Trial design
This randomized controlled clinical trial was conducted with a parallel design and lasted for 1 year, from October 2016 to October 2017. This study was based on the CONSORT Guideline.
Research hypothesis
Our hypothesis in this study was that inhalation aromatherapy with lavender and peppermint essential oils could improve the sleep quality of cardiac patients.
Sample and sampling method
The study population included all cardiac patients, admitted to the CCU of Imam Ali Hospital in Kermanshah Province, Iran. Samples were recruited through convenience sampling and randomly allocated to two intervention groups and one control group.
Random allocation was conducted by block randomization. For this purpose, A, B and C blocks were assigned to the peppermint, lavender, and control groups, respectively. The permuted blocks were ABC, ACB, BAC, BCA, CAB, and CBA. The ABC block was chosen as the first block, and the subjects were divided into peppermint, lavender, and control groups, respectively. The sequence of blocks was determined by a statistician, who was not involved in data collection. The sample size was estimated according to a study by (Moeini et al., 2010). Assuming σ = 4, the mean scores of sleep quality in the control and intervention groups were 18.68 and 13.97, respectively, at a study power of 90% and confidence level of 95%. The minimum sample size was estimated at 20 per group. Nonetheless, 35 patients were allocated to each group, all of whom remained in the study until the end.
The inclusion criteria were as follows: 1) consent to participate in the study; 2) full consciousness; 3) healthy sense of smell based on the patient’s report and the researcher’s examination for the absence of obstructions; 4) hospitalization for 48 h; 5) having stable vital signs (blood pressure of 120/80–140/90 mmHg, lack of fever, pulse rate of 60–100 per minute, and respiratory rate of 12–20 per minute) (Bikmoradi et al., 2015; Cheraghbeigi et al., 2019; Najafi et al., 2014); 6) having no history of mental disorders according to the medical records; 7) being in the age range of 18–65 years; 8) Pittsburgh Sleep Quality Index (PSQI) score > 5; 9) not having any respiratory infections, such as sinusitis and pneumonia; and 10) no smoking, alcohol use, or consumption of caffeine drinks 1 h before bedtime. On the other hand, the exclusion criteria were as follows: 1) unwillingness to continue the intervention; 2) deterioration of the patient’s condition during the study; 3) transfer to another ward; 4) patient’s death; and 5) oxygen dependence during aromatherapy.
Measurement instrument
The study instruments included a sociodemographic questionnaire, a clinical information questionnaire, and PSQI. The sociodemographic questionnaire consisted of seven questions related to age, gender, body mass index (BMI), marital status, education, occupation, and history of aromatherapy. The clinical information questionnaire consisted of five questions related to the type of cardiac disease, history of diabetes, history of hypertension, consumption of hypnotic drugs, and history of myocardial infarction. The validity of the sociodemographic and clinical information questionnaires was assessed, based on the content validity method. For this purpose, the questionnaires were distributed among 12 faculty members, and their comments were considered in revising the questionnaires.
Generally, PSQI is a standard tool used to assess sleep quality. The validity and reliability of this tool have been confirmed in previous studies (Karadag et al., 2017; Lisa Blackburn et al., 2017). Buysse et al. (1989) investigated the internal consistency of PSQI using Cronbach’s alpha method and reported a Cronbach’s alpha coefficient of 0.83 (Buysse et al., 1989). Moreover, the Persian version of PSQI has been psychometrically evaluated by Farahi-Moghadam et al. (2012), and its reliability was reported to be 0.77, based on Cronbach’s alpha method (Cheraghbeigi et al., 2019). This questionnaire contains 19 questions in seven areas of sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction. Each item is rated on a four-point Likert scale, including “very good”, “fairly good”, “fairly bad”, and “very bad”, scored from 0 to 3, respectively. The total score ranges from 0 to 21, with scores > 5 indicating a severe sleep problem (Karadag et al., 2017).
Essential oils
The peppermint and lavender essential oils, with 100% concentrations, were purchased from Zardband Pharmaceuticals Company (Yasouj, Iran). The plants had been harvested from the pastures of Yasouj, Iran. The pure essential oils were prepared in amber glass bottles, with the scientific name of the plant tagged on each bottle. They were kept at 2–8 °C in darkness, away from light and heat during sampling.
Interventions
After obtaining permission from the authorities of Imam Ali Hospital, sampling was conducted in the CCU. This hospital is the largest cardiology center in west of Iran. The CCU ward of the hospital consisted of single-bed rooms separated by curtains. First, eligible subjects were included in the study by convenience sampling and then randomly assigned to the intervention and control groups via block randomization. In the intervention groups, inhalation aromatherapy was performed using 100% pure peppermint or lavender essential oil. On the other hand, aromatic distilled water was used for the control group. In the aromatherapy groups using peppermint and lavender essential oils, three drops of each essential oil were smeared on a napkin, which was attached to a collar for 20 min at 9:00 pm. The same procedure was applied for the control group using three drops of aromatic distilled water. The duration of the intervention was seven nights, and PSQI was completed by all participants before the intervention (on the first night) and on the eighth day (in the morning). It should be noted that the researcher made every effort to keep the possible effects of environmental factors, such as light and noise, on the patients’ sleep quality to a minimum. The study process is shown in Fig. 1.
Statistical methods
Data were analyzed by the Statistical Package for the Social Sciences (SPSS v.18.0; SPSS Inc., Chicago, IL, USA). Distribution of sleep quality was examined by Kolmogorov–Smirnov test, which showed the normal distribution of data. Chi-square test was also used to determine whether the groups were homogenous in terms of nominal variables, including gender, marital status, occupation, education, and consumption of hypnotic drugs, history of hypertension, type of cardiac disease, history of diabetes, history of myocardial infarction, and history of aromatherapy. Moreover, Kruskal-Wallis H test was used to compare sleep quality between the study groups before and after the intervention. Also, Wilcoxon signed-rank test was also used to compare sleep quality before and after the intervention in each group. Finally, Mann–Whitney U test was used for two-by-two comparison of the groups in terms of sleep quality. The significance level for all tests was set at 0.05.
Ethical considerations
This trial was conducted in accordance with the Declaration of Helsinki and it was approved by the Ethical Review Committee of KUMS with reference number KUMS.REC.1395.380. The study was also registered at the Iranian Registry of Clinical Trials under the code: IRCT201601244736N10. Before the study, the objectives and methods were explained to all of the participants, and they were assured that their responses would remain confidential. Written informed consent was obtained from all participants before the study.