Assessment of neonatal ventilation during high-frequency oscillatory ventilation.

OBJECTIVE: To determine alterations in high-frequency oscillatory ventilation (HFOV) performance during clinical ventilator management. DESIGN: Clinical investigation. SETTING: Two level III intensive care nurseries in Wilmington, Delaware, and Philadelphia, Pennsylvania. PATIENTS: Thirty infants 1.49 +/- 1.01 kg with respiratory distress receiving HFOV. INTERVENTIONS: Due to the demonstrated benchtop load sensitivity of the HFOV (SensorMedics 3100), we hypothesized that measured tidal volume (Vt/kg) and high-frequency minute ventilation (HFMV) would vary inversely with respiratory rate adjustments and that ventilator performance will be affected with endotracheal tube (ETT) suctioning. Both Vt/kg and HFMV were recorded using a novel hot-wire anemometry technique at the time of ETT suctioning or changes in ventilator settings. MEASUREMENTS AND MAIN RESULTS: During HFOV it was found that Vt/kg = 2.52 +/- 0.68 mL/kg and HFMV = 69 +/- 45 ([mL/kg]2 x Hz); effective ventilation was observed in the range of HFMV = 29-113 ([mL/kg]2 x Hz). HFMV decreased with an increase in breathing frequency. Although there was a significant increase in the mean Vt/kg after suctioning events, there was no difference in Vt/kg or HFMV after disconnection of the ETT alone. There were significant alterations in HFOV performance as a result of clinical adjustments in respiratory rate and suctioning. In addition, we found that measured Vt during clinically effective HFOV is at least equivalent to expected deadspace. CONCLUSIONS: Measurement of tidal volume and HFMV may be clinically important in optimizing HFOV performance both during ETT suctioning and adjustments to breathing frequency.     

Neonatal high-frequency oscillatory ventilation

High frequency oscillatory ventilation (HFOV) is often used as a rescue strategy for neonatal lung disease. In this article we discuss our experience of using HFOV including basic ventilator settings, optimising HFOV with monitoring and how specific diseases alter management. The article is focussed on ensuring understanding and safe use of HFOV by all neonatal staff.     

Haemodynamic features during high-frequency oscillatory ventilation in preterms

Aim: To compare the haemodynamic status during high-frequency oscillatory ventilation and conventional mechanical ventilation in very preterm infants with respiratory distress syndrome. Methods: Thirty-two neonates of less than 30 wk gestation randomly assigned to high-frequency oscillatory ventilation (n = 15) or conventional mechanical ventilation (n = 17) had three echocardiographies and one cerebral Doppler-echography under the same ventilation during the first 48 h of life. Results: Mean airway pressure was 2 cm H[Formula: See Text]O higher in infants ventilated with high-frequency oscillatory ventilation at the different echocardiographies. Comparable right ventricular indexes were observed in the two groups. Reduction of the ductus arteriosus diameter and ductal closure were significant only in neonates ventilated conventionally. Left ventricular performance and left ventricular contractility did not differ between the groups. The high-frequency group had lower end diastolic velocity and a higher resistance index in the anterior cerebral artery.

Conclusion: Compared with conventional mechanical ventilation, high-frequency oscillatory ventilation was achieved without altering cardiac function. However, the inability of the left ventricle to improve its performance in the presence of a significant ductal shunt suggests a narrow range of optimal pressures under this ventilatory mode.     

Tracheal and bronchial injury in high-frequency oscillatory ventilation compared with conventional positive pressure ventilation

We compared airway histopathologic findings in premature baboons given standard positive pressure ventilation with those seen after high-frequency oscillatory ventilation. Six animals received standard frequency conventional ventilation for a mean of 9.2 days; seven received high-frequency oscillatory ventilation at 10 Hz using a piston oscillator for a mean of 10.2 days; five baboons served as controls, and were killed immediately after birth. A semiquantitative histopathologic scoring system was used to grade tissue changes in the trachea, carina, and both mainstem bronchi. Compared with the nonventilated control animals, injury was produced with both forms of mechanical ventilation (P less than 0.01 for both instruments); however, the degree of damage was mild, with no significant difference in the extent of injury between the two treatment groups. High-frequency oscillatory ventilation appears to result in no greater degree of airway damage than conventional positive pressure ventilation.     

Dependence of intrapulmonary pressure amplitudes on respiratory mechanics during high-frequency oscillatory ventilation in preterm lambs

In the healthy animal lung, high-frequency oscillatory ventilation (HFOV) achieves effective ventilation at tidal volumes (V(T)) less than or equal to dead space while generating very small pressure fluctuations in the alveolar spaces (deltaP(A)). We hypothesized that the respiratory mechanical parameters influence the magnitude of the intrapulmonary pressure fluctuations during HFOV. A computer model of the neonatal respiratory system was used to examine the independent effects of altering the compliance, nonlinear and linear resistance, and inertance of the respiratory system on V(T), and cyclic intrapulmonary pressures under homogeneous and heterogeneous conditions. The impact of low compliance on the transmission of pressure from the airway opening to the trachea (deltaP(tr)/deltaP(ao)) and alveolar compartment (deltaP(A)/deltaP(ao)) during HFOV was determined in a preterm lamb lung model. In the computer model, an increase in flow-dependent resistance to simulate changing the internal diameter of the tracheal tube from 4.0 mm to 2.5 mm halved the transmission of the pressure waveform to both the carina and the alveolar compartment. Increased peripheral resistance was associated with an increased deltaP(tr)/deltaP(ao) but a reduction in deltaP(A)/deltaP(ao). The deltaP(A)/deltaP(ao) also decreased with increasing alveolar compartment compliance, a finding that was verified in the preterm lamb lung. There was an exponential decrease in the magnitude of deltaP(A1) compared with deltaP(A2) as the ratio of the time constants of the two parallel compartments (tau(1)/tau(2)) increased in the heterogeneous computer lung model. The transmission of driving pressure amplitude to both the proximal airways and lung tissue during HFOV is dependent on lung mechanics and may be greater in the poorly compliant lung than that observed previously in experiments on healthy animals.     

Gas trapping with high-frequency ventilation: jet versus oscillatory ventilation

Gas trapping was evaluated during high-frequency jet ventilation (HFJV) and high-frequency oscillatory ventilation (HFOV) in nine adult rabbits under basal conditions and after instillation of a mixture of 20% human meconium (2 mL/kg). The anesthetized animals underwent tracheostomy and were placed inside a body plethysmograph. Respiratory compliance and resistance were calculated from airway pressure and simultaneous flow, and volume was measured with a pneumotachograph. Gas trapping was measured as the change in volume observed in the plethysmograph after clamping the jet or the oscillatory line at respiratory rates of 10 and 15 Hz and tidal volumes of 1.0 and 2.0 mL/kg. Mean airway pressure was similar with both ventilators. Inspiratory/expiratory ratios were 1:4 at 10 Hz and 1:2 at 15 Hz with HFJV, and 1:1 during HFOV. Under all conditions, gas trapping was significantly greater with HFJV than with HFOV. More gas trapping was observed with higher tidal volume (2 mL/kg) and respiratory rate (15 Hz) during HFJV, before and after meconium instillation. After meconium instillation, gas trapping during HFJV at 15 Hz and tidal volume 2 mL/kg decreased significantly (32.7 +/- 10.4 to 24.9 +/- 10.3; P less than 0.05), compared with basal conditions. This finding may be explained by the shorter time constant of the respiratory system after meconium instillation (0.118 vs 0.083 seconds, P less than 0.01). Thus gas trapping was significantly greater with HFJV than with HFOV, a difference most likely related to the active expiratory phase of HFOV.     

Measuring tidal volume during paediatric oscillatory and jet high-frequency ventilation

ObjectiveTo ascertain whether a spirometer can measure tidal volume (TV) during high frequency oscillatory ventilation (HFOV) and high frequency jet ventilation (HFJV), and to analyse the effect of changes in ventilator settings.MethodsThe study was performed with paediatric porcine lung models submitted to HFOV with a Sensormedics 3100 ventilator and HFJV with a Paravent Pat_e^R ventilator connected to a D-Fend spirometer. Programmed frequency, amplitude, and mean airway pressure (MAP) were changed in the ventilator, and TV and pressures were recorded using the spirometer.ResultsThe spirometer measured TV in the paediatric lung models and piglets, but could not measure TV less than 8 ml, when the pressure amplitude was higher than 55 cmH₂O or the MAP was higher than 30 cmH₂O. With HFOV there was a correlation between amplitude and tidal volume, and a positive correlation between pressure and TV with HFJV. With both respirators there was a negative correlation between frequency and TV.ConclusionsThe D-Fend spirometer can measure tidal volume and pressure during HFOV and HFJV. However, it does not work with volumes lower than 8 ml, and high amplitude or mean airway pressure.     

Respiratory syncytial virus pneumonia ventilated with high-frequency oscillatory ventilation

Abstract Four infants below 6 months of age with proven respiratory syncytial virus infection in need of assisted mechanical ventilation were successfully treated by high-frequency oscillatory ventilation. One of the four infants fulfilled the criteria for extracorporeal membrane oxygenation before the start of oscillation, and one on the second day on high-frequency oscillatory ventilation. However, extracorporeal membrane oxygenation was not needed in any of the infants. All survived, and three appeared to be without any pulmonary sequelae.     

Frequency, tidal volume, and mean airway pressure combinations that provide adequate gas exchange and low alveolar pressure during high frequency oscillatory ventilation in rabbits

We studied healthy and saline lavaged rabbits during high frequency oscillatory ventilation to determine what combination of frequency (f), tidal volume (Vt), and mean airway pressure (Paw) produced the lowest peak-to-peak alveolar pressure amplitude (Palv) and physiologic blood gas tensions. Sinusoidal volume changes were delivered through a tracheostomy by a piston pump driven by a linear motor. Tracheal pressure amplitude (Ptr) was measured through a tracheal catheter and alveolar pressure amplitude was measured in a capsule glued to the right lower lobe. PaO2, PaCO2, Ptr, and Palv were measured at the following settings: FiO2 = 0.5, frequency 2-28 Hz, Vt 1-3 mL/kg (50 150% dead space) and Paw 5-15 cm H2O. Many combinations of frequency and Vt resulted in the same PaO2 and PaCO2. Paw had a large effect on Palv and minimal effect on blood gas tensions. In lavaged rabbits, the composite variable f x Vt2 described the trends in Palv and blood gas tensions. As the product of f x Vt2 increased, PaO2 initially increased and then decreased, whereas PaCO2 decreased and Palv increased. No single combination of frequency, Vt and Paw simultaneously provided the lowest Palv and physiologic blood gas tensions. Adequate blood gas tensions and low Palv were obtained at frequencies less than 12 Hz, a Vt of 2 mL/kg and a Paw of 10 cm H2O. In healthy and lavaged rabbits PaO2 increased and PaCO2 decreased as frequency increased at lower Vt.PaO2 decreased as frequency increased at higher Vt in lavaged rabbits only. Palv tended to be greater in lavaged rabbits.     

Prophylactic high-frequency oscillatory ventilation in preterm infants

The role of high-frequency oscillatory ventilation (HFOV) for the treatment of respiratory disease in preterm infants remains uncertain. Several randomized trials, comparing HFOV and conventional ventilation (CV) have been performed and their results suggest that HFOV may reduce the incidence of chronic lung disease (CLD) in preterm infants. However, the trials have several limitations and it remains unclear whether HFOV might increase intracranial pathology in very prematurely born infants. UKOS, a large, UK-based, multicentre trial was conducted to establish conclusively the role of prophylactic HFOV for the prevention of CLD in infants born prior to 29 wk of gestational age. CONCLUSION: There is still a need to fully evaluate prophylactic HFOV with particular emphasis on both short and long term respiratory and neurological outcomes.     

Prophylactic high-frequency oscillatory ventilation in preterm infants

The role of high-frequency oscillatory ventilation (HFOV) for the treatment of respiratory disease in preterm infants remains uncertain. Several randomized trials, comparing HFOV and conventional ventilation (CV) have been performed and their results suggest that HFOV may reduce the incidence of chronic lung disease (CLD) in preterm infants. However, the trials have several limitations and it remains unclear whether HFOV might increase intracranial pathology in very prematurely born infants. UKOS, a large, UK-based, multicentre trial was conducted to establish conclusively the role of prophylactic HFOV for the prevention of CLD in infants born prior to 29 wk of gestational age.
Conclusion : There is still a need to fully evaluate prophylactic HFOV with particular emphasis on both short and long term respiratory and neurological outcomes.     

Lung volume recruitment in lambs during high-frequency oscillatory ventilation using respiratory inductive plethysmography

Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. We measured Delta changes in lung volume above end-expiratory volume (V(RIP)) during HFOV and studied whether changes in V(RIP) parallel changes in mean airway pressure. Calibration of the plethysmograph was made by serial injections of a known gas volume in six term (140 d gestation) and eight preterm (125 d gestation) lambs. Linear regression analysis of the relationship between injected gas volume and V(RIP) showed strong correlation (r(2) = 0.93-1.00 term animals, r(2) = 0.86-1.00 preterm animals). The pressure volume curves from the calibration with the injected gas volumes also correlated well with the pressure volume curves extrapolated from changes in V(RIP). Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.     

新生儿无创高频振荡通气的研究进展

在新生儿重症监护室,无创通气是治疗轻中度呼吸衰竭重要的呼吸管理技术,正确合理的应用可以有效避免有创呼吸机的使用及相应并发症的发生。近年研究发现,无创高频振荡通气(nHFOV)结合了经鼻持续气道正压通气(nCPAP)和高频通气(HFV)的优点,可以迅速改善氧合、有效清除二氧化碳,较好地改善呼吸衰竭,被认为是一类新型有效的无创通气模式。国际上对新生儿nHFOV技术的合理使用及有效性、安全性等进行了许多研究,取得了许多重要的经验和结果,该文就新生儿nHFOV的临床研究进展进行综述。     

Protective strategies of high-frequency oscillatory ventilation in a rabbit model

High-frequency oscillatory ventilation (HFOV) causes less severe lung injury than conventional mechanical ventilation (CMV) but the optimal frequency for HFOV has not been determined. We hypothesized that 15 Hz HFOV would be more protective than 5 Hz HFOV in a rabbit model of acute lung injury. Surfactant-depleted rabbits were ventilated at 15 Hz or 5 Hz HFOV for 4 h, or not ventilated, to characterize the extent of lung injury before HFOV. PaO(2) and PaCO(2) were measured throughout the experiment, and lung myeloperoxidase (MPO) activity, neutrophil infiltration, and histopathological changes were determined. There were no statistically significant differences in PaO(2) and PaCO(2) between groups (p > 0.05). Neutrophil counts (p = 0.013), airway injury scores (p = 0.007), airspace injury scores (p = 0.029), and total lung injury scores (p = 0.014) differed between non-HFO-ventilated and HFOV animals. Comparing the 2 HFOV regimens, 15 Hz ventilation yielded a lower tissue neutrophil score (p = 0.005). MPO activity, neutrophil count, airway injury score, airspace injury score, and total lung injury score parameters did not differ significantly between the HFOV groups (p > 0.150). We concluded that both frequencies of HFOV efficiently restored O(2) and CO(2) exchange in a rabbit model of severe lung injury, and that 5 Hz HFOV increased neutrophil infiltration relative to 15 Hz HFOV.     

The effect of a manometer on the mean airway pressure during hand ventilation,an in vitro study

The effect of an on-line manometer on the variables of ventilation i.e. peak inspiratory pressure (PIP), mean airway pressure (MAP), positive end expiratory pressure (PEEP), and inspiratory to expiratory time ratio (I:E) was studied in vitro. Analysis of PIP, MAP, PEEP, and I:E was made during hand ventilation of a resuscitation mannequin at the preselected PIP of 15 and 25 cm water with and without a manometer. Use of the manometer decreased the range of variation in PIP, but the MAP was higher. This was due to an increased I:E while PEEP remained unchanged. An on-line manometer during hand ventilation prevents excessive PIP but may increase the MAP and therefore may not prevent development of a pneumothorax.Abbreviations I:E inspiratory to expiratory time ratio - MAP mena airway pressure - PEEP positive end expiratory pressure - PIP peak inspiratory pressure     

高频振荡通气治疗新生儿重症胎粪吸入综合征

为评价高频振荡通气 (HFOV)治疗新生儿重症胎粪吸入综合征 (MAS)的疗效 ,对11例重症MAS采用HFOV治疗 ,有气漏者采用低容量策略 ,其余采用高容量策略 ,频率10Hz左右 ,通过逐渐增加平均气道压改善氧合状态 ,以达到吸入氧浓度≤0.4时 ,脉氧饱和度≥0.9 ,调节振荡压力幅度使PaCO2 维持在30～40mmHg。结果治愈7例 ,死亡2例。9例患儿HFOV满48小时 ,治疗后平均气道压由22±3.5cmH2O降至15±3.2cmH2O(P<0.05) ,吸入氧浓度由0.80±0.10降至0.33±0.12(P<0.001),氧合指数由24.0±4.5降至7.4±1.8(P<0.001) ,动脉/肺泡PO2 由0.10±0.01升至0.35±0.06(P<0.01)。治疗过程中心率、血压无明显变化。提示HFOV治疗MAS安全有效