Discussion
In this study, a prevalence of 38.5% of right ventricle dysfunction was found based on echocardiographic data in patients undergoing mechanical ventilation. This result is similar to that found in the literature, despite the scarcity of data on this topic in pediatrics. The prevalence of acute RV failure is difficult to estimate, but it is known that the mortality of these patients is around 5-17% in the adult population (9). The very definition of RV dysfunction is hindered by a lack of clear criteria for normal or abnormal RV function and the difficulty of performing RV imaging exams in critically ill patients (10). In studies conducted in adults, the prevalence of RV dysfunction ranges from 28% to 40.7% (10–12), with the majority of them being performed in patients with septic shock. In the pediatric population, the ”gold standard” for evaluating right ventricular function in the ICU is highly debatable; therefore, the definition of dysfunction is even more variable in the literature, making it difficult to estimate its prevalence (13). Himebauch et al., in a retrospective cohort study, found a prevalence of 32% to 38% of RV dysfunction based on serial echocardiographic measurements in 75 pediatric patients on mechanical ventilation for ARDS (14). While assessing right ventricle (RV) function through echocardiography can be challenging due to its retrosternal position and complex shape, it becomes even more difficult in mechanically ventilated patients, however, there are various echocardiographic measures available to evaluate the right ventricle (3). One of the most commonly used measurements is the systolic excursion of the tricuspid annular plane (TAPSE), as it is one of the easiest to reproduce, represents systolic function, and has high specificity for RV dysfunction (7). In this study, the mean TAPSE was 1.39 ± 0.43, and 24% were altered. Pediatric reference values change according to age group, with larger children having higher TAPSE values. Reduced TAPSE values may indicate an early decline in global RV systolic function, and as this marker does not depend on RV geometry and is less influenced by imaging artifacts, it becomes a very useful marker in clinical practice in children (7). This echocardiographic parameter is linearly related to the right ventricular ejection fraction (RVEF) (15), and in studies in the adult population, TAPSE < 20 mm has been correlated with a 40% decrease in RVEF; for each 1mm reduction from its baseline value, an increase of 17% in mortality was found in patients with pulmonary hypertension (8). Some authors have even found a relationship between TAPSE and altered LV function in critically ill patients in the ICU (15). Regarding other echocardiographic measures for assessing the right ventricle, this study used the S’ wave and the RV/LV ratio, with mean values of 13.1 ± 3.3 and 0.85 ± 0.15, respectively. Tissue Doppler imaging allows the evaluation of myocardial velocities. . The peak systolic annular velocity (S’ wave) can be used to obtain a qualitative evaluation of RV systolic function. An S’ wave velocity <10 cm/s is indicative of systolic dysfunction of the right ventricle (6). The RV/LV ratio alone does not indicate right ventricular dysfunction but reflects compression of the LV by the hypertensive RV and has been shown to be significantly higher in children with pulmonary hypertension (PH) than in controls, with an RV/LV ratio > 1 already being associated with an increased risk of adverse events in pediatric PH (7). According to De Backer, echocardiography can provide essential information about the hemodynamic state, suggesting that it should be performed early in patients with hemodynamic instability (16). The VIS provides an assessment of the amount of cardiovascular support and is a well-defined score for correlating clinical outcomes in patients post-cardiac surgery and has been studied for its association with mortality in sepsis, being considered a reliable marker of cardiovascular support (17). Retrospective cohort studies conducted in the pediatric population found a significant association between high VIS and mortality in pediatric septic shock (18). Comparing patients with RV dysfunction (55 patients) with those without this alteration, it was found that there was a significant relationship with higher VIS score, higher median lactate, and worse cardiac index. There was no significant association with underlying pathology, sedation status, ventilation parameters, or mortality rate. RV dysfunction is frequently observed in sepsis, and its severity is significantly correlated with the severity of left ventricular dysfunction and impacts outcomes, being associated with higher mortality (11,16). Early evaluation is essential because in the initial phase of sepsis, RV changes may be more frequent than those of the LV, as it has thin walls and lower tolerance to preload and afterload, leading to its dilation (11). Cardiac output is classically evaluated using invasive catheterization in the pulmonary artery, but it can also be assessed non-invasively through echocardiography (19). The cardiac index (CI) can be calculated using echocardiographic measurements of velocity time integral (VTI) and cross-sectional area (CSA) of the LV outflow tract, helping to assess cardiac output and patient response to treatments and can guide fluid and vasopressor therapy in patients in the intensive care unit (20,21). Reference values for CI vary from 2.5 to 4.0 L/min/m² (20,22). In this study, it was found that, among patients with altered CI, the frequency of RV dysfunction was higher (65% compared to 36% of patients classified as normal CI - p0.029). No significant difference in CI was found among patients categorized by the indication for mechanical ventilation (obstructive lung disease, compliance, or no lung disease). In this study, the mechanical pulmonary parameters were not significantly different between the groups with or without RV dysfunction. When classified according to lung diagnosis, lower TAPSE averages were observed in patients with obstructive lung disease compared to those with compliance alteration or no lung disease (1.19 vs. 1.61 vs. 1.47, respectively; p<0.001). The most prevalent obstructive lung disease in young children is acute viral bronchiolitis. A prospective cohort study conducted echocardiography in 181 children with bronchiolitis, of whom 73 required positive pressure ventilation and showed worse RV systolic function, with lower TAPSE values (p = 0.002) (23). Regarding mechanical pulmonary measurements, it was identified that pulmonary resistance, plateau pressure, and auto-PEEP were also significantly more altered in the group with obstructive lung disease (p<0.05) and showed weak correlations with TAPSE, S’ wave, and RV/LV ratio. Mechanical ventilation increases intrathoracic pressures, leading to functional alteration of the pulmonary vascular circulation, influencing right ventricle function, as inspiration causes an increase in right ventricle afterload and a decrease in its preload (5). The higher the pause pressure and circulating volume, the greater the risk of right ventricle overload. One of the paradigms of mechanical ventilation is that it can cause right ventricle alterations, inducing systemic hypotension and being associated with higher peak and plateau pressures and the use of more PEEP (5). Regarding the pediatric population, in 2011, a study was conducted on echocardiographic evaluation in 235 children on mechanical ventilation, finding that the combination of respiratory failure and mechanical ventilation significantly increased the RV load conditions, regardless of the etiology of the disease. The authors concluded that echocardiography is a feasible exam to be performed in the ICU environment because its quality is not affected by chest movement during mechanical ventilation, and the exam is a tool that complements the monitoring of cardiac load in real-time (24). According to a systematic review on the management of right ventricle dysfunction and pulmonary hypertension in adults, the incidence of acute right ventricle failure was 60% before the dissemination of protective ventilatory strategies’ knowledge, reducing to 10-25% in these patients after. Today, it is known that lower plateau pressure reduces the incidence of right ventricle failure (25). In this study, the mean plateau pressure was around 24 cmH2O for all patients, with only 4 patients out of the entire sample having plateau pressure higher than 30 cmH2O, representing less than 3% of the sample. This likely explains the weak correlation between right ventricle alteration and ventilatory parameters, as protective mechanical ventilation strategies were used in the vast majority of patients. In conclusion, although there is no clear definition of right ventricle dysfunction in pediatrics in the literature, TAPSE has been the most used index, and a significant frequency of TAPSE alteration was identified in this study. Detecting subclinical dysfunction is important as it allows for early intervention, preventing its progression to more severe forms. Bedside echocardiography is readily available, safe, and non-invasive, and can be considered routine practice that, together with clinical parameters, can assist in making decisions regarding vasopressor drugs, fluid replacement, and mechanical ventilation. The study has some limitations. Pulmonary mechanics measurements were not performed in most of the studied sample. As it is a frequency study with a convenience sample, some associations were made, and it was not possible to assess causality between variables. Variables such as duration of mechanical ventilation and the day when the examination was performed were not evaluated. It is known that higher parameters may be required in the first days, so there may have been a tendency in patient selection.