13.1 Negative Pressure Wound Therapy

Why closed suction is an advanced therapy

Negative pressure wound therapy (NPWT) is a sealed dressing attached to a controlled vacuum. Independent OpenExamPrep teaching for Certified Wound Care Nurse (CWCN) candidates treats it as an advanced modality under blueprint clusters 030402 and 030406: you recommend it when a healable, debrided cavity or a high-exudate wound needs mechanical support, and you withhold it when the machine would hide a surgical emergency. NPWT does not create arterial inflow, does not replace offloading of a plantar ulcer, and does not sterilize untreated osteomyelitis.

Two mechanical effects run at once. Macrostrain is the visible deformation. The filler collapses, wound margins are drawn toward the center, undermining volume shrinks, and interstitial edema is pulled into the tubing. Less edema can improve local perfusion and make the next dressing change a smaller hole. Microstrain is the microscopic stretch at the filler–tissue interface. Cells elongate, mitotic signaling rises, and granulation tissue fills from the base. The third job is exudate removal: proteases and inflammatory fluid leave the bed instead of bathing keratinocytes and macerating intact skin.

Those three effects assume a prepared bed. Foam on leather eschar cannot microstrain living cells. Foam on an unexplored bowel fistula can pull enteric contents into a closed system. Foam on an unprotected vessel can erode a wall. The exam item is usually the mismatch, not the brand name on the canister.

Fillers: black foam, white foam, and gauze

The filler is not decoration. Pore size and stiffness change how aggressively tissue grows into the material and how easily you can retrieve it from a tunnel.

Cut foam to the wound, not larger than the wound. Foam that rides onto intact skin becomes a macerating suction pad. In a tunnel, use a strip or white foam you can count and retrieve; never lose a fragment. A nonadherent contact layer is reasonable over tendon, a grafted surface, or a painful bed when the team still wants suction above it. Contact layers are not a license to skip surgical coverage of exposed vessels or viscera.

Pressure, continuous versus intermittent

A continuous setting near 125 mmHg is a commonly used adult starting point from the early vacuum-assisted closure literature. Independent OpenExamPrep teaching treats 125 mmHg as a typical reference, not a universal law and not a WOCNCB-mandated number. Grafts, painful wounds, ischemic edges, and some gauze systems are often run lower. Higher settings do not automatically mean faster healing; they can increase pain and bleeding risk.

Intermittent cycling (a classic research pattern is several minutes on and a shorter interval off) can increase granulation compared with continuous suction in some models, but many people feel the cycle as a repeated tug. Continuous mode is usually better tolerated, better for a tenuous seal, and the default while you establish the dressing. If pain spikes when suction starts, lower the pressure, add a contact layer, or premedicate; do not tell the person to “get used to tearing.”

Application rules that the item actually tests

Fill dead space. Loose foam that bridges a cavity leaves a pocket where fluid pools and granulation never starts. Overpacking that blanches the wall is ischemia, not thoroughness.

Protect the periwound. Barrier film, a hydrocolloid window, or a drape platform keeps adhesive off fragile skin and keeps exudate from sitting on the epidermis. A leaking edge that is “fixed” by stacking more drape on macerated skin is how you create a MARSI ring.

Obtain a seal. Suction should hold without a continuous high-intensity leak alarm. Hair, a moist crease, an enterostomy nearby, or a body contour can break the drape. A small amount of stoma paste or a drape bridge is technique; a canister that never reaches target pressure is a failed therapy.

Count pieces. Document foam fragments, tunnels packed, and the pressure and mode. A missing foam chip at removal is a retained foreign body until proven otherwise.

Contraindications and precautions

Treat these as do-not-seal problems until the underlying issue is handled. Manufacturer labels and facility policy still govern the device in front of you; the clinical pattern is stable.

Untreated osteomyelitis is a relative contraindication until debridement and antibiotics are in motion. A clean, draining cavity over treated bone is a different stem from “start the vacuum and skip the surgeon.” Malignancy in the wound is usually a withhold. Unexplored fistula to bowel, bladder, or a body cavity is a hard stop. Intact eschar is a preparation failure. Exposed vessels or organs without a surgeon’s protective plan are a hemorrhage or erosion risk.

Precautions are not automatic bans. People on anticoagulants can receive NPWT if the bed is not oozing and someone is watching the canister. An enteric fistula needs a specialized dressing that separates stool from the granulating bed; a generic black-foam pancake over a spout is not that dressing. Pain that persists after a pressure drop is a reason to change strategy.

Instillation NPWT and incisional NPWT

Instillation NPWT (NPWTi) adds a dwell of saline or a prescribed irrigant, then resumes suction. The idea is to loosen debris and dilute planktonic bacteria in a contaminated or infected cavity after debridement. Instillation is not a substitute for operative drainage of an abscess and is not a reason to skip systemic antibiotics when they are indicated. Dwell time and fluid choice follow the device order; your job is to confirm the wound was opened and cleaned first.

Incisional NPWT (closed-incision negative pressure) sits on a sutured or stapled surgical wound, not in an open cavity. The dressing holds edges, manages incision exudate, and may reduce edema in a high-risk closure—obesity, a dirty case, a groin or sternum with a history of dehiscence. You are not packing an open abdomen with an incisional sponge. If the incision opens, the therapy has left the incisional category and needs a new assessment.

Trouble: leaks, maceration, blood in the canister

A leak means the vacuum never reaches the bed. Find the channel: a wrinkle, a fistula, wet adhesive, or a tube that has lifted. Reseal; do not keep silencing the alarm through a shift.

Maceration means the periwound is wetter than the wound. Window the skin, improve the barrier, shrink foam so it stays inside the margins, and consider a more absorbent interval dressing if volume outruns the canister schedule.

Bleeding into the canister—frank blood, a sudden volume of red fluid, or a drop in blood pressure—is hemorrhage. Stop the therapy, leave a pressure dressing, notify the team, and evaluate. Do not “clear the line” and restart. Foam that was placed over an unprotected vessel, a recently debrided arterial bed, or a coagulopathic surface is the usual story.

Clinical scenario

Mr. Okonkwo, 64, has a debrided sacral Stage 4 cavity, palpable pulses, no fluctuance, and a wound culture already treated. The base is red granulation with moderate exudate. Black PU foam cut inside the margins, a hydrocolloid window on the periwound, and continuous suction near 125 mmHg is a coherent plan. Two days later the night nurse reports a canister half filled with bright blood and a soft blood pressure. Independent OpenExamPrep teaching is to stop NPWT and treat this as bleeding, not to increase suction “to pull the rest out.” If the same man had presented with intact black eschar and a suspected enteric fistula, the first move would have been exploration and debridement, not a same-day foam seal.