Meta-analysis of elective high frequency ventilation in preterm infants with respiratory distress syndrome.
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AIM: To summarise the evidence on the efficacy of elective high frequency ventilation compared with conventional ventilation in preterm infants with respiratory distress syndrome. METHODS: A search from 1987 onwards was made on Embase, Medline, and the Cochrane Library. A questionnaire was also circulated during an international meeting on high frequency ventilation. To be included in the data synthesis, studies had to be randomised controlled trials comparing elective high frequency ventilation with conventional ventilation in preterm infants with respiratory failure due to respiratory distress syndrome; indices of mortality, chronic pulmonary morbidity, and other clinically relevant outcomes were compared. Studies were assessed for methodological validity according to explicit criteria. RESULTS: Ten studies (a total number of 1345 preterm infants) were considered for data synthesis. No difference in mortality at 28 or 30 days, nor in oxygen dependency at 28 days was found between both types of ventilation. Reduced oxygen dependency at the postconceptional age of 36 weeks (RR 0.50, 95% CI 0.32-0.78) was found, but so was an increase in grades 3 and 4 intraventricular haemorrhage (IVH) (RR 1.31, 95% CI 1.04-1.66). Those studies using a high lung volume ventilatory strategy showed a significant decrease in oxygen dependency at the postconceptional age of 36 weeks (RR 0.44, 95% CI 0.27-0.73), but no increase in severe IVH (RR 0.78, 95% CI 0.45-1.37). CONCLUSIONS: Although high frequency ventilation reduces chronic lung disease, it seems to increase the risk of severe IVH. These results are dominated by an early study where the absence of benefit on pulmonary outcomes, and the increase in adverse neurological events, could be related to the low volume ventilatory strategy used. Recent studies, using a high lung volume approach, show better pulmonary outcomes without any increase in intracranial morbidity. Still, uncertainty remains about long term pulmonary and neurodevelopmental outcome. (+info)
Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation.
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This study investigated factors contributing to differences between mean alveolar pressure (PA) and mean pressure at the airway opening (Pao) during high-frequency oscillatory ventilation (HFOV). The effect of the inspiratory-to-expiratory time (I/E) ratio and amplitude of oscillation on the magnitude of - Pao (Pdiff) was examined by using the alveolar capsule technique in normal rabbit lungs (n = 4) and an in vitro lung model. The effect of ventilator frequency and endotracheal tube (ETT) diameter on Pdiff was further examined in the in vitro lung model at an I/E ratio of 1:2. In both lung models, fell below Pao during HFOV when inspiratory time was shorter than expiratory time. Under these conditions, differences between inspiratory and expiratory flows, combined with the nonlinear relationship between resistive pressure drop and flow in the ETT, are the principal determinants of Pdiff. In our experiments, the magnitude of Pdiff at each combination of I/E, frequency, lung compliance, and ETT resistance could be predicted from the difference between the mean squared inspiratory and expiratory velocities in the ETT. These observations provide an explanation for the measured differences in mean pressure between the airway opening and the alveoli during HFOV and will assist in the development of optimal strategies for the clinical application of this technique. (+info)
Exhaled nitric oxide increases during high frequency oscillatory ventilation in rabbits.
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This study compared the effects of high frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) on the homeostasis of nitric oxide (NO) in the lower respiratory tract of healthy rabbits. The mechanisms underlying a putative stretch response of NO formation in the airways were further elucidated. Male New Zealand White rabbits were anaesthetized, tracheotomized and ventilated with IMV or HFOV in random order. Total NO excretion increased from 9.6 +/- 0.8 nl min-1 (mean +/- S.E.M.) during IMV to 22.6 +/- 2.7 nl min-1 during HFOV (P < 0.001). This increase was not explained by changes of functional residual capacity ([Delta]FRC). A similar increase in NO excretion during HFOV was seen in isolated buffer-perfused lungs under constant circulatory conditions (P < 0. 05, n = 4). Intratracheal mean CO2 and NO concentrations, measured at 2.5, 5, 7.5 and 10 cm below tracheostomy, increased significantly with increasing distance into the lung during both IMV and HFOV (P < 0.001 for each comparison). At every intratracheal location of the sampling catheter, particularly low in the airways, both CO2 and NO concentrations were significantly higher during HFOV than during IMV (P < 0.01 for each comparison). We conclude that HFOV increases pulmonary NO production in healthy rabbits. Increased stretch activation of the respiratory system during HFOV is suggested as a possible underlying mechanism. The increase in mean airway NO concentrations may have biological effects in the respiratory tract. Whether it can account for some of the benefits of HFOV treatment needs to be considered. (+info)
High-frequency oscillatory ventilation is not superior to conventional mechanical ventilation in surfactant-treated rabbits with lung injury.
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The aim of this study was to compare high-frequency oscillatory ventilation (HFOV) with conventional mechanical ventilation (CMV) with and without surfactant in the treatment of surfactant-deficient rabbits. A previously described saline lung lavage model of lung injury in adult rabbits was used. The efficacy of each therapy was assessed by evaluating gas exchange, lung deflation stability and lung histopathology. Arterial oxygenation did not improve in the CMV group without surfactant but increased rapidly to prelavage values in the other three study groups. During deflation stability, arterial oxygenation decreased to postlavage values in the group that received HFOV alone, but not in both surfactant-treated groups (HFOV and CMV). The HFOV group without surfactant showed more cellular infiltration and epithelial damage compared with both surfactant-treated groups. There was no difference in gas exchange, lung deflation stability and lung injury between HFOV and CMV after surfactant therapy. It is concluded that the use of surfactant therapy in combination with high-frequency oscillatory ventilation is not superior to conventional mechanical ventilation in improving gas exchange, lung deflation stability and in the prevention of lung injury, if lungs are kept expanded. This indicates that achieving and maintaining alveolar expansion (i.e. open lung) is of more importance than the type of ventilator. (+info)
Effect of changes in oscillatory amplitude on PaCO(2) and PaO(2) during high frequency oscillatory ventilation.
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AIMS: To describe the relation between oscillatory amplitude changes and arterial blood gas (ABG) changes in preterm infants receiving high frequency oscillatory ventilation, using a multiparameter intra-arterial sensor (MPIAS). METHODS: Continuous MPIAS ABG data were collected after amplitude changes and stratified according to FIO(2): high (> 0.4) or low (< 0.3). For each amplitude change, the maximum change (from baseline) in PaCO(2) and PaO(2) over the following 30 minutes was determined. In total, 64 oscillatory amplitude changes were measured in 21 infants (median birth weight 1040 g; gestation 27 weeks). RESULTS: All amplitude increases produced PaCO(2) falls (median -0.98 and -1.13 kPa for high and low FIO(2) groups respectively). All amplitude decreases produced PaCO(2) rises (median +0.94 and +1.24 kPa for high and low FIO(2) groups respectively). About 95% of the change in PaCO(2) was completed in 30 minutes. Amplitude changes did not affect PaO(2) when FIO(2) > 0.4. When FIO(2) < 0.3, amplitude increases produced a PaO(2) rise (median = +1.1 kPa; P < 0.001) and amplitude decreases a fall (median = -1.2 kPa; P < 0.001). CONCLUSIONS: After oscillatory amplitude changes, the speed but not the magnitude of the PaCO(2) change is predictable, and a rapid PaO(2) change accompanies the PaCO(2) change in infants with mild lung disease and a low FIO(2). (+info)
Comparison of respiratory indices in predicting response to high frequency oscillatory ventilation in very low birth weight infants with respiratory distress syndrome.
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To evaluate the predictive values of oxygenation index (OI), arterial-alveolar oxygen tension ratio (a/APO)2, and alveolar-arterial oxygen gradient ((A-a)DO2) for early recognition of responsiveness to high frequency oscillatory ventilation (HFOV) in very low birth weight infants with respiratory distress syndrome (RDS), 23 infants who received HFOV treatment for severe RDS after failing to be improved with conventional mechanical ventilation from July 1995 to February 1998 were included. Twelve infants survived with HFOV (Responder group), while 11 infants could not maintain oxygenation with HFOV and died (Non-responder group). Clinical record (of each patient) were retrospectively reviewed and compared with the respiratory indices. Mean (A-a)DO2 was significantly lower in the responder group than in the non-responder group at 2 hr after HFOV (p=0.024), and the difference was more remarkable at 6 hr (p=0.005). Death in the patient with (A-a)DO2 over 350 at 2 hr after HFOV therapy was 100% in sensitivity and 80% in specificity. The earliest significant difference of mean a/APO2 between two groups was noted at 6 hr after HFOV treatment (p=0.019). OI showed no significant differences between two groups. In summary, (A-a)DO2 was the most effective and sensitive respiratory index for predicting the responsiveness to HFOV in infants with severe RDS providing due as early as 2 hr. (+info)
Detecting lung overdistention in newborns treated with high-frequency oscillatory ventilation.
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Positive airway pressure (Paw) during high-frequency oscillatory ventilation (HFOV) increases lung volume and can lead to lung overdistention with potentially serious adverse effects. To date, no method is available to monitor changes in lung volume (DeltaVL) in HFOV-treated infants to avoid overdistention. In five newborn piglets (6-15 days old, 2.2-4.2 kg), we investigated the use of direct current-coupled respiratory inductive plethysmography (RIP) for this purpose by evaluating it against whole body plethysmography. Animals were instrumented, fitted with RIP bands, paralyzed, sedated, and placed in the plethysmograph. RIP and plethysmography were simultaneously calibrated, and HFOV was instituted at varying Paw settings before (6-14 cmH(2)O) and after (10-24 cmH(2)O) repeated warm saline lung lavage to induce experimental surfactant deficiency. Estimates of Delta VL from both methods were in good agreement, both transiently and in the steady state. Maximal changes in lung volume (Delta VL(max)) from all piglets were highly correlated with Delta VL measured by RIP (in ml) = 1.01 x changes measured by whole body plethysmography - 0.35; r(2) = 0.95. Accuracy of RIP was unchanged after lavage. Effective respiratory system compliance (Ceff) decreased after lavage, yet it exhibited similar sigmoidal dependence on Delta VL(max) pre- and postlavage. A decrease in Ceff (relative to the previous Paw setting) as Delta VL(max) was methodically increased from low to high Paw provided a quantitative method for detecting lung overdistention. We conclude that RIP offers a noninvasive and clinically applicable method for accurately estimating lung recruitment during HFOV. Consequently, RIP allows the detection of lung overdistention and selection of optimal HFOV from derived Ceff data. (+info)
Resonance frequency in respiratory distress syndrome.
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AIM: To observe how the resonance frequency changes with the course of respiratory distress syndrome (RDS), by examining the effect of changing static compliance on the resonance frequency in premature infants. METHODS: In 12 ventilated premature infants with RDS (mean gestational age 26.6 weeks, mean birth weight 0.84 kg), resonance frequency and static compliance were determined serially using phase analysis and single breath mechanics technique respectively in the first seven days of life. RESULTS: The minimum number of measurements done in any one baby was three and maximum was five in this seven day study period. The first measurement in each baby was done within the first 72 hours of life. The increase in compliance in this period varied from 27% to 179%. The variation in the corresponding resonance frequency was within 2 Hz in eight babies and within 6 Hz in all recruited babies. CONCLUSIONS: The resonance frequency of the respiratory system in preterm infants with RDS remains remarkably constant in the early stages of the illness, despite relatively large changes in static compliance. (+info)