Risk factors for postoperative throat pain after general anaesthesia with endotracheal intubation at the University of Gondar Teaching Hospital, Northwest Ethiopia, 2014

Introduction Postoperative sore throat is listed from the top as patients’ most undesirable outcome in the postoperative period. It is believed to originate from mucosal dehydration or edema, tracheal ischemia secondary to the pressure of endotracheal tube cuffs, aggressive oropharyngeal suctioning, and mucosal erosion from friction between delicate tissues and the endotracheal tube. Even if the problem was indicated in many literatures, it has never been studied in our country. The study aimed to assess prevalence and factors associated with postoperative sore throat among patients who were operated under general anesthesia with endotracheal intubation. Methods Hospital based cross sectional study was conducted from February 25 - April 10, 2014 in Gondar University hospital. Patient interview and chart review were employed for data collection. Bivariate and multivariate logistic regressions were used to determine the association. Results A total of 240 out of 299 patients were included in this study with a response rate of 80.3%. The prevalence of postoperative sore throat within 48 hours after operation was 59.6%. Factors which had association with postoperative sore throat from the multivariate logistic regression were female sex (AOR = 3.3, 95% CI: 1.07, 10.375), repeated number of attempts to intubate (AOR = 3.291, 95% CI: 1.658, 6.531), and the use of nasogastric tube (AOR = 0.41, 95% CI: 0.174, 0.965) respectively. Conclusion The prevalence of postoperative sore throat was high in Gondar University Hospital. Awareness creation about the problem should be made for health professionals and postoperative sore throat management protocol need to be introduced.


Introduction
Regardless of its incidence and some preventive measures, postoperative sore throat (POST) is listed from the top as patients' most undesirable outcome in the post-operative period.
Postoperative sore throat is the commonest patient complaint, significant to patients and frequent postoperative complication [1,2].
It is well recognized that reporting of sore throat is affected by the method of questioning that is whether the questions asked directly or indirectly [3]. The expression of postoperative sore throat constitutes a number of sign and symptoms. For example sore throat is an ordinary expression of pharyngitis, which by itself can have a number of causes. It may also include a variety of symptoms including pain and discomfort, laryngitis, tracheitis, hoarseness, cough or dysphagia. Postoperatively it seems reasonable that most of the signs and symptoms are the result of mucosal injury which leads to inflammation caused by the process of air way instrumentation. Also its postulated etiology has been associated with mucosal dehydration or edema, tracheal ischemia secondary to the pressure of Endo tracheal tube cuffs, aggressive oropharyngeal suctioning, and mucosal erosion from friction between delicate tissues and the ETT [4,5].
A number predisposing factors have been identified and the most notable one seems to be the size of the endotracheal tube used, cuff pressure, use of anesthetic spray, female sex, duration of anesthesia, surgical positioning, use of succinylcholine, concurrent use of a nasogastric tube, aggressive oropharyngeal suctioning and the approach to airway management (i.e. ETT, laryngeal mask airway (LMA) or face mask) [6]. The incidence of postoperative sore throat varies in most research studies, but some report the incidence to be less than 15 % and others as high as 64% [7]. The use of a smaller ETT has consistently been shown to significantly reduce the incidence of postoperative sore throat without resulting in problems ventilating patients [8]. Studies have documented the use of 6.5mm -7 mm ETT for women and 7.5mm -8 mm ETT for men that resulted in lower rates of postoperative sore throat when compared to larger sized ETT [9]. A study conducted in Nigeria on patients aged 18-77 in 2006 indicated the incidence of POST to be 63%, which was greatly associated with the duration of intubation [10].
Many researchers have suggested that the higher incidence of females reporting POST is more directly related to a tighter fitting ETT than to a distinct difference between the sexes (11). One group of researchers admitted that their choices in ETT sizes did not truly fit the anatomy of patients (they used 8 mm for males and 7.5 mm for females), and suggest that a 7 mm ETT may be a better alternative for females. In fact, several studies seem to advocate a 7 mm sized ETT for female patients and a 7.5 mm ETT for males [4]. The other determinant factor is ETT cuff pressure. There is significant evidence to support that limiting ETT cuff pressures will reduce the incidence of postoperative sore throat [11]. There are some researches that support standard use of manometers, following tracheal intubation the cuff pressure is measured and maintained to a minimum for proper seal and has to be checked intermittently for consistency, but manometers may not be accessible straight away in all institutions [12]. The use of lidocaine lubricants and sprays is controversial; some literatures say it is the persuasive method to decrease POST, others said that it is associated with an increased incidence and severity of POST [13].
William Macewen is honored with the first orotracheal intubation for the purpose of airway protection during anesthesia in 1880 [14].
The incidence of postoperative sore throat varies in most research studies, but some report the incidence to be less than 15% and others as high as 64% [15]. The perioperative and anaesthesia related complications are expected to be higher in the developing countries than the developed countries [16].
Many studies have been performed to determine the incidence of postoperative sore throat and to find measures for its prevention.
Most of these studies have been conducted in developed and western populations. The presence of racial difference in the incidence of postoperative complication has been well documented [17][18][19][20][21]. The endotracheal tube has since evolved, but remains a critical tool in the practice of anesthesia in spite of its undesirable effects. There is also another study conducted in United Kingdom showing the incidence to be 63.9% [22]. The prevalence of POST varies from different studies in different countries. In Ethiopia there is no published research found on this topic. A literature search was conducted using the following databases Ethiopian medical journal, journal of health sciences and Ethiopian journal of health and biomedical sciences for articles containing key words in the title or abstract related to postoperative sore throat and ETT. So the incidence of POST is not known in our country. Knowing the incidence of POST and its association factors in our situation helps to recognize the magnitude of the problem and initiates actions to reduce its occurrence. This research can also help as a back ground for future researches on related topic by indicating the incidence Page number not for citation purposes 3 rate and associated risk factors of POST in this geographical area.
The aim of this study was to assess prevalence and factors associated with postoperative sore throat among patients who were operated under general anaesthesia with endotracheal intubation at the University of Gondar teaching hospital.

Socio-demographic characteristics of the study subjects
A total of 403 elective and emergency patients were operated under anaesthesia during the study period. Of these, 299 patients were operated under general anaesthesia with endotracheal intubation.
Out of 299 patients, 43 patients were <18 years old, 9 patients were critically ill and unconscious, 5 patient discharged before 24 hours, and 2 patients refused to participate in the study. A total of 240 patients were included in this study with a response rate of 80.3%. The mean age of patients participated in this study was 34.8 with a standard deviation of 9.9. The minimum and maximum ages were 18 and 71 years respectively. Patients were classified as ASA I, ASA II or ASA III (Table 1).

Factors related with anaesthesia and surgery
Among the various types of surgical procedures, the highest proportion of sore throat occurred in patients who underwent general surgery (58.6% (92/157)). Female patients reported more sore throat than male patients (65.9%vs 51.8% (87/132 vs 56/108)). Multiple intubation attempt appeared to have a direct relationship with the occurrence of postoperative sore throat, one attempt vs multiple intubation attempt (47.5% vs 76.7% (67/141 vs 76/99)). Sore throat was found to be more common with the use of nasogastric tube compared with no nasogastric tube (67.3% vs 57.2% (37/55 vs.106/185)) ( Table 2).

Prevalence and risk factors for postoperative throat pain
Postoperative sore throat was complained by 143 patients (59.6%).
In this study, female sex was significantly associated with POST. Repeated intubation attempt had also significant association with POST. Patients who had a repeated attempt were 3 times more likely to develop POST than their counter part patients who were intubated during the first attempt (AOR = 3.291, 95% CI: 1.658, 6.531) ( Table 3). The variables with a p-value of ≤0.2 from the binary logistic regression that had no association with postoperative sore throat in the multivariate analysis were age, ASA status, ETT size, age, experience of the anaesthetist, muscle relaxant, grade of intubation, and the duration of tube in place.

Discussion
Postoperative sore throat (POST) has been a well-recognized complication after general anaesthesia with endotracheal intubation.
While it is generally considered as a minor side effect, POST is important to patients and decreasing its incidence is required to improve anesthetic outcomes [7,4,20]. In this study, the prevalence of postoperative sore throat was 59.6%. This finding was high compared with studies conducted in Denmark and Canada [7,15]. This difference presumably might be due to mucosal ischemia following decreases in blood flow related to high pressures of the tube cuff since there is no standard to the cuff seal point, the erosion and dehydration of delicate mucosal tissues due to dry and nonhumidified gases, aggressive oropharyngeal suctioning and the resulting inflammation in our study. But our finding was low compared with a studies conducted in Nigeria and United Kingdom [10,22]. This discrepancy could be due to different skills and techniques among anaesthetists.  [10,20]. This might be due to trauma to mucosa during airway instrumentation and intubation since most of them were carried out by students in our study.
The use of nasogastric tube had strong association with postoperative sore throat (AOR = 0.41, 95% CI: 0.174, 0.965; p = 0.041). This finding was similar with a study conducted in United Kingdom [22]. This could be due to mucosal irritation or damage during insertion. In our study age, ASA, ETT size, experience of the anaesthetist, muscle relaxant, grade of intubation and duration of tube in place had no association with postoperative sore throat.
Even though these variables were reported as risk factors for POST in studies conducted in Canada and Pakistan [15,21]. This might be due to small sample size in our study.

Limitation of the study:
In this study the sample size was small which was difficult to see whether some variables such as age, ASA status, ETT size, experience of the anaesthetist, muscle relaxant, grade of intubation and duration of tube in place might have an effect on the prevalence of postoperative sore throat in our population. Some important risk factors for POST like tube cuff pressure were not addressed in this study due to lack of the equipment.

Conclusion
In this study the prevalence of postoperative sore throat was high (59.6%). Female sex, multiple intubation attempts and the use of nasogastric tube were the independent risk factors for postoperative sore throat in Gondar university hospital.

Competing interests
The authors decalre no competing interest.

Authors' contributions
Biruk Melkamu conceived the study and developed the proposal, collected the data, analyzed the data, and drafted the paper. Endale Gebreegziabher and Tadesse Belayneh revised the proposal and were involved in data collection, data analysis, writing of the final paper, and manuscript preparation. All authors have read and approved the final manuscript.

Acknowledgments
We thank the University of Gondar for financial support.