BIONTM Neuromuscular Stimulation for Pressure Ulcer Prevention
Hilton Marc Kaplan & Anne-Caroline Dupont Salter
Alfred Mann Institute, University of Southern California
Pressure ulcers are a debilitating pathology resulting from pressure and shear in the soft tissues of immobilized patients129. Nomenclature varies widely (decubitus ulcers, pressure sores, bed sores, ischemic sores, etc.), and a multitude of therapies exist. The fact that so many therapies are available, is ironically testament to their own inadequacies.
Etiology
The pathogenesis of pressure ulcers (PUs) derives from a host of compounding etiological factors129:
Pressure over bony prominences is key. A reciprocal relationship between pressure intensity and pressure duration has been recognized since 1930. Just as high pressures over a short time may result in PUs, so can lower pressures over a longer time. Immobility that results in the inability to shift weight plays an important role because the tissues do not experience periodic relief from the pressures on them. Friction and shear are important factors too, because they can exacerbate the soft tissue damage. Tissue that is damaged, atrophied, scarred or infected demonstrates increased susceptibility to pressure. The elderly or immune compromised patient and the patient with wound healing or collagen-vascular diseases are at greater risk too. A lack of sensation, common in many poorly mobile individuals, aggravates the situation further, because the individual may forget to move even to the extent that he or she can. Insensate tissues also demonstrate compromised neurotrophic growth and repair mechanisms. Urinary and/or fecal incontinence may also be present in individuals whose immobility derives from the injury of the spinal cord or brain. The irritation can fuel maceration of the skin and contribute to further susceptibility to the effects of pressure. As blood vessels become occluded or narrowed the soft tissues which they supply necrose (break down and die)because they are starved of nutrients and oxygen, and because they accumulate toxic wastes and metabolites.
Costs – to the Patient and Society
Age- and pathology-matched patient trials have shown that hospital stays increase 3-5 fold in patients suffering from PUs, at significant hospital expense101. One of 3.6 immobile patients will develop PUs114. One group particularly prone to PUs is the spinal cord injured (SCI) patient group. Over 250,000 individuals have SCI in the US, and approximately 10,000 new injuries occur each year102. SCI most commonly results in paralysis, as well as repeated and serious associated complications such as PUs, incontinence, sexual dysfunction, etc. Healing and rehabilitation are also impacted by the psychological ramifications of depression, resentment, etc.103. The cost of treating PUs in the US has been estimated at over $ 55 Billion annually (based on an average increase in hospital stay of 21.6 days at $2,360 per day in almost 1.1 million patients per year101).
Staging of PUs
The National PU Advisory Panel Staging112 is a widely accepted method of staging PUs:
Stage I: Non-blanchable erythema of intact skin; the heralding lesion of skin ulceration.
Stage II: Partial thickness skin loss involving epidermis and/or dermis. The ulcer is superficial and presents clinically as an abrasion, blister or shallow crater.
Stage III: Full thickness skin loss involving damage or necrosis of subcutaneous tissue which may extend down to, but not through, underlying fascia. The ulcer presents clinically as a deep crater with or without undermining of adjacent tissue.
Stage IV: Full thickness skin loss with extensive destruction, tissue necrosis or damage to muscles, bone or supporting structures (e.g. tendon, joint, capsule, etc.).
Current Treatments
Current treatments usually involve months of care and hospitalization, including:
Tissue Load Reduction:
Specialized pressure support surfaces (air-fluidized, low-air-loss, alternating-air, static flotation [air or water], foam standard or Roho dry floatation mattress126), are used to reduce the continuous pressure on tissues.
Nursing Care and Allied Therapies:
Patients are supplied with nursing care and assistance for most of their activities of daily living. Typically, they must be turned or moved at least every 2 hours (which usually involves at least 2 staff members). Physiotherapists, occupational therapists, nutritionists, social workers and psychologists are all integral to successful treatment and rehabilitation as well.
More detailed guidelines on preventive care are given by the National PU Advisory Panel124, AMA and others132:
· Skin Moisture Control:
Careful management of skin moisture is essential to prevent maceration and minimize friction. Patients should be bathed only when needed for comfort or cleanliness; skin should be cleaned as soon as soiled with urine or stool; urine leaks must be assessed and treated; skin should be protected with cream or ointment; and absorbent pads and/or briefs with quick-drying surfaces should be used.
· Prevention of Over-Drying of the Skin:
Moisturizing the skin where needed.
· Friction Reduction:
Lifting, rather than dragging, when repositioning; and using cornstarch on skin.
· Changing of Position / Turning:
At least every 2 hours if bed-ridden; at least every hour if confined to a chair; and every 15 minutes if able to shift own weight.
· Optimization of Pressure Distribution:
Keeping the patient as flat as possible if bed-ridden (raising the head of the bed as little and for as short a time as possible); using foam, gel, or air cushions to relieve pressure; and pillows or wedges to keep knees or ankles from touching each other.
· Nutritional Support:
Ensure adequate caloric intake of a balanced diet and food supplements as required.
· Physiotherapy:
Maintenance of range of motion so that a wider range of positions are possible.
Prevention of systemic deconditioning (cardiopulmonary, cardiovascular, and musculoskeletal)
· Social & Psychological resources (to encourage compliance with therapies):
Social workers and vocational rehabilitation services
Peer counseling and support groups
Formal psychotherapy &/or family therapy
Treatment of Complications and Supportive Treatment:
Where indicated:
Antibiotic cover (systemic and topical), swab cultures.
Nutritional supplementation (enteral and parenteral).
Blood transfusions, iron and folate supplementation.
Pain management.
Minimization of muscle spasticity (to optimize healing by secondary intention)125.
Wound Care and Surgical Interventions127, 132:
· Stage I:
Prevention of further skin damage.
· Stage II:
Debridement (usually not necessary).
Cleansing: isotonic saline; avoidance of high-pressure irrigation; manage hypergranulation tissue that may impede ulcer healing.
Dressings: hydrocolloid wafers, semipermeable foam, or polyurethane film (occlusive / vacuum).
· Stages III and IV:
Debridement: autolytic, mechanical (wet-to-dry dressing), enzymatic, or surgical.
Cleansing: isotonic saline, may use high-pressure irrigation; manage hypergranulation tissue that may impede ulcer healing.
Dressings: if wound is shallow and clean – hydrocolloid wafers, semipermeable foam, or polyurethane film; if wound is deep and clean – fill dead space with wet gauze; If there is necrotic debris – wet-to-dry dressings; if there is excessive exudate – absorptive dressings.
Surgical repair: once wounds are clean (< 100,000 organisms/cm2) and the patient is medically stable, a variety of reconstructive techniques may be utilized including: direct closure, skin grafts, skin flaps, musculocutaneous flaps, and free flaps.
· The Gluteal Rotation Flap:
While a variety of musculocutaneous flaps are useful in treating PUs, the gluteal rotation flap is of particular relevance to this study. The gluteal rotation flap is an axial flap based on the inferior (and/or superior) gluteal artery, located between the greater trochanter and the ischial tuberosity125 (Fig.s 1 & 2). After excising the PU wound, the muscle flap is elevated, together with an overlying skin paddle which is supplied by musculocutaneous perforators. It may then be rotated superomedially to cover sacral PU wounds, or inferomedially to cover ischial PUs (Fig.s 3 & 4). In this way healthy muscle and skin are brought in to repair the deficient area, and provide healthy tissue over bony prominences, while scars are designed to lie away from these areas.
Postoperative care and Recurrence Rates:
Typically, at Rancho Los Amigos patients are nursed as inpatients for 8 weeks postoperatively. This involves 5 weeks of complete non-weightbearing, where the patient is nursed prone or on the unoperated side; 2 weeks of limited mobilization and 1 week of gradually increased sitting until ready for discharge. The cutaneous sutures are removed at the end of week 3. Throughout this process patients are educated on pressure management and skin inspection. This regimen is in keeping with the postoperative care guidelines as recommended by the AMA and others132.
Potential postoperative complications include132:
Wound dehiscence / separation
Delayed infection and abscess
Hematoma and seroma
Initial results with muscle flaps are generally good, although recurrence of PUs is common135,133,136. In the case of musculocutaneous flaps 33% recurred over 2-12 years (with cutaneous flaps recurrence rates were as high as 43%)136. As lack of sensation in the flap may contribute to this high recurrence rate, neurosensory musculocutaneous flaps have been advocated137,138. In the sensate patient gluteal rotation flaps offer this potential advantage.
In the face of ever-increasing limitations on health-resources, very high recurrence rates and advances being made in the wound healing realm (e.g. flotation-type beds, growth factors, etc.), Disa, Carlton & Goldberg133 attempted, in 1992, to define which patients might benefit most from surgery. This group reviewed data from 40 consecutive patients with 68 pressure sores operated on under a single surgeon between 1981 and 1989. Of 66 operations performed, 55 were musculo- or fasciocutaneous flaps, and 11 were cutaneous. Over a mean followup of 21 months (1-71) they recorded a 36% operative complication rate, and no mortalities. Despite an 80% healed rate at the time of discharge, 61% of PUs and 69% of patients had recurrent ulceration within a mean of 9.3 months (1-71 mo.s). The conclusion was that surgical reconstruction of PUs did not appear to be efficacious in young posttraumatic paraplegics or the cerebrally compromised elderly.
Adjuvant Therapies:
Adjuvant therapies include: electrical stimulation, hyperbaric oxygen, infrared or ultraviolet light, low-energy laser irradiation, ultrasound therapy, and topical applications of agents as varied as growth factors and maggot therapy.
For its wound-healing effects, only electrical stimulation of the skin has been recommended by the AHCPR (US Dept of Health and Human Services, Agency for Health Care Policy and Research) as an adjunct to conventional therapy for nonhealing ulcers128.
NeuroMuscular Electrical Stimulation for PU Prevention
Neuromuscular electrical stimulation (NMES) for pressure-relief has been researched for well over 2 decades now, with multiple papers indicating the positive benefits of this therapy100,104,105. Current hypotheses of the mechanism that leads to prevention of pressure ulcers include weight shifting to relieve pressure and improve pressure distribution, increased muscle volume (more padding), and increased vascularity100,104,105.
A patent on using NMES for PU inhibition was filed with the USPTO in 1985, and issued in 1988. Assigned to The University of Michigan, it is based on transcutaneous NMES over potential PU sites and claims benefits from the resultant shifting of weight, muscle ‘blood pump’ effect, muscle hypertrophy (padding) and the ‘conditioning’ of atrophic muscles100.
In 2000 Bogie et al104 published an article in which the role of NMES in PU prevention was reviewed. They concluded that implantable NMES systems may have great potential for PU prevention, particularly for individuals who lack sensation or are physically unable to perform regular independent pressure relief.
Preliminary results of a more recent study by Bogie’s group105 were published in an abstract. They investigated the hypothesis that long-term use of NMES using an implanted stimulation system would produce a sustained improvement in tissue health, and may therefore provide an alternative technique for the prevention of pressure sores in veterans with spinal cord injury. Preliminary results show that interface pressures in the ischial region were significantly reduced (p<0.01). No details on stimulation parameters were offered.
Waiting for article / book (d.w. FJR pls Anne) to find out the particular paradigm used (what m.s were exercised, …) and what was measured (recurrence, …)?
It has been shown too that PU recurrence rates can be reduced from 20% to 6% using ES113.
Current Drawbacks
The limitations of current treatments are of great concern. Despite the wide variety of current preventive measures, PUs remain a significant pathology (as attested to by the high incidence of PUs (up to 38%150) and the extremely high recurrence rates even after flap surgery (61%133). ES – a therapy that has demonstrated significant potential benefits in the literature – remains unharnessed because of limitations imposed by the prerequisite “wiring” of patients.
BION Electrical Stimulation for Pelvic Pressure Ulcer Prevention
BIONs are injectable, wireless electrical stimulators that receive power and command signals by inductive coupling from an external transmission coil. One or more can be placed near or in various muscles and nerves and selectively activated with precise control of pulse current, duration and timing. BIONs have been demonstrated to be safe and effective in chronic studies in animals and human subjects (). They are particularly suitable for use in the proposed clinical application because of their small size (2mm diameter x 16mm long), hermetic packaging, stable fixation in connective tissue, and virtually unlimited lifetime. The transmission coil to power and command the implants can be located in a cushion, seat or back of a wheel chair, avoiding any direct contact with or penetration of already fragile skin.
Two hypotheses guide this research: First we hypothesize that BION gluteal stimulation will reduce the incidence of PUs. Second, we hypothesize that the treatment will be accepted well by the subjects because it can be self-administered outside a clinic. Using BION microstimulators to electrically stimulate the gluteal muscles is a novel way to achieve the published benefits of ES, without the usual limitations as discussed above.
Fuhrer et al report that 65% of PUs are in the pelvic111.region. Gluteus maximus (gluteus) muscle stimulation will benefit both sacral and ischial lesions. These constitute 42-54% of all PUs according to four biennial national prevalence surveys108. Of these 30% are Stage III & IV111 (where surgery is the treatment of choice). We propose to achieve such gluteal stimulation with a single BION placed along the inferior gluteal neurovascular pedicle. Preliminary anatomic dissections and 3D CT reconstructions performed at the University of Southern California to map these pedicles indicate that the nerve trunk appears at a well-defined location as it exits from beneath the inferior edge of the piriformis muscle, before branching out under and into the substance of gluteus maximus109,110. Placement of a device at this site would facilitate full and reliable stimulation of gluteus.