Postoperative cognitive impairment is one of the most common complications in elderly surgical patients. Laser laryngeal surgery is a short procedure, but characterized by high risk of disastrous airway fire. So the recommended oxygen concentration is less than 30%. For elderly patients, because of preoperatively declined cardiovascular and lung function and cognitive function, there is a potential that intraoperative low oxygen concentration may lead to drop of arterial oxygen tension, decrease of brain oxygenation, and exacerbate brain function impairment. Intravenous anesthesia and inhalation anesthesia is two commonly used technique for general anesthesia. Consequently, we carry out this study to identify whether different classes of anesthetics can affect postoperative cognitive function in old patient undergoing laser laryngeal surgery.

The allocation sequence is generated by computer random number generation, and the allocation is placed in sequentially numbered opaque sealed envelopes by a non-investigator. Enrolment and data collection are performed by trained research staff who are not involved in the care of the patients. The treating clinicians are not blinded to the assignment group, but all other staff involved in both the collection and collation of data, and administration of neurocognitive testing, are blinded to group allocation

The primary measurement is the MMS scores. The secondary measurements are intraoperative desaturation score (multiplying Spo2 < 90% by time (seconds)), extubation time, orientation time, and time to discharge from the post-anaesthesia care unit (PACU).

A sample size of 35 was determined by using a power analysis based on the assumptions that the incidence of postoperative cognitive impairment in adult after otorhinolaryngological surgery would be as high as 50 %, b) a 70% reduction (from 50% to 15%) would be of clinical significance, and c) α= 0.05, β= 0.2.

The continuous variables were expressed as means ± standard deviation (SD) whereas categorical variables were expressed as frequency and percentage for data description.

The outcome of interest is cognitive decline. A Generalized estimating equation (GEE) model with compound symmetry covariance structure was constructed to compare differences between two treatments with different time points as the repeated factors. As the effect of treatments may vary across different time points, an interaction between treatments and time was included in the model. Bonferroni-corrected post hoc test was conducted to adjust the observed significant level for multiple comparisons if the null hypothesis was rejected.

Inclusion Criteria:

• Patients scheduled for laser laryngeal surgery under general anesthesia with either Propofol or desflurane based technique.

Exclusion Criteria:

• Patients with cardiac, pulmonary, hepatic, or renal dysfunction, epilepsy, or uncontrolled hypertension, or those taking medications that influence the central nervous system, are excluded from the study. Patients who show obvious alteration of mental status, or refuse to participate, are also excluded from the study.