Explanation for the choice of comparators

Patients randomised to the control arm will get advice only. Their preoperative course will be as if they were not participating in this study, meaning they will receive inconsistent perioperative smoking cessation advice from nurses, surgeons, or anaesthesiologists but no further study-specific smoking cessation intervention. Importantly, participants in the control group will not be discouraged from using perioperative smoking cessation aids and can still obtain help on their own initiative.

Intervention description

The study intervention consists of an interview by a Tobacco Treatment Specialist (TTS) 4 weeks before surgery with individual counselling and offered nicotine substitution. All TTS have > 15 years of experience and underwent a postgraduation course for counselling smoking cessation. The intervention meeting is based on the Chronic Care Model (CCM) [11, 12] to improve the quality of ambulatory care through six interrelated system changes [13]: self-management support, decision support, delivery system design, clinical information systems, health care organisation, and community resources. In line with the CCM, the intervention will include the following elements adapted from Haas et al. randomized clinical trial [14] and are described in the treatment plan. In brief, the intervention includes:

Informative content about advantages of smoking cessation [15] using information leaflets along with decision support

Scheduling service for a motivational interview by a TSS in the office to provide educational and motivational content, explain the magnitude and profile of nicotine dependence and implement a treatment plan [16]

For participants willing to quit smoking a preoperative quit day will be scheduled after the first intervention meeting 2–3 weeks before surgery. Time of a preoperative quit day may vary between patients, since our smoking intervention focuses on as early quit attempts as possible. Therefore, there will be a variety in patients with one or more quit attempts, with or without success, and patients who quit smoking in the postoperative period, only.

Patients will be encouraged by a TSS to use nicotine replacement with patches/gums/pills at their own discretion. For smokers of 20 cigarettes per day or more, a 4-week supply of 21mg/day, 2-week supply of 14 mg/day and a 2-week supply of 7 mg/days patches will be provided. Patients who smoke between 10 and 20 cigarettes per day will receive a 4-week supply of 14 mg/day and a 4-week supply of 7 mg/day. Smokers of <10 cigarettes per day will be supplied with a 4- to 8-week supply of 7-mg/day patches. Bupropion or Varenicillin will be provided on an individual basis (all costs are covered by the patient’s insurance).

Criteria for discontinuing or modifying allocated interventions

Patient preference.

Strategies to improve adherence to interventions

TSS will schedule repeated follow-up meetings to support smoking abstinence or nicotine reduction before and after surgery for all patients. However, patients not interested in further smoking cessation counselling will not be forced to participate in additional follow-up meetings.

The patient’s general practitioners will be informed about the aim of the trial by e-mail and will be asked to further support the patient regarding smoking cessation and encourage abstinence at the end of follow-up as tobacco dependence might be better viewed as a chronic disorder, requiring repeated episodes of treatment.

Relevant concomitant care permitted or prohibited during the trial

No further concomitant care is prohibited.

Provisions for post-trial care

TSS will schedule repeated follow-up meetings to support smoking abstinence or nicotine reduction before and after surgery for all patients. However, patients not interested in further smoking cessation counselling will not be forced to participate in additional follow-up meetings.

Outcomes

The primary endpoint is the (CCI®) [9] within 90 days of surgery. The CCI is calculated as the sum of all Clavien–Dindo complications [17] (Additional file 1) that are weighted for their severity (multiplication of the median preference values from patients and physicians). The final formula yields a continuous scale that ranks the cumulative burden from any combination of complications from 0 to 100 in a single patient. As a composite complication score, the CCI has the advantage of reflecting the overall burden of the postoperative course that affects the health of patients and their quality of life. In addition, the CCI is a powerful endpoint in trials, as it allows sample size up to nine times lower compared with traditional morbidity endpoints [18]. Complications will be assessed from medical health records by an advanced nurse practitioner supported by a surgical resident and consultant, all of whom were already trained in the Clavien–Dindo classification in a pilot study. Outpatient information of complications treated at other institutions will be included.

Secondary endpoints are length and costs of hospital stay, readmission rates for inpatient hospital stay, smoking abstinence or nicotine reduction, nicotine dependence, mental health, quality of life, unplanned postoperative intermediate care or intensive care unit admissions and cost and. Secondary endpoints will be recorded up to a 12-month postoperative follow-up period and will be compared between the intervention and control group. Smoking abstinence or nicotine reduction will be assessed by measuring smoking status (cigarettes smoked per day) and nicotine dependence will be assessed using the Fagerström test [19]. Nicotine abstinence will be additionally confirmed by using the NicAlert cotinine saliva test. Quality of life will be assessed with the German version of the 36-Item Short Form Survey (SF-36; index values range from 0 to 1, with higher scores indicating better quality of life) including covering physical functioning, bodily pain, role limitations due to physical health problems, role limitations due to personal or emotional problems, emotional well-being, social functioning, energy/fatigue, and general health perceptions during the past 4 weeks [20]. Mental health will be assessed using the Hospital anxiety and depression scale (HADS) [21].

Morbidity may influence the endpoints, therefore Charlson Comorbidity Index [22] and the American Society of Anaesthesiologists (ASA) physical status classification [23] will be assessed for each patient at baseline. The following characteristics measured at baseline are further described: age, gender, surgical procedure, underlying medical conditions and the stage of the Transtheoretical Model (TTM) of behaviour change.

Participant timeline

Fig. 1 shows the participant timeline.

Fig. 1

Participant timeline. ICF, informed consent form; NicAlert, nicotine saliva test

Sample size

Based on a previous Cochrane review with meta-analysis [7], it is assumed that preoperative smoking cessation decreases the binary outcome of postoperative complications (yes or no) with a relative risk of 0.42. The mean postoperative CCI as a continuous measure in a retrospective chart review in a cohort without smoking cessation at the hospital of Lucerne was 13 and we therefore assume a CCI of 5.5 in the intervention group. The assumed standard deviation for the sample size calculation was 20. With anticipated 80% power, a two-sided significance level α of 5%, a sample size of 226 patients is planned. With an additional 10% dropout, our aim is to enrol 251 patients.

Recruitment

All patients scheduled for an intermediate or high-risk procedure (Additional file 2) at the hospital of Lucerne will be identified by the study nurse either through the tumour board lists or as soon as they are scheduled for surgery in the electronic health record program. Otherwise, clinicians can contact the study nurse to enrol patients who have been referred but not yet scheduled for surgery or presented at the multidisciplinary tumour board. To avoid an overload of the consulting capacities in the intervention arm recruitment of new trial participants may be paused.