DISCUSSION
In the data analysis of the present study, it was observed that the inspiratory muscle training protocol, applied to patients at high risk of pulmonary complications, did not show any significant difference in relation to the variables of MIP, MEP and 6MWT in patients undergoing coronary artery bypass grafting.
Pulmonary function is one of the factors that presents changes in the postoperative period, Barros et al. showed that there is a significant reduction in ventilatory capacity and muscle strength in patients who underwent MR. Still, in this same study, it was observed that the IMT helped to restore the overlapping values evaluated in the preoperative period14. Similar results have been reported by Matheus et al. who demonstrated the effectiveness of IMT in recovering the values of tidal volume and vital capacity found in the pre-surgical15. In the present study, a reduction in values was also observed when comparing pre and postoperative in patients who presented risk factors that may generate PPC, however these numbers were not significant, both in the control group and in the intervention group.
Possible justifications may be related to the reduction of ventilatory mechanics, among which are the presence of drains and pain. Sternotomy is an aggressive procedure, which causes several dysfunctions and can cause pain until the fifth postoperative day16. This symptom is common and can cause restriction of chest expansion, causing hypoventilation and making IMT difficult.
Cordeiro et al. presented different results and a similar population in relation to the current study. The researchers investigated the influence of IMT on inspiratory muscle strength and functional capacity. They observed a significant reduction in MIP in both groups, but the intervention group had a higher value for this variable at hospital discharge, compared to the control group. An analysis of functional capacity showed an improvement in the 6MWT when comparing the IMT group to the control group3.
This result is probably related to the researched sample, which was larger when compared to the present study and included other types of surgery besides MRI, considered to be large. Therefore, the greater number of patients, the different inclusion criteria, and, especially, the risk factors present increase the likelihood of PPC, heterogeneous characteristics among the studied samples.
With a more prolonged IMT protocol and with progressive load increase, Praveen et al. they also investigated the effectiveness of IMT in patients who underwent CABG and showed a reduction in MIP in both groups both in the short term and over time in the postoperative period. The group that underwent intervention presented approximate values preoperatively, however some of them increased significantly at maximum inspiratory strength17.
In the training mentioned above, patients were stimulated and instructed to perform IMT from the fourth to the nineteenth postoperative period, with a load that could increase according to the patient’s resistance. Unlike the current research, in addition to extending the intervention period, the fact of starting IMT on the fourth postoperative day can reduce characteristics such as pain, analgesic effect and the patient’s concern about sternotomy. Generally, these findings are still present in the second POD, making it possible to compromise load measurement and training17.
In this context, it is necessary to emphasize that the barriers found in the postoperative period are not limited to the restrictions of the surgical procedure. Predisposing risk factors such as: age, sex, obesity, smoking, diabetes mellitus, arterial hypertension and dyslipidemia are aggravating factors that guide the team about possible complications during or after surgery, directly affecting the recovery of functional and respiratory capacity, increasing the chance morbidity and mortality18.
A study carried out Feltrim et al. sustained the benefit of IMT in high-risk patients with factors similar to the current study and demonstrated a reduction in pulmonary complications of greater impact, acting in a protective way, training improved the strength and resistance of the respiratory musculature8. IMT could probably decrease complications in the studied population, but the functional capacity is dependent on other conditions, not influencing the postoperative risk factors.
Nery et al. also used the 6MWT to assess functional capacity in individuals who underwent MRI surgery. The patients were divided into a sedentary and active group, who performed physical exercises and IMT. In the evaluation, after two years, patients who performed exercises associated with IMT showed less loss in functional capacity, showing significant improvement in the distance covered in relation to sedentary patients. This result may be associated with IMT for a prolonged period and the performance of exercise19.
Physical exercises are beneficial in wide aspects, considerably improve hemodynamics and cardiac output. Demonstrating more effective recovery of the myocardium where they consequently improve muscle fatigue, caused by the decrease in blood distribution, reducing the feeling of tiredness. When associated with IMT, patients effectively improve functional capacity and optimize pulmonary capacity20-22.
In relation to the 6MWT, researchers evaluated the functional capacity in patients with risk factors who underwent CABG and noticed an improvement in the distance covered in older individuals, aged over 75 years, with greater benefit in relation to the distance covered, unlike the present study that had an average age of 67 years23,24. This is one of the inconstant factors, however it is understood that when there is an imminent risk in elective surgeries, it is important to carry out preventive interventions, such as preoperative training, which can train the muscles and minimize impacts on MIP and MEP and probably in the distance covered in the postoperative8.
Our work has some limitations, such as the sample size and the absence of patients’ effort evaluation (BORG scale), which could have been used to gradually increase the load. The different study protocols used by the authors are also characterized as a work limitation.