Wound Flushing: 8-15 psi, 35 mL, and the Debridement Line

Wound irrigation has one governing number: 8 to 15 psi, or 0.55 to 1.0 bar. Below 8 psi the stream pushes debris around without lifting it off. Above 15 psi it drives bacteria deeper, turning a 2 mm wound into a 6 mm pocket of contamination. A 35 mL syringe with an 18 to 19 gauge needle lands in that window; a 60 mL bulb syringe gives about 1 psi and does almost nothing.

Pressure is the technique

Pressure at the tip is plunger force divided by needle opening, so the same hand on a smaller needle makes a harder stream. The table below is the whole hardware decision.

Setup	Pressure at the tip	Typical flow	Use it for
35 mL syringe, 19 G needle	8 psi, 0.55 bar	about 250 mL per minute	Standard fresh wound, 1 to 3 cm
35 mL syringe, 18 G needle	12 psi, 0.83 bar	about 400 mL per minute	Gritty or contaminated wound
60 mL syringe, 19 G needle	6 psi, 0.41 bar	about 300 mL per minute	Large wound, fragile tissue
12 mL syringe, 18 G needle	20 to 25 psi	about 150 mL per minute	Nothing on a cat; too forceful
60 mL bulb syringe	1 psi, 0.07 bar	about 200 mL per minute	Nothing; too weak to lift debris
Squeeze bottle with a sport cap	5 to 40 psi, uncontrolled	varies with hand strength	Nothing; the number is unknown

Without needles, a 35 mL syringe with the hub pressed to the wound edge gives 2 to 4 psi: under-treatment, but safe.

3 steps in 10 minutes

Step 1, clear the field, 2 to 3 minutes. Clip fur 2 to 3 cm back from the wound edge with a clipper, not scissors, blade parallel to the skin so loose hair does not fall in. Wipe the surrounding skin, never the wound bed, with saline-soaked gauze; gauze rubbed across granulation tissue tears the capillary buds that took 24 hours to build.

Step 2, irrigate, 3 to 5 minutes. Saline at 35 to 37 C, syringe 2 to 5 cm from the surface, stream at about 45 degrees so it flows across the wound and off the far edge rather than down into it. Work from the cleanest corner to the dirtiest, one pass, no back-and-forth, because a used stream carries what it just lifted. Stop when the fluid runs clear, which for a small wound is usually 100 to 200 mL.

Step 3, close and record, 1 minute. Pat the rim dry, leave the bed moist, cover with a non-stick pad if the cat tolerates it, and write down the date, volume and what came out; that record is what decides the 48-hour call.

Volume: 50 to 100 mL per centimeter

The rule is 50 to 100 mL per 1 cm of wound length, doubled for a visibly dirty wound. A 3 cm cut needs 150 to 300 mL, which is 5 to 9 refills of a 35 mL syringe and about 4 minutes of steady work. A 1 cm puncture needs 10 to 20 mL, but a puncture should not be irrigated at pressure at all: the opening closes over the fluid and you inject the contamination you were trying to remove.

Refill from a freshly opened bottle: saline left in a syringe in the fridge for 2 days is no longer sterile. Date the bottle when you open it and discard it after 7 days.

What pressure does to the wound bed

At 8 to 15 psi, the stream lifts loose debris, bacteria and clot from the surface without crossing into healthy tissue. At 20 psi and above, the jet cuts a channel: fluid and bacteria travel 2 to 5 mm laterally into the subcutaneous fat, and the wound you clean in the morning is wider in the evening. So a shower head, a garden hose or a 12 mL syringe with a small needle is out.

The fluid matters less than the pressure. 0.9% saline at body temperature is the default because it neither damages tissue nor stings, and potable tap water beats nothing at all: 200 mL of water outworks 20 mL of the ideal solution. Never put household disinfectant into a wound; it kills the cells trying to close it.

The debridement line

Home care cleans; it does not cut. Debridement is the removal of dead tissue, and judging how much comes off belongs to someone who can see the tissue in good light and stop bleeding. Three things stay off-limits at home: cutting or pulling away black, gray or yellow leathery tissue; probing the depth of a wound with a swab or forceps; and opening a pocket to see how far it runs.

Dead tissue at the edge needs a vet within 24 hours: it is a culture medium, and the infection spreads under skin that still looks normal. A puncture, especially a cat bite, needs a vet the same day, because the surface hole closes in 6 to 12 hours over bacteria sitting 1 to 2 cm deep.

Frequency and the 48-hour rule

Once a day for a clean wound, twice for a contaminated one; the home wound routine covers the day-by-day checkpoints. Each irrigation disturbs the clot and the new capillary bed, so 4 sessions a day is a wound that never leaves the inflammatory phase. Change the cover every 24 to 48 hours, or at once when it is wet through.

At 48 hours the wound should look less angry than on day 0: less swelling, less heat, a rim that is pink rather than deep red. If it is the same or worse, stop irrigating and book an appointment. Redness that has spread more than 1 cm beyond the original edge, a wound warm to the touch, or any yellow-green discharge are the same signal.

5 habits that make a wound worse

1. Scrubbing with gauze until it bleeds, which removes the granulation tissue the wound just built.
2. Irrigating with a 12 mL syringe and a 25 G needle at 20 to 25 psi, which pushes dirt sideways into fat.
3. Soaking in a bowl or bath, which macerates the skin edge after 10 to 15 minutes.
4. Bandaging tight enough to leave a mark, which cuts blood supply at 20 to 30 mmHg of pressure and hides swelling.
5. Reusing the same syringe for 3 days without rinsing, which puts back what the last session removed. Setup hygiene, such as the scoop routine, matters too.

When it is a vet visit, not a flush

• Any wound over 2 cm long, over 1 cm deep, or one you cannot see the bottom of.
• Any cat bite or claw puncture, even a 2 mm hole that has stopped bleeding.
• Black, gray or yellow leathery tissue at the edge, or a smell that survives one irrigation.
• Bleeding that restarts after 10 minutes of firm pressure, or a wound over a joint.
• No improvement at 48 hours, spreading redness past 1 cm, or a cat that is off food with a fever.

Terms mentioned in this article

MM

Frequently asked

Related guides

• Flushing a Cat's Eye: 3 Steps, 10 mL, 20 cm
• Cat Carrying Technique: 3 Holds and a 60-Second Limit
• Home Wound Care for Cats: 1 Clean a Day, 48 Hours
• Ear Drops for Cats: 5 Steps, 30 Seconds, 6 Nevers
• Cat Eye Drops: 4 Steps, 30 Seconds, 25 Microlitres
• Liquid Medicine for Cats: 3 Methods, 2 ml a Push