Peripheral Perfusion Index-guided Fluid Resuscitation for Preventing Acute Skin Failure in Elderly Critically Ill Patients

Inclusion Criteria: 1. Age ≥ 65 years. 2. Diagnosis of sepsis (according to Sepsis-3 criteria) or other types of shock requiring early and aggressive fluid resuscitation. 3. APACHE II score ≥ 15 at ICU admission. 4. Expected ICU length of stay ≥ 72 hours. 5. Written informed consent obtained from the patient or their legally authorized representative. Exclusion Criteria: 1. Pre-existing stage III or higher pressure injury or skin necrosis at the time of enrollment. 2. Severe dermatological disease or peripheral vascular disease that could interfere with the assessment of skin or peripheral perfusion. 3. Inability to perform continuous finger pulse oximetry monitoring (e.g., due to bilateral finger injury, amputation, or severe peripheral edema). 4. Contraindications to liberal fluid resuscitation (e.g., acute cardiogenic pulmonary edema, severe heart failure with fluid overload). 5. Expected survival \< 24 hours due to terminal illness or irreversible condition. Concurrent participation in another interventional clinical trial.