Physiological predictors of survival during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

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.

Outcomes of Severe PARDS on High-Frequency Oscillatory Ventilation - A Single Centre Experience

OBJECTIVE

To describe experience with high-frequency oscillatory ventilation (HFOV) in children with acute respiratory distress syndrome (ARDS) transitioned from conventional mechanical ventilation (CMV) due to refractory hypoxemia and to assess factors associated with survival and also compare outcomes of patients who were managed with early HFOV (within 24 h of intubation) vs. late HFOV.

METHODS

This retrospective, observational study was conducted in a tertiary care hospital's pediatric intensive care unit. Thirty-four children with pediatric acute respiratory distress syndrome (PARDS) managed with HFOV were included.

RESULTS

Of 34 children with PARDS managed with HFOV after failure of conventional ventilation to improve oxygenation, 8 survived. Improvement in the Oxygenation Index (OI) at 48 h of initiation of HFOV along with percent increase in PaO₂/FiO₂ (P/F ratio) at 24 h of HFOV were predictors of survival. The response to HFOV, based on OI and P/F ratio, between 24 and 48 h of ventilation identified potential survivors. Also, lower positive end-expiratory pressure (PEEP) on CMV and shorter duration of CMV before initiation of HFOV were associated with survival.

CONCLUSIONS

Survival in pediatric ARDS patients treated with HFOV could be predicted by using trends of OI - with survivors showing a more rapid decline in OI between 24 and 48 h of initiation compared to non-survivors.

Formal guidelines: management of acute respiratory distress syndrome

Fifteen recommendations and a therapeutic algorithm regarding the management of acute respiratory distress syndrome (ARDS) at the early phase in adults are proposed. The Grade of Recommendation Assessment, Development and Evaluation (GRADE) methodology has been followed. Four recommendations (low tidal volume, plateau pressure limitation, no oscillatory ventilation, and prone position) had a high level of proof (GRADE 1 + or 1 -); four (high positive end-expiratory pressure [PEEP] in moderate and severe ARDS, muscle relaxants, recruitment maneuvers, and venovenous extracorporeal membrane oxygenation [ECMO]) a low level of proof (GRADE 2 + or 2 -); seven (surveillance, tidal volume for non ARDS mechanically ventilated patients, tidal volume limitation in the presence of low plateau pressure, PEEP > 5 cmH2O, high PEEP in the absence of deleterious effect, pressure mode allowing spontaneous ventilation after the acute phase, and nitric oxide) corresponded to a level of proof that did not allow use of the GRADE classification and were expert opinions. Lastly, for three aspects of ARDS management (driving pressure, early spontaneous ventilation, and extracorporeal carbon dioxide removal), the experts concluded that no sound recommendation was possible given current knowledge. The recommendations and the therapeutic algorithm were approved by the experts with strong agreement.

Formal guidelines: management of acute respiratory distress syndrome

Fifteen recommendations and a therapeutic algorithm regarding the management of acute respiratory distress syndrome (ARDS) at the early phase in adults are proposed. The Grade of Recommendation Assessment, Development and Evaluation (GRADE) methodology has been followed. Four recommendations (low tidal volume, plateau pressure limitation, no oscillatory ventilation, and prone position) had a high level of proof (GRADE 1 + or 1 −); four (high positive end-expiratory pressure [PEEP] in moderate and severe ARDS, muscle relaxants, recruitment maneuvers, and venovenous extracorporeal membrane oxygenation [ECMO]) a low level of proof (GRADE 2 + or 2 −); seven (surveillance, tidal volume for non ARDS mechanically ventilated patients, tidal volume limitation in the presence of low plateau pressure, PEEP > 5 cmH2O, high PEEP in the absence of deleterious effect, pressure mode allowing spontaneous ventilation after the acute phase, and nitric oxide) corresponded to a level of proof that did not allow use of the GRADE classification and were expert opinions. Lastly, for three aspects of ARDS management (driving pressure, early spontaneous ventilation, and extracorporeal carbon dioxide removal), the experts concluded that no sound recommendation was possible given current knowledge. The recommendations and the therapeutic algorithm were approved by the experts with strong agreement.

High-frequency oscillatory ventilation: still a role?

PURPOSE OF REVIEW

In light of emerging data from clinical trials, the place of high-frequency oscillatory ventilation (HFOV) in the management of acute respiratory distress syndrome (ARDS) is uncertain. This review provides an overview of these new clinical data and also explores new areas of investigation for HFOV in adults.

RECENT FINDINGS

While prior meta-analyses suggested benefit for HFOV, updated systematic reviews published this year, which include two large recent clinical trials, now show no statistically significant impact of HFOV on mortality in adults with ARDS. It is possible that HFOV would be safer and more effective with a more individualized approach to setting mean airway pressure (mPaw). Possible techniques to achieve this include titrating mPaw in response to oxygenation or hemodynamic changes after HFOV initiation, by measuring respiratory system impedance, or by following echocardiographic changes.

SUMMARY

Although not first-line, HFOV remains a tool in the armamentarium of the intensivist managing the patient with severe ARDS and refractory hypoxemia. A refinement in the approach to delivering HFOV is warranted, with more attention paid to its adverse hemodynamic consequences.

High-Frequency Oscillatory Ventilation in Adults With ARDS: Past, Present, and Future

High-frequency oscillatory ventilation (HFOV) is a unique mode of mechanical ventilation that uses nonconventional gas exchange mechanisms to deliver ventilation at very low tidal volumes and high frequencies. The properties of HFOV make it a potentially ideal mode to prevent ventilator-induced lung injury in patients with ARDS. Despite a compelling physiological basis and promising experimental data, large randomized controlled trials have not detected an improvement in survival with the use of HFOV, and its use as an early lung-protective strategy in patients with ARDS may be harmful. Nevertheless, HFOV still has an important potential role in the management of refractory hypoxemia. Careful attention should be paid to right ventricular function and lung stress when applying HFOV. This review discusses the physiological principles, clinical evidence, practical applications, and future prospects for the use of HFOV in patients with ARDS.

High-frequency oscillatory ventilation is an effective treatment for severe pediatric acute respiratory distress syndrome with refractory hypoxemia

Background and purpose

Early or primary application of high-frequency oscillatory ventilation (HFOV) has been recently suggested not to offer benefit to patients with acute respiratory distress syndrome (ARDS). However, the rescue effects of HFOV on severe pediatric acute respiratory distress syndrome (PARDS) with hypoxemia refractory to conventional mechanical ventilation (CMV) remain unclear. This study aimed to determine whether severe PARDS children would benefit from HFOV when oxygenation deteriorated on CMV and to identify any potential risk factors related to mortality.

Patients and methods

In a retrospective and observational study, 48 children with severe PARDS between January 2009 and July 2015 were divided into two groups: 26 in HFOV group and 22 in CMV group. Data regarding demographic, underlying conditions, arterial blood gases and clinical outcomes were collected and analyzed.

Results

The arterial partial pressure of oxygen (PaO₂)/fraction of inspiration oxygen (FiO₂) ratio and PaO₂ improved significantly during HFOV, whereas arterial partial pressure of carbon dioxide (PaCO₂) and oxygenation index decreased. There was no statistical difference in the in-hospital mortality between the groups (P=0.367). The odds ratio of survival in HFOV group was 2.74 (95% confidence interval 0.52 to 14.58, P=0.237). The pediatric intensive care unit length of stay and total ventilation duration were longer in HFOV group (P=0.048 and P=0.000, respectively). Vasoactive agents were used more frequently in HFOV group (P=0.007). The incidence of new air leak was similar between the two groups (P=0.674). The presence of multiple organ dysfunction syndrome and heavier body weight were identified as predictors of mortality in the HFOV group (P=0.006 and P=0.020, respectively).

Conclusion

HFOV as an efficient alternative therapy could significantly improve hypoxemia and promote CO₂ removal in severe PARDS children when oxygenation progressively worsens on CMV.

Airway Pressure Release Ventilation and High-Frequency Oscillatory Ventilation: Potential Strategies to Treat Severe Hypoxemia and Prevent Ventilator-Induced Lung Injury

Although lifesaving, mechanical ventilation can itself be responsible for damage to lung parenchyma. This ventilator-induced lung injury is especially observed in already injured lungs of patients with ARDS. New ventilatory approaches are needed to safely treat patients with ARDS, and recent studies have suggested the potential utility of open-lung strategies. Airway pressure release ventilation (APRV) and high-frequency oscillatory ventilation (HFOV) are 2 different open-lung strategies that have been proposed to treat refractory hypoxemic respiratory failure while preventing ventilator-induced lung injury. APRV provides increased airway pressure as a potential recruitment mechanism and allows spontaneous breathing, with the potential benefits of decreased sedation, shorter duration of mechanical ventilation, and improvement in cardiac performance. HFOV delivers very small tidal volumes, to prevent volutrauma, at a constant (relatively high) mean airway pressure, thus avoiding atelectrauma. Despite their theoretical benefits, the utility of APRV and HFOV remains unproven and controversial for the routine treatment of ARDS in adult patients. This review is focused on the theoretical and practical aspects of APRV and HFOV, provides an overview of the current evidence, and addresses their possible use in the treatment of ARDS.

Right over left ventricular end-diastolic area relevance to predict hemodynamic intolerance of high-frequency oscillatory ventilation in patients with severe ARDS

Background

High-frequency oscillatory ventilation (HFOV) does not improve the prognosis of ARDS patients despite an improvement in oxygenation. This paradox may partly be explained by HFOV hemodynamic side-effects on right ventricular function. Our goal was to study the link between HFOV and hemodynamic effects and to test if the pre-HFOV right over left ventricular end-diastolic area (RVEDA/LVEDA) ratio, as a simple parameter of afterload-related RV dysfunction, could be used to predict HFOV hemodynamic intolerance in patients with severe ARDS.

Methods

Twenty-four patients were studied just before and within 3 h of HFOV using transthoracic echocardiography and transpulmonary thermodilution.

Results

Before HFOV, the mean PaO₂/FiO₂ ratio was 89 ± 23. The number of patients with a RVEDA/LVEDA ratio >0.6 significantly increased after HFOV [11 (46 %) vs. 17 (71 %)]. Although HFOV did not significantly decrease the arterial pressure (systolic, diastolic, mean and pulse pressure), it significantly decreased the cardiac index (CI) by 13 ± 18 % and significantly increased the RVEDA/LVEDA ratio by 14 ± 11 %. A significant correlation was observed between pre-HFOV RVEDA/LVEDA ratio and CI diminution after HFOV (r = 0.78; p < 0.0001). A RVEDA/LVEDA ratio superior to 0.6 resulted in a CI decrease >15 % during HFOV with a sensitivity of 80 % (95 % confidence interval 44–98 %) and a specificity of 79 % (confidence interval 49–95 %).

Conclusion

The RVEDA/LVEDA ratio measured just before HFOV predicts the hemodynamic intolerance of this technique in patients with severe ARDS. A high ratio under CMV raises questions about the use of HFOV in such patients.

Trial registration: ClinicalTrials.gov: NCT01167621

Factors Associated with Survival during High-Frequency Oscillatory Ventilation in Children

Our aim is to determine indicators of survival in children with severe hypoxic respiratory failure (HRF) after transition to high-frequency oscillatory ventilation (HFOV). Single-center retrospective examination of children with HRF transitioned to HFOV. Blood gases and ventilator settings 24 hours prior to and 48 hours after HFOV in survivors and nonsurvivors were evaluated. Sixty-two children with mean age of 7 years and mean weight of 26 kg were included with an observed mortality of 29%. Mean airway pressures (Paw), oxygenation index (OI), arterial oxygen partial pressure (PaO₂)/fraction of inspired oxygen (FiO₂) (P/F) ratio, pH, bicarbonate, and arterial carbon dioxide partial pressure were similar prior to HFOV in survivors and nonsurvivors. During HFOV, mean OI and P/F ratio improved in both groups with an average Paw increase of ∼10 cm H₂O. Survivors had lower OI than nonsurvivors (21 ± 0.9 vs. 26.5 ± 2.2; p < 0.01) beginning 24 hours after HFOV. P/F ratio appears to diverge by 36 hours, with survivors having P/F ratio >200. Survivors had higher pH than nonsurvivors at 36 hours (7.40 ± 0.01 vs. 7.32 ± 0.02; p < 0.05), higher bicarbonate levels (27.1 ± 0.7 vs. 23.9 ± 1.3 mEq/L), and similar arterial carbon dioxide partial pressure with less oscillatory support (i.e., hertz and amplitude). Inhaled nitric oxide was used in 53% of patients with improvements in oxygenation but with no effect on mortality. HFOV improves oxygenation in children with severe HRF. Nonsurvivors can be distinguished from survivors at 24 to 36 hours during HFOV by higher OI, metabolic acidosis, and higher oscillatory support. These data may assist in prognostication or timing of initiating alternative therapies, such as extracorporeal membrane oxygenation.

Prognostic factors in the acute respiratory distress syndrome

Despite improvements in critical care, acute respiratory distress syndrome (ARDS) remains a devastating clinical problem with high rates of morbidity and mortality. A better understanding of the prognostic factors associated with ARDS is crucial for facilitating risk stratification and developing new therapeutic interventions that aim to improve clinical outcomes. In this article, we present an up-to-date summary of factors that predict mortality in ARDS in four categories: (1) clinical characteristics; (2) physiological parameters and oxygenation; (3) genetic polymorphisms and biomarkers; and (4) scoring systems. In addition, we discuss how a better understanding of clinical and basic pathogenic mechanisms can help to inform prognostication, decision-making, risk stratification, treatment selection, and improve study design for clinical trials.

High-frequency oscillation ventilation for hypercapnic failure of conventional ventilation in pulmonary acute respiratory distress syndrome

Introduction

High-frequency oscillation ventilation (HFOV) is regarded as particularly lung protective. Recently, HFOV has been shown to be not beneficial for acute respiratory distress syndrome (ARDS) patients in general. Due to its special physical effects, it could be beneficial, however, in inhomogeneous ARDS. This study evaluates the effect of HFOV on PaCO₂ removal in hypercapnic patients with ARDS of pulmonary origin.

Methods

Between October 2010 and June 2014 patients with ARDS of pulmonary origin with PaO₂/FiO₂ ratio >60 mmHg, but respiratory acidosis (pH <7.26) under optimized protective ventilation were switched to HFOV, using moderate airway pressure (adopting the mean airway pressure of the prior ventilation). Data from these patients were analyzed retrospectively; PaCO₂ and pH before, 1 h and 24 h after the start of HFOV were compared.

Results

Twenty-six patients with PaO₂/FiO₂ ratio 139 ± 49 and respiratory acidosis (PaCO₂ 68 ± 12 mmHg) were put on HFOV after 17 ± 22 h of conventional ventilation. Mean airway pressure was 19 cm H₂O (15 to 28). PaCO₂ decreased significantly: after 1 hour the mean difference was −14 ± 10 mmHg; P <0.01 and after 24 hours −17 ± 12 mmHg; P <0.01; n = 24. CO₂ clearance improved in all but two patients; in those, extracorporeal lung support was initiated. Oxygenation remained unchanged after 1 h and slightly increased after 24 h. No complications related to HFOV were observed. Twenty-two patients improved and could be weaned from HFOV. Twenty patients (77%) were alive on day 30.

Conclusions

HFOV could be a useful alternative in patients with ARDS of pulmonary origin with hypercapnic failure of lung-protective conventional ventilation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0935-4) contains supplementary material, which is available to authorized users.

High-frequency oscillatory ventilation for early acute respiratory distress syndrome in adults

PURPOSE OF REVIEW

High-frequency oscillatory ventilation (HFOV) has been considered a potentially ideal mode of lung-protective ventilation. A recent meta-analysis suggested improved oxygenation and reduced mortality in adults and children with acute respiratory distress syndrome (ARDS), but the use of outdated control strategies and small numbers of patients in many of the studies rendered these findings hypothesis-generating only.

RECENT FINDINGS

During 2013, two large randomized controlled trials comparing HFOV with a conventional lung-protective ventilation were published - the Oscillation for Acute Respiratory Distress Syndrome Treated Early (OSCILLATE) and the Oscillation in ARDS (OSCAR) trials. These trials suggested no benefit or even harm with HFOV in adults with early moderate-to-severe ARDS. In this article, the major characteristics of these two studies and the possible reasons for failure to achieve the expected theoretical benefits are reviewed. Moreover, future directions with potential new technical advances and the use of new bedside monitoring techniques are addressed.

SUMMARY

The OSCILLATE and OSCAR trials showed that the early application of HFOV in moderate-to-severe adult ARDS does not reduce mortality compared with conventional ventilation strategies. Future studies on HFOV will need to identify those patients who might benefit most from HFOV and to determine the best oscillator settings. Both goals require an improved capability of monitoring recruitment and overdistension, and oscillatory volumes.

Year in review 2013: Critical Care--respirology

This review documents important progress made in 2013 in the field of critical care respirology, in particular with regard to acute respiratory failure and acute respiratory distress syndrome. Twenty-five original articles published in the respirology and critical care sections of Critical Care are discussed in the following categories: pre-clinical studies, protective lung ventilation – how low can we go, non-invasive ventilation for respiratory failure, diagnosis and prognosis in acute respiratory distress syndrome and respiratory failure, and promising interventions for acute respiratory distress syndrome.

Improved oxygenation 24 hours after transition to airway pressure release ventilation or high-frequency oscillatory ventilation accurately discriminates survival in immunocompromised pediatric patients with acute respiratory distress syndrome*

OBJECTIVES

Children with an immunocompromised condition and requiring invasive mechanical ventilation have high risk of death. Such patients are commonly transitioned to rescue modes of nonconventional ventilation, including airway pressure release ventilation and high-frequency oscillatory ventilation, for acute respiratory distress syndrome refractory to conventional ventilation. Our aim was to describe our experience with airway pressure release ventilation and high-frequency oscillatory ventilation in children with an immunocompromised condition and acute respiratory distress syndrome refractory to conventional ventilation and to identify factors associated with survival.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care, university-affiliated PICU.

PATIENTS

Sixty pediatric patients with an immunocompromised condition and acute respiratory distress syndrome refractory to conventional ventilation transitioned to either airway pressure release ventilation or high-frequency oscillatory ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Demographic data, ventilator settings, arterial blood gases, oxygenation index, and PaO(2)/FIO(2) were recorded before transition to either mode of nonconventional ventilation and at predetermined intervals after transition for up to 5 days. Mortality in the entire cohort was 63% and did not differ between patients transitioned to airway pressure release ventilation and high-frequency oscillatory ventilation. For both airway pressure release ventilation and high-frequency oscillatory ventilation, improvements in oxygenation index and PaO(2)/FIO(2) at 24 hours expressed as a fraction of pretransition values (oxygenation index(24)/oxygenation index(pre) and PaO(2)/FIO(224)/PaO(2)/FIO(2pre)) reliably discriminated nonsurvivors from survivors, with receiver operating characteristic areas under the curves between 0.89 and 0.95 (p for all curves < 0.001). Sensitivity-specificity analysis suggested that less than 15% reduction in oxygenation index (90% sensitive, 75% specific) or less than 90% increase in PaO(2)/FIO(2) (80% sensitive, 94% specific) 24 hours after transition to airway pressure release ventilation were the optimal cutoffs to identify nonsurvivors. The comparable values 24 hours after transition to high-frequency oscillatory ventilation were less than 5% reduction in oxygenation index (100% sensitive, 83% specific) or less than 80% increase in PaO(2)/FIO(2) (91% sensitive, 89% specific) to identify nonsurvivors.

CONCLUSIONS

In this single-center retrospective study of pediatric patients with an immunocompromised condition and acute respiratory distress syndrome failing conventional ventilation transitioned to either airway pressure release ventilation or high-frequency oscillatory ventilation, improved oxygenation at 24 hours expressed as PaO(2)/FIO(224)/PaO(2)/FIO(2pre) or oxygenation index(24)/oxygenation indexpre reliably discriminates nonsurvivors from survivors. These findings should be prospectively verified.

Effects of manually-assisted cough combined with postural drainage, saline instillation and airway suctioning in critically-ill patients during high-frequency oscillatory ventilation: a prospective observational single centre trial

BACKGROUND

Chest physiotherapy may aid sputum clearance during conventional ventilation. However, the role of chest physiotherapy during high-frequency oscillatory ventilation (HFOV) is unclear. This study aimed to determine the effects manually-assisted cough (MAC), postural drainage, saline instillation and airway suction during HFOV.

METHODS

This was an observational study of a chest physiotherapy intervention in adult critically ill patients during HFOV. Measures included gas exchange, HFOV and haemodynamic variables 1 h before, immediately before, and 15 min, 1 h, 6 h and 12 h after intervention. Wet weight of airway secretions was also measured. Linear mixed modelling compared pre-intervention gas exchange, HFOV and haemodynamic variables with the four specified time-points after intervention.

RESULTS

Seventeen adults (ten females) with moderate to severe respiratory failure were studied (age, 49 years SD 14; Acute Physiology and Chronic Health Evaluation II score (APACHE II score) 21 SD 6; PaO2/FiO2 of 139 mmHg SD 51). There was a statistically, although not clinically significant reduction in PaO2/FiO2 for up to 1 h after intervention, but no significant changes in oxygenation index, PaCO2, pH, or haemodynamic parameters up to 12 h after intervention. A reduction in delta pressure (ΔPaw) at 15 min (p < 0.05) and 1 h (p < 0.05) post intervention was not correlated with sputum wet weight.

CONCLUSIONS

MAC, postural drainage, saline instillation and airway suctioning during HFOV in critically ill patients was well tolerated with no clinically significant effect on arterial blood gases or haemodynamics. ΔPaw decreased for up to 1 h after intervention, but was not explained by the weight of sputum removed.

Update in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by permeability pulmonary edema and refractory hypoxemia. Recently, the new definition of ARDS has been published, and this definition suggested severity-oriented respiratory treatment by introducing three levels of severity according to PaO₂/FiO₂ and positive end-expiratory pressure. Lung-protective ventilation is still the key of better outcome in ARDS. Through randomized trials, short-term use of neuromuscular blockade at initial stage of mechanical ventilation, prone ventilation in severe ARDS, and extracorporeal membrane oxygenation in ARDS with influenza pneumonia showed beneficial efficacy. However, ARDS mortality still remains high. Therefore, early recognition of ARDS modified risk factors and the avoidance of aggravating factors during the patient's hospital stay can help decrease its development. In addition, efficient antifibrotic strategies in late-stage ARDS should be developed to improve the outcome.

Re-evaluating high-frequency oscillation for ARDS: Would a targeted approach be successful?

High-frequency oscillatory ventilation (HFOV) seems ideal for lung protection in acute respiratory distress syndrome, but randomized trials have not shown a mortality reduction. The initial oxygenation response to HFOV appears to be associated with survival. Here, we discuss the mechanisms of oxygenation response to increases in airway pressure and the interpretation of the oxygenation response observed in the present study.