To assume that lumbar plexus-sciatic nerve block combined with sevoflurane can effectively diminish the incidence of cognitive dysfunction in elderly patients after hip arthroplasty.

History and current related studies Elderly patients after total hip arthroplasty often experience postoperative cognitive dysfunction (POCD) and disorders of brain function, such as memories, memory storage and concentration, perception and behavioral disorders. POCD is often transient, can be effectively controlled if measures can be taken timely; otherwise, POCD can become permanent, which may greatly affect the patient's quality of life. At present, pathogenesis and therapeutic effect of POCD are not clear in elderly patients undergoing total hip arthroplasty.

With the help of a nerve stimulator, lumbar plexus combined with sciatic nerve block achieves the precise positioning of the nerve puncture site, and achieves unilateral limb complete anesthesia. The scope of the block is limited, and it has little influence on circulation. Lumbar plexus and sacral sciatic nerve block can effectively suppress stress response to surgery and pain and improve cognitive dysfunction in patients after surgery. Basic fibroblast growth factor (bFGF) has been shown to be associated with cognitive function. The decreased bFGF expression can directly affect the function of nerve cells and cause a decrease in cognitive ability. Sevoflurane can improve cognitive dysfunction after surgery. However, whether sevoflurance can reduce the occurrence of POCD after hip arthroplasty has not been reported.

Adverse events

1. To record adverse events, including incision pain, waist-dorsal muscle pain, spinal cord and nerve injury, hypotension, nausea and vomiting, dyspnea, and bradycardia.
2. If severe adverse events occur, investigators will report details including the date of occurrence and measures taken to treat the adverse events to the principle investigator and the institutional review board within 24 hours.

Data collection, management, analysis, open access

1. Data collection: Case report forms will be collected, processed using Epidata software (Epidata Association, Odense, Denmark), collated, and then recorded electronically by data managers using a double-data entry strategy.
2. Data management: The locked electronic database will be accessible and locked only by the project manager. This arrangement will not be altered. The Affiliated Hospital of Qinghai University, China will preserve all of the data regarding this trial.
3. Data analysis: A professional statistician will statistically analyze the electronic database and will create an outcome analysis report that will be submitted to the lead researchers. An independent data monitoring committee will supervise and manage the trial data, ensuring a scientific and stringent trial that yields accurate and complete data.
4. Data open access: Anonymized trial data will be published at www.figshare.com.

Statistical analysis

1. Statistical analysis will be performed using SPSS 19.0 software (IBM, Armonk, NY, USA) and will follow the intention-to-treat principle.
2. Measurement data will be normally distributed and expressed as the mean ± standard deviation. Count data will be expressed as constituent ratio or rate.
3. bFGF expression, Mini-Mental State Examination (MMSE) score and Montreal Cognitive Assessment (MoCA) score in both groups will be compared using two-sample t-test. Above indexes at three time points in the same group will be will be compared using repeated measures analysis of variance. The incidence of adverse reactions in both groups will be compared using Pearson X2 test.
4. The correlation between serum bFGF expression and cognitive function will be analyzed using Pearson correlation analysis.
5. The significance level will be α = 0.05.

Inclusion Criteria:

• Age range: 60-70 years
• American Society of Anesthesiologists (ASA) classification: Class II and class III
• Unilateral hip arthroplasty
• Educational level: Junior high school and above, no cognitive dysfunction before surgery
• Hip joint disease treatment for the first time
• All patients or family members signed the informed consent

Exclusion Criteria:

• Nervous system disease or psychosis
• Allergy to anesthesia
• Poor compliance
• Cardiovascular system disease, severe primary liver and kidney diseases
• Other diseases affecting cognitive function or cognitive dysfunction