of traumatic injuries from deceleration injury to significant crush injury, all having their own impact on electrolyte homeostasis. Therefore, any standardised regimen of calcium replacement without POCT is likely to under treat some and over treat others. In-hospital calcium replacement in the UK is guided by POCT calcium levels and this technology is now available pre-hospital [19, 20]. As ever the challenge in the pre-hospital setting is to avoid delaying time on scene with a bleeding patient. However, for those undergoing long transfers to definitive care, the ability to tailor calcium replacement to the individual patient prior to arrival at hospital appears advantageous.

This study demonstrated variability in initial iCa based on type of blood product given. Whole blood and lyophilised plasma demonstrated positive correlations with ionised calcium levels, with increasing units associated with higher calcium concentrations. Conversely, both FFP and PRBC exhibited negative correlations in all patients, regardless of prehospital or in-hospital calcium administration. The small number of patients within this study mean it is not possible to glean specific evidence and guidance from these findings, as there are many potential confounders. However, it can be taken as a signal of a potential larger picture and as such should be investigated. Further, a survey carried out in 2024 showed that 95% of UK HEMS had an SOP for calcium replacement in patients receiving pre-hospital blood products and that 6/21 (29%) of services now had access to POCT for iCa [11]. However, the timing of iCa measurement in a bleeding patient was not specified in any services SOP, warranting further study.

Within the literature there has been ongoing discussion regarding the need to move away from SOP based protocolised medicine towards precision trauma care, with accurate, robust diagnostics and guided treatments targeted at the individual patient in front of us [21]. The results of this study, including the number of patients who were not normocalcaemic at admission, as well as the currently unexplained trends regarding blood product type, further support this notion of a move to individualised care.

Another important aspect of this project was the collection of data surrounding pre-hospital and in-hospital blood and calcium replacement given prior to first blood gas analysis in hospital for patients who received pre-hospital blood transfusion, as opposed to just that administered either pre-hospital or in-hospital. This is pragmatic, reflects real life practice, and gives a complete picture of early management of calcium replacement in patients receiving blood products, in either or both settings, prior to blood gas analysis. Further, patients requiring pre-hospital blood transfusion are a small proportion of the patients attended by UK pre-hospital critical care services nationally. This study has shown that the collection of this mixed pre- and in-hospital data is possible across multiple HEMS services, outside of a large, funded randomised controlled trial.

Limitations to this study include a small cohort of patients with high variability in the quantity and type of pre-hospital and in-hospital blood products and calcium administered prior to initial blood gas analysis. This precludes analysis of any specific subgroup due to small numbers. It is not possible to infer any potential benefit of any specific calcium replacement strategy based on the outcomes of this project. The citrate content (and therefore potential impact on iCa) varies between blood products with much higher levels in thawed FFP (5.088 mmol/unit) and WB (5.348 mmol/unit) compared to PRBC (0.385 mmol/unit). Therefore the order and type of tranfusion given to each patient will impact the iCa on arrival to hospital. The POCT iCa results represent a moment in time in the complex process of calcium homeostasis in trauma. The hypocalcaemia associated with citrate administration has been shown to be transient in healthy subjects [22], however when shock and hypoperfusion are present this can accumulate and cause hypocalcaemia [23]. Again, variability between patients in terms of their ability to metabolise citrate will lead to varied iCa measurements. It is not clear how the iCa measurements varied with time as values were only collected at a single time point. In this service evaluation the inclusion criteria included patients for whom the value of the first iCa level available at hospital was known and this was missing for 18.9% of patients, providing potential bias. Data on the number of patients not included for this reason was not explored. It has been shown that iCa is affected by pH which can in turn be affected by PaCO₂ and metabolic derangement [5, 22]. Information regarding pH on initial blood gases was not collected. All samples were fresh point of care samples which were not stored prior to analysis; however, it is possible that some patients who were significantly acidotic at the time of blood gas analysis had inaccurate iCa measurements because of low blood pH level [5].

The average 999 to in-hospital iCa level being taken time in this study was three hours and seven minutes. This represents a long time between injury and hospital arrival in this patient cohort. This likely represents a combination of the geography and systems within which these five HEMS services work, but also potentially reflects this haemorrhagic patient cohort. It does however impact the external validity of the findings of this study, as it may not be representative of the pre-hospital time between injury and arrival at hospital in other services both within the UK or internationally. Finally, it was difficult to gain follow up about longer term patient outcomes, such as survival to hospital discharge. This has been achieved at a national level in recent large clinical trials [24] however the challenge of gaining accurate follow up is still important at a service evaluation level, to inform and enhance clinical practice. The importance of this has recently been recognised by the National Data Guardian [23].

Conclusion

Patients with major trauma who receive pre-hospital blood transfusion represent a heterogeneous population with a wide range of iCa levels and are therefore not well served by existing SOP based treatment for calcium replacement. It is not possible to make recommendations on empiric pre-hospital calcium replacement strategies, however given the wide range of iCa levels on first analysis, with less than half of patients having a normal iCa level, pre-hospital POCT could be considered to minimise hypo- and hypercalcaemia at hospital arrival.

Acknowledgements

We are grateful for the support of individual local area investigators: HIOWAA: Dolly Mcpherson, Anna Barrow and James Plumb. LNAA; Mike Hughes; TAAS, Matthew Harris.

Author contributions

All authors fulfilled the CRediT taxonomy for authorship. Conceptualisation: AF/CS/JG/CL. Methodology: AF/CS/JG/CL. Data curation: JG/JB. Formal analysis: JG/JB. Writing– review and editing: AF/CS/JG. All authors read and approved the final manuscript (AF/CS/JG/JB/RL/CL).

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

Data is available upon reasonable request.

Declarations

Ethical approval and consent to participate

All data were routinely collected and met Health Research Authority (HRA, UK) criteria as service evaluation. Research Ethics Committee approval was not required. A specific Individual Data Sharing Agreement for this project was signed with all participating services: Essex and Herts Air Ambulance Trust, Lincs and Notts Air Ambulance, The Air Ambulance Charity, Hampshire and Isle of Wight Air Ambulance, Air Ambulance Charity Kent Surrey Sussex. The project was approved by the KSS Research and Innovation Committee.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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