Bench-to-bedside review: high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

Challenges in ARDS Definition, Management, and Identification of Effective Personalized Therapies

Over the last decade, the management of acute respiratory distress syndrome (ARDS) has made considerable progress both regarding supportive and pharmacologic therapies. Lung protective mechanical ventilation is the cornerstone of ARDS management. Current recommendations on mechanical ventilation in ARDS include the use of low tidal volume (VT) 4-6 mL/kg of predicted body weight, plateau pressure (PPLAT) < 30 cmH2O, and driving pressure (∆P) < 14 cmH2O. Moreover, positive end-expiratory pressure should be individualized. Recently, variables such as mechanical power and transpulmonary pressure seem promising for limiting ventilator-induced lung injury and optimizing ventilator settings. Rescue therapies such as recruitment maneuvers, vasodilators, prone positioning, extracorporeal membrane oxygenation, and extracorporeal carbon dioxide removal have been considered for patients with severe ARDS. Regarding pharmacotherapies, despite more than 50 years of research, no effective treatment has yet been found. However, the identification of ARDS sub-phenotypes has revealed that some pharmacologic therapies that have failed to provide benefits when considering all patients with ARDS can show beneficial effects when these patients were stratified into specific sub-populations; for example, those with hyperinflammation/hypoinflammation. The aim of this narrative review is to provide an overview on current advances in the management of ARDS from mechanical ventilation to pharmacological treatments, including personalized therapy.

High-frequency oscillatory ventilation guided by transpulmonary pressure in acute respiratory syndrome: an experimental study in pigs

BACKGROUND

Recent clinical studies have not shown an overall benefit of high-frequency oscillatory ventilation (HFOV), possibly due to injurious or non-individualized HFOV settings. We compared conventional HFOV (HFOV_con) settings with HFOV settings based on mean transpulmonary pressures (P_Lmean) in an animal model of experimental acute respiratory distress syndrome (ARDS).

METHODS

ARDS was induced in eight pigs by intrabronchial installation of hydrochloric acid (0.1 N, pH 1.1; 2.5 ml/kg body weight). The animals were initially ventilated in volume-controlled mode with low tidal volumes (6 ml kg^- 1) at three positive end-expiratory pressure (PEEP) levels (5, 10, 20 cmH₂O) followed by HFOV_con and then HFOV P_Lmean each at PEEP 10 and 20. The continuous distending pressure (CDP) during HFOV_con was set at mean airway pressure plus 5 cmH₂O. For HFOV P_Lmean it was set at mean P_L plus 5 cmH₂O. Baseline measurements were obtained before and after induction of ARDS under volume controlled ventilation with PEEP 5. The same measurements and computer tomography of the thorax were then performed under all ventilatory regimens at PEEP 10 and 20.

RESULTS

Cardiac output, stroke volume, mean arterial pressure and intrathoracic blood volume index were significantly higher during HFOV P_Lmean than during HFOV_con at PEEP 20. Lung density, total lung volume, and normally and poorly aerated lung areas were significantly greater during HFOV_con, while there was less over-aerated lung tissue in HFOV P_Lmean. The groups did not differ in oxygenation or extravascular lung water index.

CONCLUSION

HFOV P_Lmean is associated with less hemodynamic compromise and less pulmonary overdistension than HFOV_con. Despite the increase in non-ventilated lung areas, oxygenation improved with both regimens. An individualized approach with HFOV settings based on transpulmonary pressure could be a useful ventilatory strategy in patients with ARDS. Providing alveolar stabilization with HFOV while avoiding harmful distending pressures and pulmonary overdistension might be a key in the context of ventilator-induced lung injury.

A noninvasive high frequency oscillation ventilator: Achieved by utilizing a blower and a valve

After the High Frequency Oscillatory Ventilation (HFOV) has been applied in the invasive ventilator, the new technique of noninvasive High Frequency Oscillatory Ventilation (nHFOV) which does not require opening the patient's airway has attracted much attention from the field. This paper proposes the design of an experimental positive pressure-controlled nHFOV ventilator which utilizes a blower and a special valve and has three ventilation modes: spontaneous controlled ventilation combining HFOV, time-cycled ventilation combining HFOV (T-HFOV), and continuous positive airway pressure ventilation combining HFOV. Experiments on respiratory model are conducted and demonstrated the feasibility of using nHFOV through the control of fan and valve. The experimental ventilator is able to produce an air flow with small tidal volume (VT) and a large minute ventilation volume (MV) using regular breath tubes and nasal mask (e.g., under T-HFOV mode, with a maximum tidal volume of 100 ml, the minute ventilation volume reached 14,400 ml). In the process of transmission, there is only a minor loss of oscillation pressure. (Under experimental condition and with an oscillation frequency of 2-10 Hz, peak pressure loss was around 0%-50% when it reaches the mask.).

Adenovirus pneumonia complicated with acute respiratory distress syndrome: a case report

Severe adenovirus infection in children can manifest with acute respiratory distress syndrome (ARDS) and respiratory failure, leading to the need for prolonged mechanical support in the form of either mechanical ventilation or extracorporeal life support. Early extracorporeal membrane oxygenation (ECMO) intervention for children with ARDS should be considered if selection criteria fulfill.We report on a 9-month-old boy who had adenovirus pneumonia with rapid progression to ARDS. Real-time polymerase chain reaction tests of sputum and pleural effusion samples confirmed adenovirus serotype 7. Chest x-rays showed progressively increasing infiltrations and pleural effusions in both lung fields within 11 days. Because conventional ARDS therapies failed, we initiated ECMO with high-frequency oscillatory ventilation (HFOV) for 9 days. Chest x-rays showed gradual improvements in lung expansion.This patient was subsequently discharged after a hospital stay of 38 days. Post-ECMO and adenovirus sequelae were followed in our outpatient department.Adenovirus pneumonia in children can manifest with severe pulmonary morbidity and respiratory failure. The unique lung recruitment by HFOV can be a useful therapeutic option for severe ARDS patients when combined with sufficient lung rest provided by ECMO.

OSCILLATORY FLOW OF HFV DISTRIBUTED IN LEFT AND RIGHT LUNGS: A MODEL-BASED EXPERIMENT AND INVESTIGATION

The human respiratory system is not entirely symmetric, and regional respiratory diseases can further enlarge this difference in most cases. Therefore, the lungs perform differently. This paper explored the possibilities of suppressing and enhancing the performance of a diseased lung with different high-frequency ventilation (HFV) frequencies by experimenting, as well as modeling, the oscillatory airflow distribution between the left and right lungs. The experimental setup mainly consisted of a physical respiratory model, a signal acquisition device, and a high-frequency oscillation ventilator. This ventilator outputs a positive sinusoidal air-pressure during inspiration. On these bases, a series of experiments were also conducted with different compliances and resistances in the left and the right lungs. The experiments demonstrated that the oscillatory flow distribution is primarily correlated with the oscillation frequency and the regional lung compliance.

Deviation of tracheal pressure from airway opening pressure during high-frequency oscillatory ventilation in a porcine lung model

Oxygenation during high-frequency oscillatory ventilation is secured by a high level of mean airway pressure. Our objective was to identify a pressure difference between the airway opening of the respiratory circuit and the trachea during application of different oscillatory frequencies. Six female Pietrain pigs (57.1 ± 3.6 kg) were first ventilated in a conventional mechanical ventilation mode. Subsequently, the animals were switched to high-frequency oscillatory ventilation by setting mean airway opening pressure 5 cmH(2)O above the one measured during controlled mechanical ventilation. Measurements at the airway opening and at tracheal levels were performed in healthy lungs and after induction of acute lung injury by surfactant depletion. During high-frequency oscillatory ventilation, the airway opening pressure was set at a constant level. The pressure amplitude was fixed at 90 cmH(2)O. Starting from an oscillatory frequency of 3 Hz, the frequency was increased in steps of 3 Hz to 15 Hz and then decreased accordingly. At each frequency, measurements were performed in the trachea through a side-lumen of the endotracheal tube and the airway opening pressure was recorded. The pressure difference was calculated. At every oscillatory frequency, a pressure loss towards the trachea could be shown. This pressure difference increased with higher oscillatory frequencies (3 Hz 2.2 ± 2.1 cmH(2)O vs. 15 Hz 7.5 ± 1.8 cmH(2)O). The results for healthy and injured lungs were similar. Tracheal pressures decreased with higher oscillatory frequencies. This may lead to pulmonary derecruitment. This has to be taken into consideration when increasing oscillatory frequencies and differentiated pressure settings are mandatory.

Right ventricular function during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

OBJECTIVE

To evaluate the effect of mean airway pressure under high-frequency oscillatory ventilation on right ventricular function.

DESIGN

Prospective randomized study.

SETTING

Intensive care unit of a tertiary care hospital.

PATIENTS

Sixteen consecutive patients within the first 48 hrs of mainly pulmonary acute respiratory distress syndrome.

INTERVENTIONS

After a 6-hr-period of protective conventional mechanical ventilation, patients were submitted to three 1-hr periods of high-frequency oscillatory ventilation (+5, +10, +15) in a randomized order, with a mean airway pressure level determined by adding 5, 10, or 15 cm H2O to the mean airway pressure recorded during conventional mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Mean airway pressure was 18±3 cm H2O during conventional mechanical ventilation and was increased until 33±3 cm H2O at high-frequency oscillatory ventilation+15. Right ventricular function was assessed using transesophageal echocardiography. During conventional mechanical ventilation, nine patients presented a right ventricular dysfunction (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.6) of whom four patients had a right ventricular failure (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.9). High-frequency oscillatory ventilation+10 and +15 further worsened right ventricular function, resulting in about a 40% increase in right ventricular end-diastolic area/left ventricular end-diastolic area ratio and a 30% increase in end-diastolic eccentricity index when compared with conventional mechanical ventilation or high-frequency oscillatory ventilation+5 periods. At high-frequency oscillatory ventilation+15, 15 patients had right ventricular dysfunction and nine had right ventricular failure. High-frequency oscillatory ventilation did not improve oxygenation whatever the mean airway pressure level. A significant redistribution of tidal variation to the posterior parts of the lung was observed on electrical impedance tomography measurements when increasing mean airway pressure. However, this redistribution was not observed in patients who presented a worsening of right ventricular function (right ventricular end-diastolic area/left ventricular end-diastolic area increase>40%) at high-frequency oscillatory ventilation+15.

CONCLUSIONS

In patients with mainly pulmonary acute respiratory distress syndrome, using high mean airway pressure under high-frequency oscillatory ventilation can worsen right ventricular function when compared with protective conventional mechanical ventilation, notably in patients in whom high-frequency oscillatory ventilation produced less alveolar recruitment of the posterior parts of the lungs. This study highlights the interest of monitoring right ventricular function during high-frequency oscillatory ventilation.

The role of high-frequency oscillatory ventilation in the treatment of acute respiratory failure in adults

PURPOSE OF REVIEW

High-frequency oscillatory ventilation (HFOV) is increasingly used in adults with the acute respiratory distress syndrome (ARDS), who remain hypoxemic during conventional mechanical ventilation. In this review, we will summarize the trials evaluating HFOV in adults with ARDS and discuss issues relevant to the clinician regarding the use of HFOV.

RECENT FINDINGS

Several observational and randomized trials support the safety of HFOV and improvements in oxygenation in adult patients with severe ARDS, who remain hypoxemic during conventional mechanical ventilation.

SUMMARY

HFOV theoretically meets the goals of lung-protective ventilation. On the basis of the current evidence, HFOV is associated with improvements in oxygenation in severe, adult ARDS. However, whether HFOV influences mortality, length of ICU stay, ventilator-free days, quality-of-life factors and is cost-effective remains to be determined. Large, prospective, randomized controlled trials such as the ongoing OSCAR and OSCILLATE trials will help further define the role of HFOV in adult ARDS.

Acute lung failure

Lung failure is the most common organ failure seen in the intensive care unit. The pathogenesis of acute respiratory failure (ARF) can be classified as (1) neuromuscular in origin, (2) secondary to acute and chronic obstructive airway diseases, (3) alveolar processes such as cardiogenic and noncardiogenic pulmonary edema and pneumonia, and (4) vascular diseases such as acute or chronic pulmonary embolism. This article reviews the more common causes of ARF from each group, including the pathological mechanisms and the principles of critical care management, focusing on the supportive, specific, and adjunctive therapies for each condition.

H1N1-associated acute respiratory distress syndrome

The worldwide 2009-2010 pandemic of novel H1N1 influenza reminds us that influenza can still be a lethal disease. Acute lung injury and acute respiratory distress syndrome (ARDS) have been the most devastating complications of this pathogen. We present a case of a previously healthy 40-year-old obese man who succumbed to H1N1-associated ARDS. In this focused review, we discuss the pathophysiologic peculiarities and management of acute lung injury/ARDS related to H1N1 infection.

Comparison of "open lung" modes with low tidal volumes in a porcine lung injury model

BACKGROUND

Ventilator strategies that maintain an "open lung" have shown promise in treating hypoxemic patients. We compared three "open lung" strategies with standard of care low tidal volume ventilation and hypothesized that each would diminish physiologic and histopathologic evidence of ventilator induced lung injury (VILI).

MATERIALS AND METHODS

Acute lung injury (ALI) was induced in 22 pigs via 5% Tween and 30-min of injurious ventilation. Animals were separated into four groups: (1) low tidal volume ventilation (LowVt -6 mL/kg); (2) high-frequency oscillatory ventilation (HFOV); (3) airway pressure release ventilation (APRV); or (4) recruitment and decremental positive-end expiratory pressure (PEEP) titration (RM+OP) and followed for 6 h. Lung and hemodynamic function was assessed on the half-hour. Bronchoalveolar lavage fluid (BALF) was analyzed for cytokines. Lung tissue was harvested for histologic analysis.

RESULTS

APRV and HFOV increased PaO(2)/FiO(2) ratio and improved ventilation. APRV reduced BALF TNF-α and IL-8. HFOV caused an increase in airway hemorrhage. RM+OP decreased SvO(2), increased PaCO(2), with increased inflammation of lung tissue.

CONCLUSION

None of the "open lung" techniques were definitively superior to LowVt with respect to VILI; however, APRV oxygenated and ventilated more effectively and reduced cytokine concentration compared with LowVt with nearly indistinguishable histopathology. These data suggest that APRV may be of potential benefit to critically ill patients but other "open lung" strategies may exacerbate injury.

Combination of high frequency oscillatory ventilation and interventional lung assist in severe acute respiratory distress syndrome

BACKGROUND

The combination of high-frequency oscillatory ventilation (HFOV) and extracorporeal carbon dioxide removal with the interventional lung assist (iLA) in severe acute respiratory distress syndrome (ARDS) represents a novel treatment option.

METHODS

The study used a retrospective single-center analysis of 21 consecutive adult patients with severe ARDS, ventilated with HFOV/iLA. Efficiency, side effects, and outcome of combined treatment are presented as median (interquartile range).

MEASUREMENTS AND MAIN RESULTS

The following were used to determine patient characteristics: sequential organ failure assessment score, 14; simplified acute physiology score II, 41; and Murray score, 4. The duration of combined treatment was 6 days. The blood flow through the iLA was 1.9 L/min. The Pao(2)/inspired fraction of oxygen ratio increased from 61 (47-86) to 98 (67-116) within 2 hours and to 106 (70-135) mm Hg at 24 hours. Paco(2) decreased from 58 (50-76) to 37 (29-47) mm Hg at 2 hours with normalization of pH 7.28 (7.16-7.36) to 7.43 (7.33-7.49) after 2 hours associated with hemodynamic stabilization. In 6 patients, complications due to iLA treatment were observed, and in 3 patients, complications associated with HFOV were seen. Weaning from HFOV/iLA was successful in 10 patients. The 30-day mortality rate was 43%, and hospital mortality rate was 57%.

CONCLUSION

The combination of HFOV/iLA is an option in severe pulmonary failure if conventional ventilation fails and pumpdriven extracorporeal membrane oxygenation therapy is not available.

Loss of airway pressure during HFOV results in an extended loss of oxygenation: a retrospective animal study

BACKGROUND

Patients with acute respiratory distress syndrome (ARDS) are often ventilated with high airway pressure. Brief loss of airway pressure may lead to an extended loss of oxygenation. While using high frequency oscillatory ventilation (HFOV) in a porcine acute lung injury model, two animals became disconnected from the ventilator with subsequent loss of airway pressure. We compared the two disconnected animals to the two animals that remained connected to determine causes for the extended reduction in oxygenation.

METHODS

ARDS was induced using 5% Tween. Thirty min of nonprotective ventilation (NPV) followed before placing the pigs on HFOV. Measurements were made at baseline, after lung injury, and every 30min during the 6-h study. Disconnections were treated by hand-ventilation and a recruitment maneuver before being placed back on HFOV. The lungs were histologically analyzed and wet/dry weights were measured to determine lung edema.

RESULTS

Hemodynamics and lung function were similar in all pigs at baseline, after injury, and following NPV. The animals that remained connected to the oscillator showed a continued improvement in PaO(2)/FiO(2) (P/F) ratio throughout the study. The animals that experienced the disconnection had a significant loss of lung function that never recovered. The disconnect animals had more diffuse alveolar disease on histologic analysis.

CONCLUSIONS

A significant fall in lung function results following disconnection from HFOV, which remains depressed for a substantial period of time despite efforts to reopen the lung. Dispersion of edema fluid is a possible mechanism for the protracted loss of lung function.

Arteriovenous Extracorporeal Lung Assist Allows For Maximization Of Oscillatory Frequencies: A Large-animal Model Of Respiratory Distress

Background

Although the minimization of the applied tidal volume (VT) during high-frequency oscillatory ventilation (HFOV) reduces the risk of alveolar shear stress, it can also result in insufficient CO₂-elimination with severe respiratory acidosis. We hypothesized that in a model of acute respiratory distress (ARDS) the application of high oscillatory frequencies requires the combination of HFOV with arteriovenous extracorporeal lung assist (av-ECLA) in order to maintain or reestablish normocapnia.

Methods

After induction of ARDS in eight female pigs (56.5 ± 4.4 kg), a recruitment manoeuvre was performed and intratracheal mean airway pressure (mPaw) was adjusted 3 cmH₂O above the lower inflection point (Plow) of the pressure-volume curve. All animals were ventilated with oscillatory frequencies ranging from 3–15 Hz. The pressure amplitude was fixed at 60 cmH₂O. At each frequency gas exchange and hemodynamic measurements were obtained with a clamped and de-clamped av-ECLA. Whenever the av-ECLA was de-clamped, the oxygen sweep gas flow through the membrane lung was adjusted aiming at normocapnia.

Results

Lung recruitment and adjustment of the mPaw above Plow resulted in a significant improvement of oxygenation (p < 0.05). Compared to lung injury, oxygenation remained significantly improved with rising frequencies (p < 0.05). Normocapnia during HFOV was only maintained with the addition of av-ECLA during frequencies of 9 Hz and above.

Conclusion

In this animal model of ARDS, maximization of oscillatory frequencies with subsequent minimization of VT leads to hypercapnia that can only be reversed by adding av-ECLA. When combined with a recruitment strategy, these high frequencies do not impair oxygenation

Protective ventilation in ARDS: as soon as possible. An immediate use of HFOV

Objective

To report the immediate use of High-Frequency Oscillatory ventilation in an adult acute respiratory distress syndrome.

Design

Case report.

Setting

Intensive care unit at the Military Teaching Hospital of Toulon.

Patient

A 64-yr-old Caucasian male who developed acute respiratory distress syndrome in the course of severe falciparum malaria.

Intervention

Initial use of HFO to minimise ventilator-induced lung injury.

Measurement and Main Results

Rapid improvement of PaO2/fraction of inspired oxygen from 172 mmHg (NIV) to 310 mmHg with HFO. No ventilator-induced injury on CT scan after 5 days of invasive ventilation.

Conclusion

In contrast with previous studies, we successfully used lung protective ventilation with HFO immediately. Further studies, with immediate, rather than rescue use of HFO ventilation, are needed.

High-frequency oscillatory ventilation reduces lung inflammation: a large-animal 24-h model of respiratory distress

OBJECTIVE

High-frequency oscillatory ventilation (HFOV) may reduce ventilator-induced lung injury in experimental neonatal respiratory distress. However, these data permit no conclusions for large animals or adult patients with acute respiratory distress syndrome (ARDS), because in neonates higher frequencies and lower amplitudes can be used, resulting in lower tidal volumes (VT) and airway pressures. The aim of this study was to compare gas exchange, lung histopathology and inflammatory cytokine expression during lung-protective pressure-controlled ventilation (PCV) and HFOV in a long-term large-animal model of ARDS.

DESIGN

Prospective, randomized, controlled pilot study.

SETTING

University animal laboratory.

SUBJECTS

Sixteen female pigs (55.3 +/- 3.9 kg).

INTERVENTIONS

After induction of ARDS by repeated lavage, the animals were randomly assigned to PCV (VT = 6 ml/kg) and HFOV (6 Hz). After lung injury, a standardised lung recruitment was performed in both groups, and ventilation was continued for 24 h.

MEASUREMENTS AND RESULTS

After lung recruitment sustained improvements in the oxygenation index were observed in both groups. The mean airway pressure (mPaw) was significantly lower in the HFOV group during the experiment (p < 0.01). Histologically, lung inflammation was significantly ameliorated in the HFOV group (p < 0.05). The messenger RNA expression of IL-1-beta in lung tissue was significantly lower in the HFOV-treated animals (p < 0.01).

CONCLUSIONS

These data suggest that HFOV compared with conventional lung-protective ventilation can reduce lung inflammation in a large-animal 24-h model of ARDS. Furthermore, it was shown that lung recruitment leads to sustained improvements in gas exchange with a significantly lower mPaw when HFOV is used.