13.2 HBOT, Bioengineered Tissue, and Leech Therapy
Key Takeaways
- Hyperbaric oxygen therapy delivers 100 percent oxygen at about 2.0–2.5 atmospheres absolute so dissolved oxygen, angiogenesis, and leukocyte killing can rise in a compromised bed.
- A Wagner grade 3 or deeper diabetic foot ulcer after revascularization and infection control is a classic HBOT use; osteoradionecrosis, selected compromised flaps, and chronic refractory osteomyelitis are commonly cited UHMS-type indications.
- Untreated pneumothorax is a hard stop for HBOT; some chemotherapies, claustrophobia, and middle-ear barotrauma risk are cautions.
- Living bilayered constructs, acellular dermal matrices, allografts, and xenografts need a clean, well-perfused bed plus offloading or compression by etiology.
- Medicinal leeches treat venous congestion of a flap: hirudin anticoagulates the bite, Aeromonas prophylaxis is typically required, and hemoglobin must be watched.
Hyperbaric oxygen as a systemic adjunct
Hyperbaric oxygen therapy (HBOT) places the person in a chamber that delivers 100 percent oxygen at about 2.0–2.5 atmospheres absolute (ATA). Independent OpenExamPrep teaching for CWCN candidates treats HBOT as an advanced therapy in the same 030402 / 030406 cluster as NPWT and bioengineered tissue: you recognize when hypoxia is the remaining limiter and when the chamber is unsafe. Breathing room air at sea level dissolves little oxygen in plasma. Under pressure, plasma oxygen rises enough to diffuse farther into poorly perfused but not dead tissue, support collagen deposition and angiogenesis, and restore leukocyte oxidative burst so neutrophils can kill. Sessions often last about 90–120 minutes over a multi-week series; exact protocols belong to the hyperbaric team.
HBOT does not bypass a blocked tibial artery. If the foot is critically ischemic, the first call is vascular reconstruction or endovascular inflow, not a standing order for thirty dives. Transcutaneous oxygen measurements are sometimes used to show that a hypoxic wound can respond when oxygen is raised; a flat, nonresponsive tracing is a reason to fix perfusion first.
Commonly cited indications—not a WOCNCB list
Wound-related uses that appear in Undersea and Hyperbaric Medical Society (UHMS)–type indication lists, and that CWCN-style items often sample, include:
- Diabetic foot ulcer Wagner grade 3 or deeper (deep abscess, osteomyelitis, or more extensive necrosis) after glucose, offloading, debridement, and revascularization have been optimized
- Osteoradionecrosis and selected delayed radiation soft-tissue injury, because irradiated beds are hypovascular and hypocellular
- Selected compromised flaps or grafts that are hypoxic but still viable
- Chronic refractory osteomyelitis that has already had surgery and culture-guided antibiotics
Independent OpenExamPrep teaching presents those as commonly cited UHMS-type indications. They are not published here as an official WOCNCB indication list, and they are not a claim that every stalled wound deserves a chamber. Wagner 1 or 2 ulcers that have never been offloaded are a dressing-and-shoe problem. A wet gangrenous foot that still needs source control is an operating-room problem.
| Candidate pattern | Why HBOT is discussed | What must already be true |
|---|---|---|
| Wagner 3+ DFU | Deep infection or bone in a diabetic host after the obvious work | Perfusion optimized, infection drained, offloading in place |
| Osteoradionecrosis | Radiation left a hypovascular mandible or pelvis | Oncology and surgical plans are active |
| Compromised flap | Tissue is dusky from hypoxia, not from a dead arterial pedicle | A still-viable flap, not a black eschar |
| Refractory osteomyelitis | Biofilm and hypoxic bone impair host defense | Debridement and antibiotics already started |
Contraindications and chamber cautions
Untreated pneumothorax is the classic absolute contraindication. Expanding trapped air in a pleural space under pressure can tension. Treat the chest first.
Cautions you should be able to name:
- Some chemotherapies (bleomycin pulmonary toxicity, doxorubicin cardiotoxicity, and cisplatin in older hyperbaric teaching) need oncology clearance; the wound nurse flags the drug list rather than clearing the dive.
- Claustrophobia can make a monoplace chamber intolerable; anxiolysis or a multiplace option is a logistics issue, not stubbornness.
- Barotrauma to ears and sinuses: people who cannot equalize need tympanostomy consideration or a delay.
- Severe obstructive lung disease with CO2 retention, uncontrolled seizure disorder, and some implanted devices are program-specific screens.
Fever, a new cough, or chest pain before a dive is a same-day hold. HBOT is not a walk-in substitute for a missing ABI.
Bioengineered and cellular tissue products
These products are advanced living or processed tissues, not a thicker foam. Classes CWCN candidates should separate:
- Living bilayered constructs (cultured keratinocytes over a fibroblast-containing dermis) that can deliver living cells and matrix signals
- Acellular dermal matrices that provide a collagen scaffold for host cells to populate
- Allografts (human donor skin or dermis) used as a temporary biologic cover or scaffold
- Xenografts (typically porcine) used as a temporary cover when human tissue is not the plan
Every class fails on the same three bedside mistakes. First, the bed is dirty: slough, untreated osteomyelitis, or heavy bioburden under a living construct is an expensive culture medium. Second, the bed is ischemic: a product cannot angiogenize a foot that has no inflow. Third, the etiology is ignored: a plantar product without offloading is walked off by lunchtime; a gaiter product without compression is washed off by edema. Facility formulary and payer rules decide which named product is stocked. Your exam job is the bed, not the catalog number.
Prepare the wound as you would for a graft: debride to healthy tissue, control exudate enough that the construct can contact the bed, and confirm the person can return for the protocol’s dressing sequence. If the construct is dislodged, desiccated, or sitting in pus at the first check, the failure is usually preparation or mechanics, not a mysterious product defect.
Which description correctly states what hyperbaric oxygen therapy does at the chamber?
A person with diabetes has a plantar ulcer probing to bone. Revascularization, operative drainage, culture-guided antibiotics, and offloading are already in place. The wound remains hypoxic. Which advanced-therapy statement is most accurate?
Leech therapy for venous congestion
Medicinal leeches (Hirudo medicinalis) are an advanced salvage tool when a flap or replant has venous congestion but still has arterial inflow. The flap looks blue-purple, tense, and rapid-capillary, and pinprick yields dark blood. Arterial failure looks pale and cool with no bright bleed. Leeches do not treat arterial ischemia. Putting a leech on a white, pulseless flap wastes time the surgeon needs for a return to the operating room.
Each bite does two jobs. Mechanical blood removal unloads the congested venous bed. Hirudin and related salivary peptides anticoagulate the bite so oozing continues for hours after the animal detaches, which is the therapeutic point. That same anticoagulation is why you watch the dressing and the hemoglobin. A series of leeches on a large flap can drop the hematocrit enough to need transfusion.
The leech gut carries Aeromonas species (commonly Aeromonas hydrophila). Antibiotic prophylaxis covering Aeromonas is typically required for the duration of therapy—often a fluoroquinolone or trimethoprim–sulfamethoxazole unless cultures or allergies redirect. A fever or cellulitis during leech therapy is infection until proven otherwise, not “expected flap inflammation.”
Practical rules: use pharmacy-sourced medicinal leeches, attach to the congested skin, keep the environment moist, and confirm that each animal is accounted for so none migrate into a cavity or dressing. After detachment, the bite should continue to ooze; if it clots immediately and the flap remains tense, venous outflow is still failing. Stop if the person refuses, if bleeding is uncontrolled, or if the flap has clearly infarcted.
Clinical scenario
Ms. Brennan, 58, completed pelvic radiation years ago and now has a nonhealing sacral wound over fibrotic, hypovascular tissue. Pulses are present, the bed is clean after serial debridement, and osteoradionecrosis is in the differential. Independent OpenExamPrep teaching would support a conversation about HBOT as a commonly cited UHMS-type option for delayed radiation injury while local care continues—not a claim that the Board published that list. Her roommate, Mr. Singh, has a free-flap reconstruction that turned purple six hours after surgery, with a Doppler arterial signal still present. Leeches plus Aeromonas prophylaxis and hemoglobin checks match venous congestion. A bilayered living construct would be the wrong next product on either person if the sacral bed were still sloughy or if the flap problem were arterial. If Ms. Brennan’s medication list included recent bleomycin and an untreated pneumothorax on today’s film, the chamber would wait.
A living bilayered skin construct is being considered for a clean venous ulcer. Which prerequisite is required before the product can work?
A postoperative flap is tense, blue-purple, and still has an arterial Doppler signal. Which leech-therapy statement is correct?