Effect of Transcutaneous Electrical Diaphragmatic Stimulation on Respiratory Muscle Strength, Diaphragm Thickness and Mechanical Ventilation Time in Critically Ill Elderly Patients

1. INTRODUCTION Patients undergoing invasive mechanical ventilation (IMV) have an intense predisposition to the development of muscle weakness in the first hours after the orotracheal intubation process, since they are exposed, among other factors, to sedative drugs, immobilization and properly controlled ventilation (DEMOULE et al., 2016). It is observed that approximately 25% to 50% of patients submitted to ventilatory support have muscle weakness and, of this proportion, 85% to 95% persist with neuromuscular impairment for a period of two to five years.

In this context, the elderly deserve attention because the demographic transition process has the inversion of the age pyramid as one of its characteristics (WONG et al., 2006). This leads to a higher incidence of admissions of these patients in intensive care units compared to young people and adults, considering that they represent the largest portion of the population.

Among the muscles affected by permanence in IMV in the general population and especially in the elderly, the diaphragm can be highlighted, which evolves with a reduction in its ability to generate tension due to the atrophy of its muscle fibers. This leads to an alteration called diaphragmatic dysfunction (DD). The mechanisms involved with DD are the reduction in the number of myofibrils (proteins that involve filaments of actin and myosin responsible for the production of muscle contraction), oxidative stress (inducing the activation of the forkhead box O1 protein, involved with the processes of gluconeogenesis and glycogenolysis) and the abnormal activation of a pathway responsible for the proteolysis of adenosine triphosphate, ubiquitin-proteasome.

Considering the progressive characteristic of DD, some consequences such as increased IMV time, increased risk of respiratory complications and prolonged hospital stay can be observed, if no specific intervention is performed . Therefore, it is necessary to adopt measures that allow the early detection of diaphragmatic weakness, as well as the use of conducts that prevent or treat this clinical condition.

As for the diagnosis of DD, it can be performed using instruments that measure inspiratory muscle strength, such as the manovacuometer, in addition to imaging tests that show the diaphragmatic thickness (FDI), such as pulmonary ultrasonography (PU) . The variable referring to inspiratory muscle strength in manovacuometry is the maximum inspiratory pressure (MIP), while the thickness of the diaphragm, verified through the PU, is represented by the diaphragmatic thickening index (DTI), obtained through the difference between the diaphragm thickness total lung capacity (DTTLC) and functional residual capacity (DTFRC), divided by DTTLC. The FDI contributes to the initial diagnosis of DD and is also relevant for monitoring the evolution of diaphragm function during the period of hospitalization and ventilatory weaning. According to Goligher et al. (2015), the decrease in FDI is associated with impaired function of the diaphragm and is correlated with low values of MIP in critically ill patients.