Cardiovascular diseases are the leading cause of death in the world. In Brazil, they represent about 30% of the number of deaths. Coronary artery bypass grafting (CABG) is the most common surgical procedure used to treat coronary heart disease, with a high probability of improving ventricular function, reducing symptoms and improving patients’ prognosis.¹ The main complications of CABG are related to comorbidities that affect respiratory function, such as chronic obstructive pulmonary disease, pulmonary congestion and prolonged mechanical ventilation, in addition to systemic infections, diabetes mellitus, renal failure and hemodynamic stability.^{1 , 2}

Functionality may be altered in patients undergoing myocardial revascularization , due to the immobility and complexity of the procedure, such as degree of sedation, cardiopulmonary bypass (CPB), preoperative pulmonary and cardiac functions and mobility restriction in case of admission to the intensive care unit (ICU).^{2 , 3}

Risk scales such as the European System for Cardiac Operative Risk Evaluation (EuroSCORE) and the InsCor in cardiac surgeries are shown to be simple and objective indices to predict operative mortality. In both scores, the preoperative evaluation offers the advantage of patients’ stratification, allowing better intraoperative and postoperative planning, with similar performance and accuracy. However, these scores do not provide information about pulmonary function, since the EuroSCORE only evaluates previous chronic lung diseases and pulmonary hypertension, and the InsCor does not provide pulmonary function indices.^{4 - 7}

The functional independence measure (FIM) is a measurement tool used that can be used in these patients to assess functionality, analyzing some of its aspects including self-care, sphincter control, locomotion, cognition, bed transfer and communication.⁸

In addition, to obtain effective treatment, a careful and efficient preoperative evaluation is essential, analyzing patient's pulmonary function, considering the tendency decreased lung volumes and capacities. It is also important to pay attention to possible risks and complications, and properly advise the patient about the procedure, including the extubation process.⁹

Although these scales are validated, there is still no evidence on their possible use to predict the worsening of peripheral and respiratory muscle strength, functionality and pulmonary function of the patient. This would allow the use of these two scales in the preoperative period to identify individuals who would need different care, becoming a tool for individualization of care. The present study aims to correlate surgical risk scales with functional independence measure (FIM) and pulmonary function parameters in patients undergoing CABG.

This was a prospective cohort study conducted from January 2018 to April 2019, at the intensive care unit (ICU) of Instituto Nobre de Cardiologia, a referral center for cardiovascular care in the City of Feira de Santana, state of Bahia. This study was approved by the Research Ethics Committee of Faculdade Nobre (approval number 2.490.540), and all participating patients signed an informed consent form.

Fifty-nine patients hospitalized for myocardial revascularization surgery were included in the study. Of these, 28 were excluded because of an ICU longer than three days (n=14), death (n=2), change in the in the surgical treatment plan (n=1), rescheduling of the date of the procedure (n=1), refusal to attend data collection (7th POD) (n=4) and patients discharged before the 7th POD (n=6) ( Figure 1 ).

Figure 1

ICU: intensive care unit; POD: postoperative day

In the present the study, we found that the EuroSCORE had a strong negative correlation with MIP and FIM, while InsCor had a significant negative correlation with MIP, MEP and FIM.

There was a reduction in all variables related to pulmonary function when compared to the preoperative period. MIP had a 30% decline on the seventh postoperative day, corroborating with Schnaideret et al.,¹⁶ who also showed a reduction in MIP. We obtained a reduction in MEP value of 33% and in PEF of 10% when compared with preoperative values.

On the other hand, Annoni et al.¹⁷ observed a significant increase in MEP and PEF, which may have been correlated with the small sample size, and collaboration and learning of patients to perform the tests, since they were evaluated daily from the first postoperative period until the day of discharge.

This study also corroborated the research conducted by Cordeiro et al.,¹⁰ proving the existence of a positive relationship between a cardiac risk scale and functionality in patients undergoing cardiac surgery. Patients at higher pre-surgery risk experienced worsening of functionality.

It is possible to identify a reduction in muscle strength in patients after surgery, which may be related to several factors related to the surgery itself. Guedes et al.¹⁸ described that thoracic surgical incisions generate a reduction in respiratory muscle strength, as they affect muscle integrity, directly changing its postoperative function and increasing the length of hospital stay. Changes may occur due to dysfunction of the respiratory muscles and nerves resulting from the incision or due to changes in respiratory mechanics,¹⁹ confirming the findings of our study.

Cordeiro et al.³ reported that cardiac surgeries can cause systemic changes, given the complexity of the procedure: degree of sedation, CPB time, preoperative pulmonary and cardiac functions, which may influence the degree of functionality of these patients, besides mobility restriction due to ICU admission. As expected, there was a decline in functionality, as studies indicate the relationship of preoperative risk with worsening of functionality.^{4 , 10}

Fonseca et al.²⁰ pointed out that during the postoperative period, there is a need for pain and anxiety control. The authors mentioned that, in a study conducted by nurses in a hospital specializing in cardiology, it was identified that these factors motivate the administration of sedative and analgesic drugs, with consequent depression of the level of consciousness, increasing hospitalization time. These findings coincide with our results, leading to the hypothesis that the longer a person takes sedative drugs, the later will the functional independence be recovered.

In addition to these findings, Pardeans et al.²¹ reported that myocardial revascularization surgery and high surgical risk are associated with reduced exercise capacity for the surgical procedure. This may be related to the worsening of ventilatory muscle strength and pulmonary function, as observed in our study.

Another explanation for the decline in the variables presented in this study is sarcopenia.²² Many of our sample were elderly, which alone contributes to reduction of muscle mass and worsening of cardiac systolic function.

The development of tools that can predict outcomes is of fundamental importance to this population. Ivanov et al.²³ evaluated the use of preoperative pulmonary function testing to stratify the risk of patients undergoing cardiothoracic surgery and did not recommend its routine use due to its low sensitivity. This result reinforces the findings of our study, suggesting the need for a new assessment instrument.

Limitations of our study include the small sample size, lack of sample calculation, and insufficient data such as surgery time, medication use and pain scale, that could improve the interpretation of our results.

It was concluded that EuroSCORE had a strong negative correlation with MIP and FIM, while InsCor had a negative correlation with MIP, MEP and FIM. Given these results, it is evident that the both scales provided knowledge of the risks during surgery and detected the decline in the level of independence and pulmonary function of patients undergoing coronary artery bypass grafting. Further studies should be conducted, stratifying patients at higher risk of such decline, to implement specific interventions.