Wong R, Deakers T, Hotz J, et al. Volume and Pressure Delivery During Pediatric High-Frequency Oscillatory Ventilation. Pediatr Crit Care Med. 2017 Apr;18(4):e189-e194.
OBJECTIVE: Identify variables independently associated with delivered tidal volume (VT) and measured mean airway pressure during high-frequency oscillatory ventilation across the range of pediatric endotracheal tube sizes.
DESIGN: In vitro study.
SETTING: Research laboratory.
INTERVENTIONS: An in vitro bench model of the intubated pediatric respiratory system during high-frequency oscillatory ventilation was used to obtain delivered VT and mean airway pressure (in the distal lung) for various endotracheal tube sizes. Measurements were taken at different combinations of ventilator set mean airway pressure (Paw), amplitude (ΔP), frequency, and test lung compliance. Multiple regression analysis was used to construct multivariable models predicting delivered VT and mean airway pressure.
MEASUREMENTS AND MAIN RESULTS: Variables independently associated with higher delivered VT for all endotracheal tube sizes include higher ΔP (p < 0.001), lower frequency (p < 0.001), and higher test lung compliance (p < 0.001). A multiplicative interaction between frequency and ΔP magnifies the delivered VT when ΔP is high and frequency is low (p < 0.001). Delivered mean airway pressure becomes lower than set Paw as ΔP increases (p < 0.001) and frequency increases (p < 0.05). Ventilator set Paw is the largest determinant of delivered mean airway pressure; however, increasing ΔP resulted in a lower delivered mean airway pressure. For example, in a 4.0 mm ID endotracheal tube, increasing ΔP by 10 cm H2O resulted in an average decrease of delivered mean airway pressure by 4.5%.
CONCLUSIONS: This is the first study to quantify the interaction between ΔP and frequency in delivered VT and the effect of ΔP and frequency on delivered mean airway pressure. These results demonstrate the need to measure or estimate VT and delivered pressures during high-frequency oscillatory ventilation and may be useful in determining optimal strategies for lung protective ventilation during high-frequency oscillatory ventilation.
Ward SL, et al. Poor Adherence to Lung-Protective Mechanical Ventilation in Pediatric Acute Respiratory Distress Syndrome. Pediatr Crit Care Med. 2016 Aug 2. [Epub ahead of print]
OBJECTIVES: To determine the frequency of low-tidal volume ventilation in pediatric acute respiratory distress syndrome and assess if any demographic or clinical factors improve low-tidal volume ventilation adherence.
DESIGN: Descriptive post hoc analysis of four multicenter pediatric acute respiratory distress syndrome studies.
SETTING: Twenty-six academic PICU.
PATIENTS: Three hundred fifteen pediatric acute respiratory distress syndrome patients.
MEASUREMENTS AND MAIN RESULTS: All patients who received conventional mechanical ventilation at hours 0 and 24 of pediatric acute respiratory distress syndrome who had data to calculate ideal body weight were included. Two cutoff points for low-tidal volume ventilation were assessed: less than or equal to 6.5 mL/kg of ideal body weight and less than or equal to 8 mL/kg of ideal body weight. Of 555 patients, we excluded 240 for other respiratory support modes or missing data. The remaining 315 patients had a median PaO2-to-FIO2 ratio of 140 (interquartile range, 90-201), and there were no differences in demographics between those who did and did not receive low-tidal volume ventilation. With tidal volume cutoff of less than or equal to 6.5 mL/kg of ideal body weight, the adherence rate was 32% at hour 0 and 33% at hour 24. A low-tidal volume ventilation cutoff of tidal volume less than or equal to 8 mL/kg of ideal body weight resulted in an adherence rate of 58% at hour 0 and 60% at hour 24. Low-tidal volume ventilation use was no different by severity of pediatric acute respiratory distress syndrome nor did adherence improve over time. At hour 0, overweight children were less likely to receive low-tidal volume ventilation less than or equal to 6.5 mL/kg ideal body weight (11% overweight vs 38% nonoverweight; p = 0.02); no difference was noted by hour 24. Furthermore, in the overweight group, using admission weight instead of ideal body weight resulted in misclassification of up to 14% of patients as receiving low-tidal volume ventilation when they actually were not.
CONCLUSIONS: Low-tidal volume ventilation is underused in the first 24 hours of pediatric acute respiratory distress syndrome. Age, Pediatric Risk of Mortality-III, and pediatric acute respiratory distress syndrome severity were not associated with improved low-tidal volume ventilation adherence nor did adherence improve over time. Overweight children were less likely to receive low-tidal volume ventilation strategies in the first day of illness.
Carteaux G, et al. Failure of Noninvasive Ventilation for De Novo Acute Hypoxemic Respiratory Failure: Role of Tidal Volume. Crit Care Med. 2016 Feb;44(2):282-90.
OBJECTIVES: A low or moderate expired tidal volume can be difficult to achieve during noninvasive ventilation for de novo acute hypoxemic respiratory failure (i.e., not due to exacerbation of chronic lung disease or cardiac failure). We assessed expired tidal volume and its association with noninvasive ventilation outcome.
DESIGN: Prospective observational study.
SETTING: Twenty-four bed university medical ICU.
PATIENTS: Consecutive patients receiving noninvasive ventilation for acute hypoxemic respiratory failure between August 2010 and February 2013.
INTERVENTIONS: Noninvasive ventilation was uniformly delivered using a simple algorithm targeting the expired tidal volume between 6 and 8 mL/kg of predicted body weight.
MEASUREMENTS: Expired tidal volume was averaged and respiratory and hemodynamic variables were systematically recorded at each noninvasive ventilation session.
MAIN RESULTS: Sixty-two patients were enrolled, including 47 meeting criteria for acute respiratory distress syndrome, and 32 failed noninvasive ventilation (51%). Pneumonia (n = 51, 82%) was the main etiology of acute hypoxemic respiratory failure. The median (interquartile range) expired tidal volume averaged over all noninvasive ventilation sessions (mean expired tidal volume) was 9.8 mL/kg predicted body weight (8.1-11.1 mL/kg predicted body weight). The mean expired tidal volume was significantly higher in patients who failed noninvasive ventilation as compared with those who succeeded (10.6 mL/kg predicted body weight [9.6-12.0] vs 8.5 mL/kg predicted body weight [7.6-10.2]; p = 0.001), and expired tidal volume was independently associated with noninvasive ventilation failure in multivariate analysis. This effect was mainly driven by patients with PaO2/FIO2 up to 200 mm Hg. In these patients, the expired tidal volume above 9.5 mL/kg predicted body weight predicted noninvasive ventilation failure with a sensitivity of 82% and a specificity of 87%.
CONCLUSIONS: A low expired tidal volume is almost impossible to achieve in the majority of patients receiving noninvasive ventilation for de novo acute hypoxemic respiratory failure, and a high expired tidal volume is independently associated with noninvasive ventilation failure. In patients with moderate-to-severe hypoxemia, the expired tidal volume above 9.5 mL/kg predicted body weight accurately predicts noninvasive ventilation failure.
de Jager P, Burgerhof JG, van Heerde M, et al. Tidal volume and mortality in mechanically ventilated children: a systematic review and meta-analysis of observational studies*. Crit Care Med. 2014 Dec;42(12):2461-72.
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OBJECTIVE: To determine whether tidal volume is associated with mortality in critically ill, mechanically ventilated children.