High-frequency oscillatory ventilation: A narrative review

The effect of NHFOV on hemodynamics in mild and moderately preterm neonates: a randomized clinical trial

The aim of this study is to study cardio-respiratory effects of nasal high-frequency oscillatory ventilation (NHFOV) vs. NCPAP as an initial mode of ventilation in moderate-late-preterm infants. A randomized controlled trial was conducted in NICU of Alexandria University Maternity Hospital (AUMH). One-hundred late-moderate-preterm infants were randomly assigned to either NHFOV-group (n = 50) or NCPAP-group (n = 50). For both groups, functional echocardiography was performed in the first 24 h to detect hemodynamic changes and respiratory outcome was monitored throughout the hospital stay. The main outcomes were hemodynamic measurements and myocardial function using functional echocardiography of those infants along with the respiratory outcome and complications. Kaplan-Meier survival plot was used representing time course of NCPAP and NHFOV failure. Left ventricular output values were not significantly different in both groups with median 202 ml/kg /min and IQR (176-275) in NCPAP-group and 226 ml/kg/min with IQR (181-286) in NHFOV group. Nevertheless, ejection fraction and fractional shortening were significantly higher in NHFOV-group with P 0.001. The time to weaning, the time to reach 30%-FIO2, the need for invasive ventilation, oxygen support duration, and maximal-FIO2 were significantly more in NCAPAP group.     Conclusion: NHFOV is an effective and promising tool of non-invasive-ventilation which can be used as a primary modality of respiratory support in preterm infants with variable forms of respiratory distress syndrome without causing detrimental effect on hemodynamics or significant respiratory complications.     Trial registration: NCT05706428 (registered on January 21, 2023). What is Known: • NHFOV might be beneficial as a secondary mode of ventilation and might have an impact on hemodynamics. What is New: • NHFOV can be used as an initial mode of ventilation with CDP beyond the reported pressure limits of CPAP without causing neither CO2 retention nor adverse hemodynamic consequences.

Comparison of High-Frequency Oscillatory Ventilators

BACKGROUND

The performance of high-frequency oscillatory ventilators (HFOV) differs by the waveform generation mode and circuit characteristics. Few studies have described the performance of piston-type HFOV. The present study aimed to compare the amplitude required to reach the target high-frequency tidal volume ([Formula: see text]); determine the relationship between the settings and actual pressure in amplitude or mean airway pressure ([Formula: see text]); and describe the interaction among compliance, frequency, and endotracheal tube (ETT) inner diameter in 4 HFOV models, including Humming X, Vue (a piston type ventilator commonly used in Japan), VN500 (a diaphragm type), and SLE5000 (a reverse jet type).

METHODS

The oscillatory ventilators were evaluated by using a 50-mL test lung with 0.5 and 1.0 mL/cm H2O compliance, [Formula: see text] of 10 cm H2O, frequency of 12 and 15 Hz, and ETT inner diameters 2.0, 2.5, and 3.5 mm. At each permutation of compliance, frequency, and ETT, the target high-frequency [Formula: see text] was increased from 0.5 to 3.0 mL. The change in [Formula: see text] from the ventilator (ventilator [Formula: see text]) to Y-piece (Y [Formula: see text]) and alveolar pressure (alveolar [Formula: see text]) and the change in amplitude from the ventilator (ventilator amplitude) to Y-piece (Y amplitude) and alveolar pressure (alveolar amplitude) were determined at high-frequency [Formula: see text] of 1.0 and 3.0 mL.

RESULTS

To achieve the target high-frequency [Formula: see text], the Humming X and Vue required a higher amplitude than did the SLE5000, but the maximum amplitude in the VN500 was unable to attain a larger high-frequency [Formula: see text]. Ventilator [Formula: see text] and alveolar pressure decreased at the Y-piece with the Humming X and Vue but increased with the SLE5000. The ventilator [Formula: see text] in the VN500 decreased remarkably at a frequency of 15 Hz. The ventilator amplitude in all 4 ventilators decreased while temporarily increasing at the Y-piece in the VN500.

CONCLUSIONS

The actual measured value, such as alveolar [Formula: see text] and high-frequency [Formula: see text], varied according to the type of HFOV system and the inner diameter of the ETT, even with identical settings. Clinicians should therefore determine the setting appropriate to each HFOV model.

The effect of budesonide delivered by high-frequency oscillatory ventilation on acute inflammatory response in severe lung injury in adult rabbits

The inflammation present in acute respiratory distress syndrome (ARDS) and thereby associated injury to the alveolar-capillary membrane and pulmonary surfactant can potentiate respiratory failure. Even considering the high mortality rate of severe ARDS, glucocorticoids appear to be a reasonable treatment option along with an appropriate route of delivery to the distal lung. This study aimed to investigate the effect of budesonide therapy delivered intratracheally by high-frequency oscillatory ventilation (HFOV) on lung function and inflammation in severe ARDS. Adult New Zealand rabbits with respiratory failure (P/F<13.3 kPa) induced by intratracheal instillation of hydrochloric acid (HCl, 3 ml/kg, pH 1.5) followed by high tidal ventilation (VT 20 ml/kg) to mimic ventilator-induced lung injury (VILI) were treated with intratracheal bolus of budesonide (0.25 mg/kg, Pulmicort) delivered by HFOV (frequency 8 Hz, MAP 1 kPa, deltaP 0.9 kPa). Saline instead of HCl without VILI with HFOV delivered air bolus instead of therapy served as healthy control. All animals were subjected to lung-protective ventilation for 4 h, and respiratory parameters were monitored regularly. Postmortem, lung injury, wet-to-dry weight ratio, leukocyte shifts, and levels of cytokines in plasma and lung were evaluated. Budesonide therapy improved the lung function (P/F ratio, oxygenation index, and compliance), decreased the cytokine levels, reduced lung edema and neutrophils influx into the lung, and improved lung architecture in interstitial congestion, hyaline membrane, and atelectasis formation compared to untreated animals. This study indicates that HFOV delivered budesonide effectively ameliorated respiratory function, and attenuated acid-induced lung injury in a rabbit model of severe ARDS.

Pneumomediastinum and pneumothorax in acute respiratory distress syndrome (ARDS) patients: a narrative review

Background and Objective

Acute respiratory distress syndrome (ARDS) is a severe, life-threatening medical condition characterized by poor oxygenation due to non-compliant lungs secondary diffuse alveolar damage. Encouragingly, the incidence of ARDS has declined steadily recently, attributed mainly to implementation of keystone guidelines and continuous research efforts. Mechanical ventilation is the cornerstone of supportive care for ARDS patients. This review aims to consolidate the current knowledge on pneumothorax (PNX) and pneumomediastinum (PMD) and to enhance the understanding of the readers. The objectives are to (I) explore the etiology and risk factors of PNX and PMD, (II) discuss the various diagnostic modalities available, (III) evaluate management options, and (IV) recent advancements.

Methods

A search of the literature was conducted using PubMed, MEDLINE, and Google Scholar for relevant articles pertaining to PNX and PMD in ARDS population. The clinical presentation, diagnostic and management strategies of PNX, PMD, and ARDS were summarized, and all authors reviewed the selection and decide which studies to include.

Key Content and Findings

The adoption of lung-protective ventilation strategies, based on the review of literature from the recent years, shows that it has played a significant role in reducing the occurrence of barotrauma, such as PNX and PMD. However, PNX and PMD remains to be a challenging complication to manage. With a specific focus on PNX and PMD, this review provides valuable insights into effectively managing and understanding these critical complications among ARDS patients.

Conclusions

ARDS, with its evolving definition, continues to pose a life-threatening threat. Despite the widespread adoption of lung-protective ventilation strategies, PNX and PMD present persistent challenges in management. Further research is imperative to enhance the risk assessment of ARDS patients prone to developing PNX and PMD and to institute more effective prevention and treatment measures.

Effect of high-frequency oscillation on reduction of atelectasis in perioperative patients: a prospective randomized controlled study

BACKGROUND

Atelectasis affects approximately 90% of anaesthetized patients, with laparoscopic surgery and pneumoperitoneum reported to exacerbate this condition. High-frequency oscillation therapy applies continuous positive pressure pulses to oscillate the airway, creating a pressure difference in small airways obstructed by secretions. This process helps reduce peak airway pressure, open small airways, and decrease atelectasis incidence, while also facilitating respiratory tract clearance. This study examines the efficacy of high-frequency oscillation on reduction of atelectasis in laparoscopic cholecystectomy (LC) patients under general anaesthesia, evaluated using lung ultrasound.

METHODS

Sixty-four patients undergoing laparoscopic cholecystectomy were randomly divided into a control group and a high-frequency oscillation (HFO) group. Both groups underwent total intravenous anaesthesia under invasive arterial monitoring. The HFO group received a 10-minute continuous high-frequency oscillation therapy during surgery, while the control group received no intervention. Lung ultrasound evaluations were performed three times: five minutes post-intubation (T1), at the end of the surgery (T2), and before leaving the Post-Anaesthesia Care Unit (PACU; T3). Blood gas analysis was performed twice: prior to induction with no oxygen supply and before PACU discharge (oxygen supply off).

RESULTS

The HFO group displayed a significantly lower incidence of atelectasis at T3 (57.5% vs. 90.3%, OR 6.88, 95%CI (1.74 to 27.24)) compared to the control group. Moreover, the HFO group's PaO2 levels remained consistent with baseline levels before PACU discharge, unlike the control group. Although there was no significant difference in LUS scores between the groups at T1 (8.56 ± 0.15 vs. 8.19 ± 0.18, p = 0.1090), the HFO group had considerably lower scores at T2 (13.41 ± 0.17 vs.7.59 ± 0.17, p < 0.01) and T3 (13.72 ± 0.14 vs.7.25 ± 0.21, p < 0.01).

CONCLUSION

Our study indicates that high-frequency oscillation effectively reduces atelectasis in patients undergoing laparoscopic cholecystectomy. Additionally, it can mitigate the decline in oxygen partial pressure associated with atelectasis.

Comparison of conventional mechanical ventilation and high-frequency oscillatory ventilation in congenital diaphragmatic hernias: a systematic review and meta-analysis

Outcomes of conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation (HFOV) in patients with congenital diaphragmatic hernia (CDH) were compared through a systematic review and meta-analysis. Outcome measures included mortality and incidence of chronic lung disease (CLD). Odds ratio (OR) and 95% confidence interval (95%CI) were evaluated. Subgroup analyses were performed according to the strategy for applying HFOV in CDH patients. Group A: CMV was initially applied in all CDH patients, and HFOV was applied in unstable patients. Group B: chronologically analyzed. (CMV and HFOV era) Group C: CMV or HFOV was used as the initial MV. Of the 2199 abstracts screened, 15 full-text articles were analyzed. Regarding mortality, 16.7% (365/2180) and 32.8% (456/1389) patients died in CMV and HFOV, respectively (OR, 2.53; 95%CI 2.12-3.01). Subgroup analyses showed significantly worse, better, and equivalent mortality for HFOV than that for CMV in group A, B, and C, respectively. CLD occurred in 32.4% (399/1230) and 49.3% (369/749) patients in CMV and HFOV, respectively (OR, 2.37; 95%CI 1.93-2.90). The evidence from the literature is poor. Mortality and the incidence of CLD appear worse after HFOV in children with CDH. Cautious interpretation is needed due to the heterogeneity of each study.

Point-of-Care Ultrasound versus Chest X-Ray for Determining Lung Expansion Based on Rib Count in High-Frequency Oscillatory Ventilation

INTRODUCTION

Chest X-ray (CXR) is the most prevalent method for evaluating lung expansion in high-frequency oscillatory ventilation (HFOV). The purpose of this study was to compare the accuracy of chest radiography with point-of-care ultrasound (POCUS) in determining lung expansion.

METHODS

This prospective study included newborns who required HFOV and were monitored in a neonatal intensive care unit. A single neonatologist assessed lung expansion with CXR and POCUS to measure the costal level of the right hemidiaphragm and compared the results.

RESULTS

A neonatologist performed 55 measurements in 28 newborns with a gestational age of 32 (23.2-39.4) weeks, followed by HFOV. The rib counts obtained from anterior chest ultrasonography and posterior CXR showed a statistically high concordance (r = 0.913, p < 0.001).

CONCLUSION

Lung ultrasonography is a reliable method for the evaluation of lung expansion based on rib count in patients with HFOV.

Management of severe acute respiratory distress syndrome: a primer

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care.

A review of the utility of high-frequency oscillatory ventilation in burn and trauma ICU patients

PURPOSE OF REVIEW

The purpose was to examine the utility of high-frequency oscillatory ventilation (HFOV) in trauma and burn ICU patients who require mechanical ventilation, and provide recommendations on its use.

RECENT FINDINGS

HFOV may be beneficial in burn patients with smoke inhalation injury with or without acute lung injury/acute respiratory distress syndrome (ARDS), as it improves oxygenation and minimizes ventilator-induced lung injury. It also may have a role in improving oxygenation in trauma patients with blast lung injury, pulmonary contusions, pneumothorax with massive air leak, and ARDS; however, the mortality benefit is unknown.

SUMMARY

Although some studies have shown promise and improved outcomes associated with HFOV, we recommend its use as a rescue modality for patients who have failed conventional ventilation.

Pathophysiology of gas exchange impairment in extreme prematurity: Insights from combining volumetric capnography and measurements of ventilation/perfusion ratio

Background

Infants born extremely preterm often suffer from respiratory disease and are invasively ventilated. We aimed to test the hypothesis that gas exchange in ventilated extremely preterm infants occurs both at the level of the alveoli and via mixing of fresh deadspace gas in the airways.

Methods

We measured the normalised slopes of phase II and phase III of volumetric capnography and related them with non-invasive measurements of ventilation to perfusion ratio (V_A/Q) and right-to-left shunt in ventilated extremely preterm infants studied at one week of life. Cardiac right-to-left shunt was excluded by concurrent echocardiography.

Results

We studied 25 infants (15 male) with a median (range) gestational age of 26.0 (22.9-27.9) weeks and birth weight of 795 (515-1,165) grams. The median (IQR) V_A/Q was 0.52 (0.46-0.56) and shunt was 8 (2-13) %. The median (IQR) normalised slope of phase II was 99.6 (82.7-116.1) mmHg and of phase III was 24.6 (16.9-35.0) mmHg. The V_A/Q was significantly related to the normalised slope of phase III (ρ = -0.573, p = 0.016) but not to the slope of phase II (ρ = 0.045, p = 0.770). The right-to-left shunt was not independently associated with either the slope of phase II or the slope of phase III after adjusting for confounding parameters.

Conclusions

Abnormal gas exchange in ventilated extremely preterm infants was associated with lung disease at the alveolar level. Abnormal gas exchange at the level of the airways was not associated with quantified indices of gas exchange impairment.

Non-invasive high frequency oscillatory ventilation inhibiting respiratory motion in healthy volunteers

Precision radiotherapy needs to manage organ movements to prevent critical organ injury. The purpose of this study is to examine the feasibility of motion control of the lung by suppressing respiratory motion. The non-invasive high frequency oscillatory ventilation (NIHFOV) is a technique commonly used in the protection of lung for patients with acute lung disease. By using a very high respiratory frequency and a low tidal volume, NIHFOV allows gas exchange, maintains a constant mean airway pressure and minimizes the respiratory movements. We tested healthy volunteers NIHFOV to explore the optimal operational parameter setting and the best possible motion suppression achievable. This study was conducted with the approval of Institutional Review Boards of the Wuwei Cancer hospital (approval number: 2021-39) and carried out in accordance with Declaration of Helsinki. The study comprises two parts. Twenty three healthy volunteers participated in the first part of the study. They had 7 sessions of training with the NIHFOV. The duration of uninterrupted, continuous breathing under the NIHFOV and the optimal operational machine settings were defined. Eight healthy volunteers took part in the second part of the study and underwent 4-dimensional CT (4DCT) scanning with and without NIHFOV. Their respiratory waveform under free breathing (FB) and NIHFOV were recorded. The maximum range of motion of the diaphragm from the two scannings was compared, and the variation of bilateral lung volume was obtained to evaluate the impact of NIHFOV technique on lung volume. The following data were collected: comfort score, transcutaneous partial pressure of oxygen (PtcO₂), transcutaneous partial pressure of carbon dioxide (PtcCO₂), and pulse rate. Data with and without NIHFOV were compared to evaluate its safety, physiological impacts and effect of lung movement suppression. All the volunteers completed the training sessions eventlessly, demonstrating a good tolerability of the procedure. The median NIHFOV-on time was 32 min (22-45 min), and the maximum range of motion in the cephalic-caudal direction was significantly reduced on NIHFOV compared with FB (1.8 ± 0.8 cm vs 0.3 ± 0.1 cm, t =  - 3.650, P = 0.003); the median range of motion was only 0.3 ± 0.1 cm on NIHFOV with a good reproducibility. The variation coefficient under NIHFOV of the right lung volume was 2.4% and the left lung volume was 9.2%. The PtcO₂ and PtcCO₂ were constantly monitored during NIHFOV. The medium PtcCO₂ under NIHFOV increased lightly by 4.1 mmHg (interquartile range [IQR], 4-6 mmHg) compared with FB (t = 17.676, P < 0.001). No hypercapnia was found, PtcO₂ increased significantly in all volunteers during NIHFOV (t = 25.453, P < 0.001). There was no significant difference in pulse rate between the two data sets (t = 1.257, P = 0.233). NIHFOV is easy to master in healthy volunteers to minimize respiratory movement with good tolerability and reproducibility. It is a feasible approach for lung motion control and could potentially be applied in accurate radiotherapy including carbon-ion radiotherapy through suppression of respiratory movement.

Piezoelectric Micromachined Ultrasonic Transducers (PMUTs): Performance Metrics, Advancements, and Applications

With the development of technology, systems gravitate towards increasing in their complexity, miniaturization, and level of automation. Amongst these systems, ultrasonic devices have adhered to this trend of advancement. Ultrasonic systems require transducers to generate and sense ultrasonic signals. These transducers heavily impact the system's performance. Advancements in microelectromechanical systems have led to the development of micromachined ultrasonic transducers (MUTs), which are utilized in miniaturized ultrasound systems. Piezoelectric micromachined ultrasonic transducers (PMUTs) exhibit higher capacitance and lower electrical impedance, which enhances the transducer's sensitivity by minimizing the effect of parasitic capacitance and facilitating their integration with low-voltage electronics. PMUTs utilize high-yield batch microfabrication with the use of thin piezoelectric films. The deposition of thin piezoelectric material compatible with complementary metal-oxide semiconductors (CMOS) has opened novel avenues for the development of miniaturized compact systems with the same substrate for application and control electronics. PMUTs offer a wide variety of applications, including medical imaging, fingerprint sensing, range-finding, energy harvesting, and intrabody and underwater communication links. This paper reviews the current research and recent advancements on PMUTs and their applications. This paper investigates in detail the important transduction metrics and critical design parameters for high-performance PMUTs. Piezoelectric materials and microfabrication processes utilized to manufacture PMUTs are discussed. Promising PMUT applications and outlook on future advancements are presented.

Cardiopulmonary resuscitation of a very preterm infant using high-frequency oscillation ventilation

We present a novel approach of ventilation, using high-frequency oscillation ventilation (HFOV), during neonatal cardiopulmonary resuscitation (CPR) of a very preterm neonate. This case report highlights the importance of adequate lung inflation, which is a current topic, with neonatal resuscitation guidelines recommending a coordinated 3:1 compression:ventilation ratio during CPR. Our patient, a female infant born at 30 weeks gestational age, weighing 970 g, appeared floppy and apneic following birth in the amniotic sac. Lungs were unfolded and white-out in an x-ray done during resuscitation. The aim was to open lungs effectively using HFOV, instead of positive pressure ventilation, which was used unsuccessfully until the 7th minute of life. Heart rate continuously dropped below 60/min 15 min after birth and chest compressions with asynchronous HFOV were started, adrenalin was administered three times and surfactant was instilled endotracheally twice. It was possible to stabilize the patient after 15 min of CPR, following return of spontaneous circulation. HFOV may have enabled an alternative and rescue option of ventilation during neonatal CPR in this case.

Electrical Impedance Tomography Can Be Used to Quantify Lung Hyperinflation during HFOV: The Pilot Study in Pigs

Dynamic hyperinflation is reported as a potential risk during high-frequency oscillatory ventilation (HFOV), and its existence has been documented both by physical models and by CT. The aim of this study is to determine the suitability of electrical impendence tomography (EIT) for the measurement of dynamic lung hyperinflation and hypoinflation during HFOV. Eleven healthy pigs were anaesthetized and ventilated using HFOV. The difference between the airway pressure at the airway opening and alveolar space was measured by EIT and esophageal balloons at three mean airway pressures (12, 18 and 24 cm H₂O) and two inspiratory to expiratory time ratios (1:1, 1:2). The I:E ratio was the primary parameter associated with differences between airway and alveolar pressures. All animals showed hyperinflation at a 1:1 ratio (median 1.9 cm H₂O) and hypoinflation at a 1:2 (median –4.0 cm H₂O) as measured by EIT. EIT measurements had a linear correlation to esophageal balloon measurements (r² = –0.915, p = 0.0085). EIT measurements were slightly higher than that of the esophageal balloon transducer with the mean difference of 0.57 cm H₂O. Presence of a hyperinflation or hypoinflation was also confirmed independently by chest X-ray. We found that dynamic hyperinflation developed during HFOV may be detected and characterized noninvasively by EIT.

The effect of high-frequency oscillatory ventilator combined with pulmonary surfactant in the treatment of neonatal respiratory distress syndrome

OBJECTIVE

To investigate the efficacy of high-frequency oscillatory ventilation (HFOV) combined with pulmonary surfactant (PS) in the treatment of neonatal respiratory distress syndrome (NRDS).

METHODS

This study is a retrospective clinical study. Seventy-two NRDS neonates were selected as the subjects from November 2019 to November 2020, and divided into observation group (40 cases, HFOV treatment) and control group (32 cases, conventional mechanical ventilation treatment). All cases were treated with PS and comprehensive treatment. The therapeutic effect, arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2), Percentage of inhaled oxygen concentration (FiO2), mean arterialpressure, oxygenation index (OI), and complications were compared in the 2 groups.

RESULTS

The total effective rate of the observation group was 90.0%, significantly higher than that of the control group. After treatment, the observation group has higher PaO2 levels and lower levels of PaCO2, mean arterial pressure, FiO2, and OI than the control group. There was no significant difference in the incidence of complications between the 2 groups.

CONCLUSION

HFOV combined with PS has a significant effect on NRDS, which can improve the arterial blood gas index without increasing the incidence of complications.

Safety use of high frequency oscillatory ventilation in transport of newborn infants affected by severe respiratory failure: preliminary data in central Tuscany

Background

Neonatal Emergency Transport Services play a fundamental role in neonatal care. Stabilization before transport of newborns suffering from severe respiratory failure is often a challenging problem and some critically ill infants may benefit from High Frequency Oscillatory Ventilation (HFOV) as rescue treatment. In these cases, transition to conventional ventilation for transport may cause a deterioration in clinical conditions. HFOV during neonatal transport has been only exceptionally used, due to technical difficulties. Since May 2018, a new neonatal transport unit is available at the Neonatal Protected Transport Service of the Meyer University Hospital in Florence, equipped with a pulmonary ventilator capable of delivering HFOV. Therefore, we conducted an analysis on patients transferred in HFOV to Neonatal Intensive Care Unit (NICU), in order to evaluate the safety and feasibility of its use during neonatal transport.

Methods

A retrospective analysis was performed reviewing medical records of the neonates transported by Meyer Children Hospital’s Neonatal Transport Service between May 2018 and December 2020, and newborns treated with HFOV during ground neonatal transport were identified. Safety was assessed by the comparison of vital signs, hemogas-analysis values and pulmonary ventilator parameters, at the time of departure and upon arrival in NICU. The dose of inotropes, the main respiratory complications (air leak, dislocation or obstruction of the endotracheal tube, loss of chest vibrations) and the number of deaths and transfer failures were recorded.

Results

Out of the approximate 400 newborns transported during the analysis period, 9 were transported in HFOV. We did not find any statistically significant difference in vital parameters, hemogas-analytical values and pulmonary ventilator settings recorded before and after neonatal transport of the nine patients’ parameters (p > 0,05). No patient required additional inotropes during transport. No transport-related deaths or significant complications occurred during transport.

Conclusions

The interest of our report is in the possibility of using HFOV during inter-hospital neonatal transfer. As far as our experience has shown, HFOV appears to be safe for the transportation of newborns with severe respiratory failure. Nevertheless, further larger, prospective and multicentre studies are needed to better evaluate the safety and efficacy of HFOV during neonatal transport.

Gas Exchange Mechanism of High Frequency Ventilation: A Brief Narrative Review and Prospect

The high frequency ventilation (HFV) can well support the breathing of respiratory patient with 20%-40% of normal tidal volume. Now as a therapy of rescue ventilation when conversional ventilation failed, the HFV has been applied in the treatments of severe patients with acute respiratory failure (ARF), acute respiratory distress syndrome (ARDS), etc. However, the gas exchange mechanism (GEM) of HFV is still not fully understood by researchers. In this paper, the GEM of HFV is reviewed to track the studies in last decades and prospect for the next likely studies. And inspired by previous studies, the GEM of HFV is suggested to be continually developed with various hypotheses which will be testified in simulation, experiment and clinic trail. One of the significant measures is to study the GEM of HFV under the cross-disciplinary integration of medicine and engineering. Fully understanding the GEM can theoretically support and expand the applications of HFV, and is helpful in investigating the potential indications and contraindications of HFV.

The Physiological Basis of High-Frequency Oscillatory Ventilation and Current Evidence in Adults and Children: A Narrative Review

High-frequency oscillatory ventilation (HFOV) is a type of invasive mechanical ventilation that employs supra-physiologic respiratory rates and low tidal volumes (V_T) that approximate the anatomic deadspace. During HFOV, mean airway pressure is set and gas is then displaced towards and away from the patient through a piston. Carbon dioxide (CO₂) is cleared based on the power (amplitude) setting and frequency, with lower frequencies resulting in higher V_T and CO₂ clearance. Airway pressure amplitude is significantly attenuated throughout the respiratory system and mechanical strain and stress on the alveoli are theoretically minimized. HFOV has been purported as a form of lung protective ventilation that minimizes volutrauma, atelectrauma, and biotrauma. Following two large randomized controlled trials showing no benefit and harm, respectively, HFOV has largely been abandoned in adults with ARDS. A multi-center clinical trial in children is ongoing. This article aims to review the physiologic rationale for the use of HFOV in patients with acute respiratory failure, summarize relevant bench and animal models, and discuss the potential use of HFOV as a primary and rescue mode in adults and children with severe respiratory failure.

Examining lung mechanical strains as influenced by breathing volumes and rates using experimental digital image correlation

BACKGROUND

Mechanical ventilation is often employed to facilitate breathing in patients suffering from respiratory illnesses and disabilities. Despite the benefits, there are risks associated with ventilator-induced lung injuries and death, driving investigations for alternative ventilation techniques to improve mechanical ventilation, such as multi-oscillatory and high-frequency ventilation; however, few studies have evaluated fundamental lung mechanical local deformations under variable loading.

METHODS

Porcine whole lung samples were analyzed using a novel application of digital image correlation interfaced with an electromechanical ventilation system to associate the local behavior to the global volume and pressure loading in response to various inflation volumes and breathing rates. Strains, anisotropy, tissue compliance, and the evolutionary response of the inflating lung were analyzed.

RESULTS

Experiments demonstrated a direct and near one-to-one linear relationship between applied lung volumes and resulting local mean strain, and a nonlinear relationship between lung pressures and strains. As the applied air delivery volume was doubled, the tissue surface mean strains approximately increased from 20 to 40%, and average maximum strains measured 70-110%. The tissue strain anisotropic ratio ranged from 0.81 to 0.86 and decreased with greater inflation volumes. Local tissue compliance during the inflation cycle, associating evolutionary strains in response to inflation pressures, was also quantified.

CONCLUSION

Ventilation frequencies were not found to influence the local stretch response. Strain measures significantly increased and the anisotropic ratio decreased between the smallest and greatest tidal volumes. Tissue compliance did not exhibit a unifying trend. The insights provided by the real-time continuous measures, and the kinetics to kinematics pulmonary linkage established by this study offers valuable characterizations for computational models and establishes a framework for future studies to compare healthy and diseased lung mechanics to further consider alternatives for effective ventilation strategies.

Ventilating the blast lung: Exploring ventilation strategies in primary blast lung injury

Introduction

Primary blast lung injury (PBLI) is the most common and fatal of all primary blast injuries. The majority of those with PBLI will require early intubation and mechanical ventilation, and thus, ventilation strategy forms a crucial part of any management plan. Methods: A comprehensive, but not systematic, PubMed and Google Scholar database search identified articles that contribute to our current understanding of ventilation strategies in PBLI for a narrative educational review.

Results

A PBLI ventilation strategy must strive to minimise all four of ventilator-associated lung injury (VALI), volutrauma, barotrauma and biotrauma. The three main ventilation strategies available are conventional low tidal volume (LTV) ventilation, airway pressure release ventilation (APRV) and high frequency oscillatory ventilation (HFOV). Conventional LTV ventilation together with a variable positive end-expiratory pressure (PEEP) and permissive hypercapnia has demonstrated reduced inflammation and mortality with a greater number of ventilator-free days. APRV has the potential to reduce dynamic strain, PaO2/FiO2 ratios, levels of applied mechanical power and extravascular lung water while encouraging spontaneous breathing. HFOV is able to effectively avoid VALI while curbing inflammation and histological lung injury, though not necessarily mortality. Conclusions: Presently, PBLI should largely be managed with conventional LTV ventilation alongside a variable PEEP and permissive hypercapnia with APRV and HFOV reserved as rescue strategies for where conventional LTV ventilation fails. Clinicians should additionally consider supplementing their strategy with adjunctive therapies such as prone positioning, inhaled nitric oxide and extracorporeal membrane oxygenation that may further reduce mortality and combat severe respiratory and/or cardiac failure.

Mechanical Ventilation in Pediatric and Neonatal Patients

Pediatric acute respiratory distress syndrome (PARDS) remains a significant cause of morbidity and mortality, with mortality rates as high as 50% in children with severe PARDS. Despite this, pediatric lung injury and mechanical ventilation has been poorly studied, with the majority of investigations being observational or retrospective and with only a few randomized controlled trials to guide intensivists. The most recent and universally accepted guidelines for pediatric lung injury are based on consensus opinion rather than objective data. Therefore, most neonatal and pediatric mechanical ventilation practices have been arbitrarily adapted from adult protocols, neglecting the differences in lung pathophysiology, response to injury, and co-morbidities among the three groups. Low tidal volume ventilation has been generally accepted for pediatric patients, even in the absence of supporting evidence. No target tidal volume range has consistently been associated with outcomes, and compliance with delivering specific tidal volume ranges has been poor. Similarly, optimal PEEP has not been well-studied, with a general acceptance of higher levels of F_iO₂ and less aggressive PEEP titration as compared with adults. Other modes of ventilation including airway pressure release ventilation and high frequency ventilation have not been studied in a systematic fashion and there is too little evidence to recommend supporting or refraining from their use. There have been no consistent outcomes among studies in determining optimal modes or methods of setting them. In this review, the studies performed to date on mechanical ventilation strategies in neonatal and pediatric populations will be analyzed. There may not be a single optimal mechanical ventilation approach, where the best method may simply be one that allows for a personalized approach with settings adapted to the individual patient and disease pathophysiology. The challenges and barriers to conducting well-powered and robust multi-institutional studies will also be addressed, as well as reconsidering outcome measures and study design.

Evidence-Based Mechanical Ventilatory Strategies in ARDS

Acute respiratory distress syndrome (ARDS) remains one of the leading causes of morbidity and mortality in critically ill patients despite advancements in the field. Mechanical ventilatory strategies are a vital component of ARDS management to prevent secondary lung injury and improve patient outcomes. Multiple strategies including utilization of low tidal volumes, targeting low plateau pressures to minimize barotrauma, using low FiO₂ (fraction of inspired oxygen) to prevent injury related to oxygen free radicals, optimization of positive end expiratory pressure (PEEP) to maintain or improve lung recruitment, and utilization of prone ventilation have been shown to decrease morbidity and mortality. The role of other mechanical ventilatory strategies like non-invasive ventilation, recruitment maneuvers, esophageal pressure monitoring, determination of optimal PEEP, and appropriate patient selection for extracorporeal support is not clear. In this article, we review evidence-based mechanical ventilatory strategies and ventilatory adjuncts for ARDS.

In silico numerical simulation of ventilator settings during high-frequency ventilation in preterm infants

OBJECTIVE

Despite the routine use of antenatal steroids, exogenous surfactants, and different noninvasive ventilation methods, many extremely low gestational age neonates, preterm, and term infants eventually require invasive ventilation. In addition to prematurity, mechanical ventilation itself can induce ventilator-induced lung injury leading to lifelong pulmonary sequelae. Besides conventional mechanical ventilation, high-frequency oscillatory ventilation (HFOV) with tidal volumes below dead space and high ventilation frequencies is used either as a primary or rescue therapy in severe neonatal respiratory failure.

METHODS AND RESULTS

Applying a high-resolution computational lung modeling technique in a preterm infant, we studied three different high-frequency ventilation settings as well as conventional ventilation (CV) settings. Evaluating the computed oxygen delivery (OD) and lung mechanics (LM) we outline for the first time how changing ventilator settings from CV to HFOV lead to significant improvements in OD and LM.

CONCLUSION

This personalized "digital twin" strategy advances our general knowledge of protective ventilation strategies in neonatal care and can support decisions on various modes of ventilatory therapy at high frequencies.

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.

Effect of postoperative administration of inhaled nitric oxide combined with high-frequency oscillatory ventilation in infants with acute hypoxemic respiratory failure and pulmonary hypertension after congenital heart surgery: A retrospective cohort study

OBJECTIVE

To evaluate the effect of inhaled nitric oxide (iNO) combined with high-frequency oscillatory ventilation (HFOV) in the treatment of infants with acute hypoxemic respiratory failure (AHRF) and pulmonary hypertension (PH) after congenital heart surgery.

METHODS

A retrospective study was conducted on 63 infants with AHRF and PH after congenital heart surgery in our cardiac intensive care unit (CICU) from January 2020 to March 2021. A total of 24 infants in the A group were treated with HFOV combined with iNO, and 39 infants in the B group were treated with HFOV. Relevant clinical data were collected.

RESULTS

Comparing the two groups, the improvement of the oxygenation index, PaO₂ and PaO₂ /FiO₂ was more obvious for patients in the A group than for those in the B group after intervention (p < .05). Reexamination on the third day after the initiation of HFOV treatment indicated that the systolic pulmonary artery pressure in the A group was significantly lower than that in the B group (p < .05). In addition, the duration of mechanical ventilation and the length of CICU stay in the A group were shorter than those in the B group (p < .05). However, complications between the two groups were not statistically significant. No important adverse effects arose.

CONCLUSIONS

For infants with AHRF and PH after congenital heart surgery, iNO combined with HFOV is superior to HFOV alone to improve oxygenation, decrease pulmonary pressure, and shorten the duration of mechanical ventilation and the length of CICU stay, with no adverse effects.

Evaluation of High-Frequency Oscillatory Ventilation as a Rescue Strategy in Respiratory Failure

BACKGROUND

The use of high-frequency oscillatory ventilation (HFOV) is backed by sound physiologic rationale, but clinical data on the elective use of HFOV have been largely disappointing. Nonetheless, HFOV is still occasionally used as a rescue mode in patients with severe hypoxemia. The evidence that supports this practice is sparse.

METHODS

This was a retrospective single-center analysis that involved subjects admitted to the medical ICU at Cleveland Clinic, Cleveland, Ohio. We included all adult patients (ages > 18 y) who received rescue HFOV between January 1, 2010, and December 31, 2018, and analyzed their clinical outcomes.

RESULTS

A total of 48 subjects were included in the analysis. The most common primary diagnosis was pneumonia (n = 33 [68.8%]), followed by aspiration (n = 6 [12.5%]) and diffuse alveolar hemorrhage (n = 2 [4.2%]). Switching to HFOV improved oxygenation but also increased vasopressor requirements at 3 h. The mortality rate of the study population was 92% (44/48).

CONCLUSIONS

Our study did not support utilization of HFOV as a "last-ditch" rescue measure in subjects with respiratory failure. The delayed timing of HFOV initiation and its detrimental hemodynamic effects are among the potential reasons for the high mortality rate.

[Prospects and developments in the technologies of high frequency oscillatory ventilation]

The high frequency oscillatory ventilation (HFOV) is characterized with low tidal volume and low mean airway pressure, and can well support the breathing of the patients with respiratory diseases. Since the HFOV was proposed, it has been widely concerned by medical and scientific researchers. About the HFOV, this paper discussed its current research status and prospected its future development in technologies. The research status of ventilation model, mechanisms and ventilation mode were introduced in detail. In the next years, the technologies in developing HFOV will be focused on: to develop the branched high-order nonlinear or volume-depended resistance-inertance-compliance (RIC) ventilation model, to fully understand the mechanisms of HFOV and to achieve the noninvasive HFOV. The development in technologies of HFOV will be beneficial to the patients with respiratory diseases who failed with conventional mechanical ventilation as one of considerable ventilation methods.

Nitric Oxide Releasing Hydrogel Nanoparticles Decreases Epithelial Cell Injuries Associated With Airway Reopening

Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung condition. It is characterized by disruption of gas exchange inside the alveoli, accumulation of protein edema, and an increase in lung stiffness. One major cause of ARDS is a lung infection, such as SARS-COV-2 infection. Lungs of ARDS patients need to be mechanically ventilated for airway reopening. Consequently, ventilation might damage delicate lung tissue leading to excess edema, known as ventilator-induced lung injury (VILI). Mortality of COVID-19 patients under VILI seems to be higher than non-COVID patients, necessitating effective preventative therapies. VILI occurs when small air bubbles form in the alveoli, injuring epithelial cells (EPC) due to shear stress. Nitric oxide (NO) inhalation was suggested as a therapy for ARDS, however, it was shown that it is not effective because of the extremely short half-life of NO. In this study, NO-releasing nanoparticles were produced and tested in an in vitro model, representing airways in the deep lung. Cellular injuries were quantified via fluorescent live/dead assay. Atomic force microscopy (AFM) was used to assess cell morphology. qRT-PCR was performed to assess the expression of inflammatory markers, specifically IL6 and CCL2. ELISA was performed to assess IL6 and confirm qRT-PCR results at the protein level. Finally, ROS levels were assessed in all groups. Here, we show that NO delivery via nanoparticles enhanced EPC survival and recovery, AFM measurements revealed that NO exposure affect cell morphology, while qRT-PCR demonstrated a significant downregulation in IL6 and CCL2 expression when treating the cells to NO both before and after shear exposure. ELISA results for IL6 confirmed qRT-PCR data. ROS experiment results support our findings from previous experiments. These findings demonstrate that NO-releasing nanoparticles can be used as an effective delivery approach of NO to deep lung to prevent/reduce ARDS associated inflammation and cell injuries. This information is particularly useful to treat severe ARDS due to COVID-19 infection. These nanoparticles will be useful when clinically administrated to COVID-19 patients to reduce the symptoms originating from lung distress.

High-frequency oscillatory ventilation as a rescue for severe asthma crisis in a child

Mechanical ventilation in the asthmatic child may be complicated by dynamic air trapping leading to hemodynamic compromise and cardiac arrest. High-frequency oscillatory ventilation is relatively contraindicated because it may cause hyperinflation compared to conventional mechanical ventilation. A 2-year-old girl (weight, 11 kg) with a history of asthma was admitted because of status asthmaticus. Despite treatment with intravenous methylprednisolone, continuous albuterol, terbutaline, aminophylline, and magnesium sulfate, she had persistent respiratory distress. She required endotracheal intubation and mechanical ventilation because of worsening respiratory fatigue and hypercarbia ((PCO₂), 96 mm Hg). Severe airflow obstruction persisted, and the hypercarbia worsened despite conventional mechanical ventilation (PCO₂ > 134 mm Hg). It was judged that the patient was at risk for dynamic air trapping leading to hemodynamic compromise and cardiac arrest. High-frequency oscillatory ventilation was started to overcome airflow obstruction, and a decrease in arterial PCO₂ to 87 mm Hg was observed within 2 h. High-frequency oscillatory ventilation was discontinued after 5 h, and conventional mechanical ventilation resumed. The patient was extubated after 5 days without further complications. In summary, this case shows that high-frequency oscillatory ventilation may be considered as a rescue treatment in children who have severe status asthmaticus with persistent airflow obstruction and hypercarbia unresponsive to pharmacological therapy and conventional mechanical ventilation.

Compressive Neuropathy of the Facial Nerve Presenting as Bell's Palsy in a Pediatric Patient on High-Frequency Oscillatory Ventilation

A three-year eight-month-old female with Werdnig Hoffman disease presented with an acute onset of respiratory failure secondary to influenza infection. The patient required conventional mechanical ventilation (CMV). Due to worsening hypoxemia on maximal support, high-frequency oscillatory ventilation (HFOV) was initiated. On recovery from her respiratory failure, she was noted to have developed a left-sided Bell's palsy. A pressure ulcer in the left mastoid area through which the facial nerve transverses was noted, with no evidence of mastoiditis. The patient fully recovered after a course of oral steroid therapy. We postulate that compression pressure might have contributed to the palsy. However, it is unclear what role the acute viral illness played in this case.

AVATREE: An open-source computational modelling framework modelling Anatomically Valid Airway TREE conformations

This paper presents AVATREE, a computational modelling framework that generates Anatomically Valid Airway tree conformations and provides capabilities for simulation of broncho-constriction apparent in obstructive pulmonary conditions. Such conformations are obtained from the personalized 3D geometry generated from computed tomography (CT) data through image segmentation. The patient-specific representation of the bronchial tree structure is extended beyond the visible airway generation depth using a knowledge-based technique built from morphometric studies. Additional functionalities of AVATREE include visualization of spatial probability maps for the airway generations projected on the CT imaging data, and visualization of the airway tree based on local structure properties. Furthermore, the proposed toolbox supports the simulation of broncho-constriction apparent in pulmonary diseases, such as chronic obstructive pulmonary disease (COPD) and asthma. AVATREE is provided as an open-source toolbox in C++ and is supported by a graphical user interface integrating the modelling functionalities. It can be exploited in studies of gas flow, gas mixing, ventilation patterns and particle deposition in the pulmonary system, with the aim to improve clinical decision making.