Final answer:
The nurse should prioritize Client 3 with an oxygen saturation of 88%, indicating potential life-threatening respiratory distress.
Step-by-step explanation:
In a medical-surgical unit, the nurse should prioritize interventions for clients based on their conditions. The highest priority should be given to Client 3: 1 day postoperative, pain level 8/10, Oxygen saturation 88% (95% to 100%). This client's oxygen level is below normal, indicating potential respiratory distress which can be life-threatening and should be addressed immediately. Interventions may include administering oxygen and further assessment of respiratory status. Other clients also require attention but are less urgent compared to someone with compromised airway or breathing.