Menthol chewing gum on preoperative thirst management: randomized clinical trial *

Objective to evaluate the effectiveness of menthol chewing gum, in the relief of the intensity and discomfort of the surgical patient’s thirst in the preoperative period. Method a randomized controlled trial, with 102 patients in the preoperative period, randomized in a control group, with usual care, and an experimental group, which received menthol gum, which was the study treatment variable. The primary clinical outcome was the variation in thirst intensity, evaluated by the Numeral Verbal Scale, and the secondary, the variation of the discomfort of thirst, evaluated by the Perioperative Thirst Discomfort Scale. Mann-Whitney test was used to compare measures between groups. The significance level adopted was of 0.05. Results menthol chewing gum significantly reduced the intensity (p <0.001), with Cohen’s medium-effect d, and thirst discomfort (p <0.001), with a large-effect Cohen’s d. Conclusion menthol chewing gum was effective in reducing the intensity and discomfort of preoperative thirst. The strategy proved to be an innovative, feasible and safe option in the use for the surgical patient, in the management of the preoperative thirst, in elective surgeries. NCT: 03200197.


Introduction
Thirst is a present, intense and pre-operative stressor symptom. In this period, the patient is subjected to a series of discomforts during the preparation for the anesthetic-surgical procedure. Emotions such as fear, anxiety and stress trigger physiological reactions, among them, the inhibition of salivary production, causing dryness of the oropharyngeal cavity (1) . However, this is not the only challenge the patient faces.
In the preoperative period, as fasting time is prolonged and fluid ingestion is restricted, changes in the electrolyte balance begin to occur (2) . Among the physiological responses that occur aiming at its reestablishment, thirst is one of the most relevant, since it acts both in the genesis and cessation of the search for water intake. The thirst resulting from changes in osmolarity and dryness of the oral cavity is considered to be one of the most uncomfortable and stressful experiences for the patient in the perioperative period (3)(4)(5) . It can be identified by a self-controlling effect, called negative valence (2,6) , and is accompanied by the following uncomfortable attributes: dry mouth, lips and throat, thick tongue and saliva, poor taste in the mouth and a desire to drink water (1,7) .
The attributes related to the dry mouth, lips and throat increase, exponentially, the discomfort generated by thirst (1,7) . Saliva, which has a primordial role in hydration of the mucosa, presents a hydric regulating potential of the body. In situations where the body is deprived of water, dehydration of the oropharyngeal mucosa occurs (8) , which leads to the activation of the osmoreceptors, which, in turn, trigger the release, among others, of the antidiuretic hormone (ADH), which acts by preventing water loss, until there is water replenishment. Evidence shows that, in parallel, these osmoreceptors, through afferent pathways, activate the osmosensitive nuclei of the lamina terminalis, which are recognized as responsible for thirst control (2,6,9) .
There are two mechanisms of thirst satiety control: the post-absorptive, in which the satiety activation is slower, since the fluid must be absorbed up to of hydroelectrolite balance, and the pre-absortive satiety mechanism, in which the thermoreceptors and oropharyngeal and gastric osmoreceptors are active, which prematurely signal, to the brain, the interruption of ADH release and the consequent thirst sensation (2) .
Thus, for the surgical patient, the use of strategies that stimulate pre-absorptive satiety is the most adequate, since it occurs even with low volumes.
The use of strategies to relieve the surgical patient's thirst in the preoperative period is not part of the culture of health institutions, which still coexist with prejudices regarding the administration of any method of postoperative thirst relief. In clinical practice, even delays and surgical suspensions by anesthesiologists and surgeons are recorded, when Garcia AKA, Furuya RK, Conchon MF, Rossetto EG, Dantas RAS, Fonseca LF. design, the Consolidated Standards of Reporting Trials (CONSORT) were followed (17) . is it morning or afternoon? -; present dentition (natural or artificial); fasting for at least three hours; be available for collection at least three hours before the surgical procedure; verbalize thirst spontaneously or, when questioned, with intensity greater than or equal to three in the Verbal Numerical Scale (VNS) (18) .
The exclusion criteria were: patient with allergy to menthol; restriction to chewing and / or swallowing; presence of nausea, vomiting or pain at the time of approach; chronic xerostomia; chronic kidney patient; impossibility of communication.
The primary clinical outcome of interest was variation in thirst intensity, assessed by VNS (18) , which ranges from zero (without thirst) to ten (intense thirst). The secondary clinical outcome was the variation of thirst discomfort, evaluated by the Perioperative Thirst Discomfort Scale (PTDS), which ranges from zero (no discomfort) to 14 (very uncomfortable) and presents seven attributes: dry mouth, dry lips, tongue thick, thick saliva, dry throat, poor taste in the mouth and desire to drink water (7) .
The PTDS was elaborated and validated to measure the discomfort caused by thirst in the surgical patient, presents a content index of 0.98 and a reliability index of one, internal consistency evaluated by Cronbach's alpha of 0.91 and inter-observer equivalence of a measure by weighted Kappa coefficient (7) . The study's treatment variable was the use of menthol chewing gum, offered to the patient at least three hours before the anesthetic-surgical procedure. Sample estimation was done based on the pilot study, with a variation of 1.53 in thirst intensity.
The significance level considered 5% for the sample calculation, 95% for the confidence interval and 80% for the study power. The calculations indicated a necessary sample of 88 patients, adding 15% of this total to cases of participants' losses, making a total of 102 patients (51 per group) (19) . to the product used in the pilot test, but of a firmer consistency.
There was a reduction in intervention time for the study, from twenty to ten minutes, due to the difficulty found in the chewing time during the pilot test.
Throughout the intervention period, the researcher remained with the participant, both in the CG and in the EG. There was no change in the data collection protocol.
Data collection was from january to march 2017, following this sequence of procedures: In the CG, because the patients had intense thirst, a menthol chewing gum was offered, after final evaluation, to relieve their thirst.
The statistical analysis procedure was masked, since, before the data was available, the CG was coded in G1 and the EG in G2 to prevent the statistician from distinguishing the group that received the intervention.
For the analysis of the data, non-parametric tests were used, due to the abnormal distribution of the sample evidenced by the Shapiro-Wilk Test. Intensity and discomfort of thirst were considered as a discrete quantitative variables (20) .
Mann-Whitney test was used to compare the intensity and discomfort of the initial and final thirst and the variation between the two groups (20) . For all comparisons, a significance level of 5% was adopted, with a confidence interval of 95%.

Results
During the study period, 762 patients comprised the elective surgical lists. Of these, 547 were out of the eligibility criteria (age, be available for collection at least three hours before the surgical procedure, There was no statistically significant difference between groups in relation to demographic and clinical variables prior to randomization ( Table 1). The normality test used was the Shapiro-Wilk test, which did not show distribution symmetry. Therefore, the statistical tests used were non-parametric.
When considering the variation in thirst intensity, the EG showed a significant improvement (median = 3) when compared to the CG (median = 0) (<0.001), and Cohen's d had an average effect (0.77) (21) ( Table 2). There was a similar result to that observed in the variation of the discomfort, with the GE obtaining variation (median = 5) and the CG, without (median = 0) (p <0.001), with Cohen's d with a large effect (0.82) (21) ( Table 2).
In the evaluation of initial discomfort, a high percentage of patients with this symptom was observed in both groups. At the final moment of evaluation, the EG presented improvement, that is, a decrease in the initial values in all the attributes evaluated by PTDS (

Discussion
This study presented an innovative approach for evaluating a simple, feasible, practical, low cost, effective strategy based on physiological mechanisms that act to minimize thirst and its discomforts. In addition, it presents sustained evidences that opose the cultural paradigm that one cannot intervene on preoperative thirst. In addition, in both the pilot and the final study there were no adverse events related to the administration of the chewing gum.
Nonetheless, the team continuously reinforces the impossibility of ingesting any quantity of liquids (22)(23) .
Among the contributions of this research is the finding that the patient in the preoperative also feels thirst. In This data corroborates studies in which there was a similar result in relation to thirst intensity with the use of chewing gum, although conducted with other populations (13)(14)(15) .
Such studies indicate the use of this strategy in patients with xerostomia, in dialysis treatment, also submitted to water restriction (13)(14) . In addition, chewing gum has also been tested in patients with advanced head and neck cancer who, undergoing radiotherapy, present salivary secretion dysfunctions, leading to oropharynx dryness and therefore thirst (15) . The use of the strategy had a positive effect on the stimulation of the salivary glands and consequent increase of salivary flow, reducing thirst (13)(14)(15) .
The uncomfortable attributes of thirst were identified with high intensity in the preoperative period and are related to salivary decrease and oral dehydration (1)(2)(3)7) . In this study, the effectiveness of mentholated chewing gum on the discomforts evaluated by PTDS was evidenced.
All attributes showed significant reduction after patients received a menthol chewing gum for only ten minutes.
Results highlighted the correlation between the intensity and discomfort variables, as well as the use of mentholated chewing gum, because when one variable was reduced by the use of the strategy, the other presented the same behavior. A study of 203 patients, who evaluated their thirst in the Post Anesthesia Care Unit using PTDS, also found a correlation between intensity and discomfort of thirst (24) . This shows that besides evaluating the intensity, it is also important to measure the discomfort related to thirst. It is also suggested that preoperative feelings, such as fear, insecurity and anxiety, can generate surgical stress, oral cavity dryness, nausea and hypoglycemia, which stimulate the secretion of ADH and, consequently, sensation of thirst (5) . In one study, it was observed that chewing gum can decrease both patients' anxiety and increase salivary pH (29) . In addition, the oral humidification provided by it and increased swallowing of the salivary flow leads to decrease the secretion of ADH (9) .
Researches indicate that there is a preference for flavored strategies when compared to paraffin or flavorless chewing gum (13)(14)(15) . Several studies have used gums flavored with menthol targeting the pleasantness because of the taste, not because of their peculiarity of activating the TRPM 8 receptors, that have a relation with the neural pathways of thirst (13)(14)(15)29) .
One limitation of the study was the lack of knowledge of the type of menthol that composes the chewing gum used because the chosen gum is commercially available and its formulation is not publicly available. In addition, it was not possible to evaluate the duration of the effect of the menthol strategy on the intensity and discomfort of thirst.
Another factor for the superiority of the intervention is the presence of the sweetener called xylitol, which replaces sucrose in the composition of the gum (30) . Among its benefits are the possibility of use by diabetics (30) and its negative value of heat dissolution (-34.8 cal.g -1 ), producing a pleasant cooling effect on the mouth when it comes in contact with saliva. Due to this organoleptic property, xylitol enhances the cooling effect (30) of menthol products such as chewing gum. respectively, radiating to the supra-optic, paraventricular and subfornical organs, which are highly related areas with stimuli of thirst and secretion of ADH (2,7,9,(31)(32) . The irradiation of these innervations to the anterior cingulate cortex also occurs, more precisely for areas three, two and one of Brodmann, also called somatosensory, which allows the experimentation of distinct sensations, among them, thirst and satiety (33)(34)(35) .
In view of this, this strategy has high clinical relevance, since its use is simple and feasible in the preoperative period. In addition to being effective, it poses a challenge to the established paradigm in clinical practice regarding surgical suspension in case the patient uses it by his/her own choice (10) . Moreover, it is easily applied clinically and represents an increase in the quality of care and humanization due to the intentional look at a basic human need. Moreover this non-pharmacological intervention is low cost and has excellent acceptability by patients (36) , who reported a pleasant sensation and intense comfort with the use of the gum.

Conclusion
There were statistically and clinically significant differences regarding the effectiveness of the menthol chewing gum strategy for the relief of the intensity and discomfort of thirst in the surgical patient in the preoperative period. Given the results evidenced in this study, the conclusion is that this evidence is a simple strategy, of high clinical feasibility, low cost and good patient acceptability.
It presents itself as an innovation in the breaking of the paradigm that chewing gum cannot be offered to the surgical patient. It also contributes to the expansion of knowledge in the management of the surgical patient's thirst, particularly in the preoperative period. It represents an appreciation of nursing care in an individualized way, since it meets a basic human need so commonly neglected.