Systematic review of the efficacy of topical haemoglobin therapy for wound healing

Abstract

Hypoxia is a common cause of poor wound healing, for which a variety of oxygen therapies have been developed. In order to overcome the limitations of traditional methods of treatment, namely the type of equipment, its setting, safety and cost, local haemoglobin therapy has been developed, although no reviews have so far been published. Here, we systematically review the current evidence to establish the efficacy, scope, adverse reactions, and required precautions of this new form of therapy. A search of the literature was conducted in the PubMed, Embase, Scopus, CENTRAL, CINAHL, and Web of science databases, with 17 studies meeting the eligibility criteria, comprising one animal model study and 16 clinical studies. Local haemoglobin therapy is able to safely and effectively promote the healing of a variety of wounds, especially those that are chronic and non‐healing. However, premature discontinuation of this treatment can result in impediment to wound healing and even deterioration of the wound. The distinct benefit of the elimination of slough and relief of pain suggests that this technique may represent a new generation of debridement technology. Furthermore, its ease of use and convenience enables patient self‐management, thereby greatly reducing health care costs.

1. INTRODUCTION

Wound healing is a dynamic stepwise process, which involves three highly orchestrated phases: inflammation, proliferation, and remodelling. ¹ , ² Oxygen is critical for wound healing and is required for almost every step of the process. ³ , ⁴ Early transient hypoxia following injury initiates the wound healing process via stimulation of the release of growth factors and induction of angiogenesis. ² , ⁴ , ⁵ However, prolonged severe hypoxia leads to damaged or newly regenerated tissue becoming inert or injured due to the increased levels of oxygen free‐radicals, further resulting in perturbed wound repair and the potential for the development of a chronic wound. ⁶ Furthermore, under hypoxic conditions, the ability of cells to generate energy decreases, gradually weakening the immune system, leading to infection. ⁷ The long‐term persistence of wounds and their repeated treatment places a considerable burden on individuals that suffer with them, their caregivers, and health care systems. ⁸

As the essential role of oxygen in wound healing has become gradually recognised, hyperbaric oxygen therapy (HBOT) and topical oxygen therapy (TOT) have been developed and used in wound treatments. ⁹ , ¹⁰ Although HBOT is effective in increasing oxygen levels in blood and tissue and able to promote wound healing under specific conditions, its application is limited due to potential complications, poor cost‐effectiveness, and being feasible only in clinical settings. ¹¹ Compared with HOBT, TOT is safer because it does not rely on the damaged vascular system to deliver oxygen to the wound. ³ As bioengineering technology has developed, novel methods of delivering topical oxygen have been constantly proposed. ¹²

Traditional methods of providing local continuous oxygen therapy are to supply the wound bed with the required quantity of oxygen externally. However, due to the diffusion barrier of the exudate, oxygen cannot reach the bottom of the wound effectively, reducing the therapeutic effect. ¹³ Although local pressurised oxygen therapy can improve the situation, it has limited applicability due to the nature of the equipment. Local haemoglobin therapy is a novel method of treatment based on the principle that haemoglobin can be applied topically to the wound bed as an aqueous solution to promote oxygen diffusion. ¹⁴ It is well known that haemoglobin is the natural oxygen transporter in humans, which can reversibly bind with oxygen. ¹⁵ In a hypoxic wound, haemoglobin sprayed on the wound binds oxygen from the surrounding air and transports it to the base of the wound, from which it diffuses into the cells at a rate that depends on the differential partial pressure of oxygen that exists between the wound bed and air. This process is repeated continuously, because haemoglobin is not consumed, creating a continuous cycle of oxygen transport. ¹⁶ At present, local haemoglobin therapy is mainly applied in the form of a spray, which has received increasing attention due to its convenience and low cost. ¹⁷ However, no systematic analysis of the therapy has yet been published. The purpose of the present review is to provide a comprehensive scientific overview of the efficacy, scope, adverse reactions, and required precautions of topical haemoglobin therapy, including preclinical and clinical evidence, with a view to providing guidance for clinical decision making and future research.

2. METHODS

2.1. Search strategies

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta‐analyses (PRISMA) guidelines, the present systematic review was conducted by searching the following electronic databases: PubMed, EMBASE, Scopus, CENTRAL (the Cochrane central register of randomised controlled trials [RCTs]), CINAHL, and Web of science. The inclusion of studies was not limited to any specific date of publication, the most recent being from October 2019.

The search strategy was customised for each database. For PubMed, the strategy used Medical Subject Headings (MeSH) in conjunction with free text terms representing the definitions of topical haemoglobin spray and wound healing. A variety of strategies were then adapted for other databases, as described in Table S1.

2.2. Eligibility criteria

The inclusion criteria were as follows: (a) studies published in English in peer‐reviewed journals; (b) studies evaluating topical haemoglobin sprays for wound healing; (c) study designs included preclinical studies (ie, in vivo animal model studies) or human studies (ie, RCTs or non‐RCTs). The following type of publications were excluded: (a) reviews, editorials, or letters; (b) case reports or a case series of fewer than three patients; (c) repeated studies, trial protocols; (d) studies describing systemic administration of haemoglobin for wound healing.

2.3. Identification of eligible studies

The initial screening of titles and abstracts based on the inclusion and exclusion criteria was independently conducted by two reviewers, a third independent reviewer being involved when disagreements could not be resolved. The steps mentioned earlier were used to review the remaining full‐text articles to confirm their eligibility using the same process.

2.4. Data extraction and quality

The following variables were extracted from preclinical studies: author, year of publication, animal model, wound type, administration, intervention and control group details, dosage, observation time points, methods of assessment, and principal findings. The following variables were extracted from human studies: author, year of publication, study type, participant characteristics (number, wound type), intervention and control group details, number and timing of data points, and principal findings (rate of healing/healing duration, wound size, wound‐bed characteristics, exudate levels, pain, adverse events, and product experience). Two reviewers independently extracted data from each included study, another reviewer ensured accuracy of the extracted numerical results data. Summary characteristics of the papers and theses included in this study are reported in Tables S2 and S3.

The Cochrane Collaboration's risk‐of‐bias tool for systematic reviews of interventions version (v. 5.1.0) for RCTs ¹⁸ and the Methodological index for non‐randomised studies (MINORS) for non‐randomised experimental studies ¹⁹ were used to evaluate the quality of the human studies. For the quality assessment of animal studies, the initial Stroke Therapy Academic Industry Roundtable (STAIR) recommendations were used. ²⁰ All included studies were independently assessed and scores were finalised by consensus.

2.5. Statistical analysis

Because the included studies mostly formed a case series, with study objectives and outcome measures that were heterogeneous, a quantitative meta‐analysis was not conducted. We performed a best‐evidence synthesis to identify key results and limitations of the included studies.

3. RESULTS

A total of 732 citations were identified from searches of six databases and two additional citations from other sources. After deleting duplicates, 325 articles were evaluated based on their titles and abstract contents, of which 31 were retained. The full text of these articles was assessed, wherein 17 studies meet the eligibility criteria. Full details of the search results are summarised in Figure 1.

FIGURE 1.

Flow diagram of inclusion and exclusion of the literature

3.1. Section I: in vivo animal model study

Only one preclinical study was included in this review, which evaluated topical application of oxygenated, chemically modified bovine haemoglobin (IKOR 2084) to ischaemic wounds in a rabbit ear ischaemic wound model. ²¹ The results indicate that this treatment was able to enhance angiogenesis, as demonstrated by increased expression of CD31 protein, and greater vascular endothelial growth factor and endothelial nitric oxide synthase mRNA expression levels. In addition, cell proliferation and increased collagen deposition were also observed, which promoted the progress of healing in ischaemic wounds.

3.2. Section II: in human studies

3.2.1. Study characteristics

The majority of human studies included in this review were conducted in Europe and all studies were published from 2011 to 2018. In this study, 2 RCTs, 3 historical controlled studies, and 14 case series studies were included. The sample sizes ranged from 4 ¹⁶ to 200 ²² people and the duration of the majority of studies ranged from 4 weeks ¹⁵ , ¹⁷ , ²³ , ²⁴ , ²⁵ to 28 months. ²⁶ All human research was conducted through the application of a haemoglobin spray (Granulox, SastoMed, Georgsmarienhütte, Germany). It should be noted that number of studies were part of a series, that is, the evaluation of patients at different time points following the intervention. ¹⁴ , ¹⁵ , ²² , ²³ , ²⁵ , ²⁶ , ²⁷ , ²⁸

3.2.2. Type and location of wounds

In the present systematic review, the types of wounds treated with haemoglobin spray included chronic venous leg ulcers, ¹³ , ¹⁴ , ²³ , ²⁴ , ²⁹ pressure ulcers, ¹⁴ , ³⁰ chronic diabetic foot ulcers (DFU), ¹⁵ , ¹⁶ , ²⁵ , ²⁶ , ²⁷ sloughy wounds, ²² , ²⁸ , ³¹ chronic/acute wounds from self‐harm, ¹⁷ or postsurgical wounds from pilonidal cysts. ³² The majority of studies targeted chronic or non‐healing wounds, that is, wounds that persisted for greater than 12 weeks ¹³ , ²⁵ , ²⁶ , ²⁹ or decreased in size by less than 40% after a run‐in‐period (2 weeks for existing patients or 4 weeks for new patients) despite receiving local best practice. ¹⁵ , ²⁴ , ²⁷ , ³¹ , ³³

3.2.3. Wound healing

Results from all the studies confirmed that topical application of haemoglobin reduced wound size and promoted healing in a variety of wounds. Compared with the randomised concurrent control group and historical control group, the results indicate that reduction in wound size was most significant in the topical haemoglobin group. ¹³ , ²² , ²⁶ , ³³ Hunt et al also found that this was evident as early as the first week of treatment and was observed at all subsequent weeks, up to week 26. ²² Furthermore, all studies of chronic and non‐healing wounds found that such a therapy was effective in promoting wound healing, ¹⁵ , ²⁴ , ²⁷ , ³¹ , ³³ with two studies demonstrating a positive reduction occurring in all patients. ²⁴ , ²⁵

The rates of wound healing were consistent with the results of wound sizes, that is, the wound healing rate of the topical haemoglobin group was greater than that of the randomised control group and the historical control group that received standard treatment. ²² , ²⁹ , ³³ The healing of wounds by secondary intention following surgical intervention for pilonidal cysts and application of a haemoglobin spray also promoted wound closure and achieved excellent aesthetic appearance. ³²

3.2.4. Wound‐bed characteristics and exudate levels

The majority of studies reported the characteristics of the wound beds, especially the coverage of slough. Studies on chronic DFUs found that haemoglobin spray can markedly reduce the quantity of slough, ¹⁵ , ²⁵ , ²⁶ , ²⁷ and Hunt et al found that this method completely eliminated slough from chronic DFU patients in 4 weeks, compared with only a 10% reduction in the historical control group. ²⁶ The superior desloughing effect was also confirmed in studies of other wounds (such as chronic venous leg ulcers, pressure ulcers, sloughy wounds). ¹³ , ¹⁴ , ²² , ²⁴ , ²⁸ , ³³ However, it should be noted that a number of studies found that premature discontinuation of topical haemoglobin therapy resulted in a recurrence of slough and deterioration in the wounds. ²⁶ , ³³ In addition, studies have shown that such treatment promotes the growth of granulation tissue and epithelisation in pressure ulcers and chronic venous leg ulcers. ¹³ , ¹⁴ , ²⁴

Of the eight studies that reported exudate levels, ¹⁴ , ¹⁵ , ²² , ²⁴ , ²⁵ , ²⁶ , ²⁷ , ³³ all confirmed that the haemoglobin spray improved exudate levels in various types of wound, with even severe levels of exudate also rapidly reduced. ²⁶

3.2.5. Pain, adverse events, and product experience

Eight trials investigated the ability of topical haemoglobin to reduce pain. ¹³ , ¹⁴ , ²² , ²³ , ²⁴ , ²⁶ , ²⁹ , ³³ All studies demonstrated that the therapy quickly relieved pain regardless of wound type, with significant benefits apparent early in the course of treatment. In addition, a number of studies also demonstrated that this therapy also significantly reduced pain during the changing of dressings. ¹⁴ , ²⁹

Fourteen trials investigated adverse events, although none occurred in any study, ¹³ , ¹⁴ , ¹⁵ , ¹⁷ , ²⁵ , ²⁶ , ²⁷ , ²⁸ , ²⁹ , ³¹ , ³³ with the exception of one study reporting nine adverse events in two patients. ²⁹ However, these adverse events did not include local inflammation, allergic reaction, skin irritation, burning, or pain, which would have been indicative of an undesired event of a suspicious nature. ²⁹ All clinicians, patients, and caregivers found this type of product easy to use ¹⁷ , ²⁵ , ²⁸ , ³¹ and the patients described their experience as being excellent or good, and were willing to continue with the product. ¹⁷ , ²⁸ , ³¹

3.2.6. Risk of bias in individual studies

Risks of bias are presented in Tables S5 and S6. Only one preclinical study and two human RCTs were of poor quality. In the non‐randomised human studies, all reported a clearly stated aim and appropriate endpoints but did not calculate the study size. The majority of studies did not provide sufficient information regarding the inclusion of consecutive patients and blind evaluation of endpoints.

4. DISCUSSION

An animal model study and 19 human studies were included in the present systematic review to evaluate the effectiveness of topical haemoglobin therapy on a variety of wounds and collected evidence that indicated that this technique promoted wound healing, reduced the quantity of slough and exudate, and relieved pain.

As described earlier, the wound healing process requires a large supply of oxygen to fulfil the increased metabolic demands of physiological wound debridement, granulation of tissue growth, and defence against pathogens, with hypoxia representing a common reason for the lack of wound healing. ³⁴ , ³⁵ Various oxygen therapies have been developed to improve the local oxygen supply to wounds, such as HBOT, topical pressurised oxygen therapy, and topical continuous oxygen therapy. ³⁶ , ³⁷ , ³⁸ These methods, while effective, all require specific equipment, are inflexible, and are used mostly in a clinical setting. Researchers have created a simpler and easier solution, in which haemoglobin is applied as an aqueous solution to a wound bed by spraying, which promotes oxygen diffusion to the wound, thereby accelerating its healing. ²⁴ The results of photoacoustic imaging demonstrated a significant increase in StO₂ from a mean of 66.1% to 71% within 20 minutes of topical application of haemoglobin to patients with chronic leg ulcers. Imaging data demonstrated that local oxygenation increased not only on the surface but also up to a depth of at least 1 cm. ³⁹ Preclinical studies also verified that topical application of haemoglobin enhanced angiogenesis, cell proliferation, and collagen deposition that improved the progress of healing in ischaemic wounds. ²¹ This method promoted the healing of various kinds of wounds, especially chronic wounds, in all human studies. The studies of Haycocks et al and Bateman et al of chronic DFUs demonstrated that the vast majority of wounds exhibited positive wound reduction within 4 weeks of use of the haemoglobin spray, some benefits even persisting for 2 years, with a score of 4 using the site, ischaemia, neuropathy, bacterial infection, area and depth (SINBAD) classification system. ¹⁵ , ²⁵ A considerable number of studies of non‐healing wounds found that the therapy significantly promoted the healing of such wounds, ¹⁵ , ²⁴ , ²⁷ , ³¹ , ³³ with positive reduction observed to occur in every patient, ²⁴ , ²⁵ suggesting that local haemoglobin represents a novel strategy for the treatment of refractory wounds. It should be noted that although there was a study that used this therapy to treat acute wounds, the results of wound healing, such as wound size reduction and rate of healing, were not reported. ¹⁷ Therefore, the therapeutic effect of this therapy on acute wounds is not yet clear and requires investigation in subsequent studies. Furthermore, this effect has also been found in special types of wounds, such as secondary defects formed as a result of pilonidal cyst surgery. ³² A case report demonstrated that this method promoted the healing of a leg ulcer with Budd‐Chiari syndrome, ⁴⁰ providing a new technique for the treatment of special types of wound.

Topical haemoglobin therapy exhibits remarkable performance in relieving pain and reducing slough. It is well known that patients with chronic wounds often experience pain, especially that associated with changes in dressings, which causes distress to patients. ⁴¹ , ⁴² Haemoglobin therapy offers a potential solution to this problem. A large number of studies found that this technique was able to relieve pain to a significant degree. ¹⁴ , ²² , ²³ , ²⁴ , ²⁶ Tickle et al adopted haemoglobin therapy to treat patients with pressure ulcers and found that it not only alleviated ongoing pain but also reduced pain during the changing of dressings, a clear benefit for these patients. ¹⁴ Moreover, a number of studies of chronic wounds reported that the treatment rapidly eliminated slough over 4 weeks' treatment, ²⁵ , ²⁶ , ³³ and a study on sloughy wounds reported that, as early as week 1, the reduction in the quantity of slough in the local haemoglobin group (67%) was greater than that in the historical control group (8%). ²² Slough provides an ideal environment for the survival and growth of biofilms, which increases the risk of wound infection and a delay in wound healing. ⁴³ , ⁴⁴ Therefore, the management of slough should be addressed as an important element of wound care. Traditional treatments utilise debridement and other desloughing techniques, but repeated debridement undoubtedly causes considerable pain to patients with increased medical costs. ⁴⁴ Due to the outstanding benefits of local haemoglobin spray in reducing slough and pain relief, a number of researchers recommend haemoglobin spray as a first‐line debridement technique instead of traditional treatments. ²² However, it should be noted that a number of studies have found that premature discontinuation of haemoglobin therapy can lead to recurrence of slough and stagnation or deterioration of wound healing. ²² , ²⁶ , ³³ Thus, strict monitoring of usage is required, especially for the self‐management of patients at home.

All haemoglobin sprays included in the present study were derived from pig erythrocytes, and so far no adverse event has been reported in any study as a result of this. Holzer et al performed a safety analysis of the spray and found no nanoparticles, dust, PM 2.5, PM 10, or any harmful concentration of particles produced during its application, indicating that there was no risk of inhalation of dangerous concentrations of spray or any fine particles during its usage. ⁴⁵ In addition, unlike traditional methods of local administration of oxygen, which are susceptible to the limitations of the equipment, a local haemoglobin spray is handy and convenient. All patients and their caregivers included in the review considered this method easy to implement, which is conducive to self‐management of wounds at home. ¹⁷ , ²⁸ , ³¹ Studies have demonstrated that adoption of the spray on sloughy wounds or in patients that have self‐harmed produced positive results by self‐management, which reduces the reliance of high‐cost care. ¹⁷ , ²⁸ A cost‐analysis study adopting haemoglobin therapy to treat DFUs in Germany also confirmed that it could significantly reduce the cost of German health insurance. ⁴⁶

4.1. Limitations

The majority of existing human studies of local haemoglobin therapy were small retrospective case series studies and historical control studies, which were generally at risk of bias. Both RCTs focused on chronic venous leg ulcers. ¹³ , ²⁹ There was a lack of high‐quality studies on other wound types. In addition, it should be noted that, although the first authors of these studies were different, a considerable proportion of the studies were authored by Hunt's team and there was no guarantee that the studies did not overlap. Therefore, the strength of the evidence in this review is limited. In the future, a greater number of high‐quality studies from different teams in different countries are required to explore the effects of topical haemoglobin spray in a variety of wounds.

There are too few preclinical studies of the mechanisms of haemoglobin treatment of wounds, and additional research is required to clearly determine the mode of action, especially the mode of desloughing, which may involve bactericidal and microbial/biofilms.

5. CONCLUSIONS

In conclusion, local haemoglobin therapy can safely and effectively promote the healing of a variety of wounds, especially those that are chronic and non‐healing. However, premature discontinuation of this method without following the treatment regimen can lead to stagnant or worsened healing, requiring a medical provider to strengthen supervision. The therapy has special advantages in elimination of slough and relieving pain, and so it represents a new generation of debridement technology. In addition, its ease of use and convenience is beneficial to wound self‐management, greatly reducing medical costs.

CONFLICT OF INTEREST

The authors declare no potential conflicts of interest.

Supporting information

Appendix S1. Supporting Information.

Hu J, Guo S, Hu H, Sun J. Systematic review of the efficacy of topical haemoglobin therapy for wound healing. Int Wound J. 2020;17:1323–1330. 10.1111/iwj.13392