a b s t r a c t

Introduction: Traditionally, full thickness burns have been thought to be painless due to destruction of underlying nerves. We explored the association between patient and burn characteristics and Pain severity in burn patients and determined whether full thickness burns were less likely to be painful than more superficial burns.

Methods: We performed a structured review of medical records of patients presenting to a Burn center between 2010 and 2013. Data abstracted included baseline patient and burn characteristics. The primary end point was pain severity on patient arrival to the emergency department using a verbal numeric score of 0 to 10. univariate and multivariate analyses were used to explore the association between patient and burn characteristics and pain severity.

Results: There were 507 patients. Mean (SD) age was 29.9 (23.6); 38% were ages younger than 18, and 68% were males. The median (interquartile ranges) pain score was 5 (2-8). Of all patients, 7% had isolated full thickness burns. Median (interquartile ranges) pain scores in isolated full thickness burns were slightly lower than in more superficial burns: 4 (1-8) vs6 (2-8), respectively, P = .09. Twenty-five percent of patients with isolated full thickness burns had pain scores of 0 compared with 18% of all others (P = .28). There was no correlation between total body surface area and pain severity, however, pain scores increased with the number of burns (P = .007).

Conclusions: Pain severity is slightly less with full thickness burns; however, most patients have pain. The presence of pain should not be used to exclude full thickness burns.

(C) 2015

Introduction

Burns generally result in significant pain, and the severity of pain is supposedly related to burn depth. Pain due to burns can be complex and is due to direct injury and stimulation of the nociceptors in the epidermis and dermis. Nerve impulses are transmitted via A delta and C fibers to the dorsal horn of the spinal cord. The perception of pain is further modulated by other peripheral stimuli and descending influences from the brain [1]. Because full thickness (third degree) burns result in complete destruction of the cutaneous nerve endings, traditional teaching is that these burns are not painful [2-5]. In fact, the absence of sensitivity to painful stimuli has been traditionally used to distinguish full thickness from more superficial burns [6].

Most large burn registries do not measure or report pain severity on initial presentation to the hospital [7]. The objectives of the current

? Funding: Suffolk County Firefighters Burn Fund (Smithtown, NY).

?? Conflict of interest: none.

? Author contributions: AJS conceived the study, designed the study, and obtained re-

search funding. AJS, SS, and LB supervised the conduct of the study and data collection. LB, DDS, and JW undertook recruitment of patients and managed the data. HCT provided statistical advice on study design and analyzed the data. AJS drafted the manuscript, and all authors contributed substantially to its revision. AJS takes responsibility for the manu- script as a whole.

* Corresponding author at: Department of Emergency Medicine, HSC L3-080, 8350 SUNY, Stony Brook, NY 11794-8350. Tel.: +1 631 444 7856; fax: +1 631 444 9719.

E-mail address: [email protected] (A.J. Singer).

study were to assess the association between patient and burn characteristics and pain severity and to determine if isolated full thickness burns were less likely to be painful than partial thickness (second degree) burns.

Methods

Study design and setting

We performed a structured retrospective review of medical records

[8] of all patients presenting to a regional, academic, tertiary care, subur- ban burn center between 2010 and 2013. Our burn center has 8 beds and admits approximately 150 patients per year including children and adults of all ages.

The chart abstractors received specific training on how to abstract the data from the medical records using a practice set of medical records and standardized data abstraction forms. Case selection and variable definitions were explicitly defined and included in the training of the abstractors. Periodic meetings were held between the principal investi- gator (AJS) and the data abstractors to discuss any issues that arose dur- ing data abstraction. Interobserver agreement on a subset of 20 records that were reviewed by a second abstractor regarding burn depth and pain severity was 100% for both variables. The study was approved by the institutional review board and exempt from informed consent.

http://dx.doi.org/10.1016/j.ajem.2015.05.043

0735-6757/(C) 2015

1230 A.J. Singer et al. / American Journal of Emergency Medicine 33 (2015) 1229–1231

Patients

All patients admitted to our Burn unit during the study period were included in the study. Patients admitted to our burn unit are routinely entered into an institutional burn registry.

Measures and outcomes

Data were abstracted by trained research assistants from the electronic medical records including baseline patient demographic (age and sex) and burn characteristics (etiology, size, location, and depth). The primary outcome was pain severity on patient arrival to the emergency department (ED) using a verbal numeric score of 0 to 10 (from none to most). Determination of pain severity using the verbal numeric score on patient arrival to the ED is part of the standard of care at our institution. Burn depth and total body surface area (TBSA) were based on the initial assessment on ED arrival by a burn specialist.

Data analysis

Binary data are presented as numbers and percentages frequency of occurrence. Continuous data are presented as means and SD or medians with interquartile ranges (IQR) for parametric and nonparametric data, respectively. Univariate and multivariate analyses were used to explore the association between patient and burn characteristics and pain severity. Analysis of covariance was used to assess which factors were independently associated with initial pain scores. Because of the exploratory nature of this analysis and some of the small sample sizes, a P value of .10 was used to identify potentially significant factors affecting pain scores. All data analysis was performed using SPSS for Windows version 22.0 (SPSS Inc, Chicago, IL).

Results

There were 507 patients admitted to our burn center between the years 2010 and 2013. Patient mean (SD) age was 29.9 (23.6) years; 38% were ages younger than 18 years, and 68% were males. Main burn etiologies included scalds (44%), flame (22%), contact (13%), and chem- ical (8%) burns. The median (IQR) TBSA of the burns was 4% (2%-8%). The burns were located on the upper extremities (52%), lower extrem- ities (29%), trunk (34%), and the face/head/neck (33%). Of all burns, 79% were partial thickness, 2% were first degree, 8% were mixed partial and full thickness burns, and 4% were unspecified; 7% of all burns were isolated full thickness burns. There was no difference in TBSA between pediatric and adult patients or by sex.

The median (IQR) pain score on arrival to the hospital was 5 (2-8). Median (IQR) pain scores in isolated full thickness burns were slightly lower than in more superficial burns; 4 (1-8) vs 6 (2-8), respectively, P = .09. Of all patients, 19% had no pain or a pain score of 0 on arrival to the hospital. The percentage of patients without any pain on hospital arrival was similar among patients with isolated full thickness burns (25%) and more superficial burns (18%), P = .28. There was no associa- tion between TBSA and pain severity (Fig. 1); however, the number of burns the patient sustained was associated with pain scores (P =

.007); pain scores increased with the number of burns (Fig. 2). Older age (N 18 years old) was also associated with higher pain scores, whereas isolated head/neck/facial burns were associated with lower pain scores (Table).

Discussion

This study demonstrates that isolated full thickness burns are rela- tively rare occurring in less than 1 of 14 patients admitted to a regional burn unit. It also demonstrates that, although less painful than more superficial burns, full thickness burns are usually painful at the time of arrival to the hospital. It also shows that pain severity increases with

Fig. 1. Association between TBSA and pain severity.

an increasing number of burns (but not TBSA burned), whereas pain severity is lower in patients with isolated facial burns.

These findings are in contrast to the traditional teaching that full thickness burns are usually insensate and therefore not painful [1-6]. However, there have been reports suggesting that not all patients with full thickness burns have no pain. In a study evaluating burn pa- tients, Atchison et al [9] found that many patients with full thickness burns experienced pain during burn dressing changes. They also found a significant relationship between burn size and pain during burn dress- ing changes. However, they did not report pain scores in patients with full thickness burns before changing the dressing. They argued that most full thickness burns are often intermixed with partial thickness burn areas in which the nerve endings are intact. Furthermore, once the full thickness eschar is excised, nerve fibers in the underlying tissue become sensitive to pain. In addition, they believed that the pain might have been the result of partial regeneration of nerve endings as the burns healed. It is unclear how long after injury pain was assessed in this latter study. In our study, we grouped patients with mixed burns into the group with partial thickness burns because the presence of

Fig. 2. Association between the number of burns and pain severity.

A.J. Singer et al. / American Journal of Emergency Medicine 33 (2015) 1229–1231 1231

Table

Results of multivariate analysis

Variable P Nature of association

Age b.001 Based on binary variable (b19 vs 19+).

Older age was associated with higher pain scores

all of the limitations associated with this type of study design. Pain se- verity was only measured once at the time of initial patient presentation to the hospital, and we did not determine whether the patients had re- ceived any analgesia before their presentation to the hospital. Thus, some patients may not have had any pain due to recent administration of an analgesic leading to an underestimation of pain severity. However,

Isolated full thickness burn

Burn to head/face/neck only

Burns to both extremity and trunk

(may also have burns to head)

.10 Isolated full thickness burn was associated with lower pain scores

.02 Having a burn only to the head/face/neck was associated with a lower pain score

.07 Having burns to both extremities and

trunk was associated with a lower pain score

because most patients with full thickness burns had pain, our conclu- sion that most patients with isolated full thickness experience pain would not have changed. We did not evaluate the sensitivity of the burn to pinprick. Although patients may have experienced pain from the burn margins that may have been less deep than the burn center, our study cannot comment on whether lack of sensitivity to painful

stimuli is reliable in distinguishing between partial and full thickness

No. of burns .047 More burn diagnoses was associated with higher pain scores

even small areas of partial thickness burns was likely to result in pain. Thus, patients with isolated full thickness burns were unlikely to have (large) areas of more superficial burns. However, the pain may have emanated from the burn margins, which were likely to be more super- ficial than the burn center.

Although patients with a greater number of burns located on different anatomic areas had higher pain scores, overall burns surface area was not associated with pain severity. It is possible that larger sized burns in the same anatomic region (eg, an upper extremity) have less effect on overall pain severity than experiencing pain from multiple distinct anatomic areas (such as a lower and upper extremity, regardless of their size).

The fact remains that some patients with burns (regardless of depth) do not complain of any pain. A descriptive study of patients presenting to US EDs found that between 3% and 9% of burn patients had no pain at the time of triage [10]. However, the burn depth in these patients was unknown. Furthermore, it was unclear if and when these patients had received any analgesia before ED arrival.

Our findings suggest that the presence of pain should not be used to exclude full thickness burns especially when mixed depths are appar- ent. It also suggests that escharotomy may sometimes be painful and that analgesia or sedation may sometimes be required during these emergent procedures.

Limitations

Our study has severable notable limitations. Although data were col- lected prospectively, as patients were entered into our institutional burn registry, data analysis was performed retrospectively introducing

burns. Furthermore, a study in rats suggests that full thickness burns ac- tivate or sensitize surrounding C nociceptors that may be responsible for pain from the adjacent areas that do not have burns [11].

Conclusions

Most patients with burns experience pain regardless of burn size or depth. Pain severity is greater as the number of burns increases. Most patients with isolated full thickness burns have pain. Therefore, the presence of pain should not be used to exclude full thickness burns.

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