Prehospital locoregional anesthesia: a case series

Abstract

Background

Standard prehospital pain management relies on opioids, which involved avoidable risks. Few studies have evaluated pre-hospital locoregional anesthesia (LRA), especially fascia iliaca compartment blocks (FICB) and femoral nerve blocks (FB). We aimed to analyze the safety and opioid sparing potential of LRA in a Swiss alpine Helicopter Emergency Medical Service (HEMS).

Methods

Retrospective analysis over 36 months. Variables recorded included type of block, ultrasound guidance, provider training, injury mechanism, diagnosis, patient data, on site time, pain scores evolution, complementary medication before/after LRA and complications. Descriptive statistics and non-parametric test were used.

Results

Twenty-eight procedures were performed (0.26% of all missions): 25 FICB (89.3%) and 3 FB (10.7%). Ultrasound was used in 21.4% of cases (12% of FICBs, 100% of FBs). Ski accidents accounted for 64,3% and femoral diaphyseal fracture was suspected in 82,1%. Eight missions required hoisting, one terrestrial evacuation. Sixty percent 60.0% of blocs were performed by non-anesthesiologist. Only lidocaine 1% was used. Time on site was similar with or without ultrasound (p = 0.25). Pain score documentation (NRS) was incomplete in 50% but scores significantly decreased after LRA (p < 0.001). The need for complementary analgesic and or sedative was reduced (p = 0.025). Fentanyl use significantly decreased (p = 0.028), midazolam and ketamine did not (p = 0.16 and 0.56). No complications were documented.

Conclusions

LRA appears effective and safe in prehospital (alpine) settings, providing substantial pain relief and reducing fentanyl use. Further studies are needed to investigate whether LRA protocols could reduce opioid-related morbidity and mortality. 

Background

Pain management in the early pre-hospital phase is of capital importance in trauma patients as it may affect the prognosis directly. The inauspicious and potentially fatal pathophysiological responses of severe pain are indeed well known and may lead to multi-organ failure [1]. Nonetheless, it remains a rarely researched grey area within which protocols vary abundantly from an institution to another [2]. The current standard of severe pain treatment in the pre-hospital context consists mainly of opioid-based analgesia, which despite being an effective expedient entails otherwise avoidable risks for the victim, such as nausea, vomiting, and apnea [3, 20]. The risk of opioid addiction has been reported as well [4]. Locoregional anesthesia (LRA) has been employed as an analgesic method in the hospital setting for trauma cases with outstanding outcomes, allowing opioid sparing and therefore avoiding potentially dangerous side effects [5] in adults and in the pediatric population [6, 7]. This is particularly important in remote and austere environments such as mountains [8], caves [16], glaciers, and canyons, where unwanted complications are particularly fastidious as technicity may prolong the rescue mission [9]. Few retrospective and a handful of prospective studies exist on the pre-hospital application of LRA [10] with a limited quality. Many types of blocks have been described, although the so-called field-expedient block (low risk technical gesture) [11] fascia iliaca compartment block (FICB) and the femoral nerve block (FB) for femoral neck and shaft fractures have been more commonly investigated [12, 13]. Our aim is to analyze the safety and opioid sparing potential of LRA within the context of a Swiss alpine Helicopter Emergency Service (HEMS). 

Methods

After obtaining ethical approval from the ethics committee of the Canton Vaud, retrospective analysis of LRA procedures performed in all 4 bases of a Swiss alpine HEMS (Air-Glaciers) over a period of 36 months (01.06.2021 to 31.05.2024). The recorded variables were related to LRA (type of block, presence or absence of ultrasound (US) guidance, pharmacological substance), specialty training of the medical provider, the mechanism of injury and the supposed diagnosis, patient data (age, sex), time spent on scene, numeric rating scale (NRS) pain evaluation before and 15 min after realization of LRA, complementary medication administered before and after the procedure. The occurrence of complications in the pre-hospital phase (vascular puncture, paresthesias, signs and symptoms of LA intoxication) was also recorded. The choice of this medication was at discretion of the HEMS physician. Given that the Numeric Rating Scale (NRS) is an ordinal scale, we used non-parametric statistical tests for pain score analysis. Descriptive statistics (median, IQR) were used to summarize data distribution. To assess the difference in pre- and postprocedure NRS scores, we applied the Wilcoxon signed-rank test. To evaluate the difference in opioid use before and after LRA, we used McNemar’s test for paired categorical data where applicable. The analysis of time spent on site as a function of whether or not ultrasound was used was carried out using the Wilcoxon rank-sum test. The statistical calculations were performed using JASP (Version 0.19.3).

Results

A total of 28 LRA procedures, all performed on scene, were carried out during the observation period of 36 months i.e. 0.26% of all missions (n = 10,960) and 0.45% of all trauma missions (n = 6282). Skiing accidents represented the majority of cases (64,3%) and a femoral diaphyseal fracture was suspected in most cases (82,1%) (Table 1). Most patients were men (60.7%) on average 48.3 years old (median 53.0, IQR 31.8). The youngest patient was 7 years old and the oldest was 83 years old. The National Advisory Committee for Aeronautics (NACA) [14] score was 3.3 on average (median 3, IQR 1.0). In eight missions (28.6%) hoisting was necessary for patient evacuation, and in one mission (3.6%) terrestrial evacuation was necessary in order to reach the helicopter.

Table 1.

Trauma mechanism and presumed diagnosis

Trauma mechanism

- Skiing accident 64.3%

- Fall while walking 10.7%

- Hiking accident 10.7%

- Mountainbike/bike accident 7.1%

- Trampoline accident 3.6%

- Not indicated 3.6%

Presumed diagnosis

- Femoral diaphyseal fracture: 82.1%

- Femoral neck fracture: 10.7%

- Knee Luxation: 3.6%

- Tibial plateau fracture: 3.6%

Twelve different physicians (23% of all physicians employed by Air-Glaciers) carried out the LRA procedures. The amount of LRA procedures varies between 1 and 6 per physician (median 2, IQR 1.5). 41.7% of all physicians are board certified anesthesiologists; internal medicine specialists with a complementary training diploma in pre-hospital emergency medicine are just as many (41.7%), the remaining physicians being intensive care specialists. All physicians are board certified in pre-hospital emergency medicine.

Of 28 LRA procedures, 25 were FICB (89.3%) and 3 FB (10.7%). Ultrasound guidance was used in 21.4% of cases (12% of FICBs, 100% of FBs). Concerning specialty training of the physician performing LRA, most blocs were done by non-anesthesiologist (n = 20, 60.0%). Ultrasound guided FB were done only by anesthesiologist and ultrasound guided FICB only by non-anesthesiologists. Landmark approach for FICB (n = 22) was preeminently used by non-anesthesiologist (17 cases, 77,3%) as by anesthesiologist (5 cases, 22.7%). The only utilized local anesthetic was lidocaine 1% (range 100 mg – 640 mg, median 200 mg, IQR 167.5) without any adjuvant. No prehospital complications were documented. Time on site was not found to be different (p = 0.25) using ultrasound guidance (US +) compared with the landmark technique (US -) (Table 2).

Table 2.

Time on site in minutes (min.) according to type of block and utilization of ultrasound (US)

	All LRA		FICB		FB
	US +	US -	US +	US -	US +	US -
N	6	22	3	22	3	0
Median (min.)	24.5	35.0	32.0	35.0	20.0
IQR	12.0	15.0	16.0	15.0	7.0
p-value	0.25		0.83

Pain evaluation as assessed by NRS was completely missing at random (both before and after the LRA procedure) in 13 cases and partially missing (either before or after LRA) in one case, resulting in 50% of cases with incomplete documentation. Therefore, interpretation of the NRS reduction must be limited to the 14 cases with complete pain score documentation. In this subset, NRS score was significantly reduced (p < 0.001), from a mean value of 8.3 (median 8.0, IQR 3.0) to 2.6 (median 3.0, IQR 1.0).

All patients considered, the need for complementary analgesic and or sedative after LRA was significantly reduced with 82.1% of patients (n = 23) receiving WHO step 3 analgesia and/or sedation before LRA versus 46.4% (n = 13) after LRA. The use of fentanyl was significantly reduced (p = 0.028), though midazolam and ketamine utilization did not significantly decrease (p = 0.16 and 0.56) (Table 3).

Table 3.

Patients needing complementary analgesic and/or sedation

	Global	Fentanyl	Midazolam	Ketamine
Before LRA	23 (82.1%)	21 (75.0%)	2 (7.1%)	3 (10.7%)
After LRA	13 (46.4%)	10 (35.7%)	0 (0.0%)	4 (14.3%)
p-value	0.025	0.028	0.16	0.56

Discussion

LRA may represent a valuable alternative for out-of-hospital analgesia [15], including extreme milieu scenarios like during cave rescue [16, 17] given its potential for rapid, effective, and safe pain control with limited cardiorespiratory impact. The majority LRA procedures described in this case series were performed in the context of ski accidents. This milieu is far away from hospital conditions and many physicians may perceive it as extreme, even more if the accident took place off-piste. Frequently hoist or longline evacuation was necessary. In one case, the patient had to be carried over a longer distance to reach the helicopter. In such operations, safe and effective analgesia is even more critical, as continuous monitoring of vital signs is hardly feasible. The side effects of opioids could be the rationale behind inadequate analgesia within the pre-hospital setting. The absence of documented complications during the prehospital phase in our case series, whether related to puncture (vascular puncture, paresthesia) or medication (LA intoxication) is in line with current knowledge available in the literature describing pre-hospital LRA as a safe intervention [18].

The absence of difference concerning time on site when ultrasound was used could help to overcome some of the reluctance to perform ultrasound-guided punctures, in particular the fear of unnecessarily prolonging time spent on site. Due to our very limited data, this finding cannot be generalized and further investigations are necessary. The benefits of ultrasound guidance in the pre-hospital environment have been described as far as venous cannulation is concerned [19], but no research has been done on pre-hospital ultrasound-guided locoregional anesthesia, to our knowledge. Probably due to training and exposure issues, anesthetists are quicker to use ultrasound guidance than non-anesthetists, who only perform FICBs, which are mostly not ultrasound-guided. Our findings being based on a small sample, complementary investigations on the role of ultrasound including all types of LRA within this context are certainly needed.

Documentation of NRS was inadequate in 50% of all case. These missing data are more prone to be linked with incomplete paperwork making them completely missing at random than linked to the severity of the pain or other observable variables making a serious bias less probable. For the remaining cases with correct documentation, we report a significant reduction of pain according to the NRS as well as a significant reduction of opioid use independently of pain level documentation. Given the absence of a control group (patient without LRA), it is not possible to attribute this impact solely to LRA, as the analgesic and/or sedative medication administered prior to the procedure may have significantly played a role in the observed reduction in NRS, hence in lowering additional opioid doses.

As previously stated, opioid-based analgesia is nowadays the standard of care for severe pain in the pre-hospital setting [4], with all its risks and side effects that are the explanation behind inadequate analgesia within emergency medicine inside and outside of the hospital [20, 21]. However, we believe that the allocated advantage of opioid sparing justifies and supports the utilization of LRA in the pre-hospital setting. Investigations should be carried out in contexts other than south-western Switzerland in order to explore the effect of LRA on other pharmacological trends and protocols.

Specialty training seems to play a role in the choice of the techniques, anesthesiologist performed less prehospital LRA than non-anesthesiologist but were the only ones to perform FB with ultrasound guidance.

This study suffers several limitations. The most important being the design (unblind, non-controlled, non-randomized retrospective) and the absence of a control group (patients receiving standard care without LRA). The uncommon recurrence of LRA behind the small study sample (0.26% of all mission during the study period) may represent a selection bias. The mixing of two techniques (landmark vs ultrasound guided) and two type of LRA (FICB and FB) add noise to our results making generalization difficult. The unproper documentation of NRS score in 50% of case is also a severe limitation. As the assessment of complications was limited to the prehospital phase (with no follow-up), our conclusions on the safety of prehospital LRA cannot be generalized beyond this context. We believe that larger scale investigations should be carried out to confirm the opioid sparing potential of LRA, as well as clarify the role of ultrasound guidance for all types of LRA within the prehospital context.

Conclusions

Our data shows that out of hospital LRA may be a safe and effective analgesic method allowing opioid sparing and avoidance of their side effects, providing an ulterior security margin in austere environments such as the mountain where technically difficult patient extraction frequently requiring hoisting operations are necessary and therefore continuous monitoring of vital parameters is impossible. In our small series of 28 case, ultrasound guidance does not seem to prolong time on scene, when compared to the anatomical landmark technique but as our data are very limited regarding time on site, this finding cannot be generalized. Patients experience substantial pain relief in the field, possibly extending to the emergency department, and potentially even to the operating room. Further studies are needed to investigate if introducing LRA protocols in the prehospital field may curtail opioid-related morbidity and mortality, as well as oligoanalgesia.

Abbreviations

FICB

Fascia iliaca compartment block

FB

Femoral nerve block

HEMS

Helicopter Emergency Medical Service

LRA

Locoregional anesthesia

NRS

Numeric rating scale

US

Ultrasound

Authors’ contributions

LV has taken care of the writing of all sections of the manuscript and their adaptation according to journal requirements. CL has participated in the structural conception of the study, its statistical analysis, and has contributed to the writing. PM has provided all the data and contributed to the writing. AM has participated in the structural conception of the study and has taken part in the writing of most of the sections of the manuscript. He has carried out all statistical analyses including data sampling and organization. All authors read and approved the manuscript.

Funding

Financial expenses have been covered by Air-Glaciers except for the publication fee, wich was covered by the Hospital of Fribourg (HFR).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Ethics approval was obtained on 08.11.2024 through the “Commision cantonale d’éthique de la recherche sur l’être humain” of canton Vaud, Switzerland (Project ID: 2024–01781).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.