A nurse has just received hand-off communication at the start of their shift. After reviewing each client's status, which of the following clients should the nurse see first?

A. The 18-month-old shows signs of improving hydration status, evidenced by adequate wet diapers and food intake. This client is stable. B. The adolescent with mild postoperative pain and preparing for discharge is stable and does not require immediate attention. C. The toddler's low oxygen saturation (91%) and continued coughing indicate potential airway obstruction or impaired gas exchange, which requires immediate assessment and intervention to prevent respiratory failure. D. Although the 6-year-old with asthma should be monitored, their last use of a rescue inhaler 16 hours ago suggests they are not in acute distress.