Expired tidal volumes measured by hot-wire anemometer during high-frequency oscillation in preterm infants

Lung recruitment in neonatal high-frequency oscillatory ventilation with volume-guarantee

BACKGROUND AND OBJECTIVES

The optimal lung volume strategy during high-frequency oscillatory ventilation (HFOV) is reached by performing recruitment maneuvers, usually guided by the response in oxygenation. In animal models, secondary spontaneous change in oscillation pressure amplitude (ΔPhf) associated with a progressive increase in mean airway pressure during HFOV combined with volume guarantee (HFOV-VG) identifies optimal lung recruitment. The aim of this study was to describe recruitment maneuvers in HFOV-VG and analyze whether changes in ΔPhf might be an early predictor for lung recruitment in newborn infants with severe respiratory failure.

DESIGN AND METHODS

The prospective observational study was done in a tertiary-level neonatology department. Changes in ΔPhf were analyzed during standardized lung recruitment after initiating early rescue HFOV-VG in preterm infants with severe respiratory failure.

RESULTS

Twenty-seven patients were included, with a median gestational age of 24 weeks (interquartile range [IQR]: 23-25). Recruitment maneuvers were performed, median baseline mean airway pressure (mPaw) was 11 cm H₂ O (IQR: 10-13), median critical lung opening mPaw during recruitment was 14 cm H₂ O (IRQ: 12-16), and median optimal mPaw was 12 cm H₂ O (IQR: 10-14, p < 0.01). Recruitment maneuvers were associated with an improvement in oxygenation (FiO₂ : 65.0 vs. 45.0, p < 0.01, SpO2/FiO₂ ratio: 117 vs. 217, p < 0.01). ΔPhf decreased significantly after lung recruitment (mean amplitude: 23.0 vs. 16.0, p < 0.01).

CONCLUSION

In preterm infants with severe respiratory failure, the lung recruitment process can be effectively guided by ΔPhf on HFOV-VG.

The clinical effects of high-frequency oscillatory ventilation in the treatment of neonatal severe meconium aspiration syndrome complicated with severe acute respiratory distress syndrome

OBJECTIVE

To explore the efficacy and safety of high-frequency oscillatory ventilation (HFOV) in the treatment of severe meconium aspiration syndrome (MAS) complicated with severe acute respiratory distress syndrome (ARDS).

METHODS

A total of 65 infants with severe MAS complicated with severe ARDS were included in the study. The clinical efficacy of treatment for the HFOV group (n = 31) and the conventional mechanical ventilation (CMV) group (n = 34) was retrospectively analysed. The partial pressure of oxygen (PaO₂), partial pressure of carbon dioxide (PaCO₂), PaO₂/fraction of inspired oxygen (FiO₂), and oxygen index values before and at 6, 12, 24, 48, and 72 h after mechanical ventilation, the mechanical ventilation time, oxygen inhalation time, incidence of complications, and outcomes of the two groups were compared.

RESULTS

At 6, 12, 24, and 48 h after mechanical ventilation, the PaO₂ in the HFOV group was significantly higher than in the CMV group, while the PaCO₂ in the HFOV group was significantly lower than in the CMV group (P < 0.05). At 6, 12, 24, 48, and 72 h after mechanical ventilation, PaO₂/FiO2 in the HFOV group was significantly higher than in the CMV group, and the OI in the HFOV group was significantly lower than in the CMV group (P < 0.05). Mechanical ventilation time, oxygen inhalation time, and the incidence of air leakage were significantly lower in the HFOV than in the CMV group (P < 0.05).

CONCLUSIONS

Overall, HFOV can effectively improve lung ventilation and oxygenation function, shorten ventilator treatment time, and reduce the incidence rate of air leakage for neonatal MAS, making it a safe and effective treatment option.

High-frequency Ventilation

High-frequency ventilation (HFV) is an alternative to conventional mechanical ventilation, with theoretic benefits of less risk of ventilator lung injury and more effectivity in washout CO₂. Previous clinical studies have not demonstrated advantages of HFV in preterm infants compared with conventional ventilation, so rescue HFV has been used when severe respiratory insufficiency needs aggressive ventilator settings in immature infants. Today it is possible to measure, set directly, and fix tidal volume, which can protect the immature lung from large volumes and fluctuations of the tidal volume. This strategy can be used in preterm infants with respiratory failure needing invasive ventilation.

Impact of High-Frequency Oscillatory Ventilation Combined With Volume Guarantee on Lung Inflammatory Response in Infants With Acute Respiratory Distress Syndrome After Congenital Heart Surgery: A Randomized Controlled Trial

OBJECTIVES

Congenital heart disease (CHD) after cardiopulmonary bypass can cause systemic inflammation, and its degree is closely related to the incidence of acute respiratory distress syndrome (ARDS). The purpose of this study was to determine the effectiveness of high-frequency oscillatory ventilation (HFOV) combined with volume guarantee (VG) in reducing systemic inflammation in infants with ARDS after cardiopulmonary bypass for congenital heart surgery.

DESIGN

A randomized controlled trial.

SETTING

Single-center study in a tertiary teaching hospital.

PARTICIPANTS

A total of 58 infants with ARDS after congenital heart surgery were eligible and were randomized to the HFOV (n = 29) or the HFOV-VG (n = 29) between January 2020 and January 2021.

INTERVENTIONS

Tracheal aspirate samples for the measurement of interleukin (IL)-6, IL-8, and tumor necrosis factor-α (TNF-α) were obtained on days one, two, and three of HFOV or HFOV-VG ventilation.

MEASUREMENTS AND MAIN RESULTS

The authors found a significantly increasing trend in the HFOV group mean values of IL-6, IL-8, and TNF-α (p < 0.05 on days two and three v day one), and IL-6, IL-8, and TNF-α levels were significantly higher on day three in the HFOV group versus the HFOV+VG group (p < 0.05). In addition, the incidences of hypocapnia and hypercapnia in infants supported with HFOV-VG were significantly lower (p < 0.05). Furthermore, the postoperative mechanical ventilation duration in the HFOV-VG group also was shorter than that in the HFOV group (p < 0.05).

CONCLUSION

Compared with HFOV alone, HFOV-VG reduced proinflammatory systemic reactions after congenital cardiac surgery, decreased the incidences of hypercapnia and hypocapnia, and shortened the postoperative mechanical ventilation duration.

Target volume-guarantee in high-frequency oscillatory ventilation for preterm respiratory distress syndrome: Low volumes and high frequencies lead to adequate ventilation

BACKGROUND AND OBJECTIVES

Respiratory distress syndrome (RDS) and ventilation-induced lung injury lead to significant morbidity in preterm infants. High-frequency oscillatory ventilation with volume-guarantee (HFOV-VG) has been used as a rescue therapy and might lead to lower rates of death and bronchopulmonary dysplasia, especially when using low tidal volumes and high frequencies. The aim of the study was to define HFOV-VG parameters leading to adequate ventilation in the first 72 h of preterm RDS using a low volume and high-frequency strategy.

DESIGN AND METHODS

Retrospective cohort study in a tertiary-level neonatology unit. Infants <32 weeks with severe respiratory insufficiency needing HFOV-VG were included. Patients were ventilated following a standard mechanical ventilation aiming for low tidal volumes and high frequencies. Clinical data, perinatal characteristics and high-frequency parameters corresponding with adequate ventilation were recorded.

RESULTS

116 patients were included. Median gestational age was 25 weeks (interquartile range [IQR] = 24-27), median birth weight 724 g (IQR = 600-900 g). HFOV-VG was started at 2 h, median high-frequency tidal volume was 1.63 ml/kg (IQR = 1.44-1.84) and median frequency was 16 Hz (IQR = 15-18). Weight-adjusted tidal volumes did not depend on gestational age, antenatal corticosteroids nor chorioamnionitis, and were inversely correlated with frequencies (R ²  = -0.10, p = .001).

CONCLUSION

HFOV-VG can reach adequate ventilation at high frequencies when using adequate volumes, providing a feasible ventilation strategy that might be of help in preterm infants with RDS.

Application of high-frequency oscillation ventilation combined with volume guarantee in infants with acute hypoxic respiratory failure after congenital heart surgery

OBJECTIVE

This study aimed to evaluate the efficacy and safety of high-frequency oscillation ventilation combined with volume guarantee (HFOV-VG) compared with the safety and efficacy of HFOV alone in infants with acute hypoxemic respiratory failure (AHRF) after congenital heart surgery.

METHODS

We retrospectively analyzed the clinical data of 44 infants who were ventilated for AHRF after congenital heart surgery between January 2020 and January 2021. HFOV alone was used in 23 of the 44 infants, whereas HFOV-VG was used in the other 21 infants.

RESULTS

The average frequency tidal volume (VThf) of the HFOV-VG group was lower than that of the HFOV group, and the proportion of VThf exceeding the target range of infants in the HFOV-VG group was also lower (p < .01). In addition, the incidence of hypocapnia and hypercapnia in infants supported with HFOV-VG was significantly lower (p < .01). Furthermore, the duration of invasive ventilation and the median ventilator adjustment per hour in the HFOV-VG group was also lower than that in the HFOV group (p < .01).

CONCLUSIONS

Compared with HFOV alone, HFOV-VG decreases the fluctuation of VThf and the incidence of hypercapnia and hypocapnia. Moreover, it reduces the workload of bedside medical staff. Further studies are needed to confirm the efficacy and safety of HFOV-VG as a routine respiratory support strategy for congenital heart disease during the perioperative period.

Effects of High-Frequency Oscillatory Ventilation With Volume Guarantee During Surfactant Treatment in Extremely Low Gestational Age Newborns With Respiratory Distress Syndrome: An Observational Study

OBJECTIVE

To evaluate the effect of volume guarantee (VG) combined with high-frequency oscillatory ventilation (HFOV) on respiratory and other physiological parameters immediately after lung recruitment and surfactant administration in HFOV elective ventilated extremely low gestational age newborns (ELGAN) with respiratory distress syndrome (RDS).

DESIGN

Observational study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

Twenty-two ELGANs of 25.5 ± 1.1 weeks of gestational age requiring invasive mechanical ventilation and surfactant administration for RDS during the first 6 h of life.

INTERVENTIONS

All infants intubated in delivery room, were managed with elective HFOV and received surfactant after a lung recruitment manoeuver. Eleven infants received HFOV + VG and were compared with a control group of 11 infants receiving HFOV alone. HFOV was delivered in both groups by Dräger Babylog VN500 ventilator (Dräger, Lubeck, Germany).

MAIN OUTCOME MEASURES

Variations and fluctuations of delivered high-frequency tidal volume (VT_hf), fluctuation of pressure amplitude (ΔP) and partial pressure of CO₂ (pCO₂) levels after recruitment manoeuver and immediately after surfactant administration, in HFOV + VG vs. HFOV ventilated infants.

RESULTS

There were no significant differences in the two groups at starting ventilation with or without VG. The mean applied VT_hf per kg was 1.7 ± 0.3 ml/kg in the HFOV group and 1.7 ± 0.1 ml/kg in the HFOV + VG group. Thirty minutes after surfactant administration, HFOV group had a significant higher VT_hf/Kg than HFOV + VG (2.1 ± 0.3 vs. 1.6 ± 0.1 ml/kg, p < 0.0001) with significantly lower pCO₂ levels (43.1 ± 3.8 vs. 46.8 ± 1.5 mmHg, p = 0.01), 54.4% of patients having pCO₂ below 45 mmHg. Measured post-surfactant ΔP values were higher in HFOV group (17 ± 3 cmH₂O) than in HFOV + VG group (13 ± 3 cmH₂O, p = 0.01).

CONCLUSION

HFOV + VG maintains pCO₂ levels within target range and reduces VT_hf delivered variations more consistently than HFOV alone after surfactant administration.

Volume Guarantee High-Frequency Oscillatory Ventilation in Preterm Infants With RDS: Tidal Volume and DCO2 Levels for Optimal Ventilation Using Open-Lung Strategies

High frequency oscillatory ventilation with volume-guarantee (HFOV-VG) is a promising lung protective ventilator mode for the treatment of respiratory failure in newborns. However, indicators of optimal ventilation during HFOV-VG mode are not identified yet. In this study, we aimed to evaluate optimal high-frequency tidal volume (VThf) and the dissociation coefficient of CO₂ (DCO₂) levels to achieve normocapnia during HFOV-VG after lung recruitment in very low birthweight infants with respiratory distress syndrome (RDS). Preterm babies under the 32nd postmenstrual week with severe RDS that received HFOV-VG using open-lung strategy between January 2014 and January 2019 were retrospectively evaluated. All included patients were treated with the Dräger Babylog VN500 ventilator in the HFOV-VG mode. In total, 53 infants with a mean gestational age of 26.8 ± 2.3 weeks were evaluated. HFOV mean optimal airway pressure (MAPhf) level after lung recruitment was found to be 10.2 ± 1.7 mbar. Overall, the mean applied VThf per kg was 1.64 ± 0.25 mL/kg in the study sample. To provide normocapnia, the mean VThf was 1.61 ± 0.25 mL/kg and the mean DCO₂corr was 29.84 ± 7.88 [mL/kg]²/s. No significant correlation was found between pCO₂ levels with VThf (per kg) or DCO₂corr levels. VThf levels to maintain normocarbia were significantly lower with 12 Hz frequency compared to 10 Hz frequency (1.50 ± 0.24 vs. 1.65 ± 0.25 mL/ kg, p < 0.001, respectively). A weak but significant positive correlation was found between mean airway pressure (MAPhf) and VThf levels. To our knowledge, this is the largest study to evaluate the optimal HFOV-VG settings in premature infants with RDS, using the open-lung strategy. According to the results, a specific set of numbers could not be recommended to achieve normocarbia. Following the trend of each patient and small adjustments according to the closely monitored pCO₂ levels seems logical.

Effective Tidal Volume for Normocapnia in Very-Low-Birth-Weight Infants Using High-Frequency Oscillatory Ventilation

PURPOSE

Removal of CO₂ is much efficient during high-frequency oscillatory ventilation (HFOV) for preterm infants. However, an optimal carbon dioxide diffusion coefficient (DCO₂) and tidal volume (VT) have not yet been established due to much individual variance. This study aimed to analyze DCO₂ values, VT, and minute volume in very-low-birth-weight (VLBW) infants using HFOV and correlates with plasma CO₂ (pCO₂).

MATERIALS AND METHODS

Daily respiratory mechanics and ventilator settings from twenty VLBW infants and their two hundred seventeen results of blood gas analysis were collected. Patients were treated with the Dräger Babylog VN500 ventilator (Drägerwerk Ag & Co.) in HFOV mode. The normocapnia was indicated as pCO₂ ranging from 45 mm Hg to 55 mm Hg.

RESULTS

The measured VT was 1.7 mL/kg, minute volume was 0.7 mL/kg, and DCO₂ was 43.5 mL²/s. Mean results of the blood gas test were as follows: pH, 7.31; pCO₂, 52.6 mm Hg; and SpO₂, 90.5%. In normocapnic state, the mean VT was significantly higher than in hypercapnic state (2.1±0.5 mL/kg vs. 1.6±0.3 mL/kg), and the mean DCO₂ showed significant difference (68.4±32.7 mL²/s vs. 32.4±15.7 mL²/s). The DCO₂ was significantly correlated with the pCO₂ (p=0.024). In the receiver operating curve analysis, the estimated optimal cut-off point to predict the remaining normocapnic status was a VT of 1.75 mL/kg (sensitivity 73%, specificity 80%).

CONCLUSION

In VLBW infants treated with HFOV, VT of 1.75 mL/kg is recommended for maintaining proper ventilation.

Using very high frequencies with very low lung volumes during high-frequency oscillatory ventilation to protect the immature lung. A pilot study

OBJECTIVE

High-frequency oscillatory ventilation (HFOV) has been described as a rescue therapy in severe respiratory distress syndrome (RDS) with a potential protective effect in immature lungs. In recent times, HFOV combined with the use of volume guarantee (VG) strategy has demonstrated an independent effect of the frequency on tidal volume to increase carbon-dioxide (CO2) elimination. The aim of this study was to demonstrate the feasibility of using the lowest tidal volume on HFOV+VG to prevent lung damage, maintaining a constant CO2 elimination by increasing the frequency.

STUDY DESIGN

Newborn infants with RDS on HFOV were prospectively included. After adequate and stable ventilation using a standard HFOV strategy, the tidal volume was fixed using VG and decreased while the frequency was increased to the highest possible to maintain a constant CO2 elimination. Pre- and post-PCO2, delta pressure and tidal volume obtained in each situation were compared.

RESULT

Twenty-three newborn infants were included. It was possible to increase the frequency while decreasing the tidal volume in all patients, maintaining a similar CO2 elimination, with a tendency to a lower mean PCO2 after reaching the highest frequency. High-frequency tidal volume was significantly lower, 2.20 ml kg(-1) before vs 1.59 ml kg(-1) at the highest frequency.

CONCLUSION

It is possible to use lower delivered tidal volumes during HFOV combined with VG and higher frequencies with adequate ventilation to allow minimizing lung injury.

Flow measurement in mechanical ventilation: a review

Accurate monitoring of flow rate and volume exchanges is essential to minimize ventilator-induced lung injury. Mechanical ventilators employ flowmeters to estimate the amount of gases delivered to patients and use the flow signal as a feedback to adjust the desired amount of gas to be delivered. Since flowmeters play a crucial role in this field, they are required to fulfill strict criteria in terms of dynamic and static characteristics. Therefore, mechanical ventilators are equipped with only the following kinds of flowmeters: linear pneumotachographs, fixed and variable orifice meters, hot wire anemometers, and ultrasonic flowmeters. This paper provides an overview of these sensors. Their working principles are described together with their relevant advantages and disadvantages. Furthermore, the most promising emerging approaches for flowmeters design (i.e., fiber optic technology and three dimensional micro-fabrication) are briefly reviewed showing their potential for this application.

Impact of Volume Guarantee on High-Frequency Oscillatory Ventilation in Preterm Infants: A Randomized Crossover Clinical Trial

BACKGROUND

High-frequency oscillatory ventilation (HFOV) with volume guarantee (VG) is a new ventilation mode that allows the clinician to set a mean tidal volume to be delivered.

OBJECTIVE

This study aimed to investigate whether HFOV with a VG option may result in constant tidal volume delivery and less fluctuant CO2 levels compared to HFOV alone in premature infants with respiratory distress syndrome (RDS).

METHODS

Inborn infants at less than 32 weeks of gestation with RDS requiring invasive mechanical ventilation were eligible. Patients were randomized to receive HFOV + VG or HFOV alone as the initial ventilator mode and then crossed over to the other mode. HFOV was performed with 'optimal lung volume strategy' during both of the periods.

RESULTS

Twenty infants were evaluated. The mean high-frequency tidal volume (VThf) and CO2 diffusion coefficient (DCO2) were significantly higher in the HFOV + VG mode than HFOV alone. HFOV + VG maintains VThf within the target range more consistently than HFOV. The incidences of hypocarbia and hypercarbia were lower in HFOV with VG than HFOV alone.

CONCLUSION

This is the first prospective, randomized, short-term crossover clinical study that compared HFOV with and without VG in infants with acute RDS. Because of the lower VThf fluctuation and lower incidences of out-of-target PCO2 levels, HFOV combined with VG seems to be feasible for preterm infants. However, the results should be interpreted with caution due to the small sample size and short-term crossover design of the study.

Monitoring Lung Volumes During Mechanical Ventilation

Respiratory inductive plethysmography (RIP) is a non-invasive method of measuring change in lung volume which is well-established as a monitor of tidal ventilation and thus respiratory patterns in sleep medicine. As RIP is leak independent, can measure end-expiratory lung volume as well as tidal volume and is applicable to both the ventilated and spontaneously breathing patient, there has been a recent interest in its use as a bedside tool in the intensive care unit.

Bringing back the old: time to reevaluate the high-frequency ventilation strategy

OBJECTIVE

To examine the role of frequency in high-frequency ventilation (HFV) on carbon-dioxide (CO2) elimination and lung injury, independent of its effect on tidal volume.

STUDY DESIGN

An anatomically representative lung model was attached to a mechanical ventilator capable of providing HFV with a constant volume. CO2 was infused directly into the lung, and a commercially available end-tidal CO2 detector was used to determine CO2 elimination. CO2 elimination and amplitude of pressure transmissions were evaluated using frequencies ranging from 5 to 15 Hz. The pressure-volume index (PVI) was described as the product of the volume and pressures delivered to the lung, a surrogate for lung injury.

RESULT

The use of increasing frequencies directly correlated with improved CO2 clearance when keeping the tidal volume fixed, expressed as percent CO2 remaining in the lung at 25 s (66.5 (±1.1)%, 50.5 (±0.1)% and 37.8 (±0.3)% at 5, 10 and 15 Hz, respectively, P<0.05). With a fixed tidal volume, there was a decrease in pressure amplitudes transmitted to the lung with a decline in the PVI (53.9 (±2.7) mmHg ml(-1), 41.1 (±0.9) mmHg ml(-1) and 23.4 (±3.6) mmHg ml(-1), at 5, 10 and 15 Hz, respectively, P<0.05).

CONCLUSION

Frequency has a direct relationship with CO2 elimination when tidal volume is fixed. Using low delivered tidal volumes and high frequencies may allow for improved ventilation efficacy, while minimizing lung injury.

High-frequency oscillatory ventilation combined with volume guarantee in a neonatal animal model of respiratory distress syndrome

Objective. To assess volume guarantee (VG) ventilation combined with high-frequency oscillatory ventilation (HFOV) strategy on PaCO₂ regulation in an experimental model of neonatal distress syndrome. Methods. Six 2-day-old piglets weighing 2.57 ± 0.26 kg were used for this interventional experimental study. Animals were ventilated during physiologic lung conditions and after depletion of lung surfactant by bronchoalveolar lavage (BAL). The effect of HFOV combined with VG on PaCO₂ was evaluated at different high-frequency expired tidal volume (VThf) at constant frequency (f_R) and mean airway pressure (mPaw). Fluctuations of the pressure (ΔPhf) around the mPaw and PaCO₂ were analyzed before and after lung surfactant depletion. Results. PaCO₂ levels were inversely proportional to VThf. In the physiological lung condition, an increase in VThf caused a significant decrease in PaCO₂ and an increase in ΔPhf. After BAL, PaCO₂ did not change as compared with pre-BAL situation as the VThf remained constant by the ventilator. Conclusions. In this animal model, using HFOV combined with VG, changes in the VThf settings induced significant modifications in PaCO₂. After changing the lung condition by depletion of surfactant, PaCO₂ remained unchanged, as the VThf setting was maintained constant by modifications in the ΔPhf done by the ventilator.

Normocapnic high frequency oscillatory hyperventilation increases oxygenation in pigs

High frequency oscillatory ventilation (HFOV), contrary to conventional ventilation, enables a safe increase in tidal volume (V(T)) without endangering alveoli by volutrauma or barotrauma. The aim of the study is to introduce the concept of normocapnic high frequency oscillatory hyperventilation and to assess its effect upon oxygen gain under experimental conditions. Laboratory pigs (n = 9) were investigated under total intravenous anesthesia in three phases. Phase 1: Initial volume controlled HFOV period. Phase 2: Hyperventilation--V(T) was increased by (46 +/- 12) % when compared to normocapnic V(T) during phase 1. All other ventilatory parameters were unchanged. A significant increase in PaO(2) (by 3.75 +/- 0.52 kPa, p < 0.001) and decrease in PaCO(2) (by -2.05 +/- 0.31 kPa, p < 0.001) were obtained. Phase 3: Normocapnia during hyperventilation was achieved by an iterative increase in the CO(2) fraction in the inspiratory gas by a CO(2) admixture. All ventilatory parameters were unchanged. A significant increase in PaO(2) (by 3.79 +/- 0.73 kPa, p < 0.001), similar to that which was observed in phase 2, was preserved in phase 3 whereas normocapnia was fully re-established. The concept of high frequency normocapnic hyperventilation offers a lung protective strategy that significantly improves oxygenation whilst preserving normocapnia.

A new method for continuous monitoring of chest wall movement to characterize hypoxemic episodes during HFOV

INTRODUCTION

Monitoring ventilated infants is difficult during high-frequency oscillatory ventilation (HFOV). This study tested the possible causes of hypoxemic episodes using a new method for monitoring chest wall movement during HFOV in newborn infants.

METHODS

Three miniature motion sensors were attached to both sides of the chest and to the epigastrium to measure the local tidal displacement (TDi) at each site. A >20% change in TDi was defined as deviation from baseline.

RESULTS

Eight premature infants (postmenstrual age 30.6 ± 2.6 weeks) were monitored during 10 sessions (32.6 h) that included 21 hypoxemic events. Three types of such events were recognized: decrease in TDi that preceded hypoxemia (n = 11), simultaneous decrease in TDi and SpO2 (n = 6), and decrease in SpO(2) without changes in TDi (n = 4). In the first group, decreases in TDi were detected 22.4 ± 18.7 min before hypoxemia, and were due to airway obstruction by secretions or decline in lung compliance. The second group resulted from apnea or severe abdominal contractions. In the third group, hypoxia appeared following a decrease in FiO2.

CONCLUSIONS

Monitoring TDi may enable early recognition of deteriorating ventilation during HFOV that eventually leads to hypoxemia. In about half of cases, hypoxemia is not due to slowly deteriorating ventilation.

Comparison of two ventilator circuits for Dräger Babylog high-frequency ventilation

AIM

The Dräger Babylog 8000plus ventilator (Dräger Medical Systems, Lübeck, Germany) can provide both conventional and high-frequency ventilation (HFV). Dräger recommends specific circuits for each of these modes. We investigated the performance of the Babylog ventilator in HFV mode when used with the recommended circuits for both conventional and HFV.

METHODS

The Fisher and Paykel RT235 (conventional; Fisher and Paykel Healthcare, Auckland, New Zealand) and Hytrel (HFV; Fisher and Paykel Healthcare) circuits were studied using a 50-mL test lung. Tidal volume, high-frequency minute volume and ventilator alarms were compared at 100 combinations of mean airway pressures (10-16 cm H₂O), frequencies (6-14 Hz) and amplitudes (20-60%).

RESULTS

Tidal volume with the two circuits differed by < 5% for tidal volumes ≤ 2.5 mL. Above this, tidal volumes delivered with the HFV circuit were up to 15% more than that obtained with the conventional ventilation circuit, and high-frequency minute volume differed by up to 30%. With the exception of the highest tidal/minute volumes, the tidal volume delivered using the HFV circuit could also be achieved with adjusted frequency or amplitude when using the conventional circuit. More 'pressure measurement out of range' alarms were noted with the conventional ventilation circuit, particularly at mean airway pressure ≥ 14 cm H₂O and frequency ≤ 10 Hz.

CONCLUSIONS

The conventional ventilation circuit may allow delivery of adequate tidal volume for some infants. Where requirements are higher, the HFV circuit allows the Babylog to deliver higher tidal volumes and higher minute volume, and reduce alarms.

Comparison of the Sensormedics 3100A and Bronchotron transporter in a neonatal piglet ARDS model

The Sensormedics 3100A (Cardinal Health, Dublin, OH) (HFOV) and the Bronchotron (Percussionaire, Sandpoint, ID) (HFPV) are high-frequency ventilation devices used to support neonatal respiratory failure; however, a comparison of the devices, with respect to gas exchange at similar ventilator settings, has not been previously studied. Thus, we compared the ability of HFOV to that of HFPV to provide oxygenation and ventilation during acute lung injury in a newborn animal model. Using a saline lung lavage model, 12 neonatal piglets were randomized to initial support with either the HFOV or HFPV with settings adjusted to achieve PaCO2 of 45-60 mmHg. After stabilization, ventilator settings and arterial blood gases were serially recorded for 30 min. Animals were then crossed over to the alternative device set to deliver the same V(t), MAP, and F for an additional 30 min with the same parameters recorded. We found that the DeltaP needed to generate adequate V(t) on HFPV (35 +/- 7 cm H2O) trended higher versus HFOV (31 +/- 7 cm H2O P = 0.09) when the devices were matched for V(t), F, and MAP. No significant differences in ventilation (PaCO(2) = 50 +/- 10.7 mmHg vs. 46 +/- 10 mmHg, P = 0.22) or oxygenation (PaO2 = 150 +/- 76 mmHg vs. 149 +/- 107 mmHg, P = 0.57) between the devices were found. We conclude that HFPV ventilates and oxygenates as well as HFOV at equivalent ventilator settings. HFPV may require larger DeltaP's to generate equivalent V(t).