The main findings of this study were that age, BMI, ASA score and incidence of postoperative atelectasis were significantly higher in snorer and high risk group when compared with non-snorer and low risk group according to STOP questionnaire. To our knowledge, this study is the widest study evaluating the relationships among postoperative pulmonary complications, snoring and results of STOP questionnaire in patients with orthopaedic surgery.
OSA is a prevalent condition in general population. There are several factors which increase the rate of perioperative complications in patients with OSA . Anesthetics and analgesics increase upper airway resistance by interfering with the function of upper airway muscles and also affect respiratory control. Furthermore, trauma from airway manipulation, drugs and pain all can affect sleep architecture and regulation of upper airway muscles in the postoperative period . The most common perioperative complications in OSA patients are exacerbation of obstructive apnea due to upper airway collapse, hypoxemia, hypercapnia, difficulties of airway management, postoperative infection, atelectasis, encephalopathy, cardiac ischemia and arrhythmias [13–15].
There has been little study about perioperative complications in OSA patients. Most studies in the literature are retrospective, observational or case reports . Randomized controlled trials may be difficult to perform due to ethical consideration. The risk of respiratory complications such as hypoxemia, airway obstruction and hypoventilation was 1.3% in surgical patients given general anesthesia in one study, and although OSA risk was not investigated, the use of opioids was associated with greater perioperative pulmonary complications .
Surgical site and anesthetic technique are important factors to predict perioperative pulmonary complications. There are a number of reports of perioperative risk in OSA patients undergone upper airway surgery such as uvulopalatopharyngoplasty (UPPP) and tonsillectomy. Pang  reported 118 treated patients and 152 surgical procedures: overall peri- and post-operative complication rate was 13.8%, all patients were treated accordingly and recovered well, with no mortality. The author  concluded that patients with severe OSA (apnoea-hypopnoea index > 60 and lowest oxygen saturation < 80%) are at higher risk of post-operative oxygen desaturation.
The effect of OSA in other surgical procedures such as thoracic, abdominal or orthopaedic was less investigated. Kaw et al.  looked at 25,587 patients who underwent cardiac surgery. Out of these, 37 patients were also identified as having OSA. A higher incidence of encephalopathy, postoperative infection and increased length of stay in ICU were noted in the group with OSA after cardiac surgery. The difference in the rates of infection was mostly due to the presence of mediastinitis. Differences in the rate of reintubation, tube time, and overall postoperative morbidity were not statistically significant. There is only one study similar to our investigation which related to OSA and orthopaedic surgery. Gupta et al.  carried out a retrospective case control study of OSA patients undergoing hip or knee replacement surgery. They found an increased incidence of postoperative complications (2.5 times), an elevated intensive care unit need, and longer hospital stays in OSA patients versus controls. In our study snoring and high risk OSA according to STOP questionnaire were associated with increased incidence of postoperative atelectasis.
There are several confounding factors that can have effect on the relationships between OSA and postoperative complications. Obesity and anesthetic-analgesic drugs are the most important of these factors. Respiratory and cardiac physiology, pharmacokinetics of drugs, positioning, regional anesthetic techniques, monitoring, and postoperative care are all profoundly affected by obesity . OSA is also more prevalent in obese individuals. Population based cohort studies revealed that obesity is an independent risk factor for OSA. Sixty percent of OSA patients are obese . Some of the postoperative complications are also directly related to obesity without apnea in obese OSA patients. Obesity is associated with reduction in functional residual capacity (FRC), expiratory reserve volume and total lung capacity. FRC may be reduced in the upright obese patient to the extent that it falls within the range of the closing capacity with subsequent small airway closure, atelectasis, ventilation-perfusion mismatch, right to left shunting and arterial hypoxaemia . In our study, in snorer and high risk group BMI was significantly higher than in non-snorer and low risk group. Atelectasis is more prevalent in snorer and high risk group and this may be related to obesity.
Some potential limitations of this study should be considered, of course. Firstly, our study is retrospective and STOP questionnaire was based on self subjective reports. Furthermore STOP questionnaire should be self-administered, whereas in our study the score was reconstructed retrospectively. Secondly, there is no particular study which evaluated the reliability and validity of STOP questionnaire in our population. However, the same problems exist in other similar studies. Thirdly, we did not perform any sleep study such as oximetry or polysomnography.