The effect of surgical excision and grafting procedures on postburn lymphocyte suppression

The impact of operative time and hypothermia in acute burn surgery

BACKGROUND

Prolonged operative time and intraoperative hypothermia are known to have deleterious effects on surgical outcomes. Although millions of burn injuries undergo operative treatment globally every year, there remains a paucity of evidence to guide perioperative practice in burn surgery. This study evaluated associations between hypothermia and operative time on post-operative complications in acute burn surgery.

METHOD

A historical cohort study from January 1, 2006 to October 31, 2015 was completed at an American Burn Association verified burn centre. 1111 consecutive patients undergoing acute burn surgery were included, and 2171 surgeries were analyzed. Primary outcomes included post-operative complications, defined a priori as either infectious or noninfectious. Statistical analysis was undertaken using a modified Poisson model for relative risk, adjusted for total body surface area, inhalation injury, co-morbidities, substance abuse, and age.

RESULTS

The mean operative time was 4.4h (SD 3.7-4.7h; range 0.58-11h), and 18.6% of patients became hypothermic intra-operatively. Operative time was independently associated with the incidence of hypothermia (p<0.05), and both infectious (RR1.5; 1.2-1.9, p<0.0004) and non-infectious complications (RR2.3; 1.3-4.1, p<0.0066). In patients with major burns (TBSA≥20%), hypothermia predisposed to infectious (RR1.3; 1.1-1.5, p<0.0017) and non-infectious complications (RR1.7; 1.2-2.5; p<0.0049). Risk stratification revealed that hypothermic patients with major burns undergoing prolonged surgery had an increased risk of both infectious (RR1.4; 1.1-1.7, p<0.0068) and non-infectious complications (RR1.8; 1.1-3.0, p<0.0132) when compared with those without these risk factors.

CONCLUSIONS

Patients who undergo prolonged surgeries and become hypothermic are more likely to develop complications. We therefore advocate for diligent adherence to strategies to prevent hypothermia and recommend limiting operative time in clinical circumstances where intraoperative measures are unlikely to adequately prevent hypothermia.

Microalbuminuria: A marker of systemic endothelial dysfunction during burn excision

INTRODUCTION

Systemic endothelial dysfunction characterises both burn injury and surgery and can be monitored by serial immunoassay of urine albumin (microalbuminuria). The aim of this study was to assess microalbuminuria before and during burn excision and identify factors that may influence it.

METHODS

Serial half-hourly urine albumin/creatinine ratio (ACR, normal <2.3mg/mmol) was measured in 25 adult patients during 44 burn-excision procedures, at a median of 5 days post-injury. Median total body surface area (TBSA) excised was 12%.

RESULTS

Pre-operative median ACR was normal rising to 3.25mg/mmol at 1.5h of surgery (p<0.05). Per-operative ACR at 0.5, 1, 2 and 2.5h were all associated with % TBSA burn excised (p<0.04). Median intraoperative ACR at 1h was 2.3mg/mmol for surgery within 48h post-injury, 1.6 for surgery at 2-7 days and 25.5 during excisions later than 1 month after injury (p<0.05). ACR at 1h was associated with CRP at 48h post-surgery (p=0.04). Per-operative ACR was also significantly correlated with post-operative complications.

CONCLUSION

Systemic endothelial dysfunction of acute thermal injury assessed by microalbuminuria recurs with surgery, is minimal at 2-7 days post-burn and affected by % TBSA burn excised and post-operative complications.

The effect of antioxidant therapy on cell-mediated immunity following burn injury in an animal model

Although antioxidant therapy has been introduced into early post burn protocols to prevent oxidative injury, it is still not known how they effect the cellular immunity which was already depressed due to thermal injury. To investigate the effect of antioxidant therapy on postburn immunosuppression following burn injury in a rat model, well known antioxidants: allopurinol (50 mg/kg/day), desferrioxamine (15 mg/kg/day), PEG-catalase (PEG-CAT) (1200 U/kg/day), N-acetylcysteine (NAS) (1 mg/kg/day) and vitamin-C (Vit-C) (0.5 mg/kg/day) were given for 7 days following thermal injury. The immunologic status of the rat was studied using two in vivo measures at seventh day following (30% TBSA) full-thickness burn injury. The contact hypersensitivity response (CHR) of rats, and their ability to induce a host versus graft reaction (HVGR) in the popliteal node were used to assess immune system as in vivo measures. The use of mentioned antioxidants resulted in significant improvement (between P < 0.05 and P < 0.001) of burn induced immunosuppression as reflected by CHR. The treatment with allopurinol and PEG-CAT (P < 0.01) significantly improved, while desferrioxamine, NAS and Vit-C improved, but not significantly, HVG reaction in burned rats. This study demonstrated that a large burn was profoundly immunosuppressive and early intervention of antioxidant therapy was able to significantly restore cell-mediated immunity as reflected by two in vivo assays.

Early but not late burn wound excision partially restores viral-specific T lymphocyte cytotoxicity

OBJECTIVE

Early burn wound excision restores immunocompetence and improves patient survival, but the exact mechanisms have not yet been defined. Burn injury impairs cytotoxic T lymphocyte (CTL) activity as a function of burn size, increasing the risk of infection. The purpose of this study was to determine if early wound excision improved viral-specific CTL function.

METHODS

Anesthetized C57BL/6 mice (n = 20) received 0%, 20%, or 40% total body surface area full-thickness contact burns and were inoculated 3 days later with intraperitoneal lymphocytic choriomeningitis virus. Eight days after infection, or 11 days after burn, CTL effectors (E) were harvested and tested against infected, radiolabeled L-Dh targets (T) in a 51Cr-release assay, at varied E:T ratios. Dilution curves of CTL activity were compared by analysis of variance. In the second experiment, mice (n = 18) underwent a 30% burn that was totally excised and grafted on postburn days (PBDs) 0, 3, and 7. Control groups included sham burn and no excision of a 30% burn. In the third experiment, mice (n = 22) received a 30% burn that was partially, completely, or not excised on PBD 3. Control groups included sham burn with and without excision. All groups were infected with intraperitoneal lymphocytic choriomeningitis virus on PBD 3. Viral-specific CTL activity was determined on PBD 11.

RESULTS

Both 20% and 40% burn injury impaired viral-specific CTL function. Wound excision on PBDs 0 and 3, but not on PBD 7, partially restored CTL function. Total excision of the 30% burn improved CTL activity to a greater extent than did partial excision.

CONCLUSION

Burn injury inhibits viral-specific CTL activity. Early, complete wound excision augments CTL function. Improved CTL activity after burn may reduce the risk of infection, providing an immunologic rationale for expeditious wound excision.

Allogeneic fibroblasts used to grow cultured epidermal autografts persist in vivo and sensitize the graft recipient for accelerated second-set rejection

INTRODUCTION

Cultured epidermal autografts (CEAs) have been used for wound coverage in patients with massive burns and other skin defects. However, CEAs often display late breakdown, which may be immunologically mediated and initiated by persistent foreign fibroblasts used as a feeder layer to optimize keratinocyte growth. This study investigates whether these fibroblasts, previously shown to persist in vitro, survive after grafting and induce host sensitization to alloantigen.

METHODS

CEAs from CBA donors (H-2k) were grown on allogeneic NIH 3T3 (H-2q) or syngeneic LTK (H-2k) fibroblasts, which were removed by trypsinization 7 days later. CBA mice (n = 85) were flank-grafted with NIH allografts (positive control), CEA/3T3s, CEA/LTKs, or CBA autografts (negative control). Hosts were challenged with second set NIH tail allografts 3 weeks later. Median graft survival was compared between groups by Wilcoxon rank and chi 2 analysis. Additional CBA mice (n = 15) received CEAs that were biopsied 0, 4, and 8 days after grafting. The presence of allogeneic fibroblasts was determined by Western immunoblotting, using KL295, a monoclonal antibody that recognizes H-2q (but not H-2k) class II histocompatibility antigens.

RESULTS

Allogeneic fibroblasts persisted after grafting but decreased over time, as determined by alloantigen expression on Western immunoblots. Accelerated tail graft rejection occurred in hosts primed by NIH allografts (9 days, p < 0.05), as well as by CEAs growth with an allogeneic (10 days, p < 0.05) but not a syngeneic feeder layer (12 days, NS). Mice receiving flank autografts rejected second set tail allografts at 12 days.

CONCLUSIONS

Immunogenic fibroblasts used to grow CEAs survive in vivo and sensitize the graft recipient for accelerated second-set rejection. These persistent cells may initiate an inflammatory response that may result in late graft breakdown and limit the utility of CEAs grown with a foreign fibroblast feeder layer.

Effects of early and delayed wound excision on pulmonary leukosequestration and neutrophil respiratory burst activity in burned mice

BACKGROUND

Tissue myeloperoxidase (MPO) is a marker of neutrophil (PMN) accumulation in tissues (leukosequestration). We measured MPO in the livers, guts, and lungs of mice after burn injury and studied the additive effect of burn excision on lung MPO. Lung histologic characteristics were also examined. PMN respiratory activity was assessed by measuring intracellular H2O2 content.

METHODS

Mice received 32% total body surface area (TBSA) burns; some underwent burn excision followed by wound closure with allograft skin, either immediately or 48 hours after burn. Tissue MPO was measured by a colormetric assay, and intracellular H2O2 was quantified by flow cytometry.

RESULTS

MPO was elevated in lungs 8 to 24 hours after burn (p < 0.05) but not in the liver or ileum. Other burned mice received either immediate or 48-hour-delayed wound excision and allografting. In controls a similar-size area was excised and grafted with normal or burned skin. Burned animals had increased lung MPO compared with nonburned animals (p < 0.05). Highest lung MPO levels were seen after burn/immediate excision (p < 0.001). Lung MPO levels were not different comparing unburned mice undergoing skin excision and grafting with either nonburned or burned skin. When burn excision was delayed 48 hours, lung MPO was increased moderately (p < 0.05) but remained far below levels in mice that were excised immediately after burn. PMN influx into lung tissues was confirmed by histologic examination. PMN H2O2 production was increased in burned mice and was additionally increased after immediate wound excision.

CONCLUSIONS

Although burn injury produces pulmonary leukosequestration, the phenomenon is unrelated to local effects of burned skin. In this experimental model immediate postburn wound excision increased pulmonary leukosequestration to higher levels than after burn injury alone, and intracellular H2O2 content also increased. Pulmonary leukosequestration may predispose to lung injury, possibly limiting the benefits of wound excision performed extremely early postburn.

Early wound excision and skin grafting restores cellular immunity after severe burn trauma

Suppression of cellular immunity following thermal injury may contribute to the high incidence of postburn sepsis. Early excision and skin grafting may remove deleterious local wound factors and prevent immunosuppression. The effect on cellular immunity of early burn wound excision and skin grafting was investigated in an animal model using female Wistar rats. The development of immunosuppression shortly after burn injury was shown by popliteal lymph node assay and a 2,4-dinitrofluorobenzene skin reaction test. Excision and skin grafting 2 days after burn trauma restored parameters to normal. Burned tissue suppresses cellular immunity; this effect is preventable by early excision and skin grafting.

An alternative treatment of massive burns: skin allografts and cyclosporin immunosuppression without severe additional depression of cell-mediated immunity in an animal model

This study investigated the effects of early excision of eschar and grafting with cyclosporin immunosuppression on immunological changes following burn injury. The immunological status of the rat was studied using two in vivo measures following a (30 per cent TBSA) full skin thickness burn injury. Cyclosporin was found to be a powerful immunosuppressive agent in skin transplantation, and its risks, efficacy and possible side-effects after thermal injury have been investigated. This study demonstrated that a large burn was profoundly immunosuppressive, and early excision and grafting was able to restore cell-mediated immunity significantly as reflected by two in vivo assays. The short course of the immunosuppressive treatment to delay skin allograft rejection did not cause a severe additional effect on cell-mediated immunity after thermal injury. Allograft survival appeared to be related to immunosuppression caused mainly by cyclosporin treatment and also by the immunosuppressive effect of the burn.

Prolonged allograft survival in a patient with extensive burns using cyclosporin

A woman with very extensive burns (of over 75 per cent TBSA and 45 per cent full skin thickness) received cyclosporin to extend the survival of skin allografts obtained from several unmatched donors. The patients' wounds appeared completely healed after 3 months when the cyclosporin was discontinued. During the immunosuppressive treatment with cyclosporin there was no evidence of graft rejection or any side effects related to cyclosporin. Twelve days after discontinuing the drug rejection started. The burns were then successfully covered with autografts during two operations. The late functional results were excellent.

Donor-specific tolerance permits burn allografting without increased sepsis

Early excision and allografting of massive burns is beneficial. However, chronic immunosuppression, utilized to prolong allograft survival, increases the potential risk of infection. We have previously shown long-term skin allograft survival in mice with a 30% total body surface area (TBSA) burn by inducing donor-specific tolerance (DST) using only perigrafting administration of antithymocyte globulin (ATG) and donor bone marrow (DBM). Chronic immunosuppression is avoided. This study tests whether induction of DST compromises host resistance to infection. Resistance to a septic challenge created by cecal ligation and puncture (CLP) 10 days after a 30% TBSA burn was investigated in the following groups of mice: [table: see text] Positive blood cultures were documented for 97% of mortalities. Burn excision and grafting significantly (P less than or equal to 0.05) decreased mortality. No increased mortality was seen in allografted mice receiving ATG or ATG and DBM compared to isografted mice receiving no immunosuppression. These studies suggest that skin allografting with DST may permit the benefits of burn excision without the risks of infection seen with chronic immunosuppression.

Decreased reactivity of allosera against target lymphocytes obtained following thermal injury or long-term cyclosporine treatment

We speculated that two diverse causes of potent cell-mediated immune suppression, cyclosporine (CsA) and thermal trauma, may demonstrate some similar actions, and thus tested whether either could alter antisera reactivity against allogeneic target lymphocytes. Target splenocytes from 40% body surface area full-thickness burned Brown-Norway (BN) rats demonstrated significant (P = 0.004) decreased reactivity (agglutination) with antisera produced across a full allogeneic barrier (RT1 major histocompatibility complex (MHC) and non-MHC) compared to control splenocytes. Depression of allogeneic splenic target cell reactivity against Lewis (LEW)-anti-BN allosera was similarly observed using lymphocytes from long-term CsA-treated rats (P = 0.004). The decreased reactivity induced by burn trauma was transferable to pooled normal splenocytes or blood lymphocytes by preincubation with burn plasma (P less than 0.001), and was confirmed by a cellular enzyme-linked immunosorbent assay (CELISA) (P = 0.003). In summary, a similarity consisting of decreased antibody reactivity against lymphocytes from either burned or long-term CsA-treated animals was demonstrated. These results suggested that lymphocyte cell surface allogeneic determinants and their expression and/or availability were altered by either regimen.