Preoperative functional capacity assessment and the role of transcutaneous electrical nerve stimulation in the postoperative period of patients undergoing bariatric surgery

Abstract

Introduction: Changes in lifestyle habits, a diet rich in carbohydrates, and a decrease in physical activity are part of the context that led to an obesity pandemic. Obese individuals have reduced skeletal muscle strength, joint overload, lower cardiopulmonary capacity, high energy expenditure, and reduced effort tolerance. Such alterations result in inefficiency of the act of walking, which is the most accessible modality for weight control. Treating it is a task that requires multidisciplinary care, but in many cases conventional therapy is ineffective, requiring surgical intervention. This, in turn, is not without risks and causes important changes in lung function and functional capacity. Objective: To evaluate the functional capacity of this population in the preoperative period and to associate the pulmonary function measurement and epidemiological data in the predicted distance covered equation, in addition to verifying the effect of electroanalgesia through conventional transcutaneous electrical nerve stimulation (TENS) on pulmonary function in the postoperative period of bariatric surgery. Methods: This work was developed in two different moments. At the first moment, 367 obese were included in this research. 104 men and 263 women were evaluated at a school clinic in the city of Cascavel/Paraná and the functional capacity was evaluated through the 6-minute walk test (6MWT), spirometry, and respiratory muscle strength. In the second moment, a controlled and blinded clinical trial was carried out in 66 subjects undergoing bariatric surgery. Participants were randomized into two groups as follows: intervention group treated with TENS (n = 33) and placebo group (n = 33). Participants underwent 4 sessions of TENS and the effect on pain was verified using the visual analogue scale for pain, pulmonary function measured by spirometry, and hemodynamic data. Results: The distance covered in the 6MWT (6MWD) for men was correlated with age (r = -0.388, P = 0.0005), weight (r = -0.365, P = 0.0007), height (r = 0.285 , P=0.022), body mass index-BMI (r=-0.543, P<0.0001), forced vital capacity-FVC) (r=0.472, P<0.0001), peak expiratory flow-PEF ( r = 0.253, P = 0.031), and maximal inspiratory pressure-MIP (r = 0.313, P = 0.017). In the multiple regression analysis, BMI, FVC, and age were the only variables that independently predicted the 6MWD and explained 40% of its variability. The proposed reference equation for obese Brazilian men was 6MWD (m) = 570.5 - (3.984 × BMIkg/m2) + (1.093 × FVC%predicted) - (0.836 × Ageyears). The 6MWD for women was correlated with height (r = 0.319), age (r = -0.281), weight (r = -0.370), BMI (r = -0.561), FVC (r = 0.443), PEF (r = 0.278), MIP (r = 0.326) and maximum expiratory pressure (r = 0.259), all with P<0.0001. In the multiple regression analysis, BMI, FVC, age, and MIP were the independent predictive variables for the 6MWD, explaining 65% of its variability. The reference equation proposed for obese Brazilian women was: 6MWD (m) = 513.6 - (4.439 × BMIkg/m2) + (1.136 × predicted FVC%predicted) - (1.048 × Ageyears) + (0.544 × MIP%predicted). The assessment of pain and pulmonary function in patients undergoing electroanalgesia in the postoperative period showed the following results: the mean age of the intervention and placebo groups were 36.2 ± 8.5 and 41.3 ± 11.2 years, respectively, while the BMI of the intervention and placebo groups were 43.5 ± 4.9 and 43.3 ± 6.4 kg/m2, respectively. After the application of TENS, there was a reduction in the level of pain in the intervention group when compared to the placebo group (P = 0.001). There was maintenance of MIP in the intervention group and reduction in the placebo group when comparing the preoperative and postoperative periods [absolute delta of 0 (-29–5) vs. -5.5 (-46–0), P = 0.03)]. The placebo group showed an increase in respiratory rate during the application of electroanalgesia when compared to the intervention group [absolute delta of 2 (-1–2) vs. 0 (-2–2), P = 0.003)]. Conclusion: The inclusion of lung function and demographic data in a reference equation for the 6MWD results in a better prediction of the distance covered in this population. Regarding the evaluation of the effect of electroanalgesia, we found that it reduces pain in patients undergoing bariatric surgery. Furthermore, there is important maintenance of MIP in these patients between the preoperative and postoperative periods. However, electroanalgesia does not reflect the improvement in spirometric parameters.