Abstract
Introduction: A large number of methods and techniques of mechanical ventilation and respiratory support in general are now available for neonates. Neonates, especially premature ones, are at high risk of developing respiratory muscle fatigue, due to reduced oxidative capacity of their respiratory muscles. It is important to identify the ventilatory support techniques with the lowest work of breathing in neonates to ensure their fastest weaning from any ventilatory support. The integral of the transdiaphragmatic pressure over the inspiratory time, the diaphragmatic pressure-time product (PTPdi), reflects the energetic expenditure of the diaphragm and has been used as a measure of the work of breathing. Aim: The aim of this thesis was to compare the imposed work of breathing by measurement of the diaphragmatic pressure-time product (PTPdi) in premature infants, supported by mechanical respiratory support methods commonly used in Neonatal Intensive Care Units (NICUs), in order to determi ...
Introduction: A large number of methods and techniques of mechanical ventilation and respiratory support in general are now available for neonates. Neonates, especially premature ones, are at high risk of developing respiratory muscle fatigue, due to reduced oxidative capacity of their respiratory muscles. It is important to identify the ventilatory support techniques with the lowest work of breathing in neonates to ensure their fastest weaning from any ventilatory support. The integral of the transdiaphragmatic pressure over the inspiratory time, the diaphragmatic pressure-time product (PTPdi), reflects the energetic expenditure of the diaphragm and has been used as a measure of the work of breathing. Aim: The aim of this thesis was to compare the imposed work of breathing by measurement of the diaphragmatic pressure-time product (PTPdi) in premature infants, supported by mechanical respiratory support methods commonly used in Neonatal Intensive Care Units (NICUs), in order to determine the type of mechanical ventilation associated with the lowest work of breathing and therefore to use the optimal method always in relation to the gestational age and the maturity of the infants. A secondary aim of the thesis was to test the hypothesis that the work of breathing will not increase during a short trial of endotracheal continuous positive airway pressure (ETT-CPAP) compared to synchronized intermittent mandatory mechanical ventilation (SIMV) with a low respiratory rate in the ventilatory settings, in order to reduce the extubation failure rate of preterm infants. Material and Methods: Premature neonates supported by invasive mechanical ventilation were included and studied during weaning from mechanical ventilation in the Neonatal Intensive Care Unit - Pediatric Clinic of the University of Patras. The work of breathing was estimated by calculating the diaphragm pressure-time product (PTPdi). Neonates were supported by assisted/controlled ventilation (A/C), synchronized intermittent mechanical ventilation (SIMV), intermittent mandatory ventilation (IMV), pressure support ventilation (PSV) and endotracheal positive airway pressure (ETT-CPAP). Results: PTPdi was lower in A/C compared to IMV and SIMV (p < 0.0001), as was also lower in SIMV compared to IMV (p < 0.0001). The difference of PTPdi between A/C and IMV, as well as A/C and SIMV showed a statistically significant negative correlation with postmenstrual age. In the SIMV-PS subgroup, PTPdi was significantly higher in IMV compared to A/C (p < 0.0001) or SIMV-PS75 (p=0.0027), and in SIMV compared to A/C (p = 0.0301). Furthermore, PTPdi in ETT-CPAP was not statistically significantly different from PTPdi in SIMV (p = 0.267). The median difference of PTPdi in CPAP compared to PTPdi in SIMV (negative deltaPTPdi), was associated independently of other factors (birth weight, postmenstrual age) with gestational age (p = 0.025). Conclusions: In preterm infants supported by mechanical ventilation during weaning, synchronized ventilation methods (A/C, SIMV-PS, SIMV) result in a lower work of breathing compared to IMV. A/C is also associated with lower PTPdi compared to SIMV, a finding that could explain its reported clinical superiority. The difference in imposed diaphragmatic load between the mechanical ventilation methods examined was inversely proportional to postmenstrual age, implying that less mature infants might benefit more from assisted/controlled ventilation (A/C) methods. Furthermore, in ventilated preterm infants, a brief trial of endotracheal CPAP before extubation compared with SIMV at a low respiratory rate, does not increase the work of breathing and can be used to predict the outcome of extubation.
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