My cat was an older male cat, approximately 11–13 years old

I would like to ask for a veterinary opinion about my cat’s medical history and the cause of his deterioration. My cat was an older male cat, approximately 11–13 years old. He had been living with me for many years. He had diabetes, which had been diagnosed about three years earlier, and he also had chronic kidney problems. On June 18, 2026, he underwent a dental procedure under general anesthesia, including dental cleaning and multiple tooth extractions. The medications recorded in the veterinary report included midazolam, butorphanol, medetomidine (Domitor), Antisedan, Clamox, and meloxicam. Before the dental procedure, he was eating normally. About 36 hours after the dental procedure, he stopped eating completely. He continued drinking and urinating, and there was no significant vomiting. About six days after the procedure, his condition became serious enough that he was taken to an emergency veterinary clinic and hospitalized for several nights. During that hospitalization, he was found to have severe hyperglycemia and significant kidney abnormalities/acute kidney injury. His glucose was reported to be above 540 mg/dL at one point, and his creatinine and BUN were also elevated. He was dehydrated and had lost weight. He received IV fluids and supportive treatment. After he stabilized, he returned home. For approximately the next 10 days he appeared relatively stable. He was eating again and was receiving subcutaneous fluids at home (about 40 mL per day). His glucose later improved substantially, from around 500 mg/dL to approximately 140 mg/dL. Approximately 20 days after the dental procedure, he suddenly developed severe breathing difficulty. He was taken to the veterinarian, and chest X-rays showed a large amount of free air in the chest cavity (pneumothorax). The veterinarian drained approximately 2–3 liters of air, but his condition did not improve adequately and the air continued to accumulate. The veterinarian suspected a rupture involving lung tissue and considered it a spontaneous pneumothorax. There was no known trauma or accident. The veterinarian also considered his chronic disease, weight loss/cachexia, and poor tissue condition as part of his overall medical condition. My main question is about the cause of the pneumothorax. Could a complication from the endotracheal tube used during the dental anesthesia realistically cause a pneumothorax that appears approximately 20 days later, especially when the cat had been hospitalized, stabilized, returned home, and remained relatively stable for about 10 days? There was no obvious subcutaneous emphysema reported, and the pneumothorax appeared much later rather than immediately after anesthesia. I would like to know, based on veterinary medicine and the timeline, whether an anesthesia/endotracheal-tube complication is medically plausible, or whether this pattern would be more consistent with a spontaneous pneumothorax or an underlying lung problem. The cat ultimately deteriorated and died from the respiratory crisis.