The purpose of this study was to measure cerebrospinal fluid density in aged patients and to see if there was a correlation between these factors and cerebrospinal fluid density by using the electronic medical record system to understand the patient's gender, blood glucose, blood biochemical electrolytes and blood levels.

Hip joint injury is one of the common injuries in the elderly, and hip arthroplasty is a treatment method that allows patients to get out of bed and return to social life as soon as possible. Currently, the common position for hip arthroplasty is the lateral position; and combined spinal and epidural anesthesia or subarachnoid anesthesia is also the common anesthesia method for hip arthroplasty. In the lateral position, the patient's affected limb is often on top and the healthy limb is on the bottom; the healthy side position is also the usual position for hip arthroplasty. In this position, it may be optimal to use a lighter specific gravity local anesthetic drug because it tends to anesthetize only the upper affected limb and does not require a return to the supine position after anesthesia due to changes in the plane of block, minimizing pain and hemodynamic fluctuations during anesthesia and position changes.

Currently, light specific gravity is more of a concept. Because in the available data, only the range of cerebrospinal fluid density of ordinary healthy adults is available, there is little literature and data to describe and analyze what the cerebrospinal fluid density of elderly patients actually is. Therefore, when we administer subarachnoid anesthesia to elderly patients, we cannot determine whether the dispensed local anesthetic drug is a light specific gravity.

In this study, we intend to collect cerebrospinal fluid from elderly patients who underwent hip arthroplasty under combined lumbar and rigid anesthesia or subarachnoid anesthesia, and measure the cerebrospinal fluid density in elderly patients, and observe whether there is a correlation between the above factors and cerebrospinal fluid density through the electronic medical record system to understand the patient's gender, blood glucose, blood biochemical electrolytes and routine blood levels; thus, we can better guide the use of lighter specific gravity drugs in clinical practice.

Inclusion Criteria:

• Receiving combined spinal and epidural anesthesia or subarachnoid anesthesia ASA Ⅰ or Ⅱ patients No significant neurological pathology No recent history of cerebral infarction No recent history of cerebral hemorrhage No central nervous system inflammation No spinal inflammatory disease No history of spinal surgery Patients who have given pre-operative informed written consent

Exclusion Criteria:

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Selected aged patients who had hip arthroplasty in our hospital between December 2022 and May 2023