A cat usually comes home within 24 to 48 hours of a urethral obstruction, often with the catheter still in place and a bag taped to the flank. Three things decide whether the next week goes smoothly: the bag stays below the bladder, the system stays closed, and you watch urine volume every few hours. Pink to light red urine for the first 24 to 48 hours is expected. A cat that strains and produces nothing after the catheter comes out is an emergency again, no matter how recently it was treated.
Hanging the bag so it drains by gravity
The collection bag must sit below the level of the bladder at all times, usually 30 to 50 cm below the cat, so urine runs downhill and never flows back up the tube. Backflow carries bacteria straight into the bladder, which is the single most common way a closed system stops being closed.
Loop the tubing so there is no U-shaped dip where urine can pool, and tape the line to the flank or the top of the tail with soft tape rather than clamping it to the cage. When you carry the cat, lift the bag first — a bag dragged along the floor siphons air and urine in the wrong direction. Cats should stay in a large dog crate or a small room with low furniture for the first 24 to 48 hours, because a jump off a shelf pulls the catheter and can inflate the balloon against the neck of the bladder.
How often to empty and when to change
Empty the bag every 8 to 12 hours, and sooner if it reaches two thirds full, because a full bag weighs down the line and pulls on the catheter. Record the volume each time in milliliters, not "a little" or "a lot" — that number is how the vet decides whether the kidney is recovering.
- Wipe the drain spout with an alcohol pad before and after emptying.
- Never disconnect the tubing from the catheter to empty it; that breaks the sterile seal.
- Change the whole bag and line every 24 to 72 hours, or immediately if the tubing looks cloudy or kinked.
- Keep the bag off the floor and out of the litter box, and rinse the outside with water if it gets soiled.
Expect roughly 1 to 2 ml per kg of body weight per hour of urine in a well-hydrated cat, so a 4 kg cat produces 100 to 200 ml a day at minimum, and often 250 to 300 ml after the diuresis that follows unblocking. Sudden drops below half of the previous day's total matter more than a single low reading.
Blood in the urine: what is normal and what is not
The catheter irritates the urethral lining, so pink, rose, or light red urine is common for 24 to 48 hours and fades toward straw color. Small clots the size of a grain of rice are also seen. What is not normal: urine that stays deep red past 48 hours, clots large enough to block the tubing, a bag that suddenly stops filling while the cat is drinking, or urine that smells strongly ammonia-like with grit visible in the line.
Blood alone rarely needs a night visit. Blood plus a cat that is straining, vocalizing, or has a hard, painful bladder does. Post-obstruction cats are also at risk of re-obstruction from inflammation and spasm, not only from stones, which is why the first 7 days get the most attention.
The 7 day watch list
| Day | What to check | Red flag |
|---|---|---|
| Day 1 to 2 | Bag volume every 8 to 12 hours, bag position, tubing kinks | Under 50 ml in 12 hours |
| Day 2 to 3 | Catheter site: swelling, discharge, licking | Swollen prepuce or cloudy seepage |
| Day 3 to 4 | After removal: first urine within 24 hours | No urine 24 hours after removal |
| Day 4 to 5 | Size and frequency of urine clumps in litter | Many tiny clumps, straining |
| Day 5 to 7 | Appetite, water intake, activity, weight | Refusing food, hiding, weight loss |
Re-obstruction within the first week is the risk that shapes the follow-up plan. Published clinical series commonly put the recurrence rate in the range of 15 to 25 percent in the weeks after an initial episode, with most of those happening inside the first 7 days, which is why many clinics schedule a recheck at 5 to 7 days rather than 14.
Water, food, and litter during recovery
Dilute urine is the goal. Offer wet food only, or add 2 to 4 tablespoons of warm water to each meal, and consider a fountain — many cats drink more from moving water. A common target is 40 to 60 ml of water per kg per day including what is in the food, so a 4 kg cat needs roughly 200 ml total.
Litter should be non-clumping paper or pellet type for the first week so you can count output, and it should be in a low-sided box in a quiet corner. Do not switch to a prescription urinary diet mid-recovery without asking; a sudden diet change in a cat that is already inflamed can cause vomiting and refusal. Antibiotics are not routine after uncomplicated unblocking, and finishing a course you were sent home with still matters.
Pain, spasm, and the drugs sent home
Most cats leave on a painkiller, often buprenorphine or robenacoxib, and sometimes prazosin to relax the urethral muscle. Give them at the intervals written on the label, not "when the cat looks sore", because the point is preventing spasm rather than chasing it. Do not add human drugs, and do not share a dog's medication.
Watch for the cat that sits in the box for minutes producing a thin stream, then returns ten minutes later. Frequency with small volume is the earliest sign of trouble, and it shows up hours before a full blockage.
Five things to do tonight
- Measure the height of the bag against the cat and confirm it hangs 30 to 50 cm lower.
- Write the time and volume of every bag empty on a sheet taped to the fridge.
- Set phone alarms at 8 hour intervals for the first two days.
- Photograph the catheter site once a day so swelling is easy to compare.
- Ask the clinic for the exact recheck day and the number to call at 2 am.
Getting the water math right matters as much as the bag: the food and water calculator converts body weight into daily milliliters so you are not guessing. Swelling or a hot, painful lump near the catheter site after an insect sting is a different problem, covered in stings and snakebite. If a tick was attached near the prep site, follow tick removal for cats rather than picking at the wound.
Frequently asked
The urine is pink. Should I go back to the hospital?
Pink or rose-colored urine for the first 24 to 48 hours is expected because the catheter scrapes the urethral lining, and it should fade toward straw yellow. Go back if the color is still deep red after 48 hours, if clots are large enough to slow the tubing, or if the bag stops filling while the cat keeps drinking.
How do I know the catheter is not blocked?
Compare bag volume every 8 hours. A 4 kg cat should produce roughly 100 to 200 ml a day and often more during post-obstruction diuresis. If output drops below half of the previous day, or the bag is unchanged over 12 hours while the cat drinks normally, call the clinic. A blocked catheter is a same-day problem, not a tomorrow problem.
Can I take the bag off to let him move around the house?
No. Disconnecting the line breaks the sterile seal and lets bacteria climb into the bladder, which is the main cause of infection in catheterized cats. Move the cat in a carrier, lift the bag before walking, and keep the bag 30 to 50 cm below the bladder. Freedom of the house resumes after the catheter is removed and the first urine is passed.