Introduction
Coronary artery disease is one of the most common diseases that has endangered the lives of many patients [1, 2]. Patients with this disease need medical treatment for the rest of their lives. If medical treatments fail, it is necessary to use Coronary Artery Bypass Graft (CABG) surgery to save patients’ lives and reduce the signs and symptoms of the disease [3]. Nearly 686000 CABG operations are performed annually in the United States and more than 40000 in Iran [4]. The majority of patients undergoing CABG are middle-aged or old [5]. The CABG surgery can cause short-term complications that increase the risk of falls during hospitalization [6, 7]. The most common complications after CABG are cognitive impairment and delirium. A study showed that 24.5% of patients undergoing CABG develop temporary delirium [8]. Moreover, the occurrence of cardiac arrhythmias after CABG may increase the risk of falling by impairing cerebral circulation [9, 10, 11].
One of the most important nursing care after CABG is to get patients out of bed after cardiac intensive care [12]. However, this early walking may be associated with an increased risk of falling in patients [13]. Although many medical centers assess the risk of falls in patients at the beginning of hospitalization, variables that may increase the risk of falls after CABG operation have not been considered [14]. Complications such as sudden cardiac arrhythmias, temporary cognitive impairments, and sudden loss of blood supply to the brain may increase the risk of falling in patients after getting out of bed [15, 16, 17, 18, 19]. Therefore, this study was performed to determine the frequency of falls and related factors after CABG in Rasht in north of Iran.
Materials and Methods
This research is an analytical study with a cross-sectional design. The study population consisted of patients who had undergone CABG at one of the specialized hospitals in Rasht City, Iran. The results of a similar study stated that the risk of falling due to atrial fibrillation was 0.6 times higher than those without this disorder [15]. Considering this probability, a test power of 80%, and a significance level of 95%, the sample size was determined 132. Since 34 individual and disease-related variables are examined in the present study, 5 samples were considered for each variable and, thus, the final sample size was set at 302. A sequential method was used for sampling. The inclusion criteria were as follows: no musculoskeletal disorders that prevent the patient from getting out of bed, no history of heart surgery (due to increased risk of complications from surgery), no epilepsy or use of antiepileptic drugs, and no blindness. Considering that a part of the questionnaire was completed before surgery and the rest after surgery, complications such as bleeding or arrhythmia that caused the patient to return to the Intensive Care Unit (ICU) were criteria for exclusion from the study.
The data collection tool was a questionnaire with two sections. The first section has several parts and collects patients’ demographics, disease, and operation-related information. The first part collected demographic information, including age, sex, height, and weight of the patient. The next part collected disease-related information, including a history of underlying diseases such as hypertension, diabetes, myocardial infarction, kidney disease, cerebrovascular disorders, history of chronic respiratory diseases, history of surgery, left main coronary artery stenosis, presence of valvular disorders, and the Left Ventricular (LV) ejection fraction. The other part collected surgery-related information in three periods: preoperative, intraoperative, and postoperative. 
The preoperative factors include checking hemoglobin, hematocrit, platelets, and electrolytes such as potassium, sodium and urea nitrogen, creatinine, and blood sugar in the morning of surgery immediately before surgery. The intraoperative factors include checking emergency or elective surgery, receiving inotropic drugs, receiving intraoperative shock, intraoperative antiarrhythmic drugs, arterial blood oxygen saturation at the end of cardiopulmonary bypass pump and also at the entrance to the operating room, aortic cross-clamp duration, cardiopulmonary bypass time per minute, the number of transplanted vessels, mean temperature on pump, mean hemoglobin, hematocrit, serum potassium, sodium and glucose levels during pump, urinary output on pump, cell pack intake during surgery and Mean Arterial Pressure (MAP) during pump and LV ejection fraction during surgery. 
The postoperative factors consisted of the duration of endotracheal tube retention in minutes, mean temperature from entry into Intensive Care Unit (ICU) ICU to the removal of the endotracheal tube, mean systolic and diastolic pressure at admission into ICU until removal of the endotracheal tube, type of anesthesia in the ICU, the occurrence of cardiac arrhythmia while attending the ICU, use of pacemaker generator during hospitalization, use of the inotropic drug in the first 24 hours after entering the ICU, receiving cell packs and other blood products in the ICU, levels of hemoglobin, platelets, calcium, magnesium, potassium, sodium, urea nitrogen, creatinine and blood sugar at the time of entering the ICU, the incidence of respiratory complication of atelectasis, pneumothorax, and hemothorax in the ICU, and anatomical disorders not related to movement. These study variables were determined based on similar studies [8, 16] and were reviewed and approved by a cardiac surgeon and six nurses of patients with heart disease or undergoing heart surgery to determine their validity. There was no need to evaluate the reliability of this questionnaire.
The second section was the Morse Fall Scale (MFS). This scale has 6 items assessing history of falling: immediate or within 3 months, secondary diagnosis, ambulatory aid: bed rest/nurse assist crutches/cane/walker, IV/heparin lock, gait/transferring: normal/bedrest/immobile, weak, impaired, and mental status: oriented to own ability, forgets limitations. The total score ranges from 0 to 125. Scores of 0-24 indicate low risk, 25-50 a moderate risk, and scores> 51 show a high risk of falling [20]. The MFS is widely used in medical centers to assess the possibility of patients’ falling at the beginning of hospitalization and has acceptable validity and reliability.
After receiving ethical approval from Guilan University of Medical Sciences, the researcher attended cardiac surgery departments and completed the questionnaires. Data collection in this study was done before, during, and after surgery. Variables related to demographic information, disease, and fall were completed before surgery, and variables related to surgery, including intraoperative and postoperative variables and the MFS, were completed after surgery and discharging from the ICU and transferring to the cardiac surgery ward. A research team member collected all information, and the data collection lasted from November 2019 to July 2020. During the sampling period, 327 patients underwent CABG in the study ward, and 302 patients with inclusion criteria were included in the research.
The obtained data were analyzed in SPSS v.16 software using descriptive statistics and statistical tests, including the Kolmogorov Smirnov, Wilcoxon, Mann-Whitney U, Kruskal-Wallis, and Spearman correlation. Rank regression was used to determine the factors related to the probability of fall after surgery. P values less than 0.05 were considered the significance level of the tests.
Results
The Mean±SD age of the participants was 59.35±8.37 years, 70.53% were male, and 46.03% were overweight (BMI range: 25-29.9 kg/m2). The majority of them had hypertension (82.45%), hyperlipidemia (76.49%), and diabetes (42.72%). Only 24.27% had the left main coronary artery stenosis. In total, only about 4% had a history of cerebrovascular disorders. Regarding preoperative factors, the Mean±SD hemoglobin value in the morning (just before transferring to the operating room) was 11.82±1.14 mg/dL. The Mean±SD blood sugar at this time was 129.94 ±55.83 mg/dl. Descriptive statistics related to postoperative factors are presented in Table 1.


The Mean±SD risk of falling after transfer from the ICU was 39.97±12.38, while it was 15.5±7.07 at the beginning of hospitalization and before surgery. According to the results, 13.91% of patients had a high risk of falling after surgery. 
The Wilcoxon test results showed that the difference in the MFS scores at hospitalization and after surgery was significant (P=0.001). Moreover, the Kruskal-Wallis and Mann-Whitney U test results showed that the difference in the mean MFS scores after transferring from the ICU and at the time of being allowed to move and leave the bed was significantly associated with age (P=0.001), high blood pressure (P=0.003), and intake of an intraoperative antiarrhythmic drug (P=0.004). 
The Spearman test showed that the risk of falls after CABG and transfer from ICU to cardiac surgery ward had a significant relationship with age (P=0.001, r=0.291), hemoglobin level (P=0.04, r=-0.115), sodium level (P=0.04, r=-0.118), urea level (P=0.001, r=0.212), and calcium level (P=0.03, r=-0.122) all in the morning of surgery as well as the duration of cardiopulmonary pump use (P=0.01, r=-0.138), receiving cell pack intake during surgery (P=0.002, r=-0.177), sodium level at the time of entering the ICU (P=0.02, r=-0.129), and serum urea level at the time of entering the ICU (P=0.01, r=0.139) (Table 2).


The results of rank regression showed that the variables of age (P=0.003), history of high blood pressure (P=0.046), preoperative urea level (P=0.01), preoperative creatinine increase (P=0.001), hemoglobin level lower than the normal range, and increased preoperative sodium (P=0.009) were associated with increased risk of fall after transfer from the ICU (Table 3).


Thus, 6.6% of demographic factors, 18.7% of disease-related factors, and 30.1% of both demographic and disease-related factors were associated with the risk of falling after CABG. The ROC (Receiver Operating Characteristic Curve) was used to determine the relationship of demographic factors, disease-related factors (preoperative, intraoperative, and postoperative factors), and both demographic and disease-related factors. Area Under Curve (AUC) was not significant for demographic factors alone (P=0.1, AUC=0.566), while it was significant for disease-related factors (P=0.001, AUC=0.687) and demographic and disease-related factors together (P=0.001, AUC=0.701) (Figure 1). Discussion
The present study results showed that the risk of falls in patients after CABG and after discharge from the ICU increased significantly compared to before surgery. Few studies have examined the risk of a fall after CABG. Manemann’s study using the MFS showed that 38% of patients with cardiovascular disease were at high risk of falling [16]. Partridge et al. showed that after surgery and in the hospitalization phase, more than half of arterial vascular surgical subjects had physical dysfunction [17], increasing the risk of falls. Gringauz et al., who examined the frequency of falls in hospitalized patients using the MFS tool, also showed that patients were more likely to fall [15]. Shirvani et al. [18] suggested cognitive disorders such as delirium as one of the reasons for the increased risk of falls after CABG. They recommended that early mobilization be planned for these patients to reduce the progression of their cognitive impairments. The presence of cognitive impairments in these patients may be a factor in increasing the risk of falls.
The present study results showed that the risk of falling had a significant relationship with age, such that the falling risk increased with increasing age. Rank regression also showed that aging could predict the risk of falls after CABG. Lim et al. [19] and Lee et al. [21] also showed that the risk of falling increases with aging. This high risk may result from increasing age and movement problems in patients, especially patients with coronary artery disease, which reduces the blood supply to the central and peripheral nervous systems, leading to an increased risk of falling. Moreover, heart surgery as a major stressor can cause fear and anxiety in patients. The results of Paryad showed that these patients suffer from postoperative anxiety. Patients’ anxiety may also increase their fear of being forced, leading to an increased risk of falling [22].
The present study results showed that CABG patients with hypertension were more likely to fall. This finding is consistent with the results of Van Rensburg [23]. Khovasova’s study showed that arterial hypertension could increase the risk of patients falling [11]. Hypertension may be associated with impaired blood flow to patients’ central nervous systems and affect their balance when getting out of bed and moving. Another variable associated with the increased risk of falls after CABG was the increased preoperative urea and creatinine. People who high urea and creatinine levels before surgery were at higher risk for falls after surgery. The results of Davis showed that patients with elevated serum urea might show some degree of consciousness loss [24]. 
Lack of full consciousness may increase the risk of falls in patients after CABG. Hemoglobin deficiency on the morning of surgery was also associated with an increased risk of falls after CABG. Lucero’s study showed that serum hemoglobin could be related to an increased risk of falls in patients [25]. A decrease in hemoglobin is associated with a reduction in the transfer of oxygen to vital organs, causing the possibility of weakness, changes in blood pressure, and subsequent cognitive impairments. All of these complications can affect the patient’s balance after heart surgery. The increase in serum sodium was also associated with an increased risk of falls in CABG patients. 
Elevated serum sodium can be one of the factors influencing the rise in blood pressure, and the resulting hypovolemia may cause dizziness and muscle weakness. Such symptoms can increase the patient’s risk of falling. Leong’s study reported nervous dysfunction, muscle weakness, decreased fluid volume, and tachycardia following elevated serum sodium levels. All of which may increase the risk of falls. The final model confirmed the significant effect of the variables of age, history of high blood pressure, increased preoperative urea and creatinine, and increased preoperative sodium on the risk of fall in CABG patients. It seems that paying attention to the above variables in developing care programs for patients who have undergone CABG can reduce the risk of falling after surgery. 
According to the results of this study, the probability of falling after CABG surgery and after transferring from the ICU to the general cardiac ward was significantly different from the fall probability rate at the beginning of hospitalization. This finding indicates that it is necessary to estimate the risk of falling after transfer from the ICU. Determining the risk of falls at the beginning of hospitalization is necessary but not sufficient; determining the risk of falls after CABG surgery and discharge from the ICU can be helpful in care planning for nurses. Due to the increase in the daily function of patients after CABG, it is recommended to estimate the risk of falls on a daily basis until the patients get discharged. In this case, a suitable daycare plan can be designed for these patients based on their falling risk.
Conclusion
Many patients experience severe anxiety before and after heart surgery, affecting their fear and anxiety about moving after surgery. However, this factor was not measured in the present study, which can be one of its limitations. Demographic and disease-related factors predicted 70% of the risk of falls after CABG surgery. This result emphasizes the above variables in predicting the risk of falls in CABG patients. Since the number of CABG surgeries is increasing, it is recommended to conduct studies in different medical centers to determine the factors related to the risk of falls in these patients. The use of various facilities in different care departments, the number of nurses present in each ward, and the presence of a physiotherapy team to help move these patients can reduce the risk of falling after CABG surgery.

Ethical Considerations
Compliance with ethical guidelines
Before the study, ethical approval was obtained from the Ethics Committee of Guilan University of Medical Sciences (Code: IR.GUMS.REC.2019.370). All participants signed an informed consent form before the study, and their information was kept confidential.

Funding
This study was extracted from a MSc. thesis of the first author in nursing. It was financially supported by the Deputy for Research and Technology of Guilan University of Medical Sciences.

Authors' contributions
Study design and conceptualization: Maryam Rajabi, Ezzat Paryad, and Atefeh Ghanbari Khanghah; Data collection: Maryam Rajabi; Data analysis: Ehsan Kazemnezhad leili, Ezzat Paryad, and Atefeh Ghanbari Khanghah; Initial draft preparation: Maryam Rajabi and Ezzat Paryad; Final approval: All authors.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank the patients who participated in the research and the staff of the cardiac surgery wards of Dr Heshmat Hospital in Rasht City, Iran.



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