Comparison of Postoperative Pulmonary Complications Between Smokers and Nonsmokers: A Prospective Cohort Study
Conditions: Coughing, Post Operative Complications, Wheezing, Smoking, Tobacco
Sponsor: mehmet özkılıç

Comparison of Postoperative Pulmonary Complications Between
Smokers and Nonsmokers: A Prospective Cohort Study
Study Protocol and Statistical Analysis Plan
NCT Number: NCT06982911
Date: May 2025
1. Background and Rationale
Postoperative pulmonary complications (PPCs) are among
the most common and clinically significant causes of
morbidity and mortality following surgery. Risk factors
contributing to the development of PPCs include
preexisting lung disease, thoracic and upper airway
surgeries, and cigarette smoking.
It is estimated that smokers have up to a sixfold increased
risk of PPCs compared to nonsmokers. Previous studies
suggest that smoking cessation for at least 6–8 weeks
before surgery can significantly reduce the incidence of
complications. Despite these findings, there remains a lack
of prospective data comparing PPCs between smokers and
nonsmokers undergoing elective abdominal surgery. This
study aims to better characterize the impact of smoking on
PPCs and guide preoperative risk assessment strategies.
2. Objective
The primary objective of this study is to compare the
incidence of postoperative pulmonary complications
between smokers and nonsmokers undergoing elective
abdominal surgery under general anesthesia.
3. Expected Benefits
The findings of this study will clarify the risk posed by
active smoking in the postoperative period, particularly for
pulmonary complications. This may enhance clinical
decision-making during preoperative evaluation and
reinforce the importance of smoking cessation counseling.
4. Study Design and Setting
This study is designed as a prospective observational cohort
study and will be conducted at Gazi Yasargil Training and
Research Hospital, Diyarbakir, Turkey. Data collection is
planned between February 1, 2025, and August 1, 2026.

5. Participants and Eligibility Criteria
Inclusion Criteria:
- Adults aged 18–60 years
- Undergoing elective abdominal surgery under general
anesthesia
- ASA physical status I, II, III
Exclusion Criteria:
- Pregnancy
- Difficult intubation or re-intubation
- Recent upper or lower respiratory tract infection (within
the last 30 days)
- Chronic pulmonary conditions (e.g., asthma, COPD,
OSA)
- Emergency surgery
- Surgical duration longer than 2 hours
- Morbid obesity (BMI >35)
- Hemoglobin <10 g/dL
Patients will be categorized into two cohorts based on their
smoking status:
- Smokers: ≥10 pack-year history
- Nonsmokers: Never smoked or quit ≥1 year ago
6. Sample Size Calculation
Sample size estimation was based on prior findings by
Reddy et al., where the PPC rate was 54% in smokers and
16% in nonsmokers. With a power of 90% and a
significance level of 5%, the required sample size was
calculated to be 62 participants per group. To account for a
potential 10% data loss due to dropouts or missing data, the
final target sample size was adjusted to 70 participants
7. Data Collection Methods
Demographic data (age, gender, BMI), smoking status,
intraoperative variables (FiO2, PEEP, Ppeak, duration of
surgery), and postoperative respiratory findings (cough,
secretion, wheezing, SpO2) will be recorded using a
standardized case report form. Observations will be made
at 6 and 24 hours postoperatively.
8. Outcome Measures
Primary Outcome:
- Incidence of PPCs within 24 hours postoperatively
Secondary Outcomes:
- Frequency of suctioning
- VAS score for cough severity at 6 and 24 hours

- Presence of wheezing, laryngospasm, SpO2 <90%
- Need for respiratory physiotherapy
- Length of PACU stay
9. Statistical Analysis Plan
Descriptive statistics will include means and standard
deviations for continuous variables (or medians and
interquartile ranges, depending on distribution) and
frequencies/percentages for categorical variables.
Normality will be assessed with the Shapiro-Wilk test.
Between-group comparisons will be made using:
- Independent t-test or Mann-Whitney U test for continuous
variables
- Chi-square or Fisher's exact test for categorical variables
Multivariate logistic regression analysis will be used to
determine independent predictors of PPCs. Adjusted odds
ratios (aORs) with 95% confidence intervals (CIs) will be
reported.
Receiver Operating Characteristic (ROC) curve analysis
will assess predictive performance of continuous variables
like Ppeak or BMI. Area under the curve (AUC), cut-off
values, sensitivity and specificity will be provided.
Sensitivity analyses will include subgroup comparisons. A
post-hoc power analysis will confirm statistical adequacy
based on observed effect sizes.
10. Ethical Considerations
This study was approved by the Clinical Research Ethics
Committee of Gazi Yasargil Training and Research
Hospital (Approval No: 257, Date: 07.02.2025). All
participants will provide written informed consent.
11. Contact Information
Principal Investigator:
Dr. Mehmet Özkılıç
Specialist in Anesthesiology and Reanimation
Gazi Yasargil Training and Research Hospital
Diyarbakir, Turkey
ozkilicmehmet@gmail.com
+90 507 006 8313