Title: Impact of prior smoking cessation on postoperative pulmonary complications in the elderly
Abstract: Editor, Postoperative pulmonary complications (PPCs) include respiratory infection, respiratory failure, pleural effusion, atelectasis, pneumothorax, bronchospasm and aspiration pneumonia.1 The occurrence of PPCs is associated with poorer outcomes in surgical patients, including prolonged hospital stay and increased mortality after surgery.2 Many studies have investigated the association between preoperative smoking and PPCs; however, the optimal duration of preoperative smoking cessation is still unclear.3 It is generally believed that stopping smoking before surgery helps to reduce the occurrence of PPCs, and that a longer duration of smoking cessation is associated with a lower risk of PPCs.4 The purpose of the study was to determine the duration of preoperative smoking cessation that was not associated with increased risk of PPCs in elderly patients who underwent noncardiac, nonneurologic surgery. This was a predefined secondary analysis of a previous multicentre cohort study ‘Incidence and risk factors of perioperative stroke in patients undergoing noncardiac and nonneurologic surgery’. The study protocol was approved by the Clinical Research Ethics Committee of Peking University First Hospital [2013(547)] and registered in ClinicalTrials.com (NCT01758952). Written informed consent was obtained from each patient or their authorised surrogate. Patients who were 60 years or older and scheduled to undergo noncardiac, nonneurological surgery were recruited from 13 May 2013 to 7 November 2015. Baseline and perioperative data were collected. The exposure of interest was the smoking status before surgery. The smoking index (pack-years of smoking) was calculated by multiplying the number of packs (one pack contains 20 cigarettes) smoked per day by the number of smoking years. A smoking history was defined as having a smoking index of one or more.A current smoker was defined as having a duration of smoking cessation of less than 7 days at the time of surgery. Each patient was followed up routinely three times for complications three times: the first and third days after surgery, and before hospital discharge. For patients who stayed in hospital for more 30 days after surgery, the third follow-up was performed on the 30th postoperative day for patients who were discharged before 30 days after surgery, a fourth follow-up by telephone was performed on the 30th day after surgery. The primary outcome was the occurrence of PPCs within 30 days after surgery, which were diagnosed according to the previously published criteria.1 Continuous variables were compared with unpaired t-test or Mann–Whitney U test. Categorical variables were compared with χ2 tests or continuity correction χ2 tests. Generalised additive models were used to analyse the nonlinear effects of the duration of smoking cessation on the risk of PPCs. Logistic regression analyses were used to calculate the odds ratios (OR) of smoking status in predicting PPCs. Statistical analyses were performed using SPSS version 14.0 software (SPSS, Chicago, Illinois, USA) and R (3.0.2) software. Among the 1962 patients who completed the 30-day postoperative follow-up, 140 (7.1%) developed PPCs. These included respiratory infection (116 cases, 5.9%), atelectasis (19 cases, 1.0%) and pleural effusion (13 cases, 0.7%). A generalised additive model plot revealed that when the duration of smoking cessation was longer than 93 days, the probability of PPCs would not be higher than baseline (nonsmokers) (Fig. 1). After adjustment for confounding factors in a multivariate logistic regression model, the existence of a preoperative smoking history was associated with an increased risk of PPCs [OR 1.786, 95% confidence interval (CI) 1.222 to 2.611, P = 0.003].Fig. 1: Generalised additive model plot for the effect of stop smoking duration on the risk of developing PPCs. The S in the S (duration of stop smoking) represented the risk of developing PPCs, where S of more than 0 indicates an increased risk and S of less than 0 indicates a decreased risk. The results showed that patients with a smoking cessation of more than 93 days may have a lower risk of PPCs. PPCs, postoperative pulmonary complications.When compared to nonsmokers, a smoking index of more than eight pack-years was associated with an increased risk of PPCs (OR 1.730, 95% CI 1.169 to 2.560, P = 0.006); for those with a smoking index of eight pack-years or less, the risk of PPCs was increased but did not reach statistical significance (OR 2.450, 95% CI 0.941 to 6.378, P = 0.066). When compared to nonsmokers, current smokers (OR 1.709, 95% CI 1.043 to 2.802, P = 0.034) and former smokers with a smoking cessation of 93 days or less (OR 3.785, 95% CI 1.803 to 7.943, P < 0.001), but not former smokers with a smoking cessation of more than 93 days (OR 1.423, 95% CI 0.811 to 2.495, P = 0.219), were associated with increased risk of PPCs. The optimal duration of smoking cessation before surgery remains controversial. Some authors suggest that preoperative smoking cessation of at least 4 weeks (or 1 month) was helpful in reducing postoperative complications (including PPCs).5 Others suggest that a longer period of smoking cessation (6 to 8 weeks or more than 2 months) was required to reduce the incidence of PPCs.6 In a recent retrospective study of 246 patients undergoing elective oesophagectomy, Yoshida et al.7 found that a preoperative smoking cessation of more than 90 days was needed to reduce morbidities after surgery. In the present study, a general additive model was used to determine the relationship between the duration of smoking cessation and the risk of PPCs and we found that a minimum duration of 93 d was required, a result similar to that of Yoshida et al.7 Two meta-analyses also show that a longer duration of smoking cessation is associated with a lower risk of PPCs.4,6 These findings suggest that a short period of smoking cessation (median 4 weeks before surgery) does not restore a normal respiratory system. The study has several limitations. First, as a secondary analysis, the fixed patient population has the potential to produce bias. Second, the data on preoperative smoking were collected according to reports of patients themselves, raising the possibility of recall bias. Third, the sample size in this study was not designed for detecting the association between smoking status and the risk of PPCs. For example, only 49 patients had a smoking cessation of 93 days or less; and among them, only 13 patients developed PPCs. This lowered the power of the analyses and so results here may only be considered to be exploratory. In conclusion, for elderly patients with a smoking history scheduled to undergo noncardiac, nonneurological surgery, a preoperative smoking history, a high smoking index (>8 pack-years) or a short duration smoking cessation (≤93 days) was associated with an increased risk of PPCs. A smoking cessation of more than 93 days may be helpful to reduce PPCs, but requires further study. Acknowledgements relating to this article Assistance with the study: the authors would like to thank doctors Chun-Mei Deng and Ting Ding for their help in collecting data, and Ms. Xue-Ying Li for her help in statistical analysis. Financial support and sponsorship: the work was supported by a grant from Chinese Medical Association, Beijing, China. The study sponsor had no role in study design, in the collection, analysis and interpretation of data, in the writing of the report or in the decision to submit the report for publication. The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the Chinese Medical Association. Conflicts of interest: none.
Publication Year: 2017
Publication Date: 2017-12-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 6
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