Abstract
BackgroundAnalysis of respiratory mechanics during mechanical ventilation (MV) is able to estimate resistive, elastic and inertial components of the working pressure of the respiratory system. Our aim was to discriminate the components of the working pressure of the respiratory system in infants on MV with severe bronchiolitis admitted to two PICU’s.MethodsInfants younger than 1 year old with acute respiratory failure caused by severe bronchiolitis underwent neuromuscular blockade, tracheal intubation and volume controlled MV. Shortly after intubation studies of pulmonary mechanics were performed using inspiratory and expiratory breath hold. The maximum inspiratory and expiratory flow (QI and QE) as well as peak inspiratory (PIP), plateau (PPL) and total expiratory pressures (tPEEP) were measured. Inspiratory and expiratory resistances (RawI and RawE) and Time Constants (KTI and KTE) were calculated.ResultsWe included 16 patients, of median age 2.5 (1–5.8) months. Bronchiolitis due to respiratory syncytial virus was the main etiology (93.8%) and 31.3% had comorbidities. Measured respiratory pressures were PIP 29 (26–31), PPL 24 (20–26), tPEEP 9 [8–11] cmH2O. Elastic component of the working pressure was significantly higher than resistive and both higher than threshold (tPEEP – PEEP) (P < 0.01). QI was significantly lower than QE [5 (4.27–6.75) v/s 16.5 (12–23.8) L/min. RawI and RawE were 38.8 (32–53) and 40.5 (22–55) cmH2O/L/s; KTI and KTE [0.18 (0.12–0.30) v/s 0.18 (0.13–0.22) s], and KTI:KTE ratio was 1:1.04 (1:0.59–1.42).ConclusionsAnalysis of respiratory mechanics of infants with severe bronchiolitis receiving MV shows that the elastic component of the working pressure of the respiratory system is the most important. The elastic and resistive components in conjunction with flow profile are characteristic of restrictive diseases. A better understanding of lung mechanics in this group of patients may lead to change the traditional ventilatory approach to severe bronchiolitis.
Highlights
Analysis of respiratory mechanics during mechanical ventilation (MV) is able to estimate resistive, elastic and inertial components of the working pressure of the respiratory system
Data obtained from these measurements show that the elastic component of the respiratory system and not the airway resistance is the main determinant of the work imposed upon MV
We found that the calculated resistance and time constant were similar during the expiratory and inspiratory phase, showing that an increase in expiratory resistance is not the main alteration in patients with severe bronchiolitis under mechanical ventilation
Summary
Analysis of respiratory mechanics during mechanical ventilation (MV) is able to estimate resistive, elastic and inertial components of the working pressure of the respiratory system. Our aim was to discriminate the components of the working pressure of the respiratory system in infants on MV with severe bronchiolitis admitted to two PICU’s. Bronchiolitis, the most common lower respiratory infection in infants, continues to be a major pediatric public health problem [1, 2]. Research over the past 30 years has led to significant improvement in our understanding of its pathophysiology, in Bronchiolitis is usually a self–limited disease, but some children may develop respiratory failure with increased work of breathing (WOB), hypoxemia and hypercarbia requiring mechanical ventilation (MV) in addition to usual supportive measures [7, 8]. Research has mostly focused on gas exchange and criteria for respiratory failure, and the efficacy of various treatments to improve gas exchange, reduce WOB, and hasten recovery [9]. Little work has been done studying respiratory mechanics in children with severe bronchiolitis under MV [4, 5].
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