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Temporary Wound Dressings 

Temporary Wound Dressings
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Temporary Wound Dressings
DOI:
10.1093/med/9780198849360.003.0005
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date: 29 November 2020

Summary

  1. 1. Consider a saline-soaked dressing covered with an occlusive layer for open fractures in prehospital settings and in the emergency department.

  2. 2. Following initial wound excision, if the wound cannot be closed primarily, use a simple non-adherent dressing.

  3. 3. When internal fixation is used, perform definitive soft tissue cover at the same time.

  4. 4. Prolonged application of negative pressure wound therapy (NPWT) should not be used to downgrade the requirements for definitive soft tissue reconstruction, which should be performed within 72 hours of injury.

Introduction

Temporary dressings are used to cover the wound from the time of injury through to definitive soft tissue closure. Frequent dressing changes should be avoided to reduce contamination by nosocomial organisms.

Immediately after injury, the wound is contaminated by organisms from the environment at the time of the trauma. However, the available evidence suggests that environmental contamination does not reflect the organisms typically responsible for subsequent deep tissue infection (1), except in specific areas such as farmyard and aquatic conditions. Therefore, the initial dressing should be simple to apply and maintain tissue viability by preventing desiccation, e.g. gauze soaked in normal saline and covered with an occlusive film as per the National Institute for Health and Care Excellence (NICE) guidance (2). Following wound excision, if immediate soft tissue cover cannot be achieved, a simple non-adherent dressing should be applied. NICE previously recommended the application of negative pressure wound therapy (NPWT) (2).

NPWT

Popularised by the first English language publications in the late 1980s and 1990s (3, 4, 5) NPWT is a closed system that applies suction to a deformable filler material in contact with a wound bed, producing positive pressure with microscopic focal areas of negative pressure where partially deformed filler pores abut the wound (6,7). NPWT works by a combination of macromechanical deformation, micromechanical deformation (stimulating mesenchymal mechanoreceptor-mediated proliferation and differentiation), permissive hypoxia-mediated angiogenesis (as a consequence of positive pressure to the wound bed), and the removal of oedema (8). At a molecular level NPWT suppresses the expression of pro-inflammatory cytokines TNF and IL-1β‎ and promotes expression of anti-inflammatory cytokines such as IL-10 and growth factors VEGF and TGF-β‎ (9).

Therapy variables include the magnitude of negative pressure, the periodicity of application of negative pressure (continuous or intermittent), the material and deformational properties of the wound filler, and the use of an additional interface layer between the wound filler and wound bed, which may reduce granulation tissue ingrowth into the filler, confer antibacterial properties, and influence the deformational characteristics of the wound filler and the transmission of pressure to the wound bed (10). Whilst early studies reported enhanced local blood flow with the use of an intermittent NPWT regimen (the 5 minutes on; 2 minutes off regime), the conclusions drawn from these data have been contested (5). Furthermore, whilst there is some evidence to suggest that intermittent application of NPWT may enhance wound healing in experimental models, this has not yet translated into a reliable therapeutic strategy (11,12). The available evidence for the influence of magnitude of negative pressure would suggest that –80 mmHg should be used as a default (13) as higher pressures are unlikely to confer additional clinical advantage and may even be detrimental to local tissue perfusion (14). The most commonly utilised wound filler is polyurethane (PU) foam. Under topical negative pressure the collapsible porous structure results in macromechanical wound deformation that may not be desirable in some areas, for example, a flexure crease over a joint. Additionally the porosity encourages granulation tissue ingrowth that leads to painful dressing changes as friable, bleeding tissue within the porous structure is pulled from the wound as the dressing is changed. The limited ability of PU foam to conform to complex wound geometry has led to the use of gauze, such as polyhexanide-impregnated Kerlix™ as an alternative filler (15) without demonstrable differences in macro- and micromechanical wound deformation and pressure transduction (16, 17). Whilst the use of a single layer of interface material probably makes little difference to the application of pressure to the wound bed, non-adherent interface materials may be used to protect vital structures such as vessels and nerves.

The influence of NPWT on the bacteriology of the subjacent wound remains controversial. Experimentally, acute, chronic, and pre-contaminated wounds have all been investigated to answer this question, but intermittent surgical wound excision and the simultaneous use of systemic antibiotics have complicated data analysis and interpretation. Early studies hypothesised that NPWT suppressed bacterial growth, although more recent data suggest that this is an oversimplification. A recent systematic review aimed at establishing whether NPWT acts in part by improving bacterial clearance of the wound included 20 studies of which 10 were experimental studies, 4 were randomised controlled trials, and 6 clinical series.

Four additional studies (2 experimental studies and 2 clinical series) evaluated NPWT when used with periodic installation of antibacterial solutions. The authors concluded that the influence of NPWT on bacterial growth kinetics is probably species-specific. NPWT may selectively suppress the replication of Gram negative rods such as Pseudomonas spp. thereby depopulating the niche that is then filled by Gram positive cocci (18). The solution to this problem may lie in the use of antibacterial wound fillers and interface materials such as silver-impregnated foam and gauze. Whilst one study reported that the use of a silver-impregnated interface markedly suppressed growth of Staphylococcus aureus (19), corroborative data are, as yet, lacking.

NPWT works as a closed system. Leaks in the transparent membrane result in the continuous inflow of air from the external environment, risking contamination and wound desiccation. The NPWT pump sounds an alarm when the seal is breached. Maintenance of the seal can be challenging where the wound geometry is complex or where adjacent orifices preclude a reliable seal. Wounds under continuous (or intermittent) suction risk large losses of fluid, including blood. Therefore, it is important to examine the contents of the reservoir and document volumes collected at regular intervals and to take the patient back to the operating theatre should any concerns be raised over ongoing losses.

What is the evidence for NPWT in open fractures?

Several series have evaluated the use of NPWT in the immediate management of open fractures, i.e. the use of NPWT after the first surgical wound excision in those wounds that cannot be closed by direct suturing of the wound edges. The outcomes included infection, the subsequent reconstructive requirement of the wound, and the permissible delay between injury and definitive reconstruction.

NPWT and deep tissue infection

A prospective study of 58 patients with 62 open fractures randomised to NPWT or control (standard dressings) with wound excision and dressing changes every 48–72 hours until definitive closure reported 2 deep infections among 37 patients in the NPWT cohort and 7 deep infections among 25 patients in the control cohort. Overall, NPWT resulted in a significant reduction in deep infections, with an odds ratio of 0.199 (20). A retrospective cohort study of 229 open tibial fractures concluded that, when compared with conventional dressings, the use of NPWT reduced the rate of deep tissue infection by 80% (21). However, a UK-based, multicentre randomised controlled trial compared NPWT with standard dressings in 460 participants with lower limb open fractures of Gustilo–Anderson grade II (15%) or III (85%). Approximately 82% of the participants had tibial fractures. The investigators found no difference in self-reported disability rating index (DRI 45.5 NPWT, 42.4 standard dressing) or deep surgical site infection rates (7.1% NPWT, 8.1% standard dressing) at 12 months following injury, with superficial surgical site infections rates within 3 months of injury also being similar between the two groups (15.5 NPWT, 14.1% standard dressings) (22). The authors found that NPWT was not cost effective in improving outcomes.

NPWT and the subsequent reconstructive requirement of the wound

There is little evidence that the use of NPWT downgrades the reconstructive requirements of the wound. A prospective study of 16 patients with high-energy open fractures concluded that the use of NPWT is a useful temporising adjunct and does not downgrade the reconstructive requirements (23). Retrospective studies have reported that NPWT can be used to promote granulation tissue through prolonged application and thereby reduce the requirement for flap coverage (24, 25, 26, 27), but most report unacceptably high deep infection rates.

NPWT and the permissible delay to definitive reconstruction

A retrospective study of 103 patients and 105 free tissue transfers for (mainly Gustilo–Anderson IIIB and IIIC) open lower limb fractures concluded that NPWT did not permit a delay in definitive soft tissue reconstruction as increased rates of flap take-back, failure, and deep metalwork infection were noted in the NPWT cohort after 72 hours (28). Whilst smaller retrospective series have reached various conclusions regarding permissible delay (29, 30, 31), the weight of evidence analysed and presented in the NICE Guideline concluded that definitive reconstruction should be undertaken within 72 hours (2).

Incisional NPWT over open fractures closed directly

A study of 249 patients with 263 lower extremity fractures (pilon, tibial plateau, and calcaneal) considered to be at high risk for wound dehiscence following definitive open reduction and internal fixation reported that the use of prophylactic NPWT over the closed incision significantly reduced wound dehiscence and risk of subsequent infection (32). However, a multicentre randomised controlled trial with 1548 participants found no difference in the deep surgical site infection rates at 30 and 90 days, patient-reported disability, health-related quality of life, surgical scar assessment, or chronic pain (33, 34). At 30 days, deep surgical site infection occurred in 5.84% of patients treated with NPWT compared with 6.68% of patients in the standard dressing group; absolute risk difference, −0.77%[95%CI, −3.19% to 1.66%]; P = .52) (34).

Other dressing modalities

A small uncontrolled study of Gustilo–Anderson grade II and III open fractures, utilising nanocrystalline silver-impregnated dressings as an interface with NPWT reported a favourable deep infection rate of 1 case in 17 (35).

The use of antibiotic-impregnated cement has been proposed as an alternative to intravenous antibiotics for delivery of a high concentration of antibiotics in the vicinity of the injury. Both polymethylmethacrylate (PMMA) and plaster of Paris have been studied as delivery vehicles (36). In a study reporting the outcomes of patients with primary open lower limb fractures randomised to receive either tobramycin-impregnated PMMA beads or intravenous (IV) antibiotics, there were 2 infections in the 24 managed using beads and 2 infections in the 38 managed by IV antibiotics, with no significant difference between the two groups (37). By contrast, a retrospective, non-randomised study of 704 open fractures (35% of which were Grade III) managed with systemic antibiotics with (547) or without (157) tobramycin-impregnated PMMA beads reported infection rates of 17% (26/157) and 4.2% (23/547), respectively. Sub-analysis revealed a significant reduction in osteomyelitis in Gustilo–Anderson IIIB fractures (26% to 6.3%) when beads were used in addition to systemic antibiotics (38). Another non-randomised retrospective study reported a significant reduction in deep infection rate (16% (4 in 25) to 4% (2 in 53)) when an antibiotic bead pouch was used in addition to systemic antibiotics (39).

Large animal models have been used to investigate the influence of NPWT on the elution of antibiotics from spacer beads. The use of NPWT concurrently with antibiotic beads may enhance elution of antibiotic from the beads leading to lower locally available concentrations (40, 41). Thus, antibiotic beads should not be used in combination with NPWT.

Conclusion

Whilst NICE previously recommended that NPWT be considered as a temporary dressing for managing open fractures following wound excision, a more recent large randomised clinical trial has shown that the NPWT provides no benefit over standard dressings provided. This finding was supported by the latest Cochrane review of negative pressure wound therapy for open traumatic wounds (42). These data would suggest that provided the other principal recommendations in these Standards are followed, including timely wound excision performed jointly by consultant plastic and orthopaedic surgeons and prompt definitive wound coverage within 72 hours of the injury, the precise dressing used in the intervening period is relatively unimportant. Current evidence suggests that if definitive soft tissue closure of the wound is delayed beyond 3 days the deep infection rate rises steeply and NPWT should not be used to delay definitive closure. This calls into question the strategy of using NPWT for prolonged periods to reduce the reconstructive requirements of the wound. There is low-level evidence to suggest that silver-impregnated dressings or antibiotic-impregnated beads may reduce deep soft tissue and bone infections, respectively, following high-energy open fractures. There is a need for further randomised trials of alternative types of wound dressings and wound management strategies in open fractures. The role of NPWT in managing closed incisions at high risk of wound complications, such as those associated with open fractures, has recently been assessed in a large randomised clinical trial that had shown that the NPWT provides no benefit over standard dressings (42).

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