Background
Nausea and vomiting are among the toxic side effects most frequently associated with antineoplastic chemotherapy, having a devastating effect on the quality of life of cancer patients [
1,
2]. Although nausea and vomiting can result from surgery and radiotherapy, chemotherapy-induced nausea and vomiting (CINV) is potentially the most serious and distressing [
1]. CINV can be classified as acute (occurs minutes or hours after the chemotherapeutic treatment and generally disappears within 24 h), delayed (occurs at least 1 day after chemotherapy and can last five or more days) and anticipated (occurs before chemotherapy and is a conditioned response to previous CINV episodes) [
3]. When left untreated, CINV can affect 60 to 80% of cancer patients [
4]. Moreover, this condition can undermine the antineoplastic treatment results, including, in some cases, the need to discontinue chemotherapy [
5‐
8].
Vomiting is an instinctive defensive reaction caused by the somatoautonomic nervous reflex, which is integrated into the bulb of the encephalic trunk (brainstem). The vomiting caused by cytotoxic drugs is associated with an increase in the concentration of 5-hydroxytryptamine (5-HT) in the intestine and in the encephalic trunk (brainstem). It is believed that cytotoxic drugs cause the release of 5-HT in enterochromaffin cells in the intestinal mucosal barrier and that the 5-HT that is released stimulates the 5-HT receptors in the adjacent vagal afferent nerves. The depolarization of vagal afferent nerves stimulates the center of vomiting in the encephalic trunk (brainstem) and, eventually, causes a vomiting reflex [
9]. The medications normally used to control the CINV include serotonin (5-HT
3) receptor antagonists (RAs), neurokinin 1 (NK-1) RAs, corticosteroids, and metoclopramide, among others [
10‐
12]. There is evidence that after prophylaxis with these antiemetic medications, the effects of acute and delayed nausea and vomiting can be avoided in up to 50% of the cases [
13]. However, the high cost of these agents and their side effects, such as extra pyramidal disorders, hypotension, headache, constipation, fatigue, mouth dryness, vertigo, diarrhea, and irritability, have limited the use of these medications [
14‐
16].
Given the growing preferences for complementary and alternative therapies (CAT), patients are interested in alternatives to standard pharmacological treatments to CINV, or even associating the use of these therapies to traditional allopathic interventions [
17,
18]. The CAT generally do not require a medical prescription, they can be accessed in the community and have gained more attention in the scientific community recently [
18]. According to one of the evidence directives for the practice provided by the Oncology Nursing Society, the stimulation of acupuncture points was considered a promising intervention for CINV handling [
13]. One of the fields of acupuncture is auriculotherapy, which has been used for approximately 2500 years, with the goals of diagnosis and treatment of physical and psychosomatic disorders [
19]. Auriculotherapy is one of the non-pharmacological methods that has been used to control CINV [
10]. This intervention must be performed by qualified healthcare professionals. In Brazil, for instance, the Ministry of Health, by means of the
Coordenação Nacional de Práticas Integrativas e Complementares em Saúde (National Coordination of Integrative and Complementary Healthcare Practices) offers a free course for “Auriculotherapy qualification for healthcare professionals of the basic attention sector,” with the objective of qualifying these professionals so they can work in the Primary Healthcare Attention sector.
The technique consists of stimulating specific points in the auricular pavilion, which is considered one of the main microsystems of the human [
20,
21]. This therapy seeks to harmonize the functions of organs, viscera, and physical and mental infirmities, from the reflex that the stimulus causes in the points of the central nervous system, by means of finger acupressure, laser, electricity, different types of needles, magnetic balls, and seeds [
21,
22]. In China, the birthplace of acupuncture, the existing correlation between the ear and the body was described in 500 A.C. in the classical text
Huang Di Nei Jing, showing that all the body meridians converged towards the ear [
21,
23,
24]. A modern form of the technique was developed by the end of 1950, by the French physician Paul Nogier, who created the inverted fetus map, in a way that the auricular points are displayed in this configuration [
21,
24]. According to the principles of the Traditional Chinese Medicine, this therapy can restore and raise the flowing cycle
Qi (vital energy) and
Xue (blood) and, consequently, harmonize the functions of all living organs and tissues [
25,
26]. In the Western perspective, the effects of this intervention are related to the nervous, neuroendocrine, and immune systems, in order to promote relief of the signs and symptoms of different illnesses, on top of possessing preventive aspects [
19,
27]. Furthermore, the effects of auriculotherapy in the organism can be explained by neurophysiology and by reflexology [
21]. The four mixed cranial nerves give the ear more than half of its innervation through the trigeminal, facial, glossopharyngeal, vagus, and cervical plexus nerves (C2/C3). This nervous composition means that the ear is a unique neurovascular organ [
28]. There is evidence that suggests that areas of the encephalic trunk (brainstem) can be influenced by stimulating the ear [
29].
The available literature concerning the therapeutic effects of auricular stimulation in symptoms of many disorders has been steadily growing [
29]. In the case of surgery patients, there is evidence that suggests that auriculotherapy is a viable intervention for the treatment of postoperative nausea and vomiting, due to the safety, cost, and patient satisfaction [
30]. Recently, a systematic review was carried out to evaluate the effectiveness of acupressure in CINV control, and according to the results, acupressure has a protective effect for this condition [
31]; however, this review did not include studies with auriculotherapy. In a clinical test that determined the auricular acupressure effect in the CINV relief among women with breast cancer, the researchers concluded that the use of this intervention, along with other therapies, can alleviate CINV, without side effects [
10].
As auriculotherapy is being considered a potential treatment to control CINV but there is no literature review of the available evidence regarding the effects, harms, and benefits of this intervention, the objectives of this review are as follows:
1. To synthesize the available evidence in the literature regarding the auriculotherapy effects in the CINV treatment of cancer patients.
2. To develop a clinical protocol that guides the use of auriculotherapy as a CINV treatment for cancer patients.
3. To identify possible adverse effects originated from the uses of auriculotherapy as a CINV treatment for cancer patients.
4. To suggest a core outcome sets (COS) based on the treatment of CINV using auriculotherapy.
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