Final answer:
The highest priority collaborative problem for an older post-knee replacement surgery patient with limited mobility is the potential complication of venous thromboembolism, due to the increased risk of deep vein thrombosis and pulmonary embolism.
Step-by-step explanation:
The collaborative problem that the nurse should identify as a priority for an older patient who had knee replacement surgery and is only tolerating being out of bed twice a day with physical therapy is potential complication: venous thromboembolism (VTE). Limited mobility can lead to a higher risk of blood clots forming in the deep veins, commonly referred to as deep vein thrombosis (DVT). Such clots can travel to the lungs, causing a potentially fatal pulmonary embolism (PE). Venous stasis due to immobility, endothelial injury from surgery, and hypercoagulability contribute to the increased risk of VTE in postoperative patients. Nursing measures to mitigate this risk include ensuring adequate hydration, promoting mobility as tolerated, and potentially using pharmacologic prophylaxis and compression devices.
While hypovolemic shock, fluid and electrolyte imbalance, and impaired surgical wound healing are also concerns, these are less likely to be primary concerns at this stage in the absence of specific indicators such as hemorrhage, abnormal lab values, or signs of infection or poor wound healing. Considering the clinical context and the fact that the patient is two days post-operation, VTE prevention aligns with standard postoperative care protocols for patients with reduced mobility.