Are there any specific approaches or techniques to build a better rapport with patients who initially don't warm up to you?

Focus on the necessary tasks, and on the patient's comfort. Stay objective. Often, as the minutes, hours and/or days pass, the reasons will surface (anxiety or fear, for instance). Bear in mind that, despite your efforts and expertise, there will be those times where it never resolves.

All of us want good rapport with our patients, but reality is that not everyone is going to warm up to you, no matter what you do. Kindness and sincere interest tell the patients you really see them as individuals, and that never goes wrong. Some people are more introverted than others and do not warm up easily or feel the need to do so; some do not trust readily if at all; some are anxious and just want to get a medical visit over with quickly and have no desire to prolong it with friendly exchanges - they are the "get me outta here!" crowd. Still others may be affected by certain geographic or cultural mores - for them warming up to a professional is not normal or usual, and may be downright uncomfortable. You do you and be kind, courteous, interested and honest. If they are going to warm up, that will follow. I want to say personally that I was heartened to see someone ask this question. Strengthens
my faith in modern nursing!