Apparently, the incidence of post-operative delirium after knee replacement surgery is rather high - 32% according to a study. Mr. Flink and others did an experiment to see what pre-existing medical conditions are associated with post-operative delirium in knee replacement surgery patients. Their results are published in the April edition of the Anesthesiology Journal and showed that 27 of 106 (or 25.5%) patients developed post-op delirium after their knee surgery. Of note, these patients were all elderly. Among patients with obstructive sleep apnea (OSA), 53.3% had post-op delirium, compared to 20.9% of patients without OSA. After multiple statistical analyses, only OSA was consistently a significant independent predictor of post-op delirium, among the medical conditions monitored. The reason why OSA may contribute to post-op delirium is not known. The study authors mention repeated oxygen level drops as a cause, which is possible. OSA can also cause general inflammation, which apparently can increase the chance of developing post-op delirium. I wonder if delirium is more common because OSA causes sleep fragmentation, even if the oxygen levels do not decrease dangerously low. More studies are needed for sure.
Interestingly, post-op delirium still occurred in those patients who used their CPAP in the hospital, but the incidence of delirium was less than in those with OSA that did not use their CPAP in the hospital. But there were not enough patients in the sample to be statistically significant. My clinical experience is that patients do better when they bring their CPAP to the hospital for use before and after surgery. It will be interesting to see if a larger study shows an objective decrease in post-op delirium with the use of CPAP.