Pressure Blister

A blister caused by sustained pressure, often with shear, that compresses and damages the skin and the underlying tissue. It may be an early partial thickness pressure injury (stage 2) or a result of other causes of pressure and immobility.

• Mechanisms: capillary closing pressure is about 32 mmHg, so sustained pressure above that level, particularly over bony prominences, causes ischaemia. Ischaemia for about 2 hours, with shear and moisture, causes epidermal separation and a blister.
• Sites: sacrum, heels, ischial tuberosities, greater trochanters, malleoli, elbows, occiput and under devices (splints, casts, oxygen tubing, catheters, braces and prostheses).
• Risk factors: immobility, spinal cord injury, stroke, sedation, coma, frailty, malnutrition, incontinence, diabetes, peripheral vascular disease, oedema, low body weight, poor sensation, dementia and prolonged surgery.
• Related types:
  • Coma blisters: tense bullae on the palms, soles and pressure areas, in patients unconscious from drug overdose (barbiturates, benzodiazepines, opioids, tricyclic antidepressants, carbon monoxide), usually within 24 hours of coma onset, and associated with rhabdomyolysis.
  • Diabetic bullae (bullosis diabeticorum): sudden, painless, tense blisters on the feet and legs in diabetes, without trauma, which heal in 2 to 6 weeks.
  • Blisters from fractures, swelling and tight casts or dressings, and from compartment syndrome.

• A red or purple area of non-blanching erythema, followed by an intact or ruptured, serum filled or blood filled blister over a pressure point, with an exposed pink or red moist wound bed after rupture. Pain may be absent in patients with impaired sensation.
• Coma blisters: tense bullae, with surrounding erythema, on dependent areas, and with muscle swelling and tenderness.
• Deep tissue injury shows a purple or maroon discolouration, or a blood filled blister, that can evolve into a full thickness ulcer over days.
• Features of infection: purulent drainage, odour, spreading erythema, warmth, fever, and increasing pain.
• Differential diagnosis: friction blister, second degree burn, bullous pemphigoid, epidermolysis bullosa acquisita, porphyria cutanea tarda, bullous drug eruption, bullous cellulitis, necrotising fasciitis, frostbite, vascular occlusion (acute limb ischaemia), and fixed drug eruption.
• Red flags: dusky skin with pain out of proportion, rapidly spreading blisters, crepitus, compartment syndrome (pain, tense swelling, pain with passive stretch), or rhabdomyolysis.
• Complications: progression to deeper pressure ulcers, infection, osteomyelitis, sepsis, rhabdomyolysis and acute kidney injury (coma blisters), and compartment syndrome.

• Clinical. Stage the injury, measure the wound, and describe the base, edges, exudate and surrounding skin. Check for non-blanching erythema.
• Assess risk with a validated pressure risk scale (Braden or Waterlow) on admission and after any change in condition.
• Assess nutrition (weight, albumin, prealbumin, vitamin D, zinc), glucose or HbA1c, perfusion (pulses, ankle brachial pressure index), continence, mobility and medicines.
• Swab only clinically infected wounds. Take blood cultures if systemic signs are present.
• In coma blisters or immobile patients measure creatine kinase, electrolytes, urea, creatinine, myoglobin in urine, and drug levels or toxicology.
• Biopsy with direct immunofluorescence when blisters are widespread, appear at non-pressure sites, or the cause is unclear.
• X-ray, MRI or bone biopsy if osteomyelitis is suspected in a deep wound.

• Offload pressure, the basis of treatment:
  • Reposition every 2 hours in bed, using the 30 degree side lying position and avoiding direct pressure on the trochanter. Avoid positioning on the blister. Keep the head of the bed at or below 30 degrees unless a medical need, to reduce shear.
  • Use a pressure redistributing mattress or overlay (alternating pressure or high specification foam), and heel offloading devices that float the heel.
  • For sitting, change position every 15 to 30 minutes with weight shifts, and use a pressure relieving cushion. Limit sitting to 1 hour at a time if there is an ischial or sacral injury.
  • Check and rotate medical devices and tubing, and pad under them.
• Blister care:
  • Protect an intact blister with a silicone foam or hydrocolloid dressing. Do not puncture unless it is large, tense, or at risk of rupture, in which case aspirate with a sterile needle at the edge and leave the roof.
  • Ruptured blister or stage 2 wound: clean with sterile saline, and cover with a hydrocolloid, polyurethane foam, or silicone faced dressing. Change every 3 to 7 days or when soiled or lifting.
  • Avoid massage over bony prominences, and avoid ring cushions that cause venous congestion.
  • Deep tissue injury: monitor closely, keep pressure off, and expect evolution; debride only when demarcated.
• Skin care: keep skin clean and dry, manage incontinence with prompt cleaning, pH-balanced cleanser, and barrier cream (zinc oxide or dimethicone), and moisturise dry skin.
• Nutrition: protein 1.25 to 1.5 g/kg per day and energy 30 to 35 kcal/kg per day for patients with pressure injury, with correction of deficiencies. Give a multivitamin or zinc and vitamin C only when deficient.
• Infection: topical antiseptic cleansing with polyhexanide or dilute povidone iodine for local infection, and for cellulitis or systemic signs give flucloxacillin 1 to 2 g IV 6 hourly, or cefazolin 1 to 2 g IV 8 hourly, with vancomycin 15 to 20 mg/kg IV 8 to 12 hourly adjusted to levels if MRSA is likely, and add metronidazole 500 mg IV 8 hourly if anaerobes are suspected. Treat osteomyelitis for 6 weeks or more, with surgery.
• Analgesia: paracetamol 1 g orally 6 hourly, with an opioid for severe pain, and give analgesia before dressing changes.
• Coma blisters and rhabdomyolysis: treat the cause of coma, give intravenous 0.9% sodium chloride at 200 to 300 mL/hour (aim for urine output of 200 to 300 mL/hour in adults) while monitoring for overload, and check potassium and creatine kinase every 6 to 12 hours. Compartment syndrome needs urgent surgical fasciotomy.
• Diabetic bullae: protect, aspirate large tense blisters, apply non-adherent dressings, optimise glucose, and look for infection and neuropathy.
• Surgical options for full thickness wounds: debridement of necrotic tissue, negative pressure wound therapy, flap closure, and diversion in severe sacral injury. Refer to plastic surgery.
• Special groups:
  • Spinal cord injury: daily skin inspection, a pressure relieving cushion, and training in pressure relief.
  • Elderly and frail: regular skin checks on admission and each shift, and early nutrition support.
  • Children: pad devices carefully (tubing, splints), reposition frequently, and examine bony prominences.
  • Pregnancy: left lateral positioning with pressure relief, and wound care with saline cleansing and a hydrocolloid or foam dressing.
  • Renal impairment: adjust antibiotic doses, and watch the fluid balance with rhabdomyolysis.
• Follow up: inspect daily, review wounds weekly with measurement, and expect healing of stage 2 wounds in 1 to 3 weeks. If there is no 30 to 40% reduction in size in 2 to 4 weeks, reassess perfusion, infection, nutrition and offloading, and refer to a wound or plastic surgery service.