This was the first intervention study involving a change in the angle of the head affects the respiratory mechanics of MV patients in our unit. It was possible to identify that the elevation of the head of the bed to 30º and 45º increased the tidal volume in pediatric patients. This knowledge is fundamental and should be used as an adjunct in pulmonary protection ventilation strategies. In our casuistic the median age was 16.5 months and 57.7% were male. The average age of pediatric patients receiving mechanical ventilation according to the literature is 12 months 24. The predominance of males is prevalent in several studies in the pediatric population, especially when the causes of hospitalization are respiratory [24-26].
In the present study, the main diagnosis on patient admission was acute respiratory failure and the vast majority with sepsis with pulmonary focus, of which 5 (10.0%) died. Lanetzkiet et al. (2012) in his study with 433 pediatric patients in the PICU, observed that respiratory causes occupy the first three positions of diagnoses at admission with 1.8% mortality. In a study by Batista et al. (2015), with 609 hospitalized patients, the respiratory system was the most affected (71.0%) and the death rate was 15.6% [25,27]. The median time on mechanical ventilation was seven and a half days. In 2004, Farias et al. found in their study that the average time spent on mechanical ventilation in these patients was 6 to 7 days, which corroborates with the present study [26]. Important studies on the indication of IMV in children have determined that, on average, one in six children admitted to the Pediatric Intensive Care Units need this support and its main indication is acute respiratory failure. But regardless of the indication, IMV is a significant cause of morbidity and mortality in pediatric patients [28,29]. Study patients were ventilated in controlled pressure mode. The PICU uses the controlled pressure mode for the ventilation of its patients. The main advantages of controlled pressure ventilation are obtaining higher mean airway pressure with lower inspiratory pressure, better oxygenation rates and better alveolar ventilation. In addition, controlled pressure ventilation has been used as part of the pulmonary protection strategy in patients with hypoxemic respiratory failure [11]. Regarding the values of peak pressure, plateau pressure, mean airway pressure and pulmonary distension pressure, during the headboard positions, no statistically significant difference was observed. In the present study, pulmonary distention pressure was maintained on average ? 12.2 cmH2O. The mechanical ventilation data used in the studied period are in accordance with the recommendations recommended in the current world literature [23,26,27,30-32].
The tidal volume was recognized as the variable that must be controlled during passive mechanical ventilation in order to avoid ventilator-induced lung injury, but recent data indicate that pulmonary distention pressure above 15 cmH20 is closely related to mortality in patients using mechanical ventilation [30-32]. Current mechanical ventilation devices calculate the tidal volume, where the use of tidal volumes around 6 ml/kg of predicted weight in children seems to be ideal and recommended in the literature. In PICU the increase in tidal volume, with a decrease in airway resistance and an increase in lung compliance, are considered an important goal [17-20]. Ventilation of the lungs involves expiration of resistance to flow, inertia and elastic properties of the respiratory system. The amount of pressure needed to move a volume is derived from the complacency of the respiratory system and the resistance of the airways. The measures of lung resistance and compliance are not constant during the respiratory cycle, using pressure-controlled ventilation. As the patient's resistance and complacency change, the volume released varies [4,22].
It is important to recognize that pressure, volume and flow change over time and are therefore variable. When pulmonary compliance decreases, airway resistance increases or when combined they constitute an overload for the respiratory and ventilator muscles. It is known that with increased tidal volume and increased lung compliance, there is less trans pulmonary pressure to deliver tidal volume to the lungs. Therefore, the increase in lung compliance reduces respiratory work and, in fact, increases the chances of success in removing the patient from the ventilator [2,27-29]. It is believed that a ventilator support with tidal volumes of 6ml / Kg of predicted weight, with pulmonary distention pressure <15 cmH2O and PEEP levels sufficient to prevent the collapse of the airways and alveoli, can guarantee an adequate gas exchange. In addition, the proper positioning of the patient on the bed can increase these protective measures [30,31]. Regarding hemodynamic data, an increase in heart rate was observed when the headboard was positioned at 60º. The variables systolic and diastolic blood pressure increased in the 30º, 45º and 60º positions progressively. Although without clinical relevance. Changes in HR, defined as heart rate variability, are normal and expected and indicate the heart's ability to respond to multiple physiological and environmental stimuli. The increase in HR is a consequence of the greater action of the sympathetic pathway and the lower parasympathetic activity [33,34].
The monitoring of the cardio circulatory system aims to prevent and detect instability of the clinical condition [34]. Blood pressure can be influenced by cardiac, respiratory and vasomotor actions. The acute rise in blood pressure is regulated by the sympathetic nervous system, being influenced by increases in heart rate, blood volume, ejection volume and increased peripheral vascular resistance [35]. The SpO2 is an estimate of your arterial blood saturation used to monitor patients in inpatient units. When using VMI, SpO2 is used to indicate if there is a need for adjustments in the ventilator support. It was observed in the study that there was an increase in SpO2 as the head of the 0º-30º and 0º- 45º position was changed, which did not happen from 0º- 60º. This improvement in SpO2 is related to the improvement in tidal volume, increased compliance and reduced resistance, which are interfering variables in gas exchange [36]. Rice et al. (2007) in their pioneering study on the SatO2/FiO2 ratio, observed that the SatO2/FiO2 values of 235 and 315 corresponded, respectively, to a PaO2/ FiO2 of 200 and 30037. Therefore, the SatO2/FiO2 data showed excellent sensitivity and good specificity in predicting the corresponding fraction of PaO2/FiO2. It is observed in the present study that the SatO2/FiO2 ratio had an increase in the positions 30º and 45º of elevation of the head of the bed. The assessment of the SatO2/FiO2 ratio in a non-invasive and continuous way can facilitate the early diagnosis of acute respiratory distress syndrome, in addition to reducing the number of arterial blood samples collected from patients under IMV [3,37]. Monitoring lung volumes at the bedside is important for a better understanding of the patient's evolution, optimizing the adjustments of ventilator parameters and ensuring the effectiveness of MV16. The scarcity of similar research in the current scientific literature on the positioning of mechanically ventilated patients and the small sample size were limitations of this study. However, relevant outcomes were addressed and the results were consistent and can be extrapolated to clinical practice in a Pediatric Intensive Care Unit. However, there is a need for more studies that address the topic.
