Local Anaesthesia for Enzymatic Debridement of Cutaneous Burns: A Prospective Analysis of 27 Cases

SUMMARY

Enzymatic debridement (ED) is increasingly used for cutaneous burns. Compared with surgical debridement, ED has better preservation of viable dermis, less blood loss and autografting, however ED is painful. Current recommendations suggest local anaesthesia (LA) is useful for minor burns, but the evidence base is minimal. In our centre, we routinely use LA with good analgesic effect. This study was a single-centre, prospective analysis conducted at the Queen Victoria Hospital (UK). Patients had at least superficial partial thickness burns and received subcutaneous LA prior to ED during a 1-year period (October 2019-September 2020). Pain was assessed using a numeric scale of 1-10, recorded before, during and after the procedure. In total, 27 patients were included (n=17 males) with a median age of 47 (18-88 years). The mean total burn surface area was 1.5% (0.3-5.0). Treated sites included head and neck (1), trunk (5), upper limb (9) and lower limb (16). The most used LAwas bupivacaine 0.25% (n=25), followed by lidocaine 1% (n=2). Some required additional oral analgesia (n=8) or a regional blockade (n=2). Average pain score during debridement was 1.9 We have found LA effective, with favourable pain scores in comparison to previous studies with oral analgesia or regional blockade. LA is quick and easy to perform, as opposed to nerve blocks, which require trained personnel with ultrasound guidance. LA is a useful analgesic for patients with minor cutaneous burns undergoing ED. In some cases, it is sufficient without additional oral analgesia or regional blockade.

Introduction

Within the last decade, enzymatic debridement (ED) has become an increasingly prevalent method in treating mid to full thickness burns, particularly with mixed depth patterns. NexoBrid, a bromelainbased collagenase derived from the stems of pineapples, selectively removes the necrotic tissue, whilst preserving the viable dermis beneath.¹ Numerous studies have proven the efficacy of ED^2-5 and it is considered a safe alternative to surgical debridement, the current standard of care (SOC). Advantages of ED over the SOC include reduced blood loss, incidence of burn wound infection, and necessity for autografting.^1,3 Additionally, ED results in shorter length of hospital stay and cheaper costs in comparison to the SOC.⁶ However, ED is still a painful procedure,^7,8 with the magnitude of pain experienced influenced by the afflicted anatomical site, the total burn surface area (TBSA), its depth, and the presence of any concomitant injuries or other conditions.⁹

Pain management is vital in burn care. However discrepancies between practice standards for treatment of burn pain have long been noted.^10,11 Inadequate analgesia can lead to an increased perception of pain, poor compliance to rehabilitation therapies, and a loss of faith in the burns team.¹² Poor experience with acute burn pain increases the incidence of chronic pain, depression and suicidal ideation.^13,14

During ED, sufficient analgesia is required at least 15 minutes before application, throughout the 4-hour procedure and upon removal of the Nexo-Brid. Due to the intricacies of the pain experienced, an interdisciplinary approach is recommended.¹⁵ According to the European Consensus Guidelines, it is preferable to use analgosedation over general anaesthetic.^8,16 Local anaesthesia has been suggested as being useful for minor burn wounds treated by ED, however the evidence-base for its use is minimal. In our centre, we frequently use LA with good analgesic effect. The purpose of our analysis was to evaluate the safety of LA and understand if it is a reliable option for ED. Here we describe our experience of routine use of subcutaneous LA injections for ED and assess its analgesic outcomes using a prospectively maintained database.

Materials and methods

Study design

This was a single-centre, prospective collected analysis of patients treated with ED at the Queen Victoria Hospital in East Grinstead, UK. The data covered a 1-year period, between October 2019 to September 2020 as this coincided with a change in our data collection that allowed more detailed analysis.

Study population

Twenty-seven consecutive patients, 17 male and 10 female, were identified from our database. All patients had to have a partial thickness, deep dermal or full thickness burn treated with ED and to have had LA as the primary form of anaesthesia/analgesia.

Standard protocol for LA in ED

The patients received cutaneous LA prior to undergoing ED. We assessed their perceived pain using a standardised numeric scale before, during and after the procedure. The patient would describe their comfort level from 1 to 10, with 1 = no pain and 10 = the worst pain possible. We also recorded whether additional rescue analgesia, either with oral medication or regional anaesthesia, was necessary.

Data analysis

Data was collected and entered into Microsoft Excel (2013, Microsoft, USA), and data analysis was performed upon it using this software. All data was checked for accuracy and completeness prior to statistical analysis.

Results

In total, 27 consecutive patients were included (n=17 males) with a median age of 47 (range 18-88 years) (Table I). The mean TBSAwas 1.5% (0.3-5.0). Five patients had a partial thickness burn, 13 had a deep dermal burn and the remaining 9 had a full thickness burn. Treated sites included the head and neck (1), trunk (5), upper limb (9) and the lower limb (16). ED was performed a median of 3 days post-injury, with a range of 1-4. The most commonly used LA was bupivacaine 0.25% with adrenaline (n=25), followed by lidocaine 1% with adrenaline (n=2). Doses of bupivacaine ranged from 0-120 ml, whereas for lidocaine both patients received 30ml. None of the patients reached the maximum safe dose of LA. Eight patients required additional oral analgesia, receiving between 5-20mg morphine or an alternative medication. Two patients required an additional regional block, one received a right lower limb block, and the other a femoral and popliteal block.

Table I.

Patient characteristics

	Median	Minimum	Maximum
Age	47	18	88
Days post-burn	3	1	4
	Mean	Minimum	Maximum
%TBSA	1.5	0.3	5
Burn site	Head/neck = 1	Trunk = 5	Upper limb = 9 Lower limb = 16
Burn depth	Partial thickness = 5	Deep dermal = 13	Full thickness burn = 9

The average pain score prior to ED was 2.1 (Table II). During the procedure it decreased to 1.9 and then after ED had been completed to a further 1.4. Separating the 9 patients with burns to the upper limbs, the average pain score before ED procedure was also 2.1, during the procedure it was 1.7, and after ED it decreased to 0.1. A single patient had a high pain score increasing the average, but his pain score was very high before the procedure as well.

Table II.

Results

LA	Bupivacaine 0.25% = 25	Lidocaine 0.1% = 2
Additional analgesia	Oral = 8	Block = 2
Average pain score (1-10)	Before = 2.1	During = 1.9	After = 1.4
Average pain score (1-10) upper limb	Before = 2.1	During = 1.7	After = 0.1

Discussion

This cohort study evaluating LA for ED is one of the largest in the published literature. Our practice at QVH has evolved to routinely use LA for minor burn wounds. We have found LA highly effective, with favourable pain scores in comparison to previous studies using oral analgesia or regional blockade. Most patients with an upper extremity burn (n=7/9) received adequate analgesia with LA, without the need for regional blockade, which is the recommended modality for burn wounds at this site.

In the initial European Consensus Guidelines,⁸ only 1 of the 10 centres had experience with ED under LA, however they had reported significant and prolonged pain after this procedure. In the updated guidelines, 4 out of 12 of the participating centres had used LA, however there was still paucity in the literature regarding its use during ED.¹⁶

Thermal burn wounds can cause significant pain. Partial thickness burns elicit pain due to the tissue damage exposing nerve endings, whereas full thickness burns can be insensate due to the loss of the underlying nociceptors. However, this is not always the case, as deep burns may have areas of shallower burn injury, where the nerve endings may not have been completely destroyed.¹⁷ Another issue faced by burn wounds, is that the pain does not stop after injury, but can be exacerbated by frequent dressing changes, physiotherapy, and other interventions. Procedural burn pain is challenging to manage, due to its variability and intensity.¹⁸ NexoBrid evokes procedural pain,⁴ to the extent that it has been theorised that pain is limiting its wider utilisation.¹⁹ The pain is attributable to the activation of myelinated A-delta fibres, which produce an initial extremely sharp pain, and unmyelinated C fibres, which prolong the pain further.²⁰

Previous studies have shown regional anaesthesia to be a good modality for managing pain during ED.^2,8 This is also comparable to other procedures besides ED. Shank et al. demonstrated lower pain scores using regional anaesthesia than with just LA infiltration alone during paediatric reconstructive burn surgery.²¹ This was cited as being most likely attributed to greater precision of administration of the anaesthetic due to the use of ultrasound guidance. However, regional anaesthesia, although it does alleviate the necessity to undergo the procedure in the operation theatre, must still be performed by an anaesthetist or a doctor with specific training including use of ultrasound. It also is dependent upon knowledge of the local anatomy, due to the potential risk of neurovascular injury from trauma due to the block needle.²² The randomised control trial by Tarsia et al. for the treatment of facial lacerations found that regional anaesthesia was more painful to administer, with a greater chance of failure, resulting in rescue LA, than just infiltration with LA alone.²³

LA is cheaper than both regional and general anaesthesia. This is attributable to the decreased duration of hospital stay, equipment requirement, and utilisation of the operating theatre.²⁴ Direct infiltration with LA is also hypothesised to have a positive effect on wound healing, due to its antimicrobial and anti-inflammatory properties, influence on wound pH and scar formation.^25-27 The increased risk of infection should also be considered with the application of regional anaesthesia, as burn patients have some of the highest rates of nosocomial infections, due to the prolonged hospitalisation, disruption of the skin barrier and dysregulation of the immune response.²⁸ Placement of peripheral catheters through the skin can lead to catheter-associated infections,²⁹ and epidural anaesthesia can lead to the formation of an epidural abscess, albeit this is a rare occurrence.³⁰

Another point to consider for peripheral nerve blocks of the extremities is the necessity for early mobilisation. Early splinting with mobility and range of motion therapy is highly beneficial to burn wound/graft healing.^31,32 Complete motor block under spinal anaesthesia may last up to 120 minutes, however there is great variability of duration.³³ If LA could be routinely utilised by other burn centres, this could greatly improve the utilisation, efficacy, and patient experience of ED.

Our study has several limitations that require acknowledgement. Despite being one of the largest studies for LA use in ED in comparison to the rest of the literature, the population size does still limit the statistical analysis that can be performed.

The nature of application of LA and regional anaesthesia does not allow for blinding of neither patients nor practitioners. The pain scoring system used to quantify the pain experience is standardised, however pain is a subjective experience, and is subject to many variables.

In conclusion, LA is a safe approach for the ED of small burns, whether given alone or with additional analgesia. We still recommend following a stepwise pain management approach, and to ensure appropriate rescue analgesia is available if required. All patients undergoing ED should be discussed with anaesthetics, even if LA is the only approach planned for.