You won't encounter any enemy units in your immediate vicinity, so you won't have to spend a lot of time scanning the area. Start off by jumping over two fences. Locate an entrance to a new ventilation shaft afterwards which can be found to your right. Head forward and eventually you'll be forced to enter a second shaft.
Follow the second tunnel to its end. Drop down to a lower section without any additional delays. The entrance to third and final shaft is located to your left. Use this shaft to reach Sanatorium area. You'll have to decide here whether you want to travel left or right. The latter seems like a better idea.
Exit the shaft and quickly use your hook to grapple up to the nearest gargoyle. You should now take your time to look around and to scout enemy positions. It'll be to quite difficult to succeed here, because the room is being patrolled by several armed thugs.
I would strongly recommend that you use the exact same tactics as during your previous "silent encounter". Eliminate enemies one by one using Glide Kick abilities and takedowns. Each time you've successfully neutralized an opponent return to the gargoyles and wait for the situation to cool down before attacking other foes.
Make sure to remain hidden all the time, because you may lose a lot of health points as a result of enemy gunfire. If you do get caught move between gargoyles quickly to confuse enemy units. Once you've dealt with all the inmates drop down to the ground floor and locate a small group of rescued doctors (near the elevator). Talk to them in order to find out about their taken friends.
Turn around once the conversation has ended and proceed to the lower floor. Move north to find an exit from this area. You should end up standing in the Upper Corridor. There are three doctors for you to rescue and you can visit their locations in any order you want. I would recommend heading towards doctor Young first, so you should be moving east. Use the yellow line painted on the floor if you're having problems finding the correct path.
Keep moving east, however you will turn south-east in a short while. A couple of thugs will attack you near the door, but eliminating them shouldn't be a problem. Once it's safe locate a door leading to the X-Ray Room.
You'll have to act quickly here, because otherwise doctor Young is going to be executed by her captors. Your objective will be to plant two explosive devices on the weak walls of the central room. The walls are located on the western and on the northern side and you can take a look at my screenshots for additional help. Use an Explosive Gel on the first wall and then run to the second wall to repeat this action.
Once you've planted the second device detonate both charges without any additional delays. The explosions will stun all the inmates, so you won't have to worry about finishing them off. Enter the room and talk to doctor Young.
You may return to the Upper Corridor. Head back to the junction you've past through while leaving the Sanatorium area and proceed towards an unexplored corridor. This time you'll be following the red line to the area where doctor Chen is being held. Keep moving north until you find a door leading to the Surgery Room.