Final answer:
The nurse would document the drainage as serosanguineous, which is a mixture of serous fluid and blood-tinged sanguineous fluid, typical of a normal healing process.
Step-by-step explanation:
If a nurse observes drainage from a post-operative client's closed wound drainage system that is thin with a pale pink-yellow color, the nurse would document the drainage as serosanguineous. This type of drainage typically indicates a normal healing process, containing a mixture of clear serous fluid and sanguineous, or blood-tinged fluid. It is neither purely serous (clear, watery fluid) nor purely sanguineous (bright red blood), which are indicators of different types of wound healing or complications. Moreover, it is not purulent, which would be indicative of an infection and would typically appear thick and yellow or green with a foul odor, a sign that might warrant antibiotic treatment.