Endotracheal Tube Intolerance and Respiratory Airflow Perception

Breathing Patterns, Coughing Responses at Tracheal Extubation

Oronasal Breathing Pattern, Endotracheal Tube Intolerance, Emergence from General Anaesthesia, Nested Case-Control Study

This is a case-control study designed to enroll 224 patients who will undergo tracheal intubation for general anesthesia in the operating rooms of Peking University People's Hospital between July 20, 2026, and October 31, 2026. The case group will consist of patients who develop coughing before extubation (N=112), while the control group will comprise those without coughing before extubation (N=112). Data to be collected include general demographic characteristics, smoking and smoking cessation history, comorbid conditions (with particular attention to snoring during sleep and sleep apnea-hypopnea syndrome \[SAHS\]), history of pulmonary diseases, mode of spontaneous breathing, surgical and anesthetic data, as well as blood pressure and heart rate before, during, and after extubation, pain scores, and sedation levels. Continuous variables will be presented as mean ± standard deviation (for normally distributed data) or median with interquartile range (IQR) (for non-normally distributed data). Categorical variables will be described using frequencies and percentages (e.g., sex, smoking history). Baseline differences between the case and control groups will be compared using the chi-square test (for categorical variables), Student's t-test (for normally distributed continuous variables), or the Mann-Whitney U test (for non-normally distributed continuous variables). Multivariable logistic regression analysis will be employed to evaluate the independent association between the mode of spontaneous breathing and coughing before extubation, with adjustment for potential confounding factors, and odds ratios (ORs) with their 95% confidence intervals (95%CI) will be calculated. All statistical analyses will be performed using SPSS or R software.

Eligible patients will be enrolled for observation. Based on whether coughing occurs before extubation after emergence from anesthesia, patients will be divided into a case group (those who develop coughing) and a control group (those who do not). Non-invasive cuff blood pressure readings will be recorded before, during, and after extubation. Post-extubation pain scores and sedation levels (assessed using the Ramsay Sedation Scale) will also be documented. General demographic characteristics, smoking and smoking cessation history, presence of snoring during sleep, comorbid conditions (with particular emphasis on sleep apnea-hypopnea syndrome), history of pulmonary diseases, mode of spontaneous breathing, and surgical and anesthetic data will be collected. Primary outcome: occurrence of coughing before extubation after emergence from anesthesia. Definition of coughing: Coughing is defined as the occurrence of cough in a patient who has emerged from anesthesia after administration of reversal agents at the end of surgery, while the tracheal tube is still in place and connected to the ventilator in manual ventilation mode (with the adjustable pressure limiting \[APL\] valve set at 0 cmH₂O), and when extubation criteria have been met but the tube has not yet been removed. Severity of coughing is graded as follows: 0 = no cough; 1. = single cough; 2. = more than one non-sustained cough; 3. = sustained and repetitive cough with head lifting. Data collection methods: General demographic and surgical/anesthetic data will be retrieved retrospectively from the patients' medical and anesthesia records. Other relevant data, including the occurrence and severity of coughing, pain scores, sedation levels, and mode of spontaneous breathing, will be recorded directly by the investigators in the case report forms (CRFs). Investigators: research staff who have undergone standardized training. This is an exploratory, unmatched case-control study designed to investigate the association between coughing during emergence from general anesthesia and the mode of spontaneous breathing (nasal vs. oral) in patients. In the pilot study, the proportion of nasal breathing in the case group (cough) was 65%, while that in the control group (no cough) was 35%. With a two-sided significance level (α = 0.05) and a statistical power of 90%, the required sample size per group was calculated using the Schlesselman formula to be 89 patients. Accounting for a 20% dropout rate, a total of 224 patients (112 per group) are planned for final enrollment. If the observed difference in exposure proportions is smaller than anticipated, the recruitment period will be extended or the analytical strategy will be adjusted accordingly.

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