Abstract

Background: This study aims to evaluate the relationship between chest pain intensity and physiological indicators in patients undergoing coronary artery bypass grafting.

Methods: In this correlational study, chest pain intensity and physiological responses of a total of 126 coronary artery bypass grafting patients (104 males, 22 females; mean age 62.3±8.5 years; range, 45 to 80 years) during respiratory exercise were evaluated in a referral hospital setting between December 2016 and March 2018. On the second day after surgery, pain intensity was measured by a numerical rating scale. Physiological indicators were collected using the Nihon Kohden (MU65) monitoring device.

Results: The mean pain intensity score was 7.8±1.9 (range, 1 to 10). There was no significant correlation between the pain intensity and physiological indicators (p>0.05). There was a negative correlation between the pain intensity and age of the patient (r=- 0.183 and p=0.04). Pain intensity was not significantly different between male and female gender (p=0.064).

Conclusion: Our study results show no significant relationship between the chest pain intensity and physiological responses in patients undergoing coronary artery bypass grafting.

Coronary artery bypass grafting (CABG) is one of the therapeutic modes in some cardiac disorders such as coronary artery diseases.[1] Despite therapeutic effects of open heart surgery, postoperative patients may experience many biological and psychological conditions.[2] Thoracotomy and post-sternotomy pain is an unpleasant feeling experienced by most of the patients after CABG.[3,4] Usually, %75 of patients suffer from pain postoperatively. In addition to discomfort, this pain affects the patient's physiological responses such as respiration, pulse, blood pressure, myocardial oxygen consumption, and cardiac output.[5]

Since pain management is an indicator of the quality of care,[6] pain evaluation is one of the important tasks of nurses and other health care personnel to tailor an appropriate caring program. Pain perception is a complex process and is related to various factors such as level of anxiety, previous experiences, and individuality of patients.[7] Using pain scales is a usual method for pain evaluation in the clinical setting. Most of the pain scales are self-report measures which evaluate pain severity according to patients" expressions. However, the methods of self-report may not be adequate due to lack of patients" collaboration or altered level of consciousness of the patient.[8] Also, self-report methods measure pain subjectively and mostly do not provide an exact and reliable assessment of pain.[6] Physiological responses indicate the threatening status of diseases.[9] Therefore, many clinicians and scientists have emphasized that an objective assessment of pain is more essential for pain management.[10] However, there is not enough evidence for a clear relationship between the severity of pain with physiological responses. In this regard, Block et al. found no relationship between vital signs and self-reported pain intensity.[11]

Despite the variety of pain evaluation methods, it seems that there is still no established consensus regarding the most optimal way to measure pain. Therefore, further researches are needed to specify how the patient responses to a painful condition in the clinical setting.[12] In the present study, we aimed to investigate the possible relationship between chest pain intensity and physiological indicators in patients undergoing CABG.

Methods

In this correlational study, chest pain intensity and physiological responses of a total of 180 CABG patients during respiratory exercise were evaluated in a referral hospital setting in Iran between December 2016 and March 2018. However, 126 eligible patients (104 males, 22 females; mean age 62.3±8.5 years; range, 45 to 80 years) were enrolled.[13] Inclusion criteria were as follows: being cooperative, having an ability to establish verbal communication, and having the first experience of open heart surgery and not receiving analgesic medication within the last four hours. Exclusion criteria were as follows: being under mechanical ventilation, having delirium, hallucinations, severe depression, or surgery abscess, bleeding, and current or recent use of analgesic medications. A written informed consent was obtained from each patient. The study protocol was approved by the Ethics Committee of Semnan University of Medical Sciences, Semnan, Iran (No: IR.SEMUMS. REC.1395.96 /23.09.2016). The study was conducted in accordance with the principles of the Declaration of Helsinki.

All patients were operated by a single surgeon. The patients were hospitalized in the bed and their sternum stability were the same. In addition, a single sternal fixation technique was used in all patients. The fixation was performed by stainless steel wires of the same size (No. 7 USP; Dispomedica GmbH, Hamburg, Germany).

Data collection and measurements
On the second day after surgery, all patients received a non-steroidal anti-inflammatory drug (Gelofen® 400 mg capsule; Daana Pharmaceutical Company, Tabriz, Iran) at 05:00 am. Then, during respiratory exercise at 10:00 am, chest pain intensity and physiological indicators of systolic and diastolic blood pressure, heart rate, respiratory rate, oxygen saturation, and mean arterial pressure were measured. All measurements were performed at bedside. The chest pain severity was measured by a numerical rating scale (NRS) of pain which was validated by several studies.[14,15] The physiological indicators were measured using the Nihon Kohden (MU65) monitoring device (Nihon Kohden, Tokyo, Japan) which was calibrated for each measurement.

Statistical analysis
Statistical analysis was performed using the IBM SPSS for Windows version 23.0 software (IBM Corp., Armonk, NY, USA). Descriptive data were expressed in mean ± standard deviation (SD) or number and frequency. The normality of data was analyzed using the Kolmogorov-Smirnov test. The chi-square test was used to describe demographic variables. Independent Student's t-test and Mann-Whitney U test were used to compare variables between two independent groups. The Pearson correlation analysis was used to evaluate possible relationship between the chest pain intensity and physiological indicators. A p value of <0.05 was considered statistically significant.

Results

Of all patients, 51.6% were diabetics and 48.4% were non-diabetics. There was no significant difference between diabetic and non-diabetic patients in terms of pain intensity and physiological indicators.

The mean pain intensity score was 7.8±1.9 (range, 1 to 10). There was no significant correlation between the pain intensity and physiological indicators (p>0.05) (Table 1).

Table 1: Correlation between physiological indicators and pain intensity

However, the Pearson correlation analysis revealed a negative and significant correlation between the pain intensity scores and age of the patient (r=-0.183 and p=0.04), and older patients reported lower pain intensity. In addition, there was a negative and significant correlation between the age and oxygen saturation (p=0.001), and older patients had lower oxygen saturation levels.

Furthermore, diastolic blood pressure, heart rate, and mean arterial pressure were significantly higher in women than men. However, other physiological indicators and pain intensity were not significantly different between men and women (Table 2).

Table 2: Pain intensity and physiological indicators according to gender

Discussion

Post-sternotomy pain is a common problem in patients after CABG. Most patients experience various degrees of postoperative pain.[16] Evaluation of pain intensity is one of the important action of nurses and other health care personnel in the clinical setting. In the present study, we analyzed the possible relationship between chest pain intensity and physiological indicators. The results of the study showed that there was no significant relationship between the pain intensity and physiological indicators in CABG patients. Similarly, Ledowski et al.[8] found no relationship between the pain severity and hemodynamic and autonomic responses in patients after surgery. Daoust et al.[17] also concluded that vital signs should not be used as an estimation tool for pain intensity. In an observational study in the emergency setting, Marco et al.[18] reported no clinically significant relationship between the self-reported pain intensity and heart rate, blood pressure, and respiratory rate. On the other hand, in some studies, the pain was found to be correlated with physiological responses. Zamunér et al.[19] observed a correlation between the pain intensity and sympathetic activity in fibromyalgia patients. Helfer and McCubbin[20] also found an inverse correlation between the resting blood pressure and pain intensity in healthy young adults. In addition, Hallman et al.[21] reported that patients with chronic neck and shoulder pain had heart rate variability than healthy individuals. According to the aforementioned studies, it seems there is no clear evidence indicating a relationship between post-sternotomy pain intensity and physiological responses among CABG patients. However, this can be attributed to several reasons. In the present study, we evaluated pain intensity on the second day after surgery, in which the patients were in a stable condition. Also, due to the acute nature of post-sternotomy pain, physiological responses might have not been affected, while chronic pain decreases the activity of the parasympathetic system, leading to an increase in the heart rate and blood pressure.[22] Therefore, further studies are warranted to clarify the relationship between the pain intensity and physiological responses in the clinical setting.

In our study, although the mean pain intensity in women was higher than men, the difference was not statistically significant. Similarly, Kállai et al.[23] found no significant difference in the intensity, threshold, and tolerance of pain between the male and female patients. However, Zeidan et al.[24] found higher pain scores and morphine consumption in women than men in the postoperative period. The results of Hussain et al.'s study[25] also showed an increase in the pain intensity of women than men. The lack of a significant difference in the pain intensity between male and female patients in our study can be explained by the lower number of female patients.

On the other hand, some physiological indicators such as heart rate, diastolic pressure, and mean arterial pressure were significantly higher in women than men in our study. However, Aslaksen and Flaten[26] reported that pain did not affect the heart rate. Hence, we recommend further studies to investigate and clarify the relationship of pain with gender and physiological responses.

Furthermore, we found a negative and significant correlation between the pain intensity and age of patient. In contrast, Moradi-Farsani et al.[27] concluded that the patients aged between 53 and 70 years had more intense pain than younger patients. In our study, the age ranges from 45 to 80 years, indicating that pain perception might have been influenced by advanced age. Also, type of medical conditions and pain perception might have affected pain response.

The main limitations of this study include a small sample size due to rigorous inclusion criteria and the lack of younger patients. Therefore, further largescale studies including younger patients are needed to confirm our findings.

In conclusion, our study results show no significant relationship between the chest pain intensity and physiological responses in patients undergoing coronary artery bypass grafting. Although identification of perceived pain can play a role in screening patients, further studies are required to establish a definite conclusion on this topic.

Acknowledgements
We would like to thank the Nursing Care Research Center of Semnan University of Medical Sciences for providing facilities for this work and all patients that participated in this study and their sincere cooperation. This study was part of a Master's Thesis in critical care nursing, which was conducted at Semnan University of Medical Sciences, Semnan, Iran.

Declaration of conflicting interests
The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Funding
The authors received no financial support for the research and/or authorship of this article.

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