Unexpected cat death, hoping for help figuring this out

Hi. My 7 year-old Maine Coon Paws had to be put to sleep three days ago after developing pneumothorax. He had battled several health problems in the past, but we didn’t see this coming and I feel I need to try and understand what happened as best I can. (Just to be clear, this isn’t a request for a second opinion and I am completely happy with how our vet treated the cat - what I’m struggling with is whether there is anything we could have done differently at home to prevent this, or any info that might help me understand it, given that we have other cats and I don’t want any of them to go through this.) Paws had survived an episode of acute renal failure three and a half years ago; at the time he was given only a 10% chance of survival but amazingly he came through it. We don’t know what caused it (our cats are allowed outside, so we’re not able to fully monitor them.) After that he had his bloods monitored every 3-6 months and they were nearly always satisfactory, occasionally his kidney values would creep up but then they’d settle again. This year he seemed to have a run of poor health - pancreatitis in April (which he had to be hospitalised for, but seemed to recover from) then later in the year he was diagnosed with herpes after developing an eye discharge which we treated with the appropriate ointments. This mostly seemed to clear up (although one of his eyes still discharged on the odd occasion) but I have read that it can lead to respiratory issues. Over the last couple of weeks it seemed at times as if Paws was under the weather, and he didn’t always come for his meals (and sometimes ate less when he did come) but it was very difficult to tell what was going on because at other times he seemed totally his normal self - purring, interested in food, wanting strokes, playful/affectionate etc. Also hard to tell how much he was eating because we have 3 other cats, so lots of bowls in the house, biscuits always on offer, etc. A week or so ago we noticed some weight loss and started to watch him more closely, his appetite seemed to be picking up so we wondered if he’d picked up some bug but was on the mend, but we made an appointment with the vet to be on the safe side. That was on Monday of this week. They couldn’t fit us in till Wednesday but advised us to bring him in sooner if he seemed to deteriorate. Monday evening my husband noticed some odd behaviour when Paws was trying to eat, mouth movements that looked like it was difficult for him to eat and breathe at the same time, so he took him in. They couldn’t immediately tell what was wrong, did bloods and they seemed fine, but an ultrasound and subsequently a CT scan the next day revealed pneumothorax. We don't know what caused it - no injuries as far as anyone was able to tell so I think the vet was going with the theory that he had an infection of some kind, possibly pneumonia. (Cancer was discussed as a possibility but apparently the vet who viewed the CT scan result considered it less likely than infection.) Vet showed us/explained the scans. A lot of air/fluid in each lung and Paws’s breathing was obviously affected but he was still in good spirits, social/friendly etc, but the vet also told us the lungs themselves looked in poor shape. Later that afternoon vet managed to remove most of the air/fluid, but Paws’s breathing worsened and we were called. Just as we arrived, he crashed and had to be put to sleep. 😿😿😿 I realise it’s impossible to make a long-range diagnosis on a deceased cat and that’s not what I’m looking for. However, given that we have other cats including a sibling of Paws’s, I’m anxious to avoid this happening again and can’t help wondering whether there’s anything we could have done differently. The vet said there would have been no way to predict the pneumothorax, but I can't help thinking we must have been missing signs/symptoms of underlying illness at home as I just don’t understand the speed of the lung deterioration at the end. Given all his previous illnesses, though, I’m also wondering if these could have weakened Paws’s system and/or predisposed him towards other illnesses? Any thoughts or advice would be much appreciated, thanks in advance and sorry this is so long (I thought it best to set out all the facts).

Also apologies for the long chunk of text - I thought I put paragraph breaks in, but it doesn't look like they worked!

Hello!  I have the same problem here regarding paragraphing text - please don't worry!  I'm very sad to hear about Paws.  It sounds as though he was a much loved cat and had been taken to the vets appropriately and had some quite detailed investigations done, above and beyond the technological limitations of most first opinion vets, to try to help him.  As you say, it sounds as though it would have been difficult to have predicted that pneumothorax; it is certainly not something I saw coming as I read through the case.  Immune systems often do become less effective in the face of other disease.  Pancreatitis is often desribed as an idiopathic disease (to quote an old lecturer of mine, idiopathic means 'We idiots don't yet know what the underlying pathology is') but according to Professor Gunn-More in 2013, it can often be linked to autoimmune disease, inflammation or infection.  Therefore there may be a possibly that there was something linking these disease processes in a way that I don't actually fully understand.

Regarding Paws, he was clearly a loved cat and you sound to.have done a lot for him. Losing a cat can be devastating and there is website called the Ralph Site that may have information on it that will interest you.  Wishing you all the best.

Thanks for the insights, Liz, and for replying so quickly - it's really helpful. I'll check out the resource you mentioned.